DEPENDENCE OF TG AND TLL ON TACTICITY OF PMMA BY DIFFERENTIAL SCANNING CALORIMETRY
DEPENDENCE OF TG AND TLL ON TACTICITY OF PMMA BY DIFFERENTIAL SCANNING CALORIMETRY
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DOI：
10.1080/00222348608248039
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发表时间：
1986-01-01
期刊：
影响因子：
--
通讯作者：
ELIAS, HG
中科院分区：
文献类型：
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作者：
DENNY, LR;BOYER, RF;ELIAS, HG
采用差示扫描量热仪（DSC）对PMMA的多重跃迁（弛豫）谱进行了研究（升温速率为10 K/min）： Tβ< Tg；Tg, Tll> Tg；和Tlρ> Tll，作为战术的函数。标本的特征是分数阶三元含量：等规（it-）， Xii；syndiotic (st-), Xss；无规（at-）， x。7个试样的值分别为-，1.0；，为-，0.495 ~ 0.750；圣- 0.958。关于t β的结果尚无定论。我们的研究结果澄清了先前文献中的一些差异。线性最小二乘回归分析得出：Tg（°C） = 56.6 + 76.6 Xss（我们的数据）Tg（°C） = 49.1 + 87.3 Xss（我们的数据加上选择的文献数据）Xss = 1的外推Tg分别为133.2°C和136.1°C，而Thompson的外推值为160°C。同样，我们的DSC数据Tg（°C） = 99.5 + 71.6（1−Xii）。Xss = 1的外推温度为171.1°C。塔利的强度在st-和它-是高的，在at-区域有一个广泛的最小值。第二种液态过程Tlρ> Tll在149℃时发生，但高于at和st-的测量范围。DSC的Tll（at-）通过各种技术与文献报道的值比较有利。Tlland tlρ的所有策略都与其他地方报道的热刺激电流（TSC）技术在同一组标本上的伴随研究结果一致。这包括战术对强度的影响。通过各种方法进行的交叉比较表明，无论是tll还是tlρ都不是DSC技术的产物。Frenkel片段-片段接触假说倾向于解释长度大于三联段的tlr序列的分子起源，这可能需要改进tgr和tlr与弹性的相关性。
A differential scanning calorimeter (DSC) investigation (heating rate 10 K/min) is presented on the multiple transition (relaxation) spectra of PMMA: Tβ< Tg; Tg, Tll> Tg; and Tlρ> Tll, as a function of tacticity. Specimens are characterized by fractional triad content: isotactic (it-), Xii; syndiotactic (st-), Xss; and atactic (at-), Xis. Values for the seven specimens are it-, 1.0;, at-, 0.495 to 0.750; st-, 0.958. Results on Tβwere inconclusive. Our Tgresults clarify some discrepancies in the prior literature.Linear least squares regression analyses give: Tg(°C) = 56.6 + 76.6 Xss (our data) Tg(°C) = 49.1 + 87.3 Xss (our data plus selected literature data)Extrapolated Tg's for Xss = 1 are 133.2°C and 136.1°C, respectively, in contrast to Thompson's extrapolated value of 160°C. Similarly Tg(°C) = 99.5 + 71.6 (1−Xii) for our DSC data. The extrapolated Tllfor Xss = 1 is 171.1°C. The intensity of Tllis high for st-and it-, with a broad minimum over the at-region. A second liquid state process, Tlρ> Tll, occurs at 149°C for it-, but is above the measured range for at-and st-. Tll(at-) from DSC compares favorably with reported literature values by a variety of techniques. Tlland Tlρat all tacticities agree well with those from a companion study by the thermally stimulated current (TSC) technique on the same group of specimens, as reported elsewhere. This includes the influence of tacticity on intensity. These cross-comparisons by a variety of methods indicate that neither Tllnor Tlρis an artifact of our DSC technique. The Frenkel segment-segment contact hypothesis is favored to explain the molecular origin of TllSequences longer than triads may be needed for improved correlations of Tgand Tlρwith tacticity.