Poly , isotactic hydrolysis

Isotactic poly(methyl methacrylate/methacrylic acid), a copolymer of methyl methacrylate and methacrylic acid, was synthesized by the partial hydrolysis of isotactic poly(MMA) according to the method of Klesper et al. (10-13). A hydrolyzing mixture of 8 mL dioxane and 4 mL methanolic KOH (10% by weight K0H) was mixed with 250 mg of polymer in closed vials at 85°C for 48 hr. Saponified polymer separated from the solution and adhered to the walls of the vial. The precipitated polymer was dissolved in water and then precipitated again with a few drops of HC1. The solution was warmed and the coagulated polymer removed, washed with water, and dried in vacuo at 50°C. The nmr spectrum indicated approxi-... 

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. 

Derivation of polymer also serves as a useful method for tacticity determination. Poly(triphenylmethyl methacrylate) is easily converted to PMMA by hydrolysis and the subsequent methylation with diazomethene. The polymers obtained by anionic polymerization not only in toluene but also in tetrahydrofuran are highly isotactic.189 Even the radical polymerization of the monomer gives an isotactic polymer. 

PVPA can also be obtained by hydrolysis of poly(dimethyl vinylphosphonate) (PDMVP), which was synthesized both through free radical and anionic polymerization. Structural analysis revealed that PDMVP obtained by anionic polymerization is isotactic-rich. 

The first attempts to synthesize poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMAA) were the hydrolysis of poly(acid derivatives) such as esters, acylchlorides, nitriles, or amides. The hydrolysis has to be quantitative otherwise, one obtains a copolymer of acid and derivative [472]. On the other hand, hydrolysis in boiling alkaline solution can diminish the molar masses [473]. One possibility is to polymerize methyl methacrylic ester and to hydrolyze the resulting PMMA in acetic acid by the addition of a small amount of -toluenesulfonic acid as a catalyst. The solution is kept at 120 °C for 18 h and the methylacetate fonned is removed by distillation [474]. The degree of hydrolysis depends strongly on the tacticity of the original polymer. Syndiotactic PMMA is hydrolyzed slowly, but isotactic polymer is hydrolyzed very rapidly [475]. The polymers examined had molar masses up to 125,000. 

Up to now the only way to get isotactic poly(acrylic acid) or poly(methacrylic acid) has been by hydrolysis of isotactic poly(acrylates) or poly(methacrylates) [476]. Direct routes to get isotactic polymers would be anionic and coordination polymerization. But these polymerizations are not practicable, because the acid function would destroy the initiator. Kargin et al. [477] prepared isotactic poly(acrylic acid) by reaction of isotactic poly(isopropylacrylate) in toluene as solvent with potassium hydroxide in propanol. Propanol and the formed isopropanal were removed after reflexing for 6 h by distillation. Complete hydrolysis was reached after 10 h. Aylward synthesized isotactic and syndiotactic poly(methacrylic acid) by quantitative hydrolysis of poly(trimethylsilyl methacrylate) [478]. 

It will have been noted already that the degree of hydrolysis of poly-(acrylates) and poly(methacrylates) frequently does not appear to be complete. In part this may be due to difficulties with the anlytical procedures and with other factors. In part, however, this may also be the result of hydration of the product. In fact, isotactic poly(acrylic acid) may crystallize as a hydrate containing as much as one molecule of water associated with two monomer units [19]. Procedure 2-4, for the preparation of isotactic poly(acrylic acid), is said to be the most effective method of twelve different procedures studied [19]. 

Table III summarizes a variety of observations on the alkaline hydrolysis of several acrylic polymers. To be noted is that the difference in the rates of hydrolysis of isotactic and syndiotactic poly(methyl methacrylate) is sufficiently great that mixtures of such polymers may be separated on the basis of this behavior [18].

The alkaline hydrolysis of acrylic esters requires, as shown in Table III, considerable time. The procedure involves a heterogeneous reaction in its early stages and may actually be accompanied by oxidative degradation of the polymeric chains [20]. The acid hydrolysis, on the other hand, is a homogeneous reaction and is thought not to lead to chain scission [3]. Again, poly(acrylates) hydrolyze more rapidly than the poly(methacrylates), and the isotactic poly(methacrylates) are more easily converted to poly(methacrylic acids) than the syndiotactic poly (methacrylates) [18]. 

Optically active poly(7V-formylpropylenimine) made from L-4-methyloxazoline is isotactic. The barrier to rotation about the N—CHO bond results in two effects (a) fine structure in the C NMR spectrum of the polymer and (b) mutarotation when the polymer is dissolved in water. These effects are absent in the hydrolysis product, polypropylenimine tacticity effects are readily observed in the latter, provided that is is first converted to the polyhydrochloride. 

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... 

On the other hand, if the initial cyclopolymer is heated in presence of pyridine, isomerization of the syndiotactic form into the isotactic one is observed, probably by enolization of the position in a, whose hydrolysis gives rise to isotactic poly(acrylic acid) the latter can easily be transformed into polyanhydride by thionyl chloride ... 

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