立体規則性高分子アイソタクチックポリプロピレンの平衡融点と結晶化の分子量依存性
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Topological nature in crystallization of polymers was studied by using isotactic polypropylene (iPP) as a typical model of stereoregular polymers. From the following results, topological mechanism of the crystal growth and the formation of superstructure were universally confirmed for polymers. A method to determine a reliable T_m^0 was proposed by using the Gibbs-Thomson plot. It is important to eliminate lamellar thickening by using thick lamellae (lamellar thickness > 20nm) and the effect of the "melting kinetics" on melting temperature (T_m) by applying slow heating (heating rate ≦ O.O1K/min). One typical experimental method is to use optical microscope (OM) and transmission electron microscope (TEM) for the measurements of T_m and lamellar thickness (l), respectively. Another typical method is to use differential scanning calorimeter (DSC) and TEM. As s result, _m^0 = 186.1℃ was obtained for iPP (M_n = 64 × 10^3). _m^0 increased with increase of molecular weight (M). Solid to solid transition (α2-α2'form transition) was also confirmed by the breakings in slopes of l against T_c and that of T_m against T_c. It was also confirmed that α2' phase of iPP is a mobile phase by experimental facts that l and Tm increased significantly in α2' phase due to the significant lamellar thickening during isothermal crystallization. The transition temperature (T_α2-α2') also increased with increase of M. A power law of M dependence of lateral growth rate (V) of iPP,V_∞MH^H, where H = 0.6 was obtained. It was shown that V is strongly controlled by the chain sliding diffusion within the interface between crystalline phase and the melt. Power Hs of iPP (H_<iPP) were smaller than that of polyethylene (PE) (H_<PE>). H_<iPP> is close to HPE of hexagonal phase, because chain conformation of iPP is similar to that of hexagonal phase. It was concluded that the difference in H was caused by chain packing in the unit cell due to the chain conformation. It was also found quantitatively that the degree of cross-hatching decreased with increase of tacticity and crystallization temperature. It was shown that chain sliding diffusion occurred easily when defect of mol- ecules decreased or crystallization temperature became high. It was concluded that the topological nature of polymers also controls the formation of superstructure.