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Titolo: Rouse and reptation dynamics of linear polybutadiene chains studied by H2NMR transverse relaxation
Autore: Klein, PG; Adams, CH; Brereton, MG; Ries, ME; Nicholson, TM; Hutchings, LR; Richards, RW;
 Indirizzi:
 Univ Leeds, IRC Polymer Sci & Technol, Leeds LS2 9JT, W Yorkshire, EnglandUniv Leeds Leeds W Yorkshire England LS2 9JT S2 9JT, W Yorkshire, England Univ Durham, Durham DH1 3LE, England Univ Durham Durham England DH1 3LEUniv Durham, Durham DH1 3LE, England
 Titolo Testata:
 MACROMOLECULES
fascicolo: 25,
volume: 31,
anno: 1998,
pagine: 8871  8877
 SICI:
 00249297(199812)31:25<8871:RARDOL>2.0.ZU;2Y
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 MAGNETICRESONANCE; POLYMERCHAINS; STAR POLYMERS; NETWORKS; MELTS; ENTANGLEMENTS; MODEL;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Physical, Chemical & Earth Sciences
 Citazioni:
 18
 Recensione:
 Indirizzi per estratti:
 Indirizzo: Klein, PG Univ Leeds, IRC Polymer Sci & Technol, Leeds LS2 9JT, W Yorkshire, England Univ Leeds Leeds W Yorkshire England LS2 9JT Yorkshire, England



 Citazione:
 P.G. Klein et al., "Rouse and reptation dynamics of linear polybutadiene chains studied by H2NMR transverse relaxation", MACROMOLEC, 31(25), 1998, pp. 88718877
Abstract
Deuterium NMR has been used to investigate two different types of dynamicsof linear polybutadiene chains in the melt. The transverse relaxations of short Rouse chains of molecular weight 6403000 were biexponential, which has been attributed to separate decays of the methylene and methine deuterons. Interpretation of the transverse relaxation rates using a model for Rouse dynamics, combined with molecular simulations, gave the shortest Rouse unit as approximately 4.4 monomers and the shortest Rouse time as 8.3 x 10(7) s. The reptation dynamics of higher molecular weight entangled chains were investigated using ABA isotopic triblock copolymers, of total molecular weight 14000135000, where A is protonated polybutadiene of molecular weightgreater than the entanglement molecular weight and B is a deuterated block. These polymers were specifically synthesized so that the fast motion of the Rouselike chain ends should not complicate the signal. The fundamental parameters found for the Rouse chain were used in the reptation model, assuming fast dynamics, and gave an entanglement molecular weight, Me, of 5380or approximately 21 Rouse units. This Me is more than twice the conventional value, obtained from rheology, and is more suggestive of the critical molecular weight Mc, consistent with previous NMR work. The theoretical analysis used in this work is based on the assumption that the chain dynamics are fast on the time scale set by the NMR deuterium quadrupolar interaction. The highest molecular weight samples were found to not satisfy this criterion and indicate the molecular weight at which a new theoretical approach is needed.
ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
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