Copolymerization of propylene with poly(ethylene-co-propylene) macromonomer and branch chain-length dependence of rheological properties

A series of isotactic polypropylene (PP) samples with poly(ethylene-co-propylene) long chain branching were produced by a semibatch copolymerization of poly(ethylene-co-propylene) macromonomer (EPR), prepared in a high-temperature continuous stirred tank reactor (CSTR), and propylene using rac-dimethylsilylenebis(2-methylbenz[e]indenyl) zirconium dicholoride/modified methylaluminoxane. The branch frequency and branch length of the copolymers were controlled by varying the stoichiometry and molecular weight of the EPR macromonomer, respectively. Long chain branch frequencies of up to 2.8 branches per chain were achieved, while the branch length was varied from 2500 to 17 000 g/mol. The effects of macromonomer concentration, macromonomer molecular weight, and reaction temperature on the copolymer chain properties were investigated. The rheological responses of the EPR-branched PP were determined. Branches below 7000 g/mol had little influence on the rheological behavior of the polymers. The zero shear viscosity, shear thinning property, and loss and storage moduli were found to be dependent on the branch length and branch frequency when the branch M-n was above 7000 g/mol. Elevated flow activation energies were observed with measured values of up to 51 kJ/mol. The physical and chemical properties of the copolymers were analyzed by gel permeation chromatography (GPC), FTIR, parallel-plate rheometry, and C-13 NMR.