Free Radical Synthesis of Rubbers Made Entirely From Highly Unsaturated Vegetable Oils and Derivatives

摘要

In recent years, the scientific community has increasingly focused its efforts on the development of biorenewable materials for the fabrication of plastics and rubbers. Until now, plastics have been primarily petroleum-based, which results in the economic and environmental problems we are all familiar with. Recently, a growing number of bio-based substances have been shown, under the proper reaction conditions, to be viable alternatives to petroleum-based monomers. Carbohydrates, like cellulose or chitin, and proteins, such as soy or cheese protein are examples. In the search for newer options, the fatty acids present in vegetable oils are quite attractive, since they have been successfully introduced in the printing industry as part of fast drying inks, and as a glue for wood materials, but the synthesis of high molecular weight polymers from these materials has thus far been mostly unproductive. Vegetable oils appear to be particularly promising as bio-based monomers. They consist of triglycerides differing primarily in their chain lengths and the number of carbon-carbon double bonds present in the triglyceride unit. The presence of the double bonds makes these oils suitable for polymerization, either by cationic or free radical polymerization processes. The reactivity of the oils towards different polymerization techniques depends on the number and nature of the double bonds. Conjugated double bonds are known to be more reactive towards these types of polymerizations. Our research group has recently prepared and characterized a wide variety of plastic, elastomeric, adhesive, and rubbery materials made from a variety of vegetable oils. We have also succeeded in producing thermoplastics synthesized by the thermal copolymerization of highly reactive tung oil. The free radical copolymerization of epoxidized acrylated soybean oil (Ebecryl 860) has been reported by another research group. The free radical polymerization technique has always been appealing to industry, since it is a robust and generally cheap process that permits the use of a wide variety of monomers with or without relatively sensitive functionality due to the less rigorous reaction conditions it requires compared with other chain growth processes. Tung oil is readily available as a major product from the seeds of the tung tree. This oil is a triglyceride composed mainly (～84%) of alpha-elaeostearic acid (cis-9, trans-11, trans-13-octadecatrienoic acid). The high unsaturation and conjugation of the C=C bonds in tung oil makes this an excellent drying oil at room temperature. The Ebecryl 860 is a chemically modified soybean oil, which possesses –OH groups, and acrylic functionality that enhances its reactivity towards free radical polymerization. The synthesis of this modified vegetable oil has previously been reported by Dr. Wool’s research group. The present work describes the conversion of tung oil and Ebecryl 860 into solid rubbery materials by free radical copolymerization using t-butyl peracetate (TBPA) as the initiator. We also present chemical and mechanical data that further describe the properties associated with these new materials.