Curing of UPE Resin

Consequently, the radicals are destroyed and the curing reaction cannot proceed. This is why accelerators are added in a very small amount (0.02 wt%, and never more than 0.3 wt %). 

As discussed in earlier sections, UPE resins are a mixture of an unsaturated polyester, styrene and an inhibitor. When the resin is mixed with a peroxide initiator and activator (cobalt octoate/napthenate), free radicals are formed. At the initial stage, all or most of the free radicals generated are consumed by the inhibitor. The driving force for the preferable reaction of free radicals with the inhibitor is the higher stability of inhibitor radicals. Once the inhibitor molecules are depleted, free radicals, produced from the initiator, initiate polymerisation of the polyesters. Styrene serves as an agent to link the adjacent polyester molecules. The curing of UPE resin (polyester + styrene) involves different types of reactions  

The kinetics of crosslinking reaction has been investigated. The crosslinking reaction is reported to be an autocatalytic reaction, as discussed in Chapter 1. The reaction rate is affected by the styrene content of the resin. Zlatanic and co-workers [75] carried out detailed rheological studies of acrylate-terminated UPE resins of different compositions e.g., poly [(tetramethylene maleate)-co-(tetramethylene phthalate)] 

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