Epichlorohydrin cationic polymerization mechanism

Epichlorohydrin Elastomers without AGE. Polymerization on a commercial scale is done as either a solution or slurry process at 40—130°C in an aromatic, ahphatic, or ether solvent. Typical solvents are toluene, benzene, heptane, and diethyl ether. Trialkylaluniinum-water and triaLkylaluminum—water—acetylacetone catalysts are employed. A cationic, coordination mechanism is proposed for chain propagation. The product is isolated by steam coagulation. Polymerization is done as a continuous process in which the solvent, catalyst, and monomer are fed to a back-mixed reactor. Pinal product composition of ECH—EO is determined by careful control of the unreacted, or background, monomer in the reactor. In the manufacture of copolymers, the relative reactivity ratios must be considered. The reactivity ratio of EO to ECH has been estimated to be approximately 7 (35—37). 

Several dyes have been found to sensitize the cationic polymerization of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether initiated by diaryliodonium salts (109,110). Acridinium dyes such as acridine orange and acridine yellow were found to be effective sensitizers. One example of a benzothiazolium dye (setoflavin T) was also reported, but no other class of dye nor any other example of a dye absorbing at longer wavelengths were discovered. Crivello and Lam favored a sensitization mechanism in which direct energy transfer from the dye to the diaryliodonium salt occurred. Pappas (12,106) provided evidence that both energy transfer and electron transfer sensitization were feasible in this system. 

Although butyl rubber is by far the most important commercial elastomer to be synthesized by cationic polymerization, several heterocyclic monomers provide useful elastomeric materials via this mechanism also. Epichlorohydrin can be polymerized to high molecular weight using a complex catalyst formed from a trialkylaluminum compound and water as shown in Eq. (58) [64, 130-132], For copolymerizations with ethylene oxide, a catalyst formed from a trialkylaluminum compound, water, and acetylacetone is useful [64,130], The mechanism proposed for these polymerizations is... 

Okamoto [92] has studied the cationic polymerization of epichlorohydrin in the presence of ethylene glycol, using as initiator triethyloxonium hexafluoro-phosphate, and proposed a propagation mechanism similar to living polymerization. 

Polyepichlorohydrin is manufactured by a continuous solution polymerization process using aluminum-based catalysts with base monomers of epichlorohydrin (ECH), ethylene oxide (EO), and AGE. A cationic coordination mechanism is suggested as the chain propagation mechanism. The commercial polymer is 97%-99% head-to-taU and has been shown to be stereo random and atactic. The CO, GCO, ECO, and GECO polymers are amorphous and linear [1]. 

Polyethers are prepared by the ring opening polymerization of three, four, five, seven, and higher member cyclic ethers. Polyalkylene oxides from ethylene or propylene oxide and from epichlorohydrin are the most common commercial materials. They seem to be the most reactive alkylene oxides and can be polymerized by cationic, anionic, and coordinated nucleophilic mechanisms. For example, ethylene oxide is polymerized by an alkaline catalyst to generate a living polymer in Figure 1.1. Upon addition of a second alkylene oxide monomer, it is possible to produce a block copolymer (Fig. 1.2). 

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