Book Description

Polymeric materials have been prevalent in our everyday lives for quite a long time. Most of today's polymeric materials are derived from nonrenewable petroleum-based feedstocks. Instabilities in the regions where petroleum is drilled, along with an increased demand in petroleum, have driven the price of crude oil to record high prices. This, in effect, increases the price of petroleum-based polymeric materials, which has caused a heightened awareness of renewable alternatives for polymeric feedstocks. Cellulose, starch, proteins and natural oils have all been examined as possible polymeric feedstocks. Natural oils are commercially available on a large scale and are relatively cheap. It is projected that the U.S. alone will produce 21 billion pounds of soybean oil in the period 2008/2009. Natural oils also have the advantages of inherent biodegradability, low toxicity, high purity and ready availability. Most natural oils possess a triglyceride structure as shown in Figure 1. Most natural oils have a unique distribution of fatty acid side chains, along with varying degrees of unsaturation per triglyceride. Common fatty acid side chains in naturally occurring oils are palmitic acid (C16:0), a 16 carbon fatty acid with no unsaturation; stearic acid (C18:0), an 18 carbon fatty acid with no unsaturation; oleic acid (C18:1), an 18 carbon fatty acid with one double bond; linoleic acid (C18:2), an 18 carbon fatty acid with two double bonds; and linolenic acid (C18:3), an 18 carbon fatty acid with three double bonds. Of course, there are other fatty acids with varying degrees of unsaturation, but their abundance is usually minimal. All of the unsaturated fatty acids mentioned have naturally occurring cis double bonds, which is common for most unsaturated fatty acids. In addition, the afore mentioned fatty acids have the first double bond at the position of carbon 9 (C9), followed by carbon 12 (C12), if there are two degrees of unsaturation, then at carbon 15 (C15), if there are three degrees of unsaturation. In addition, the double bonds are not in conjugation. Table 1 gives the fatty acid make-up of linseed oil. It can be seen that linseed oil has an average of 6.0 double bonds per triglyceride. Its fatty acid content consists of 5.4% palmitic acid (C16:0), 3.5% stearic acid (C18:0), 19% oleic acid (C18:1), 24 % linoleic acid (C18:2) and 47% linolenic (C18:3). Table 1 also gives the fatty acid composition and varying degrees of unsaturation for various other naturally-occurring natural vegetable oils. The regions of unsaturation in natural oils allow for interesting polymer chemistry to take place. Some of this interesting polymer science, however, involves chemical modification of the regions of unsaturation. Acrylated epoxidized soybean oil (AESO) is prepared by epoxidation of the double bonds, followed by ring opening with acrylic acid. The resulting oil has both acrylate groups and hydroxyl groups. Wool and colleagues have further reacted the hydroxyl groups within the oil with maleic anhydride to produce maleated acrylated epoxidized soybean oil (MAESO). The MAESO has been copolymerized with styrene free radically to produce promising thermosetting sheet molding resins. Petrovi? and co-workers have directly ring opened the epoxidized oil to produce polyols that produce promising polyurethanes through condensation polymerization with diisocyanates. Our group's work initially focused on direct cationic copolymerization of the double bonds or conjugated double bonds of natural oils with monomers, such as styrene and divinylbenzene, to produce promising thermosetting resins. The only modification of the oils that was carried out in these studies was conjugation of the double bonds to enhance the reactivity of the oil. This work has been expanded recently with the incorporation of glass fiber to produce promising composites. We have also explored thermal polymerization techniques to make novel thermosets. This dissertation is divided into four chapters. The first chapter discusses the synthesis and characterization of biobased thermosets prepared by the free radical polymerization of conjugated linseed oil with commercially available monomers. The second chapter covers the synthesis and characterization of a chemically modified castor oil and its copolymerization with cyclooctene via ring opening metathesis polymerization (ROMP). The third chapter looks at the ROMP of a commercially available vegetable oil containing an unsaturated bicyclic moiety with dicyclopentadiene (DCPD) and characterization of the resulting materials. The fourth chapter discusses the reinforcement of a ROMP resin using short glass fibers to make composite materials.