Fluorinated polymers volume 2 applications polymer chemistry series

RSC Polymer Chemistry SeriesEditor-in-Chief: Professor Ben Zhong Tang, The Hong Kong University of Science and Technology, Hong Kong, China Professor Christoph Weder, University of Fribo

Fluorinated PolymersVolume 2: Applications

RSC Polymer Chemistry Series

Editor-in-Chief:

Professor Ben Zhong Tang, The Hong Kong University of Science and

Technology, Hong Kong, China

Professor Christoph Weder, University of Fribourg, Switzerland

Titles in the Series:

1: Renewable Resources for Functional Polymers and Biomaterials

2: Molecular Design and Applications of Photofunctional

Polymers and Materials

3: Functional Polymers for Nanomedicine

4: Fundamentals of Controlled/Living Radical Polymerization

5: Healable Polymer Systems

6: Thiol-X Chemistries in Polymer and Materials Science

7: Natural Rubber Materials: Volume 1: Blends and IPNs

8: Natural Rubber Materials: Volume 2: Composites and Nanocomposites9: Conjugated Polymers: A Practical Guide to Synthesis

10: Polymeric Materials with Antimicrobial Activity: From Synthesis toApplications

11: Phosphorus-Based Polymers: From Synthesis to Applications

12: Poly(lactic acid) Science and Technology: Processing, Properties,Additives and Applications

13: Cationic Polymers in Regenerative Medicine

14: Electrospinning: Principles, Practice and Possibilities

15: Glycopolymer Code: Synthesis of Glycopolymers and their Applications16: Hyperbranched Polymers: Macromolecules in-between DeterministicLinear Chains and Dendrimer Structures

17: Polymer Photovoltaics: Materials, Physics, and Device Engineering18: Electrical Memory Materials and Devices

19: Nitroxide Mediated Polymerization: From Fundamentals to

Applications in Materials Science

20: Polymers for Personal Care Products and Cosmetics

21: Semiconducting Polymers: Controlled Synthesis and Microstructure22: Bio-inspired Polymers

23: Fluorinated Polymers: Volume 1: Synthesis, Properties, Processing andSimulation

24: Fluorinated Polymers: Volume 2: Applications

How to obtain future titles on publication:

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Book Sales Department, Royal Society of Chemistry, Thomas Graham House,Science Park, Milton Road, Cambridge, CB4 0WF, UK

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RSC Polymer Chemistry Series No 24

A catalogue record for this book is available from the British Library

rThe Royal Society of Chemistry 2017

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Because of the increasing need for better performing materials endowedwith specific properties for high-tech applications, fluoropolymers haveundergone a rapid development Since their discovery in the 1930s, theseniche specialty polymers have been regarded as unique macromoleculeswith an exceptional combination of characteristics (derived from the strongC–F bond, such as chemical resistance, heat and light stability, electricalinsulation and liquid and soil repellency) to provide superior performance inthe chemical, medical, aerospace, automotive, electrical and electronicsindustries

The relationship between the structures of the monomers and the erties of the resulting (co)polymers is of increasing interest in order to tunethese properties towards the most appropriate applications

prop-These fluoroplastics or fluoroelastomers have already been involved inmany applications, ranging from surfactants, optical fibers, biomaterials,liners or ultrathin layers, electronics, seals and O-rings for the aerospaceand automotive industries, coatings, piezoelectric devices, electrolytes andseparators for lithium ion batteries and back-sheets for photovoltaics tomembranes for seawater desalination and fuel cells These polymers arenowadays experiencing enormous growth and their production is increasing

by 7% yearly In the last decade, around 10 reviews, chapters and books havebeen published that witness the great interest in these materials

Fluorinated Polymers is composed of two volumes and includes 23 chapterswritten by internationally recognized industrial and academic experts,outlining fundamental concepts and applied topics, starting with a generalintroduction Then, emphasis is placed on recent developments andchallenges, and most chapters describe comprehensive techniques ofsynthesis, characterization and properties of fluoropolymers (FPs) Volume 1

