Monitoring Polymerization Reactions E-Book

Wayne F. Reed

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

Seitenzahl: 1393

Veröffentlichungsjahr: 2013

Beschreibung

Offers new strategies to optimize polymer reactions

With contributions from leading macromolecular scientists and engineers, this book provides a practical guide to polymerization monitoring. It enables laboratory researchers to optimize polymer reactions by providing them with a better understanding of the underlying reaction kinetics and mechanisms. Moreover, it opens the door to improved industrial-scale reactions, including enhanced product quality and reduced harmful emissions.

Monitoring Polymerization Reactions begins with a review of the basic elements of polymer reactions and their kinetics, including an overview of stimuli-responsive polymers. Next, it explains why certain polymer and reaction characteristics need to be monitored. The book then explores a variety of practical topics, including:

• Principles and applications of important polymer characterization tools, such as light scattering, gel permeation chromatography, calorimetry, rheology, and spectroscopy
• Automatic continuous online monitoring of polymerization (ACOMP) reactions, a flexible platform that enables characterization tools to be employed simultaneously during reactions in order to obtain a complete record of multiple reaction features
• Modeling of polymerization reactions and numerical approaches
• Applications that optimize the manufacture of industrially important polymers

Throughout the book, the authors provide step-by-step strategies for implementation. In addition, ample use of case studies helps readers understand the benefits of various monitoring strategies and approaches, enabling them to choose the best one to match their needs.

As new stimuli-responsive and "intelligent" polymers continue to be developed, the ability to monitor reactions will become increasingly important. With this book as their guide, polymer scientists and engineers can take full advantage of the latest monitoring strategies to optimize reactions in both the lab and the manufacturing plant.

