Single- and pauci-chain aggregate samples in amorphous state were prepared from aerosols of isotactic polystyrene (i-PS) in a concentration range of 1×10^－3～2×10^－5 g•mL^－1 by the freeze-drying procedure. It was found that as the concentration decreases, the i-PS chain coils would be well separated in solution and the resulting intrachain entanglements may decrease, therefore, the amount of single- and pauci-chain coils, within collected particles obtained via the freeze-drying procedure, increases gradually. The results of freeze-drying samples by DSC indicated that the crystallization temperature shifts lower, the melting point and the crystallinity decrease as the solution concentration decreases. The samples prepared from 2×10^－5 g•mL^－1 solution are melt-crystallized at 468.3 K for 60 min, then single-chain single-crystal with an average volume of 1.5×10⁴ nm³ was obtained. The crystal grain size was about 20 to 50 nm by the SEM micrograph. By means of the polarized optical microscopy (POM), the spherulite growth rates of i-PS single or pauci-chain congeries are calculated at various crystallization temperatures. With described by the theory of Hoffmann, the critical nucleation parameters of single-chain single-crystal of i-PS were calculated as follows: the fold surface free energy (σ_e) was 30.2 erg•cm^－2; the lateral surface energy (σ) was 5.7 erg• cm^－2 and the work of chain folding (q) was about 4.5×10^－13 erg•molecule^－1. Compared to the values reported in literatures, the results indicate that entanglements have a pronounced effect on the crystallization behavior of polymer.

Key words: isotactic polystyrene, freeze-drying procedure, single- and pauci-chain aggregate, crystallization