is devoted to the basic aspects of FPs, including the chemistry, synthesis of

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vii

key reactants and techniques of polymerization, processing, and simulation,while Volume 2 concerns specific characterization and applications.Regarding syntheses, those of initiators (especially peroxides, Chapter 1,Volume 1), monomers (Chapter 2, Volume 1), oligomers (Chapter 4, Volume1), well-defined fluorotelomers (Chapter 11, Volume 1 and Chapter 1,Volume 2) and alternating copolymers (Chapters 9 and 10, Volume 2), arehighlighted, in addition to fluoroplastics and fluoroelastomers (Chapters 3and 4, Volume 2) and key (co)polymers such as polyacrylates (Chapter 8,Volume 1 and Chapters 1 and 2, Volume 2), polyaromatics (Chapter 5,Volume 1), PVDF (Chapter 6, Volume 2), polyphosphazenes (Chapter 3,Volume 2), perfluoropolyethers (Chapters 5 and 7, Volume 2), copolymersand terpolymers based on vinylidene fluoride (Chapter 7, Volume 1 andChapter 6, Volume 2), tetrafluoroethylene (Chapter 9, Volume 2), orchlorotrifluoroethylene (Chapters 5 and 10, Volume 2) In addition, commonsynthetic methods such as anionic polymerization (Chapter 3, Volume 1)and radical polymerization in supercritical CO2(Chapter 7, Volume 1) andspecific processes such as electrochemical (Chapter 6, Volume 1) and meltprocessing (Chapter 10, Volume 1) complete these aspects, while Chapter 11,Volume 1 brings an insight into simulation.

This book also outlines some characterizations of FPs such as the surfaceproperties of poly(acrylate)s (Chapter 8, Volume 1 and Chapters 1 and 2,Volume 2), self-assembly of well-architectured FPs (Chapter 9, Volume 1) andtheir applications in paints and coatings (Chapters 5 and 6, Volume 2),energy storage and conversion (Chapter 5, Volume 1 and Chapters 7, 8 and 9,Volume 2) and nanomaterials for specific applications (Chapters 11 and 12,Volume 2) In addition, environmental aspects (Chapters 1 and 2, Volume 2)are also supplied

We would like to thank all contributors for their valuable chapterslisted above

These volumes, for immediate use by today’s engineers and industrial andacademic scientists and researchers, and also for graduate students, working

in the fields of materials science, polymer chemistry and energy applications

of polymers have been arranged to facilitate self-managed reading andlearning They are both a source of data and a reference

Bruno AmeduriHideo Sawada

Volume 1SYNTHESISChapter 1 Fluorinated Peroxides as Initiators of Fluorinated

1.3.3 Bond Dissociation Energy of Alkanoyl/

Fluoroalkanoyl Peroxides and Radicals 121.3.4 Thermal Decomposition of

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ix

2.2 General Aspects of the Addition of Perfluoroalkyl

2.3 Process for the Formation of Head-to-head Type

Styrene Dimers Bearing Two FluoroalkylEnd-groups, as a Basic Principle for Reactions

2.4 Synthesis and Characteristic Properties of Styrene

Dimers, as the Smallest Model Unit for Fluoroalkyl

3.2 Anionic Polymerization Reactivity of Fluorinated

3.3 Anionic Polymerization Reactivity of Fluorinated

Susanta Banerjee and Anindita Ghosh

5.1 General Introduction to Aromatic Fluorinated

5.4.1 Preparation of Fluorinated Poly(Ether

5.6.5 Fluorinated Polymers withPerfluorocyclobutyl (PFCB) Units 1685.6.6 Fluorinated Polymers with

5.6.7 Fluorinated Phosphorus-containing

5.6.8 Fluorinated Microporous Copolymer as

5.6.9 Quaternized Fluorinated Copolymers as

Chapter 6 Synthesis of Fluoro-functional Conjugated Polymers by

6.3 Electrochemical Fluorination of Conjugated

6.3.1 Electrochemical Polymer Reactions 1976.3.2 Anodic Fluorination of Polyfluorene Derivatives 1986.3.3 Fluorination of Polyaniline by the CRS

6.4 Surface Modification of Conjugated Polymers withFluoro-functional Groups by Electrochemical

6.4.2 Electro-click Reaction on Conjugated

Chapter 7 Supercritical Carbon Dioxide as Reaction Medium for

Fluoropolymer Synthesis and Kinetic Investigations into

Benjamin Hosemann, Rebekka Siegmann and

Sabine Beuermann

7.2 Supercritical Carbon Dioxide as Reaction Medium

7.3 In-line Monitoring of Vinylidene Fluoride

Homo- and Copolymerizations in the HomogeneousPhase with Supercritical Carbon Dioxide 215

