Depolymerisation hydrolytic

Stepwise thermal- or base-eatalysed hydrolytic depolymerisation initiated from the hemi-formal chain end with the evolution of formaldehyde. The main reasons for end-capping and copolymerisation mechanisms described above are carried out in order to minimise this reaction. 

The hydrolytic depolymerisation of PETP in stirred potassium hydroxide solution was investigated. It was found that the depolymerisation reaction rate in a KOH solution was much more rapid than that in a neutral water solution. The correlation between the yield of product and the conversion of PETP showed that the main alkaline hydrolysis of PETP linkages was through a mechanism of chain-end scission. The result of kinetic analysis showed that the reaction rate was first order with respect to the concentration of KOH and to the concentration of PETP solids, respectively. This indicated that the ester linkages in PETP were hydrolysed sequentially. The activation energy for the depolymerisation of solid PETP in a KOH solution was 69 kJ/mol and the Arrhenius constant was 419 L/min/sq cm. 21 refs. 

REACTIVE EXTRUSION FOR THE HYDROLYTIC DEPOLYMERISATION OF POLYETHYLENE TEREPHTHALATE... 

The Pectolyase Y-23 catalytic activity was studied on several solutions of pectin at pH 3.0 and 6.0 and of polygalacturonic acid at pH 4.1. During pectin depolymerisation, the PL activity is about 20 times lower than the one of the PG and reaches its saturation value after about 30 min whereas the PG activity increases regularly with time. This dual behaviour is probably connected to the competitive hydrolytic action of PE that quickly transforms the pectin into the polygalacturonic acid. Accordingly, the reducing group formation is mainly due to the PG action and the pectin depolymerisation derives from the sequential action of PE and PG. 

The synthesis of low-dispersion oligomethylphenylsiloxanes is based on the separate hydrolytic condensation of trimethylchlorosilane and methyl-phenyldichlorosilane. It comprises three stages the hydrolytic condensation of trimethylchlorosilane and subsequent distillation of pure hexame-thyldisiloxane the hydrolytic condensation of methylphenyldichlorosilane and subsequent depolymerisation of the formed methylphenylcyclosilox-anes the catalytic regrouping of the mixture of hexamethyldisiloxane and methylphenylcyclotrisiloxane. 

The production of polydimethylsiloxane elastomer comprises three main stages the hydrolytic condensation of dimethyldichlorosilane the depolymerisation of the products of hydrolytic condensation the polymerisaton of dimethylcyclosiloxanes. 

Using this technique of the hydrolytic condensation of dimethyldichlo-rosilane, one can increase the yield of dimethylcyclosiloxanes by 8-10%, but it is impossible to eliminate the by-formation of linear oligodimethylsi-loxanes completely. Thus, the product of the hydrolytic condensation of dimethyldichlorosilane is sent to depolymerisation in the presence of potassium hydroxide at reduced pressure. Linear oligomethylsiloxanes are completely transformed into dimethylcyclosiloxanes. 

Polyvinylmethyldimethylsiloxane elastomers (SKTV) are prepared by the hydrolytic cocondensation of dimethyldichlorosilane and vinylmethyldi-chlorosilane with subsequent copolymerisation of the mixture of the hydrolysate and the depolymerisate obtained in the production of SKT elastomer. The process comprises two main stages the hydrolytic cocondensation of dimethyldichlorosilane and vinylmethyldichlorosilane the copolymerisation of vinylmethyldimethylcyclosiloxanes and dimethylcyclosiloxanes. 

The hydrolytic cocondensation of dimethyldichlorosilane and vinylmethyldichlorosilane occurs in the depolymerisate medium, forming a mixture of vinylmethyldimethylcyclosiloxanes... 

When SKTN elastomers are produced, dimethylcyclosiloxanes are polymerised with 2 N potassium hydroxide solution (0.005% of the amount of the polymerised substance) the molecular weight of the polymer is regulated by water supply (diluting the alkali). The raw stock for polymerisation can be the depolymerisate obtained at the depolymerisation stage of the product of hydrolytic condensation of dimethyldichlorosilane in the production of polydimethylsiloxane elastomer SKT. 

As we have indicated above, the ageing of fibres like flax often results in the formation of acidic degradation products. These, together with adsorbed acidic atmospheric pollutants, can continue to promote further damage through the hydrolytic depolymerisation of cellulose. So, in relation to its stability, it seemed important to estimate the acid content of the Victory sailcloth. There are two approaches that can be taken surface measurements on the fabric and acid extractions. 

Due to the hydrolytic instability, most biodegradable polyesters undergo depolymerisation in aqueous mediums. Their degradability by simple hydrolysis of the ester backbone in aqueous environments such as body fluids is obviously a great advantage for them to be used in some biomedical applications (Eubeler et al., 2009 2010 Gijpferich, 1996). The degradation products are ultimately metabolised to carbon dioxide and water or are excreted via the kidney. 

Studies on the waste from PET bottles hydrolytically depolymerised in a high-pressure autoclave equipped with a stirrer concluded that the degree of degradation of PET increases as the particle size of PET decreases, reaching a maximum of 24.61 % at a size of 1 mm x 1 mm [a.396]. The rate constants of hydrolysis of PET were found to be greater at higher particle size, in contrast to lower particle size, if catalyst (lead acetate) is used. Further,... 

Hydrolytic scission of peroxide, without creation of radicals, due to the presence of acids Chain scission (depolymerisation)... 

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