Abstract: 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.

Key words: Isotactic polystyrene, Single chain, Pauci chain, Crystallization