Polyester-Styrene Systems

The purpose of this work was to correlate catalytic activity with chemical structure for various aromatic and heterocyclic carbonyl compounds. Gel time, gel time as a function of initiator concentration, and gel time as a function of temperature were used to measure catalytic activity for the unsaturated polyester styrene systems used throughout this work. 

Yang and Suspene (1991) and Malkin and Kulichikin (1991) showed that for melamine formaldehyde and polyester-styrene systems prone to microgel formation the following chemoviscosity models were relevant ... 

Since the cross-linking of polyester-styrene system occurs by a free-radical chain-reaction mechanism across the double bonds in the polyesters with styrene providing the cross-links, the curing reaction does not give rise to volatile by-products (unlike phenolic and amino resins) and it is thus possible to cure without applying pressure. This fact as well as that room temperature cures are also possible makes unsaturated polyesters most useful in the manufacture of large structures such as boats and car bodies. 

Acrylate coatings are generally harder than polyester coatings and can be tougher or more flexible in thin films. Ingredients can be chosen to be substantially involatile at room temperature, while styrene is similar in volatility to xylene. Acrylates and methacrylates are, however, just as prone to air-inhibition as polyester/styrene systems. 

Unsaturated polyesters 44 containing multiple electron-deficient maleate and/or fumarate double bonds along the polymer chain are readily prepared by the reaction of maleic anhydride or fumaric acid with a diol. In many cases, other diacids or dianhydrides are also included as comonomers to improve the final mechanical properties. The polyester is combined with styrene monomer and photopolymerization is carried out using a radical photoinitiator. Due to the reactivity ratios of the two vinyl components, there is a tendency toward alternation. However, the length of crosslinks between the polymer chains can be controlled by the amount of excess styrene present. This allows appreciable control over the structure of the network polymer formed, and this has a considerable impact on its mechanical and chemical properties. Photocurable unsaturated polyester-styrene systems have found numerous uses, but the major applications are in wood... 

The tendency of thick sections of DMC structural parts to crack has been overcome by using low-profile polyester resins (or low-shrink resins). These are prepared by making a blend of a thermoplastic (e.g., acrylic) polymer-styrene system with a polyester-styrene system. Moldings of this blend cured at elevated temperatures exhibit negligible shrinkage and minimal warpage and have very smooth surface, to which paint may be applied with very little pretreatment. 

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