Perspective
Crosslinked Polymers Based on Monomers Derived from Renewable Resources and Their Application Potential
Veronika Strehmel* and Bernd Strehmel
Niederrhein University of Applied Sciences, Faculty of Chemistry and Institute for Coatings and Surface Chemistry, Adlerstrasse 32, D-47798 Krefeld, Germany
E-mail: veronika.strehmel@hsnr.de
Abstract
Possible structural variation of a bio-based dimethacrylate derived from oleic acid and ethylene glycol is discussed as well as sources to obtain the starting material for manufacturing of this monomer. Furthermore, aspects influencing the transfer of a newly developed product or further scientific result to application are included into the discussion as well focusing to manufacturing processes and development of a new product for the market.
KEYWORDS
bio-based monomer, dimethacrylate, photo-initiated polymerization, crosslinked polymer, application potential
INTRODUCTION
Nowadays, there is no doubt that the modern society demands to search for alternative materials having the capability to replace fossil resources partially or completely in the future. Generation of fossil resources has needed a long period in the earth’s history. Nevertheless, they have been used with continuous increasing amount in the last two centuries to generate materials. Thus, this topic closely relates to the chemical industry that has used fossil resources as both starting material for product manufacturing and energy source, which appears as very important for the usually highly energy intensive chemical processes. Two ways appear purposeful to solve this problem. These ways include both renewable energy sources and renewable materials. Sunlight seems useful as direct or indirect renewable energy source. Various plants produce a broad variability of biomass catalyzed by enzymes in the presence of sunlight as well. Discussions have continued in the literature to search regarding selection of available plant species outside the competition with food production for humans and animals, efficiency of product manufacturing from biomass, and re-using the material after its application.[1-4] Beside the high molecular weight natural products, such as cellulose, hemicellulose and lignin, low molecular weight compounds have received increased interest recently.[4-6] The latter include terpenes and triglycerides, as well as products derived from triglycerides like glycerin and various fatty acids. Nevertheless, some of them interfere the food chain, which appears critical in countries with high population density or regions with food shortage. Thus, resources based on waste have moved into the focus.
Furthermore, several bio-based linear aliphatic, aromatic, and cycloaliphatic compounds have been successfully converted into (meth)acrylates that are interesting monomers for manufacturing of polymers.[7-14] Among these bio-based monomers is a new dimethacrylate synthesized in three steps as shown in Scheme 1. The synthesis starts with esterification of oleic acid with ethylene glycol, it continues with epoxidation of the two double bonds of the ethylene dioleate, and ring opening reaction of the resulting diepoxy compound with methacrylic acid is the final step.[12] Moreover, the new bio-based dimethacrylate was polymerized in thin film using photoinitiated radical polymerization mechanism applying ultraviolet-technology (Scheme 1) to form an insoluble crosslinked polymer film showing high hydrophobicity detected by contact angle measurements.[12]Crosslinking polymerization of the bio-based dimethacrylate alone or in the presence of further bio-based methacrylates comprising aromatic structures resulted in glass transition temperature increase of the highly hydrophobic crosslinked polymer films that makes them interesting for application e. g. as water-repellent coating for surface protection. The latter may be of importance for surface protection against corrosion. Such materials possess additionally potential in medical application as long as the natural origin would not cause incompatible responses of the body that synthetic materials sometimes do.