Differential Scanning Calorimetry Evidence for the Existence of a First-Order Thermal Transition in Ultraoriented at-Poly(acrylonitrile)
Differential Scanning Calorimetry Evidence for the Existence of a First-Order Thermal Transition in Ultraoriented at-Poly(acrylonitrile)
复制标题
差示扫描量热法证明超取向聚（丙烯腈）中存在一级热转变
DOI：
10.1021/ma971248k
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发表时间：
1998
期刊：
影响因子：
5.5
通讯作者：
R. Porter
中科院分区：
文献类型：
--
作者：
D. Sawai;T. Kanamoto;R. Porter
介绍。研究表明，采用两段拉伸技术，超高分子量（UHMW）无规聚丙烯腈（at-PAN）凝胶膜可拉伸至总拉伸比(DRt)< 110-160。DRt是两个阶段的拉伸比的乘积。这种高度拉伸的样品表现出极端的形貌，表现为高链取向函数（fc） 0.996)和高拉伸模量（28 GPa），与不确定的x射线晶体模量相当。根据x射线赤道反射在2θ) 17 （Cu KR辐射）附近的温度变化，发现这种超取向样品在150℃左右表现出从正交向六方链堆积的晶体/晶体转变。这种聚合物的弛豫和/或热跃迁已经通过多种技术进行了广泛的研究，包括动态力学分析（DMA）， 4,5介电测量，6红外吸收光谱，7双折射，8和x射线衍射。这些研究报告了在100℃和150℃左右存在弛豫，这分别对应于晶体区和非晶体区（玻璃化转变）的分子运动。然而，目前还没有关于用DSC研究at-PAN的一阶热转变的报道。在本文中，我们报道了差示扫描量热法（DSC）和DMA对具有大范围DRt（1-100）的at-PAN薄膜的研究。仅在DRt g 60的超拉伸样品中，DSC加热扫描在142-150℃时清楚地发现了一阶热转变。x射线衍射研究表明，这种转变是可逆的晶体/晶体转变。本文还讨论了这种转变对动态存储模量、E′和tan δ峰的贡献。
Introduction. It has been shown that gel films of ultrahigh molecular weight (UHMW) atactic poly (acrylonitrile)(at-PAN) are ultradrawable to a total draw ratio (DRt)< 110-160 by a two-stage draw technique. 1, 2 DRt is the product of draw ratios in the two stages. Such highly drawn samples show an extreme morphology, indicated by a high chain orientation function (fc) 0.996) and a high tensile modulus (28 GPa), comparable to the uncertain X-ray crystal modulus. 3 Such ultraoriented samples are found to exhibit a crystal/crystal transition from orthorhombic to hexagonal chain packing around 150 C, as determined from the temperature variations of the X-ray equatorial reflections around 2θ) 17 (Cu KR radiation). 1The relaxation and/or thermal transitions in this polymer have been extensively studied by several techniques, including dynamic mechanical analysis (DMA), 4, 5 dielectric measurements, 6 infrared absorption spectroscopy, 7 birefringence, 8 and X-ray diffraction. 9-11 These studies report the existence of relaxations around 100 and 150 C, which correspond to the molecular motion in (para) crystalline regions and that in noncrystalline regions (glass transition), respectively. However, no report has been published on any first-order thermal transition in at-PAN, studied by DSC. In this Communication, we report differential scanning calorimetry (DSC) and DMA studies on at-PAN films having a wide range of DRt (1-100). A first-order thermal transition was clearly found at 142-150 C on DSC heating scans only in ultradrawn samples of DRt g 60. This transition is ascribed to the reversible crystal/crystal transition, revealed by an X-ray diffraction study. 1 The contribution of this transition to the dynamic storage modulus, E′, and tan δ peak is also discussed.