Molecular mechanical analysis of polymer conformation, 2.Relation between chain conformation and birefringence of stretched non‐crystalline polyurethanes with various substituent groups

摘要

AbstractThe relationship between birefringence and polymer structure was studied both by theoretical and experimental analyses of a series of non‐crystalline polyurethanes (PU) with different side groups. The most probable steric structures of PUs were estimated by molecular mechanical calculation (MM2) of their oligomeric model compounds, and their birefringence was theoretically calculated on the structural data obtained. In addition, some of the PUs were practically synthesized and melt‐spun into thin fibers, which were drawn to a maximum draw ratio to measure the values of birefringence. The comparison of the measured and estimated values revealed that the present estimation method is effective for simulating the chain conformations and the birefringence of fully or partially extended polymer chains, which ought to be formed by drawing and melt‐flow of glassy materials. Of particular interest was that phenyl‐substituted PUs exhibit an unexpectedly larger birefringence than methyl‐substituted PUs. This fact was reasonably explained by the angular rotation of the highly polarizable phenyl group, which is energetically easily allowed and influences strongly the value of bire