Nuclear magnetic resonance investigations in highly entangled polybutadiene chains. Temporary elasticity and flexibility

摘要

The property of temporary elasticity is studied from the relaxation of the transverse magnetization of protons attached to high molecular weight poly(butadiene) chains in concentrated solutions. The relaxation time tgr; measured from poly(butadiene) is found to be a function of the polymer concentration fgr; in cyclohexane, the glass transition temperatureTg(fgr;), and the inverse of the modulus of temporary elasticityG0Naccording to the formula tgr;=8times;10minus;3lsqb;Tminus;Tg(fgr;)minus;50rsqb;(1+4.5/G0Nfgr;2.2); tgr; is expressed in millisecond units andG0Nis in 106dynthinsp;cmminus;2. The quantitiesG0NandTg(fgr;) are varied by changing the chain microstructure. The front factor lsqb;Tminus;Tg(fgr;)minus;50rsqb; is ascribed to an effect of chain flexibility disclosed from nuclear magnetic resonance. It is identified with a free volume term that also governs viscoelastic measurements. It is shown that the flexibility effect is associated to orientational correlations concerning three skeletal bonds along a given segment.