Ethoxysilyl-modified hyperbranched polyesters as mulitfunctional coupling agents for epoxy-silica hybrid coatings

Partially ethoxysilyl-modified hyperbranched aliphatic aromatic polyesters (HBPs) were effectively used as toughening as well as multi-site coupling agents in the preparation of organic inorganic UV-thermal dual-cured epoxy/TEOS coatings. Through chain transfer reaction of the phenolic terminal units of the HBPs effective incorporation in the epoxy resin is achieved in the photo-initiated cationic polymerization whereas the ethoxysilane groups allow effective formation of a strongly interconnected inorganic organics network during the in-situ sol-gel process with TEOS by binding the organic to the inorganic phase. Under those conditions, the addition of the inorganic precursor to the epoxy/HPB (20 wt%) system induced an increase of the storage modulus and more important, an improvement of the viscoelastic properties by extending the performance of the elastic modulus to higher temperatures. Thus, highly transparent hybrid coatings with enhanced thermal-mechanical and surface hardness properties resulted by the use of the partially ethoxysilyl-modified HBPs as multifunctional coupling agents. (C) 2011 Elsevier Ltd. All rights reserved.