7.4 Kinetic Investigations for Vinylidene Fluoride

Homo- and Copolymerizations in Supercritical

D Pospiech, D Jehnichen, P Chunsod, P Friedel,

F Simon and K Grundke

9.3 Preparation and Self-assembly of Non-linear

Correlations to Molecular Structure and Tailoring

Harald Kaspar

10.3.1 Fluoropolymer Melts in Shear Flows 314

10.4.1 General Considerations on the Molar

10.4.2 Key Rheology Parameters and Dependence

10.4.3 Diagnosing the Molar Mass Distribution

10.5 Customizing Concepts for Linear Chains 32910.5.1 Controlling the Average Molar Mass 32910.5.2 End-group Considerations in View of

SIMULATIONChapter 11 Molecular Simulation of Fluorinated Telomer and Polymers 361

François Porzio, E´tienne Cuierrier, Alexandre Fleury,

Bruno Ame´duri and Armand Soldera

11.4.4 The TS Quasi-partition Function 37811.4.5 The Free Reactant Partition Function per

11.4.7 The Rate Constants and the Chain

1.3 Functionalized Oligomers and Their Applications 9

2.4 Expression Mechanism of Water Repellency of

2.5 Molecular Design Concept for Short-chain

Chapter 3 Structural Diversity in Fluorinated Polyphosphazenes:

Exploring the Change from Crystalline Thermoplastics toHigh-performance Elastomers and Other New Materials 54Harry R Allcock

3.11 Optical Properties: Controlled Refractive Index

Chapter 4 Fluoroplastics and Fluoroelastomers – Basic Chemistry

Masahiro Ohkura and Yoshitomi Morizawa

4.1 Properties of Fluorine and Brief History of

Chapter 5 Fluorinated Specialty Chemicals – Fluorinated Copolymers

for Paints and Perfluoropolyethers for Coatings 110Taiki Hoshino and Yoshitomi Morizawa

5.1 Synthesis and Coating Application of Partially

5.1.4 Examples of Coating Applications of Partially

5.2 Synthesis and Application of Perfluoropolyethers 119

5.2.2 Types and Characteristics of

James T Goldbach, Ramin Amin-Sanayei, Wensheng He,

James Henry, Walt Kosar, Amy Lefebvre, Gregory O’Brien,

Diane Vaessen, Kurt Wood and Saeid Zerafati

Chapter 7 The Role of Perfluoropolyethers in the Development of

Polymeric Proton Exchange Membrane Fuel Cells 158

M Sansotera, M Gola, G Dotelli and W Navarrini

7.2 Interaction of PFPE Chains on Carbonaceous

7.3 Effects of PFPE on Carbon Black and Carbon Fibers 163

7.3.2 Effects of PFPE on Carbon Fibers 1667.4 Effects of PFPE in PEMFC Gas Diffusion Layers 168

Chapter 8 Fluorinated Ionomers and Ionomer Membranes: Monomer

Takeshi Hirai and Yoshitomi Morizawa

8.1 Introduction and Brief History of Fluorinated

8.2 Synthesis of Representative Ionomer Membranes 181

9.2 Co- and Terpolymers of Tetrafluoroethylene and

9.2.1 Co- and Terpolymers of Tetrafluoroethylene

9.2.2 Co- and Terpolymers of Tetrafluoroethyleneand Alkyl Trifluorovinyl Ethers 2159.2.3 Co- and Terpolymers of Tetrafluoroethyleneand Perfluoroalkyl Trifluorovinyl Ethers 2179.2.4 Co- and Terpolymers of Tetrafluoroethyleneand Fluorinated Alkyl Vinyl Ethers Having

9.2.5 Co- and Terpolymers of Tetrafluoroethyleneand Fluorinated Alkyl Vinyl Ethers

Having Multiple Ether Linkages on the

and Fluorinated Alkyl Vinyl EthersHaving Multiple Vinyl Ether

9.6 Co- and Terpolymers of Tetrafluoroethylene with

Cyclic Monomers and Tetrafluoroethylene-based

Chapter 10 Chlorotrifluoroethylene Copolymers for Energy-applied

10.3.4 CTFE-containing Copolymers Bearing

Chapter 11 Fabrication of Flexible Transparent Nanohybrids with

Heat-resistance Properties Using a Fluorinated Crystalline

Atsuhiro Fujimori

11.1 Flexible Transparent Fluorinated Nanohybrids

with Innovative Heat-resistance Properties:

New Technology Proposal for the Fabrication ofTransparent Materials Using a ‘‘Crystalline’’ Polymer 301

