Introduction to Industrial Polypropylene E-Book

Dennis B. Malpass

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 424

Veröffentlichungsjahr: 2012

Beschreibung

This introductory text is an important resource for new engineers, chemists, students, and chemical industry personnel to understand the technical aspects of polypropylene which is the 2nd largest synthetics polymer in manufactured output. The book considers the following topics: * What are the principal types of polypropylene and how do they differ? * What catalysts are used to produce polypropylene and how do they function? * What is the role of cocatalysts and how have they evolved over the years? * How are industrial polypropylene catalysts tested and the resultant polymer evaluated? * What processes are used in the manufacture of polypropylene? * What are the biopolymer alternatives to polypropylene? * What companies are the major industrial manufacturers of polypropylene? * What is the environmental fate of polypropylene?

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Dedication

List of Tables

List of Figures

Preface

Chapter 1: Introduction to Polymers of Propylene

1.1 Origins of Crystalline Polypropylene

1.2 Basic Description of Polypropylene

1.3 Types and Nomenclature of Polypropylene

1.4 Molecular Weight of Polypropylene

1.5 Transition Metal Catalysts for Propylene Polymerization

1.6 Questions

References

Chapter 2: Polymer Characterization

2.1 Introduction

2.2 Polymer Tacticity

2.3 Molecular Weight and Molecular Weight Distribution

2.4 Polymer Bulk Density

2.5 Particle Size Distribution and Morphology

2.6 Questions

References

Chapter 3: Ziegler-Natta Catalysts

3.1 A Brief History of Ziegler-Natta Catalysts

3.2 Definitions and Nomenclature

3.3 Characteristics of Ziegler-Natta Catalysts

3.4 Early Commercial Ziegler-Natta Catalysts

3.5 Supported Ziegler-Natta Catalysts

3.6 Prepolymerized Ziegler-Natta Catalysts

3.7 Mechanism of Ziegler-Natta Polymerization

3.8 Questions and Exercises

References

Chapter 4: Propylene Polymerization Catalysts

4.1 Introduction

4.2 Zero Generation Ziegler-Natta Catalysts

4.3 First Generation ZN Catalysts

4.4 Second Generation ZN Catalysts

4.5 Third Generation ZN Catalysts

4.6 Fourth Generation ZN Catalysts

4.7 Fifth Generation ZN Catalysts

4.8 ZN Catalysts for Atactic Polypropylene

4.9 Metallocenes and Other Single Site Catalysts

4.10 Cocatalysts for ZN Catalysts

4.11 Kinetics and ZN Catalyst Productivity

4.12 Concluding Remarks

4.13 Questions

References

Chapter 5: Aluminum Alkyls in Ziegler-Natta Catalysts

5.1 Organometallic Compounds

5.2 Characteristics of Aluminum Alkyls

5.3 Production of Aluminum Alkyls

5.4 Reducing Agent for the Transition Metal

5.5 Alkylating Agent for Creation of Active Centers

5.6 Scavenger of Catalyst Poisons

5.7 Chain Transfer Agent

5.8 Safety and Handling of Aluminum Alkyls

5.9 Questions

References

Chapter 6: Single Site Catalysts and Cocatalysts 6.1 Introduction

6.1 Introduction

6.2 The Structures of Metallocenes and SSCs

6.3 Non-Metallocene Polymerization Catalysts

6.4 Cocatalysts for SSCs

6.5 Supports for SSCs

6.6 Characteristics of mPP

6.7 Selected Applications of mPP Resins

6.8 Metallocene Synthesis

6.9 Syndiotactic Polypropylene

6.10 Commercial Reality and Concluding Remarks

6.11 Questions

References

Chapter 7: Catalyst Manufacture

7.1 Introduction

7.2 Development of the Manufacturing Process

7.3 Chemistry of Catalyst Manufacture

7.4 Raw Materials Storage and Handling

7.5 Catalyst Preparation

7.6 Catalyst Drying

7.7 Catalyst Packaging

7.8 Recovery and Recycle of Spent Solvents

7.9 Prepolymerization at the Catalyst Manufacturing Plant

7.10 Plant Size

7.11 Site Safety

7.12 Quality Control and Specifications

7.13 Diagram of a Hypothetical Plant

7.14 Custom Manufacture

7.15 Brief Consideration of Metallocene Catalyst Manufacture

7.16 Concluding Remarks

7.17 Questions

References

Chapter 8: An Overview of Industrial Polypropylene Processes

8.1 Introduction

8.2 Slurry (Suspension) Processes

8.3 Bulk (“Liquid Pool”) Process

8.4 “Loop Slurry” Process (Chevron Phillips Chemical)

8.5 Gas Phase Processes

8.6 Solution Process

8.7 Hybrid Processes

8.8 Kinetics and Reactivity Ratios

8.9 Emergency Stoppage of Polymerization

8.10 Questions

References

Chapter 9: Laboratory Catalyst Synthesis

9.1 Introduction

9.2 General Synthesis Requirements

9.3 Equipment Requirements

9.4 Synthesis Schedule

9.5 Handling TiCl4

9.6 Handling Diethylaluminum Chloride

9.7 Spent Liquids

9.8 Synthetic Procedure for Fourth Generation Supported Catalyst

9.9 Synthetic Procedure for Second Generation Precipitated TiCl3 Catalyst

9.10 Catalyst Analysis

9.11 Questions

References

Chapter 10: Polymerization Catalyst Testing

10.1 Introduction

10.2 Facility Requirements

10.3 The Autoclave

10.4 Key Equipment Items

10.5 Raw Materials

10.6 Polymerization Conditions

10.7 Autoclave Preparation

10.8 Polymerization Test Procedure

10.9 Reproducibility

10.10 Testing Metallocene Catalysts

10.11 Questions

References

Chapter 11: Downstream Aspects of Polypropylene

11.1 Introduction

11.2 Additives

11.3 Fabrication Methods

11.4 Biopolymers

11.5 Environmental

11.6 Questions

References

Chapter 12: Overview of Polypropylene Markets

12.1 Introduction

12.2 The Supply Chain for Polypropylene

12.3 The Global Polypropylene Market

12.4 Questions

References

Chapter 13: The Future of Polypropylene

13.1 Introduction

13.2 Key Growth Markets for Polypropylene

13.3 Polypropylene and Free Markets

13.4 Questions

References

Appendix A: Glossary of Abbreviations, Acronyms and Terminology

Appendix B: Answers to Questions

Appendix C: Registered Trademarks

Index

Introduction to Industrial Polypropylene

Scrivener Publishing

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Library of Congress Cataloging-in-Publication Data:

ISBN 978-1-118-06276-0

This book is dedicated to the memory of Professor Jerome F. Eastham, Sr., who lived his life with courage and élan. He was a mentor, a scholar and a true Tennessee gentleman. The world is a poorer place without him.

