waterborne & solvent based surface costings & their applications, vol. 1, vinyl acrylic by m. barbour

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VOLUME I

_ _ Waterborne

& Solvent Based Acrylic:

: and their

End User Applications

M Barbour BSc, | Clarke GRSC, D Fone BSc,

A Hoggan BSc, R James, P Jones Grad PRI, ộr Lam PhD BSc, C Langham LTSC, K O'Hara LRSC,

P Oldring PhD BA, G Raynor BSc, | Royston BSc,

N Tuck PhD BSc, R Usher BSc

ks Edited by sả

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ap AN

VOLUME |

Waterborne

& Solvent Based Acrylics and their End User Applications

M Barbour BSc, J Clarke GRSC, D Fone BSc,

A Hoggan BSc, R James, P Jones Grad PRI, Peter Lam PhD BSc, C Langham LTSC, K O'Hara LRSC,

P Oldring PhD BA, G Raynor BSc, | Royston BSc, 0 N Tuck PhD BSc, R Usher BSc

Edited by Dr P Oldring PhD BA and Dr P Lam PhD BSc

JOHN WILEY & SONS

CHICHESTER @ NEW YORK @ WEINHEIM @ BRISBANE đ TORONTO @ SINGAPORE Published in association with

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Contents II II IV Table of Contents Chapter I

THE CHEMISTRY OF ACRYLIC RESINS

INTRODUCTION 3 ADDITION POLYMERISATION 4

1 Initiation 5

2 Propagation 6

3 Termination 7

() — Termination by CombÙd{ÍOH v.v hy ky rerrvevereerkkrriee 7 (ii) Termiation by DiSpTODOFTÍÍOH àà SA TS riry 7

/2NWW12,,), 128/1 MA ẢẢẢ ọ

4 Transfer Mechanisms 10

(i) Transfer to Soèerf 10

(ii) Transfer to Monomer 12

(ili) Transfer to @ Modifier mẽ ẽaẽeaeaaA 14

5 Chain Transfer Agents 14

6 Inhibitors 16 THE KINETICS OF THE FREE RADICAL POLYMERISATION

OF ACRYLIC MONOMERS 17

1 Initiation 17

2 Propagation 17

3 Termination 18

4 Polymer Chain Length 19

5 Degree of Polymerisation 19

6 Effect of Reaction Conditions on Chain Length 22 CHEMISTRY OF ACRYLIC MONOMERS 24

1 The Major Acrylic Monomers 24

N08 nan 27

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u Contents

(tii) Epoxy Functionality 27

DU /72 na ốn 28

2 Relationship between Monomer Structure and Reactivity csssscsccscssssssscnsee 30

3 Curing and Film Forming Reactions 32 (i) Reactions of Hydroxyl Containing Polymers with Amino

Kormaldehyd€ R€SHLS con nh HH HH gà g0 00 ngơ 32

(ii) Reactions of Hydroxyl Containing Polymers with Isocyanate sssssssecssevees 34 (iii) Reactions of Hydroxyl Containing Polymers with Polyanhydrides - 34 (iv) Reactions oƒ Hydroxyl Contaiming Polymers with Epoxy GTOMDS 35 (v) Reactions of Hydroxyl Containing Polymers with Carboxyl Groups 3S (vi) Reaction oƒ Carboxyl Contaừựing Polymers with Epoxy Groups 35 (vit) ReacHon oƒ Carboxyl Comtatng Polymers with ẽsocyanate GrOMps 36 (viii) Reaction of Carboxyl Containing Polymers with

Alkoxyl Methyl Ether GTOMDS <e 36 (ix) Reaction of Glycidyl Containing Polymers with Epoxy GTOHDS 37 (x) Reaction oƒGlycidyl Cormtaiming Polymers with Amine CTODS 37 (xi) Reaction of Glycidyl Containing Polymers with

Amino Formaldehyde Resins .:csssceccsseveesesseessessonevesaeesacesesenestecsenaneevesenss 37 (xii) Reaction of Glycidyl Containing Polymer with

Phenol Formaldehyd€ ÍẹGSÙTLS ơso HÀ TT HT HH TH tớ HH nhện 38 (xiii) Reactions of Methylol Containing POlmFS àcerhetskrerererseseserrer 38 (xiv) Reactions of Methylol Comtaining Polymers with Epoxy GTOHMDS 39

COPOLYMERISATION 41

1 Copolymer Composition Equation 42

2 Reactivity Ratios 43

3 Terpolymers and Multi-Component Systems 46

4 Qande Values 47

5 Qand e Values as Applied to Multi-component SySẫ€TS .-oe<oeseesee ô48

POLYMER PROPERTIES 49

1 Orientation of the Repeating Unit 49 (i) Electrostatic Forces

(4) Steric Himdrance cccccsccssssceseessensesssecessqeessceessuersacencnssessscsenessneecsnenessuseeuacesesaes 50 U22, 02.2 1n hố ne 30

2 Polymer Tacticity 51

3 Molecular Weight 52

4 Molecular Weight Distribution 54

(i) Degree of Polymerisation 55

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Contents Ul

5 Influence of Molecular Weight 56

(i) Non Volatile Content vs Molecular Weight at Constant ViscoSify 56 () — Durablluy vs Molecular Weight (Polymethyl Methacrylate) ô s 37 6 Relationship between Molecular Weight and Ÿiscosity svevstaceeceseens 57 (i) — Establishing Values for K and Œ Ăn, 58

7 Glass Transition Temperature 59

(i) Tp ửoƒ Acrylic CopolWH€FS HH HH Hào 6l

8 Techniques of Polymerisation 62

(i) —— Bulk Podymerisation 0.0 65 (ii) — Suspension PolymeriSation 66

VI SOLUTION POLYMERISATION 68

1 Factors Influencing Solution Polymerisation 70 ( — ẹeaction TeImD€TdHF€ HH TH HH HH TH HH th ưy 70 U NHL.(( , A9 n nh .e 70 DI" nh he - 70

(iv) Concentration of Initiator 71

(V) Chain Transfer Agents .cccccccsesccccccessecssetneneccececcceuatuanessettaceaeuatnessaetnntesaaeentnaess 71 (VE) Tromsdor ff Effect cccccccccccccccessescessnecuscesseeseesscscessaneateaessseeseecsensensessaneeeecsaeseeaes 71

