Porous Plastics E-Book

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

Seitenzahl: 470

Veröffentlichungsjahr: 2022

Beschreibung

POROUS PLASTICS A unique book by a well-known polymer scientist on a subject that is trending in plastics/polymer engineering. Porous polymers are materials that are having pores in their design. Porous polymers are important for various fields of application and are used with pores of different sizes, i.e., from macropores to micropores. This book focuses on the issues of porous polymers as well as low molecular compounds that can be introduced in porous polymers. The book begins with a chapter about polymers that are used for porous materials. Here, among others, microporous polymer networks, hyper-crosslinked polymers, and rigid ladder-type porous polymers are detailed. Related issues are also detailed in the subsequent chapters. In the next chapter, the major synthesis methods for porous polymers are described. Then, the properties and material testing methods, such as standards, are described in a chapter. In the following chapters, special fields of applications of porous polymers are described in detail, such as: medical uses, thermal insulation, membranes, separation methods, and other fields of use. Audience The book will be used by plastics engineers, materials scientists and polymer scientists/researchers in both industry and academia./p>

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Preface

1 Materials

1.1 Styropor

1.2 Porous Coordination Polymers

1.3 Networks

1.4 Rigid Ladder-Type Porous Polymers

1.5 Photocatalysts

References

2 Synthesis Methods

2.1 Porogens

2.2 Living Radical Polymerization

2.3 Emulsion Polymerization

2.4 Solvent-Free Polymerization

2.5 Suspension Polymerization

2.6 Multistage Polymerization Techniques

2.7 Azo Coupling

2.8 Precipitation Polymerization

2.9 Microfluidics

2.10 Photocatalysis

2.11 Thermal Drawing

2.12 Biodegradable Foam

2.13 Biocompatible Porous Three-Dimensional Polymer Matrices

2.14 Breath-Figure Method

2.15 Superabsorbent Polymers

2.16 Functionalization Methods

References

3 Properties

3.1 Special Materials

3.2 Standard Test Methods

References

4 Medical Uses

4.1 Medical Diagnostics

4.2 Medical Devices

4.3 Medical Applications

4.4 Biomedical Applications

References

5 Thermal Insulation

5.1 Prediction Models

5.2 Radiative and Conductive Heat Transfer

5.3 Studies of Thermal Conductivity

5.4 Poly(ethylene) Foams

5.5 Rigid Foams

5.6 Microporous Foams

5.7 Resilient Porous Polymer Foams

5.8 Electrically Conductive Networks

5.9 Electroconducting Polymer Coatings

5.10 Foam Insulation Structure

5.11 Passive Cooling

5.12 Sulfur-Containing Polymers

5.13 Nanocellular Polymers

5.14 Household Applications

5.15 Fluid Storage Tank

5.16 Thermal Insulation for High Explosives

5.17 Aerogels

References

6 Membranes

6.1 Cellulose Acetate

6.2 Poly(vinylidene fluoride)

6.3 Poly(amino acid)s

6.4 Hyper-crosslinked Polymers

6.5 Membrane for Specific Molecular Separation

6.6 Treatment of Water

6.7 Enzyme Reactors

6.8 Electrolyte Membranes

6.9 Membranes for Batteries

6.10 pH-Sensitive Gating in Membranes

References

7 Separation Methods

7.1 Chromatography

7.2 Oil Spill Control

7.3 Sorbents

7.4 Recovery of Organic Materials

7.5 Metal Recovery

References

8 Other Fields of Use

8.1 Ceramic Articles

8.2 Polymer-Modified Porous Cement

8.3 Flame Retardant Foams

8.4 Clay-Containing Composites

8.5 Lubricant Additives

8.6 Cosmetic Compositions

8.7 Packaging Materials

8.8 Char Layer

8.9 Batteries

8.10 Light Emission

8.11 Sorbents

References

Index

Acronyms

Chemicals

General Index

Also of Interest

End User License Agreement

List of Illustrations

Chapter 1

Figure 1.1

1,1’-Bis(4-carboxybenzyl)-4,4’-bipyridinium dichloride.

Figure 1.2

Synthesis of a porous coordination polymer-ionic liquid composite (10...

Figure 1.3

Acids in Table 1.1.

Figure 1.4

Building blocks (15).

Figure 1.5

Reactions for the synthesis (15).

Figure 1.6

Pyrazole-benzothiadiazole-pyrazole polymer (35).

Figure 1.7

Pyrazole-benzene-pyrazole polymer (35).

Figure 1.8

Compounds for photocatalytic materials.

Figure 1.9

Triformylphloroglucinol.

Figure 1.10

Side chain engineering.

Chapter 2

Figure 2.1

(Meth)acrylic monomers.

Figure 2.2

Crosslinking monomers.

Figure 2.3

Toughening monomers.

Figure 2.4

Emulsifiers.

Figure 2.5

Electrocyclic reaction and aromatization (35).

Figure 2.6

Sulfonic acids.

Figure 2.7

Monomers for porous polymer networks (35).

Figure 2.8

Fiber draw tower (74).

Figure 2.9

Monomers used in the breath-figure technique (80).

Figure 2.10

Monomers.

Figure 2.11

Monomers for crosslinking (84).

Figure 2.12

Photopolymerization initiators.

Figure 2.13

Thermal polymerization initiators.

Figure 2.14

SEM image (84).

Figure 2.15

Lauryl methacrylate.

Chapter 4

Figure 4.1

Compounds mentioned in method 4–1.

Figure 4.2

Fabrication of a PPM filter (2).

Figure 4.3

Porosity of the filter (2).

Figure 4.4

Compounds for vesicle characterization.

Figure 4.5

Monomers for bioabsorbable elastomeric polymers.

Figure 4.6

Anti-proliferative agents.

Figure 4.7

Pullulan.

Figure 4.8

D

-Phenylalanyl-

N

-[(3

S

)-6-carbamimidamido-1-chloro-2-oxo-3-hexanyl]-

L

-...

Figure 4.9

Geldanamycin.

Figure 4.10

Anti-inflammatory agents.

Figure 4.11

Anesthetic agents.

Figure 4.12

Protein kinase and tyrosine kinase inhibitors.

Figure 4.13

Antimicrobial agents.

Figure 4.14

Prostacyclin analogs.

Figure 4.14

Drugs.

Figure 4.15

Structure of MOFNF (64).

Figure 4.16

Gentamicin C1.

Figure 4.17

Cholesterol.

Figure 4.18

Monomers for hemocompatible polymers (76).

