半晶聚对苯二甲酸乙二酯中的受限非晶相

当半晶聚对苯二甲酸乙二酯 (PET)的结晶度 (Xwc)处于一定范围内时 ,其物理老化后在差示扫描量热(DSC)曲线上的玻璃化转变区有吸热双峰出现 .通过对此吸热双峰分别与完全非晶试样和具有相当高Xwc 的半晶试样物理老化后在DSC曲线上出现的吸热单峰的比较 ,表明半晶PET中存在两种性质极为不同的非晶区 ,即自由非晶区和受限非晶区 .动态力学热分析 (DMTA)曲线上显示的损耗正切 (tanδ)双峰进一步证实了这两种不同非晶区的存在 .这两种不同非晶区的产生是由于试样中晶粒对非晶相中高分子链段活动性的不同限制作用所致 .研究发现 ,对于由冷结晶得到的半晶试样来说 ,出现两种不同非晶区所需的Xwc 上下限都随结晶温度 (Tc)的升高而增高 .还发现 ,在物理老化过程中 ,虽然非晶相的总量基本保持不变 ,但部分自由非晶区却逐渐转变为受限非晶区 .上述实验结果很好地符合Struik的“扩展玻璃化转变”模型 .

CONSTRAINED AMORPHOUS PHASE IN SEMICRYSTALLINE POLY(ETHYLENE TEREPHTHALATE)

When the degree of crystallinity (Xw c) of semicrystalline poly(ethylene terephthalate) (PET) was within a definite range,there were dual endothermic peaks appearing in the glass transition region of differential scanning calorimetry (DSC) traces of physically aged samples.By comparing the dual endothermic peaks with the single endothermic peak of physically aged wholly amorphous samples and semicrystalline samples with a fairly high Xw c,respectively,it can be concluded that there were dual amorphous regions with quite different characteristics in the semicrystalline samples:the free amorphous region and the constrained amorphous region.The dual tanδ loss peaks in dynamic mechanical thermal analysis (DMTA) curves also confirmed the existence of the dual amorphous regions.The dual amorphous regions were found to be produced due to the different constraints that the crystallites exerted on the amorphous phase.For the semicrystalline sample crystallized from glassy state,both the lower and the upper limit of the Xw c increased with increasing crystallization temperature (T c).With the proceeding of physical aging,some of the free amorphous regions became constrained amorphous regions,while the gross amount of the amorphous phase kept almost unchanged.The struik's model of “extended glass transition” was proved to be the most successful model for our experimental results.