ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Porton and carbon spin-lattice relaxation times T1 and nuclear Overhauser enhancements are interpreted in terms of motions likely in linear polyisobutylene. Most of the interpretation is based on relaxation data in the literature, but some additional 1H and 13C pulse Fourier transform experiments were conducted to resolve a disagreement in the literature concerning cross relaxation between the two types of protons present in polyisobutylene. Spin relaxation in solution and the bulk is accounted for by three specific motions considered as independent sources of motional modulation of the dipole-dipole interaction. The first motion is overall isotropic rotatory diffusion which has a known dependence on molecular weight, intrinsic viscosity, and solvent viscosity for polymers in solution, and a known dependence on molecular weight and viscosity for bulk polymers. The effects of overall tumbling account for a decrease of T1 for the methylene and methyl carbons with increasing molecular weight in solution and increase of T1 of methylene carbons with molecular weight in bulk. The second motion considered is backbone rearrangements caused by the three-bond jump. This motion dominates relaxation of the methylene carbons either in solution or in the bulk allowing for the determination of the associated correlation time. The correlation time characterizing the occurrence of the three-bond jump in a 5% (wt/vol) solution in CCI4 at 45°C is 58 psec, and in the bulk at 45°C it is 11 nsec. The last motion included in the model is methyl-group rotation about the threefold symmetry axis. The methyl-group rotational correlation time is 0.20 nsec in a 5% (wt/vol) solution in CCI4 at 45°C and 0.33 nsec in the bulk at 45°C. The concentration dependence of the backbone motion contrasts strongly with the corresponding dependence of methyl-group rotation.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1978.180160912
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