Epoxide polymerization reaction routes

Carbon dioxide is a widely available, inexpensive, and renewable resource. Hence, its utilization as a source of chemical carbon or as a solvent in chemical synthesis can lead to less of an impact on the environment than alternative processes. The preparation of aliphatic polycarbonates via the coupling of epoxides or oxetanes with CO2 illustrates processes where carbon dioxide can serve in both capacities, i.e., as a monomer and as a solvent. The reactions represented in (1) and (2) are two of the most well-studied instances of using carbon dioxide in chemical synthesis of polymeric materials, and represent environmentally benign routes to these biodegradable polymers. We and others have comprehensively reviewed this important area of chemistry fairly recently. Nevertheless, because of the intense interest and activity in this discipline, regular updates are warranted. 

Diels-Alder reactions of a -ethenylidenecyclanonesJ These dienophiles (1) are readily obtained by reaction of lithium acetylide with epoxides followed by oxidation, but tend to polymerize when heated. Fortunately catalysts, such as BF3 etherate or ZnCl2, permit Diels-Alder reactions to proceed at low temperatures. This cycloaddition provides a regio- and stereoselective route to spirocylic dienones (2) in fair to good yield. 

Researchers at Bayer AG addressed these critical issues and developed successful solutions enabling commercial application of Julia-Colonna-type epoxidation [35-40]. Starting with optimization of catalyst preparation, a straightforward synthesis based on inexpensive reagents and requiring a shorter reaction time was developed for the poly-Leu-catalyst [35], In particular, the reaction time for the new polymerization process was only 3 h when the process was conducted at 80 °C in toluene, compared with 5 days under classic reaction conditions (THF, room temperature). Furthermore, the catalyst prepared by the Bayer route is much more active and does not require preactivation [35-40],... 

Using route II [1], the desired silanes are accessible in a two-step synthesis The ft)-epoxyalkenes are obtained by partial epoxidation of the corresponding a,dienes with w-chloroperbenzoic acid. The lower product yields (47-50 %) compared to the direct epoxidation of side-reaction. The subsequent hydrosilylation requires the ethoxysilane HSi(OEt)3 as educt in order to exclude ring opening during the otherwise nescessary alcoholysis step. The lower reactivity of HSi(OEt)3 compared to chlorosilanes significantly reduces the formation of isomers but, on the other hand, considerably decreases the product yields (31-70 %). 

The previous studies of the reactions of polymeric organo-lithium compounds with epoxides suggested that these reactions might provide a facile route to a variety of functionalized polymers by attaching other substituents to the epoxide ring. Therefore, the functionalization of PSLi with styrene oxide was investigated. If this functionalization were efficient, a variety of substituents and more than one substituent at a time could be placed on the benzene ring of styrene oxide to form a variety of functionalized polymers as shown in eqn [9]. 

The condensation of an alcohol with an acid to give an ester with water as a by-product is a classical way to make polymers (Table 17.1,1). In alkyd resin cooking (Section 13.4), it was mentioned that additional reactions are those between anhydride and alcohol or epoxide and between free acid and alcohol and esters (transesterification). The simple polyester with its repeating dyadic structure can be dissolved in styrene (about 70 parts polyester to 30 parts styrene) and polymerized at room temperature by a free-radical route using a redox couple. (Methyl ethyl ketone peroxide plus cobalt naphthenate would be typical.) Glass-reinforced boat hulls and automobile bodies are made from such systems. In some cases, monomers more expensive than styrene can be justified. Methyl methacrylate, triallyl cyan-urate, and diallyl phthalate have been suggested by various sources. Flammability... 

---