科研之友
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摘要
The structure of styrene-butadiene rubbers (SBRs) consists of chains attached to cross-links of relatively small number density. These rubbers show an alpha-relaxation process that is attributed to segmental motions of the attached chains. To investigate how an SBR's rubber-like behavior would change when free chains interpenetrate its structure, we prepared one SBR of mol wt 120 x 10(3) containing 3-4% free chains of identical mol wt, and studied its dynamic mechanical relaxation. For 0.1 Hz frequency measurements, the alpha-relaxation peak appeared at 210 K, and a second relaxation peak, which we refer to as alpha(R)-relaxation, at 300 K. A third relaxation of small magnitude was resolved at temperatures between the alpha(R)- and the alpha-relaxation peaks, and its origin was discussed in relation to other studies. Spectral features of the alpha(R)-and the alpha-relaxations were found similar. We investigated the merits of the time-temperature superposition of the alpha- and of the alpha(R)-relaxations. The alpha(R) relaxation vanished when the free chains were extracted from the SBR by swelling-extraction procedure. The features of alpha-relaxation can be interpreted as segmental motions of the SBR, but the features of the alpha(R)-relaxation is be interpretable only in terms of tube model for diffusion of free chains in a lightly cross-linked structure. We estimated the mol wt of these free chains and the Mass between entanglements, and then used these quantities to calculate, by using the Doi-Edwards formalism, the relaxation time of the alpha(R)-process at 293 K. This relaxation time agrees with the experimental value. The alpha(R)-relaxation seems consistent with the tube model for diffusion of free chains in the cross-linked structure of SBR.
- 出版日期2014-9-26
