EVALUATION OF THE COMONOMER DISTRIBUTION IN ETHYLENE COPOLYMERS USINGDSC FRACTIONATION

The microstructures of ethylene random copolymers are evaluated using DSC fractionation by the degree of crystallinity. This method is based on the same principle of separation as temperature-rising elution fra ctionation (TREF) which uses a crystallization/dissolution procedure; however it does not physically separate the fractions. The resulting c opolymers are sorted by crystallite sizes: the crystallite size and la mellae thickness are directly related to the ethylene block length. Co polymers including E/VA, E/nBA, E/nBA/CO, E/nBA/VA, E/MAA, E/AA and LL DPE have been analyzed by DSC fractionation to elucidate structural di fferences. We see that (a) specimens with high comonomer content are l ess crystalline; the ethylene segments are shorter, (b) the comonomer type makes a difference in fractionation if H-bonding is involved, (c) the narrow comonomer distribution, i.e. narrow ethylene-segment-lengt h distribution, has fewer DSC fractions; the broad distribution has mo re fractions, (d) fractionation by crystallinity is affected if the mo lecular weight/viscosity is very high, (e) branch content reduces the crystallinity and shortens the ethylene blocks, and (f) there is no di rect relation to molecular weight distribution or comonomer content.