Comparing Crystallization Kinetics Among Two G-resin Samples And IPP Via Flash DSC Measurement

The non-isothermal and isothermal crystallization kinetics of two G-resin samples(isotactic polypropylene randomly copolymerized with a few 1-butene,for two molecular weights separately labeled as MT 12-s and MT 18-s)and homopolymer isotactic polypropylene(iPP)were investigated by using fast-scan chip-calorimeter Flash DSC1.Because of its excellent performance,isotactic polypropylene has become one of the most-used polyolefin products in our daily life,used in a wide variety of applications.This study will help us to understand better the effect of comonomer chemical confinement on polymer crystallization and also benefits the processing design of G-resins for the better performances of plastic products in the future.In this work,the experimental method was divided into three parts:a cooling,a heating,and an isothermal crystallization experiments.The purpose of cooling and heating crystallization experiments is to find sufficiently high cooling/heating rates in order to complete suppression of crystallization and even cold crystallization within the samples.The results for the first part showed that:for both G-resins,the crystallization can be suppressed for the cooling rate beyond-100 K/s;for iPP,we need the cooling rate beyond-500 K/s to suppress the crystallization on cooling.We need even the cooling rate-2000 K/s to suppress crystal nucleation on cooling of two G-resin samples.The results for the second part showed that:for both G-resins and iPP,the heating rate at 5000 K/s and 20000K/s or above can respectively prohibit spontaneous crystal nucleation for cold crystallization,implying no longer cold crystallization on heating after fast cooling.The results of isothermal crystallization showed that two G-resin samples crystallize slower than homopolymer iPP sample because of the chemical confinement effect of 1-butene on iPP crystallization.For two G-resin samples,at low temperatures,MT18-s can crystallize faster than MT12-s because of MT18-s has a lower molecular weight with higher chain mobility.Higher mobility makes crystallization faster at low temperatures.