Atactic poly hydrolysis

In Older to investigate the effect that unneutralized atactic poly(methacrylic acid) (at-PMAA) has on the rate of a neutral hydrolysis reaction, several acyl-activated esters (1) and a series of l-acyl-l,2,4-triazols (2) were chosen as subtrates [47] ... 

The poly(vinyl alcohol) made for commercial acetalization processes is atactic and a mixture of cis- and /n j -l,3-dioxane stereoisomers is formed during acetalization. The precise cis/trans ratio depends strongly on process kinetics (16,17) and small quantities of other system components (23). During formylation of poly(vinyl alcohol), for example, i j -acetalization is more rapid than /ra/ j -acetalization (24). In addition, the rate of hydrolysis of the trans-2iQ. -A is faster than for the <7 -acetal (25). Because hydrolysis competes with acetalization during acetal synthesis, a high cis/trans ratio is favored. The stereochemistry of PVF and PVB resins has been studied by proton and carbon nmr spectroscopy (26—29). 

Because of acid-catalyzed hydrolysis of N-vinylpyrrolidone in water, polymerization was carried out in organic solvent - DMF. Three types of samples of poly(methacrylic acid) were used syndiotactic - obtained by radiation polymerization, atactic - obtained by radical polymerization, and isotactic - obtained by hydrolysis of isotactic poly(methyl methacrylate). It was found that in all cases the rate enhancement appeared in comparison with the blank polymerization (without template). The rate enhancement became more pronounced with increasing chain length and syndiotacticity of the template. According to the authors, the rate enhancement is connected with the stronger complex formation between poly(vinyl pyrrolidone) and syndiotactic poly(methacrylic acid) then with isotactic template. This conclusion was supported by turbimetric titration in DMF/DMSO system and by model considerations. It is worth noting, however, that... 

Poly(vinyl alcohol) is typically obtained by alcoholysis of poly(vinyl esters), for example from polyfvinyl acetate) and methanol in the presence of NaOH. The process can be completed or only partially conducted. In this latter case a copolymer (alcohol/ester) is obtained. Other synthetic procedures are used, most of them also based on the hydrolysis of poly(vinyl esters). Poly(vinyl alcohol) is typically used in the atactic form, but isotactic or syndiotactic poly(vinyl alcohols) also are known. 

Poly(vinyl alcohol) has an atactic chain structure, and it is consequently amorphous. However, it can be stretched into a crystalline fiber. The small size of the OH groups permits them to fit into a crystal lattice. Poly(vinyl alcohol) is available in various grades defined by the molecular weight and by the degree of hydrolysis, which determines polymer water solubility. 

PVA is an atactic polymer obtained by free radical polymerization of vinyl acetate and successive hydrolysis. The hydrolysis of poly(vinyl acetate) (PVAc) does not convert all the acetate groups into hydroxyl groups, but gives rise to PVA polymers with a partial degree of hydrolysis that depends on the extent of the reaction. 

Free-radical polymerization in methyl ethyl ketone at 60°C Hydrolysis of poly(methacrylic anhydride) at 40°C Hydrolysis of esters having appropriate configurations 57% syndiotactic triads Atactic Syndiotactic... 

On the basis of a study of molecular models, it had been proposed that the polymerization of 2,4,6-triphenylbenzyl methacrylate would only result in the formation of syndiotactic polymer. However, upon hydrolysis of this sterically hindered polyester with phosphonium iodide, the resultant poly(acrylic acid) could be separated into an atactic and a syndiotactic fraction on the basis of differences in solubility. This method of hydrolysis is of particular interest since it evidently permits relatively rapid saponification of syndiotactic poly(esters). 

It is interesting to reconsider the case of a poly(acrylic acid) dehydration reaction where two different steps can be distinguished for the atactic polymer the first step is five to six times faster than the second one and obviously corresponds to dehydration of meso dyads (isotactic sequences). Hydrolysis of syndiotactic... 

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