Free‐radically initiated polymerisations for reaction injection moulding (RIM): Some observations on polymer blends involving poly(methyl methacrylate) as one of the components

Abstract

AbstractThe rapid growth of interest in reaction injection moulding (RIM) and reinforced reaction injection moulding (RRIM) has focused attention on polymerisation reactions which can generate useful solid polymeric mouldings with moulding cycle‐times of less than three minutes. Free‐radically initiated polymerisations have long been used in reactive processing, for example, in the casting of acrylic sheet materials and for the cure of polyester resin, but the overall polymerisation times for these reactions has been relatively long. Adapting existing free‐radical polymerisations for RIM and RRIM technology raises many interesting chemical, kinetic and thermodynamic problems. We have been exploring the use of radical processes for very fast processing techniques such as RRIM using a novel computer controlled and monitored RRIM machine developed in our laboratories. Both polyester and acrylic based materials have been reactively processed to give 2–4 kg plaque mouldings in cycle‐times of less than two minutes. Of particular scientific interest are polymer blends and interpenetrating polymer network systems (IPNs) (where one of the concurrent polymerisations is initiated by a free radical mechanism) since these systems give considerable scope in the design of product properties through composition. The principles of reaction injection moulding are briefly described together with some experimental results obtained for an acrylate/polyurethane composite material given emphasis to fundamental aspects of radical polymerisation reactions raised by the need for very rapid and complete conversion of the methyl methacrylate component.