Steps in the transition of an entangled polymer melt to the partially crystalline state
Steps in the transition of an entangled polymer melt to the partially crystalline state
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DOI：
10.1088/1367-2630/1/1/317
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发表时间：
1999-01-01
影响因子：
3.3
通讯作者：
Strobl, G.
中科院分区：
文献类型：
--
作者：
Heck, B.;Hugel, T.;Strobl, G.
对于s-聚丙烯、三种不同的s-聚(丙烯-辛烯)、两种聚(乙烯-辛烯)和聚(ε-己内酯)，我们通过进行时间和温度相关的小角X射线散射实验确定了结晶温度T-c、晶体厚度d(c)和熔融峰值温度T-f之间的关系。作为一般定律，dc 与特征温度 T-c（无穷大）以下的过冷度成反比，根据吉布斯-汤姆逊方程的应用，该温度始终位于平衡熔点之上。 T-c(无穷大)不(对于基于聚丙烯的共聚物)或仅微弱地(对于基于聚乙烯的共聚物)依赖于共单元含量。 “结晶线”T-c 相对于 d(c)(-1) c 和吉布斯-汤姆逊熔线 T-f 相对于 d(c)(-1) c 限制了可达到的部分结晶态的范围。两条明确定义的独立边界线的出现可以理解为表明，对于均聚物和共聚衍生物来说，从熔体到部分结晶态的转变通常是一个两步过程，首先在结晶线处建立低级的初始形式，然后该形式变得稳定，最终处于在T-f下熔融的层状形态的状态。 d(c) 无需改变即可实现稳定。 AFM 和 TEM 观察表明，初始结构可能由平面组件中的晶体块组成。然后，它们合并成连续的薄片，从而实现稳定。建议块的大小代表保持内在稳定性所需的最小值。进一步的结果发现，等温结晶过程结束时达到的结晶度在较大的 T-c 范围内保持不变，这与结构长度尺度的变化形成对比。
For s-polypropylene, three different s-poly(propene-co-octene)s, two poly(ethylene-co-octene) s and poly(epsilon-caprolactone) we determined the relationships between the crystallization temperature T-c, the crystal thickness d(c) and the melting peak temperature T-f by carrying out time- and temperature-dependent small-angle x-ray scattering experiments. As a general law, dc is found to be inversely proportional to the supercooling below a characteristic temperature, T-c(infinity), which is always located above the equilibrium melting point following from an application of the Gibbs-Thomson equation. T-c(infinity) is not (for the polypropylene-based copolymers) or only weakly (for the polyethylene-based copolymers) dependent on the co-unit content. The 'crystallization line' T-c versus d(c)(-1) c and the Gibbs-Thomson melting line T-f versus d(c)(-1) c limit the range of the accessible partially crystalline states. The occurrence of two well defined independent boundary lines may be understood as indicating that the transformation from the melt into the partially crystalline state is generally, for homopolymers and copolymerized derivatives likewise, a two-step process, beginning with the building up of an initial form of lower order at the crystallization line which then becomes stabilized to end up in the state with layer-like morphology melting at T-f. Stabilization is achieved without a change in d(c). AFM and TEM observations suggest that the initial structure could be composed of crystal blocks in planar assemblies. The stabilization then would result from their merging into a continuous lamella. It is proposed that the size of the blocks represents the minimum necessary to retain intrinsic stability. As a further result it was found that crystallinities reached at the end of isothermal crystallization processes remain invariant over larger ranges of T-c, in contrast to the changing length scales of the structure.