Leseprobe

Contents

PREFACE

INTRODUCTION

CONTRIBUTORS

SECTION 1: OVERVIEW OF POLYMERIZATION REACTIONS AND KINETICS

1 FREE RADICAL AND CONDENSATION POLYMERIZATIONS

1.1 INTRODUCTION

1.2 FREE RADICAL POLYMERIZATION

1.3 CONDENSATION POLYMERIZATION

1.4 CONCLUSIONS

REFERENCES

2 OVERVIEW OF CONTROLLED/LIVING POLYMERIZATION METHODS OF VINYL MONOMERS

2.1 SCOPE

2.2 DEFINITION OF LIVING POLYMERIZATIONS

2.3 SIGNIFICANCE OF LIVING POLYMERIZATIONS

2.4 ATTRIBUTES OF A CONTROLLED/LIVING POLYMERIZATIONS

2.5 THERMODYNAMIC CONSIDERATIONS FOR CONTROLLED/LIVING POLYMERIZATIONS

2.6 TYPES OF LIVING POLYMERIZATIONS

2.7 CONTROLLED RADICAL POLYMERIZATIONS

2.8 ARCHITECTURAL POSSIBILITIES WITH CONTROLLED/LIVING POLYMERIZATION METHODS

2.9 CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

3 STIMULI-RESPONSIVE POLYMERS VIA CONTROLLED RADICAL POLYMERIZATION

3.1 INTRODUCTION

3.2 SYNTHESIS OF STIMULI-RESPONSIVE POLYMERS

3.3 BLOCK COPOLYMERS IN SOLUTION

3.4 CROSS-LINKED MICELLES

3.5 STIMULI-RESPONSIVE COPOLYMERS IN BIOCONJUGATES

3.6 CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

4 REACTIONS IN HETEROGENEOUS MEDIA: EMULSION, MINIEMULSION, MICROEMULSION, SUSPENSION, AND DISPERSION POLYMERIZATION

4.1 INTRODUCTION

4.2 DESCRIPTION OF DIFFERENT POLYMERIZATION TECHNIQUES

4.3 EMULSION POLYMERIZATION

4.4 MINIEMULSION POLYMERIZATION

4.5 MICROEMULSION POLYMERIZATION

4.6 SUSPENSION POLYMERIZATION

4.7 DISPERSION POLYMERIZATION

REFERENCES

SECTION 2: POLYMERIZATION CHARACTERIZATION AND MONITORING METHODS

5 POLYMER CHARACTERISTICS

5.1 INTRODUCTION

5.2 POLYMER CONFORMATIONS AND DIMENSIONS

5.3 MOLECULAR WEIGHT DISTRIBUTIONS (MWDs) AND AVERAGES

5.4 POLYMER HYDRODYNAMIC CHARACTERISTICS

5.5 ELECTRICALLY CHARGED POLYMERS AND COLLOIDS

5.6 THERMODYNAMICS OF POLYMER SOLUTIONS

5.7 RHEOLOGY

5.8 CHARACTERISTICS OF POLYMERIZATION REACTIONS

5.9 SUMMARY

REFERENCES

6 INFRARED (MIR, NIR), RAMAN, AND OTHER SPECTROSCOPIC METHODS

6.1 INTRODUCTION

6.2 FUNDAMENTALS

6.3 MODEL BUILDING AND CALIBRATION

6.4 MONITORING AND CONTROL OF POLYMERIZATION REACTIONS

6.5 CONCLUSIONS

REFERENCES

7 CALORIMETRY, CONDUCTIVITY, DENSIMETRY, AND RHEOLOGICAL MEASUREMENTS

7.1 INTRODUCTION

7.2 REACTION CALORIMETRY

7.3 CONDUCTIVITY

7.4 DENSIMETRY

7.5 RHEOLOGICAL SENSORS

7.6 CONCLUSIONS

REFERENCES

8 LIGHT SCATTERING

8.1 INTRODUCTION

8.2 DYNAMIC LIGHT SCATTERING

8.3 STATIC LIGHT SCATTERING; ISOTROPIC SYSTEMS

8.4 STATIC LIGHT SCATTERING: ANISOTROPIC SYSTEMS

8.5 NOMENCLATURE

REFERENCES

9 GPC/SEC AS A KEY TOOL FOR ASSESSMENT OF POLYMER QUALITY AND DETERMINATION OF MACROMOLECULAR PROPERTIES

9.1 INTRODUCTION

9.2 BASIC CONCEPTS OF SEC

9.3 SEC ASPECTS OF SEPARATION

9.4 SEC ASPECTS OF DETECTION

9.5 COMPREHENSIVE 2D CHROMATOGRAPHY

REFERENCES

10 MASS SPECTROSCOPY: ESR AND NMR APPLICATIONS TO POLYMER CHARACTERIZATION AND POLYMERIZATION MONITORING

10.1 INTRODUCTION

10.2 MASS SPECTROSCOPY

10.3 APPLICATIONS OF MS METHODS TO POLYMER CHARACTERIZATION AND REACTION MONITORING

10.4 APPLICATIONS OF ESR SPECTROSCOPY TO POLYMER CHARACTERIZATION AND POLYMER REACTION MONITORING

10.5 APPLICATIONS OF NMR SPECTROSCOPY TO POLYMER CHARACTERIZATION AND POLYMER REACTION MONITORING

10.6 CONCLUSIONS

REFERENCES

SECTION 3: AUTOMATIC CONTINUOUS ONLINE MONITORING OF POLYMERIZATION REACTIONS (ACOMP)

