拉伸异相成核作用下的PB-1晶型转变

Crystal form transition of polybutene-1 under stretched heterogeneous nucleation

本文采用溶液共混的方式制备聚碳酸酯/聚丁烯-1(PC/PB-1)共混样品,施加不同的应变,高温条件下进行PB-1分子链的松弛,研究取向的刚性PC分子链对PB-1结晶形貌和结构的影响,进而对晶型转变的规律进行分析.偏光显微镜观察发现,随着应变的增加,PB-1倾向于异相成核方式进行结晶,该溶液共混方法有效影响了PB-1的结晶行为.差示扫描量热仪和广角X射线衍射分析发现,结晶首先生成晶型Ⅱ,并向晶型Ⅰ进行转变.取向异相晶核的存在有利于晶型Ⅱ和Ⅰ成核,但更有利于晶型Ⅱ的形成.随着应变的增加,PB-1的熔点、结晶度和最终晶型Ⅱ→Ⅰ转变度显著提高.

Polybutene-1(PB-1) is an α-polyolefin material with potential application value due to its excellent physical and mechanical performance and is called "plastic gold". However, it′s application is limited by some problems. For example, metastable crystal form Ⅱ(molecular chain conformation is 11/3 helix) is often firstly obtained from melt crystallization, and this crystal form will spontaneously transform into thermodynamically stable crystal form Ⅰ(molecular chain conformation is 3/1 helix). This process often takes an awfully long time, at least one week. At present, people are paying more and more attention to the regulation of PB-1 crystal form transformation. There are still many controversies about the crystal form transformation process and discussions of the mechanism are still vague especially when it is related to tensile conditions. This paper is the first attempt to heterogeneous nucleation from the viewpoint of the design of the oriented pre-ordered structure prior to crystallization and expected to help understand the crystallization behavior and polymorphic transformation of PB-1 from a new perspective. Herein, a solution blending method is used to prepare polycarbonate/polybutene-1(PC/PB-1) blended samples, and different strains are applied. At a designed high-temperature, the oriented PB-1 chains relaxed, and oriented rigid PC chains are retained. The influence of the oriented rigid PC molecular chains on the crystalline morphology and structure of PB-1 is studied, and the relationship between crystal form transformation and nucleation way, and the mechanism of crystal form transformation are explored. Through polarized light microscope observation, it was found that with the increase of strain, PB-1 tends to crystallize towards heterogeneous nucleation mode. The solution blending method effectively affects the crystallization behavior of PB-1. Differential scanning calorimeter and wide-angle X-ray diffraction technical analysis showed that crystal form Ⅱ firstly formed and later transformed into form Ⅰ. The oriented heterogeneous crystal nuclei which facilitated the nucleation of crystal forms Ⅱ and Ⅰ is more conducive to the formation of crystal form Ⅱ. With increasing strain, the melting point, crystallinity and final transition degree of crystal form Ⅱ→Ⅰ in PB-1 increased significantly. Through observing the transition degree, even under the condition of 100% strain, the transformation of the crystal form Ⅰ increases slowly at the initial stage of crystallization, with an induction period of 10 h. The increased tensile strain superficially does not promote the conversion efficiency of PB-1 crystal form. In fact, the oriented nuclei structure induced the formation of a large amount of form Ⅱ in PB-1 during the initial crystallization period, and significantly improves the final perfection degree of crystal form Ⅰ. The total crystallinity of PC/PB-1 and transition degree of crystal form Ⅰ were both increased under the induction of oriented rigid PC molecular chains.