Synthesis And Properties Of Novel Polyolefin Elastomers

Thermoplastic elastomer(TPE),combing the physical and chemical properties of both the rubbers and plastics,is usually composed of the crystalline or glassy chains as the “hard” segments and the amorphous chains as the “soft” segments.TPE can be directly molded into final products without vulcanization and be processed and recycled at high temperature,making it be an attractive candidate for the vulcanized rubbers.The polyolefin elastomers(POEs),which are usually prepared through the direct copolymerization of ethylene and ?-olefin,are widely used in many applications from automative industry to material modification.However,it is difficult to improve the elastomeric properties and service perfomance of ethylene/?-olefin copolymers POEs,while keep high tensile strengthen and high modulus.In view of these problems in the development of TPE,we carried out the works as follows:(1)A series of polypropylene-based elastomers were prepared using two different copolymerization methods.Firstly,the polypropylene-based elastomers(P/C)with side chain length of C8,C12,C16,C20 were synthsized by copolymerization of propylene with higher ?-olefins.The graft density and length were adjusted to obtain P/C copolymers with high toughness and excellent elastic recovery.Besides,we designed a new “Tandem” copolymerization strategy to prepare the long-chain branched polypropylene-based elastomers(iPP-g-PE),of which both the iPP backbone and PE grafts can crystallize,giving rise to high tensile strength.The iPP-g-PE copolymers exhibit excellent compatibilization performance towards the immiscible high-density polyethylene and isotactic polypropylene(HDEP/iPP)blends.Tensile tests showed that the iPP-g-PE copolymers can significantly improve the elongation at break of HDPE/iPP blends.(2)The dynamic cross-linking network in the POE-vitrimers were prepared by introducing reversible boronic ester bonds.By controlling the cross-linking density,the toughness,elastic modulus,elastic recovery,and tensile strength of POE-vitrimers were optimized.The POE-vitrimers also exhibited excellent tensile dynamic stability,heatand solvent-resistance,and thermal mechanical properties under harsh environment.Moreover,these POE-vitrimers can relax quickly at high temperature and thus have the ability of thermal processability.(3)The memory effect of poly(1-butene)-based elastomer was investigated by introducing polycyclic aromatic groups,including phenyl(Ph)group,naphthyl(BN)group and anthracyl(BA)group.The influence of comonomer type and concentration on the memory effect was firstly studied.When the comonomer concentration is low,no memory effect was observed in the Phx and BNx copolymers containing polycyclic aromatic groups of small steric hindrance,while the BAx copolymers appear memory effect above the equilibrium melting point at much low comonomer incorporation(0.6mol%).Moreover,with increasing melting time,the crystallization point and the intensity of memory effect increased for all Phx,BNx and BAx copolymers.(4)The influence of TPE with different molecular architectures on the phase structure of HDPE/iPP blends was systemically studied.The results show that the PPO copolymers can compatibilize the immiscible HDPE/iPP blends and promote the coalescence of dispersed droplets,which eventually lead to phase inversion.The mechanism for the phenomena of phase inversion in compatibilized ternary HDPE/iPP/TPE blends was investigated by controlling melt mixing time.The results show that the PPO copolymers can be easily removed from interface owing to the low complex viscosity and can provide interfacial bending energy for stabilizing cocontinuous structures.The PPO compatibilizers with longer graft length and higher graft density can significantly promote the formation of the cocontinuous interval in HDPE/iPP blends.