r NMR Spectroscopy of Polymers Edited by ROGER N. IBBETT Courtaulds Research and Technology Coventry BLACKIE ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hall London Glasgow New York Tokyo Melbourne Madras
Contents Editorial introduction R.N. IBBETT xiii 1 Introduction to NMR and its use in the study of polymer stereochemistry 1 F. HEATLEY 1.1 Introduction 1 1.2 Basic principles of NMR 1 1.3 The form of a liquid-state NMR spectrum 5 1.3.1 Chemical shifts 5 1.3.2 Spin-spin (scalar) coupling 8 1.3.3 Intensities in NMR spectra 10 1.3.4 Spin-decoupling s 11 1.4 Nuclear magnetic relaxation 12 1.4.1 Basic principles 12 1.4.2 Practical implications of relaxation. 13 1.4.3 The nuclear Overhauser effect in 13 C NMR 14 1.5 Experimental practice in high-resolution solution-state NMR of polymers 16 1.5.1 The spectrometer 16 1.5.2 The sample 17 1.6 Advanced Fourier transform techniques 18 1.6.1 One-dimensional techniques 19 1.6.2 Two-dimensional NMR spectroscopy 22 1.7 A survey of applications of high-resolution solution-state NMR to polymers 26 1.7.1 Determination of functional groups and composition of composite systems 26 1.7.2 Determination of end-groups 26 1.7.3 Statistical characterisation of the structure of irregular chains 27 1.8 The observation of polymer stereochemistry (tacticity) by NMR 28 1.8.1 Stereochemistry of vinyl polymers 28 1.8.2 Application of 2-D techniques for the assignment of tacticity-related peaks 39 1.8.3 Tacticity sequence statistics in vinyl polymers 40 1.8.4 Stereochemistry of poly(epoxides) 44 1.8.5 Geometrical isomerism in polydienes 46 1.9 Summary 47 References 48 Statistical analysis of copolymer sequence distribution 50 I.R. HERBERT 2.1 Introduction 2.2 Copolymerisation statistics and models 50 51
Vlll CONTENTS 2.2.1 Copolymer number-average sequence lengths and necessary relationships 52 2.2.2 Statistical models 54 2.2.3 Statistical models and polymer propagation 58 2.3 Examples of the use of copolymer statistics 61 2.3.1 Copolymers with Bernoullian sequence distributions 61 2.3.2 Copolymers with first-order Markov sequence distributions 63 2.3.3 Penultimate model polymers and complex participation 66 2.3.4 Other copolymers 68 2.4 In situ methods and simulation techniques 71 2.5 Polymer modification 75 2.6 Summary 77 References 78 Solution-state NMR determination of polymer end-groups, substituents and minor structures 80 J.C. BEVINGTON, J.R. EBDON and T.N. HUCKERBY 3.1 Introduction 80 3.1.1 General remarks 80 3.1.2 Comments on experimental procedures 82 3.2 End-groups 85 3.2.1 Introductory remarks 85 3.2.2 Azo initiators 86 3.2.3 Peroxides 95 3.2.4 Other initiators 102 3.2.5 Transfer agents and retarders 104 3.2.6 Main-chain scission 106 3.3 In-chain units 108 3.3.1 Regioselectivity in growth reactions 108 3.3.2 Abnormal units 110 3.4 Branching 112 3.4.1 General remarks 112 3.4.2 Low density polyethylene 113 3.4.3 Polymers from other vinyl monomers 114 3.4.4 Amino and phenolic resins 116 3.4.5 Polysiloxanes 117 3.5 Chemical modification of polymers 118 3.5.1 Synthetic polymers 118 3.5.2 Natural polymers 119 3.6 Concluding comments 121 References 121 Liquid state NMR studies of polymer dynamics and conformation 125 O.W. HOWARTH 4.1 Introduction 125 4.2 NMR relaxation theory 128 4.2.1 The flow of spin populations 129 4.2.2 Microscopic relaxation theory 132 4.2.3 Relaxation mechanisms jjfe> 135 4.3 The dynamics of flexible molecules and macromolecules 138 4.3.1 Applications 146 4.4 The conformational states of polymers 149 4.4.1 Relation of conformation to NMR properties 152