2 Conversion of Monomer into Polymer 71

(i) 'L x1 h.- 72 (lỡ) — Continuous Additon or Drip Feed PTOCSS à SH re 73

3 Choice of Initiator 74

(i) | Free Radical Generation oe " 74 (ii) Examples of Commonly Used IHÍHGFOFS- à chen key 77 UUON/Q 7 7 ,.nnnhe 78 (iv) Efect oƒ Solvent TYpD€ OFi LỤ,, Ăn TY KH HH HH HH KH Tà HH HH BI

4 Solvent Selection 82

(i) — Solubility and Solubility Parameters 0 ccccccescccssecesseveseeeeeseseeeeseneeneseetaeass 85 5 Solution Polymerisation Plant and Process 89

Formulations and Methods for the

Preparation of Solution Acrylic Resins 91 (i) | Preparation of an Acrylic Copolymer in Methyl Ethyl Ketone 92 (ti) Preparation oƒa Thermoplastic Acrylic Resim in Solution 93 (iii) Preparation of Thermosetting Acrylamide ẹe$i' c-cvceeisikeceerkee 93 (iv) Three Methods oƒ Preparing Thermosetting Acrylamide Resins 96

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iv = & Contents Chapter IT

THE CHEMISTRY OF WATERBORNE ACRYLICS

MECHANISM OF EMULSION POLYMERISA TION e e 105

1 Choice of Components for Emulsion Polymers 111 (i) WWG€T À GHI HT TH 02 84 th 9 TA ill (ii) Acrylic Monomers

(ii) Surfacldmts

(EV) INIT ALOT S oi eeceeeececetsensscstcsseeensetsasesceseeneesecsassnsansassseaceseesageseseeessasenseessaaaseesassess BI NA .a— (vi) ĐHÍƒ€FS Ă.H"nH> Hà Hàn Hàn KT HH HH nhà HH rệt

VARIATIONS ON CONVENTIONAL EMULSION

POLYMERISATION 118

1 Polymerisation Technique Variations 118 DA °đ đ n 118 (ii) Emulsifier Free Latices - Resin Supported SŠVSÍCT che 119 I2 0) nnnnh 120 2 Water Based Acrylic Polymers Used as Additives in Coating Formulations 120 (i) — Pigment Dispersing Agents csccscssccsccsetsccsssesssesencensensenscotsseseseeeceseeseeseensans 12] (ii) | Carboxylated Acrylic Thickeners and Rheology Modilfiers 122 (iii) Manufachưing Process for Acrylic THỈCk€H€FS ii 123 DIỚNN: 2.2278 , 0nn Ắ 126

FILM FORMATION 128 EXAMPLES OF LATEX FORMULATIONS &

PREPARATIVE METHODS 131

1 Methyl Methacrylate Homopolymer: 131

2 Vinyl Acetate - Methyl Methacrylate Copolymer eesceseencesesesneescoe eeveessecsescees 132 3 Vinyl Acetate - Acrylic Terpolymer 134

4 Styrene Acrylic Copolymer 136

5 Thermosetting Acrylic Emulsion 137

6 Preparation of an Acrylate Copolymer Latex Containing Acidic Groups 138 7 Preparation of a Water Soluble Acrylic Copolymer "1 139 8 Example of Preparation Method for Stabilisers

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Contents VI VII YMI II II WATERBORNE SYSTEMS

1 Preparation of Acid Functional Acrylic Resin .-eeeceseseessssesesseenesesasssseae 2 Preparation ofa Water Reducible Acrylic Resin ô-cessesesesesseseseseessssese 3 Solvent Distillation Process for Preparing Waterborne Acrylic Resins 4 Examples of Water Reducible Resins -

VeoVa Based Water Soluble Resin (Courtesy oƒ Shell ChemiCdẽS)-ôôesôeesssessssessses 149

ELECTRODEPOSITION 151

1 The Electrodeposition Process in Practice 151 2 Considerations when Formulating Electrodeposition Resins ô- 158 DÀNH A/, ẽn ố 158 (l) Glass TransHion TeD€TQ[HF€ SH HH ciờ 158 UUIC S8 ,.A/,., ah n 158 DI 8 nn e 159 (V) Application Ắ ằ ẻ 162

3 Acrylic Formulation 162

( — ACcrylic ẹGSÙN HH nh KH H1 KT HH HT gtn tươ 162 (ii) Application of Electrodeposition Resins -

General Formulating PTÙTCÍDẽ€S cà HH nàn nhe, 165

WATERBORNE EPOXY ACRYLICS 166

1, Epoxy Chemistry 166

2 Waterborne Resin Chemistry 169

REFERENCES 176

Chapter III

THERMOPLASTIC ACRYLICS APPLICATIONS

INTRODUCTION 179

GENERAL CONSIDERATIONS IN PAINT FORMULATION s000 180

1 Resin Selection 180

2 Binder Modifications 182

3 Solvent Selection 183

4 Pigmentation 184

5 Additives 184

MAJOR END USERS 185

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vi IV VI II Contents DA //2 0i 8 186 (ii) — Thermoplastic Acrylic Refinish Topcodt LACQH€FS cà eieeiesereve 188 (iii) Aerosol Spray Paints

2 Coatings for Plastic

(i) — Types of Plastic SMPSÍTQf€ Ă HH HỆ HH HH ng vi 193 UDINẰđ 1 " — 197 (iii) Formulation for Coatings for Plastic and Materials Functionality 199

3 Masonry Coatings 206

() — Thermoplastic Acrylics Soluble in Polar SOèV€HIS chen neeeeesve 207 (ii) Acrylic Based Polymers Soluble in Aliphatic Hydrocarbon Solvers 208 II (19 anh nhe 209 (iv) Concrete and Terrazo Š€Qè€TS ST HH TH TH Tnhh 209

4 Coatings for Metal 211

DN.( i9 ủ69s an 211 HIẾN: .0 ai an ố 212 (iii) Marine and Offshore Coating ŠÿSÍ€HHS chư, 213 (iv) High Durability Coil Coating Enamels for

Metal Cladding Poly Vinylidene Fluoride (PVFa Coatings) 214 MISCELLANEOUS APPLICATIONS FOR