Jerome F Eastham, Sr was born September 22, 1924 in Daytona Beach, FL. He grew up in Lake City, FL and completed high school in Hazard, KY. He served in the US infantry in World War II. After the war, he attended The University of Kentucky and graduated in 1948. He then attended graduate school at The University of California in Berkeley and received a PhD in organic chemistry. Following fellowships at the University of London and the University of Wisconsin, he accepted an assistant professorship in 1953 at The University of Tennessee in Knoxville. During his early years at UT, he became well known for his work in organic and organometallic chemistry. He was a dynamic instructor and inspired many graduate students over his long tenure at UT. In the late 1960s, he made a bold decision to change careers and entered medical school to pursue an interest in neurochemistry. An author of this text (DBM) was privileged to be Prof Eastham’s final graduate student in organometallic chemistry before Prof Eastham entered medical school. After obtaining his doctor of medicine in Memphis, Eastham returned to Knoxville where he became an attending physician in the Department of Internal Medicine at the UT Research Hospital. Synchronously (one of his favorite lecture words), he resumed teaching organic chemistry to new generations of students. He completed a career that spanned 39 years with the University of Tennessee and retired in 1995. He passed away on August 22, 2008.

List of Tables

Table 1.1 Characteristics of Types of Polypropylene

Table 2.1 Selected Characterization Methods for Polypropylene

Table 2.2 Successive Extractions of Polypropylene by Different Solvents

Table 2.3 Mixed Catalysts to Improve Polymer Bulk Density Table 4.1 Isotacticity from Early Catalyst Screening’

Table 4.2 Relative Polymerization Performance of 1st and 2nd Generation Titanium Trichloride

Table 4.3 Properties of DEAC and TEAL

Table 4.4 Generations of Ziegler-Natta Propylene Polymerization Catalysts

Table 4.5 Comparison of TIBAL and TEAL Typical Analyses

Table 5.1 Principal Commercially Available Aluminum Alkyls

Table 5.2 Thermal Stability of Selected Aluminum Alkyls

Table 5.3 Comparative Cost of Selected Trialkylaluminum Compounds

Table 6.1 Occurrence of 2,1 Insertions in Polypropylene

Table 6.2 Some Characteristics of mPP Resins

Table 6.3 Reagents Used for the Preparation of Dimethylsilandiyl-bis-(2-cyclohexylmethyl)-4-(4’-tertbutylphenyl)-1-indenyl-zirconium Dichloride Catalyst on Silica

Table 7.1 Examples of Mg-Containing Support Precursor Formation with Controlled Morphology for Propylene Polymerization Catalysts

Table 8.1 Features of Industrial Polypropylene Processes

Table 10.1 Polymerization Grade Propylene Allowable Impurities Levels

Table 10.2 Polymerization Test Conditions

Table 11.1 MFR of Homopolymer vs. Multiple Extrusions

Table 12.1 Major Polypropylene Producers

Table 12.2 One Hundred and One Polypropylene Consumer Products

List of Figures

Figure 1.1 20th Century Milestones in Polypropylene

Figure 1.2 Schematic Representation of Stereoisomers of Polypropylene

Figure 1.3 Polypropylene Pellets

Figure 1.4 Types of Industrial Polypropylene in Market in 2008

Figure 1.5 Extrusion Plastometer

Figure 1.6 Mw vs. MFR for Polypropylene Homopolymer

Figure 2.1 Enchainment of Propylene Monomers

Figure 2.2 Four Important Tacticities of Regioregular Polypropylene

Figure 2.3 Chiral Relationship of a Polypropylene Diad

Figure 2.4 Single Insertion Error in Isotactic Chain Propagation

Figure 2.5 Pentad Assignments for Methyl Groups in the 13C NMR Spectrum of Atactic Polypropylene

Figure 2.6 Soxhlet Extraction Apparatus

Figure 2.7 Mill for Suitable for Reducing Polymer Particle Size

Figure 2.8 Correlation of Pentad Isotacticity and Xylene Solubles

Figure 2.9 Example of an HT GPC Instrument: Viscotek System

Figure 2.10 HT GPC Chromatogram of a Bimodal Isotactic Polypropylene

Figure 2.11 Ubbelohde Viscometer

Figure 2.12 Intrinsic Viscosity vs. Mw in Decalin at 135°C

Figure 2.13 Crossection of a Thermostatted Capillary Column of a Melt Flow Plastometer

Figure 2.14 Relationship of Intrinsic Viscosity and MFR

Figure 2.15 SEM Micrograph of a Polypropylene Particle

Figure 2.16 Two Dimensional Representation of Packing of Monodispersed and Multimodally Dispersed Spheres

Figure 2.17 Sieve Stack in an Automatic Shaker in an Acoustically Insulated Cabinet

Figure 2.18 Example of Polymer Particle Size Distribution Plot

Figure 2.19 Polypropylene Sample

Figure 3.1 The Ziegler Growth (“aufbau”) Reaction

Figure 3.2 The Phenomenon of Replication

Figure 3.3 Replication of Particle Size Distribution

Figure 3.4 Regioselectivity in Propylene Polymerization

Figure 3.5 Stereoselectivity in Propylene Polymerization

Figure 4.1 Historical Catalyst Productivity

Figure 4.2 Transformations of Titanium Trichloride

Figure 4.3 Effect of Milling Upon TiCl3 Activity

Figure 4.4 Stauffer Chemicals Levigator for Milling TiCl3

Figure 4.5 Apparatus to Form Spherical Support Particles

Figure 4.6 Comparison of Supported Catalyst Particles and Resultant Polypropylene Particles

Figure 5.1 Selected Types of Organometallic Compounds

Figure 5.2 Schematic Representations of Electron-deficient Bonding in TMAL Dimer

Figure 6.1 Schematic Representation of an Activated Ansa-Metallocene

Figure 6.2 Schematic Representation of Restricted Rotation of an Ansa-Metallocene

Figure 6.3 Some Recent Metallocene Structures for Polypropylene

Figure 6.4 Structural Types in Methylaluminoxane

Figure 6.5 Metallocene Activation by Excess MAO

Figure 6.6 Synthesis of Dimethylsilandiyl-bis-(2-cyclohexyl methyl)-4-(4’-tertbutylphenyl)-1-indenyl-zirconium dichloride, Supporting Steps Omitted.

