Carboxylic acid anhydride cross-links

The monomer in (12.30) was made from glycerol, acetone, and acetylene. The alternating copolymer with maleic anhydride cross-links on standing in a moist atmosphere.156 (The carboxylic acid that results from the action of water on the anhydride catalyzes the cleavage of the ac-... 

As shown in Table 3.2, 5% BTCA in the presence of 10% SHP and 0.1% TiO (as a cocatalyst) was nsed, and the addition of TiO as a cocatalyst further increased WRA by 58.5%. This was becanse both TiO and SHP accelerated the catalytic reaction throngh the formation of ester bonds between the cyclic anhydride ring and the hydroxyl gronp of cellulose. The improvement of WRA by the addition of TiO in the BTCA treatment was probably dne to the nniqne photocatalytic properties of TiO, which is a kind of N-type semicondnctor. The hydroxyl radical (-OH) and snperoxide anion (-0 -) formed may have acted as catalysts to accelerate the formation of anhydrides from poly (carboxylic) acids. Fnrthermore, the effect of hydroxyl radical (-OH) and superoxide anion (-O -) on the increase of charge localization of the sohd cellulose medium in which esterfication and cross linking occur may also have been significant. Therefore, WRAs of cotton fiber treated with 5% BTCA, 10% SHP, and 0.2% TiO further increased to 61.3% compared with those of the untreated cotton fabric. The increment was proportional to the increase of TiOj from 0.1 to 0.2% in the BTCA treatment bath (Lam et al., 2011). 

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

In an alternate synthesis, the formation of thermoplastic vulcanizate (TPV) is accomplished with two polymers, wherein one polymer is grafted with a carboxylic acid anhydride, which then is reacted with an aminosilane, which reacts with the acid anhydride and then cross-links with moismre. The vulcanizates exhibit good mechanical properties and lower melt-flow index than the starting polymers. 

Many observations, however, have provided strong evidence that site-site interactions are quite facile. Carboxylic acids bound to polystyrenes of varying degrees of cross-links have been observed to undergo anhydride formation even at low levels of functionalization 140,14I). The observation that cross-Claisen condensation products result from polymers on which two esters are attached also supports the view that intersite reactions can occur in polymer matrices142). Barany and Merrifield U) analysed a number of situations under which intersite reactions occured and found that they usually occur when... 

Photocationic initiators. Epoxy resins can be cross-linked by compounds containing active hydrogen, e.g., carboxylic acids, anhydrides, amines, phenols etc., or by the ionic polymerization process. Lewis acids such as BF3 and usually a crystalline complex of BF3 with amines, e.g., BF3 NH2C2H5, can be used for curing reaction at 80-100° C [124]. 

The mechanism of nonconventional bonding based on mixtures of diamines with PVC was explained (82) on the basis of the reported ability of the two materials to partially cross-link (180) (Scheme 3). Epichlorohydrin, used occasionally as an additive, polymerizes with polyfunctional amines (181) (Scheme 4) and reacts with lignin in the presence of amines or carboxylic acids (182). Even simpler to visualize is the cross-linking of the mixture of maleic anhydride and PVA by formation of ester linkages (118) that attach to the hydroxyls of the wood surface. 

There are two options for the other component of an epoxy resin system. Use of mono- or di-anhydrides as curing agents, usually catalyzed by a tertiary amine, causes reactions with the residual secondary hydroxyls in the repeating unit of the prepolymer forming esters and free carboxylic acids. The carboxylic acids formed also react with the epoxide end groups forming cross-links and further free secondary hydroxyl groups. Maleic anhydride, phthalic anhydride, or pyromellitic dianhydride are suitable for this process (Eq. 21.27). 

Increases in the levels of water swell of the PVA hydrogels were initially presumed to be possible according to the mechanism commonly followed by covalently cross-linked hydrogels, namely, the incorporation of monomer components with exceptional affinities for water (typically, charged species such as carboxylic acid functional monomers). Thus, copolymers of VTFA and maleic anhydride were prepared, which when solvolyzed in methanolic ammonium hydroxide, would be expected to give poly [(vinyl alcohol)-co-(maleic acid)] products. Film samples of such copolymer hydrogels were prepared, and surprising sensitivity of water swell to acidic comonomer content was observed (Table IV). 

Examples of the resin components of expoxies are listed in Table 1. Several chemical substances can be used as hardeners for epoxies [5,6], The two main groups of cross-linking agents used in industry are two or more functionalized amines and anhydrides of carboxylic acids. Cross-linking with amines is possible at room temperature as well as at elevated temperatures, depending on the chemical structure of the amines (Table 2). Anhydrides of carboxylic acids react at elevated temperatures only. 

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