11.1.4 Formation and Thermal Behavior of

‘‘Crystalline’’ Transparent Nanohybrid 31011.1.5 Fine Structural Analysis of ‘‘Crystalline’’

11.1.6 Improvement in Physical Properties of

‘‘Crystalline’’ Transparent Nanohybrid 318

11.2 Fabrication of Antibacterial Transparent Flexible

Nanohybrid with Heat Resistance UsingHigh-density Amorphous State Formation and

11.2.5 Fine Structural Analysis of ‘‘Crystalline’’

Transparent Nanohybrid with

11.2.6 Improvement in the Behavior of the

Physical Properties of ‘‘Crystalline’’

Transparent Nanohybrid with

Chapter 12 Creation of Superamphiphobic, Superhydrophobic/

Superoleophilic and Superhydrophilic/Superoleophobic

Surfaces by Using Fluoroalkyl-endcapped

Vinyltrimethoxysilane Oligomer as a Key Intermediate 353Hideo Sawada

APPLICATIONS

*Email: rdams1@mmm.com

In the early 1930s, researchers of IG-Farbenindustrie in Frankfurt (Germany)studied systematically the first polymerizations of fluoroethenes; theHoechst researchers had already prepared polychlorotrifluoroethylene(PCTFE) and polytetrafluoroethylene (PTFE), including copolymers, re-cognizing the outstanding properties of these polymers.1 The first patentapplication for a fluoropolymer was filed in October 1934 by Schloffer andScherer.2 PTFE was also discovered in 1938 in the USA by Plunkett of

E I DuPont de Nemours while investigating fluorinated refrigerants Theunique properties of PTFE were recognized during the Manhattan Project,where there was an urgent need for a material that would withstand thehighly corrosive environment during the process of separating the isotopes

of UF6 for the first atomic bomb PTFE apparently fulfilled all the needs,spurring the development of processing and production methods for thisunique polymer In 1946, PTFE was commercialized by E I DuPont deNemours under the trade name Teflon.3

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The unique properties of fluoropolymers are due to the fact that the polymerbackbone is formed by strong carbon–carbon bonds (C–CB340 kJ mol1

) andextremely stable carbon–fluorine bonds (C–FB490 kJ mol1

; for comparison,C–H B420 kJ mol1

) Substitution of fluorine for hydrogen in a materialimproves three key physical properties:

 increased service temperatures and reduced flammability;

 low surface energy, providing non-stick properties/anti-adhesiveness,low coefficient of friction, self-lubricating effects and lower solubility inhydrocarbons;

 excellent electrical and optical properties resulting in low frequency-loss rates and low refractive indices

high-PTFE, PCTFE and all other fluoropolymers (see Table 1.2) gained diate acceptance during commercialization in the various markets

imme-During the following decades, many fluoropolymers, including thermoplastics and fluoroelastomers, were developed The worldwideannual sales volume of fluoropolymers is today more than 230 000 tonnes(world consumption of fluoroplastics in 2012 wasB216 000 tonnes;4

fluoro-worldconsumption of fluoroelastomers in 2009 wasB20 000 tonnes5

) The totalmarket value is more than US$6 billion

In contrast to the higher molecular weight polymers, oligomers arecharacterized by a low number of repeating units, usually less than 50, and alow molecular weight, often not higher than 20 000 Da (as measured by gelpermeation chromatography)

Many synthetic routes to oligomers have been described, including radicaloligomerization, oligocondensation, ionic oligomerization and ring-openingreactions.6 Telomerization is an oligomerization by a chain-transfer re-action, carried out in the presence of a large amount of chain-transfer agent,

so that end-groups are essentially fragments of the chain-transfer agent.7

In Sections 1.2 and 1.3, some of the results of the research and ment work carried out at 3M using functionalized fluorinated oligomers arediscussed

1.2.1 Fluorinated Monomers

All industrial routes for the synthesis of the five major C2/C3fluoromonomersare based on chlorination/fluorination of C1/C2 hydrocarbons, mostlyincluding a de(hydro)chlorination step at high temperature8(Scheme 1.1).Some of these manufacturing processes are fairly energy consuming(e.g the preparation of 1 ton of TFE requires 410 000 kWh) Also, specialcare has to be taken in producing and handling TFE owing to its tendency toself-decompose into carbon and tetrafluoromethane In Table 1.1 an over-view of monomers to produce fluoropolymers is given