Figure 4.19

Porogens (76).

Figure 4.20

[(2-methacryloyloxy)ethyl]-dimethyl-3-(sulfopropyl) ammonium hydroxi...

Chapter 5

Figure 5.1

Monomers for alkenyl aromatic polymers (14).

Figure 5.2

Blowing agents.

Figure 5.3

Plasticizers for PVC-based sheets (17).

Figure 5.4

Foaming agents for PVC-based sheets.

Figure 5.5

Isocyanate monomers.

Figure 5.6

Blowing agents (19).

Figure 5.7

Catalysts.

Figure 5.8

Monomers for conjugated microporous polymers.

Figure 5.9

Surfactant and radical initiator.

Figure 5.10

Density of F-NR/CNTs composite foams (31).

Figure 5.11

Physical blowing agents.

Figure 5.12

Monomers for aromatic poly(isocyanate)s.

Figure 5.13

Tertiary amine catalysts.

Figure 5.14

Tin catalysts.

Figure 5.15

Curing catalysts.

Figure 5.16

Silicone monomers.

Chapter 6

Figure 6.1

Triphenyl(vinyl)phosphonium bromide.

Figure 6.2

Phthalic esters.

Figure 6.3

Membrane bubble-point vs. water flux (10).

Figure 6.4

Componds for prepolymers .

Figure 6.5

Dyes in wastewater.

Figure 6.6

Filtration apparatus with a membrane bioreactor (1).

Figure 6.7

Nitrification/denitrification membrane bioreactor (1).

Figure 6.8

Hybrid bioreactor (38).

Figure 6.9

Membrane bioreactor system (41).

Figure 6.10

Reactive Blue 50.

Figure 6.11

Reactive Green 19.

Figure 6.12

Tryptophan.

Figure 6.13

Asparagine.

Figure 6.14

Trans-configuration and cis-configuration of the 4-methacryloyloxy)p...

Figure 6.15

Methionine.

Figure 6.16

Trace comonomers.

Figure 6.17

Conventional porous body (63).

Figure 6.18

Produced porous body (63).

Figure 6.19

1-Ethyl-3-methylimidazolium-tetrafluoroborate.

Figure 6.20

Benzimidazole-containing polymers.

Figure 6.21

Nitrogen-containing electrolytes (78, 79).

Figure 6.22

Compounds for polymer electrolytes.

Figure 6.23

Monomers for poly(vinylidene fluoride-

co

-hexafluoropropylene).

Figure 6.24

Monomers for a poly(ether ketone) membrane.

Figure 6.25

Glutamic compounds.

Chapter 7

Figure 7.1

Compounds for spiking.

Figure 7.2

Acyclic amines.

Figure 7.3

Cyclic secondary amines (4).

Figure 7.4

Methocel.

Figure 7.5

Thymidine.

Figure 7.6

Compounds for ligand exchange chiral stationary phases.

Figure 7.7

Macrocyclic chiral selectors (12).

Figure 7.8

Monomers for monolithic thin layers.

Figure 7.9

Fluorescamine.

Figure 7.10

Monomers for porous organic cage materials.

Figure 7.11

Substances of a sorbent.

Figure 7.12

Cytochrome C.

Figure 7.13

5,10,15,20-Tetrakis (4-bromophenyl)porphyrin.

Figure 7.14

Momomers.

Figure 7.15

Solvents for membrane fabrication (34).

Figure 7.16

Plasma etching process (34).

Figure 7.17

Monomers for benzimidazole-linked polymers.

Figure 7.18

Acteoside.

Figure 7.19

Tenax and toxic organic materials.

Figure 7.20

Compounds for synthesis.

Figure 7.20

Toxic compounds.

Figure 7.21

Model compounds.

Figure 7.22

Synthesis of Polycalixarene (60).

Figure 7.23

Rigid crosslinking agents (63).

Figure 7.24

Organic pollutants.

Figure 7.25

Monomers for lysozyme extraction.

Figure 7.26

Crosslinking agents.

Figure 7.27

Compounds for derivatization (68).

Figure 7.28

5,10,15,20-Tetrakis (4-nitrophenyl)-21

H

,23

H

-porphyrin.

Figure 7.29

Porphyrin polymer (71).

Figure 7.30

3-Mercaptopropyltrimethoxysilane.

Figure 7.31

Thiol-ene surface functionalization with tetraethyl but-3-ene-1,1-di...

Figure 7.32

Compounds for surface functionalization (74).

Figure 7.33

1-Hydroxy-2-pyridinone.

Figure 7.34

Material for polymerization.

Chapter 8

Figure 8.1

Porosity and permeability (1).

Figure 8.2

Catalysts.

Figure 8.3

Flame retardants.

Figure 8.4

Dimethyl diallyl ammonium chloride.

Figure 8.5

Dibenzothiophene.

Figure 8.6

2,6-Bis(Benzimidazo-1-yl) pyridine.

Figure 8.7

Synthesis of a Ru-incorporated porous organic polymer.

Figure 8.8

N

,

N

’-methylenebisacrylamide.

Figure 8.9

Chemical vapor deposition and deposition temperature (19).

Figure 8.10

Porous polymer framework (26).

Figure 8.11

3,5-Dimethylpyrazole.

Figure 8.12

Tetraphenylethylene-based oxacalixarene (29).

Figure 8.13

Tetraphenylcyclopentadiene.

List of Tables

Chapter 1

Table 1.1

Porous coordination polymers (10).

Table 1.2

Building blocks with different geometries (15).

Table 1.3

Reactions for preparation of conjugated polymers.

Chapter 2

Table 2.1

Polymers and oligomers for porogens (1).

Table 2.2

Porosity (23).

Table 2.3

Porous materials prepared by suspension polymerization.

Table 2.4

Additional monomers (84).

Table 2.5

Internal crosslinking agents (84).

Table 2.6

Composition of polymers (88).

Chapter 3

Table 3.1

ASTM standard test methods for porous polymers.

Chapter 4

Table 4.1

Melting points and glass transition temperatures of some polymers (3).

Table 4.2

Monomers for hemocompatible polymers (76).

Table 4.3

Porogens (76).

Table 4.4

Aqueous phase composition reagents (78).

Table 4.5

Organic phase compositions (78).

Table 4.6

In-vitro

endotoxin removal (78).

Chapter 5

Table 5.1

Monomers for alkenyl aromatic polymers (14).

Table 5.2

Blowing agents (14).

Table 5.3

Process conditions (14).

Table 5.4

Plasticizers for PVC-based sheets (17).

