Temperature Dependence of the Linear Steady-State Shear Compliance of Linear and Long-Chain Branched Polyethylenes

The linear steady-state shear compliances J(e)(0) of two linear short-chain branched metallocene-catalyzed polyethylenes (mLLDPE), two long-chain branched metallocene-catalyzed polyethylenes (LCB-mLLDPE), and two classical low density polyethylenes (LDPE) were determined in creep-recovery tests in shear between 130 and 190 degrees C. In order to investigate the dependence of J(e)(0) on the molecular structure the polyethylenes were characterized by high-temperature size-exclusion chromatography coupled with a multiangle laser light scattering device (SEC-MALLS). For the linear mLLDPE the lowest J(c)(0) independent of temperature were observed. For the LCB-mLLDPE having similar polydispersities as the linear mLLDPE not only an increase Of J(e)(0) by about I order of magnitude compared to the linear mLLDPE but also a significant decrease in J(e)(0) with increasing temperature was found. For the LDPE possessing long-chain branches as well as higher polydispersities, the highest J(e)(0) values were detected, which were also temperature dependent. For the LDPE, the decrease of J(e)(0) with increasing temperature is less pronounced than for the LCB-mLLDPE. However, for both material types the temperature dependence of J(e)(0) is much stronger than expected from the rubber elastic theory.