In situ ozonolysis of polypropylene during extrusion to produce long-chain branches with the aid of TMPTA
The introduction of long-chain branches (LCBs) in polypropylene (PP) during the extrusion process is normally induced by peroxide chemicals which are known to lead to the formation of secondary products in the resin. Here we report a novel synthesis method to prepare LCB-PP via in situ ozonolysis during reactive extrusion in the presence of a multifunctional agent. Depending on the fast ozonation of molten PP molecules, free radicals can be generated in PP macromolecules and induce chain scission reactions during extrusion. LCB structures of PP could be formed when a multifunctional agent, trimethylolpropane triacrylate (TMPTA), was added into the PP matrix during extrusion. The effect of reaction temperature, polymer flow rate and TMPTA concentration on the LCB-PP structures is discussed. Molecular parameters of LCB-PP were detected by MALS SEC technique. Various rheological plots including elongation rheological properties were applied to distinguish the LCB structures in PP samples. Without residues and by-products of peroxide in the final polymer resin, this synthesis method of LCB-PP has highly efficient and easily adjustable merits.