Model Studies Towards Alternative Cross-Linking of Unsaturated Polyesters

Abstract

Abstract: Fumaric and maleic acid esters are functionalised with propargylamine. A subsequent Pd/Cu-catalysed oxidative homo-coupling of two alkyne moieties yields the corresponding dimers. Hence, a model ofan unsaturated polyester chain is cross-linked in a well-defined, metal-mediated reaction in a very high yield. Keywords : Unsaturated polyester, cross-linking, catalytic, alkyne coupling. INTRODUCTION Unsaturated polyester resins are heterochain polymers,containing repeating ester groups and aliphatic double bondsin the backbone [1]. These chains are generally co-polymerised in a free-radical chain-growth process, with avinyl monomer, usually styrene, to yield the final product, athree-dimensional cross-linked network [1, 2]. Sinceenvironmental legislation becomes more and more stringentconstantly reducing the amount of monomeric components,which can be used in unsaturated polyester products, thedevelopment of alternative cross-linking methods, reducingor completely avoiding possible emissions of harmful,volatile compounds, e.g. of styrene, is of particular interest.Radical cross-linking processes do not yield very welldefined products, instead they give rise to different chainlengths of the linkages, irregular, incomplete consumptionof the double bonds of the polyester heterochain and directlinking of the latter. In addition, side-reactions such ashomopolymerisation of styrene occur [3]. So, we opted for awell-defined metal-mediated reaction that could circumventthese problems. Further considering an unsaturation in thelinkage a desirable feature, since it provides the possibilityfor additional cross-linking if demanded to alter theproperties of the final product, the metal-catalysed couplingof alkynes is highly attractive for its wide scope [4]. Here wereport a model reaction for an alternative cross-linking ofunsaturated polyesters