Effects of Switching Frequency of a Periodic Switching Polymerization Process on the Microstructures of Ethylene-Propylene Copolymers in Polypropylene/Poly(ethylene-co-propylene) in-Reactor Alloys

This work deals with the effects of the switching frequency of a periodic switching polymerization process (PSPP) with a Ti-based Ziegler-Natta catalyst on the microstructures of ethylene-propylene copolymers in polypropylene/poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys. The compositions and structures of PP/EPR in-reactor alloys are investigated by solvent fractionation, C-13 NMR, gel permeation chromatography (GPC), successive self-nucleation and annealing (SSA) by differential scanning calorimetry (DSC), and statistical deconvolution. The sequence distributions of ethylene-propylene random copolymer (EPR) and ethylene-propylene segmented copolymer (EPS) are successfully deconvoluted from the C-13 NMR spectra of fractionated samples. The results are consistent with the expected effects of the switching frequency on the composition and microstructures of EPR and EPS. A higher switching frequency between the homopolymerization of propylene and the copolymerization of ethylene and propylene increases not only the ratio between the EPS and EPR but also the fractions of long PP segments and long PE segments in the EPS. The effect of the mean residence time on the composition and microstructure of PP/EPR in reactor alloys is also discussed.