Crystallization kinetics of isotactic polystyrene. II. Influence of thermal history on number of nuclei
Crystallization kinetics of isotactic polystyrene. II. Influence of thermal history on number of nuclei
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全同立构聚苯乙烯的结晶动力学。
DOI：
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发表时间：
1968
期刊：
影响因子：
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通讯作者：
D. V. Krevelen
中科院分区：
文献类型：
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作者：
J. Boon;G. Challa;D. V. Krevelen
本文用差示扫描量热法定量研究了各种热预处理对等规聚苯乙烯成核的影响。可以区分仍然存在于熔点以上的核（“抵抗”核）和由严重过冷产生的核（“诱导”核）。球晶形成的数量已被确定为不同的组合的过冷和结晶温度。假设在严重过冷时产生诱导核，在较高温度下诱导核可生长成有效核，结果得到了满意的解释。严重过冷聚合物的结晶完全由这些诱导核控制，因为它们的数量超过了抵抗核的数量级。通过纯化聚合物（去除催化剂残留物）可以减少诱导核的数量。当冷却的聚合物被加热到刚好高于熔点的温度时，诱导核被破坏（“可逆熔化”），使得只有数量很少的抗性核保留下来。这些抗性核控制着先前未被冷却的聚合物的结晶行为。它们的数量在加热到远高于熔点的温度时减少。
The influence of various thermal pretreatments on the nucleation of isotactic polystyrene has been studied quantitatively by dilatometry. A distinction can be made between nuclei still present above the melting point (“resistant” nuclei) and nuclei created by severe supercooling (“induced” nuclei). The number of spherulites formed has been determined for different combinations of supercooling and crystallization temperatures. The results are interpreted in a satisfactory manner by assuming that in severe supercooling induced nuclei are created, which may grow into effective nuclei at higher temperatures. The crystallization of a severely supercooled polymer is completely governed by these induced nuclei, because they outnumber the resistant nuclei by some orders of magnitude. The number of induced nuclei can be decreased by purifying the polymer (removing catalyst residues). When cooled polymer is heated to temperatures just above the melting point, the induced nuclei are destroyed (“reversible melting”), so that only the resistant nuclei, which are few in number, remain. These resistant nuclei govern the crystallization behavior of a polymer which has not previously been cooled. Their number decreases on heating to temperatures far above the melting point.