Long-chain branching melt elasticity

It is well known that LCB has a pronounced effect on the flow behavior of polymers under shear and extensional flow. Increasing LCB will increase elasticity and the shear rate sensitivity of the melt viscosity ( ). Environmental stress cracking and low-temperature brittleness can be strongly influenced by the LCB. Thus, the ability to measure long chain branching and its molecular weight distribution is critical in order to tailor product performance. 

The CG catalysts produce highly processable polyolefins with a unique combination of narrow MWD and long chain branches. Ethylene-octene copolymers produced with CG catalysts have useful properties across a range of densities and melting indexes. These novel copolymer families are called polyolefin plastomers (POP) and polyolefin elastomers (POE). POPs possess plastic and elastic properties while POEs containing greater than 20 wt% octene comonomer units have higher elasticity. 

Melt strength and elasticity may be increased by adding a high-MW polymer or one with long-chain branching. 

Long chain branching (LCB) has several benefits relating to the polymer processability because it affects melt viscosity, temperature dependence of viscosity, melt elasticity, shear thinning, and extension thickening. The effect of LCB on the melt-state properties of polyethylene depends on the number, length, and distribution of the branches, on molecular weight, and on MWD. 

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