EFFECT OF CHAIN MICROSTRUCTURE ON MODULUS OF ETHYLENE-ALPHA-OLEFIN COPOLYMERS

A family of copolymers of ethylene and alpha-olefin resins with homoge neous branching distribution, which behaves as elastomers at high shor t-chain branching levels and acts as typical thermoplastics at low sho rt-chain branching levels, is now available. Control of this broad ran ge of properties stems from the ability to control the molecular archi tecture more effectively using Dow's INSITE(R)dagger technology than i n the past. Due to the unique combination of narrow short-chain branch ing distribution (SCBD) and narrow molecular weight distribution (MWD) , these resins provide a unique opportunity to model structure/propert y relationships in branched ethylene-alpha-olefin copolymers. The modu lus in branched ethylene-alpha-olefin copolymers with aliphatic branch es is shown to be primarily dictated by crystallinity. It is shown tha t the branch distribution and the branch type have an insignificant ef fect on the modulus of ethylene copolymers containing aliphatic branch es at a given crystallinity. Modulus data have been successfully model ed 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. (C) 199 4 John Wiley & Sons, Inc.