Temperature dependence of the linear steady-state shear compliance of linear and long-chain branched polyethylens

The linear steady-state shear compliances J_e⁰ of two linear short-chain branched metallocene-catalyzed polyethylenes (mLLDPE), two long-chain branched metallocene-catalyzed polyethylenes (LCBmLLDPE), and two classical low density polyethylenes (LDPE) were determined in creep-recovery tests in shear between 130 and 190°C. In order to investigate the dependence of J_e⁰ 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_e⁰ independent of temperature were observed. For the LCB-mLLDPE having similar polydispersities as the linear mLLDPE not only an increase of J_e⁰ by about 1 order of magnitude compared to the linear mLLDPE but also a significant decrease in J_e⁰ 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_e⁰ with increasing temperature is less pronounced than for the LCB-mLLDPE. However, for both material types the temperature dependence of J_e⁰ is much stronger than expected from the rubber elastic theory.