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Titolo:
Rouse and reptation dynamics of linear polybutadiene chains studied by H-2NMR 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:
0024-9297(199812)31:25<8871:RARDOL>2.0.ZU;2-Y
Fonte:
ISI
Lingua:
ENG
Soggetto:
MAGNETIC-RESONANCE; POLYMER-CHAINS; 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 H-2NMR transverse relaxation", MACROMOLEC, 31(25), 1998, pp. 8871-8877

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 640-3000 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 14000-135000, 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 Rouse-like 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, M-e, of 5380or approximately 21 Rouse units. This M-e is more than twice the conventional value, obtained from rheology, and is more suggestive of the critical molecular weight M-c, 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
Documento generato il 30/10/20 alle ore 09:14:11