A quantitative electron-microscopic investigation of α-phase lamellae in isotactic polypropylene fractions
A quantitative electron-microscopic investigation of α-phase lamellae in isotactic polypropylene fractions
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DOI：
10.1016/j.polymer.2009.09.038
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发表时间：
2009-11
期刊：
影响因子：
4.6
通讯作者：
H. White;D. Bassett;P. Jääskeläinen
中科院分区：
文献类型：
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作者：
H. White;D. Bassett;P. Jääskeläinen
用线性成核法测量了两个系列的α-全同立构聚丙烯中的片层厚度和交叉影线频率，以提供大排列的取向片层，用于取样。一个系列是分子量为0.6 × 104至0.8 ×105的高立构规整度聚合物，另一个系列是分子量为0.9 × 104和0.2 × 105的低立构规整度和高立构规整度材料。这些都允许分子量和立构规整度的不同影响进行评估。片层厚度随分子量的增加而增加，到105 × 105后趋于稳定。这与折叠表面随着其结构逐渐变得更加复杂而使较长分子的自由能增加约20%一致。除最低层外，由于差异增厚，交叉影线层的厚度小于径向相邻层。交叉影线的频率是最大的最小的规立构分数，但线性下降与分子长度。这种依赖性表明，链端可能通过在外延取向中铺设第一段而在引发中起关键作用。这一建议也可以解释球晶中心和高交叉影线密度区域的热稳定性降低的原因，在这些区域中，增厚和交叉影线之间存在对链端的竞争。在一行的最末端的层片曲率反映了层片厚度与分子质量的依赖关系，并允许纤毛压力，强烈参与导致球晶生长下的层片发散的因素，被估计为100 Pa。
Lamellar thicknesses and cross-hatching frequencies in α-isotactic polypropylene have been measured for two series of fractions using linear nucleation to provide large arrays of oriented lamellae in row structures for sampling. One series is of high tacticity polymers differing in molecular mass from ∼6×104to ∼8×105, the other has low and high tacticity materials for ∼9×104and ∼2×105masses. These have allowed the differing influences of both molecular mass and tacticity to be evaluated. Lamellar thicknesses increase with molecular mass to ∼5×105then level off. This is consistent with the fold surface increasing its free energy by ∼20% for longer molecules as its structure becomes progressively more complex. Except for the lowest fraction, the thickness of cross-hatching lamellae is less than that of its radial neighbours because of differential thickening. The frequency of cross-hatching is greatest for the least tactic fraction but decreases linearly with molecular length. This dependence suggests that chain ends play a key role in initiation probably by laying down the first segment in epitaxial orientation. This suggestion could also account for the reduced thermal stability of spherulite centres and regions of high cross-hatching density where there is competition for chain ends between thickening and cross-hatching. The curvature of lamellae at the very end of a row mirrors the dependence of lamellae thickness with molecular mass and allows cilia pressure, the factor strongly involved in causing the lamellar divergence underlying spherulitic growth, to be estimated as ∼100Pa.