Figure 6.7 Racemic and Meso Metallocene Isomers

Figure 6.8 Metallocene with Interconverting Structures

Figure 7.1 Schematic Flowsheet for a Hypothetical Catalyst Plant

Figure 8.1 Polypropylene by Technology Platform

Figure 8.2 Flowsheet for Early Slurry Process

Figure 8.3 Flowsheet for Chevron Phillips Loop Slurry Process

Figure 8.4 Simplified Flow Diagram for Unipol Gas Phase Process

Figure 8.5 Simplified Flow Diagram for Lummus-Novolen (BASF) Gas Phase Process

Figure 8.6 Simplified Flow Diagram for Amoco-Chisso (INEOS) Gas Phase Process

Figure 8.7 Simplified Flow Diagram for LyondellBasell Spheripol Process

Figure 8.8 Simplified Flow Diagram for LyondellBasell Spherizone Process

Figure 9.1 Supported 4th Generation Catalyst Synthesis Flowchart

Figure 9.2 Precipitated TiCl3 Synthesis Flowchart

Figure 9.3 Synthesis Apparatus

Figure 9.4 Reagent Transfer Apparatus

Figure 9.5 Titanium Tetrachloride Smoke

Figure 10.1 Propylene Vapor Pressure vs. Temperature

Figure 10.2 Polymerization Test Apparatus Schematic Diagram

Figure 10.3 Vacuum Atmospheres Inert Atmosphere Glove Box

Figure 10.4 One Gallon Polymerization Test Reactor

Figure 10.5 Vortex from Pitched Blade Turbine Impeller

Figure 10.6 Septum Bottle and Accessories

Figure 11.1 Exemplary Free Radical Degradation Reactions of Polypropylene

Figure 11.2 Global Consumption of Antioxidants in Plastics

Figure 11.3 Global Consumption of Antioxidants by Resin

Figure 11.4 Structures of Hindered Phenol Antioxidants

Figure 11.5 Principal Processing Methods for Polypropylene

Figure 11.6 Skeletal Structure of Organic Peroxide Used for CRPP

Figure 11.7 Poly (Lactic Acid)

Figure 11.8 Municipal Solid Waste in USA in 2010

Figure 11.9 Paper and Plastics in Municipal Solid Waste

Figure 11.10 A Landfill for MSW

Figure 11.11 SPI Coding of Plastics

Figure 11.12 Greenpeace Pyramid of Plastics

Figure 12.1 Global Market Shares of Plastics

Figure 12.2 Supply Chain for Polypropylene

Figure 12.3 Growth of Polypropylene

Figure 12.4 Uses of Polypropylene

Figure 12.5 Polypropylene in the Automotive Industry

Figure 13.1 Lightweight Polypropylene in Cars

Figure 13.2 Polypropylene Baby Bottles

Preface

Crystalline polypropylene was discovered in the early 1950s and commercial production began in 1957 in Italy, Germany and the USA. Since that modest beginning, polypropylene has become among the most important synthetic polymers produced by humankind, ranking second only to polyethylene. (Actually, polypropylene ranks first if polyethylene is separated into its various types, e.g., HDPE, LLDPE, LDPE, EVA, etc.) Estimates indicate that approximately 55 million metric tons (~121 billion pounds) of polypropylene were manufactured globally in 2011. Within the few minutes it takes to read this preface, about 600,000 pounds of PP will have been manufactured at facilities scattered around the world. Though production has slowed in recent years (especially 2009) because of the global recession, polypropylene has resumed its historic healthy growth. Polypropylene is manufactured in various forms on 6 continents and its applications are ubiquitous in daily life, from the fiber in your carpets and the upholstery in your living room furniture to the casings for the power tools in your garage.

The intent of this book is to provide chemists, engineers and students an introduction to the essentials of industrial polypropylene—what it is, how it is made and fabricated, how it is characterized, the markets it serves, and its environmental fate. Technical aspects are described in a straightforward way with minimal discussion of esoteric theory such that a person with a modicum of training in chemistry should be able to grasp. Our purpose is to provide practical, down-to-earth discussions of polypropylene technology. Extensive theoretical discussions are considered outside the scope of this book and have been largely avoided, but details are available in excellent handbooks and encyclopedia articles, many of which are included as references at the end of each chapter. Because of the industrial focus of the book, we also cite a number of relevant US patents.

Another key objective of this text is to supply perspective on recent innovations in the polypropylene industry. There has been tremendous hoopla about single site catalysts since their industrial use began in the early 1990s and the role they may play in revolutionizing the polyolefins business. That may well occur in the future, but, for now, these catalysts must be factually described as minor contributors to industrial polypropylene. Separating hyperbole from reality, we learn that single site catalysts are estimated to account for less than 3% of today’s global production of polypropylene. Of far greater immediate import has been the emergence of innovative cascade processes (also called tandem or “hybrid” processes) such as Spheripol, Spherizone and Borstar (see Chapter 8). Nevertheless, SSC are technologically important and in Chapter 6 we shall address key features of single site catalysts and the cocatalysts commonly employed, including a recent innovation that renders the historic SSC cocatalysts unnecessary. We ask only that the reader keep in mind the relatively minor contribution of SSC-derived polypropylene to today’s marketplace.

We also intend the text to be useful as a supplement to college courses on polymer chemistry. In addition, Chapters 2, 9, and 10 provide a practical basis for developing a laboratory program, which is a unique feature among texts on this subject. This book will answer fundamental questions such as:

What are the principal types of polypropylene and how do they differ?

What catalysts are used to produce polypropylene and how do they function?

What is the role of cocatalysts and how have they evolved over the years?

How are Ziegler Natta catalysts prepared industrially and in the laboratory?

How are industrial polypropylene catalysts tested and the resultant polymer evaluated?

What processes are used in the manufacture of polypropylene?

What are biopolymer alternatives to polypropylene?

What companies are the major industrial manufacturers of polypropylene?

What is the environmental fate of polypropylene?

Terminology used in industrial polypropylene technology can be baffling to the neophyte. This text will educate readers in the jargon of the industry and demystify the chemistry of catalysts and cocatalysts employed in the manufacture of polypropylene. Unlike ethylene, propylene must be polymerized in a regioregular and stereoregular manner to obtain the crystalline version of polypropylene (“isotactic”) that has so many uses in the home, workplace and in transportation.

