Bio-based polymer networks by thiol-ene photopolymerization of allylated l-glutamic acids and l-tyrosines

Abstract

Triallylated l-glutamic acid and l-tyrosine (A3E amd A3Y) and their tetraallyl derivatives (A4E and A4Y) were synthesized by reactions of l-glutamic acid and l-tyrosine with allyl bromide in the presence of potassium carbonate, respectively. Thiol-ene photopolymerizations of the allylated amino acids and a pentaerythritol-based tetrathiol (S4P) at allyl/SH 1/1 in the presence of photo-initiators produced photo-cured products (pA3E-S4P, pA3Y-S4P, pA4E-S4P and pA4Y-S4P). Furthermore, thermal post-curing after photo-curing of allylated amino acid/S4P mixtures containing photo-initiators and a thermal initiator produced photo and thermal cured products (ptA3E-S4P, ptA3Y-S4P, ptA4E-S4P and ptA4Y-S4P). Although the thermally post-cured products became dark in color, all the cured films were flat and had smooth surfaces. The FT-IR analysis revealed that allyl and thiol conversions increased by the thermal post-curing for all the curing systems. The glass transition temperature (Tg), 5% weight loss temperature (Td5), tensile strength and tensile modulus of each thermally post-cured product were higher than those of the corresponding photo-cured product, reflecting the increase of crosslinking density by the thermal post-curing. Also, A4E- and A4Y-based cured products exhibited higher Tgs, Td5s, tensile strengths and moduli than the corresponding A3E- and A3Y-based cured products, respectively. Especially, ptA4Y-S4P exhibited the highest Tg (24.4 °C), Td5 (319 °C), tensile strength (18.2 MPa) and tensile modulus (1037 MPa) among all the cured products.