THEORETICAL PREDICTION OF TIE-CHAIN CONCENTRATION AND ITS CHARACTERIZATION USING POSTYIELD RESPONSE

In the past, relative tie-chain concentration has been semiquantitativ ely characterized by infrared dichroism on a stretched sample and from brittle fracture strength. The probability of tie-molecule formation has also been theoretically estimated from chain dimensions and the se micrystalline morphology of the polymers. In this article the probabil ity of tie-chain formation of monodisperse and homogeneous single-site ethylene copolymers has been estimated over a range of densities and molecular weights using the model proposed by Huang and Brown. The rel ative tie-chain concentration is obtained by multiplying tie-chain pro bability with the volume fraction crystallinity of polymer. A modified rubber elasticity theory is applied to calculate the concentration of chain links between junction points (crystallites) of the INSITE dagg er technology polymers (ITPs) from measured rubber modulus. It is expe cted that the chain-link concentration should relate to the tie-chain concentration. The calculated rubber modulus, or the chain-links conce ntration, of the ITPs increases with an increase in density in the 0.8 65 to 0.910 g/cc range and did not change significantly in the density range of about 0.91 g/cc to 0.954 g/cc. Normalized rubber modulus and relative tie-chain concentration data shows that the relative tie-cha in concentration predicted by Huang and Brown model and measured using the modified rubber elasticity theory are quantitatively similar belo w 0.91 g/cc density. However, above 0.91 g/cc density, the measured ru bber modulus is influenced by additional tie-chain formation during de formation due to breakdown of crystallites and, hence, the discrepancy exists between the two methods of estimating relative tie-chain conce ntration. (C) 1996 John Wiley & Sons, Inc.