Deformation-induced linear chain-ring transition and crystallization of living polymer sulfur
Deformation-induced linear chain-ring transition and crystallization of living polymer sulfur
复制标题
变形诱导的线性链环转变和活性聚合物硫的结晶
DOI：
10.1021/ma071803a
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发表时间：
2007-12-25
期刊：
影响因子：
5.5
通讯作者：
Hong, Shiming
中科院分区：
文献类型：
--
作者：
Shao, Chunguang;An, Haining;Hong, Shiming
用原位广角X射线散射研究了活性聚合物硫的形变诱导结晶，其中断链起着关键作用。结晶的开始总是发生在屈服点后的最小应力点，虽然施加不同的拉伸速率。当拉伸速率较大时，形变作用决定了链的断裂和线性的链-环转变，导致线性链纤维相的形成，而当拉伸速率较小时，只有环八硫晶体的形成，其中热作用是链-环转变的主要原因。线性链的断裂不仅产生结晶的结构单元，而且从缠结中释放链，从而提高它们的流动性和结晶速率。在中间拉伸速率下发现了一个临界点，在该临界点处，在样品完全断裂之前没有发生结晶。在大拉伸速率和小拉伸速率下，结晶速率均大于形变或热效应引起的断链速率;在断裂前先结晶，纤维相和环硫晶体分别起交联和填充作用。在临界拉伸速率下，晶体的成核速率比断链速率慢，样品在结晶开始前就已断裂。
Deformation-induced crystallization of living polymer Sulfur was studied with in situ wide-angle X-ray scattering, where chain scission plays a critical role. The onset of crystallization always occurs at the minimum stress point after the yield point, though different drawing rates were applied. With large drawing rates, deformation effect dictates the chain scission and linear chain-ring transition, which leads to the formation of linear chain fibrous phase, while only cyclooctasulfur crystals form at small drawing rates where the thermal effect is mainly responsible for the chain-ring transition. The scission of linear chains not only generates the building units for crystallization but also releases chains from entanglement and consequently enhances their mobility and crystallization rate. A critical point is found at an intermediate drawing rate where no crystallization occurs before the complete breakage of the samples. With the large or small drawing rates, the crystallization rate is faster than rates of chain scission induced by deformation or the thermal effect; crystallization Occurs before sample breaking, where fibrous phase and cyclosulfur crystals act as cross-link and filler, respectively. With the critical drawing rate, the nucleation rate of crystals is slower than that of chain scission, and the sample breaks before the onset of crystallization.