A key-intermediate in the preparation of vinyl ethers and their oligomers ishexafluoropropylene oxide (HFPO) HFPO is prepared from HFP via directoxidation with oxygen, by electrochemical oxidation or by reaction withhypochlorides or hydrogen peroxide:8

O

CF3– CF=CF2+ “O” CF3–CF–CF2HFPO reacts readily with nucleophiles; for example, in the presence offluoride salts (e.g NaF, KF, CsF) it forms the intermediate perfluoropropyloxide salt, which reacts with the next HFPO to form an acid fluorideafter elimination of a fluoride ion This compound is the precursorfor perfluoro(propyl vinyl ether) (PPVE), which is obtained by reactionwith alkali/alkaline earth metal carbonates and subsequent pyrolysis(Scheme 1.2).9

HFPO can also be oligomerized to produce higher molecular weight (up to

15 000 Da) perfluorinated polyethers having following general structure:

C3F7O(CF–CF2O)n–CFY–CF3 Y = H, F, COF

CF3Other important perfluorinated vinyl ethers are synthesized by reaction

of fluorinated alkoxides with HFPO followed by pyrolysis; the fluorinatedalkoxides are usually prepared in situ from the corresponding acid fluorides(Scheme 1.3).8

An attractive, alternative route to perfluoro(methyl vinyl ether) (PMVE) isbased on the reaction of perfluoromethyl hypofluoride and dichloro-difluoroethene followed by dehalogenation (Scheme 1.4).9 Solvay SpecialtyPolymers has mastered this synthesis and transferred it into large scaleproduction

Starting materials with functional groups can be prepared by direct

or electrochemical fluorination (ECF) or by standard synthesis10(Scheme 1.5)

The synthesis of comonomers for the preparation of perfluorinatedamorphous polymers with high glass transition temperatures (Tg) involvesmultiple steps and has recently been described in detail11(Figure 1.1)

Scheme 1.1 Industrial routes for the synthesis of fluoromonomers

Industrial Aspects of Fluorinated Oligomers and Polymers 5

Table 1.1 Monomers used in commercial fluoropolymers.

Monomer

CAS registry

Pcrit/MPa

CF CF

C CF OCF 3

1.2.2 Perfluoroalkyl Building Blocks

1.2.2.1 Chemical Routes

Fluorochemical building blocks containing a perfluorinated chain can bemade on an industrial scale by methods including TFE/C2F5I telomerization,ECF and direct fluorination.17

Scheme 1.2 Synthesis of PPVE

R F COF + MeF R F CF 2 OMe R F -CF 2 O-CF-COF

Industrial Aspects of Fluorinated Oligomers and Polymers 7

Telomerization allows the synthesis of oligomers of the type

CnF2n11–CH2CH2I, whereas ECF produces perfluoroalkyl carbonyl fluorides,

RfCOF, or sulfonyl fluorides, RfSO2F The perfluorinated chain may containfrom one up to 16 carbon atoms Telomer iodides and the carbonyl andsulfonyl fluorides can be converted on an industrial scale into alcohols and(meth)acrylate monomers.12–17 The acrylic monomers have the generalstructures shown in Scheme 1.6

1.2.2.2 Environmental, Health and Safety Aspects

The first surfactants and textile treatments, containing perfluoroalkylchains, were commercialized by 3M in the 1960s.34 Since then, major ap-plications that were developed included fire-fighting agents, emulsifiers forfluoropolymers, oil and water repellents and paint and coating additives

O

CF2O

C CF

O RfO

Most of the fluorochemicals contained C6F13, C7F15or C8F17perfluoroalkylgroups In the late 1990s, PFOS and related compounds were identified atparts per billion levels in the sera of the general population In May 2000,3M announced the manufacturing phase-out of ‘‘C8’’ chemistry Duringthe following years, new materials based on C4F9technology that addressedthe bioaccumulation and toxicity concerns associated with longer chainfunctional perfluoroalkyls, were developed and commercialized in selectedmarkets.56 Environmental groups and governmental agencies are moni-toring the use of higher perfluoroalkyl homologs and low molecular weightfluorochemicals very closely.

