Synthesis and photoinduced radical polymerization of bio-based methacrylates comprising one to three methacrylate groups

Abstract

Bio-based methacrylates substituted with one methacrylate group (9-hydroxy-10-methacryloyloxy iso-propyl stearate/9- methacryloyloxy-10-hydroxy iso-propyl stearate, 9-hydroxy-10-methacryloyloxy n-butyl stearate/9-methacryloyloxy-10-hydroxy n-butyl stearate) or two methacrylate groups (ethane-1,2-diyl-bis(9-methacryloyloxy-10-hydroxy octadecanoate)/ethane-1,2-diyl-9-hydroxy-10-methacryloyloxy-9′-methacryloyloxy-10′-hydroxy octadecanoate/ethane-1,2-diyl-bis(9-hydroxy-10-methacryloyloxy octadecanoate) and propane-1,3-diyl-bis(9-methacryloyloxy-10-hydroxy octadecanoate)/propane-1,3-diyl-9-hydroxy-10-methacryloyloxy-9′-methacryloyloxy-10′-hydroxy octadecanoate/propane-1,3-diyl-bis(9-hydroxy-10-methacryloyloxy octadecanoate)) were synthesized in three steps starting from oleic acid by esterification in the first step, epoxidation in the second step, and epoxy ring opening reaction with methacrylic acid in the third step. Further methacrylates were obtained from eugenol (1(1- methacryloyloxy-2-hydroxy propyl)-3-methoxy-4-lauroyloxy benzene/1(1-hydroxy-2-methacryloyloxy propyl)-3-methoxy-4-lauroyloxy benzene) and trioleine, respectively by epoxidation in the first step and epoxy ring opening reaction with methacrylic acid in the second step, and from cardanol (methacryloyloxy cardanol) by esterification of cardanol with methacryloyl chloride. Depending on the starting material for methacrylate synthesis, atom economy ranges from 12 % to 50 %. Furthermore, renewable carbon is between 58 % and 85 % for the methacrylates although it may increase up to 100 % if bio-based methacrylic acid would be used for monomer synthesis. The methacrylates were investigated in photoinitiated radical polymerization using photo-DSC. Significant differences were observed in both the polymerization rate and conversion of the methacrylates. Furthermore, soluble polymethacrylates were obtained from the monomethacrylates, although crosslinked films were received using photoinitiated polymerization of the dimethacrylates and the trimethacrylate. The crosslinked polymer films were investigated by DMA resulting in glass transition temperature and β-relaxation as well as crosslink density. Crosslinking of the bio-based methacrylates may be interesting for application in coatings and adhesives.