Optimal Experimental Conditions for Improving the Yield of Poly(limonene) from Photoinduced Polymerization

Abstract

Limonene represents a possible candidate for the synthesis of polymers from renewable sources. However, because of some structural characteristics, the process yield tends to be considerably low (< 10%). In this sense, the evaluation of still unexplored alternative controlled strategies of synthesis, together with techniques of process optimization, can enable the increase in the polymer yield. Taking this into consideration, this study presents, for the first time, the optimal conditions for maximizing the poly(limonene) yield using a photoinduced polymerization route. The reactions were all conducted at a mild temperature (40 °C) and the polymer was characterized by nuclear magnetic resonance (1H-NMR and 13C-NMR). A face-centered design (FCD) was proposed for interpreting the effects of the reagent ratio (initiator, catalyst, and electron donor amine) on the polymerization. The monomer molar ratio was set to 100 with 6 h of polymerization time. All reagents exerted significant and positive effects on the yield, with the initiator having the most pronounced effect. The optimal conditions for maximizing the yield were as follows: molar ratios of the electron donor amine (PMDETA): 5‒8.5; catalyst (TX): 1‒1.7; and initiator (TBE): 1.7. Thus, ~ 18% yield could be achieved using a molar ratio of 100:8.5:1.7:1.7 (monomer:PMDETA:TX:TBE). It was observed that the polymer had good adhesion to steel when dried and moderate adhesion to glass. The polymer was insoluble in water and soluble in ethanol, tends to form suspension in solution of ethanol/water, in addition to being partially soluble in tetrahydrofuran and chloroform. These characteristics indicate that the material prepared herein is a promising renewable additive for coatings, films, or adhesives.