Synthesis and photo-initiated radical polymerization of methacrylates derived from bio-based ω-hydroxycarboxylic acids

The bio-based methacrylates 9-(methacryloyloxy)-10,18-dihydroxyoctadecanoic acid/9,18-dihydroxy-10-(methacryloyloxy)octadecanoic acid isomer mixture and 22-methacryloyloxydocosanoic acid were synthesized from 9,10-epoxy-18-hydroxyoctadecanoic acid and 22-hydroxydocosanoic acid. The white crystalline 9,10-epoxy-18-hydroxyoctadecanoic acid and cream-colored 22-hydroxydocosanoic acid were isolated from both the bark of Betula pendula and cork of Quercus suber after extraction of the milled plant materials with methanol, treating the insoluble residues with 2-propanole containing suspended sodium hydroxide, application of a working up procedure developed in this work for the resulting mixture, and purification of the products obtained. The new bio-based methacrylates show higher reactivity in the photoinitiated polymerization in comparison with the commercial laurylmethacrylate as detected by photo-differential scanning calorimetry (DSC). For comparison, traditional free radical polymerization of the new bio-based methacrylates was carried out in dimethylsulfoxide using 2,2'-azobis-(2-propionitrile) as initiator. Furthermore, the quantitative conversion of the bio-based monomers during the photoinitiated polymerization makes these bio-based monomers interesting for application in coatings. As expected, the photopolymer made from the 9-(methacryloyloxy)-10,18-dihydroxyoctadecanoic acid/9,18-dihydroxy-10-(methacryloyloxy)octadecanoic acid isomer mixture is amorphous. Interestingly, the photopolymer made from the 22-methacryloyloxydocosanoic acid contains crystalline structures as detected by DSC investigation.