Table 5.5

Foaming agents for PVC-based sheets (17).

Table 5.6

Isocyanate monomers (19).

Table 5.7

Blowing agents (19).

Table 5.8

Co-blowing agents (19).

Table 5.9

Catalysts (19).

Table 5.10

Compositions of N-NR/CNTs composites (31).

Table 5.11

Properties of the N-NR/CNTs composites (31).

Table 5.12

Properties of the porous structure of the supports (32).

Table 5.13

Physical blowing agents (33).

Table 5.14

Monomers for aromatic poly(isocyanate)s (45).

Table 5.15

Tertiary amine catalysts (45).

Table 5.16

Formulations for viscoelastic foams (45).

Table 5.17

Poly(urethane) composition (47).

Table 5.18

Water contact angles and pore volume (55).

Chapter 6

Table 6.1

Polymeric membranes (1).

Table 6.2

Polymers for membranes (19).

Table 6.3

Properties of pluronic polyols.

Table 6.4

ζ

-Potential vs. pH (8).

Table 6.5

Bisphenol compounds (41).

Table 6.6

Maximum adsorption capacities (34).

Table 6.7

Vanadium redox flow battery membranes (87).

Chapter 7

Table 7.1

Acyclic amines (4).

Table 7.2

Cyclic secondary amines (4).

Table 7.3

Brush-type chiral selectors (12).

Table 7.4

Model compounds (59).

Table 7.5

Properties of oil types.

Table 7.6

Crosslinking agents.

Table 7.7

Organic groups for polymer derivatization (68).

Table 7.8

Fields of use for the described materials (68).

Guide

Cover

Table of Contents

Title Page

Copyright

Preface

Begin Reading

Index

Also of Interest

End User License Agreement

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Porous Plastics

Johannes Karl Fink

Montanuniversität Leoben, Austria

This edition first published 2022 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA

© 2022 Scrivener Publishing LLC

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For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com.

Limit of Liability/Disclaimer of Warranty

While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials, or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read.

Library of Congress Cataloging-in-Publication Data

ISBN 978-1-119-89638-8

Cover image: Pixabay.com

Cover design by Russell Richardson

Set in size of 11pt and Minion Pro by Manila Typesetting Company, Makati, Philippines

Printed in the USA

10 9 8 7 6 5 4 3 2 1

Preface

Porous polymers are materials that are having pores in their design. Porous polymers are important for various fields of application, as described below. They are used with pores of different sized, i.e. from macropores to micropores.

This book focuses on the issues of porous polymers as well as low molecular compounds that can be introduced in porous polymers.

The book begins with a chapter about polymers that are used for porous materials. Here, among others, microporous polymer networks, hyper-crosslinked polymers, and rigid ladder-type porous polymers are detailed. Related issues will also be detailed in the subsequent chapters. In the next chapter, the major synthesis methods for porous polymers are described.

Then, the properties and material testing methods, such as standards, are described in a chapter.

In the following chapters, special fields of applications of porous polymers are described in detail, such as:

Chapter 4

:

Medical uses,

Chapter 5

:

Thermal insulation,

Chapter 6

:

Membranes,

Chapter 7

:

Separation methods, and

Chapter 8

:

Other fields of use.

The text focuses on the literature of the past decade. Beyond education, this book will serve the needs of industry engineers and specialists who have only a passing knowledge of the plastics and composites industries but need to know more.

How to Use This Book

Utmost care has been taken to present reliable data. Because of the vast variety of material presented herein, however, the text cannot be complete in all aspects, and it is recommended that the reader study the original literature for more complete information.

The reader should be aware that mostly US patents have been cited where available, but not the corresponding equivalent patents in other countries. For this reason, the author cannot assume responsibility for the completeness, validity or consequences of the use of the material presented herein. Every attempt has been made to identify trademarks; however, there were some that the author was unable to locate.

Index

There are four indices: an index of trademarks, an index of acronyms, an index of chemicals, and a general index.

In the index of chemicals, compounds that occur extensively, e.g., “acetone,” are not included at every occurrence, but rather when they appear in an important context.

Acknowledgements

I am indebted to our university librarians, Dr. Christian Hasenhüttl, Margit Keshmiri, Friedrich Scheer, Christian Slamenik, Renate Tschabuschnig, and Elisabeth Groß for support in literature acquisition. I also want to express my gratitude to all the scientists who have carefully published their results concerning the topics dealt with herein. This book could not have been otherwise compiled.

Last, but not least, I want to thank the publisher, Martin Scrivener, for his interest in publishing this book. In addition, my thanks go to Jean Markovic, who made the final copyedit with utmost care.

Johannes Fink

Leoben, May 2022

1Materials

Porous materials are typically categorized into three classes that have different pore sizes (1):

Macroporous with pore diameter larger than 50

nm

,

Mesoporous (pore diameter between 2

nm

and 50

nm

), and

Microporous materials (pore diameter smaller than 2

nm

).

While conventional polymer networks undergo pore collapse upon solvent removal as polymer strands can adopt many conformations in order to pack space efficiently, recent research efforts have popularized several classes of polymer networks that possess permanent porosity based on the use of rigid components.

1.1 Styropor

Otis Ray McIntire (1918-1996), a chemical engineer at Dow Chemical, rediscovered a process first patented by Swedish inventor Carl Munters (2).

According to the Science History Institute, "Dow bought the rights to the Munters method and began producing a lightweight, water-resistant, and buoyant material that seemed perfectly suited for building docks and watercraft and for insulating homes, offices, and chicken sheds (3). In 1944, Styrofoam was patented.

Before 1949, chemical engineer Fritz Stastny (1908-1985) developed pre-expanded poly(styrene) beads by incorporating aliphatic hydrocarbons such as pentane. These beads are the raw material for molding parts or extruding sheets. BASF and Stastny applied for a patent that was issued in 1949. The molding process was demonstrated at the Kunststoff Messe in Düsseldorf in 1952. These products were named Styropor (3).

The crystal structure of isotactic poly(styrene) was reported by Giulio Natta (4). In 1954, the Koppers company in Pittsburgh, Pennsylvania, developed expanded poly(styrene) foam under the trade name Dylite (5).

1.2 Porous Coordination Polymers

The design, analysis and applications of coordination polymers have been descried in a monograph (6).

A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands. More formally, a coordination polymer is a coordination compound with repeating coordination entities extending in 1, 2, or 3 dimensions (7, 8)

Examples of coordination polymers are lanthanoid coordination polymers, organometallic networks, and organic-inorganic hybrids (6).

