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

Molecular, rheological, and thermal study of long‐chain branched polypropylene obtained by esterification of anhydride grafted polypropylene

“…In particular, the approach suggested by Vyazovkin has been successfully applied in the determination of Δ E χ. According to this technique where ( dχ/dt ) χ and T χ are the rate of crystallization and the temperature at a given level of crystallization χ, respectively. The activation energy of crystallization can be obtained from the slope of the plot of ln( dχ/dt ) χ as a function of 1/ T χ .…”

“…A parameter that may be calculated from the crystallization curves is the activation energy of crystallization, Δ E χ . Several methods have been proposed in the literature for estimating thermal activation energies . In particular, the approach suggested by Vyazovkin has been successfully applied in the determination of Δ E χ.…”

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A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

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Rheological, crystallization and electrical properties of poly vinylidene fluoride filled with micron iron

“…As we can see that the value of t 1/2 was reduced with increasing cooling rate. The curve was fitted with power model of non‐linear regression, it can be empirically as : …”