Structural parameters in relation to the rheological behavior and properties of PP/EPR in-reactor alloy synthesized by multi-stage sequential polymerization



The morphology and molecular structure of an in-reactor polypropylene/ethylene propylene rubber alloy, synthesized by multi-stage sequential polymerization, were studied with respect to the rheological behavior and final properties of the alloy. The polymer alloys, based on different structural morphologies, were characterized by SEM, GPC, 13C NMR, DSC, rheological analysis, and mechanical testing. The scanning electron microscopy of samples showed that the size of the dispersed phase particles is decreased as the switch frequency of copolymerization timing is increased. The GPC results showed that switch frequency slightly altered the molecular weight distribution of the copolymer although it had no effect on PP homopolymer. 13C NMR results were used for the evaluation of compatibility between the two phases with changes in switch frequency. DSC results showed that Tm and Tc were almost independent of switch frequency, even though the size of dispersed phase was decreased and the blend crystal content increased with ΔH of about 13%. The small amplitude oscillation rheometry showed that storage modulus and viscosity shifted to higher values when switch frequency increased. In studying the mechanical properties it was revealed that, especially the impact strength increased by about 62% when the size of the dispersed particles was decreased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011