The Structures And Properties Of Isotactic Polypropylene Obtained By Supercritical Polymerizaton

The structure and properties of isotactic polypropylene(SC-iPP), which produced by supercritical polymerization at 95℃ 55bar, were investigated systemically, the structure and properties include morphologies of particle, particle diameter and distribution, microstructure, initial crystallinity and crystalline properties etc. All the results compare with the relativlely properties of isotactic polypropylene(C-iPP) which produced by slurry polymerization at 70℃ 32bar. Furthermore effects of propolymerization temperature and catalyst system were investigated on structure and properties for supercritical isotactic polypropylene (SC-iPP).Firstly, particle morphologies were studied by SEM, and particle diameter and distribution were obtained by paticle measurement. The results found that particles diameter of SC-iPP are bigger, and the surface is tightness and no distinct ravines. On the contrary, particles diameter of C-iPP are smaller, the surface is coarse and have distinct ravines. The results are still found that catalyst system, including main catalyst, cocatalyst, electon donor, has an important effect on morphologies of SC-iPP.Secondly, initial crystalline, melt point and crystalline degree were investigated with WAXD, high pressure DSC and general DSC. The results were found that SC-iPP has two kinds of crystalline α and γ , but C-iPP has only one crystalline α. The melt points and crystalline degree of SC-iPP are higher than C-iPP's. With the high pressure DSC results, it are found that melt point of SC-iPP is decrease with increasing pressure. In addition, effects of propolymerization temperature on SC-iPP's crystalline are small, but the effects of catalyst systyme are big. Melt points and crystal degree are different for iPP with different molecular weight and particle diameter.Finally, crystallization kinetics of isotactic polypropylene were investigated. Isothermal crystallization kinetics were observed with DSC and optical microscope. It is found that crystal rates of SC-iPP is faster than C-iPP's, crystal degree is higher, and spherulite crystal is negative character. And it is easy to tend heterogeneous nucleation. Additionally, nonisothermal crystallization kinetics were observed with DSC. The results found that crystal rates of SC-iPP is faster than C-iPP's. Furthermore, propolymerization temperature has little effect on nonisothermal crystallization kinetics but activity energy of crystallization of obtain produce. The influence of catalyst and molecular weight on activity energy of crystallization of obtain produce have the same with front.