Polyethers with Reactive Side Chains—Hydroxy Polyethers

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Abstract
The author' work on preparing polyethers with reactive side chains is reviewed with emphasis on hydroxy polyethers. High molecular weight hydroxy polyethers were prepared by polymerizing epoxides containing a hydroxyl group protected with an appropriate group such as SiMe3 and then removing it by hydrolysis. Atactic and isotactic polyglycidol were made in this way using coordination catalysts. The isotactic polymer was found to be unusual since it did not crystallize readily from the melt and was relatively low melting (60°C). Poly(cis-1,4-dihydroxy-2,3-epoxybutane), PDHEB, was prepared, preferably from the cyclic acetone ketal which polymerized with i-Bu3Al-0.7H2o cationic catalyst at −78°C to a moderate molecular weight (ηinh up to 0.7) atactic polymer. This polymer is readily hydrolyzed with aqueous HCl treatment to atactic, amorphous, water-soluble PDHEB with a Tg of 80°C. PDHEB is melt stable to 200°C and can be molded to give brittle, clear films which readily pick up 5–10% H2O from the atmosphere to give properties like plasticized poly(vinyl chloride). The bis(trimethylsilyl) ether of cis-1,4-dihydroxy-2,3-epoxybutane was polymerized cationically with the i-Bu3 Al-0. 7H2O catalyst at −78°C to a fairly tactic, presumably racemic diisotactic, amorphous polymer, with ηinh of 0.16. A mechanism is proposed for this stereoregular polymerization based on a complexation of the Si side group of the last chain unit with the propagating oxonium ion. Hydroxy polyethers, in general, merit extensive future study since they are analogues of the biochemically important polysaccharides.