THERMOPLASTIC SOLUTION ACRYLICS cccccosssessocssssesseesescenssosscers 217

1 Road Marking Paints 217

2 Temporary Protective Coatings 217

3 Additives to Alkyd Paints 218

4 Fluorescent Coatings 218

5 Metal Decorating Coating Systems 219

REFERENCES 220

BIBLIOGRAPHY 220

Chapter IV

THERMOSETTING ACRYLICS APPLICATIONS

INTRODUCTION 223

MAJOR CROSS LINKING MECHANISMS sescccccscccsscccssccssccccssoscccens DOE

1 Acrylamide Based Acrylics 224

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Contents vii 3 Carboxy Functional Acrylics 228 4 Choice of Co-reactants 229 (BE) HN2.2/ 229

(4E) — AMIO RESINS 1a Ắ 229

UUON, 1y 0n nh 232

(iv) Alkyd Modification an nn 232

(v) Other Binder Modifications 233 Tt PIGMENT SELECTION 234 1 Whites 234 2 Blacks 234 3 Blues 234 4 Greens 234 5 Reds 234 6 Yellows & Oranges 235 7 Transparent Iron Oxides 235 IV SOLVENT SELECTION 236 V CATALYSTS 237 1 Acid Catalysis 237 2 Metal Catalysis 237 VI MAJOR END USES FOR THERMOSETTING ACRYLIC RESING 238

1 Automotive Finishing 238 () — Sohuion Thermosetting ACTVèÍCS SH HH Hàn HH HH LH ki, 239 (ii) Thermoset Non Aqueous Dispersions 239 LUON (mo nan 240

(iv) Clear Over Basecoat Systems (CO) ch Y nà ng cua, 242 ANH 1 8 i6 nan 243

2 Acrylamide Acrylics in Domestic Appliance Finishing ee.se-ô.e- „248 3 Hydroxy Functional Acrylics for General Industrial Stoving Finishes

(i) High Performance OH Acrylics in Tractors and Construction Equipment ccccccccccscccscsscscsssssescscasseasesansstsacenanesunseaeessensseessessess 251 (ii) | General Purpose Stoving Acrylics for the General Industrial Market 254

4 Metal Decorating - Solvent

DA n (ii) The Use of Acrylic Resins in Metal Decorating

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vi Contents

(iv) Vinyl Coatings for Internals

V22 (vi) Pigmentation (vii) Solvents (vill) Additives

(ix) External Coatings oƒ Caps, Closures and General Line -.-.- 269 (X) FOTIHHỈQIÍOPHS ĂĂ.ĂQ TS HHằ HT HH ngờ 272 (xi) Commercial Acrylic Resims for Metal Decordting cs<vvexvxes 285

VH REFERENCES 286

Chapter V

TWO COMPONENT ISOCYANATE CURED ACRYLICS APPLICATIONS

II II INTRODUCTION 289

PAINT & VARNISH FORMULATIONS 292

1 Co-reactants 292 2 Modifying Resins 296 3 Pigmentation 296 4 Solvents 296 5 Additives 297 CE) NT đ 1 297 (i) Ultra Violet (UV) Light 7 ee 298 (ili) Reactive Diluents

CURING, APPLICATION AND FILM PROPERTIES , .ccccsossoreeconsseeees 299

1 Curing 299

2 Application Methods 299

MAJOR END USERS 300

1 Automotive Finishes 301

(2) Automotive OEM ccccccccccccaccccsscssessesasesseensesssscesesenecacensseeadausaeeseceeeesansnenaneess 301

THẾ 2) 18 nan 304 2 Transport Finishing (Commercial Vehicles) 306

3 Wood Finishing 309

(i) Solvents

(li) Isocyanates

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Contents ix

4 Industrial Protective Coatings 315

Đ Acrylic Polyurethanes for Agricultural and

Construction Equipment (ACE) 316

Acrylic Polyurethanes for Information Technology (IT) Finishing 00 319 7 Two-component Ísocyanate Cured Acrylics for PlasficS .-.-.ô-<- 321

Vv MAJOR EUROPEAN SUPPLIERS OF HYDROXY

FUNCTIONAL ACRYLICS 324 VỊ, REFERENCES 325

Chapter VI

TWO COMPONENT NON-ISOCYANATE ACRYLICS APPLICATIONS

I INTRODUCTION 329

II PAINT & VARNISH FORMULATIONS 333

1 Modifying Resins 333 2 Pigmentation 333 3 Solvents 334 4 Additives 334 (i) DV AbSOTLS Đà TT HH HH KH TK HH4 K41 KH 516 vỏ xxx 334 867/2 1 .ễỎ 334 ĐI 9đ Ắ 334 I CURING, APPLICATION METHODS & FILM PROPERTIES 335

1, Curing 335

2 Curing Aspects Related to Chemistry 335 CE) — CAD OX YS CD OXY 335 UING,(/2, 0 .0n6nn 335 (ili) Ketimine/Activated HVđdFrOBH ỏc HH HH HH HH ng ng, 335 (iv) J2, -./(2 3.8 Ầ 336 D2, /2.2:Ắ 336 3 Cure Aspects Related to End User 336

4 Application Methods 337

IV MAJOR END USES 338

Vv FORMULARY & TYPICAL PROPERTIES cses.e<<eessee „339

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Contents

VII REFERENCES 346 Chapter VII

WATERBORNE ACRYLIC SYSTEMS FOR INDUSTRIAL APPLICATIONS

Il II IV INTRODUCTION 349

1, Volatile Organic Compound Content - VOC’s 350

2 Waterborne Systems 352

(i) —- Properties Of Water da cố 354 (BE) Starface Temsion cccccccsseccsasccsscsessesseesecsneeecescesstsnseaseneaeecacseaeessecueeaeecatenseessenee

(iii) Evaporation Rate

TYPES OF WATERBORNE SYSTEMS 359

1 Thermoplastic Emulsions 360

2 Thermosetting Emulsions 360

3 Water Reducible Resins 361

4 Waterborne Resins Used in Surface Coatings 361

WATER REDUCIBLE POLYMERS 362

1, Polymer Neutralisation 363 2 Cosolvents 3 Polymer Types (i) Processing HIAA"` 0) 370 EMULSIONS 371

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Contents VI VIL TX xỉ

6 Application of Emulsion Polymers in Paints 384 DANH 385 TA an e< 385 7 General Properties of Emulsion Films 386 NEW DEVELOPMENTS FOR WATERBORNE SYSTEMG cccccsssssese 387