Several techniques have been used to make the text “user friendly.” A thorough glossary is included as Appendix A. The glossary not only provides definitions of acronyms and abbreviations, but also concisely defines terms commonly encountered in the context of production and properties of polypropylene. An extensive index with liberal cross-referencing enables the reader to find a subject quickly. Also, questions and exercises at the end of each chapter allow the reader to assess whether he or she has mastered the content. Answers are provided in Appendix B.

The following is an overview of the content and purpose of each chapter:

Chapter 1 is used to recount the history of crystalline polypropylene and to describe basic properties and nomenclature for this versatile polymer. In addition, the most important industrial catalysts used for the manufacture of polypropylene are introduced. Also covered in Chapter 1 is an overview of stereochemistry, a crucial aspect that underpins properties and ultimately how polypropylene may be used in fabricated goods

.

Key polymer characterization methods in support of research and commercial production of polypropylene are discussed in Chapter 2

.

Features of catalysts and cocatalysts crucial to the manufacture of polypropylene are covered in Chapters 3–5. Chapter 3 discloses the origins of crystalline polypropylene, introduces key characteristics of Ziegler-Natta catalysts and includes an overview of mechanistic features of ZN polymerization. Chapter 4 describes the various generations of industrial polypropylene

catalysts. Chapter 4 also reviews intermediate catalyst developments and the evolution of modern, supported high-activity catalysts that control both stereoregularity and particle morphology. Chapter 5 includes a description of aluminum alkyls, the organometallics that are absolutely essential to the functioning of industrial Ziegler-Natta catalysts. Chapter 5 also cites precautions that should be taken for the safe handling of hazardous aluminum alkyls, a topic of critical importance to all manufacturers of polypropylene

.

Chapter 6 is a discussion of single site catalysts, the most important of which are metallocene catalysts. Chapter 6 also covers the most common cocatalysts historically used with SSC and touches on a recent innovation wherein supported activators that require no cocatalysts are used

.

Chapter 7 describes the large-scale manufacture of polypropylene catalysts, including a description of the array of equipment required and the importance of recycle streams

.

Chapter 8 provides an introduction to the wide range of process technologies historically used to manufacture polypropylene and reviews industry trends, including the transition to “hybrid” processes

.

Chapter 9 illustrates synthetic procedures and safety precautions for the laboratory synthesis of 2

nd

and 4

th

generation polypropylene catalysts

.

Chapter 10 is concerned with laboratory polymerization testing protocols and procedures used in support of commercial catalysts

.

Chapter 11 surveys downstream aspects of polypropylene (additives, fabrication methods, environmental issues)

.

Chapter 12 is a review of the global market, including a listing of the major producers of polypropylene that illustrates how the locus of manufacturing has shifted in recent years

.

Finally, Chapter 13 provides an assessment of the future of polypropylene, including a survey of key growth markets and an evaluation of emerging threats to the polypropylene supply chain. Chapter 13 also touches on new technologies developed for extraction of natural gas from shale, a positive development that could have huge long-range implications for the future of industrial polypropylene in the US. This is true because there are enormous shale deposits in the US and natural gas is a potential source of propylene monomer

.

This book should be considered complementary to Introduction to Industrial Polyethylene published jointly in 2010 by Scrivener Publishing, LLC and John Wiley & Sons, Inc. Because there are many commonalities between polyethylene and polypropylene, portions of text (especially in Chapters 3–5) have been reproduced with permission here. For example, aluminum alkyls function in generally the same way in Ziegler-Natta catalysts for polyethylene and polypropylene. Also, though there are subtleties having to do with stereochemistry and regiochemistry in propylene polymerization, essential features of the mechanism of Ziegler-Natta polymerization are very similar and textual similarities are inevitable.

The authors wish to thank former colleagues, friends and associates for their assistance in the production of this book. Thanks go to several former Akzo Nobel colleagues:

William Summers and Jim Hatzfeld for their reviews of the information on the manufacturing and testing of industrial PP catalysts.

Dr Biing Ming Su and Dr William Joyce for their comments on several sections, especially their help on analytical methods.

The authors would like to express gratitude to Drs Balaji Singh, Clifford Lee and JN Swamy of Chemical Marketing Resources, Inc. in Webster, TX for help on various aspects of the global polypropylene market. Thanks also to Dr Bill Beaulieu of Chevron Phillips Chemical, who provided a schematic depicting the Chevron Phillips “loop slurry” process for polypropylene.

Finally, the authors also greatly appreciate cogent input from the following:

Dr Johst Burk, retired from AkzoNobel

Dr Max McDaniel of Chevron Phillips Chemical

Dr Roswell (Rick) King of BASF (formerly Ciba)

Dr Rajen Patel of Dow Chemical

These men are accomplished professionals and have a combined total of more than 100 years’ industrial experience. Each has expertise in one or more aspects of the polypropylene industry and each reviewed much or all of the manuscript and provided comments and suggestions for improvement. We are sincerely grateful for their help. However, we assume responsibility for any errors that may have survived the winnowing process.

With this book, we have endeavored to present essentials of the polypropylene industry in a way that would be readily grasped by chemists and engineers just beginning their journey in the fascinating universe of polypropylene. In the 1968 movie The Graduate, a man advised recent college graduate Benjamin to remember one word: “plastics.” That one word could just as appropriately have been “polypropylene.” Though few moviegoers would have known anything about polypropylene and script writers usually try to avoid polysyllabic words, few career choices at that time could have been as challenging, rewarding and professionally satisfying. We hope that the text will be a valuable reference for young graduates entering the polypropylene industry for years to come.

Dennis B. MalpassMagnolia, TexasMarch 21, 2012

Elliot I. BandPleasantville, New YorkApril 19, 2012

Chapter 1

Introduction to Polymers of Propylene

1.1 Origins of Crystalline Polypropylene

Crystalline polypropylene (PP*) was unknown to the world before the 1950s. Though oligomeric and polymeric forms of propylene had been made before that time, they were typically amorphous, low molecular weight oils [1]. These liquid/oily polymers were produced by polymerization or oligomerization of propylene using free radical initiators or acidic/cationic catalysts at high temperature and pressure and were of marginal commercial value.

