Transparent Barrier Urethanes Based on Polyethylene Soft Segments

Abstract

A series of polyurethane elastomers has been synthesized through copolymerization of polyethylene soft segments and methylene bis(4-phenylisocyanate) (MDI) and hydrogenated MDI (H12MDI). Polyethylene soft segments were prepared by the hydrogenation of polybutadiene polyols, either before or after copolymer synthesis. Polyols from three different suppliers were used as precursors and ranged in branch content from 15% to -90%. Flexible, transparent materials were produced. The mechanical and barrier properties of these urethanes were evaluated for comparison with the performance of traditional flexible barrier materials (e.g., butyl rubber). Solvent uptake and swelling measurements were used to evaluate barrier performance. Branch content in the soft segment was found to affect both mechanical properties and solvent resistance, with low branch content leading to superior performance. Solvent diffusion coefficients for the materials were in the 10" -cm /s range, comparable to those exhibited by flexible high barrier materials.

Microphase Separation in Ion Containing Polyurethanes

“…At lower temperatures, the shift factors show distinct deviations from the shift factors for E1250. Quantitative analysis showed that block length had a very large effect on the terminal properties of polyurethane melts with terminal viscosity varying as approximately (block length) 4 ' 5 . At sufficiently high temperature the polyurethanes had a relaxation spectrum similar to that of a homopolymer of low molecular weight, indicating that either the polyurethanes were homogeneous at high temperatures or microphase separation did not affect the relaxation spectrum.…”