Research On Macromolecular Structure And Performance Of Polypropylene Based On Ozonolysis Reaction

Polypropylene(PP)which is produced via Ziegler–Natta or metallocene catalysis is one of the commodity polymers with the largest share in the present market.Due to the poor flowability and low melt strength of linear PP,it is limited in thin-wall injection molding and thermoforming.Reactive extrusion using peroxides as a radical initiator is the most commonly approach to regulated the flowability and molecular structure of PP.But utilizing organic peroxide as initiator has its own disadvantages,namely,limited controllability and easily excessive and non-homogenous degradation in PP.This thesis reports a novel synthesis method to prepare controlled-rheology PP(CR-PP)and long-chain branched PP(LCB-PP)via in-situ ozonolysis during reactive extrusion with or witout multifunctional agent.The specific contents are as follows:(1)CR-PP was obtained via in-situ ozonolysis during reactive extrusion in just several seconds period.The results of the melt flow index(MFI)and rheological measurement experiments showed that the higher polymer throughput,screw speed and reactive temperature,the lower MFI of CR-PP.Thus,we can adjust the processing parameters to control the desired flowability of CR-PP.(2)LCB-PP was obtained via in-situ ozonolysis during reactive extrusion in the presence of multifunctional agent,trimethylolpropane triacrylate(TMPTA).The maximum branching point density of the LCB PP was 0.495/1000 C.LCB-PP showed a significant influence on the viscoelastic properties of the melts,such as high elasticity,high zero shear viscosity,low loss coefficient and long relaxation time.The LCB-PP samples showed a distinct strain hardening behavior in elongational flow with changing strain rate dependence.The crystallization and melting temperatures of LCB-PP were higher than virgin PP.The results of WAXS indicating that the incorporation of LCBs did not change the crystal structure of PP backbones,but the grain became smaller.Thus the incorporation of LCBs improved mechanical properties of PP.By analysing the rheological measurement,the low TMPTA concentration,high extrusion temperature,low feeding speed and high screw speed accelerated degradation and the LCB PP could not be prepared.(3)To adjust of the degree of branching of LCB-PP,we used the monofunctional agent(GMA)and bifunctional agent(HDDA).The different functionalities of multifunctional agent effected on the branching reaction process and branching structure of polypropylene.It was found that PP grafted GMA(PP-g-GMA)was obtained via in-situ ozonolysis during reactive extrusion in the presence of GMA.At high HDDA concentration(2.0wt% or more),it can effectively initiate PP to form long chain.It couldn't effectively initiate PP to form long chain branched structure,at low concentration(1.0wt% or less)of HDDA.The results of GPC showed that the maximum branching point density of the LCB PP was 0.346/1000 C.