Giulio Natta is widely regarded as the discoverer of crystalline polypropylene, resulting from an experiment Natta performed in his lab in Milan, Italy on March 11, 1954 [2]. Without question, Natta contributed mightily to the fundamental understanding of crystalline polypropylene and its stereochemistry and richly deserved the admiration accorded him. However, with respect to US patent rights, who first prepared crystalline polypropylene remained a litigious issue for many years. Ownership of the US patent rights for crystalline polypropylene was resolved only after nearly three decades of legal wrangling (interferences, appeals and much rancorous debate). Testimony in the case resulted in about 14,000 pages of text and 4,600 exhibits [3]. Nuances of polypropylene discovery and patent rights are beyond the purview of this text, but the interested reader can find more information in references [1–4]. In the final analysis, the courts awarded priority to Phillips Petroleum Company, tacitly acknowledging that Phillips chemists J. Paul Hogan and Robert L. Banks had first prepared crystalline polypropylene in an experiment conducted on June 5, 1951. On March 15, 1983, some 30 years after the original application, a definitive patent was finally issued to Hogan and Banks and rights assigned to Phillips covering solid polypropylene “having a substantial crystalline polypropylene content” [5].

In their discovery experiment, Hogan and Banks used a chromia-NiO catalyst supported on silica-alumina. Later, they demonstrated that it was the chromium portion of the catalyst that was responsible for polymerizing propylene to the crystalline polymer. Hogan and Banks were belatedly honored for their contributions to polyolefin technology with several awards, including the 1987 Perkin Medal by the Society of Chemical Industry. Hogan and Banks were also inducted into the National Inventors Hall of Fame in 2001 and the building in Bartlesville, Oklahoma in which they made their seminal discoveries on polyolefins was designated an “historic landmark” by the American Chemical Society [6]. Ironically, while it is true that the Phillips catalyst is today enormously important in manufacture of polyethylene (accounting for approximately a quarter of all polyethylene produced globally), it is unsatisfactory for commercial production of polypropylene [7].

In March of 1954, nearly 3 years after the Hogan-Banks discovery experiment, Natta synthesized crystalline polypropylene using a transition metal catalyst (and a metal alkyl cocatalyst) of the type that emerged from the remarkably fruitful work of Karl Ziegler in polyethylene. In recognition of the pioneering work of Karl Ziegler and Giulio Natta, polyolefin catalysts involving combinations of transition metal compounds with metal alkyl cocatalysts have become known as Ziegler-Natta catalysts [8]. Today, the vast majority (>97%) of industrial polypropylene as well as huge quantities of polyethylene are produced with modern versions of Ziegler-Natta catalysts. Ziegler and Natta shared the Nobel Prize in chemistry in 1963. A timeline of 20th century milestones in polypropylene is provided in Figure 1.1. More information on the origins and evolution of stereoregular polypropylene and Ziegler-Natta catalysts will be provided in Chapters 3 and 4.

Figure 1.1 20th century milestones in polypropylene.

1.2 Basic Description of Polypropylene

Propylene (aka propene) has molecular formula C3H6. Other than ethylene, it is the simplest alkene, but in the parlance of the polypropylene industry is more commonly called an olefin. Propylene may be polymerized through the action of catalysts (eq 1.1). To obtain satisfactory quantities of stereoregular polypropylene, polymerization must be conducted under proper conditions using a transition metal catalyst and a metal alkyl cocatalyst. Other catalysts (free radical, cationic, etc.) typically produce low molecular weight amorphous polypropylene that is of limited commercial value.

(1.1)

Note that the basic repeating unit of polypropylene contains a primary (1°), a secondary (2°) and a tertiary (3°) carbon atom. Note further that the tertiary carbon atom is chiral. Consequences of these characteristics will be developed in subsequent discussions. Ziegler-Natta catalysts are the most important transition metal catalysts for industrial polypropylene and titanium is, by far, the most widely used transition metal. We will introduce key aspects of Ziegler-Natta catalysts in section 1.5 below, and examine Ziegler-Natta catalysts in greater detail in Chapters 3 and 4.

Like Ziegler-Natta catalysts, single site catalysts (SSC) employ transition metal compounds and can be used to polymerize propylene. In the mid-1970s, Kaminsky and Sinn [9] found that SCC of extraordinarily high activity could be obtained if methylaluminoxanes (rather than conventional aluminum alkyls) are used as cocatalysts. This discovery sparked a renaissance in polyolefin catalyst research and a surge in literature and patents touting the attributes of polymers made with SSC. Single site catalysts exhibit exceptional activity and permit unprecedented control over the molecular architecture of polymers (see Chapter 6). However, it is important to keep SSC in perspective relative to industrial polypropylene. As of this writing, the quantity of commercial polypropylene produced with single site catalysts is very small (<3%). As more cost-effective SSC are developed, the percentage of polypropylene made with SSC will undoubtedly grow in the coming years. However, Ziegler-Natta catalysts will remain the dominant catalysts for industrial polypropylene well into the 21st century.

Conditions for polymerization vary widely and polypropylene compositions also differ substantially in structure and properties. In eq 1, subscript n is termed the degree of polymerization (DP) and is greater than 1000 for most of the commercially available grades of polypropylene. As removed from industrial-scale reactors under ambient conditions, stereoregular polypropylene is typically a white powdery or granular solid with a density of ~0.90 g/cc. This density is significantly lower than most forms of polyethylene, which means that less weight of polypropylene is required to make an article relative to polyethylene.

Unlike ethylene polymerization, regiochemistry and stereochemistry possibilities exist in propylene polymerizations. Usually, propylene adds in a “head-to-tail” manner with Ziegler-Natta catalysts, but the reverse mode of addition (a “regioerror”) is also possible. As noted above, the methine carbon atom in the polymer structure (eq 1) is chiral which creates a variety of stereoisomeric possibilities. The configuration of the methyl group in the polymer chain is indicative of what is called the polymer’s “tacticity.” If the methyl groups are predominantly oriented in the same direction, the polymer is designated “isotactic,” a nomenclature derived from the Greek word for “same” or “ordered” proposed by Natta (following a suggestion from his wife who was a linguist) [10]. Isotactic polypropylene is by far the most common form of industrial polypropylene and contains substantial crystalline content. If the methyl group uniformly alternates from side to side along the polymer chain, the stereoisomeric form is termed “syndiotactic,” and, like isotactic, also contains substantial crystalline content. If the methyl group is randomly oriented, the polymer is termed “atactic” and is a rubbery, amorphous, tacky material, generally considered to be undesirable. However, at least one company purposely manufactures atactic polymer, which has uses as an adhesive, among other applications. The three most common stereoisomeric forms are schematically illustrated in Figure 1.2. A variety of polymorphic forms and other tacticities are possible, but will not be discussed here. However, more information on stereochemistry and regiochemistry of polypropylene will be provided in Chapter 2.

