Accessibility, hydrolytic degradation

Hydrophobic solubilizates such as styrene (S) decrease the saponification rate of the EUP. Accordingly, the EUP-molecules in micelles containing S are more resistant against hydrolytic degradation than molecularly dissolved EUP-mole-cules. Obviously, the access of the base to the hydrophobic interior of these micelles and microemulsion droplets is more difficult. 

Recently, attention was drawn to a readily accessible bacterial polyglucose A well-defined B-(l- S)-glucan with (DPj ) 540 from cultured Alcali-qenes faecalis var. myxogenes displayed significant host-mediated inhibitory effects against various transplantable tumors. Hydrolytic degradation products (DPn l6) retained some activity. 105... 

It is of particular interest that PBS has a higher hydrolytic degradation rate than poly(butylene succinate-co-butylene adipate) (PBSA) copolymers, as shown in Fig. 17 (Ahn et al. 2001). It is suggested that the presence of butylene adipate units may promote the hydrophobic nature of copolyesters, which would negatively influence the hydrolytic susceptibility by sterically hindering the access of nucleophiles. 

Polyurethanes obtained from renewable resources, such as carbohydrates, have attracted much attention in recent years [110,111]. This new interest results from great biomass access and their potential as replacements for some petroleum-based polymer precursors. The polymers obtained from natural products are expected to be biodegradable and non-toxic. The inclusion of hydrophilic monomers, such as carbohydrates, into the polymer chain facilitates water attack, increasing the hydrolytic degradation. 

Since erosion of the polymer in enzymatic degradation proceeds at the sample surface, the shape and size of the specimen influence the rate of degradation. Cross-linking, which reduces the crystallinity, facilitates the hydrolytic degradation as a bulk process, due to the easier penetration of water into the amorphous phase. On the other hand, enzyme-catalyzed degradation, as a surface process, is affected in the opposite direction, i.e. the rate of degradation is slower due to the formation of a network structure which reduces the access of the enzymes to the polymer. ... 

Acid hydrolysis of these samples led to the results to be expected, i.e., a lowering of LODP and residue value by NH3 pretreatment and mercerization as well as by mechanical disintegration prior to the hydrolytic treatment (Table XII). With regard to residue value, an NH3 pretreatment again proved to be more efficient in enhancing accessibility than a mercerization, while the rate constant of chain-length degradation was increased somewhat more by mercerization. 

These studies suggest the hydrophilic nature of PEG that increases the accessibility of water to the polymeric matrix. Also, PCL has been known to degrade very slowly because of its hydrophobic structure that does not allow fast water penetration [88]. PCL degradation by random hydrolytic chain scission of the ester linkages was documented by Pitt et al. [89]. 

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