1 Hydrosols 387

2 Group Transfer Polymerisation 387

3 Aqueous Microgels 388

4 Core /Shell Polymers 388

5 Crosslinking Resins 388

FORMULATIONS FOR WATERBORNE COATINGS BASED

UPON VINYL AND ACRYLIC POLY MERS c-<<<<<<-<<essee 389 1 General Considerations in Paint Formulation 390 CE) EMULSIONS hS 39] (it) — Dispersions (Inverted SOèHH[OPN) Ăn TH HH cư rưy 391 2 Additives Common to both Emulsions and Water Reducible Systems ô 392 (1) —_ Dispersing/Wetting Agents 392 (EE) — DC fO IMCS ec ceccccvececscssccessasessteescesssasceesseanectsuaecsuesaeesssnssaessessecsaeeseeaenetneneaess 394 (ii) Viscosity and Rheology Modifiers ơ ễễễễễ 394 (EV) Rust [nhibiters 0 396 (V) Urethane Modifications ccccccccccceeieesesseeseeeeteeneeeeveeneeeeseesaeseceesntessenenesennntes 396 (Vi) — Mimo Additives c.cccccccesccsceessensecssesssessesaecsasecsessesasensesnseaeceteaersacesceesaeensnreanees 397

CROSSLINKING SYSTEMS 398

1 Self-Crosslinking Systems 398

2 External Crosslinking Systems 398

DA" hanh 398 CH) — Polycarbodtirmides .ccscccccccccccessccevsesecesessctenssssncssatsensenncsasseecsensceseeeesenersesseese 399 (UE) — PolyisOCYGNGLES 0 e 399 (4V) ROP ANIC SALES ceccccscensessceesnsseesscusecsesscensneetenecaseaseessenseenseaeaeesaeeeseeaeeaseeeaaes 400 2N, ai 7n - 400 (VE) 7221 400

SUMMARY AND FUTURE OUTLOOK 401

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xi X XI XI Contents II N 8 7 408 II 7 7 ẽm 408 (iv) NT) 2.5 na ne 409 HH 2 gốc 7a n 409 20 2:8 m 409

2 Water Based Formulations for Wood Finishes

(i) Water Based Self-Crosslinking ủqs€COdI càng (i) A Self-Crosslinking Satin LACQM€F LH HH HH ghe UUONG, ỏc 7 an — 412

(iv) A Spray Applied White PTÙH€T cv nh HH HH Thành (v) White Roller Coating Basecoat (vi) Spray Applied Satin White LACQM€T HH HH HH co 415 (vii) A Formulation for Clear Flat Furniture FHlGè Hee 416 (viii) A Formulation for a Matt Finish for FUTHÍIHF€ cover 417 WATER BASED FORMULATIONS FOR MASONRY AND FLOOR COATINGS 418 1 Masonry and Floor Coatings 418 (1) —- Good Quality Masonry Paint ccccccccecceeesccsetscsssnetaceaeeneceeseneeseeeeteenenstteteees 418 (ii) A Basic Sprayable Exterior Masonry Coating Formulatfion 419

(iii) Formulation for a Marble and Terrazzo Polish .cccccccscsscssseseensensceeeterectseeetes 419 (iv) Formulation for Floor Coating (v) Floor Coating for Vinyl Composite Tiles (vi) Formulation for Low Cost ConCrete S€Qè€T, -c se se ceeeseseersrrrrerseree 423 PLASTIC COATINGS 424 1 Formulations for Waterborne Plastic CoatẽnpS eoeessesssssssesessessessnsesnen 425 (i) — A White Waterborne Plastic Coating ĐH te ng ng rrry 425 (ii) A Clear Waterborne Plastic Coating cc-cccccccrcreeiEreeriee (iii) Water Based Metallic Basecoat for Plastics (iv) Waterborne Coating for POèySET€H HH HH Hà TH TH hy tườ GENERAL INDUSTRIAL COATINGS FOR METAL PROTECTION 429 1 Waterborne Formulations for Metal Protection sesesesessesssessesesersssessse 429 (i) Metal Primer N72 0u6, 7 ỐốỐồỐ 431

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Contents xửi

(v) — Waterborne White Industridl tODCOQI HH Hy He, 434 (vi) A Waterborne Acrylic Stoving EHaH€ẽ cà nhe rrerverrrerkerree 435 XIIL WATERBORNE COATINGS FOR METAL DECORA TION 437

Introduction 437

2 Two Piece Beverage Can Fabrication 440 Waterborne Acrylics in DWI Externals 441 (i) | White Water Reducible Acrylic for DWI Aiuminium Cans 444 4 Waterborne Internal Lacquers for DWI Beer and Beverage Cans 445 (1) DWI Irmternal Spray LLACQM€T Hs KH HH TH khen 449 (ii) The Spray Application of Two Piece DWI Internal Can Coating Lacquers .450

5 Evaluation and Testing of DWI Internal LaCQU€TS ô-sesesssesecsessssssessesee 455

Ha T1 ae 455 N2 ) 455 (ili) Flavour DU ẽẽh 456 2 Nư 2 an -.4 ':.:A -"'.'.ồ'.' 456 J8 N 1: 7 - 456 Electrodeposition (Electrocoating) 456

7 Water Based Sheet Fed Lacquers 463

(i) Sheet Fed Water Based Lacquer for Food Can ènternaès 464

XIV REFERENCES 465

XV BIBLIOGRAPHY 466

Chapter VITI

SOME MAJOR SUPPLIERS FOR SOLUTION ACRYLICS 467

Chapter IX

SOME MAJOR SUPPLIERS FOR WATERBORNE ACRYLICS 00 471

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CHAPTER I

THE CHEMISTRY OF ACRYLIC RESINS

by PETER JONES Grad PRI

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I- The Chemistry of Acrylic Resins 3

Chapter One

I INTRODUCTION

The vinyl! and acrylic group of resins is one of the most widely used in surface coating

applications

Vinyl and acrylic resins may be used on their own or in blends with other resins Coating resins can be divided into two distinct categories:

e Thermoplastic polymer coatings e Thermoset polymer coatings

The thermoplastic types are long chain polymers with high molecular weights and they film form without external chemical reaction The thermosetting types are shorter chain polymers containing reactive groups which can be ‘cured’ by the application of heat or usually by reaction with another chemical type to form a crosslinked film

Thermoplastic films harden by solvent evaporation, whereas thermoset films harden by chemical reaction

Vinyl resins are produced by the addition polymerisation of viny! monomers The term

‘vinyl monomer’ is applied to the species of molecules which contain a reactive C=C

double bond Individual molecules (termed ‘monomers’) of a vinyl compound are capable of undergoing a reaction to form long chains of monomer units linked via C-C bonds (termed ‘polymer’) The monomer units in the molecular chain may be exclusively of one species (a ‘homopolymer’) or the polymer may comprise two or more species of monomer (‘co-polymer’, ‘terpolymer’, etc.)

