ISOTHERMAL THICKENING AND THINNING PROCESSES IN LOW-MOLECULAR-WEIGHT POLY(ETHYLENE OXIDE) FRACTIONS .1. FROM NONINTEGRAL-FOLDING TO INTEGRAL-FOLDING CHAIN CRYSTAL TRANSITIONS
ISOTHERMAL THICKENING AND THINNING PROCESSES IN LOW-MOLECULAR-WEIGHT POLY(ETHYLENE OXIDE) FRACTIONS .1. FROM NONINTEGRAL-FOLDING TO INTEGRAL-FOLDING CHAIN CRYSTAL TRANSITIONS
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DOI：
10.1021/ma00013a030
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发表时间：
1991-06-24
期刊：
影响因子：
5.5
通讯作者：
ZSCHACK, PR
中科院分区：
文献类型：
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作者：
CHENG, SZD;ZHANG, AQ;ZSCHACK, PR
基于时间分辨同步辐射小角X射线散射（SAXS）和差示扫描量热法（DSC）实验，在低分子量聚环氧乙烷（PEO）组分中发现了非整折叠链（NIF）晶体。 该晶体首先作为瞬态生长，随后通过等温增厚或变薄过程形成整体折叠链（IF）晶体。 在具有MW = 4250的PEO级分中，观察到根据NIF晶体的热力学稳定性发生对IF（n = 0）晶体的等温增稠或对IF（n = 1）晶体的变薄。 在较低的结晶温度下，主要过程是等温变稀;在中等温度下，观察到增稠和变稀过程;在高温下只能看到等温增稠。 这一观察结果表明，NIF晶体在宽的结晶温度范围内作为晶体生长的初始步骤而存在。 该NIF晶体的折叠长度是结晶温度依赖性的，类似于聚合物层状晶体的折叠长度的观察到的变化的行为。 系统研究了从NIF到IF晶体的折叠长度随时间的变化，得到了这种转变的动力学图。 这一过程与固态中链状分子沿晶体学c轴沿着运动有关。
On the basis of time-resolved synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) experiments, a nonintegral-folding chain (NIF) crystal can be found in low molecular weight poly(ethylene oxide) (PEO) fractions. This crystal grows first as a transient state, and integral-folding chain (IF) crystals form later through an isothermal thickening or thinning process. In a PEO fraction with MW = 4250, it is observed that either isothermal thickening to the IF (n = 0) crystal or thinning to the IF(n = 1) crystal occurs depending upon the thermodynamic stability of the NIF crystal. At low crystallization temperatures, the main process is isothermal thinning; at intermediate temperatures, both thickening and thinning processes are observed; only isothermal thickening can be seen at high temperatures. This observation indicates that the NIF crystal exists as an initial step of the crystal growth over a wide crystallization temperature range. The fold length of this NIF crystal is crystallization temperature dependent, a behavior similar to the observed changes of fold length of polymer lamellar crystals. Systematic study in changes of fold length from the NIF to IF crystals with the time has resulted in a kinetic map of such transitions. This process is related to the chain molecular motion along the crystallographic c-axis in the solid state.