Polyamides carboxylic anhydrides

Introduction Controlled Degradation of Polyamides by Carboxylic Acids and Carboxylic Anhydrides... 

The following results indicate that not only carboxylic anhydride but also carboxylic acid groups show very high activity during polyamide melt processing at temperatures above 230°C. The controlled degradation of thermoplastic polyamides like PA-6, PA-66, and PA-12 by carboxylic acid and carboxylic anhydride... 

The characteristic values MFl and r ed show a significant degradation of PA-6 during the extrusimi process after adding trimellitic anhydride and special oligo-amide 6. The results are further evidence for the high activity of carboxylic anhydride and carboxylic acid compounds under polyamide melt processing... 

The reverse reaction is an intramolecular acidolysis of amide group by the o-carboxyhc acid to reform anhydride and amine. This unique feature is the result of an ortho neighboring effect. In contrast, the acylation of an amine with ben2oic anhydride is an irreversible reaction under the same reaction conditions. The poly(amic acid) stmcture (8) can be considered as a class of polyamides. Aromatic polyamides that lack ortho carboxylic groups are very... 

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 ... 

Blends based on polyolefins have been compatibilized by reactive extrusion where functionalized polyolefins are used to form copolymers that bridge the phases. Maleic anhydride modified polyolefins and acrylic acid modified polyolefins are the commonly used modified polymers used as the compatibilizer in polyolefin-polyamide systems. The chemical reaction involved in the formation of block copolymers by the reaction of the amine end group on nylon and anhydride groups or carboxylic groups on modified polyolefins is shown in Scheme 1. 

When the -OH of a carboxylic acid is replaced by an -NH2, the compound produced is an amide. Amides are neutral to mildly basic compounds. They can be made from acids, acid chlorides, acid anhydrides, and esters by reaction with ammonia or primary and secondary amines. The amide linkage is found in polyamide resins such as nylon. 

There have been efforts to form aromatic polyamides directly from diacids at moderate temperatures by using various phosphorus compounds for in situ activation of the carboxyl groups [Arai et al., 1985 Higashi and Kohayashi, 1989 Krigbaum et al., 1985]. A useful agent is diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate, which probably activates the carboxyl group by forming a mixed carboxylic-phosphoric anhydride [Ueda, 1999 Ueda et al., 1991]. 

Carboxylic acids react with aryl isocyanates, at elevated temperatures to yield anhydrides. The anhydrides subsequently evolve carbon dioxide to yield amines at elevated temperatures (70—72). The aromatic amines are further converted into amides by reaction with excess anhydride. Ortho diacids, such as phthalic acid [88-99-3], react with aryl isocyanates to yield the corresponding N-aryl phthalimides (73). Reactions with carboxylic acids are irreversible and commercially used to prepare polyamides and polyimides, two classes of high performance polymers for high temperature applications where chemical resistance is important. Base catalysis is recommended to reduce the formation of substituted urea by-products (74). 

This section presents and discusses a few examples of reactive blending during the preparation of polyester and polyamide blends, by reaction of epoxy/carboxylic acid (polyesters blends) and anhydride/amine (polyamide blends) groups. 

The other most popular method of synthesizing commercial PAI uses the so-called isocyanate route. This is the primary route to polyamide-imides which are then utilized as wire enamels or fibers. This PAI chemistry involves the reaction of a di-isocyanate, often -methylenediphenyldi-isocyanate (MDI) (Fig. 12.3) with trimellitic anhydride (TMA) (Fig. 12.4). To overcome the lower reactivity of the carboxylic acid functionality in... 

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