Effect of long chain branching on nonisothermal crystallization behavior of polyethylenes synthesized with constrained geometry catalyst

Abstract Nonisothermal crystallization behavior of linear and long chain branched (LCB) polyethylene (PE) samples having similar molecular weight but different long‐chain branching densities (LCBD) up to 0.44 C per 1000 carbons was investigated using differential scanning calorimetry (DSC) at various scanning rates. The LCB PE samples were prepared in our high‐temperature, high‐pressure continuous stirred‐tank reactor (CSTR) system using the constrained geometry catalyst. The existence of LCB was found to affect the PE crystallization behavior considerably. The enthalpy of crystallization and the ultimate degree of crystallinity decreased with the increase of LCBD. At the relatively low cooling rates, the small amount of LCB promoted nucleation but restrained chain movement and reduced the crystal growth rate. There was ∼ 17% of crystallinity generated from a secondary crystallization. The energy barrier became significant with the LCB structure, resulting in chain diffusion limitations and lower LCB PEs overall crystallization rates than their linear counterpart. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers