When does a molecule become a polymer?

被引:99
作者
Ding, YF [1 ]
Kisliuk, A [1 ]
Sokolov, AP [1 ]
机构
[1] Univ Akron, Dept Polymer Sci, Akron, OH 44325 USA
关键词
D O I
10.1021/ma035618i
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
Using light scattering spectroscopy, we demonstrate that a transition from small molecular behavior to Rouse dynamics in poly(dimethylsiloxane) (PDMS) is a smooth function of molecular weight, M-w. The asymptotic Rouse behavior is achieved when the chain begins to display Gaussian behavior. Surprisingly, the molecular weight dependence of physical properties such as T-g and density also level off at the same molecular weight. A comparison of PDMS and polystyrene (PS) demonstrates that neither molecular weight between entanglement (M-e) nor Kuhn segment length l(K) is important for T-g and density. We speculate that there may be a third important parameter of molecular weight, in addition to M-e and l(K), which characterizes chain statistics and determines the molecular weight dependence of some physical properties. We introduce the molecular weight of a random step, m(R), as such a parameter. m(R) is estimated to be similar to560 for PDMS and similar to5100 for PS. The molecular weight dependence of Tg in PDMS and PS appears to be the same when presented as a function of M-w/m(R). Moreover, our analysis shows that a molecule becomes a polymer (approaches Gaussian coil) at M-w similar to 10-20m(R).
引用
收藏
页码:161 / 166
页数:6
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