This mechanism for resin formation is totally different from that for any other class of resins

Alkyds and polyesters are formed by condensation reactions which generate water of reaction Polyurethanes are formed by chemical reactions which do not involve the generation of any by-product Vinyl and acrylic resins alone are formed by addition polymerisation of the carbon carbon double bond

In this chapter, the theory, mechanisms, kinetics and types of addition polymerisation will be considered The acrylic monomers which can be used and the properties that they impart, will be discussed, as will their effects on polymerisation Crosslinking reactions and functional monomers, which can participate in them, are the basis of industrial

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4 1 - The Chemistry of Acrylic Resins

The four methods of polymerising acrylic monomers, namely bulk, suspension, solution

and emulsion are considered Chapter I concerns itself with the chemistry of acrylic

polymerisation and solvent based acrylics Chapter II is devoted to waterborne resins,

especially emulsion polymerisation, because of its significant differences from the other

types of polymerisation

Much of the discussion about solvent based solution polymerisation of acrylic monomers is also relevant to waterborne systems, where the monomers are polymerised in solution in a water soluble solvent, neutralised and then dispersed or inverted into water

However, the basis of acrylic addition polymerisation needs to be considered first

Il ADDITION POLYMERISATION

Long chain molecules can be formed by the addition polymerisation of monomers of the general formula CH, = CRX

Where R may be H, CH; or a halogen and X includes halogen, aryl, amide, ester,

substituted ester, nitrite and carboxyl groups The polymerisation reaction can be represented as

nCH2 = CRX > [CH2-CRX}

and there are three quite distinct stages in addition polymerisation a) Initiation: Attack on the C=C bond by an initiating species

b) Propagation: Growth of the polymer chain by successive addition of monomer units

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I - The Chemistry of Acrylic Resins 5

1 Initiation

Polymerisation may be initiated by one of three mechanisms: a) Free Radical Initiation

RR,—>R + R,,then R” + CH, = CHX —> RCH, — CHX

initiator free free monomer

radical radical + monomer radical

b) Anionic Initiation

BA +CHa=CHX > A-CH2-CHX Br c) Cationic Initiation

A Bù+CHa=CHX > B-CH2-CHX*A™

Although most vinyl! and acrylic monomers will undergo any of the above types of initiation, some of the polyether monomers can only be polymerised when ionic initiation techniques are used

In practice ionic initiation is restricted to the production of the so called "high" polymers used in structural applications Polymers for surface coating applications are normally prepared exclusively using free radical initiation techniques

The initiator is consumed during the course of the polymerisation and the reaction mixture requires “topping up” or “spiking” with initiator at regular intervals to maintain

the free radical concentration at the desired level, to ensure a high degree of conversion

of monomer to polymer

Free radicals are extremely reactive, and the monomer units in the reaction mixture have

to compete with other species for the free radical This includes competition with other free radicals

The rate of initiation is defined in terms of the rate of formation of polymer chains and is expressed as:

Rị = 2fka[l]

where: Ri is the rate of initiation

f is the frequency factor for free radicals reacting with monomer units

ka is the decomposition rate for the initiator

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6 I - The Chemistry of Acrylic Resins

The number of chain ends present at any given time can be determined by: Ni = 2fkafljt

where: Ni is the number of initiated chains at time t The number of chain ends per monomer unit is given by

Mp

where: Mi is the number of chain ends per monomer unit Mm _ is the molecular weight of the monomer Mp _ is the mass of polymer formed during time t

Example: A monomer of molecular weight 62.5 shows a conversion of 6% over a7 hour reaction time, the mass of polymer formed being 18.2 grammes from a 5 molar solution of the monomer and 0.1 molar solution of initiator

f = 100% kg = Đ8.0x 10-4hrs-1 No = 2S} = 2x1x(80x102)x0.1x7 N — NxMm _ 2x1x(8B0x10')x0.1x7 Ộ ~ Mp ~ 18.2 Ni (number of chain ends present) = 3.8 x 10-3 2 Propagation

Once the monomer radical has been formed, propagation proceeds rapidly as the number of monomer units increases successively to produce a growing polymer chain After each successive addition, the free radical is retained on the vinyl carbon atom of the end chain unit RO—CH,— CHX + CH, = CHX —đ RO—CH,—CHX — CH,— CHX CH,= CHX RO—CH,—CHX—CH,—CHX: ——?—”*> RO—CH,—CHX +cn,— chx} CH,—CHX n Figure 1-1

Trang 21

The ease with which a monomer forms a free radical and the reactivity of the radical, once formed, determines the rate at which propagation proceeds Each propagation step proceeds at a speed determined by the propagation rate k, which is constant for a given monomer at a given temperature The propagation rate is independent of the degree of polymerisation of the growing chain

For homopolymerisation, the reaction rate (R,) is given by the equation

Rp = kẹ [M] [M']

where: Rp _ is the reaction rate

p is the rate constant for propagation of monomer M [Mj is the molar concentration of monomer M

[M] Ăis the molar concentration of monomer radicals M'

3 Termination

In order to terminate a growing polymer chain, it is necessary to effect the removal of the free radical from the polymer chain This may be accomplished in one of several ways,

but all involve either a “combination” reaction, a “disproportion” reaction or a “transfer”

reaction The exact mechanism will be dependent on the chemical structure of the monomer, the polymer chain and the nature of any other species present

(i) Termination by Combination

This is the simplest form of chain termination It involves two growing polymer chains which combine with the mutual extinction of the radicals

This type of termination reaction will result in a “head to head” linkage of the two

polymer chains involved

(ii) Termination by Disproportion

This occurs when the radical of a propagating chain, abstracts an H atom from another propagating polymer chain, to achieve the mutual extinction of the radicals

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In this case the two polymer chains do not combine, but remain as separate entities, one chain containing an unsaturated end unit, and the other a saturated end unit