1.3 Functionalized Oligomers and Their Applications 1.3.1 Synthesis

Many of the functionalized fluorinated oligomers used on an industrial scaleare made by ring-opening reactions of HFPO, photo-oxidation of fluoro-olefins and telomerization of fluorinated (meth)acrylates with functionalmercaptans

1.3.1.1 Perfluoropolyether Derivatives

Perfluoropolyethers (PFPEs) are a class of low molecular weight polymers(500–15 000 Da) that were originally developed in the mid-1960s.18 Func-tionalized PFPEs are commercially available, for example under the tradenames Krytox (E I DuPont de Nemours), Demnum (Daikin Industries) andFomblin (Solvay Specialty Polymers) Their synthesis is summarized inScheme 1.7, where X represents a COF group.16,18

These PFPE carbonyl fluorides can be further converted into other tional groups, such as hydroxy, (meth)acrylate, nitrile and trialkoxyalkyl-silane.45A few examples are discussed below

func-1.3.1.2 Functionalized Oligomeric (Meth)acrylates

The synthesis of functionalized fluorinated oligomers can be carried out byradical oligomerization of acrylic monomers in the presence of a functionalmercaptan, such as 2-mercaptoethanol.19–23A similar strategy was used toprepare oligomers with molecular weights ranging between 1500 and 10 000 Daand one or more functional groups, such as hydroxy, carboxy, amine ortrimethoxysilane.24–29 The oligomers have an aliphatic backbone with aplurality (usually between 4 and 16) of pendant fluoroaliphatic groups andthe majority of them are endcapped with the functional group(s) Theoligomers contain a mixture of compounds with a range of repeating units;for example, if a monomer to mercaptan molar ratio of 4 : 1 is used, a mix-ture of compounds with molar ratio ranging from 1 : 1 to about 8 : 1 is ob-tained after oligomerization The synthesis is summarized in Scheme 1.8

Industrial Aspects of Fluorinated Oligomers and Polymers 9

Using the same synthetic procedure, mixed co-oligomers can also beprepared using fluorine-free hydrophilic and hydrophobic comonomers.24

In the case of hydrophilic monomers containing alkylene oxide segments or

an ionic group, such as salts of an acid (as present in, for example, sodiumacrylate) or a quaternary ammonium group (as present in, for example,diethylaminoethyl methacrylate hydrochloride salt), surfactants can beprepared having an anionic, cationic, amphoteric or non-ionic character.30,31Such surfactants provide efficient and effective lowering of the static anddynamic surface tension of liquids and increase the wetting of a coating on asubstrate surface.56

C F3

O F

F F

F catalyst C F3C F2C F2O (C F C F2O )nC F F

-O

C F3 C F3

C2F4

O2

XCF2O(CF2O)m(C2F4O)nCF2X

Solvay Specialty Polymers – Fomblin Y, Z Fluids

Daikin Industries Demnum Fluids

E I DuPont de Nemours – Krytox Fluids

Scheme 1.7 Synthesis of perfluoropolyethers

S OO

N

S OO

N

S O O

1.3.2 Derivatives of Functional Oligomers and Their

Applications

1.3.2.1 Introduction

Functional oligomers can be reacted and blended with many differentcompounds through their functional group(s) For example, fluorinatedoligomeric alcohols can be used in combination with isocyanates to make(poly)urethanes24,26 or in combination with carboxylic acids to make(poly)esters.32Oligomeric acids can be condensed to (poly)amides.33Thesecondensates can be used as surface modifiers for commodity polymers such

as poly(methyl methacrylate) (PMMA) or polyamide 6 (PA 6).28 In the lowing, examples and applications are discussed

fol-1.3.2.2 Oil- and Water-repellent Treatments for Fibrous

Substrates

1.3.2.2.1 Introduction Fluorochemical oil and water repellents for tile fabrics were discovered in the 1950s by researchers at 3M34and, sincethen, many commercial products have been developed for a wide variety

tex-of surfaces by different companies.35–37The repellent properties are the sult of the low surface energy, typically between about 12 and 15 mN m1,

re-of a textile fabric treated with a fluorochemical repellent material Waterand oily substances will not be able to wet and spread on such a treatedsurface, resulting in water and oil repellency of the treated fabric38(Figure 1.2)

Many fluorine-containing repellents are based on poly(meth)acrylates.These acrylic polymers can be visualized as consisting of pendantperfluoroalkyl groups (Rf) and hydrocarbon groups (Rh), an acrylic polymerbackbone and non-fluorinated linkages between the two The compositionand ratio of the comonomers in such polymers affect the repellent

Figure 1.2 Water drops on a treated fabric

Industrial Aspects of Fluorinated Oligomers and Polymers 11

properties Comonomers with a crosslinking function, such as2-hydroxyethyl acrylate, glycidyl methacrylate or N-methylolacrylamide,are used to increase the durability of the repellent treatment.35–37 Suchcopolymers can be represented as shown in Figure 1.3.

