Glass transitions of topologically interpenetrating polymer networks

Two component topologically‐interpenetrating polymer networks were made of the SIN type (simultaneous interpenetrating network) composed of two polyurethanes (a polyether‐based and a polyester‐based) in combination with an epoxy resin, a polyacrylate and two unsaturated polyesters. The linear polymers and/or prepolymers were combined in solution and in bulk together with the necessary crosslinking agents and catalysts. Films were cast and chains extended and crosslinked in situ . All of the IPN's exhibited one glass transition ( T g ) intermediate in temperature to the T g 's of the component networks, and as sharp as the T g 's of the components. This suggests that phase separation may not occur and thus some chain entanglement (interpenetration) of the two networks is involved. The observed T g 's are always several degrees lower than the arithmetic means of the component T g 's. A theory based on interpenetration is developed to account for this.