Figure 1.2 Schematic representation of stereoisomers of polypropylene. where dashed lines represent the “backbone” of the polymer and solid lines indicate configuration of methyl groups along the chain.

Melting characteristics of various forms of polypropylene have been studied and results are not as straightforward as one might expect [11, 12]. Nevertheless, the melting point (Tm) of isotactic polypropylene is typically reported to be in the range 160–170°C. Tm may be affected by a range of factors, including tacticity, molecular weight, and thermal history. Copolymers have lower Tm and lower crystallinity.

Though polyethylene is the least costly of the major synthetic polymers, polypropylene has higher Tm and is tougher (higher modulus and tensile strength) and can be used in applications where these attributes make polypropylene the material of choice. Like polyethylene, stereoregular polypropylene is a thermoplastic with excellent chemical resistance and toughness and can be processed in a variety of ways. Injection molding, fiber extrusion and film extrusion are fabrication methods that account for nearly 90% of all polypropylene applications. More information on fabrication methods will be provided in Chapter 11.

Because of the tertiary carbon atom, polypropylene is especially prone to attack by oxygen in ambient air, commonly termed “autoxidation” (see section 11.2 and Figure 11.1). To minimize oxidative degradation, the raw polymer is usually melted immediately after manufacture and an antioxidant is introduced. (Additives are essential to improve stability and enhance properties of polypropylene. See section 11.2) The molten product is shaped into translucent pellets and supplied in this form to processors (Figure 1.3). Pelletization increases resin bulk density resulting in more efficient packing and lower shipping costs. It also reduces the possibility of dust explosions while handling.

Figure 1.3 Raw polypropylene resin is melted and shaped into pellets of the type shown above. Pelletization increases bulk density, improves handling characteristics and reduces shipping costs. Pellet size is typically ~3 mm (or ~0.1 in).

(Reproduced from Introduction to Industrial Polyethylene, with permission of Scrivener Publishing LLC).

As noted above, polypropylene is a thermoplastic material. That is, it can be melted and shaped into a form which can then be subsequently remelted and shaped (recycled) into other forms.

Propylene may be copolymerized with a range of other olefins, such as ethylene and α-olefins (1-butene, 1-hexene, etc.). The other olefins are termed comonomers and are incorporated into the growing polymer chain. Some types of vinylic comonomers cannot be used. For example, Ziegler-Natta catalysts are usually poisoned by oxygen-containing polar comonomers such as vinyl acetate. Consequently, copolymers of propylene and VA are not available from Ziegler-Natta catalysts. However, certain single site catalysts are more tolerant of oxygen-containing compounds. Hence, copolymers of propylene with polar comonomers may be available from single site catalysts (see Chapter 6) in the not-too-distant future. Such copolymers may have unique properties and applications.

Ethylene is the most commonly used comonomer. Some products also employ higher alpha olefins (1-butene, 1-hexene, etc.). Often, the pattern of incorporation of comonomer along the polymer chain is not statistical because of differences in reactivity (see discussion of kinetics and reactivity ratios in Chapter 8). This results in nonuniformities in content and distribution of comonomers along the polymer chain. This is called the composition distribution (CD) and may be determined by 13C NMR analysis in combination with chromatographic methods discussed in Chapter 2.

Of course, regioerrors are not possible when ethylene is incorporated as comonomer, since carbons are equivalent. However, the polymer chain may contain “blocks” of ethylene units resulting from multiple insertions. This heterogeneity is termed “blockiness” and is represented schematically below.

In addition to blockiness, alpha-olefin comonomers (1-butene, 1-hexene, etc.) may be incorporated in ways that result in regioerrors.

When propylene is copolymerized with large amounts (>25%) of ethylene, an elastomeric copolymer is produced, commonly known as ethylene-propylene rubber (EPR) or ethylene-propylene monomer (EPM) rubber. When a diene, such as dicyclopentadiene, is also included, a terpolymer known as ethylene-propylene-diene monomer (EPDM) rubber is obtained. EPR and EPDM may be produced with single site and Ziegler-Natta catalysts and are important in the automotive and construction industries. However, EPR and EPDM are produced in much smaller quantities (~1 million mt/y) relative to polypropylene. Moreover, EPR and EPDM are amorphous, while the most important type of industrial polypropylene (“isotactic”) has substantial crystalline content. Accordingly, these elastomers are considered outside the scope of this text and will not be discussed further. However, random copolymers and impact copolymers are important products involving propylene and ethylene (at levels up to about 25%) and will be addressed in this text.

End groups of propylene polymers are most often saturated (simple alkyl groups). This is largely a consequence of using hydrogen as chain transfer agent. However, there are low levels of unsaturated sites owing to termination reactions by chain transfer via β-hydride elimination and hydride transfer to monomer. Termination reactions are addressed in the context of the mechanism of polymerization in Chapter 3.

Of course, there is abundant short chain branching (SCB) in polypropylene owing to the methyl group of propylene and other alpha olefins that are occasionally used. By convention, SCB implies 6 or fewer carbons. Long chain branching (LCB) in polypropylene is very low and is difficult to detect via the usual analytical methods [13].

Several grades of polypropylene are used in food packaging, e.g., blown film for candy and snack foods. In Europe, Canada, Japan, the USA and other developed countries, the resin must satisfy governmental regulations for food contact. Catalyst residues are quite low in modern polypropylene and are considered to be part of the basic resin. In the USA, the resin (including additives; see Chapter 11) must be compliant with FDA requirements for food contact, such as hexane extractables. The procedure for registration of polymers with governmental agencies can be complicated and protracted. Normally, the registration specifies the permitted uses.

Polypropylene is available in a dizzying array of compositions, with different microstructures, various comonomers, a range of molecular weights, etc., predicated by selection of catalyst, polymerization conditions and other process options. Since 1951, when a small quantity of a crystalline polymer was obtained unexpectedly from a laboratory experiment in Bartlesville Oklahoma, stereoregular polypropylene has grown enormously and is used today in megaton quantities in innumerable consumer applications. Though all forms of polyethylene (HDPE, LDPE, EVA, LLDPE, etc.) if taken, together, remain the largest volume plastic, a recent analysis suggests that polypropylene is the’ single largest volume plastic produced globally, exceeding even that of HDPE which is the largest type of polyethylene manufactured. Global polypropylene production in 2010 was estimated to be about 48 million metric tons (~106 billion pounds) [14].