11 BACKGROUND AND PRINCIPLES OF AUTOMATIC CONTINUOUS ONLINE MONITORING OF POLYMERIZATION REACTIONS (ACOMP)

11.1 OVERVIEW OF ACOMP PRINCIPLES AND APPROACH

11.2 ACOMP INSTRUMENTATION

11.3 MEASURING SPECIFIC CHARACTERISTICS

11.4 SUMMARY

REFERENCES

12 APPLICATIONS OF ACOMP (I)

12.1 INTRODUCTION

12.2 FREE RADICAL POLYMERIZATION

12.3 HETEROGENEOUS PHASE POLYMERIZATION

12.4 POSTPOLYMERIZATION MODIFICATIONS

12.5 CONTROLLED RADICAL POLYMERIZATION

12.6 ACOMP WITH SIMULTANEOUS CONTINUOUS DETECTION AND DISCRETE AUTOMATIC SEC

12.7 SUMMARY

ACKNOWLEDGMENTS

REFERENCES

13 APPLICATIONS OF ACOMP (II)

13.1 KINETICS AND MECHANISTIC STUDIES

13.2 CONTINUOUS REACTORS

13.3 SEMIBATCH REACTORS AND PREDICTIVE CONTROL

13.4 SECOND GENERATION ACOMP

13.5 SUMMARY

REFERENCES

14 COGNATE TECHNIQUES TO ACOMP

14.1 INTRODUCTION

14.2 SIMULTANEOUS MULTIPLE SAMPLE LIGHT SCATTERING

14.3 PARTICULATES COEXISTING WITH POLYMER POPULATIONS

14.4 AUTOMATIC CONTINUOUS MIXING (ACM)

14.5 SUMMARY

REFERENCES

15 OUTLOOK FOR INDUSTRIAL ACOMP

15.1 INTRODUCTION

15.2 COMPARISON OF FEATURES FOR R&D ACOMP VERSUS INDUSTRIAL ACOMP

15.3 BENEFITS OF ACOMP, OUTLOOK, AND CONCLUSION

15.4 CONCLUSION AND OVERALL OUTLOOK FOR INDUSTRIAL ACOMP

15.5 ACKNOWLEDGMENTS

REFERENCES

SECTION 4: REACTOR CONTROL AND DESIGN: BATCH, SEMI-BATCH, AND CONTINUOUS REACTORS

16 MATHEMATICAL MODELING OF POLYMERIZATION REACTORS

16.1 MATHEMATICAL MODELING TECHNIQUES

16.2 KINETIC ANALYSIS OF POLYMERIZATION MECHANISMS

REFERENCES

17 DESIGN AND OPERATION OF POLYMERIZATION REACTORS

17.1 REACTOR TYPES

17.2 SELECTION OF REACTOR TYPE

17.3 REACTOR DYNAMICS

17.4 REACTOR CONTROL AND OPTIMIZATION

REFERENCES

18 OPTIMIZATION OF THE PARTICLE SIZE IN EMULSION POLYMERIZATION

18.1 INTRODUCTION

18.2 PROCESS OPTIMIZATION: OVERVIEW

18.3 OPTIMIZATION OF THE POLYMER PARTICLE SIZE DISTRIBUTION

18.4 ZERO–ONE SYSTEM MODELING FOR OPTIMIZATION PURPOSES

18.5 OFF-LINE DYNAMIC OPTIMIZATION

18.6 ONLINE OPTIMAL CONTROL

18.7 CONCLUSIONS

REFERENCES

SECTION 5: INDUSTRIAL APPLICATIONS

19 WATER-SOLUBLE FREE RADICAL ADDITION POLYMERIZATIONS

19.1 INTRODUCTION

19.2 POLYACRYLAMIDES

19.3 POLYACRYLATES

19.4 POLYDIALLYLDIMETHYLAMMONIUM CHLORIDE

19.5 POLYVINYL ALCOHOL

19.6 POLYMER CHARACTERIZATION

19.7 MONITORING PRODUCTION

19.8 ONLINE PROCESS MONITORING

19.9 SUMMARY

ACKNOWLEDGMENTS

REFERENCES

20 PROTEIN AGGREGATION IN PHARMACEUTICAL BIOTECHNOLOGY

20.1 INTRODUCTION

20.2 PROTEIN MOLECULAR ASSEMBLY AND AGGREGATE STRUCTURE

20.3 MECHANISTIC ASPECTS

20.4 EXAMPLES OF AGGREGATION AND ITS IMPACT

20.5 SOURCES OF AGGREGATION

20.6 AGGREGATE ANALYSIS AND CONTROL

20.7 FINAL COMMENTS

ACKNOWLEDGMENTS

REFERENCES

21 RUBBERS AND ELASTOMERS

21.1 INTRODUCTION

21.2 INDUSTRIALLY PRODUCED RUBBERS AND ELASTOMERS

21.3 POLYMERIZATION REACTIONS

21.4 PROCESS MONITORING

21.5 COMPUTER SIMULATION AND MODELING

REFERENCES

22 POLYMERS FROM NATURAL PRODUCTS

22.1 OILS AND FATS

22.2 THE PRODUCTION OF BIODIESEL

22.3 POLYMERIZATION

REFERENCES

SUPPLEMENTARY IMAGES

INDEX

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Library of Congress Cataloging-in-Publication Data:

