Glass transition and structural relaxation in semi-crystalline poly(ethylene terephthalate):: a DSC study
Glass transition and structural relaxation in semi-crystalline poly(ethylene terephthalate):: a DSC study
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DOI：
10.1016/s0032-3861(02)00236-7
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发表时间：
2002-07-01
期刊：
影响因子：
4.6
通讯作者：
Ribelles, JLG
中科院分区：
文献类型：
--
作者：
Alves, NM;Mano, JF;Ribelles, JLG
本工作的目的是测定半结晶聚对苯二甲酸乙二酯(PET)中无定形相协同构象重排的驰豫时间，并与非晶态PET的计算结果进行比较。用淬火法制备了近无定形聚合物样品，并将无定形聚合物样品冷结晶到不同温度，得到了不同结晶度的样品。差示扫描量热仪(DSC)对从玻璃化转变温度上直接冷却的样品测量的差示扫描量热仪(DSC)热图显示，单一的玻璃化转变在高结晶度样品的情况下比在无定形或低结晶度PET样品中要宽得多。为了阐明这一行为，在DSC测量加热扫描之前，样品在不同的温度和不同的时间进行了热处理。在低结晶度的样品中测得的热图清楚地显示了两个具有不同构象迁移率的非晶相的存在，这两个相被称为相I和相II。相I包含具有与纯非晶态聚合物相似的迁移率的高分子链，而相II表现出更有限的迁移率，可能对应于非晶态区域内的构象变化。模型模拟可以确定H相驰豫时间与温度的关系，它与样品中的结晶度分数无关，比相同温度下的非晶态聚合物的驰豫时间长约20年。(C)2002爱思唯尔科学有限公司。保留所有权利。
The aim of this work is to determine the relaxation times of the cooperative conformational rearrangements of the amorphous phase in semi-crystalline poly(ethylene terephthalate) (PET) and compare them with those calculated in amorphous PET. Samples of nearly amorphous polymer were prepared by quenching and samples with different crystallinity fractions were prepared from the amorphous one using cold crystallisation to different temperatures. The differential scanning calorimetry (DSC) thermograms measured on samples rapidly cooled from temperatures immediately above the glass transition show a single glass transition which is much broader in the case of high-crystallinity samples than in the amorphous or low-crystallinity PET. To clarify this behaviour, the samples were subjected to annealing at different temperatures and for different periods prior to the DSC measuring heating scan. The thermograms measured in samples with low crystallinity clearly show the existence of two amorphous phases with different conformational mobility, these are called Phases I and II. Phase I contains polymer chains with a mobility similar to that in- the purely amorphous polymer, while Phase II shows a much more restricted mobility, probably corresponding to conformational changes within the intraspherulitic regions. The model simulation allows to determine the temperature dependence of Phase H relaxation times, which are independent from the crystallinity fraction in the sample and around two decades longer than those of the amorphous polymer at the same temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.