1.3 Types and Nomenclature of Polypropylene

The most important types of commercially available polypropylene are:

homopolymer (HP)

random copolymer (RACO, aka RCP)

impact copolymer (also called heterophasic copolymer or HECO, aka ICP)

Key characteristics of each major type of polypropylene are summarized in Table 1.1. Figure 1.4 shows the approximate percentages of each type sold into the merchant market in 2008. The polymer produced in eq 1.1 is known as polypropylene or poly (propene).

Table 1.1 Characteristics of types of polypropylene.

Figure 1.4 Types of industrial polypropylene in market in 2008. The total market in 2008 was estimated to be about 46 million metric tons (~101 billion pounds).

Source: C. Lee and B. Singh, Chemical Marketing Research, Webster, TX, June, 2009.

Either is an acceptable name for homopolymer, according to IUPAC. However, polypropylene is by far the more commonly used name in industry and will be used exclusively in this text.

IUPAC nomenclature for copolymers is also not commonly used in industry. Since ethylene is the comonomer most often employed for RACO and HECO, the IUPAC name for such copolymers would be poly (propylene-co-ethylene).

Abbreviations for polypropylene are sometimes used to indicate the catalyst employed in its production or its stereochemistry. For example, polypropylene produced with metallocene catalysts (see Chapter 6) are often designated mPP. Isotactic and syndiotactic polypropylene are sometimes abbreviated iPP and sPP, respectively.

In addition to the nomenclature discussed above, manufacturers use their own registered trademarks. There are far too many trade names to include a comprehensive listing here, but examples are given below (along with the company that owns the trademark).

Pro-fax (LyondellBasell)

Vistamaxx (ExxonMobil)

Achieve (ExxonMobil)

VERSIFY (Dow)

Fortilene (Solvay)

Innovene (INEOS)

INSPIRE (Braskem)

Marlex (Chevron Phillips)

Clyrell (LyondellBasell)

Borstar (Borealis)

TAFMER (Mitsui)

As is evident from Figure 1.4, more than three-quarters of the global industrial polypropylene market is homopolymer. Lesser amounts of copolymer are produced for specialized applications where specific attributes are desired, such as film clarity or superior impact resistance. While ethylene is most often used as comonomer, 1-butene and 1-hexene may also be used. Moreover, terpolymers are increasing in importance.

1.4 Molecular Weight of Polypropylene

Polypropylene manufacturers routinely supply data that correlate with molecular weight and molecular weight distribution. A measurement called the melt flow rate (MFR) is determined by the weight of polypropylene extruded over 10 minutes at 230°C through a standard die using a piston load of 2.16 kg. Reported in g/10 min or dg/min, melt flow rate is measured using an instrument called an extrusion plastometer (see Figure 1.5.) according to ASTM D 1238-04c Condition 230/2.16, where the latter numbers refer to the temperature and the load in kg on the piston of the plastometer, respectively. Melt flow rate is inversely proportional to molecular weight, i.e., molecular weight decreases as MFR increases.

Figure 1.5 Melt flow rate of polypropylene may be measured on an instrument called an extrusion plastometer.

(Photo courtesy of Zwick/Roell.)

The term melt index (MI) is sometimes applied (erroneously) to the low load MFR for polypropylene. ASTM suggests that MI (determined at 190°C) be reserved for polyethylene and MFR be used for all other plastics, regardless of conditions used (see note 27 on p 10 of ASTM D 1238-04c).

Another melt flow rate value for polypropylene may also be measured on the plastometer at 230°C, but under a load of 21.6 kg (ASTM D 1238-04c Condition 230/21.6). This MFR is also reported in g/10 min or dg/min. Dividing the MFR measured at high load by the MFR at low load affords what is called the flow rate ratio (FRR) as in eq 1.2. FRR is a dimensionless number which gives an

(1.2)

indication of breadth of the molecular weight distribution. As FRR increases, MWD broadens.

MFR and FRR measurements are inexpensive, relatively easy to conduct and are indicative of molecular weight and molecular weight distribution. Actual molecular weights may be determined using a variety of analytical methods, including gel permeation chromatography (GPC), viscometry, light scattering and colligative property measurements. (GPC is also called size exclusion chromatography or SEC.) However, these methods require more sophisticated instruments that are usually operated by highly trained technical personnel. Procedures are more costly and difficult to perform and do not lend themselves to routine quality control. Nevertheless, expressions having to do with molecular weight and molecular weight distribution of polypropylene obtained using these instrumental methods often appear in discussions of PP properties in patent and journal literature. The most important values are called the number average molecular weight and the weight average molecular weight . The ratio is called the polydispersity index (PDI, also known as heterogeneity index and dispersity index) and is an indication of the broadness of molecular weight distribution. As polydispersity index increases, MWD broadens. Polydispersities typically range from 4–8 for polymer produced with Ziegler-Natta catalysts. However, polypropylene made with single site catalysts show polydispersities of 2–3 indicating a much narrower MWD.

The number average molecular weight is calculated from the expression:

(1.3)

where Mx is the molecular weight of the xth component and Nx is the number of moles of the xth component. Weight average molecular weight is calculated using the second order equation:

(1.4)

The third order equation provides the “z-average molecular weight” and is calculated from the; expression:

(1.5)

Higher order molecular weight averages may also be calculated, but are less important than and . For polydisperse polymers, such as polypropylene, the following relationship holds:

Direct comparisons between melt flow rate and molecular weight of polypropylene should be made with caution. Such comparisons are appropriate only when the polymers have similar histories (made using the same catalyst, by the same process, etc.). An example of the relationship between melt flow rate and weight average molecular weight (determined from intrinsic viscosity) for polypropylene with similar histories is shown in Figure 1.6. However, polypropylene used in the latter study was produced using early generation ZN catalysts. An equation relating melt flow rate and molecular weight has also been published for “modern” polypropylene [15]:

Figure 1.6 MW vs. MFR for PP homopolymer.

(from E. Vandenberg and B.C. Repka, High Polymers, John Wiley, 29, 365, 1977)

A graphical representation of the relationship between MFR and intrinsic viscosity for polypropylene prepared with modern ZN catalysts was shown by Del Luca, et al. [16]. Molecular weight measurement is discussed further in Chapter 2.

1.5 Transition Metal Catalysts for Propylene Polymerization

As previously mentioned, propylene may be polymerized by use of transition metal catalysts. To put these in perspective, one must recognize that transition metal catalysts have been used to produce virtually 100% of the cumulative trillion+ pounds of the global industrial output of polypropylene since commercial operations began in 1957. Transition metal catalysts are at the very heart of commercial processes used to manufacture polypropylene. Indeed, industrial polypropylene would be essentially unknown without transition metal catalysts.