Monitoring polymerization reactions : from fundamentals to applications / edited by Wayne F. Reed, Tulane University, New Orleans, Louisiana, USA, Alina M. Alb, Tulane University, New Orleans, Louisiana, USA.       pages cm   Includes index.

   ISBN 978-0-470-91738-1 (cloth)1. Polymerization. 2. Chemical reactions. I. Reed, Wayne F. II. Alb, Alina M.   TP156.P6M585 2014   668.9′2–dc23

2013018919

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

PREFACE

Monitoring polymerization reactions has both fundamental and applied motivations. At the basic level, simultaneous monitoring of the various reaction characteristics, such as the evolution of copolymer composition and molecular weight, can reveal the underlying kinetics and mechanisms involved in reactions and also illuminate ways in which the reaction may deviate from what is ideally thought to occur. The ability to monitor reactions will become increasingly important as new, stimuli-responsive, and “intelligent” polymers are developed at the frontiers of twenty-first century materials science.

From the practical viewpoint, optimization of reaction conditions at the laboratory and pilot plant level can be an important step in process development. Ultimately, application of monitoring and subsequent feedback control to full-scale industrial reactors will lead to improved efficiency in the use of energy, feedstocks, and other nonrenewable resources, as well as plant and labor time, enhanced product quality and reliability, and the reduction of emissions.

While it is not possible to be all encompassing in scope, this book attempts to be as self-contained as possible. Hence, the basic elements of different types of polymer reactions and their kinetics are reviewed in Section 1, including a brief overview of stimuli-responsive polymers. This is followed in Section 2 by a description of the most relevant polymer and reaction characteristics to be monitored. The section then explains the principles and applications of some of the most important polymer characterization tools, such as light scattering, gel permeation chromatography, calorimetry, rheology, and various types of spectroscopy. Section 3 is devoted to Automatic Continuous Online Monitoring of Polymerization (ACOMP) reactions, which is a flexible platform that allows characterization tools discussed in Section 2 to be employed simultaneously during reactions in order to obtain a comprehensive and quantitative record of multiple reaction features. The chemical engineering community has devoted considerable effort to the modeling of polymerization reactions, and Section 4 provides an account of the theoretical and experimental bases for these efforts, as well as a treatment of the type of modeling and numerical approaches used. Finally, Section 5 gives a short selection of industrially important polymers and perspectives on their production and how monitoring can be employed to optimize their manufacture.

INTRODUCTION

Observing processes as they occur is a widespread approach in many areas of inquiry and industry because it allows fundamental understanding of the mechanisms involved in the process and offers the possibility for control. The many areas of process monitoring are striking: time-lapse photography of plant growth, embryology, crystallization processes; electrophysiological monitoring of vital signs; using the electromagnetic wave spectrum to detect and monitor the expansion of the universe; the dynamic flows of ocean currents; and the paths of hurricanes.

As the focus turns to chemistry, science and engineering have developed rich and deep layers of useful theory and modeling concerning reaction kinetics and processes. In the realm of the vast chemical industry, monitoring temperature, pressure, and other parameters, the presence of specific small molecules, particulates, and pollutants has allowed enormous gains in efficiency, safety, product quality, and reduction of negative environmental impact.