1.2.1 Multifunctional Pillared-Layer Material

A multifunctional pillared-layer porous coordination polymer, has been constructed based on a flexible viologen derivative, 1,1’-bis(4-carboxybenzyl)-4,4’-bipyridinium dichloride, and an oxalate co-ligand. 1,1’-Bis(4-carboxybenzyl)-4,4’-bipyridinium dichloride is shown in Figure 1.1.

Figure 1.1 1,1’-Bis(4-carboxybenzyl)-4,4’-bipyridinium dichloride.

Single-crystal X-ray analysis showed that the compound possesses multichannels with dimensions of about 6.1×6.6 Å along the [110] and [-110] directions and 4.2×7.6 Å along [100], and a void space of about 41.4%.

Hydrogen adsorption measurements at 77 K and 1 atm indicated that the compound exhibits a hydrogen uptake of 0.71%. Owing to the incorporation of bipyridinium acceptor units, the compound can selectively accommodate aromatic donors into its nano-sized pores based on charge-transfer interactions in an elastic way, and afford a specific color to different guests.

Furthermore, the effect of perturbation exerted by the guest molecules on its magnetic properties has been investigated. The results indicated that the donor inclusion has little effect on its antiferromagnetic behavior, whereas dehydration of the compound decreases the strength of the magnetic exchange couplings and results in a change of the antiferromagnetic transition temperature from 14.7 K to 9.8 K (9).

1.2.2 Porous Coordination Polymer-Ionic Liquid Composite

A porous coordination polymer-ionic liquid composite has been described that includes an insulating structure composed of a porous coordination polymer, and an ionic liquid retained inside pores of the porous coordination polymer. The porous coordination polymer preferably has a main chain containing a typical metal element (10).

It has been proposed to apply an ionic liquid owing to high ionic conductivity thereof to an electrochemical device as an electrolyte for a battery or an electrical double-layer capacitor. The ionic liquid has extremely high flame retardance, and hence when used as the electrolyte for the electrochemical device, there is no need for a combustible organic solvent, thus ensuring the electrochemical device with high safety (10).

A schematic diagram that shows that an ionic liquid is filled with particles of the porous coordination polymer to form particles after filling is shown in Figure 1.2.

Here a a plurality of particles 111 composed of a porous coordination polymer are filled with a ionic liquid 12. The composite 131 obtained by a molding process. The structure 11, which is used as an electrolyte for a battery or an electrical double-layer capacitor, has a dense structure, thus making it easier for ion conduction pathways between the particles to be connected to each other. Hence, the composite 131 is a satisfactory ion conductor. In the case of using the structure 11 obtained by subjecting a plurality of the particles 111 composed of the porous coordination polymer to compression molding, a plurality of voids are respectively formed between the particles 111 of the porous coordination polymer (10).

Figure 1.2 Synthesis of a porous coordination polymer-ionic liquid composite (10).

Examples of the porous coordination polymer are collected in Table 1.1.

Table 1.1 Porous coordination polymers (10).

Compound

Shortcut

Zn(MeIM)2

ZIF-8

Al(OH)[BDC]

MIL-53(A1)

Cr(OH)[BDC]

MIL-53(Cr)

Fe(OH) [BDC]

MIL-53(Fe)

Zn2 (DOBDC)

MOF-74(Zn)

Mg2 (DOBDC)

MOF-74(Mg)

Al(OH)(1,4-NDC)

Cr3F(H2O)2O(BDC)3

MIL-101(Cr)

Al8(OH)12(OH)3(H2O)3 [BTC]3

MIL-110(Al)

Abbreviation

Compound

HMeIM

2-Methylimidazole

H2BDC

1,4-Benzenedicarboxylic acid

H4DOBDC

2,5-Dihydroxyterephthalic acid

H2NDC

1,4-Naphthalenedicarboxylic acid

H3BTC

1,3,5-Benzenetricarboxylic acid

H2BPDC

4,4’-Biphenyldicarboxylic acid

H2TPDC

4,4”-

p

-Terphenyldicarboxylic acid

The acids in Table 1.1 are shown in Figure 1.3.

Examples of hard acids, hard bases, soft acids, soft bases, intermediate acids, and intermediate bases are described in a monograph (11).

Figure 1.3 Acids in Table 1.1.

1.3 Networks

1.3.1 Microporous Polymer Networks

Microporous materials are defined as materials containing interconnected pores of less than 2 nm in diameter (12)

Due to their large surface area, many conventional microporous materials, such as zeolites and activated carbons, are widely used as catalysts, sorbents, and separation membranes. Recently, the field has evolved rapidly with the development of several novel types of microporous polymer networks. These materials not only benefit fundamental research by introducing modular approaches to accessing numerous sophisticated structures, but also provide new opportunities for various emerging applications (1).

The central design principle for introducing permanent microporosity into polymer networks involves the use of rigid building blocks. Such rigidity precludes the network strands from behaving effectively as entropic molecular springs and prevents the collapse of microporous structures upon solvent removal; consequently, the mechanical properties of these materials are stiff yet brittle.

Furthermore, the rigidity of the monomers prevents small loop formation and allows for establishing long-range order in the presence of self-error-correcting mechanisms, e.g., a reversible bond formation (1).

So, microporous polymer networks can be either amorphous or crystalline. Aside from the general use of very rigid components, the basic concepts of microporous polymer network synthesis are similar to those discussed above for either covalent or physical polymer networks.

1.3.2 Amorphous Microporous Polymer Networks

Amorphous microporous polymer networks of different types have been denoted by various names, such as:

Polymers with intrinsic microporosity (PIMs) (13),

Porous organic polymers (POPs) (14),

Conjugated microporous polymers (CMPs) (15), and

Hyper-crosslinked polymers (16).

It has been suggested to divide these materials into two categories, based on whether or not the strands are covalently crosslinked (1).

1.3.2.1 Conjugated Microporous Polymers

Conjugated microporous polymers (CMPs) are a class of organic porous polymers that combine p-conjugated skeletons with permanent nanopores, in sharp contrast to other porous materials that are not p-conjugated and with conventional conjugated polymers that are nonporous. As an emerging material platform, CMPs offer a high flexibility for the molecular design of conjugated skeletons and nanopores.