In this section, we will introduce key characteristics of transition metal catalysts. From the standpoint of industrial polypropylene, Ziegler-Natta catalysts are by far the most important. Additional details on Ziegler-Natta catalysts will be provided in Chapters 3 and 4. As noted in section 1.2, the two most important catalysts are Ziegler-Natta and single site, both to be discussed in more detail in subsequent chapters. “Metallocene” catalysts (Chapter 6) may be considered to be a subset of what are more broadly designated as “single site catalysts.” However, not all metallocenes are effective as catalysts for propylene polymerization and not all single site catalysts are metallocenes.

Polypropylene catalysts are most often produced using compounds from Groups 4-6 of the Periodic Table. Cocatalysts are required with all industrial versions of polypropylene catalysts. (Single site catalysts that do not require cocatalysts have been discovered, but are not yet used in industrial processes for polypropylene). In the vast majority of catalyst systems, alkylaluminum compounds (see Chapter 5) are used as cocatalysts. Modern Ziegler-Natta catalysts for polypropylene, are usually derived from inorganic titanium compounds and are most often supported on magnesium chloride. Industrial single-site catalysts (Chapter 6) commonly involve metallocene compounds of Zr, Hf or Ti. Non-metallocene single site catalysts based on late transition metals, especially Pd, Fe and Ni, began to emerge in the mid-1990s, though these are not industrially significant at this writing.

For industrial viability, transition metal catalysts for polypropylene must fulfill several key criteria:

Activity must be high enough such that catalyst residues are sufficiently low in the final polymer to obviate post-reactor treatment to remove catalyst residues. As a rule of thumb, this requires that catalyst activity exceed about 150,000 lb of polypropylene per lb of transition metal.

The catalyst must polymerize propylene with proper stereochemical control. In most industrial polypropylene processes, the desired stereoisomer is the isotactic version. Obtaining product with high isotactic content (usually >94%) makes it possible to forgo costly steps to remove atactic content.

The catalyst must polymerize propylene with minimal “regioerrors.” That is, polymerization must be selectively “head-to-tail” (see discussion in section 2.2.1).

The catalyst must be capable of providing a range of polymer molecular weights. For Ziegler-Natta and single site catalysts, molecular weight is controlled primarily by use of hydrogen as chain transfer agent. Catalyst reactivity with hydrogen to control polymer molecular weight is called its “hydrogen response.”

Control of polydispersity is achieved primarily with the catalyst. Though each type of catalyst provides polypropylene with a characteristic range of molecular weight distributions, measures can be taken to expand marginally the range of achievable polydispersities. PDI are typically 4-8 for Ziegler-Natta catalysts and 2-3 for single site catalysts.

If a RACO or HECO is the target resin, amounts and regiochemistry of comonomer incorporation must be acceptable. Quantities of comonomer, as well as the uniformity of incorporation (or lack thereof), are measures of whether satisfactory copolymerization has occurred. For example, a “blocky” copolymer is sometimes desired. (“Blockiness” of a copolymer can be determined by analysis of its composition distribution.)

Additional details will be provided in subsequent chapters on the composition and functioning of transition metal catalysts.

As noted above, transition metal catalysts are essential for the manufacture of polypropylene. It is not hyperbole to state that production of stereoregular polypropylene would not be possible without these catalysts. It is difficult to imagine a world without the huge number of products made from these versatile polymers in our homes, vehicles and workplaces. Ziegler-Natta will continue to be the dominant catalysts for the various forms of polypropylene well into the 21st century. However, as single site catalyst technologies mature, they will increase in importance and complement Ziegler-Natta catalysts in manufacture of polypropylene.

1.6 Questions

1. Who was the first to prepare crystalline polypropylene? When?

2. What percentage of industrial polypropylene is manufactured with Ziegler-Natta catalysts?

3. What are the three principal types of industrial polypropylene and what is the approximate percentage of each?

4. Why are copolymers of propylene with vinyl acetate not commercially available?

5. What is melt flow rate? How is it measured? What is it significance?

6. What is FRR? What is its significance?

7. What is the polydispersity index? What is its significance?

8. Provide key criteria for performance of industrial polypropylene catalysts.

References

1. RB Seymour, Advances in Polyolefins, Plenum Press, New York, 8, 1985.

2. N. Pasquini (editor), Polypropylene Handbook, Hanser (Munich), 9, 2005.

3. JP Hogan and RL Banks, History of Polyolefins, (R. Seymour and T. Cheng, editors), D. Reidel Publishing Co., Dordrecht, Holland, 105, 1985.

4. FM McMillan, The Chain Straighteners, MacMillan Publishing Company, London, 1979.

5. JP Hogan and RL Banks, US Patent 4,376,851, March 15, 1983.

6. MP McDaniel, Handbook of Transition Metal Catalysts, (R Hoff and R Mathers, editors), Wiley, 291, 2010.

7. ibid, 293.

8. J Boor, Jr., Ziegler-Natta Catalysts and Polymerizations, Academic Press, Inc., 34, 1979.

9. H. Sinn and W. Kaminsky, Adv. Organometal. Chem., 18, 99, 1980. See also W. Kaminsky, History of Polyolefins, (R. Seymour and T. Cheng, editors), D. Reidel Publishing Co., Dordrecht, Holland, 257, 1985.

10. FM McMillan, The Chain Straighteners, MacMillan Publishing Company, London, 127, 1979.

11. RA Phillips and MD Wolkowicz, Polypropylene Handbook (N. Pasquini, editor), Hanser (Munich), 160, 2005.

12. YV Kissin, Alkene Polymerizations with Transition Metal Catalysts, Elsevier, The Netherlands, 57, 2008.

13. T Jinghua, Y Wei, and Z Chixing, Polymer, 47, 7962, 2006.

14. H. Rappaport, International Conference on Polyolefins, Society of Plastics Engineers, Houston, TX, February, 2011.

15. M Dorini and G ten Berge, Handbook of Petrochemicals Production Processes, (RA Meyers, editor), McGraw-Hill (New York), 16.8, 2005; see also R Rinaldi and G ten Berge, Handbook of Petrochemicals Production Processes, (RA Meyers, editor), McGraw-Hill (New York), 16.26, 2005.

16. D Del Luca, D Malucelli, G Pellegatti and D Romanini, Polypropylene Handbook (N. Pasquini, editor), Hanser (Munich), 308, 2005.

* Please see glossary for definition of abbreviations, acronyms and terms.

Chapter 2

Polymer Characterization

2.1 Introduction