Preparation And Adjusting Reaction Selectivity Of Long Chain Branched Polypropylene Through Melt Reaction

Polypropylene (PP) is one kind of most important polymer materials, and it is widely used in our daily life. However, the application of commercial PP is limited in foaming, thermoforming and blowing molding due to low melt strength and a lack of strain hardening phenomenon. Introducing long chain branching to the PP backbone can largely increase the melt strength of PP. High melt strength PP (HMSPP) is widely used in foaming, thermoforming and blowing molding. The melt radical reaction is considered to be a preferable method to modify PP. But, there are several tough problems need to be considered during melt radical modification of PP, i.e.,how to mediate the ?-scission of PP macroradicals, the grafting reaction between functional monomer and PP macroradicals, and the homopolymerization of monomer.The ?-scission of PP or the formation of gel will lead to poor mechanical of PP.Homopolymerization of monomers leads to poor branching efficiency of monomers.Based on the preliminary work, we explored methods to address these three issues in this paper. Firstly, the grafting monomer containing double bond with different reactive activities (BAC?BMVB) was synthesized and was used in melt free radical grafting, which could reduce ?-scission of PP and the formation of gel.Secondly, ZDMC agents were introduced to mediate the polymerization of branching monomer and increase the branching efficiency. At last, the mechanism of melt reaction was illuminated which was mediated by the combination of branching monomers and RAFT agents and established a new method to prepare LCBPP. The kinetics results of nonisothermal crystallization verified the opposite effects of LCB structure on the crystallization process of PP backbones in modified sample: on one hand, the indolent LCB structure could perform the function of heterogeneous nucleation to facilitate the crystallization; on the other hand, the mobility and reptation ability of PP backbones were restrained by the LCB structure, which hindered the crystallization process.