Preparation Of Toughened Polypropylene By Suspension Grafting Polymerization

The low temperature brittleness of polypropylene (PP) limits its applications. In this paper, with porous PP granules which are prepared by the reactor granular technology as substrate and benzoyl peroxide(BPO) as initiator, cross linked copolymer was grafted onto PP by water-solid phase suspension grafting polymerization. Cross linked copolymer microdomains which functioned as rubber phase to improve the toughness of PP. The main researches are as followes:(1) With butyl acrylate (BA) as grafting monomer and poly(propylene glycol) dimethacrylate (PPGDMA) as crosslinking monomer,the grafting polymerization of PP-g-(BA-co-PPGDMA) was investigated.The effects of reaction conditions on the polymerizations of PP-g-(BA-co-PPGDMA) were studied. GP of the grafting reaction increased and MFI value of grafted product decreased with the increase of comonomer content. Mechanical properties showed that the notched impact strength increased with the increasing comonomer content initially and then decreased. The tensile strength descended and then remained constant. When the comonomer content (based on PP) and comonomer ratio (PPGDMA/BA) were fixed at 10% and 1/7, respectively. The notched impact strength of PP-g-(BA-co-PPGDMA) was 6.7 kJ/m2 (2.6 times as much as pure PP). The tensile strength was 39.2 MPa (1.1 times as much as pure PP).(2) With BA as grafting monomer and acrylated castor oil (ACO) as crosslinking monomer, the grafting polymerization of PP-g-(BA-co-ACO)was investigated. The MFI of grafted PP was decreased with the addition of ACO monomer. GP ascended from 5.8% to 21.3% with growing comonomer content. The crosslinked copolymer decreased the relative crystallinity of PP. Dynamic mechanical thermal analysis showed that the glass transition temperature of PP decreased slightly from 220C to 15?.The addition of 5% comonomer led to an increase of notched impact strength from 2.0 kJ/m2 of pure PP to 3.8 kJ/m2 of grafted copolymer(nearly doubled) and a marginal decrease (95% of pure PP) of the tensile strength of PP-g-(BA-co-ACO). Then with further addition of comonomer, the notched impact strength increased to 9.0 kJ/m2 (4.5 times as much as pure PP) while the tensile strength was maintained at 30.0 MPa (81% of pure PP).