Following these criteria, a solvent-free reaction of the lactate esters with methacrylic anhydride using the ion exchange resin Amberlyst 15 as a means of heterogeneous catalysis was found to be a very efficient method for incorporating photopolymerizable groups. Using Amberlyst 15 as a catalyst provides the main benefit of being easily recoverable and reusable for subsequent reactions. The reaction conditions were initially established for ethyl lactate. Impressively, > 95% conversion was obtained after just 1 h of reaction at 70 °C with a final yield of 77% after an aqueous work-up to remove methacrylic acid. The successful introduction of the methacrylate group was confirmed by NMR spectroscopy (Figure ), with characteristic peaks at 6.19, 5.62 and 1.96 ppm stemming from the two alkene protons and the methyl group. Notably, testing the re-usability of the catalyst by using it in 10 consecutive reactions showed no decrease in the conversion (SI Figure ). Furthermore, we compared the use of Amberlyst 15 with 4-(dimethylamino)pyridine (DMAP), a commonly chosen catalyst for methacrylation reactions. Using DMAP resulted in a conversion of 81% after 5 days, while Amberlyst 15 shortened the reaction time to just 1 h with an even higher conversion of 96%. In a second step, the reaction was adapted to methyl and butyl lactate to provide a wider range of biobased monomers that can later be used for 3D printing. As before, the reactions were monitored using NMR spectroscopy (Figure ). When comparing the results of the functionalization reactions using the different lactate esters, it could be observed that the alkyl chain length of the lactate esters inversely correlates with the reaction time and conversion (see Table ). While methyl lactate reached a conversion of 100% after 1 h, the functionalization of butyl lactate progressed more slowly with a conversion of 88% after 14 h. An effect of the chain length on the reaction times was expected, as the use of an ion exchange resin leads to sterical hindrance governing the reaction kinetics, while the inductive effect of the alkyl chain plays a subordinate role. Notably, the overall reaction yields of 77%, 74% and 84% for MeLMA, ELMA and BuLMA, respectively, exhibit an opposite trend. This is caused by an increase in the hydrophobicity with longer alkyl chains, which lowers product loss during the aqueous work-up. The present reaction conditions outperform those previously reported in terms of efficiency and from a green chemistry standpoint by using a reusable catalyst.