Two calorimetric glass transitions do not necessarily indicate immiscibility: The case of PEO/PMMA
Two calorimetric glass transitions do not necessarily indicate immiscibility: The case of PEO/PMMA
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DOI：
10.1002/polb.20735
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发表时间：
2006-02-15
影响因子：
--
通讯作者：
Haley, JC
中科院分区：
文献类型：
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作者：
Lodge, TP;Wood, ER;Haley, JC
差示扫描量热法已被用于检测聚环氧乙烷（PEO） （M-n = 300 g/mol）和聚甲基丙烯酸甲酯（PMMA） （M-n = 10,000 g/mol）在整个组成范围内的混合物。PEO相对较低的摩尔质量使结晶的干扰降到最低。在成分的中间范围，类似于25-70%的PEO，两个广泛但明显的玻璃化转变被解决了。正如洛奇和麦克利什的自集中模型所预测的那样，这被解释为两种成分的不同玻璃化转变。观察到的跃迁的组成依赖性被自集中方法很好地描述，使用大约三分之二的库恩长度的长度尺度。结果与先前对PEO/PMMA共混体系和其他混相体系的测量结果进行了比较。主要的、一般的结论是，在可混溶的聚合物共混物或聚合物溶液中，实际上应该预料到两次玻璃化转变；两个过渡表示不混溶的经验法则是不正确的。此外，试图在不完全分段混合或其他未指定的“纳米异质性”的基础上合理化两种转变，在许多情况下可能是不合理的。(c) 2006 Wiley期刊公司
Differential scanning calorimetry has been used to examine blends of a poly(ethylene oxide) (PEO), M-n = 300 g/mol, and a poly(methylmethacrylate) (PMMA), M-n = 10,000 g/mol, across the complete composition range. The relatively low molar mass of the PEO minimizes interference from crystallization. In the midrange of composition, similar to 25-70% PEO, two broad, but distinct, glass transitions are resolved. These are interpreted as distinct glass transitions of the two components, as anticipated by the self-concentration model of Lodge and McLeish. The composition dependence of the observed transitions is well described by the self-concentration approach, using lengthscales of approximately two-thirds of the Kuhn length. The results are compared with previous measurements on PEO/PMMA blends and other miscible systems. The principal, general conclusion is that one should actually expect two glass transitions in a miscible polymer blend or polymer solution; the rule of thumb that two transitions indicate immiscibility is incorrect. Furthermore, attempts to rationalize two transitions on the basis of incomplete segmental mixing, or other unspecified '' nanoheterogeneity,'' may not be justified in many cases. (c) 2006 Wiley Periodicals, Inc.