Constraint Release in Moderately Entangled Monodisperse Star Polyisoprene Systems

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• 作者：Xiuying Qiao ; Toshiaki Sawada ; Yumi Matsumiya ; Hiroshi Watanabe
• 刊名：Macromolecules
• 出版年：2006
• 出版时间：October 17, 2006
• 年：2006
• 卷：39
• 期：21
• 页码：7333 - 7341
• 全文大小：230K
• 年卷期：v.39,no.21(October 17, 2006)
• ISSN：1520-5835

文摘

For examination of a constraint release (CR) contribution to relaxation in monodisperse systemsof moderately entangled six-arm star polyisoprenes (PI), viscoelastic measurements were conducted for blendsof these star PI and a high molecular weight (M) linear PI. In the blends, the linear PI was dilute and entangledonly with the matrix star chains. The terminal relaxation of this dilute linear probe occurred through competitionof reptation and Rouse-type CR, as confirmed from its relaxation mode distribution. The probe relaxation timemages/gifchars/tau.gif" BORDER=0 >_probe measured in the blends was utilized in the following way to elucidate the CR relaxation in the star matrices:Since the CR time mages/gifchars/tau.gif" BORDER=0 >^CR of the star matrix is expressed as (2N_a)²mages/gifchars/tau.gif" BORDER=0 >_life with 2N_a and mages/gifchars/tau.gif" BORDER=0 >_life being the entanglementnumber per two arms (span length) and the effective entanglement lifetime in the system, mages/gifchars/tau.gif" BORDER=0 >^CR can be evaluatedif the mages/gifchars/tau.gif" BORDER=0 >_life value is known. For determination of the mages/gifchars/tau.gif" BORDER=0 >_life value, the mages/gifchars/tau.gif" BORDER=0 >_probe data of the linear probe in the starmatrices was compared with the previously obtained mages/gifchars/tau.gif" BORDER=0 >_probe data of the same probe in linear PI matrices under amolecular idea that mages/gifchars/tau.gif" BORDER=0 >_life should be the same in a pair of star and linear matrices giving the same mages/gifchars/tau.gif" BORDER=0 >_probe value. Themolecular weight M_L,mat of the linear matrix paired with each star matrix was thus specified, and the value of mages/gifchars/tau.gif" BORDER=0 >_lifein the star matrix was determined by utilizing this M_L,mat value in a previously obtained empirical equation of mages/gifchars/tau.gif" BORDER=0 >_lifein the linear matrices (mages/gifchars/tau.gif" BORDER=0 >_life = 2.5 × 10^-18M_L,mat³ s at 40 mages/entities/deg.gif">C). For the monodisperse systems of the star PI, the mages/gifchars/tau.gif" BORDER=0 >^CR(=(2N_a)²mages/gifchars/tau.gif" BORDER=0 >_life) thus evaluated was close to the measured relaxation time, indicating that the CR mechanismsignificantly contributes to the star relaxation. This result was in harmony with the validity of the molecularpicture of partial dynamic-tube-dilation (p-DTD) confirmed for the star PI.