DESIGN AND SYNTHESIS OF POLYPROPYLENE-b-POLYPHOSPHATE BLOCK COPOLYMERS

Novel phosphorus-containing polypropylene diblock copolymers were synthesized and their thermal decomposing behaviors and flammability were characterized by thermo-gravimetric analysis (TGA) and microscale combustion calorimetry (MCC). First, a reactive polypropylene precursor with a terminal styryl group (PP-t-St) at polymer chain end was synthesized via controlled chain transfer reaction to 1,4-divinylbenzene and hydrogen in metallocene-mediated propylene polymerization. Then PP-t-St was reacted with hydrogen bromide through Markovnikov addition in a quasi-quantitative manner, affording 1-bromoethylbenzene group-terminated polypropylene (PP-t-BzBr). ATRP of phosphorous-containing vinyl monomer such as diethyl-(4-vinylbenzyl) phosphonate (DEVBP) was carried out in toluene at elevated temperatures with PP-t-BzBr suspending in the reactant solution, with CuCl/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as catalyst. Diblock copolymers containing different amounts of DEVBP units (up to 64. 3 wt%) were obtained by adjusting polymerization durations. Differential scanning calorimetry (DSC) experiments indicated that both the crystallinity and crystallization rate of PP were largely retained in PP-b-PDEVBP diblock copolymers. TGA and MCC results showed that char residues increased while heat release rates reduced upon forming the diblock copolymers as compared to the precursory PP-t-BzBr as well as PP-t-St. Overall, this research may lead to a new solution to inherently flame-retardant polypropylene.