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Library of Congress Cataloging-in-Publication Data
Bovey, Frank Alden, date
NMR of Polymers / by Frank A. Bovey. Peter A Mirau
p. cm
Includes index.
ISBN 0-12-1 19765-4 (alk paper)
I. Nuclear magnetic resonance spectroscopy 2. Macromolecules-
-Analysis. I Mirau. Peter A II Title.
QP519.9N83B6X 1996
574.19'285-dc20 96-28240
CIP
PRINTED IN THE UNITED STATES OF AMERICA
96 97 9 R 9 9 0 0 0 1 B C 9 8 7 A 5 4 3 2 1
Con tents
Preface ix
1
F U N D A M E N T A L S O F N U C L E A R
M A G N E T I C R E S O N A N C E
1.1 Int roduc t ion 1
1.2 N u c l e a r S p i n a n d the N M R P h e n o m e n o n 2
1.3 T h e Detec t ion of the Resonance P h e n o m e n o n 7
1.4 N u c l e a r R e l a x a t i o n 11
1.4.1 Spin-Lat t ice Relaxation 11
1.4.2 Sp in -Sp in Relaxation and Dipolar Broadening 19
1.4.3 The Bloch Equations 23
1.4.4 Nuclear Electric Quadrupole Relaxation 29
1.5 M a g n e t i c S h i e l d i n g a n d the C h e m i c a l Shi f t 30
1.5.1 The Basis of Molecular Shielding:
Proton Chemical Shifts 30
1.5.2 Carbon-13 Chemical Shifts 42
1.5.3 Other Nuclei ( 1 9F, 31P, 1 4 N , 15N) 46
1.6 Indi rec t C o u p l i n g o f N u c l e a r S p i n s 47
1.6.1 Introduction 47
1.6.2 Proton-Proton Couplings and Spectral Analysis 49
vi Contents
1.6.3 C a r b o n Pro ton C o u p l i n g s a n d
C a r b o n - C a r b o n C o u p l i n g s 53
1.6.4 O t h e r N u c l e i (19F, 31P, 14N, 15N) 53
1.7 R a t e P h e n o m e n a : A v e r a g i n g o f C h e m i c a l S h i f t s a n d
J C o u p l i n g s 5 5
1.8 E x p e r i m e n t a l M e t h o d s 5 7
1.8.1 Int roduc t ion 57
1.8.2 T h e M a g n e t i c F i e l d 57
1.8.3 Refe renc ing 59
1.8.4 D e c o u p l i n g Gl
1.8.5 S o l i d S ta te M e t h o d s 63
1.8.6 T h e O b s e r v a t i o n of N u c l e a r R e l a x a t i o n 72
1.8.7 T w o - D i m e n s i o n a l N M R 87
1.8.8 S p e c t r a l E d i t i n g and S i m p l i f i c a t i o n 105
2
T H E M I C R O S T R U C T U R E OF
P O L Y M E R C H A I N S
2.1 I n t r o d u c t i o n 117
2 .2 P o l y m e r M i c r o s t r u c t u r e 118
2.2.1 H e a d - t o - T a i l ve r sus H e a d - t o - H e a d - T a i l - t o - T a i l
I somer i sm: R e g i o i s o m e r i s m 118
2.2.2 Ste reochemica l C o n f i g u r a t i o n 118
2.2.3 I s o m e r i s m in D i e n e P o l y m e r C h a i n s 122
2.2.4 V i n y l P o l y m e r s w i t h O p t i c a l l y A c t i v e S i d e c h a i n s 128
2.2.5 P o l y m e r s w i t h A s y m m e t r i c C e n t e r s i n the M a i n C h a i n 129
2.2.6 B r a n c h i n g a n d C r o s s L i n k i n g 129
2.2.7 C o p o l y m e r Sequences 131
2.2.8 O t h e r T y p e s o f I s o m e r i s m 133
2 .3 C o n f i g u r a t i o n a l S t a t i s t i c s a n d P r o p a g a t i o n M e c h a n i s m 133
2.3.1 B e r n o u l l i a n d F i r s t - O r d e r P r o p a g a t i o n M o d e l s 133
2.3.2 F i t t i n g of L o n g e r Sequences o f the F i r s t - O r d e r
M a r k o v M o d e l 139
2.3.3 M o r e C o m p l e x P r o p a g a t i o n M o d e l s 143
2.4 P r o p a g a t i o n E r r o r s 151
2.4.1 C o p o l y m e r Propaga t i on 153
Contents v i i
3
T H E S O L U T I O N C H A R A C T E R I Z A T I O N O F
P O L Y M E R S
3.1 Int roduc t ion 155
3.2 Resonance A s s i g n m e n t s 158
3.2.1 Resonance Assignments from Model Compounds 158
3.2.2 Assignment by Intensity and Chemical Shift
Calculations 160
3.2.3 Two-Dimensional N M R 165
3.3 M i c r o s t r u c t u r a l C h a r a c t e r i z a t i o n of P o l y m e r s i n S o l u t i o n 167
3.3.1 Regioisomerism 168
3.3.2 Stereochemical Isomerism 181
3.3.3 Geometric Isomerism 196
3.3.4 Branches and End Groups 199
3.3.5 Copolymer Characterization 212
3.4 T h e S o l u t i o n S t r u c t u r e of P o l y m e r s 220
3.4.1 Chain Conformation 220
3.4.2 Intermolecular Association of Polymers 232
4
T H E S O L I D - S T A T E N M R O F P O L Y M E R S
4.1 Int roduc t ion 243
4.2 C h a i n C o n f o r m a t i o n i n the S o l i d S ta te 245
4.2.1 Semicrystalline Polymers 245
4.2.2 Amorphous Polymers 255
4.2.3 Sol id-Sol id Phase Transitions 261
4.2.4 Other Studies 267
4.3 T h e O r g a n i z a t i o n of P o l y m e r s i n the S o l i d Sta te 274
4.3.1 The Organization of Semicrystalline Polymers 279
4.3.2 Multiphase Polymers 289
4.3.3 Polymer Blends 300
4.3.4 N M R Studies of Oriented Polymers 331
4.4 N M R I m a g i n g of P o l y m e r s 337
vi Contents
5
T H E D Y N A M I C S O F M A C R O M O L E C U L E S
5.1 Int roduc t ion 353
5.2 P o l y m e r D y n a m i c s i n S o l u t i o n 358