R—CH,— chx-[cH,— cnx-} CH,— CHX + XHC— CHzƑxHC _ cH} XHC+CH,—R n m | R—CH,—CHX + CH,— cux CH,—CH,X + XHC=CH fxnc _ cH} XHC—CH—R n m Figure 1-3

A special case of intra-molecular abstraction can occur when the H atom is removed from the same chain as the abstracting radical This process (called “backbiting") may occur where long chain polymers take up configurations which bring labile H atoms on the polymer chain, into close proximity with the radical at the chain end This process

will result in the termination of the growing chain and give rise to a C=C bond at the

position on the polymer chain where the abstraction occurred

Whether a polymer terminates by a disproportionation or by a combination reaction depends upon the configuration of the monomers involved If there are no labile H atoms available, then termination will be by a combination reaction, e.g isobutyl styrene homopolymers If labile H atoms are available, then termination may occur by both combination and disproportionation reactions, e.g acrylic monomers

When disproportionation occurs, the product wil! contain polymer chains with

unsaturated chain ends or with unsaturated sites along the polymer backbone, as a result of the abstraction of H atoms

These C=C bonds are capable of reactivation by a free radical

Where the unsaturation is at the chain ends, propagation will continue, in the presence of sufficient monomer, as before

Where the unsaturated sites are along the polymer backbone, the restart of chain propagation will result in branching of the polymer chain

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I - The Chemistry of Acrylic Resins 9 R—CH,— CHX — CH,= CX— CH,— CHX— CH,—CHX + R | R—CH,—CHX—CH,— CXR — CH,— CHX— CH,— CHX | nCH,=CHX R—CH,— CHX— CH,— CXR — CH,— CHX— CH,— CHX CH, | CHX n-1 1" *CHX Figure 1-4 (iii) Termination by Transfer

This involves the removal of the radical from the propagating chain and the transfer of the radical to another chemical species

Both combination and disproportionation reactions result in the extinction of radicals

However, in the case of transfer reactions, the radical is not destroyed, but merely removed from the propagating chain and transferred to another species The new radical may, dependent upon its stability, act to initiate the propagation of another polymer chain R+cH,—cHx+ CH,—CHX + AB n R 4 CH,— cHx} CH,— CHXA + B n Figure 1-5

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The species AB in the example above, can be a solvent, a polymer, a modifier added

specifically as a chain transfer agent, or an inhibitor

If the radical B’ does initiate polymerisation, then the overall rate of propagation is unaffected by the transfer reaction However, the molecular weight of the polymer formed under these conditions, will be lower than that formed without the occurrence of transfer reactions

If B’ does not initiate polymerisation, it can be considered to be an inhibitor for the polymerisation, since it has, in effect, stopped chain growth and removed a free radical from the system

There are various forms which the transfer reaction can take It is often used as a means of modifying the length of the propagating chain, and hence, controlling the molecular weight of a polymer In general, the qualitative effect of transfer reactions on the molecular weight of the polymer is the same, by whatever mechanism it occurs The effect of unsaturated chain ends or residual unsaturation along the polymer backbone, is a source of chemical weakness in a surface coating system For example, an exterior coating made from polymer with unsaturated chain ends would be particularly susceptible to degradation from UV attack

4 Transfer Mechanisms (i) Transfer to Solvent

Here the polymerisation solvent acts as a transfer medium

Consider the following example of polystyrene homopolymerisation in carbon tetrachloride solvent:

The solvent participates in the reaction resulting in the termination of the

‘ ; ; R+cH

propagating chain, and the formation

of a new free radical species "

The “CCl, radical so formed, is

active and may initiate polymerisation

R tocu,- CH+CH,—-CHCI + CCI,

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1 - The Chemistry of Acrylic Resins 11

CCl,+ CH = CH, ———đằ CH— CH,CCI,

a oO

Figure 1-7

The frequency with which transfer occurs will depend on the chemical structure of the

solvent, the monomer and the solvent radical

The transfer constant can be quantified in:terms of the ratio of the reactivity of a given polymer radical towards the chain transfer agent and the reactivity of the given polymer towards the monomer

ks

ZG

where: kz = transfer constant

Ks = rate coefficient for transfer to solvent

Kp = rate coefficient for propagation of the polymer radicals

The k, varies with temperature and solvent type, but in general, solvents are relatively weak chain transfer agents Typical examples of chain transfer constants are listed in the table below

TABLE 1-1: CHAIN TRANSFER CONSTANTS AT 60°C

Solvent Acrylonitrile Methaorylate Styrene any Acetone 0.000095 0.00036 0.023 0.0016 Acetonitrile 0.00017 - 0.0023 0.0013 Aniline 1.05 0.0075 0.011 0.026

Benzene 0.00021 0.0014 0.00017 0.00016 Methy! ethyl ketone 0.00055 0.00089 0.028 0.0097 Carbon tetrachloride 0.000073 0.0043 0.57 1.18 Chloroform 0.00049 0.00089 0.00345 0.02 Ethyl acetate 0.00022 0.00027 0.0091 0.0004 Ethyl! alcohol : 0.00071 0.0085 0.0033 Triethy! amine 0.155 : 0.017 0.049

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In a free radical polymerisation, where the rate of radical formation is kept constant, the degree of polymerisation is proportional to the concentration of monomer

The degree of polymerisation, multiplied by the molecular weight of the monomer gives the polymer molecular weight Chain transfer to the solvent not only reduces the molecular weight of the polymer formed initially, but it also affects the polydispersity which increases as the polymerisation proceeds

Normally, when carrying out solution polymerisation on a commercial scale, solvents with chain transfer coefficients below 0.001 would be employed, unless a low molecular weight product is required

(ii) Transfer to Monomer

Transfer to monomer can occur in one of two ways Both involve an abstraction process through which a hydrogen atom is transferred to the propagating chain The free radical

is transferred to the monomer to form a monomer radical

a) Abstraction from the Vinyl Carbon Atom

R†cn,—cnx} CH,— CHX + CH,= CHX

|

RTcn,~cHx} CH,—CH,—X + CH,= CX

Figure 1-8

The monomer radical formed is free to initiate the propagation of another polymer chain

CH,=CX + nCH,=CHX ——> CH,=CX tcr,—cHxt CH,CHX

n-1

Figure 1-9

The newly propagated chain will have an unsaturated end group This end group is available for re-initiation

