Poly molecular hydrolytic

In addition, polyester polyols are made by the reaction of caprolactone with diols. Poly(caprolactone diols) are used in the manufacture of thermoplastic polyurethane elastomers with improved hydrolytic stabiHty (22). The hydrolytic stabiHty of the poly(caprolactone diol)-derived TPUs is comparable to TPUs based on the more expensive long-chain diol adipates (23). Polyether/polyester polyol hybrids are synthesized from low molecular weight polyester diols, which are extended with propylene oxide. 

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. 

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

Synthesis of hydrolytically stable siloxane-urethanes by the melt reaction of organo-hydroxy terminated siloxane oligomers with various diisocyanates have been reported i97,i98) -yhg polymers obtained by this route are reported to be soluble in cresol and displayed rubber-like properties. However the molecular weights obtained were not very high. A later report56) described the use of hydroxybutyl terminated disiloxanes in the synthesis of poly(urethane-siloxanes). No data on the characterization of the copolymers have been given. However, from our independent kinetic and synthetic studies on the same system 199), unfortunately, it is clear that these types of materials do not result in well defined multiphase copolymers. The use of low molecular weight hydroxypropyl-terminated siloxanes in the synthesis of siloxane-urethane type structures has also been reported 198). 

A detailed analysis of the effect of mixed monolayers of 15 and DMPC on the activity of phospholipase A2 was reported by Grainger et al. [53]. Monolayers composed of different ratios of DMPC and either 15 or primarily poly 5 were characterized by Langmuir isotherms and isobars. The phospholipse-A2-mediated hydrolysis of selected monolayer compositions was usefully employed to ascertain the effectiveness of the enzyme. Both 15 and polyl5 were resistant to hydrolysis. The DMPC hydrolysis was sensitive to its molecular environment in a manner that suggests the phase separation of the polyl5 from DMPC. Phospholipase A2 activity is known to be sensitive to the concentration of the hydrolytic products, i.e. the fatty acid and lysophospholipid. The effect of these reaction products of the activity of phospholipase A2 on mixed monolayers of nonpolymerizable lipids is the subject of a series of interesting studies which are beyond the scope of this review. Ahlers et al. reviewed some of this research [54],... 

Poly((3-PL) has been hydrolytically degraded in a buffered salt solution (pH 7.2) at 37 °C [125,175], Oriented fibers and unoriented fibers showed different mechanical properties on degradation. The changes in tensile strength were slower for the oriented material. The molecular weight decreases rapidly during the first 50 days while the crystalline phase increases, probably due to an anneal-ing-like effect caused by the temperature at which the degradation was performed and rapid water absorption [175]. 

IM-IM cooperation. It is difficult to establish the IM-IM" cooperation in poly(4(5)-vinylimidazole), since pK2 value is more than 14.5 (74). The IM-IM" cooperation can be observed in hydrolyses of PNPA(5) and 4-acetoxy-3-nitrobenzoic acid [n = 0 in (8)] by poly(5(6)-vinylbenzimidazole), of which pK2 value is estimated to be 12.7 (26). The hydrolyses rates increase sharply as the pH approaches the pK2 value of the polymer. In contrast, such a drastic enhancement in the rate is not observed in the benzimidazole-catalysed hydrolysis, nevertheless, pK2 value of the benzimidazole being 12.7. N-Alkylated polymers such as poly(N-vinylimidazole), poly(NIM), and poly(2-methyl-N-vinylimidazole), poly(2MIM), which have no anionic form in imidazole moieties, show the hydrolytic activities slightly less than that of poly(4(5)-vinylimidazole). In cases of low molecular weight analogues, such as N-methylimidazole and imidazole, the hydrolytic activity of the former is about 75% of the activity of imidazole (75, 76). These phenomena appear to support the IM-IM" cooperation in poly(4(5)-vmylimidazole) indirectly. In the hydrolyses of NABS(l) and NABA(3) by poly(5(6)-vinylbenzimidazole), the activity enhancement is about 50-fold compared with the activity of benzimidazole, in spite of these anionic substrates being used (23, 26). 

The equilibrium 20 is important not only in the synthesis of linear polysiloxanes but also in their applications. The effects of water vapor on inducing chain cleavage at high temperature are not only reduced molecular weights but also a dramatic increase in the rates of chemically induced stress relaxation at 250 °C in cross-linked poly(dimethylsiloxane) networks under load (70). Slow hydrolytic bond cleavage in cross-linked networks is seen even in studies of stress relaxation in air at room temperature, and appreciable rates of stress relaxation in the loaded networks are measured at temperatures as low as 70 (7i). The stress relaxation is greatly accelerated... 

Therefore, most likely high heating rates prevail de-polymerization of hydrolytic lignin accompanied by removal of low molecular fragments. At low heating rates important become the slow processes of poly-condensation and thickening of low molecular aromatic compounds required to form microstructures with the smallest pores. 

Additional work has shown that it is also possible to induce the ROP of [IJsilaferrocenophanes in solution at ambient temperatures by using anionic initiators (55). For example, the reaction of 13 (R = R = Me) with approximately 10 mol % ferrocenyllithium (FcLi) followed by hydrolytic workup yields a moderate molecular weight poly(ferrocenylsilane) 15 (R = R = Me) with A/ 9500 and Mn 8000. With approximately equimolar... 

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