Polyurethanes are an important class of engineering plastics with widespread applications as elastomers, foams, coatings, and sealants, among others. Owing to their microphase separated morphologies and extensive physical crosslinks, these polymers possess superior mechanical performance, abrasion resistance, toughness, and durability. Inspired by these properties, an approach to produce strong and tough materials using renewable protein feedstocks is presented, where proteins are covalently bonded to another chemically incompatible polymer chain through free radical copolymerization. Materials are synthesized using a two-step process, where the protein group is (meth)acrylated and then copolymerized with comonomers in the blend that make up the rubbery domain. The microphase separated material resembles polyurethane in both morphology and presence of physical crosslinks within the protein domain. Unlike the bulk polymerization approaches employed for liquid resin blends and isocyanates in polyurethane production, modification and copolymerization of proteins is typically performed in the solution state, which requires removal of solvent post polymerization. A solvent-free, bulk polymerization approach is developed to enable materials to be prepared without excessive shrinkage that occurs as materials are dried. Protein-miscible monomers, and low volatility ionic liquids and deep eutectic solvents (DES) are explored as replacements for conventional solvents. The monomer N,N-dimethylacrylamide, which has been shown to be a good solvent for protein mixture zein, is blended with non-volatile plasticizers and bulk polymerized with proteins to form thermosets. Polymerizable solvents are also developed through the introduction of polymerizable groups onto cations or anions of ionic liquids, and as the hydrogen bond donor in DES. Mechanical properties and morphology of the protein copolymers are studied using dynamic mechanical analysis (DMA), small angle X-ray scattering (SAXS) and microscopy.

Bulk polymerization of polyurethane-like protein copolymers

254th National Meeting (2017)

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