When it comes to monitoring polymer reactions, however, the nature of the task shifts. This is because polymer characterization is a complex and challenging field even “offline.” In principle, polymers have definable molecular weight distributions, conformations, and interactions in different solvents and at different concentrations and temperatures, architectures, hydrodynamic properties, comonomer compositions, sequence length distributions or comonomer blockiness, propensities to aggregate, and so forth. The experimental measurement of these quantities and behaviors requires many instrumentational and methodological approaches. Hence, polymer characterization is a great interdisciplinary undertaking, which has united efforts from diverse areas of the physical and biological sciences and engineering. It has rapidly incorporated the advances in fields such as light, x-ray, and neutron scattering, nuclear and electron magnetic resonance, ultraviolet, visible, and infrared spectroscopies, thermal measurements, ultrasonics, viscometry, time-of-flight mass spectroscopy, and microscopies.

Given the challenges that exist for the characterization of polymers in equilibrium, taking the next step to provide characterization while polymer reactions occur requires new concepts and strategies but is rewarding for both fundamental science and improved industrial manufacturing.

In this book, all characterization will be of the type that can be made while polymers are in solutions, bulk, or melts, but not in the solid state. Hence, issues of crystallinity, and mechanical, electrical, optical, and other properties of polymers used in their solid state are not treated. There are possibilities for incorporating and automating such measurements into the manufacturing process; however, these will require certain delay times and conditioning steps.

The term “polymer reactions” is used in a very broad sense. It refers not only to the usual step growth and chain growth reactions that produce polymers, but also to postpolymerization modifications, conjugation, degradation processes, noncovalent polymers, physical reactions producing aggregates and gels, and supramacromolecular assemblies.

As regards the building of covalently bonded polymer chains, attention will be paid to both chain growth and step growth methods. In both these categories, some of the newer “living”-type approaches will be presented as well as the features that can make these advantageous. In the area of copolymers, block, statistical, and gradient copolymers will be treated, along with the extra dimensions of characterization work required. Copolymers produced by postpolymerization modifications, such as hydrolysis, functionalization, grafting, and conjugation are an interesting alternate route to forming copolymers, where architecture can also be controlled.

While the differences between chemists’ and chemical engineers’ approaches may not be obvious to people outside these fields, they become readily apparent in the polymer industry, to the point where a common adage suggests that if a manufacturer is producing polymers in batch reactors then the company founders were likely chemists, whereas if the manufacture is via continuous reactors the founders were likely chemical engineers. Likewise, in their approach to understanding and controlling polymer properties, one will often see the chemist focused on the types of detailed organic reactions and side reactions used, while the chemical engineer focuses more on mixing, spatial inhomogeneity, heat and mass transfer, shear effects, viscosity, and the like.

Although polymer reaction monitoring is of great interest to both the polymer scientist in a research laboratory and the process engineer in a production plant, their motivations differ and the approaches can differ. Whereas the laboratory scientist has the knowledge and means to both understand and run complex analytical instrumentation yielding information-rich data, and to invent and change chemistry, the process engineer wants to be able to produce a fixed range of products reliably and efficiently with minimum amount of instrumentation, such as monitoring. Hence, the laboratory monitoring platform can be complex, multifaceted, delicate, and rather challenging to interpret, whereas factory monitoring is simplified to follow the synthesis process with the least amount of operator intervention and interpretation possible.

There are a vast number of polymers produced in university and industrial research laboratories, but far fewer in industrial production. This book does not intend to cover all types of polymers; rather it will use some of the best known classes to illustrate reaction monitoring. It is important to put into perspective the height of the “macromolecular pyramid.” At the base of the pyramid are the many billions of pounds per year of commodity plastics, such as polyolefins. Working up the pyramid are the highly developed markets for both engineering plastics, such as polycarbonates and polysulfones, and specialty polymers, such as customized water-soluble copolymers, used in water purification, secondary oil recovery, personal care, etc. They have higher performance specifications than commodity plastics and are under more strict regulations.

Intertwined throughout the base, middle, and peak of the pyramid are the many natural products used in industries such as food, flavoring and fragrances, pharmaceuticals, biotechnology, personal care, nanostructures, hybrid materials, and others. In keeping with the book’s broad definition of polymer reactions, fermentation processes involving natural products, as well as degradation reactions leading to biofuels, are open and exciting areas for online monitoring.

