Biobased Vinyl Levulinate as Styrene Replacement for Unsaturated Polyester Resins Sylvain Cousinet, 1 Ali Ghadban, 1 Ime ` ne Allaoua, 1 Fr ed eric Lortie, 1 Daniel Portinha, 1 Eric Drockenmuller, 1,2 Jean-Pierre Pascault 1 1 Universit e Claude Bernard Lyon 1, INSA-Lyon, Ing enierie des Mat eriaux Polyme ` res (UMR CNRS 5223), 69622, Villeurbanne Cedex, France 2 Institut Universitaire de France (IUF) Correspondence to: E. Drockenmuller (E - mail: eric.drockenmuller@univ-lyon1.fr) or J.-P. Pascault (E - mail: jean-pierre.pascault@ insa-lyon.fr) Received 30 July 2014; accepted 5 September 2014; published online 00 Month 2014 DOI: 10.1002/pola.27397 ABSTRACT: Vinyl levulinate (VL) is used as a biobased reactive diluent in styrene (St)-free unsaturated polyester resins (UPR). The reactivity ratios for the radical copolymerization of VL with diethyl fumarate (DEF) are determined by the Jaacks method (r VL 5 0.01 and r DEF 5 0.81 at 60  C in DMSO-d 6 ). The properties of UPRs having a stoichiometric ratio between unsaturated groups from the UPR and either St or VL are compared. Defect-free, slightly yellow, transparent, and rigid thermosets are obtained after a mild curing cycle. Due to unfavorable reac- tivity ratios about 5.5 wt % of unpolymerized VL remains inside the network and acts as plasticizer. Consequently, compared with St-based ones, VL-based UPRs exhibit lower a relaxation (T a 5 180 and 100  C, respectively), lower elastic moduli at the rubbery plateau (G 0 5 10 8 and 10 7 Pa) and lower mechanical properties as measured by three points bending tests. Strain at break (e f 5 1.8 6 0.2%) and Charpy impact strength (2.7 6 0.3 kJ m 22 ) are comparable independently of the RD chemical nature. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 00, 000–000 KEYWORDS: mechanical properties; polyester resins; radical polymerization; renewable resources; thermosets INTRODUCTION Unsaturated polyester resin (UPR) formula- tions are classically composed of a low molar mass unsatu- rated polyester (UP) prepolymer, which is solid at room temperature and of styrene (St), which acts as reactive dilu- ent (RD). 1,2 The UP prepolymer is generally a multifunctional oligomer, which contains about 5–15 fumarate (F) groups per chain depending on the number average molar mass (M n 5 1000–3000 g mol 21 ; Scheme 1). Upon annealing, radi- cal copolymerization occurs between St and F double bonds yielding a crosslinked polymer network. Experimental reac- tivity ratios determined either by the terminal model (r F 5 0.07 and r St 5 0.30) 3 or considering a penultimate effect (r F 5 0.02 and r St 5 0.22) 4 both reveal a well- pronounced tendency for alternating copolymerization between the two reactants with St being more reactive than F. These formulations are widely used as coatings or as con- stitutive matrices of chopped glass fiber-based composites such as sheet molding (SMC) and bulk molding (BMC) com- pounds. The combination of good mechanical properties, low density, and low cost has made these formulations very pop- ular in construction, transportation, and electronic applica- tions. Vinyl ester resins (VERs), which also constitute an important class of thermosetting formulations, are mainly produced by the esterification of the diglycidyl ether of bisphenol A with methacrylic acid. Although both VERs and UPRs use St as RD, VER possesses properties better suited for high performance applications. One of the main roles of the RD is to reduce the viscosity of the formulation to ensure good processability and properties of the final material. However, the use of St brings many safety concerns and as early as in 1982 P. E. Froehling wrote: 5 “In recent years two problems have risen concerning the use of St. First, the toxicity of the monomer may be a possible threat to the health of workers in the polyester processing industries. Secondly, the strong smoke evolution which occurs when St-cured polyesters are subjected to fire conditions forms a serious limitation in the application of these materials in building.” As an alternative to St, Froeh- ling proposed a combination of vinyl propionate and dime- thacrylate as a good compromise between reactivity and properties. But 30 years later, even if toxicity of St has been Additional Supporting Information may be found in the online version of this article. V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 00, 000–000 1 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE