Poly alcohol hydrolysis rate

Figure 3. Change in the relative hydrolysis rates (based on sulfuric acid) of dextrin with the mole ratio of vinyl alcohol to vinylsulfonic acid repeating units at 80°C, keeping the concentration of vinulsulfonic acid unit constant at 5.00 X I0"3N. (O) In the presence of the random copoly (vinyl alcohol-vinylsulfonic acid) (%) in the presence of poly (vinyl alcohol)-poly(vinylsulfonic acid) mixture. [Substrate] = 2.00 X 10"2M.

The inhibition effect of poly (vinyl alcohol) on the amylose hydrolysis was investigated. Figure 7 shows Lineweaver-Burk plots of the amylose hydrolysis rates catalyzed by the random copolymer in the presence of poly (vinyl alcohol). The reaction rate is found to decrease with increasing the concentration of poly (vinyl alcohol), and all of the straight lines obtained in the plots cross with each other at a point on the ordinate. This is a feature of the competitive inhibition in the enzymatic reactions. In the present reaction system, however, it is inferred to suggest that the copolymer and poly (vinyl alcohol) molecules competitively absorb the substrate molecules. The elementary reaction can be described in the most simplified form as in Equation 3 where Z, SI, and Kj[ are inhibitor, nonproductive complex, and inhibitor constant, respectively. Then the reaction rate is expressed with Equation 4. 

Figure 7. Lineweaver-Burk plots of amylose hydrolysis rates catalyzed by the random copolymer in the presence of poly(vinyl alcohol). [Catalyst] = 2.00 X 10 3N. [Poly(vinyl alcohol)] = (O) 0 ( ) 4.0 X 10 2M (A) 8.0 X 10 2M. Km and Kr calculated according to Equation 4 are 0.083 and 0.22 M, respectively.

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). 

Chain transfer also occurs to the emulsifying agents, leading to their permanent iacorporation iato the product. Chain transfer to aldehydes, which may be formed as a result of the hydrolysis of the vinyl acetate monomer, tends to lower the molecular weight and slow the polymerisation rate because of the lower activity of the radical that is formed. Thus, the presence of acetaldehyde condensates as a poly(vinyl alcohol) impurity strongly retards polymerisation (91). Some of the initiators such as lauryl peroxide are also chain-transfer agents and lower the molecular weight of the product. 

Poly(vinyl alcohol) can be recovered from the desizing Hquid by means of commercial ultrafiltration equipment. Recovery rates and effluent losses ate inversely proportional to the PVA solution viscosity and independent of the degree of hydrolysis. 

Barrier Layers. Depending on composition, barrier layers can function simply as spatial separators or they can provide specified time delays by swelling at controlled rates or undergoing reactions such as hydrolysis or dissolution. Suitable barrier materials include cellulose esters and water-permeable polymers such as gelatin and poly(vinyl alcohol) (see Barrier polymers). 

The degree of hydrolysis of poly(vinyl alcohol) influences the emulsion polymerization of vinyl acetate. The lower the degree of hydrolysis, the better the emulsifying action of the protective colloid and the faster the rate of polymerization [146]. In coimection with this statement we must point out that the terminology a poly(vinyl alcohol) of low degree of hydrolysis is widely... 

The poly(vinyl alcohol) (PVOH) used in this study is Elvanol grade HV from DuPont chemicals. The material is derived from poly(vinyl acetate) (PVAc) by hydrolysis and is in powder form as received. The degree of hydrolysis for Elvanol HV is 99.8% (0.2% residual acetate groups). The molecular of the material used in this investigation is Mw =105,600 - 110,000. PVOH films were produced as described elsewhere 14). Samples were drawn in tension at a strain rate of 1.4 x 10 sec to a maximum draw ratio = 3.08 at 22 C. As-cast material has an equilibrium water content of 5.3 wt% at 22 C and 50% relative humidity (RH) giving a Tg value of 3rc. The HOPE is Hoechst unfractionated Hostalen GF 7660, Mw = 1.06x10 M = 1.01x10. Hydrostatic extrudon, with extrusion temperatures from 60-100 C and strain rates from 2.5 x 10 sec tol.4 x 10 sec" was us to vary draw ratio (die size was varied) with a maximum draw ratio Xm = 16. The maximum draw ratios were limited by fracture. 

The rate of the alkaline hydrolysis of neutral and charged esters in hexanol-water catalysed by quatemized poly(ethylenimine) increases with decreasing water content. The polymers absorb water strongly and selectively from the aqueous alcohol. ... 

The hydrolysis of dextrin (as a model for cellulose) has been studied in the presence of poly(vinyl alcohol-vinylsulphonic acid). Although the rate of hydrolysis increased with decreasing molecular weight of the substrate, the rates in the presence of copolymer were always greater than those with sulphuric acid on substrates of the same molecular weight. Both the enthalpy and the entropy of activation in the presence of the copolymer were smaller than those with... 

The feasibility of designing polymer-chelator conjugates from which release of the chelator is triggered reversibly by the appearance of the target (toxic) metal in the circulatory system was tested by synthesis and measurement of the rates of metal-catalysis hydrolysis of the ester of poly(vinyl alcohol) and quinaldic acid at pH 7.5. Hydrolysis in 50% aqueous ethanol solution in the presence of the four m.etals, Cu(II), Ni(II), CodI) and Zn(II) at pH 7.5 was first order, with half lives of 67, 71, 172 and 476 min., respectively. The rate of hydrolysis in the absence of metals was not measurable. A double reciprocal plot of kobs vs. [M] for Ni(II) exhibited the expected linearity. For films of the ester, the deviation from first order kinetics was consistent with a contributing diffusion process. 

---