Hydrolytic degradation, of polymers

Hydrolytic degradation of polymers is still the main reason for the occurrence of faults in processing. This form of degradation commonly causes a reduction of the IV, associated with a deterioration in the mechanical properties, particularly the tensile strength. Therefore, it is important to ensure sufficient drying of the raw materials. Drying is a crucial prerequisite of any polyester processing... 

D. Hofmann, E.C.K. Karl, L. Andreas, Knowledge-based approach towards hydrolytic degradation of polymer-based biomaterials. Adv. Mater. 21, 3237-3245 (2009)... 

How does hydrolytic degradation of polymers take place ... 

Poly(L-malate) decomposes spontaneously to L-ma-late by ester hydrolysis [2,4,5]. Hydrolytic degradation of the polymer sodium salt at pH 7.0 and 37°C results in a random cleavage of the polymer, the molecular mass decreasing by 50% after a period of 10 h [2]. The rate of hydrolysis is accelerated in acidic and alkaline solutions. This was first noted by changes in the activity of the polymer to inhibit DNA polymerase a of P. polycephalum [4]. The explanation of this phenomenon was that the degradation was slowest between pH 5-9 (Fig. 2) as would be expected if it were acid/base-catalyzed. In choosing a buffer, one should be aware of specific buffer catalysis. We found that the polymer was more stable in phosphate buffer than in Tris/HCl-buffer. 

In dentistry, silicones are primarily used as dental-impression materials where chemical- and bioinertness are critical, and, thus, thoroughly evaluated.546 The development of a method for the detection of antibodies to silicones has been reviewed,547 as the search for novel silicone biomaterials continues. Thus, aromatic polyamide-silicone resins have been reviewed as a new class of biomaterials.548 In a short review, the comparison of silicones with their major competitor in biomaterials, polyurethanes, has been conducted.549 But silicones are also used in the modification of polyurethanes and other polymers via co-polymerization, formation of IPNs, blending, or functionalization by grafting, affecting both bulk and surface characteristics of the materials, as discussed in the recent reviews.550-552 A number of papers deal specifically with surface modification of silicones for medical applications, as described in a recent reference.555 The role of silicones in biodegradable polyurethane co-polymers,554 and in other hydrolytically degradable co-polymers,555 was recently studied. 

In summary, practical experience with predicting the hydrolytic degradation of polyethylene terephthalate is an example of the use of Arrhenius extrapolation, a demonstration of the problems encountered when there are changes in the state of the polymer as the temperature is raised, and an example of the large variability in prediction of lifetime due to the logarithmic scale. 

Allen, N. S., Edge, M., Mohammadian, M. and Jones, K., UV and thermal hydrolytic degradation of poly (ethylene terephthalate) importance of hydroperoxides and benzophenone end groups, Polym. Degrad. Stabil., 41, 191-196 (1993). 

Hydrolytic degradation of poly(e-CL)/PLLA block copolyester at pH 7.4 and 37 °C over a 5-week period is controlled by the initial crystallinity of the poly(e-CL) and its overall composition. The rate of degradation increased with increasing PLLA content [203 ]. Microorganisms, such as Fusarium solani and Fusarium moniliforme, that secrete poly(e-CL) depolymerase (cutinase), were more effective with those polymers that had longer poly(e-CL) sequence lengths [218]. The... 

Block copolymers (228), consisting of a hydrophilic poly(ethylene glycol) and a hydrophobic polyphosphazene residue, have been investigated with respect to their micelle formation in aqueous solution Micelle formation in water has also been observed for polymers (229) with ethyl glycinato substituents. Hydrolytic degradation of these polymers has been studied in aqueous thf. ... 

In a previous paper (21) we characterized aromatic acids trapped in lignite coal, and have found that these acids are quite similar qualitatively to those obtained from the present oxidation of the same pretreated coal. This indicated that the trapped acids were derived mainly from the hydrolytic degradation of lignin-like polymers. We also have observed that no trapped organic acid is isolated from the anthracite coal that no longer contains lignin-like polymers. 

Many Investigators of hydrolytic stability of polymers utilize hardness measurements since the readings are very easy to take and the tests are essentially nondestructive, thus obviating the need for many test specimens. This work emphasizes that high retention of hardness does not prove that the material has displayed a good retention of other physical properties or withstood extensive degradation. 

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