Epoxidized polydienes

After 1965 it was discovered that expoxidized polydienes cannot substitute for classical epoxy resins, since they are inferior in some properties, especially a high viscosity brought about by the oxiranic oxygen content [95]. Possessing other valuable properties epoxidized polydienes, represented in the main by epoxidized polybutadiene, have found their own specific uses, in which they cannot be rivaled by epoxy resins. Literamre still appears in regard to some liquid polydiene epox-idation, covering appUcations of manufactured products as well as new commercial products [203—205]. 

The structure of epoxidized oligomers depends on the microstructure of the initial products, on their degree of epoxidation, and on the working conditions employed. In terms of these factors, in the epoxidized polydienes besides oxiranic groups there have been identified unreacted double bonds, too, as well as other structural motifs like acyloxy, hydroxyl, ketonic, and aldehydic groups and etheric links. 

The main property of epoxidized polydienes is their reactivity, due in the main to oxiranic groups and remaining unsaturation. 

Unsaturated double bonds in epoxidized polydienes can participate in the hardening process with the aldehydes provided that peroxidic initiators are also introduced into the system. Thermorigid materials appear with satisfactory dielectric constants under high-temperature conditions [215]. 

The systems made up of epoxidized polydienes and vinylic monomers (e.g., styrene) with mixtures of (especially unsaturated) anhydrides react in ionic catalysis or with radicalic initiators, yielding solid products with various applications. Mixed with other unsaturated polymers, epoxidized polydienes can become solid materials in the presence of radicalic initiators or can participate in sulfur vulcanization of rubber mixtures. 

A simple procedure for modifying epoxidized polydienes is their controlled hydrolysis. Thus, hydrophilic products can be produced with applications in the fibers industry [216] ... 

Numerous methods of modifying epoxidized polydienes aim at introducing into the structure of these resins some unsaturated groups with increased reactivity. One of these is the reaction of oxiranic groups with unsaturated carboxylic acids (acrylic, methacrylic, itaconic) [222] and, more frequently, with acrylic hydroxy esters, like 2-hydroxyethylmethacrylate, 2-hydroxyethylaciylate, and especially reaction products of the semiester type obtained by the reaction between hydroxyalkylmethacrylates and polycarboxylic acid anhydrides [223,224]. 

In the literature, two additional reactions following addition esterification have been treated using the cascade theory the addition esterification followed by polyetherification with epoxide groups in excess (a reaction used for crosslinking of carboxyl terminated polydienes) and addition esterification followed by transesterification. Transesterification often interferes wherever hydroxyester groups are formed, for example, in synthesis of linear oligomeric polyesters from diepoxide and acids. As has been explained before, polyetherification is an initiated reaction and, therefore, the statistical treatment offerend in Refs. should be revised. Below we show the treatment of transesterification for a system composed of a diepoxide and a dicar boxylic acid. 

Solution reactions of polydienes illustrate the diversity of chemical modifications on polymers (Scheme 11). Such polymers can be isomerized, cyclized, hydrogenat, epoxidized, and reacted with carbenes or enophiles. Most of these transformations increase the Tg s of the polymers with a consequent change in the physical/mechanical properties of the materials. 

Hydrocarbon solubility is important for diene polymerization, where a high 1,4 polymer microstructure is often desired. Polar solvents have a tendency to decrease the 1,4 content and elevate the 1,2 addition product. Hydrocarbon solubility is less of an issue for styrene or epoxide polymerization. Thus, the hydrocarbon soluble t-butyldimethylsilyl (TBDMS) protected initiator (5) (Table I) is recommended for high 1,4 polydienes. Most of the other conpounds in Table I can be used with other anionic monomers or where high 1,4 microstructure is not needed. 

The index m in Eqs. [10.33] and [10.34] is a measure of ability of a liquid to mpture a physical network of elastomer. Table 10.13 presents the values of the m parameter obtained at 298K for swelling of PBU crosslinked polydiene urethane epoxide, PDUE, crosslinked elastomers of butadiene-nitiile mbbers SCN-40, SCN-26, SCN-18 and also for crosslinked polyether urethane, PEU, synthesized from polytetramethylene oxide diol having M. 1000. Dibutyl phthalate, DBP, and tributyl phosphate, TBP, were used. 

Kona, B., Weidner, S.M., and Friedrich, J.F. (2005) Epoxidation of polydienes investigated by MALDI-TOF mass spectrometry and GPC-MALDI coupling. Int. J. Polym. Anal. Character., 10, 85-108. 

In general, epoxidation modifies the physical properties of liquid polydienes. Bleaching, increased specific weight, and increased viscosity are the main effects. If the first is an advantage, the last represents a disadvantage. It was found that this increase in viscosity is less prenounced in polydienes with an increased content in 1,2-struclures. 

It should be noted that the syndiotactic 1,2-PB epoxidation by the sodium hypochlorite and percarbonic acid salts carried out in the alkaline enables to prevent the disclosure reactions of the epoxy groups and a gelation process of the reaction mass observed at polydiene epoxidation by aliphatic peracids [31, 32], The functionalization degree of 1,2-PB in the reactions with the stated epoxidizing agents (a <16%, Table 3.1) is determined by the content of inner double bonds in the polymer. 

Along with the electronic factors determined by different electron saturation of the >C=C< bonds in 1,2- and 1,4-units of polydiene addition and the catalyst nature used in modification, the steric factors may also influence the reaction and the syndiotactic 1,2-PB functionalization degree. The examples of the steric control may serve the poly diene reactions with aromatic amines and maleic anhydride apart fi om the above considered epoxidation reactions of syndiotactic 1,2-PB by tret-huty hydroperoxide. 

The epoxidation of PBD with dimethyl dioxirane (DMD) as the oxidizing species shows that the epoxidation proceeds as expected with high stereoselectivity cis double bonds give c -epoxides. The latter was confirmed by NMR spectroscopic analysis. DMD can be prepared by conversion of acetone with Oxone, a potassium monopersulfate compound (Scheme 9). Prepared in situ or purified by distillation, DMD is an efficient oxidizing species for polydienes (Scheme 10) [127, 130]. 

The swelling kinetics of polydiene-urethane epoxide crosslinked elastomer (PDUE) was investigated for the experimental verification of the theoretical analysis. It was pro-... 

---