5.2.1 Introduction 358
5.2.2 Modeling the Molecular Dynamics of Polymers 359
5.2.3 Observation of Polymer Relaxation in Solution 367
5.3 P o l y m e r D y n a m i c s i n the S o l i d Sta te 379
5.3.1 Introduction 379
5.3.2 The Dynamics of Semicrystalline Polymers 394
5.3.3 The Dynamics of Amorphous Polymers 412
5.3.4 The Dynamics of Polymer Blends 436
5.3.5 The Dynamics of Multiphase Polymer Systems 445
Index 455
P r e f a c e
Over the past three decades, NMR spectroscopy has emerged as one
of the most important methods for polymer characterization. In the
early history, high resolution solution NMR spectra played a key role
in characterizing polymer microstructure and in understanding poly-
merization mechanisms. More recently, solid-state NMR has been
developed and used to probe the structure, conformation, organiza-
tion, and dynamics of polymers in their native state. In fact, the
solid-state characterization of polymers is such an important topic
that it has driven the development Qf new solid-state NMR methods.
A further revolution occurred with the introduction of multidimen-
sional NMR, making it possible to observe polymers with much
higher resolution, leading to a more detailed understanding of poly-
mer microstructure and to the molecular level assignments of the
dynamics that have long been measured by dielectric and dynamic
mechanical spectroscopy. The current importance of NMR in polymer
characterization can be judged from the many papers published in
polymer science that rely on NMR to elucidate the properties of
polymers.
The goal of this book is to provide an overview of the applications
of NMR to polymer characterization. The book begins with a review of
the fundamental principles in Chapter 1 and polymer structure in
Chapter 2. The high resolution solution state NMR of polymers is
presented in Chapter 3 and includes multinuclear NMR studies and
the two-dimensional NMR methods used to study polymer mi-
crostructure, chain conformation, and the structure of associating
polymers. The solid-state NMR of polymers is presented in Chapter 4
and includes NMR determination of chain conformation in semicrys-
talline and amorphous polymers, polymer blends, and multiphase
ix
X Preface
polymer systems, as well as the NMR methods used to study chain
organization on longer length scales. The molecular dynamics of
polymers is covered in Chapter 5, where the methods used to study
polymer dynamics both in solution and in the solid state are pre-
sented. Included in this chapter are the wideline and multidimen-
sional NMR methods that have been used to relate the transitions
measured by other spectroscopies to the chain dynamics at the atomic
level.
This book is intended for academic and industrial researchers and
does not reference all the data collected on the NMR of polymers. It
does, however, illustrate the types of problems in polymer science
that can be solved by NMR spectroscopy. In certain instances it is
most instructive to show the data from some of the early, classic
experiments in polymer NMR, while in other cases experiments from
the most current literature are provided.
FUNDAMENTALS OF
NUCLEAR MAGNETIC
RESONANCE
1.1 INTRODUCTION
NMR spectroscopy is a method of great interest and importance for
the observation of every aspect of the structure and properties of
macromolecular substances. The first studies were reported by Alpert
(1) only about a year after the discovery of nuclear resonance in bulk
mat ter (2,3). It was observed that natural rubber at room tempera-
ture gives a proton linewidth more like that of a mobile liquid than of
a solid, but that the resonance broadens markedly at temperatures
approaching that (ca. -70~ now known as the glass temperature.
These phenomena were recognized as being related to the presence
(and cessation) of micro-Brownian motion. We shall relate these
matters in more detail when we deal with the vital topic of polymer
NMR in the solid state. For the present we note that this field was
well developed before high-resolution spectra of synthetic polymers in
solution were first reported by Saunder and Wishnia (4), Odajima (5),
and Bovey et al. (6). From today's perspective it is difficult to under-
stand why the observation of such spectra was so long delayed,
especially since the NMR spectroscopy of small molecules was in an
advanced state. It appears that solution spectra were generally ex-
pected to be very complex and to exhibit resonances too broad to be
usefully interpreted. As we shall see, such fears were in general not