A lot of chemical reactions, building blocks and synthetic methods have been developed and a broad variety of CMPs with different structures and specific properties have been synthesized, driving the rapid growth of the field. CMPs are unique in that they allow the complementary utilization of p-conjugated skeletons and nanopores for functional exploration; they have shown great potential for challenging energy and environmental issues, as exemplified by their excellent performance in gas adsorption, heterogeneous catalysis, light emitting, light harvesting and electrical energy storage. This review describes the molecular design principles of CMPs, advancements in synthetic and structural studies and the frontiers of functional exploration and potential applications.

Building blocks with different geometries are listed in Table 1.2.

The structures of some building blocks with different geometries, sizes and reactive groups for the synthesis of CMPs are shown in Figure 1.4.

To construct a conjugated skeleton, the synthetic reaction must covalently link the building blocks with a p-conjugated bond.

The chemical reactions utilized for the preparation of linear conjugated polymers can also be employed for the synthesis of CMPs. The special reactions are listed in Table 1.3 and are shown in Figure 1.5.

Because building blocks can have different geometries, reactive groups, and P systems, this structural diversity significantly enhances the flexibility of the design of both skeletons and pores.

Table 1.2 Building blocks with different geometries (15).

C2 Compounds

1,4-Dibromobenzene

1,2-Dibromobenzene

1,4-Dibromo-2-methyl-benzene

1,4-Dibromo-2-trifluoromethyl-benzene

2,5-Dibromofluorobenzene

1,4-Dibromo-2-nitro-benzene

4,7-Dibromo-2,1,3-benzothiadiazole

2,5-Dibromo pyridine

2,5-Dibromobenzoic acid

2,5-Dibromonitrobenzene

1,4-Dibromo-2,5-difluorobenzene

1,4-Dibromo-2,5-dimethylbenzene

1,4-Dibromo-2,5-dihydroxybenzene

1,4-Dibromo-2,5-dimethoxybenzene

1,3-Dibromobenzene

2,6-Dibromophenol

2,4-Dibromoaniline

2,6-Dibromoaniline

3,5-Dibromo pyridine

3,5-Dibromo-

N

,

N

-dimethyl-4-pyridinamine

2,7-Dibrom-9

H

-carbazol

1,6-Dibromo-2-naphthol

2,6-Dibromonaphthalene

9,10-Dibromoanthracene

4,4’-Dibromobiphenyl

5-Bromo-2-(4-bromophenyl)pyridine

5,5’-Dibromo-2,2’-bipyridine

4,4’-Dibromooctafluorobiphenyl

1,4-Diiodobenzene

4,4’-Diiodobiphenyl

1,4-Diaminobenzene

4,4’-Diaminobiphenyl 1,2-Dicyanobenzene

1,3-Dicyanobenzene

1,4-Dicyanobenzene

4,4’-Diacyanobiphenyl

1,1’:4’,1”-Terphenyl-4,4”-dicarbonitrile

C3 Compounds

1,3,5-Tribromobenzene

1,3,5-Tris(3-bromophenyl)benzene

1,3,5-Tris(4-bromophenyl)benzene

2,4,6-Tris(p-bromophenyl)-s-triazine

1,3,5-Tris(4-bromophenylethynyl)benzene

1,3,5-Tris(4-aminophenyl)benzene

C4 Compounds

1,2,4,5-Tetrabromobenzene

1,3,6,8-Tetrabromopyrene

1,3,6,8-Pyrenetetracarbaldehyde

1,2,4,5-Tetraaminobenzene

2,2’,7,7’-Tetrabromo-9,9’-spirobifluorene

2,2’,7,7’-Tetraamino-9,9’-spirobifluorene

1,1’,1”,1”’-(1,1,2,2-Ethenetetrayl)tetrakis (4-bromobenzene)

C6 Compounds

1,2,3,4,5,6-Hexabromobenzene

1,2,3,4,5,6-Hexakis(4-bromophenyl)benzene

Table 1.3 Reactions for preparation of conjugated polymers.

Reaction name

References

Suzuki cross coupling reaction

(17, 18)

Yamamoto reaction

(19, 20)

Sonogashira-Hagihara reaction

(21, 22)

Oxidative coupling reaction

(23–25)

Schiff base reaction

(26–28)

Friedel-Crafts reaction

(29)

Phenazine ring fusion reaction

(30)

Cyclotrimerization

(31, 32)

Figure 1.4 Building blocks (15).

Figure 1.5 Reactions for the synthesis (15).

1.3.2.2 Hyper-Crosslinked Polymers

Hyper-crosslinked polymers (HCPs) are a series of permanent microporous polymer materials (16).

They were initially reported by Davankov ad Tsyurupa (33), and have received an increasing level of research interest.

In recent years, HCPs have experienced rapid growth due to their remarkable advantages such as diverse synthetic methods, easy functionalization, high surface area, low cost reagents and mild operating conditions (16).

The judicious selection of monomers, appropriate length crosslinkers and optimized reaction conditions yielded a well-developed polymer framework with an adjusted porous topology. Post fabrication of the as developed network facilitates the incorporation of various chemical functionalities that may lead to interesting properties and enhance the selection toward a specific application. To date, numerous HCPs have been prepared by post-crosslinking poly(styrene)-based precursors, one-step polycondensation or external crosslinking strategies.

The advent of these methodologies has prompted researchers to construct well-defined porous polymer networks with customized micromorphology and functionalities. In this review, we describe not only the basic synthetic principles and strategies of HCPs, but also the advancements in the structural and morphological study as well as the frontiers of potential applications in energy and environmental fields such as gas storage, carbon capture, removal of pollutants, molecular separation, catalysis, drug delivery, sensing, and other fields (16).

1.4 Rigid Ladder-Type Porous Polymers

A porous ladder polymer network was designed and synthesized as the model material via cross coupling polymerization and subsequent ring-closing olefin metathesis, followed by a characterization with solid-state nuclear magnetic resonance spectroscopy (34).

It could be shown that a rigid ladder-type backbone is more entropically favorable for gas adsorption and leads to a high gas uptake per unit surface area (34). The material exhibited a remarkable methane uptake per unit surface area, which outperformed those of most reported porous organic materials. Variable-temperature thermodynamic adsorption measurements corroborated the significantly less negative entropy penalty during high-pressure gas adsorption, compared to its non-ladder-type counterpart.

So, the here described method provides an orthogonal strategy for multiplying volumetric methane uptake capacity of porous materials. In addition, the entropic approach offers the opportunity to increase deliverable gas upon pressure change while mitigating the performance decline in high-temperature applications (34).

1.5 Photocatalysts

Conjugated microporous polymers (CMPs) are an emerging class of promising photocatalysts because of their large specific surface areas and adjustable optical band gaps. To avoid metal contamination, metal-free synthetic procedures for making CMPs for photocatalytic water splitting are highly desired.