At the tip of the pyramid is the vibrant activity in synthetic polymer chemistry. Creative concepts are used to produce a new generation of twenty-first century polymeric materials, including organic electronic and optical devices, self-healing polymers, drug delivery, device interfaces, nanocomposites, and polymers that react to environmental stimuli. Among these latter “stimuli-responsive polymers” are those that can change conformation, go through phase transitions, micellize, and associate with other substances when conditions such as irradiation, presence of specific agents, and changes in temperature, pH, and ionic strength occur. And, of course, to accompany the ferment of activity at all levels of the pyramid are the evolving techniques and methodologies necessary to characterize polymers of all types.

In the following chapters, the experience and thoughts of many leading scientists and engineers from very different parts of the great interdisciplinary field of macromolecules are brought together around the theme of polymer reaction monitoring.

WAYNE F. REEDALINA M. ALB

CONTRIBUTORS

Brooks A. Abel, University of Southern Mississippi, Hattiesburg, MS, USAAlina M. Alb, Tulane University, New Orleans, LA, USAJosé M. Asua, University of the Basque Country, Donostia-San Sebastián, SpainGuy C. Berry, Carnegie Mellon University, Pittsburgh, PA, USAMark L. Brader, Biogen Idec Corp, Cambridge, MA, USAJosé C. de la Cal, University of the Basque Country, Donostia-San Sebastián, SpainMichael F. Drenski, Advanced Polymer Monitoring Technologies, Inc., New Orleans, LA, USA; Tulane University, New Orleans, LA, USAJoel D. Flores, University of Southern Mississippi, Hattiesburg, MS, USADaniela Held, PSS Polymer Standards Service GmbH, Mainz, GermanyMatthew Kade, University of Chicago, IL, USAPeter Kilz, PSS Polymer Standards Service GmbH, Mainz, GermanyJose R. Leiza, University of the Basque Country, Donostia-San Sebastian, SpainMarcelo K. Lenzi, Universidade Federal do Paraná, Curitiba, BrasilAndrew J. D. Magenau, Carnegie-Mellon University, Pittsburgh, PA, USARobert T. Mathers, Carnegie-Mellon University, Pittsburgh, PA, USAKrzysztof Matyjaszewski, Carnegie-Mellon University, Pittsburgh, PA, USACharles L. McCormick, University of Southern Mississippi, Hattiesburg, MS, USATimothy McKenna, Queens University, Kingston, ON, CanadaAline Nicolau, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, BrasilJosé C. Pinto, Universidade Federal do Rio de Janeiro, Rio de Janeiro, BrasilAlex W. Reed, Advanced Polymer Monitoring Technologies, Inc., New Orleans, LA, USA; Tulane University, New Orleans, LA, USAWayne F. Reed, Tulane University, New Orleans, LA, USAJosé A. Romagnoli, Louisiana State University, Baton Rouge, LA, USAMiriam B. Roza, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, BrasilDimitrios Samios, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, BrasilAlexandre F. Santos, Universidade Tiradentes, Aracaju, Brasil.F. Joseph Schork, School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USAKristin Schröder, Carnegie-Mellon University, Pittsburgh, PA, USAFabricio M. Silva, Universidade de Brasília, Brasilia, BrasilDeeDee Smith, University of Southern Mississippi, Hattiesburg, MS, USAJorge Soto, Lion Copolymer LLC, Baton Rouge, LA, USAMatthew Tirrell, University of Chicago, Chicago, IL, USARadmila Tomovska, University of the Basque Country, Donostia-San Sebastián, SpainWesley L. Whipple, Nalco, An Ecolab Company, Naperville, IL, USAJoseph Zeaiter, American University of Beirut, Beirut, LebanonHua Zheng, Nalco, An Ecolab Company, Naperville, IL, USAZifu Zhu, Tulane University, New Orleans, LA, USA

