Vinyl-acetate-methanol-water mixture

One early publication advocated the precipitation of poly(vinyl acetate) from toluene solution with a methanol-water mixture or from an acetone solution with 50% water in methanol at 25°C [58]. 

Since the volumes of solvents and nonsolvents become quite large during fractional precipitation, a change in the composition of the precipitant may be desirable. Wagner, for example, precipitates a solution of 150 gm of poly(vinyl acetate) in 2300 ml of acetone with up to 3900 ml of 1 1 (v/v) methanol-water. Further fractions were isolated by the gradual addition of up to 800 ml of a 1 2 (v/v) methanol-water mixture at 30 C [61]. 

Concentrated aqueous HC1 (36%) (0.5 ml) is added to a mixture of 0.10 mol of the vinyl ether adduct and 50 ml of methanol. The mixture is heated for -15 min in a bath at 50 C, then the acetaldehyde acetal and the greater pan of the solvent is removed using a rotary evaporator (note 1). Water (-50 ml) is added, after which the product is extracted with Et20. The ethereal solution is washed with water, then dried over MgSC>4 or K2C03. The product is isolated in the usual manner. 

To stop the polymerization reaction, a polymerization inhibitor is added to reaction mixture. Unreacted ethylene gas is evaporated and removed from the solution. Further, unreacted vinyl acetate is extracted from the copolymer solution. Eventually, methanol is recovered by precipitation with a water containing separating and purifying solution. The vinyl acetate and methanol thus recovered may be reused in the copolymerization process. 

To a three-necked flask equipped with a stirrer, condenser, and dropping fiinnel are added 1700 gm of water, 500 gm (2.6 mole) of A-vinylcarbazole, 3 ml of a 3% solution of 86-89% hydrolyzed poly(vinyl acetate), and 0.5 gm sodium acetate. The mixture is stirred at 80°C while 5 gm of azobisisobutyronitrile is added. In 2 min the temperature rises to 97°C and after 5-10 min it drops. The polymer suspension is cooled and filtered. The residue is washed with methanol and acetone, and then extracted for several hours with acetone in a Soxhlet extractor. The polymer weighs 400 gm (80%). 

Addition of solvents as solubilizers is important in the dissolution of polymers. Poly(vinyl acetate) is insoluble in pure ethanol, but dissolves fairly readily in ethanol containing 3% water. Cellulose triacetate is sparingly soluble in pure trichloromethane, but is readily soluble in trichloromethane containing 3% methanol. Many paint resins dissolve more readily in aromatic-containing naphtha fractions than in pure naphtha. Poly(vinyl chloride) is sparingly soluble in acetone and carbon disulfide, but is more readily soluble in a mixture of the two solvents. 

Coxon (1993) has recommended a spot test to identify the presence of acetates present in cellulose acetate and poly (vinyl acetate). Four pre-mixed reagents in turn are applied to a sample of the unknown plastic. One millilitre of a 6 per cent solution by weight potassium hydroxide in methanol is added to the sample. Next, 1 to 2 drops of a saturated solution of hydroxylamine hydrochloride in methanol are added and the mixture is either left to stand for at least 3 minutes or warmed gently. One drop 1 per cent ferric chloride in water is added and the mixture shaken. Finally, a 10 per cent solution of hydrochloric acid is added dropwise with shaking until a colour develops. Burgundy red indicates the presence of cellulose acetate or poly (vinyl acetate). Pale purple-red colouration is said to indicate cyanoacrylate or cellulose nitrate, but the diphenylamine test should be carried out if cellulose nitrate is suspected. 

A methyl acetate-water mixture is produced in large quantities by the purification of terephthalic acid (PTA). The manufacture of poly vinyl alcohol (PVA) also produces large quantities of methyl acetate (1.68 kg/kg PVA). Methyl acetate is a comparatively low-value solvent, hence it has to be sold at a lower price. Alternatively, it can be hydrolyzed efficiently to recover methanol and acetic acid for reuse in the process [26-28]. 

Figme 6.17. Trajectories of heteroextractive distillation (a) distillate from azeocolumn to decanter and a stream of the entrainer from decanter and additional entrainer to azeocolumn for separation vinyl acetate(l)-methanol(2)-water(3) mixture (b) distillate from azeocolumn to decanter and a stream of the entrainer from decanter and additional entrainer to azeocolumn for separation chloroform(l)-acetone(2)-water(3) mixture. Regions of two Kquid phases Reg/,i /,2 are shaded. 

Alternative LC methods in the separation of NPEO resulting in a separation based on EO number include the use of an alumina column using an ethylene oxide-n-hexane mixture as mobile phase [37], of a cyanosilica column and a mobile phase gradient of toluene and a 10 88 2 mixture of 0.5 mmol/1 sodium acetate in toluene, methanol, and water [38], and of a poly(vinyl alcohol) column and 10-55% acetonitrile in 30 mmol/1 aqueous ammonium acetate as mobile phase [39]. Ion-pair LC-MS, using 5 mmol/1 triethylamine in the mobile phase, was applied in the analysis of phenols and NPEC [33]. 

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