(A) Study on introducing long chain branches onto polypropylene by chemical modification

Abstract

In order to increase melt strength of polypropylene (PP), long chain branching reaction was studied. Polypropylene was chemically modified in melt state by a multifunctional monomer of pentaerythritol triacrylate (PETA) using dicumyl peroxide (DCP) initiator. Another approach was to chain-extend the maleated PP with aliphatic diamine. In the chemical modification of PETA on PP melt, DCP concentration was varied from 100 to 400 ppm and the PETA concentration was changed from 1 to 5 wt%. The resulting polymer contained branched structures and microgels. MI of modified PP increased with increasing DCP concentration at low PETA concentration. However, at 5 wt% PETA concentration, MI shows minimum at DCP concentration of 200 ppm. The amount of microgel in the modified PP has been found to increase with increasing PETA and DCP concentrations. Decrease in $T_m$ and increase in $T_c$ were found in modified PP, which indicated that long chain branches and microgels were formed. In the measurement of molecular weight of the modified PP by GPC, most of the microgels were remained during filtering step and the molecular weight data do not represent the true molecular weight of the modified PP. At 1 wt% PETA concentration, molecular weight in GPC decreases with DCP concentration, but at 3, 5 wt% PETA concentration molecular weight shows maximum at 200 ppm DCP concentration. In the rheological property measurement, viscosity decreased with DCP concentration when 1 wt% and 3 wt% PETA were used. At 5 wt% PETA concentration, viscosity increased with the DCP concentration up to 200 ppm, then decreased. The storage modulus G` at low frequencies of many of these modified PPs were larger than that of the virgin PP, which is caused by the long chain branching. Strain hardening behaviour indicating the existence of long chain branch was also observed in the elongational viscosity measurement. In the reactive melt processing of maleated polypropylene (PP-g-MA) with hexamethylene d...