Effect of oxirane groups on curing behavior and thermal stability of vinyl ester resins

Abstract

ABSTRACT:The effects of oxirane groups in vinyl ester (VE) resin and reactive diluent on curing characteristics and thermal behavior of cured resins are described. Stoichiometric (0.5:1, sample A) as well as nonstoichiometric (0.5:0.85, sample B) ratios of the diglycidyl ether of bisphenol-A (DGEBA) and methacrylic acid (MA) were used for the synthesis of VE resins. Resin sample B had more residual epoxy groups because of the stoichiometric imbalance of the reactants. VE resins thus obtained were diluted with methyl methacrylate (MMA; 1:1, w/w), and controlled quantities of epoxy groups were introduced by partial replacement of MMA with glycidyl methacrylate (GMA), keeping the overall ratio of resin and reactive diluent constant. Increase of GMA content in resin A or B resulted in a decrease in gel time, indicating that the curing reaction is facilitated by the presence of epoxy groups. An increase in initiator content also reduced the gel time. In the differential scanning calorimetry (DSC) scans, a sharp curing exotherm was observed in the temperature range 107 Ϯ 3-150 Ϯ 1°C. The onset temperature (T onset ) and peak exotherm temperature (T exo ) decreased with increase in GMA content. Heat of curing (⌬H) also increased with increase in GMA content. A broad exotherm was observed after the initial sharp exotherm that was attributed to the etherification reaction. Cured VE resins were stable up to 250 -260°C, and started losing weight above this temperature. Rapid decomposition was observed in the temperature range 400 -500°C.

New trends in vinyl ester resins

“…Neat VERs having high viscosity (10 5 cps) may vary from semisolid to solid. Reactive or nonreactive diluents are used to provide workable viscosity levels and enhanced reactivity (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.…”

Green methacrylated lignin model compounds as reactive monomers with low VOC emission for thermosetting resins

“…These VE resins encompass exceptional mechanical and chemical properties coupled with outstanding corrosion resistance and heat performance, which makes them a good selection for many end uses, such as polymer matrix composites and especially fiber reinforced polymer (FRP) for construction applications [1][2][3], coatings for solvent storage tanks, sewer pipes [4][5][6] and adhesives [7], etc. Petroleum based reactive monomers, i.e., styrene and different acrylates, also act as a linear chain extender and improve the polymer performance such as crosslink density, mechanical strength, percent elongation, hardness, chemical resistance, scratch resistance and surface finish, etc., as they delay the onset of gelation during curing and also address the diffusion limitation issue [8][9][10][11][12][13][14]. However, as these petroleum based reactive monomers have been designated as a hazardous pollutant due to their high VOC, the attempts are being made to replace these monomers either with bimodal blends of VE monomers [15,16] or with non-volatile fatty acid monomers obtained from renewable resources [17] in order to reduce emission.…”

Synthesis, characterization, and kinetics study of thermal decomposition of epoxidized soybean oil acrylate

“…8 In addition, it is copolymerized with a low molecular weight species, such as styrene, to modify the properties of the polymer and lower the resin viscosity. 9 The low viscosities of this resin make it ideal for inexpensive polymer composite fabrication processes, such as vacuumassisted resin-transfer molding.…”