Rheological and Mechanical Study of Comb-Branched Polyolefin Elastomers Containing Macromer Residues

Comb-polyolefin elastomers (CPOEs) with crystalline long-chain branches (LCBes) demonstrate superior mechanical properties and processability. However, fully understanding the effect of LCBes on their material performance remains a huge challenge due to the residue of unreacted polyethylene macromers (PE-Ms). Here, we report a method of blending CPOEs with PE-Ms to study the structure–activity relationship of CPOEs via extrapolation. CPOE samples with different numbers of LCBes (q) between 0.0 and 9.9 and PE-Ms with an Mw value similar to the LCBes were prepared and studied. Blending CPOEs with 20–40 wt % of PE-Ms increased the melt fluidity and reduced the zero-shear viscosity (η0) value from 4590 Pa·s to 980 Pa·s without causing phase separation. These CPOEs exhibit dynamic responses with a similar temperature dependence where the time shift factors could be fitted by the same Williams–Landel–Ferry parameters with C1 at 4.88 and C2 at 443 K. For CPOEs with LCBes, as q increased from 1.1 to 9.9, the number of entanglements between the graft points (Zg) decreased from 11.78 to 0.93, and the chain conformation changed from sparse comb (SC) to dense comb (DC), respectively. The maximum η0 value of CPOEs occurs at the turning point of SC and DC, where Zg is equal to the entanglement number of the branched chain −Zbc of 4.72. Our study distinguished the different effects between the grafted and free PE-Ms on the CPOEs, enabling an in-depth understanding of macromolecular engineering in polymer and facilitating the future development of higher-performance CPOEs or other grafted polymers.