Triazine-based conjugated microporous polymers were synthesized through a simple, efficient, metal-free catalyzed approach. The compound is shown in Figure 1.6.

Through linking donor-acceptor type pyrazole-benzothiadiazole-pyrazole light-absorbing units by triazine units, the polymer has an ideal optical band gap of about 2.3 eV and exhibits a high hydrogen evolution rate of 50 µmol h−1 under visible light illumination (λ ≥ 420 nm) and apparent quantum efficiency as high as 3.58% at 420±20 nm. However, by replacing electron-neutral benzene instead of the electron-withdrawing benzothiadiazole, c.f., Figure 1.7, such a polymer shows an obvious hypochromatic shift in the absorption and large optical band gap of about 2.9 eV, as well as poor photocatalytic property (35).

1.5.1 Compounds for Photocatalytic Aerobic Oxidation

Heptazine-based porous organic polymers (POPs), as new potential photocatalytic materials, have spurred extensive research interest (36).

Four heptazine-based POPs were prepared by using cyameluric chloride as precursor, piperazine (POP-1), p-phenylenediamine (POP-2), biphenyl diamine (POP-3) and 4,4”-diamino-p-terphenyl (POP-4) as basic blocks. Compounds for photocatalytic materials are shown in Figure 1.8.

Figure 1.6 Pyrazole-benzothiadiazole-pyrazole polymer (35).

The effects of the composition and structure of POPs on their spectrum, specific surface area, interface contact in acetonitrile, electronic structure, carrier separation and photocatalytic aerobic oxidation of amine through experiments and density functional theory calculations were systematically studied.

The results show that with the increase of the benzene rings and electron density of diamine linker, the electron-donating ability of these heptazine-based POPs is significantly enhanced, which reduces the band gap of the materials, improves their electronic donor-acceptor interaction with heptazine and promotes the transfer and separation of photogenerated carriers, thus endowing them with significantly higher photocatalytic performance (36).

Notably, POP-4 shows the best photocatalytic aerobic oxidation activity of benzylamine, which is significantly higher than that of g−C3N4. The conversion and selectivity of benzylamine to corresponding imine are both >99% within 4 h under 10 W 420 nm light-emitting diode light irradiation (36).

Figure 1.7 Pyrazole-benzene-pyrazole polymer (35).

1.5.2 Floating Photocatalysts

A floating photocatalysis material has a big advantage over a powder- suspension one for the deep purification of pollutants in colored wastewater. So, the design and synthesis of floating photocatalysts are of great importance (37).

The preparation of metal-free triazine-based porous organic polymer has been presented. Here, a visible-light photocatalyst based on biomass waste poplar catkins is used to construct a reusable floating photocatalysis system via a soft synthesis. A trigonal-symmetrical melamine is coupled with triformylphloroglucinol as monomer to obtain a photoactive conjugated material loaded on soft and light poplar catkin microfibers. Triformylphloroglucinol is shown in Figure 1.9.

When this microfiber material is floated on the polluted water, it can convert 100% Cr(VI) 80 min into Cr(III) species, which are then partly synchronously immobilized (56.9%) to lessen the rerelease of Cr element, or degrade 100% methylene blue after 100 min of visible-light irradiation.

Figure 1.8 Compounds for photocatalytic materials.

Figure 1.9 Triformylphloroglucinol.

Moreover, the film-like flexible self-supporting material also exhibits good catalytic activities and an excellent reusability for multipurpose water purification under real natural conditions.

So, the assembly of green floating photocatalysis systems allows a versatile solid surface activation for establishing a more energy efficient and robust catalysis process under visible light (37).

1.5.3 Photocatalysts with Side Chains

Conjugated polymers have been investigated as photocatalysts for hydrogen production. An efficient design has been demonstrated to enhance the hydrogen evolution rate of conjugated polymers through the modification of surface chemistry by introducing the hydrophilic adenine group onto the side chain (38).

An adenine group with plentiful nitrogen atoms can form multiple hydrogen bonds with water molecules, which improve the interactions between the resulting polymer surface and water molecules, leading to an improved hydrophilicity and dispersity of the polymer photocatalyst in photocatalytic reaction solution.

A density functional theory calculation indicated that the introduction of adenine groups also leads to the enhanced separation of the electrostatic potential on the surface of polymer photocatalyst, which is favorable for the photocatalytic hydrogen evolution reaction. Therefore, a high hydrogen evolution rate of 36.43 mmol h−1g−1 could be achieved by the adenine-functionalized polymer PF6A-SF, c.f. Figure 1.10, without using a Pt cocatalyst, which is almost 42 times higher than that of the alkyl-functionalized polymer (38).

So, a rational design of side-chain engineering is an effective design for organic photocatalysts with a high photocatalytic activity (38).

Figure 1.10 Side chain engineering.

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2Synthesis Methods

Microfluidics, membrane/microchannel, suspension, dispersion, precipitation, multistage polymerizations and a few other less known methods were detailed (1). Also, the ability to yield nonspherical particles for these methods and size monodispersity, pore characteristics and chemical functionality of the obtained particles was discussed.

2.1 Porogens

Porogens are substances that can yield a porous nature of certain particles. Reactive porogens and immiscible porogens cannot really dilute a monomer mixture (1).

2.1.1 Polymers and Organic Solvents

Several polymers and oligomers can be used for polymerization, generally together with a solvent as the porogen. In this case the pore formation occurs via ξ-induced syneresis.

Examples of polymers and oligomers that can be used as porogens are shown in Table 2.1.

It was found that the amount and the nature of a polymeric porogen may either induce a porous or a nonporous hollow final structure (2, 3).

Also, differences between the use of a good solvent (toluene), a non-solvent (dodecanol) and a polymeric porogen (poly(styrene) (PS) in toluene, 15%) for the synthesis of a copolymer of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDM) were shown (8). With a good solvent, non-solvent and a polymeric porogen, the specific surface area decreases below 1 m2g−1, whereas the size of the microglobules and the total pore volume increase.

Table 2.1 Polymers and oligomers for porogens (1).

Compound

Reference

Poly(methyl methacrylate)

(4)

Poly(styrene)

(5)

Poly(ethylene oxide)

(6)

Poly(propylene oxide)

(7)

Poly(dimethyl siloxane)

(7)

A bimodal pore size distribution can be obtained in some cases by using a mixture of toluene (good solvent, inducing micropores) and poly(dimethyl siloxane) (PDMS) (polymeric porogen, inducing macropores) for a bead composed of divinylbenzene (DVB) alone (7).

