Research on performances and retarded recovery process of disentangled long chain branched polypropylene prepared by solution method

Freeze-drying of dilute polymer solution is a widely accepted method to yield disentangled polymer. Many researches have pointed out that reduction of entanglement density has a big impact on rheology and crystallization behavior of polymer, but the re-entangling would take place in the case of reheating, which is unfavorable to the secondary processing of disentangled polymer. The branched structure of polymer could slow down the relaxation process of the molecular chain, which may delay the recovery of entanglement. In this work, the disentangled long chain branched polypropylene (LCB-PP) was prepared by solution method. The rheological behavior, crystallization behavior, entanglement recovery and mechanical performance of disentangled LCB-PP were investigated. The results showed that the moduli and complex viscosity of LCB-PP decreases with entanglement density decreasing. The disentanglement of LCB-PP has significantly positive effect on crystallization kinetics, while slightly affects the yield strength, elastic modulus and elongation at break. The entanglement recovery time of LCB-PP is much longer than that of i-PP which indicates the retardation effect of LCB structure on entanglement recovery.