晶间链接确定动力学在聚丁烯-1中的II到I型多晶型转变的动力学。,Macromolecules

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晶间链接确定动力学在聚丁烯-1中的II到I型多晶型转变的动力学。
Macromolecules ( IF 5.1 ) Pub Date : 2017-07-13 00:00:00 , DOI: 10.1021/acs.macromol.7b00771
Yongna Qiao _{1,

2} , Yongfeng Men _{1,

2}

Affiliation

通过差示扫描量热法和小角度X射线散射技术研究了包含连接分子和纠缠环的晶间键对不同分子量的聚丁烯1（PB-1）中从晶型II到晶型I的多晶型转变的影响。PB-1样品在一定温度范围内进行等温结晶，以形成亚稳态的II型结晶修饰，该修饰具有不同的层状厚度，长间距和非晶相中的晶间键数目。塔曼（Tammann）的两阶段晶核发展方法被用来促进从晶型II到晶型I的更快的多态转变。也就是说，在低温的早期阶段形成了I型核，而在高温的后期阶段形成了I型晶体。在给定的退火条件下，发现高分子量样品中的转变速率随先有形式II的结晶温度的升高而增加，而低分子量样品中的转变速率与结晶温度之间呈负相关。结果可以理解如下。高分子量PB-1的长间距小于熔体中链的回转半径，从而导致形成折叠链晶体并极有可能产生晶间键。在从较高的结晶温度冷却到退火的第一温度阶段期间，由于非晶态和晶态相的不平衡收缩引起的更高的内部应力将会建立。对于低分子量样品，在升高的结晶温度下，形成层间连接的可能性随着层状厚度的增加而降低。对于在两个样品中均可发现晶间键的低结晶温度，低分子量样品因其较高的链迁移率而显示出更快的转变。本文讨论了这些分子机制。

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Intercrystalline Links Determined Kinetics of Form II to I Polymorphic Transition in Polybutene-1

The effect of intercrystalline links containing tie molecules and entangled loops on polymorphic transition from form II to form I in polybutene-1 (PB-1) of different molecular weights has been investigated by differential scanning calorimetry and small-angle X-ray scattering techniques. The PB-1 samples were isothermally crystallized at a range of temperatures to develop metastable form II crystalline modification of different lamellar thickness, long spacing, and number of intercrystalline links in the amorphous phase. Tammann’s two-stage crystal nuclei development method was applied to promote a faster polymorphic transition from form II to I; that is, form I nuclei were developed at the early low temperature stage, and form I crystals were formed at the later high temperature stage. At a given annealing condition, the transition rate in the high molecular weight sample is found to increase with the increase of the prior form II crystallization temperature, while it shows a negative correlation between transition rate and crystallization temperature in the low molecular weight sample. The results can be understood as follows. The long spacing of high molecular weight PB-1 is smaller than the radius of gyration of the chains in the melt, leading to formation of folded-chain crystals and high possibility of generating intercrystalline links. Higher internal stress induced by unbalanced shrinkage of amorphous and crystalline phases would be built up during cooling from higher crystallization temperature to the first temperature stage of annealing. For low molecular weight samples, the probability of forming intercrystalline links decreases with the increasing lamellar thickness at elevated crystallization temperature. For a low crystallization temperature where intercrystalline links could be found in both samples, the low molecular weight sample shows a faster transition for its higher chain mobility. These molecular mechanisms are discussed in this article.

更新日期：2017-07-13

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