Rev Chem Eng 2014; 30(6): 567–581 Shipra Jaswal and Bharti Gaur* New trends in vinyl ester resins Abstract: Vinyl ester resins (VERs) are high-performance unsaturated resins derived by the addition reaction of var- ious epoxide resins with α-β unsaturated carboxylic acids. These resins have always been classified under unsatu- rated polyester resins. However, VERs have remarkable corrosion resistance and superior physical properties as compared with these conventional polyester resins, which make VERs a class of their own and hallmark of today’s resin industries. Hence, there is a need to review the avail- able literature on this important class of thermosetting resins separately. In this article, an attempt is made to review the state of the art of VERs, including synthesis, characterization, curing, thermal, chemical, oxidative properties, and applications. The main focus is on the lat- est developments in this area. Keywords: corrosion resistance; cross-linking reactions; mechanical properties; thermosetting resins; vinyl ester resins. DOI 10.1515/revce-2014-0012 Received February 20, 2014; accepted July 14, 2014; previously pub- lished online September 6, 2014 1 Introduction Vinyl ester resins (VERs) are widely used thermosetting resins in solvent storage tanks, sewer pipes, building and construction, coating, automobile structural parts, swim- ming pools, and marine composites (Brown and Mathys 1997, Mouritz and Mathys 1999, Varma and Gupta 2000, Zhang et al. 2000, Brody and Gillespie 2005) because of their low cost, excellent chemical and corrosion resist- ance, outstanding heat performance, favorable mechani- cal properties, and better processibility. These are the addition products of epoxy resins and α-β unsaturated carboxylic acids (Young 1976, Launikitis 1982) and are structurally similar to unsaturated polyester (UPE) resins (Figure 1). Shell Chemical Co. first commercialized these resins in 1965 under the trade name Epocryl. Dow Chemi- cal Co. then introduced a similar series of resins under the name Derakane. VERs are used in place of UPE resins since the unreacted carbon-carbon double bonds and the ester group, present in the backbone of UPE resins after curing, provide sites for hydrolytic attack, oxidation, and halo- genation, which make the cured UPE resin unsuitable for aggressive environments (Mallision 1987, Cheremisinoff and Cheremisinoff 1995, Juska and Puckett 1997), whereas in VERs, the ester linkages are present only at the terminal ends of the chains. VERs incorporate the thermal stability and mechanical strength of the epoxy backbone, and the presence of double bonds at the chain ends provides it the ease of cure that is comparable with that in UPE resins. These resins are costlier than UPE resins but are still widely used since they have excellent chemical resistance, low water absorption, as well as low shrinkage during cure as compared with polyester resins. Moreover, unlike epoxy resins, vinyl esters (VEs) have controlled cure rate and do not need any curing agent to form a cured network. Neat VERs having high viscosity (10 5 cps) may vary from semi- solid to solid. Reactive or nonreactive diluents are used to provide workable viscosity levels and enhanced reactiv- ity (Varma et al. 1985, Bhatnagar and Varma 1989, Gaur and Rai 1992a,b, Choudhary and Varma 1993, Malik et al. 2001) to control the cross-link density and affect strength, percentage elongation, hardness, chemical resistance, scratch resistance, and surface finish. The physical and handling properties of VERs depend on the source of vinyl termination (methacrylate or acrylate), the amount and type of co-reactant, and the molecular weight of the resin backbone. Although acrylate VERs are more suscep- tible to hydrolysis than methacrylate VERs are, they are preferred in radiation cure inks and coatings because of better reactivity (Launikitis 1982). The use of other unsatu- rated acids such as crotonic and cinnamic acids has also been reported (Jackson 1980, Zaske 1998). Although con- siderable work has been done on VERs, a comprehensive review dealing with the state of the art of these resins has not been published. In this paper, an attempt was made to review the synthesis, characterization, and physicochemi- cal, thermal, and mechanical properties of VERs. VERs with wide structural variation can be prepared by the reaction of different epoxide resins with various unsaturated acids (Figure 2). *Corresponding author: Bharti Gaur, Department of Chemistry, National Institute of Technology, NIT Hamirpur (H.P.) 177005, India, e-mail: bhartigaur@gmail.com Shipra Jaswal: Department of Chemistry, National Institute of Technology, NIT Hamirpur (H.P.) 177005, India Brought to you by | University of Utah Authenticated Download Date | 11/27/14 1:30 PM