It was not expected that from a single porogen the combination of high surface area and high pore volume could be reached. However, it was found that polymeric DVB particles exhibit a surface area equal to 720 m2g−1, together with a very high pore volume of 68%, when prepared in the presence of 1-chlorodecane alone, which is a non-solvent for a DVB polymer (9).

An important problem due to the use of a non-solvent as the porogen is the possibility of the formation of a dense and often impermeable polymer layer on the surface of particles, although the internal structure is highly porous (1).

A non-solvent should possess a solubility parameter that significantly differs from that of the polymer. However, when the difference in the solubility parameter is too large, a skin formation is promoted (10). Here, the difference in the solubility parameter was increasing by a decreasing polarity of the porogen.

Since the continuous phase was water in their system, highly nonpolar porogens disliked being present in the water/oil interface due to the high interfacial tension. Thus, the interface became rich in monomer and polymer, resulting in a skin layer, while the interior was porous (1).

2.1.2 Water as Porogen

A porogen that is immiscible with the initial monomer mixture can be utilized to synthesize porous particles. The most common example of such a strategy is the usage of water as porogen. A water-in-oil-in-water (W/O/W) double emulsion is formed by adding oil soluble surfactants to the discrete monomer (oil) phase. Water is absorbed from the continuous water phase by the monomer droplets as a result of the stabilizing effect of the oil-soluble surfactants (11).

Although porogen water droplets should have been separated initially inside the monomer phase, highly porous polymer beads with pore sizes around 80 nm and surface area values reaching up to 200 m2g−1 (proving the interconnectivity of pores) are obtained after polymerization. The same authors also published that a combination of surfactants can produce hollow porous beads (12).

2.1.3 Solid Porogens

Immiscible porogens can be a solid instead of water, which results in the realization of solid-in-oil-in-water dispersions. Here, pores are formed after the removal of solid particles embedded on polymer beads via washing or etching. Washing is needed to get the porous structure.

As an example for a solid-in-oil-in-water dispersion, ∼0.8 µm CaCO3 particles were dispersed in a monomer mixture of EGDM and GMA and suspension polymerized this solid to oil dispersion in water (13). After removal of CaCO3 via HCl etching, the beads exhibited pores as large as 10 µm and a surface area value of 79 m2g−1.

In another report (14), a mixture of solid CaCO3, non-solvent (dodecanol) and good solvent (cyclohexanol) porogens are utilized all together for the suspension polymerization of the same EGDM-GMA monomer mixture. Together with a total surface area of 91 m2g−1, the formation of a bimodal distribution of micropores (10–90 nm) and macropores (180–4000 nm) is observed.

2.2 Living Radical Polymerization

Porous particles can be made of an organic polymer. They have a substantially spherical shape (15). Each of the porous particles has an interconnected pore structure in which through-holes provided inside the porous particle communicate with each other, and ends of the through-holes are open toward the outside of the porous particle.

The raw material monomer constituting the polymer forming the porous particles may be radical polymerizable or ion polymerizable. When a radical polymerizable monomer is subjected to free radical polymerization, a polymer of a particle agglutination type is liable to be formed.

Thus, in order to cause a spinodal decomposition, it is preferable to use living radical polymerization that proceeds in a consecutive manner. Ion polymerization and condensation polymerization also are consecutive reactions, so that it can be said they also are suitable for causing spinodal decomposition (15).

The ion polymerizable monomer may be an anion polymerizable monomer or a cation polymerizable monomer, for example. Examples of the radical polymerizable monomer include poly(ethylene) derivatives and poly(acrylic acid) or poly(methacrylic acid) derivatives. Examples of the ion polymerizable monomer include epoxy monomers; styrene, 1,3 butadiene and derivatives thereof, vinylpyridine, methacrylic esters; and acrylonitrile.

The monomer used for forming the porous particle of the present invention may be a monomer other than the radical polymerizable monomer, and may be an ion polymerizable monomer (15).

2.3 Emulsion Polymerization

2.3.1 High Internal Phase Emulsion Polymerization

High internal phase emulsion (HIPE) polymerization is a relatively new technique that has found a wide variety of applications in tissue engineering scaffolds, enzyme immobilization, gas storage and separation media (16–19).

Recently, it was shown that p-conjugated highly porous polymer scaffolds can combine the hierarchically interconnected pore structure of highly porous polymer scaffolds and the p-conjugated polymer backbone throughout the network, showing high efficiency as a heterogeneous photosensitizer for singlet oxygen generation under visible light (20).

Also, the micropore engineering and photocatalytic activity of conjugated microporous highly porous polymer scaffolds was reported for highly selective oxidation of organic sulfides to sulfoxides under visible light (21).

Actually, the photopolymerization of methyl methacrylate using p-conjugated porous HIPE polymers as a heterogeneous photoinitiator could be efficiently achieved under visible light (22).

A method for producing a HIPE foam has been described (23).

Here, a water bath is used to polymerize a HIPE. The characteristics of the polymerized HIPE foam may be varied depending on the composition and characteristics of the water bath. The HIPEs are produced using a continuous process, for example, by having a HIPE pumped into a water bath while traveling through the bath.

The HIPE foams produced from this method are useful for the absorption of liquid materials. A HIPE consists of two phases. One phase is a continuous oil phase that contains monomers that are polymerized to form a HIPE foam and an emulsifier to help to stabilize the HIPE. The monomer component may be present in an amount of from about 80% to about 99%, and under certain conditions from about 85% to about 95% by weight of the oil phase. The emulsifier component, which is soluble in the oil phase and suitable for forming a stable water-in-oil emulsion, may be present in the oil phase in an amount of from about 1% to about 20% by weight of the oil phase. The emulsion may be formed at an emulsification temperature of from about 20°C to about 130°C and in certain embodiments from about 50°C to about 100°C.

In general, the monomers will include from about 20% to about 97% by weight of the oil phase at least one substantially water-insoluble monofunctional alkyl acrylate or alkyl methacrylate.

For example, monomers of this type may include C4−C18 alkyl acrylates and C2−C18 methacrylates, such as ethylhexyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, isodecyl acrylate, tetradecyl acrylate, benzyl acrylate, nonyl phenyl acrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, isodecyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, and octadecyl methacrylate. Some of these compounds are shown in Figure 2.1.

Figure 2.1 (Meth)acrylic monomers.

