单链和寡链等规聚苯乙烯聚集体的结晶行为

自1960年Hoffman等提出聚合物结晶成核理论以来，人们对聚合物结晶生长速率、片晶的侧向尺寸随过冷度的变化等现象成功地进行了理论描述．1997年，Hoffman等对聚合物结晶成核理论进行修正，将de Gennes的聚合物“蛇行”概念。引入表面成核理论，通过对单根分子链从过冷熔体“卷绕”到晶体前沿所需的时间进行估算，其结果远远低于Flory预言时间约3～5个数量级，据此，Hoff-man认为，在聚合物结晶过程中，分子链在强迫稳态下的“蛇行”运动有足够的时间解缠结和结晶。

Crystallization Behavior of Single or Pauci Chain Congeries of Isotactic Polystyrene

Single- and a few-chain aggregates of isotactic polystyrene(i-PS) were prepared by the freeze-drying procedure from dilute solutions with the concentration from 1×10^-3 to 2×10^-5 g/mL.It was found that the melting point of crystals was gradually shifted to lower temperatures as the solution concentration decreased by the differential scanning calorimetry(DSC).As a result, the thickness of the lamellas of bulk samples and the samples prepared by the freeze-drying procedure from 2×10^-5 g/mL solution decreased from 19.3 nm to 12.6 nm,respectively.The half crystallization time(t₁/2) of samples by freezing-dried from 1×10^-4 g/mL solution was about 36 s,it was merely a tenth of the period of the bulk sample annealed at 468.3 K.In addition,the growth rate of spherulite(dr/dt) of the samples prepared from 2×10^-5 g/mL solution was more faster than ones of the bulk samples annealed at 478.3 K.All these should be attributed to the samples with less entanglement prepared by freeze-drying procedure from dilute solution.A preliminary study on the crystallization of the samples indicates that entanglements has a pronounced effect on crystallization behavior of polymer.