Temperature of Melting of the Mesophase of Isotactic Polypropylene
Temperature of Melting of the Mesophase of Isotactic Polypropylene
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DOI：
10.1021/ma901797b
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发表时间：
2009-10-13
期刊：
影响因子：
5.5
通讯作者：
Schick, Christoph
中科院分区：
文献类型：
--
作者：
Mileva, Daniela;Androsch, Rene;Schick, Christoph
聚丙烯.在全同立构聚丙烯（iPP）中形成胰蛋白酶最早是在20世纪50年代后期报道的，在成功引入该聚合物的立体特异性合成之后不久。在广角X射线散射（WAXS）图中，通过在约0.59 nm和0.41 nm的间距处存在两个特征晕来识别它，所述间距与中间相中平行排列的链之间的平均距离有关，所述间距被分配给大分子的全同立构序列的31螺旋内的重复周期。3r5在将静止液体骤冷至环境温度时形成中间相，并且在该温度下与处于被抑制的亚稳热力学状态内的无定形结构共存。有人建议，平行排列的螺旋不同的手随机排列在一个伪六方晶格。1r3淬火iPP的WAXS数据的替代解释包括建议的更高程度的本地秩序比在近晶相，也就是说，六方结构的细微晶6r8或小和无序的单斜微晶的存在。9在最近的一项研究中，证实中间相含有平行排列的链束，具有3倍螺旋构象，在链轴方向上通过螺旋反转或其他构象缺陷终止。特别是，在拉伸中间相的纤维衍射图案中，在定义明确的层线上观察到宽峰，表明链段的有序构象，并且在拉伸的链段的原子之间仅存在短程相关性。不同链段之间的横向相关性被描述为更接近单斜晶格而不是六方晶格，尽管这种结构不能用一种类型的晶胞来描述，即使在局部尺度上也是如此。10r12
Polypropylene. Mesophase formation in isotactic polypropylene (iPP) has first been reported in the late 1950s, 1r3 shortly after the successful introduction of stereospecific synthesis of this polymer. It is recognized in the wide-angle X-ray scattering (WAXS) pattern by the presence of two characteristic halos at spacings of about 0.59 nm, which is related to the average distance between parallel aligned chains in the mesophase, and 0.41 nm, which has been assigned to the repeating period within the 31 helix of an isotactic sequence of the macromolecule. 3r5 The mesophase develops upon quenching the quiescent liquid to ambient temperature and coexists at this temperature with amorphous structure within an arrested metastable thermodynamic state.Initially, the structure of the quenched form of iPP has been described as a paracrystalline smectic arrangement of molecular stems. It was suggested that parallel aligned helices of different handedness are randomly arranged within a pseudohexagonal lattice. 1r3 Alternative interpretations of the WAXS data of quenched iPP include the suggestion of a higher degree of local order than in a smectic phase, that is, the presence of fine crystallites of hexagonal structure6r8 or of small and disordered monoclinic microcrystals. 9 In a more recent study it was confirmed that the mesophase contains bundles of parallel aligned chains with a 3-fold helix conformation, being terminated in direction of the chain axis by helix reversals or other conformational defects. In particular, the observation of broad peaks on well-defined layer lines in the fiber diffraction pattern of the stretched mesophase indicated an ordered conformation of chain segments and only short-range correlations between atoms of neighbored chain segments. The lateral correlation between different chain segments was described to be closer to a monoclinic rather than a hexagonal lattice, though the structure cannot be described by one type of unit cell, even at local scale. 10r12