CONTENTS 4.5 Application of conformational theory to relaxation and NOE 156 4.6 Experimental methods 158 References 159 IX High-resolution solid-state NMR studies of polymer chemical and physical structures 161 A.E. TONELLI 5.1 Introduction 161 5.2 High-resolution NMR spectroscopy of solids 162 5.2.1 Dipolar coupling 162 5.2.2 Chemical shift anisotropy 166 5.2.3 Cross-polarization 169 5.3 Acquisition and analyses of solid-state 13 C NMR spectra 171 5.4 Applications of high-resolution CPMAS/DD NMR to polymer solids 181 5.4.1 NMR determination of crystalline polymer conformation 181 5.4.2 Solid-state NMR observations of copolymer sequences and their distribution between crystalline and amorphous phases 184 5.4.3 NMR observations of solid-state polymer reactions 187 5.4.4 Solid-state NMR observation of polymer blends and interphases 190 5.4.5 NMR observations of orientation in solid polymers 193 5.5 Summary 195 References 195 High-resolution solid-state l3 CNMR studies of local motions and spin dynamics in bulk polymers 198 F. LAUPRETRE 6.1 Introduction 198 6.2 "CNMR investigation of local dynamics in bulk polymers at temperatures well above the glass-transition temperature 199 6.2.1 Models for local dynamics 199 6.2.2 Experimental studies - 201 6.2.3 Temperature dependence 205 6.2.4 Factors controlling the local dynamics 207 6.2.5 Conclusion 209 6.3 l3 CNMR investigation of local dynamics in bulk polymers at temperatures below the glass-transition temperature 210 6.3.1 Chemical shift anisotropy 211 6.3.2 Spectrum lineshape 214 6.3.3 Relaxation times and linewidths 216 6.3.4 13 C-'H dipolar interaction 220 6.4 6.3.5 Conclusion 222 13 CNMR study of the molecular organization of some solid heterogeneous polymer systems 222 6.5 Conclusion 228 References 228 Solid-state proton NMR studies of polymers 231 A.M. KENWRIGHT and B.J. SAY 7.1 Introduction 7.2 Heterogeneity in solid polymers 231 232
X CONTENTS 7.3 Underlying theory: the dipolar interaction 233 7.3.1 The static part 235 7.3.2 Suppressing the dipolar interaction 237 7.3.3 The non-static part 237 7.3.4 Relaxation in heterogeneous systems 240 7.3.5 Heteronuclear effects 241 7.4 Experimental methods 242 7.4.1 FID/lineshape measurement 242 7.4.2 Longitudinal relaxation, 7\ 244 7.4.3 Relaxation in the rotating frame, T l 244 7.4.4 Experimental details 245 7.4.5 Treatment of results 246 7.5 Lineshape/FID analysis of polymers 246 7.5.1 Semi-crystalline homopolymers 246 7.5.2 Filled elastomers and block copolymers 249 7.5.3 Glassy systems 250 7.5.4 Highly mobile systems: melts 250 7.6 Relaxation time analysis of polymers 251 7.7 Spin diffusion in relaxation methods for polymers 255 7.8 Attempts to observe spin diffusion directly 258 7.9 Attempts to suppress spin diffusion in relaxation measurements 262 7.10 High-resolution proton methods for polymers, MAS and CRAMPS 264 7.11 Carbon detection of proton magnetisation 267 7.12 Oriented polymers 268 7.13 Conclusions 270 References 271 Deuterium NMR of synthetic polymers 275 D.M. RICE 8.1 Introduction 275 8.2 Experimental theory 276 8.2.1 Basic pulse sequences 278 8.2.2 A vector model for spin 1 dynamics 280 8.2.3 Experimental methods 281 8.3 Polymer orientation 283 8.3.1 Stretched films of poly(p-phenylene vinylene) 283 8.3.2 Planar orientation of polyethylene terephthajate 286 8.4 Polymer motion 288 8.4.1 Ring-flip motion of poly(p-phenylene vinylene) 289 8.4.2 Chain motion of poly(p-phenylene vinylene) 293 8.4.3 Segmental dynamics of Nylon 295 8.5 Multi-dimensional experiments 298 8.5.1 Exchange spectra of isotactic polypropylene 300 8.5.2 Chain motion of poly(vinylidene fluoride) 301 8.5.3 Diffusive motion of atactic polypropylene near T g 301 8.6 Conclusions 303 Acknowledgements 304 References 304 NMR in polymers using magnetic field gradients: ф imaging, diffusion and flow 308 P.T. CALLAGHAN 9.1 Introduction 9.2 Theory 308 309
CONTENTS 9.2.1 Magnetic field gradients and NMR imaging 309 9.2.2 Pulsed gradient spin echo NMR 313 9.2.3 Dynamic NMR imaging 319 9.3 Applications of NMR imaging in polymers 320 9.3.1 Solid-state imaging 320 9.3.2 Elastomer imaging and solvent imaging 323 9.3.3 Monomer and solvent imaging 325 9.4 Pulsed gradient spin echo diffusion studies in polymers 326 9.4.1 Centre of mass diffusion in polymer liquids 326 9.4.2 Internal motions in high polymers 331 9.4.3 Diffusion of small molecules in polymer systems 333 9.5 Flow studies using dynamic NMR imaging 333 9.6 <j-space imaging of morphology in colloidal and polymeric systems 336 9.7 Conclusions 339 References 339 XI 343