R + CH, =CX fch,- cHx} R_ ——> R-cHr-Cx {cn— cHx†} R

n n

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1- The Chemistry of Acrylic Resins 13

Propagation will lead to the formation of a branched polymer chain

R—CH— Cx + CH,— cHx} R + mCH=CHX n R—cH— Cx +1 CH,— chx} R | n [cn.- crx| |: m1 CH, | CHX Figure 1-11 b) Abstraction from a Side Chain

This type of reaction is typified by vinyl acetate, but may also occur with acrylic monomers with alkyl side groups

R fon cut CH,— CH + CH=CH | 7" | |

C—O—CH, C—O—CH, C—O—CH,

Il Il ll

o O Oo

Propagating species monomer

R cH cut CH, — CH, + CH,= CH

TP" |

C—O—CH; C—O—CH, C—O—CH,

|| ll lè

O O O

terminated polymer chain monomer radical

Figure 1-12

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(iii) Transfer to a Modifier

Modifiers are species that contain a labile atom (most usually hydrogen or halogen) which can be abstracted by the propagating chain

Propagation of the chain is terminated and the radical is transferred to the modifier

R+cH- cHx} CH,— CHX + R—-—H

n

R +en— cHx} CH,— CH,X + R n

Figure 1-13 The modifier radical can then act in one of two ways:

a) It can act to initiate the propagation of a new polymer chain The net result in this case is that the modifier has acted as an agent in the transfer of the radical from one propagating chain to another Examples of such “Chain Transfer Agents” (CTA) are carbon tetrabromide, ethane thiol and tertiary butyl mercaptan

or

b) ‘It can form a stabilising free radical which will not take part in further initiation

reactions In effect, the free radical has been removed from the system, and the

modifier has acted as a polymerisation inhibitor Examples of such “Inhibitors” are hydroquinone and nitrobenzene

5 Chain Transfer Agents

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The effectiveness of a chain transfer agent is measured in terms of its ability first to terminate a growing polymer chain, and then to initiate the propagation of another polymer chain

This is quantified as the transfer rate constant C,, which is temperature dependent and is different for different monomer types

In general, long chain alkyl mercaptans give the best performance as CTA’s They are extensively used in commercial polymerisations of acrylate monomers as modifiers to control the molecular weight of the final polymer

The number of chain ends arising from transfer reactions can be obtained from the equation:

S Ns = 2Cs {8}

[M]

where: Neg = number of chain ends containing modifier per monomer unit in the polymer

Cs = rate co-efficient of transfer for the modifier [S] = molecular concentration of modifier [M] = molecular concentration of monomer

This has been related empirically to the molecular weight of the polymer by Mayo in his equation:

where: P degree of polymerisation in presence of modifier Po degree of polymerisation without modifier

Cs, [S] & [M] are as before

TABLE 1-2: COMPARISON OF C,; FOR VARIOUS COMMONLY

ENCOUNTERED CTA’s

Chain Transfer Agent Homopolymerisation at 60°C Methyl

Methacrylate Styrene Carbon tetrachloride 0.27 2.2 Butane thiol 0.66 22.0

t-butyl mercaptan 0.18 3.6

Ethyl mercapto acetate 0.63 58.0

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6 Inhibitors

Inhibitors act by removing free radicals from the system Depending on the relative

reactivities of the inhibitor and the radical concerned, the free radicals may be removed

either as fragments of initiator decomposition or as very short chain radicals Commonly encountered inhibitors include nitrobenzene

NO, AXxx(CH-CH + Ay CH= CHX AWWW CH,— CHX — 0 \ — l O ci NO, NZ / H Figure 1-15

and Ferric chloride

AWW CH,-CHX + FeCl, ~———ằ AAWVCH—CHGI + FeCl,

NWW CH CHXC] + FeCl, ———đ AWW CH=CHX + HCI + FeCl, Figure 1-16

The radical formed with benzoquinone is resonance stabilised and thus will not initiate polymerisation oO Il + CH,— CHX —> CH,— CHX—O lI oO p-benzoquinone ơ

resonance stabilised radical

Figure 1-17

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Il THE KINETICS OF THE FREE RADICAL

POLYMERISATION OF ACRYLIC MONOMERS

1 Initiation

Initiation proceeds in two stages:

a) decomposition of initiator into free radicals

ka

>

| 2R°

b) attack by the free radical on the monomer molecule forming a monomer radical kj

>

R'+M RM '

If every radical from each initiator molecule reacts with a monomer molecule the rate of reaction will be given by:

Ri = 2ka{l]

where: kd is the rate dissociation constant

[I] is the initiator concentration

Usually it is not every free radical, produced by initiator decomposition, which reacts with a monomer molecule and the equation is modified to become

RĂ = f2ka[l]

where: f is the initiator frequency 2 Propagation

It has been shown experimentally that the propagating chain length has no effect on the Treaction rate Each propagation step proceeds at the same rate for a homopolymerisation

k

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18 1- The Chemistry of Acrylic Resins

3 Termination

This proceeds in accordance with the equation

Mx + My a Mx My (combination)

or

‹ - Kt

Mx + My 4 Mx + My (disproportionation)

Rate of termination R, = 2k,[M]J° which applies to termination by combination or

disproportionation

Thus an overall equation for acrylic polymerisation can be written as

— kel PL)! = kota ally

Rp = kp MKC 2M) é kp[MK kt )

where: [ẽ] = concentration of initiator

[M] = concentration of monomer

fkq = frequency and decomposition constants for the initiator

kt = rate coefficient of chain termination

thatis: Rpo[M] and Rpa[l]”

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1- The Chemistry oƒ Acrylic Resins 19

4 Polymer Chain Length

Kinetic Chain Length v is defined as the number of molecules reacting with a reactive centre from its formation to its termination

y Be _ Bp _ kp[MIM] _ kp[MIM] Ri Ri 2k [Mấ 2fka[l]

thus;

y= KeIML _ ke IMI? 2ki[M] 2Kt Rp

So that the Kinetic Chain Length is inversely proportional to the rate of polymerisation 5 Degree of Polymerisation

The degree of polymerisation, i, is defined as the number of monomer units in a polymer molecule

Assuming that little or no transfer occurs then the relationship between v and i will depend on the mode of termination

a) Termination by combination - two radicals of kinetic chain length v combine to form one molecule with a degree of polymerisation i, that is:

i= 2v

b) Termination by disproportionation - two radicals of kinetic chain length v react to form two molecules each with a degree of polymerisation i, that is:

i=v Since, as we have seen above

_ Keim?

