Xintong Zhao, Yihua Zhao, Zhongbao Jian, Ying Lu, Yongfeng Men
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The crystallization kinetics of form II in dPB-1 is essentially similar to that of hPB-1. The kinetics of the II to I transition in dPB-1 at the isothermal crystallization temperature exhibits a two-step process with the first one with kinetics nearly the same as the crystallization and the second one much slower. The results indicate a very low overall free energy barrier for the II to I transition in dPB-1 suggesting a critical role of the amorphous phase. Indeed, unlike in hPB-1 the conformational energy of 3/1helix in form I is even slightly higher than the 11/3 helix in form II in dPB-1 meaning that the driving force for the II to I transition from inside the crystalline phase is at most similar in both hPB-1 and dPB-1. It turns out that the entropy in the amorphous phase of the dPB-1 is much lower than that of hPB-1 because the vibrational entropy of bonds in both systems is largely different. 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The dPB-1 shows similar crystallization habit as hPB-1, i.e., crystallizing into metastable form II, which then transforms into stable form I. This peculiar polymorphic transition in hPB-1 normally occurs after cooling to lower temperatures after the crystallization of form II crystals because an internal stress along the lamellar normal built-up during cooling helps to overcome the nucleation barrier of the transition. Surprisingly, a spontaneous form II to I transition at the isothermal crystallization temperature is observed in dPB-1. The crystallization kinetics of form II in dPB-1 is essentially similar to that of hPB-1. The kinetics of the II to I transition in dPB-1 at the isothermal crystallization temperature exhibits a two-step process with the first one with kinetics nearly the same as the crystallization and the second one much slower. 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引用次数: 0
摘要
我们分别使用氚代 1-丁烯和氢代 1-丁烯单体合成了氚代异方向聚丁烯-1(dPB-1)(Mw:349 kg/mol)及其氢代异方向聚丁烯-1(hPB-1)(Mw:346 kg/mol)。dPB-1 显示出与 hPB-1 相似的结晶习性,即结晶为可转移的形式 II,然后转变为稳定的形式 I。形式 II 晶体结晶后冷却到较低温度时,hPB-1 通常会发生这种奇特的多态转变,因为冷却过程中沿薄片法线形成的内应力有助于克服转变的成核障碍。令人惊讶的是,在 dPB-1 中观察到了在等温结晶温度下形式 II 向形式 I 的自发转变。dPB-1 中形式 II 的结晶动力学与 hPB-1 基本相似。在等温结晶温度下,dPB-1 中 II 型向 I 型转变的动力学过程分为两步,第一步的动力学过程与结晶过程几乎相同,而第二步则要慢得多。结果表明,dPB-1 中 II 到 I 转变的总自由能垒非常低,这表明非晶相起着关键作用。事实上,与 hPB-1 不同,dPB-1 中形态 I 的 3/1 螺旋的构象能甚至略高于形态 II 的 11/3 螺旋,这意味着在 hPB-1 和 dPB-1 中,从结晶相内部从 II 到 I 的转变的驱动力最多是相似的。事实证明,dPB-1 非晶相中的熵要比 hPB-1 低得多,因为这两种体系中键的振动熵有很大不同。因此,dPB-1 中 II 到 I 转变的自由能障要小得多,从而可以观察到自发转变。
Deuterated Isotactic Polybutene-1 Exhibits Fast Form II to I Transition at Isothermal Crystallization Temperatures
Deuterated isotactic polybutene-1 (dPB-1) (Mw: 349 kg/mol) and its hydrogeneous counterpart (hPB-1) (Mw: 346 kg/mol) have been synthesized using deuterated 1-butene and hydrogeneous 1-butene monomers, respectively. The dPB-1 shows similar crystallization habit as hPB-1, i.e., crystallizing into metastable form II, which then transforms into stable form I. This peculiar polymorphic transition in hPB-1 normally occurs after cooling to lower temperatures after the crystallization of form II crystals because an internal stress along the lamellar normal built-up during cooling helps to overcome the nucleation barrier of the transition. Surprisingly, a spontaneous form II to I transition at the isothermal crystallization temperature is observed in dPB-1. The crystallization kinetics of form II in dPB-1 is essentially similar to that of hPB-1. The kinetics of the II to I transition in dPB-1 at the isothermal crystallization temperature exhibits a two-step process with the first one with kinetics nearly the same as the crystallization and the second one much slower. The results indicate a very low overall free energy barrier for the II to I transition in dPB-1 suggesting a critical role of the amorphous phase. Indeed, unlike in hPB-1 the conformational energy of 3/1helix in form I is even slightly higher than the 11/3 helix in form II in dPB-1 meaning that the driving force for the II to I transition from inside the crystalline phase is at most similar in both hPB-1 and dPB-1. It turns out that the entropy in the amorphous phase of the dPB-1 is much lower than that of hPB-1 because the vibrational entropy of bonds in both systems is largely different. As such, a much smaller free energy barrier is obtained for the II to I transition in dPB-1 so that a spontaneous transition is observed.
期刊介绍:
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