Polydicyclopentadiene

Polydicyclopentadiene (PDCPD) is a polymer which is formed through ring opening metathesis polymerisation (ROMP) of dicyclopentadiene (DCPD). The difference between the various systems lies in the type of catalyst used to create the polymer, but the final polymer properties are similar. Polydicyclopentadiene (PDCPD) is a polymer which is formed through ring opening metathesis polymerisation (ROMP) of dicyclopentadiene (DCPD). The difference between the various systems lies in the type of catalyst used to create the polymer, but the final polymer properties are similar. The reacting system is formulated in such a way that two components need to be mixed at equal volume (1:1 ratio). Both components contain mainly DCPD with some additional additives. The difference between both components is crucial, but constitutes only a small fraction of the total formulation: the catalyst system is divided into two parts, each part going into a separate component. When both components are mixed, the complete catalyst system is recombined and becomes active. This is an important difference from other Reaction Injection Moulding (RIM) systems like polyurethane, since the reaction is not stoichiometric. The 1:1 ratio for DCPD moulding is not critical since this is not a combination of two different chemical elements to form a specific matrix. Significant changes in ratio will slow down the system's reactivity because fewer active reaction nuclei are being formed. This also changes the final properties somewhat. The current industrial pumps used on RIM equipment are accurate enough to ensure that the mixing ratio stays within the necessary limits. DCPD resins are transformed using high pressure RIM equipment as used in the polyurethane industry, with some small changes to be considered. As a reference, a widely used machine to inject DCPD resins is the Cannon A-100 fitted with a DCPD kit. The most important change is that the resin can never be in contact with air or moisture, which required a nitrogen blanket in the tanks. The tools or moulds are closed tools and are being clamped using a hydraulic press. Because the resins shrink about 6% in volume during reaction, these presses (also called clamping units) don't have to handle high pressures such as for Sheet Moulding Compound (SMC) or expanding polyurethane. Most tooling for PDCPD is made from aluminium. Flat parts can be made from machined aluminium while deeper 3D-shaped parts are often made in cast aluminium tools. It is important to take volumetric shrinkage into account, so, there cannot be any undercuts, and gaskets must be used around all cavities.