Automated measurement of spin-lattice relaxation times:  optimized pulsed nuclear magnetic resonance spectrometry

Polybutadiene networks were prepared by peroxide crosslinking of monodisperse 1,4‐polybutadienes both in solution and in bulk. The effect of the entangled sol fraction on the elastic modulus of high‐molecular‐weight polybutadiene was observed in stress relaxation measurements. Sol fraction was shown to make a large contribution to the Mooney–Rivlin 2C2 term. This effect was also observed on the molecular level in NMR spin‐spin relaxation measurements. For networks crosslinked in bulk the stress relaxation measurements suggest the presence of trapped entanglements. The 2C2 term is insensitive to sol extraction in these networks. NMR spin‐lattice relaxation measurements in the rotating frame at 4.68 kHz verify the presence of additional effective crosslinks in these networks.

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NMR study of polyethylene crystallization kinetics under high pressure

Brown

Jonáš

1984

J. Polym. Sci. Polym. Phys. Ed.

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Crystallization of polyethylene under hydrostatic pressures of 1–4.5 kbar is directly observed using pulsed proton NMR. The rate of growth of extended‐chain polyethylene crystals is measured over this pressure range and to a maximum temperature of 227°C. The observed crystallization isotherms are superimposable on a log time scale; this implies a consistent mechanism for extended‐chain growth over this pressure range. Avrami coefficients for high‐pressure extended‐chain crystallization are determined to be 1.3–1.7. A decrease of crystal nucleus surface free energies with increasing pressure is indicated. Findings are consistent with Wunderlich's model of initial folded‐chain crystallization followed immediately by chain extension. Future applications of this NMR technique are briefly considered.

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Automated measurement of spin-lattice relaxation times: optimized pulsed nuclear magnetic resonance spectrometry

Cited by 20 publications

References 20 publications

Methods of measuring spin‐lattice (T1) relaxation times: An annotated bibliography

Methods of measuring spin‐lattice (T1) relaxation times: An annotated bibliography

Entanglements and elasticity in polybutadiene networks

NMR study of polyethylene crystallization kinetics under high pressure

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