Effect of chain microstructure on modulus of ethylene–α‐olefin copolymers

A family of copolymers of ethylene and α‐olefin resins with homogeneous branching distribution, which behaves as elastomers at high short‐chain branching levels and acts as typical thermoplastics at low short‐chain branching levels, is now available. Control of this broad range of properties stems from the ability to control the molecular architecture more effectively using Dow's INSITE Trademark of The Dow Chemical Co. technology than in the past. Due to the unique combination of narrow short‐chain branching distribution (SCBD) and narrow molecular weight distribution (MWD), these resins provide a unique opportunity to model structure/property relationships in branched ethylene‐α‐olefin copolymers. The modulus in branched ethylene‐α‐olefin copolymers with aliphatic branches is shown to be primarily dictated by crystallinity. It is shown that the branch distribution and the branch type have an insignificant effect on the modulus of ethylene copolymers containing aliphatic branches at a given crystallinity. Modulus data have been successfully modeled in such systems using a lamellar fiber‐reinforced amorphous matrix composite model. Switching from aliphatic branches to cyclic branches significantly affected the modulus at similar crystallinities.