Enzymatic synthesis and polymerization of isosorbide-based monomethacrylates for high-T_g plastics

Isosorbide is a stiff bicyclic diol derived from glycose-based polysaccharides, and is thus an attractive building block for novel rigid bioplastics. In the present work a highly regioselective biocatalytic approach for the synthesis of isosorbide 5-methacrylate was developed. The Lipozyme RM IM (Rhizomucor miehei lipase) catalyzed process is straightforward, easily scalable and chromatography-free; a simple extractive workup afforded the monomer at >99% purity and in 87% yield. The developed strategy was applied for the synthesis of a series of monomethacrylated isosorbide derivatives. Radical polymerization of the monomers produced rigid polymethacrylates with a certain side group in either endo or exo configuration, exclusively, which generated materials with great diversity of properties. For example, the two regioisomeric polymers carrying hydroxyl groups reached a glass transition temperature at T_g = 167 °C. The polymer tethered with dodecanoate chains in exo position showed crystallinity with an unexpectedly high melting point at T_m = 83 °C. In contrast, the corresponding sample with dodecanoate chains in endo positions was fully amorphous with T_g = 54 °C. Efficient biocatalytic synthesis combined with attractive polymer properties opens up possibilities for production of these bio-based polymers on an industrial scale.