Blends of these monomers can have the desired glass transition temperature (Tg) of the resulting HIPE foams. The oil phase may also comprise from about 2% to about 40%, and in certain embodiments from about 10% to about 30%, by weight of the oil phase, a substantially water-insoluble, polyfunctional crosslinking alkyl acrylate or methacrylate.

This crosslinking comonomer is added to confer strength and resilience to the resulting HIPE foam. Examples of crosslinking monomers of this type comprise monomers containing two or more activated acrylate, methacrylate groups, or combinations thereof.

Examples of this group include 1,6-hexanediol diacrylate, 1,4-butanediol dimethacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate, 1,12-dodecyldimethacrylate, 1,14-tetradecanedioldimethacrylate, ethylene glycol dimethacrylate, neopentyl glycol diacrylate (2,2-dimethylpropanediol diacrylate), hexanediol acrylate methacrylate, glucose pentaacrylate, sorbitol pentaacrylate. Some of these compounds are shown in Figure 2.2.

Figure 2.2 Crosslinking monomers.

Other examples of crosslinking agents contain a mixture of acrylate and methacrylate moieties, such as ethylene glycol acrylate-methacrylate and neopentyl glycol acrylate-methacrylate. The ratio of methacrylate:acrylate group in the mixed crosslinking agent may be varied from 50:50 to any other ratio as needed.

Any third substantially water-insoluble comonomer may be added to the oil phase in weight percentages of from about 0% to about 15% by weight of the oil phase, in certain embodiments from about 2% to about 8%, to modify the properties of the HIPE foams.

In certain cases, toughening monomers may be desired which impart toughness to the resulting HIPE foam. These include monomers such as styrene, vinyl chloride, vinylidene chloride, isoprene, and chloroprene. Some of these compounds are shown in Figure 2.3

Figure 2.3 Toughening monomers.

It is believed that such monomers aid in stabilizing the HIPE during polymerization to provide a more homogeneous and better formed HIPE foam which results in better toughness, tensile strength, and abrasion resistance.

Monomers may also be added to confer flame retardancy as shown previously (24). The monomers may be added to confer color, e.g., vinyl ferrocene, fluorescent properties, radiation resistance, opacity to radiation, (e.g. lead tetraacrylate), to disperse charge, to reflect incident infrared light, to absorb radio waves, to form a wettable surface on the HIPE foam struts, or for any other desired property in a HIPE foam.

In some cases, these additional monomers may slow the overall process of conversion of HIPE to HIPE foam, the tradeoff being necessary if the desired property is to be conferred. Thus, such monomers can be used to slow down the polymerization rate of a HIPE. Examples of monomers of this type comprise styrene and vinyl chloride. The oil phase may further contain an emulsifier used for stabilizing the HIPE.

Emulsifiers used in a HIPE can include (24):

Sorbitan monoesters of branched C

16

−C

24

fatty acids,

Linear unsaturated C

16

−C

22

fatty acids; and linear saturated C

12

−C

14

fatty acids, such as sorbitan monooleate, sorbitan monomyristate, and sorbitan monoesters, sorbitan monolaurate diglycerol monooleate (DGMO), polyglycerol monoisostearate (PGMIS), and polyglycerol monomyristate (PGMM),

Polyglycerol monoesters of branched C

16

−C

24

fatty acids, linear unsaturated C

16

−C

22

fatty acids, or linear saturated C

12

−C

14

fatty acids, such as diglycerol monooleate, diglycerol monomyristate, diglycerol monoisostearate, and diglycerol monoesters,

Diglycerol monoaliphatic ethers of branched C

16

−C

24

alcohols, linear unsaturated C

16

−C

22

alcohols, and linear saturated C

12

−C

14

alcohols, and mixtures of these emulsifiers.

Some of these compounds are shown in Figure 2.4.

Another emulsifier that may be used is polyglycerol succinate, which is formed from an alkyl succinate, glycerol, and triglycerol. Such emulsifiers, and combinations thereof, may be added to the oil phase so that they comprise between about 1% and about 20%, in certain embodiments from about 2% to about 15%, and in certain other embodiments from about 3% to about 12% by weight of the oil phase. In certain embodiments, coemulsifiers may also be used to provide additional control of cell size, cell size distribution, and emulsion stability, particularly at higher temperatures of, for example, greater than about 65°C.

Examples of coemulsifiers include phosphatidyl cholines and phosphatidyl choline-containing compositions, aliphatic betaines, long chain C12−C22 dialiphatic quaternary ammonium salts, short chain C1−C4 dialiphatic quaternary ammonium salts, long chain C12−C22 dialkoyl(alkenoyl)-2-hydroxyethyl, short chain C1−C4 dialiphatic quaternary ammonium salts, long chain C12−C22 dialiphatic imidazolinium quaternary ammonium salts, short chain C1−C4 dialiphatic imidazolinium quaternary ammonium salts, long chain C12−C22 monoaliphatic benzyl quaternary ammonium salts, and long chain C12−C22 dialkoyl(alkenoyl)-2-aminoethyl, short chain C1−C4 monoaliphatic benzyl quaternary ammonium salts, short chain C1−C4 monohydroxyaliphatic quaternary ammonium salts. In certain embodiments, ditallow dimethyl ammonium methyl sulfate (DTDMAMS) may be used as a coemulsifier.

Figure 2.4 Emulsifiers.

Another component that may be present in the aqueous phase is a water-soluble free radical initiator. The initiator can be present at up to about 20 mol% based on the total moles of polymerizable monomers present in the oil phase. In certain embodiments, the initiator is present in an amount of from about 0.01 mol% to about 10 mol% based on the total moles of polymerizable monomers in the oil phase. Suitable initiators include ammonium persulfate, sodium persulfate, potassium persulfate, 2,2’-azobis(N,N’-dimethyleneisobutyramidine)dihydrochloride, and other suitable azo initiators. To reduce the potential for premature polymerization which may clog the emulsification system, the addition of the initiator to the monomer phase may be done just after or near the end of the emulsification process.

The HIPEs and their subsequent polymerization into absorbent foams are illustrated in the following example (23):

Preparation 2–1: HIPE foams are prepared from a HIPE (5% oil in 95% water). The oil phase is prepared from a 3.35:1 ratio of EHA: ethylene glycol dimethacrylate and 12% polyglycerol succinate as surfactant. The aqueous phase is 2% NaCl and 0.33% NaPS in water. The HIPE is injected into the water bath in the form of fibers. The water baths can be maintained at 85°C and have varying compositions of deionized water, 2%NaCl, 0.33% NaPS, and both 2% NaCl.