Gamma-phase of isotactic polypropylene

Figufe 1 Four unit cells of the v-modification of iPP according to the nonparallel chain packing model of Meille ef nL [31. The spherical entities represent the methyl groups. 

Calculations of the packing energies of the 7- and a-modifications show that the 7-modification should be slightly more stable than the a-modification. There are several ways to influence the formation of different crystal modifications of iPP. The content of the 7-modification in iPP can be increased in the case of 14]  

using iPP prepared with metallocene catalyst systems having a relatively large number of stereo- and regioirregularities in the chain or by using very low-molar mass samples  

application of high pressure during the crystallization process  

using random copolymers of propene with other 1-olefins with 1-olefin contents between 2.5 and 20wt.%  

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The effect of low-doses gamma radiation on the quenched forms of isotactic polypropylene was the subject of our previous work (1). In this work, we have studied the effects of gamma radiation on the monoclinic and hexagonal phase. The macrostructural states of iPP before and after irradiation were followed and the noticed effects were then related to its melting behaviour and molecular weight changes. 

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