It was observed that organizing the fluorinated groups, Rf, into smalldomains improves their efficiency and effectiveness as oil and water repel-lents.24This organization into fluorochemical domains can be achieved byusing fluorochemical-functionalized oligomers and chemical methods toconnect the oligomers to a backbone (Figure 1.4)

1.3.2.2.2 Isocyanate Derivatives of Oligomers Much of the researchand development work at 3M involved the combination of hydroxy-functionalized oligomers with isocyanates and fluorine-free mono-, di- orpolymeric alcohols, amines, thiols and other isocyanate-reactive materials

to form urethanes, ureas, thioureas or their polymeric analogs such aspolyurethanes.24–27,39 These reactions are carried out in organic solvents,such as ethyl acetate, usually in the presence of catalysts such as certainSn-compounds (e.g dibutyltin dilaurate) Crosslinking of such urethanederivatives can be achieved by incorporating specific blocking agents such

as oximes or imidazoles, thus forming thermolabile urethane groups.These thermolabile groups decompose at the curing temperature of thefabric treatment, typically 150–170 1C, generating in situ isocyanate func-tionalities that will react with any hydroxy, amino or carboxy grouppresent on the fiber surface, creating a chemical bond between the textilefabric and the fluorochemical agent, resulting in improved laundering anddry-cleaning resistance.37

An interesting class of isocyanate-derived repellents are carbodiimides,40,41since the carbodiimide group, –N¼C¼N–, itself can reactwith functional groups present at the surface of the textile fabric.42 Poly-carbodiimides containing fluorinated oligomer segments were prepared andfound to have very good durable repellent properties without the use of anisocyanate blocking group.24

Another important finding was the discovery of functionalized fluorinatedspacer oligomers, prepared by radical oligomerization of spacer monomerswith functional mercaptans.43The fluorinated spacer monomers can be pre-pared by combining a fluorinated alcohol, e.g C4F9SO2N(CH3)CH2CH2OH,with a diisocyanate, e.g MDI (4,40-diphenylmethane diisocyanate) and ahydroxy-terminated alkyl(meth)acrylate, such as 2-hydroxyethyl methacrylate.Fluorochemical textile treatments provide excellent oil and waterrepellency and stain-repellent finishes, but for the release of soil andstains, water needs to displace the contaminants and the launderingdetergent must be able to wet the fabric Treatments with both hydrophilicand hydrophobic/oleophobic segments were developed, which in dryconditions provide repellent properties (due to the fluorochemical tails),but in water the structure ‘‘inverts’’ and exposes the hydrophilic parts,resulting in good soil-release (‘‘flip-flop’’ mechanism).27,34,57

1.3.2.3 Oil- and Water-repellent Treatments for Siliceous

Surfaces

1.3.2.3.1 Introduction By applying fluorinated compounds, especiallyfluorinated trialkoxysilanes, to siliceous surfaces, such as glass or cer-amics, such substrates can be given a low surface energy, typically around10–15 mN m1, even when solutions with very low concentrations of0.01–0.2% by weight are used.44Very high thermal and oxidative stabilitieswere also observed Fluorinated silanes have the ability to form chemicalbonds with the hydroxy groups present on the glass through the formation

of Si–O–Si bonds.15

1.3.2.3.2 Perfluoro(polyether silanes) Perfluoro(polyether silanes) can

be easily prepared by reaction of the corresponding esters withaminopropyltrialkoxysilanes45 or the corresponding alcohols with iso-cyanatopropyltrialkoxysilanes.46 Some structures are shown in Figures 1.5and 1.6

These silanes can be easily applied to siliceous surfaces, such as showerpanels or bathroom ceramics, by applying dilutions in alcohols, such asethanol or 2-propanol, in combination with catalytic amounts of acid In afirst step, the trialkoxysilanes are hydrolyzed into silanols, which thenundergo condensation reactions (silanols reacting with themselves) andcrosslinking, where the fluorochemical is chemically bonded to the hydroxygroups of the siliceous surface The PFPE layer is very thin (about 20–100 nm)and provides excellent repellent and easy-to-clean properties and very good

