Residue vinyl acetate monomer process

The other benefit is that PVC /vinyl acrylate copolymers tend to have lower volatile organic contents (VOCs) than PVC/vinyl acetate copolymers. This is because the reaction kinetics favor consumption of the vinyl acrylate monomer during polymerization, yielding very low levels of residual vinyl acrylate monomer. Most PVC/vinyl acetate copolymers have residual vinyl acetate monomer, which can volatilize during processing or during the use life of the aiticle. The lower VOC content typical of PVC/vinyl acrylate copolymer resins versus their PVC/vinyl acetate counterparts make them an option in automotive applications with stringent fog requirements. 

Poly(vinyl alcohol) used to manufacture the poly(vinyl acetal)s is made from poly(vinyl acetate) homopolymer (see Vinyl polymers, vinyl alcohol polymers Vinyl POLYMERS, VINYL ACETATE POLYMERS). Hydrolysis of poly(vinyl acetate) homopolymer produces a polyol with predominantly 1,3-glycol units. The polyol also contains up to 2 wt % 1,2-glycol units that come from head-to-head bonding during the polymerization of vinyl acetate monomer. Poly(vinyl acetate) hydrolysis is seldom complete, and for some applications, not desired. For example, commercial PVF resins may contain up to 13 wt % unhydrolyzed poly(vinyl acetate). Residual vinyl acetate units on the polymer help improve resin solubility and processibility (15). On the other hand, the poly (vinyl alcohol) preferred for commercial PVB resins has less than 3 wt % residual poly (vinyl acetate) units on the polymer chain. 

The effect of oxygen on the polymerization characteristics of the monomer is quite dramatic. In bulk polymerization of reasonably purified vinyl acetate, the process is autoaccelerated from the start and goes nearly to completion with a residual monomer content of 2-4%. When the monomer distillation is carried out in contact with air, inhibiting impurities form quite rapidly. These lead to dead-end polymerizations with 30-40% unreacted monomer left in the product [17]. 

Polyvinyl alcohol is typically produced by the hydrolysis of polyvinyl acetate in a continuous process [52, 53], Although specialty grades of polyvinyl acetate may be formed using a batch process, the majority of commercial polyvinyl acetate is formed by the free radical polymerization of a vinyl acetate solution in methanol using a continuous process. Polymerization reactions are typically conducted at 55-85 °C, where heat is removed from the reaction mixture by condensing the monomer. At the end of the process, residual vinyl acetate and methanol are stripped from the reactor and recycled. Polyvinyl acetate formed by this process has long and short chain... 

Poly(vinyl alcohol) (PVA) is produced by alcoholysis of poly(vinyl acetate), because vinyl alcohol monomer does not exist in the free state [29]. (The term hydrolysis is often used incorrectly to describe this process.) Either acid or base catalysts may be employed for alcoholysis. Alkalien catalysts such as sodium hydroxide or sodium methoxide give more rapid alcoholysis. The degree of alcoholysis, and hence the residual acetate content, is controlled by varying the catalyst concentration. 

Vinyl acetate is polymerized free radically in bulk, emulsion, or suspension. Bulk polymerization occurs at the boiling temperature of the monomer (72.5 C at 1 bar), and yields highly branched polymer because of chain transfer via the ester groups (see also Section 20.4.3). Commercially, the polymerization is taken to a specific yield and the residual monomer is removed by thin-layer evaporation. Alternatively, continuous polymerization can be carried out in a tower. But this method only produces moderate degrees of polymerization since the tower process requires that the polymer should flow and the flow temperature should lie below the decomposition tempera-... 

The post-polymerisation of vinyl acetate (Vac)-containing latexes with tert-butyl hydroperoxide TBH/ascorbic acid (AsA) as a redox initiation system is investigated. Volatile organic compounds (VOCs) such as acetone and tert-butyl alcohol are produced in this process. The influence of the TBH/AsA ratio, initiator concentration, reaction temperature and feeding time on the reduction of residual VAc and VOC formation during the post-polymerisation is investigated. A total reduction of residual VAc monomer is achieved, with the formation of VOCs kept within acceptable limits. 11 refs. 

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