Generation and structure–property behavior of novel liquid crystalline foams produced via a gas supersaturation technique

Linear and star‐branched polyoxybenzoate–polyoxyphenoxybenzoate copolymers (POB‐ co ‐POPB) at a 65/35 molar ratio were synthesized via melt acidolysis using AB‐type monomers and branching agents. By controlling the molecular weight and topology of these polymers, both melt processability and solid‐state CO 2 gas absorption behavior were enhanced. POB–POPB copolymers with a molar ratio 65/35 showed a glass transition of 143°C and completion of melting at ca. 300°C. POB–POBP copolymers with a systematically increasing branching agent content showed a systematically decreasing peak intensity in wide‐angle X‐ray diffraction, indicating that increasing branch‐point concentration leads to a decrease in liquid‐crystal ordering. Star‐branched POB–POPB copolymers showed greatly enhanced carbon dioxide gas absorption behavior relative to their linear counterparts. Whereas CO 2 blown foams of linear POB‐ co ‐POPB produced by the gas supersaturation technique had a relatively high density and showed highly anisotropic bubble growth, well‐defined, nearly isotropic foams of star‐branched POB‐ co ‐POPB with a mean cell size from 200 to 400 μ were made using the gas supersaturation technique. Structural features were characterized via scanning electron microscopy, and mechanical properties were determined by indentation testing with a 0.25 in. ball indenter. These LCP foams exhibit relative mechanical properties similar to polystyrene and microcellular polycarbonate foams. A strong inverse relationship was noted between cell size and modulus for liquid crystalline foams with a cell size below 400 μm. © 1994 John Wiley & Sons, Inc.