SECTION 1

OVERVIEW OF POLYMERIZATION REACTIONS AND KINETICS

1

FREE RADICAL AND CONDENSATION POLYMERIZATIONS

MATTHEW KADEAND MATTHEW TIRRELL

1.1 INTRODUCTION

Polymers are macromolecules composed of many monomeric repeat units and they can be synthetic or naturally occurring. While nature has long utilized polymers (DNA, proteins, starch, etc.) as part of life’s machinery, the history of synthetic polymers is barely 100 years old. In this sense, man-made macromolecules have made incredible progress in the past century. While synthetic polymers still lag behind natural polymers in many areas of performance, they excel in many others; it is the unique properties shared by synthetic and natural macromolecules alike that have driven the explosion of polymer use in human civilization. It was Herman Staudinger who first reported that polymers were in fact many monomeric units connected by covalent bonds. Only later we learned that the various noncovalent interactions (i.e., entanglements, attractive or repulsive forces, multivalency) between these large molecules are what give them the outstanding physical properties that have led to their emergence.

In recent years, the uses of synthetic polymers have expanded from making simple objects to much more complex applications such as targeted drug delivery systems and flexible solar cells. In any case, the application for the polymer is driven by its physical and chemical properties, notably bulk properties such as tensile strength, elasticity, and clarity. The structure of the monomer largely determines the chemical properties of the polymer, as well as other important measurable quantities, such as the glass transition temperature, crystallinity, and solubility. While some important determinants of properties, such as crystallinity, can be affected by polymer processing, it is the polymerization itself that determines other critical variables such as the molecular weight, polydispersity, chain topology, and tacticity. The importance of these variables cannot be overstated. For example, a low-molecular-weight stereo-irregular polypropylene will behave nothing like a high-molecular-weight stereo-regular version of the same polymer. Thus, it is easy to see the critical importance the polymerization has in determining the properties and therefore the potential applications of synthetic polymers. It is therefore essential to understand the polymerization mechanisms, the balance between thermodynamics and kinetics, and the effect that exogenous factors (i.e., temperature, solvent, and pressure) can have on both.

1.1.1 Structural Features of Polymer Backbone

1.1.1.1 Tacticity

Tacticity is a measure of the stereochemical configuration of adjacent stereocenters along the polymer backbone. It can be an important determinant of polymer properties because long-range microscopic order (i.e., crystallinity) is difficult to attain if there is short-range molecular disorder. Changes in tacticity can affect the melting point, degree of crystallinity, mechanical properties, and solubility of a given polymer. Tacticity is particularly important for a, a′-substituted ethylene monomers (e.g., propylene, styrene, methyl methacrylate). For a polymer to have tacticity, it is a requirement that a does not equal a′ because otherwise the carbon in question would not be a stereocenter. The tacticity is determined during the polymerization and is unaffected by the bond rotations that occur for chains in solution. The simplest way to visually represent tacticity is to use a Natta projection, as shown in Figures 1.1–1.3 using poly (propylene) as a representative example.

FIGURE 1.1 Isotactic polypropylene.

FIGURE 1.2 Syndiotactic polypropylene.

FIGURE 1.3 Atactic polypropylene.

An isotactic chain is one in which all of the substituents lie in the same plane (i.e., they have the same stereochemistry). Isotactic polymers are typically semicrystalline and often adopt a helical configuration. Polypropylene made by Ziegler–Natta catalysis is an isotactic polymer.

A syndiotactic chain is the one where the stereochemical configuration between adjacent stereocenters alternates.

An atactic chain lacks any stereochemical order along the chain, which leads to completely amorphous polymers.

1.1.1.2 Composition

Copolymer composition influences a number of quantities, including the glass transition temperature. One commercially relevant example of this effect is with Eastman’s copolymer Tritan™, which has been replacing polycarbonate in a number of applications due to concerns over bisphenol-A’s (BPA’s) health effects. Tritan™ can be considered poly(ethylene terephthalate) (PET), where a percentage of the ethylene glycol is replaced by 2,2,4,4-tetra-methyl-1,3-cyclobutane diol (TMCBDO). In the case of beverage containers, must be greater than 100 °C so they can be safely cleaned in a dishwasher or autoclave. The of Tritan is engineered to be ~110 °C by tuning the relative incorporation of the ethylene glycol (low ) and TMCBDO (-increasing) diol monomers.