2kt Rp

and for the steady state

Ri = Ri and

fka[l]-›

Rp = kp My (“2lly’s

it follows that the rate constant for propagation k, (in the early stages of the reaction) will

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20 1- The Chemistry oƒ Acrylic Resins

If f (the initiator frequency or efficiency) is independent of [M] then the rate of propagation is proportional to [M]

that is:

Rp o [M]

This holds experimentally where the initiator frequency f is high Where f is low then:

f a [M]

and

Rạp ơ [MỸ

Plots of R, versus [I] give a straight line graph with a slope approximately 0.5 as illustrated below:

methyl methacrylate with AZDN initiator methyl methacrylate with benzoyl peroxide initiator “styrene with benzoyl peroxide initiator IH —> Figure 1-19

If the initiator concentration does not vary much during polymerisation (as for example when using a continuous addition or ‘drip feed’ process) and the initiator frequency f is independent of the monomer concentration (as is the case when f approaches 1) then

Rp a [MỊ

and the polymerisation will proceed in accordance with the principles of first order

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An example is included here to illustrate this

Methy] acrylate is polymerised in xylene at 50°C using azo di-isobutyronitrile (AZDN)

If [1] = 1 x 10? mole litre!

Initiation rate constant ka = 1.2 x 10 sec!

Termination rate constant k; = 7.2 x 10’ litres mole? sec’! Calculate [M "7 when f=1 _ fafllZ M- M'] rk) [1 x 1.2x 10Š x 1x 10312 M'] = ; MI (7.2 x 107] = 1.28x 10 molelitres

Under the conditions of polymerisation [M’] reaches a maximum value within a few seconds of the start of the reaction and thereafter remains constant as illustrated below

[M]

time ——>

Trang 36

The following table taken from the literature compares [M] and [I] for two monomers

commonly encountered in acrylic polymers The initiator is AZDN and a reaction

temperature of 50°C was quoted

TABLE 1-3 Kp kt m [M] after 1 ho Monomer ur

(litre mole! sec!) | (mole? sec!) (mole litre") at 50°C

Styrene 176 7.2x107 1x103 0.989 1x102 0.964 1x101 0.891 Methyl 734 3.7x102 1x103 0.935 methacrylate 1x102 0.809 1x101 0.513

6 Effect of Reaction Conditions on Chain Length

2 [M]?

2k,R P

Since, as we have seen Vv =

If the monomer concentration is kept constant then the kinetic chain length relationship is;

va +

Rp

As the rate of polymerisation increases with increase in temperature the molecular weight will decrease:

vơ[Mj

and

l

vo

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1 - The Chemistry of Acrylic Resins 23

The degree of polymerisation will be given by:

2R i -_í “ẤP i=2v= R fka[l] 4: — ae[đf]smm = 2fka [I] 1 \% [M I= ke)” nh

Examples for styrene in xylene using AZDN at 50°C and assuming f=1

{I}=1x10° mole! [M] =1 mole litre’

(1) (1)

i = 176 (1.2x10°x7.2x107)% (1x 107%)”

i = 186

Molecular weight of styrene monomer = 104

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24 I- The Chemistry oƒ Acrylic Resins

IV CHEMISTRY OF ACRYLIC MONOMERS

1 The Major Acrylic Monomers

TABLE 1-4: THE MAJOR ACRYLIC MONOMERS

Acrylonitrile CH,— CH— CN 97

Acrylic acid CH,—CH— COOH 106

Methy! acrylate CH= CH— COOCH, 10

Ethyl! acrylate CH,= CH— COOC,H, -24

Butyl acrylate CH;—CH— COOC,H, -54

2 ethyl hexyl —nH_—_

acrylate CH,— CH— COOC,H,, -70 Methoxyethyl —nH_——

acrylate CH= CH— COOCH,CH,OCH, -33 Dimethylamin —

A erylate mino CH,—CH—COOCH,CH,N(CH,), — -38

Methacrylic acid CH„— ẹ —COOH 228

CH, Methyl CH,—C — COOCH, 105 methacrylate CH, Ethyl CH,= C— COOC,H, 65 methacrylate | CH, Butyl CH= C — COO—CH;— CH;—CH,—CH, methacrylate | CH, 20 lsobutyl CH—=C—COO —CH„—CH—CH, 53 methacrylate i | CH, CH,

2-ethyl hexyl CH,— C — COOC,H,, -10

methacrylate CH, |

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TABLE 1-4: THE MAJOR ACRYLIC MONOMERS (continued)

Lauryl CH= C — COOC,H„„ 65 methacrylate | CH, n=8-18 Stearic CH„—C — COOC,H¿„„; -100 methacrylate | CH, n=16-20

Dimethyl amino CH;C — COOCH,CH,N(CH,), 19

methacrylate |

CH, n=16-20

Allyl CH,=C —COOCH,—CH=CH, 45

methacrylate CH, |

2 Hydroxy ethyl CH,=CH—COOCH.,—CH;— OH -85

acrylate

2 Hydroxy propyl CH;„— CH COO —CH; CHĐ—CH, -93

acrylate

T OH

2 Hydroxy ethyl CH,=C —COO—CH;—CH;-OH 55

methacrylate |

CH,

2 Hydroxy propyl CH—C —COO—CH;-CH—CH, 73

methacrylate | | CH, OH Acrylamide CHz—CH— CONH, 165 Methacrylamide CHz—C — CONH, ` | CH,

Glycidy! acrylate â CH;=CH—COO—CH,;—CH—CH, - N_⁄

*Styrene CH=CH — (C,H.) 100

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Of particular importance in surface coating applications are the two series of related monomers derived from acrylic acid and methacrylic acid These monomers are termed “acrylates” and “methacrylates” respectively and polymers derived from either species are known collectively as acrylic resins Typical acrylate and methacrylate monomers are shown in the table above

Acrylic esters have the common structure: CH= 1"

COR

|

O Figure 1-21 Whilst methacrylic esters have the common structure:

CH,=C— CH, i O Figure 1-22 Typical examples are:

CH,= CH CH,= oe CO,C,H, CO,C,H; Butyl Acrylate Butyl Methacrylate

Figure 1-23

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