GB819291A - Improvements in or relating to the preparation of polyvinyl acetate - Google Patents

Abstract

Vinyl acetate is polymerized using, as catalyst, a mixture of a vanadium compound and an organometallic compound of an alkali or alkaline earth metal, zinc or aluminium. Crystalline polyvinyl acetate may thus be produced. Hydrolysis with an alkaline agent, e.g. alcoholic alkali or acid, yields polyvinyl alcohol with a very high degree of crystallinity, and particularly suitable for fibres which are stronger and less soluble than usual polyvinyl alcohol fibres. Polymerization may be batch-wise or continuous in an inert liquid medium, e.g. hexane, heptane, cyclohexane, benzene, toluene, xylene, ethyl chloride, methyl chloride, methylene chloride, ethylene chloride, chlorbenzene, diethyl ether, dioxane or tetrahydrofuran. Temperatures may be - 50 DEG to 150 DEG C. and pressure may be atmospheric or sub- or super-atmospheric. Suitable vanadium compounds are the dichloride, trichloride, trifluoride, oxychloride, oxydichloride, pentoxide or trioxide, alkyl vanadates and vanadium oxyacetylacetonate. Suitable organometallic compounds are butyl-lithium, amyl sodium, phenylsodium, dimethyl magnesium, diethyl magnesium, diethyl zinc, butyl magnesium chloride, phenyl magnesium bromide, triethylaluminium, tributylaluminium, triisobutylaluminium, trioctylaluminium, tridodecylaluminium, dimethyl aluminium chloride, diethylaluminium bromide, diethylaluminium chloride, ethylaluminium dichloride, aluminium sesquichloride, dipropylaluminium fluoride, diisobutylaluminium fluoride, diisobutylaluminium chloride, diethylaluminium hydride, ethyl aluminium hydride, diisobutylaluminium hydride, sodium aluminium tetraethyl, lithium aluminium tetraoctyl and sodium aluminium triethyl chloride. The vanadium compound may combine, e.g. with reduction to a lower valency state, with the organometallic compound, in which case additional organometallic compound (the same or different) must be added before polymerization. The catalysts may be added as solutions or suspensions. They are preferably finely divided. If desired a complexing agent for the organometallic compound which is an ester, ether, tert. amine, ketone or nitroaromatic compound, e.g. diethyl ether or tetrahydrofuran, may also be added. In Example (1) vinyl acetate was polymerized in an atmosphere of nitrogen, in diethyl ether containing a mixture of tri-isobutyl aluminium and vanadium trichloride in n-heptane. Anhydrous ethanol was added to stop polymerization. The polymer was extracted with boiling cyclohexanone, dried, dissolved in boiling xylene, filtered and recovered. It was crystalline. Example (2) is similar using tetrahydrofuran as reaction medium. The polyvinyl acetate was dissolved in methanol sodium methoxide added, and the mixture refluxed. The resulting polyvinyl alcohol had a very high degree of crystallinity and yielded strong insoluble fibres. Example (3) is similar to Example (2) but uses triethylaluminium instead of triisobutylaluminium.