(OR) 3 Si–(CH 2 )n–N(H)–C(O)–CF 2 O–(CF 2 CF 2 O)n–(CF 2 O)m–CF 2 C(O)–N(H)–(CH 2 )n–Si(OR) 3Figure 1.5 Structure of a PFPE-trialkoxysilane

Industrial Aspects of Fluorinated Oligomers and Polymers 13

durability against aggressive chemicals, such as acids or bases, and againstmechanical abrasion.46

Methods for aqueous delivery of PFPE-silanes were also developed Onemethod consists of making a non-aqueous concentrate containing the PFPE-silane and a fluorosurfactant, diluting the concentrate in water and applyingthe aqueous formulation to the siliceous surface.47Another way is to preparecationic perfluoro(polyether silanes), which are readily soluble or dispersible

in water, and applying them to the siliceous surface followed by roomtemperature drying and curing.48

1.3.2.4 Fluoropolymers with Low Glass Transition

Temperatures (Tg)

1.3.2.4.1 Introduction A wide variety of fluoropolymers have beendeveloped and produced on an industrial scale for a broad range of appli-cations.49,50 However, except for fluorosilicones,51 fluoropolymers with alow Tgare not widely available

1.3.2.4.2 Triazine-containing Fluoropolyether Elastomers Recently,chemistries and methods were developed to prepare fluoroelastomers withperfluoropolyether segments and having a Tgof less than40 1C Startingmaterials include low molecular weight perfluoro(polyether dinitriles),such as shown in Figure 1.7, and fluorinated amidines, such as

H2NC(¼NH)(CF2)8C(¼NH)NH2, or other reagents that allow the formation

of triazine groups.58–60

Fluoroelastomers containing perfluoropolyether segments and triazinegroups were obtained after curing; their Tg was about 112 1C.52 Fluoro-elastomers containing perfluoropolyether segments and low Tg were alsoprepared starting from PFPE-diiodides, such as ICF2O(CF2O)n(CF2CF2O)mCF2I,according to a radical curing mechanism,53,54and PFPE-dinitriles using clickchemistry, involving azides or alkynes.55The fluoropolyether elastomers ob-tained have unique attributes as far as Tgand other physical properties areconcerned (Table 1.2)

Si O

O

O O

O

O O

CF3CF2CF2-O-(CFCF2-O)k-CF-CO-

CF3 CF3

Figure 1.6 Structure of a PFPE-triethoxysilane containing a urethane linking group

1.4 Overview of Fluoropolymers

1.4.1 Fluoropolymer Production and Applications

The principal method for synthesizing fluoropolymers is free-radical merization, as other typical methods, e.g cationic polymerization, are in-effective owing to the electrophilic nature of fluoroolefins Fluoroolefins can

poly-be polymerized using anionic catalysts, but termination by fluoride ionelimination prevents the formation of high molecular weight polymers.Coordination catalysts do not lead to polymerization of fluoroolefins.The free-radical polymerizations are mostly water based, either as aqueoussuspension polymerization (mostly applied for PTFE polymers) or as aque-ous emulsion polymerization in the presence of emulsifiers, most preferably

in the presence of fluorinated emulsifiers

In the past, most commonly the ammonium salt of perfluorooctanoic acid(PFOA) (C7F15COONH41) was used as an emulsifier However, owing toenvironmental concerns, the US Environmental Protection Agency (EPA)initiated a program to reduce the emissions of PFOA and to work towards theelimination of PFOA by 2015.61–63Therefore, fluoropolymer producers haveimplemented PFOA replacements (see Chapter 13) and have also developedtechnologies using hydrocarbon emulsifier64–72 or even emulsifier-freetechnologies.73–76

In early times, radical copolymerization of fluorinated olefins in ated fluorocarbon solvents (e.g R113, CF2Cl–CFCl2) was widespread; also,many work-up processes (e.g agglomeration steps) used chlorofluoro-carbons Owing to the high emissions of these ozone-depleting solvents and

chlorin-to the Montreal Prochlorin-tocol, these processes had chlorin-to be changed so as chlorin-to useeither environmentally friendly solvents [e.g CF3(CF2)4CF2H] for ETFEpolymerizations77or water-based systems

Polymerization in supercritical (sc) media (e.g in scCO2) – originallyintroduced as an alternative ‘‘green’’ polymerization technology – did not

Low-temperature FKMs (TFE/VDF/PFVE)  40 Excellent

Industrial Aspects of Fluorinated Oligomers and Polymers 15