CHEMICAL MODIFICATION OF POLYPROPYLENE WITH PEROXIDE PENTAERYTHRITOL TRIACRYLATE BY REACTIVE EXTRUSION/

To explore the possibility of producing branched polypropylene (PP) by a reactive extrusion (REX) process, isotactic PP was reacted with a p olyfunctional monomer, pentaerythritol triacrylate (PETA), in the pres ence of 2,5-dimethyl-2,5(t-butylpeloxy) hexane peroxide (Lupersol 101) . Experiments were carried out in an intermeshing, corotating twin-scr ew extruder at 200 degrees C using three concentrations of peroxide (2 00, 600, and 1000 ppm) and four concentrations of PETA (0.64, 1.8, 2.8 , and 5.0%, by weight). Shear viscosity and MFI of the whole polymers was found to increase with PETA concentration and decrease with increa sing the peroxide concentration at a given PETA concentration. The mac rogel amount in the materials produced was determined in refluxing xyl ene using Soxhlet extraction and at PETA concentrations higher than 1. 8 wt % the macrogel content increased with increasing peroxide concent ration. No macrogel was detected at low PETA concentrations (<0.64%) a t all three peroxide levels, suggesting that low concentrations of PET A and peroxide should he used in order to minimize the formation of ma crogels. The xylene soluble portions (sols) of the modified materials were characterized by FTIR and DSC. Generally, the relative intensitie s A(1740)/A(841) in the FTIR spectra increased with increasing PETA in corporated into PP. Two melting peaks (T-m1 and T-m2) were observed in the DSC traces of some of the sols, and the crystallization temperatu res (T-c) were higher than those of the virgin and degraded polypropyl enes. The DSC behavior of the sols suggests that the modified PPs cont ain branched and/or lightly crosslinked chain structures. (C) 1996 Joh n Wiley & Sons, Inc.