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

Abstract

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 M w 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 (Z g) 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 −Z bc 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.

High-Performance Olefin Thermoplastic Elastomer Based on Dynamically Cross-Linking Crystalline Macromers and Elastic Backbones

“…The enhanced melt strength at high temperatures can be attributed to the grafted PE-M and dynamic cross-linking structure, for they increase chain entanglements and limit chain motion. 9,22,40 The G′ of P1− P4 descends successively with the reducing content of crosslinked POE, agreeing with the DMA results above. Besides, the terminal slopes of G′−ω curves decrease from 0.24 in P1 to 0.16 in P4, suggesting that the higher content of cross-linked POE facilitates the bond exchange of the boronic ester and promotes the chain untangling.…”

“…The residual PE-M can form cocrystallization with the backbone to enhance interfacial interactions and improve melt fluidity for reprocessing. , Thus, P1–P4 were directly used without removing the unreacted PE-M avoiding the cumbersome extraction step. We tested the uniaxial static tension of P1–P4 at room temperature to obtain typical stress–strain curves (Figure a).…”

Comb Polyurethanes Consisting of Hard Segment Backbones and Dangling Soft Segments for Tailoring Mechanical Properties of Thermoplastics

“…The contribution of polymer topology, including branch, , cyclic, and network structures, is a critical aspect in the study and design of mechanical and rheological properties of bulk polymer materials, as is typically found in polyethylene. − Among the various topologies, comb and bottlebrush polymers (graft polymers), which consist of a single backbone with multiple side chains, have recently drawn significant attention due to their tailored mechanical properties and distinct softened mechanical properties (Figure ). ,− Graft polymers encode mechanical properties using the structural parameters including backbone length ( n bb ), side chain length ( n sc ), and branching point spacing ( n g ), allowing for the replication of the mechanics of diverse soft materials. − However, for solid thermoplastics, which account for much of the synthetic polymer industry, the inherent chemical properties such as intermolecular interactions, conformational attributes, phase-separated structures, and crystalline constructs often overshadow this topological designability of mechanical properties.…”

The Effect of Feeding Sequence on the Structure and Properties of the Ethylene/1-Octene Copolymer in the Semi-Continuous Polymerization Reaction System

“…Due to the high comonomer content, the polymer chain consists of a crystalline resin and amorphous rubber phases. As a result, this material exhibits both the high elasticity of rubber and the plasticity of thermoplastic resins, making it easy to process and mold [ 1 , 2 ]. POE is widely used in photovoltaics, automobiles, buildings, cables, etc.…”