End groups carboxylate

Figure 14.3 Reaction of 1,4-PBO chain extender with PET end groups (carboxylic acid groups) to give linear chain extension of PET (leading to a polyamide-polyester) 1,4-PBO, 1,4-phenylenebisoxazoline...

Phenolic-epoxy adhesive systems for structural bonding use similar formulations but are frequently modified with a linear polymer having reactive end groups (carboxyl, amino) for toughness and vibration resistance. 

The oxidative thermal stability is markedly affected by the concentration of both carboxylic and basic end groups. Carboxylic acid groups initiate the homolytic decomposition of 6-hydroperoxy-6-hexanelactam. Thus, alkoxyl and hydroxyl radicals are formed as intermediates. Eventually, the monoamide of adipic acid is formed. PAs with carboxylic end groups are oxidized in a similar way. The rate of oxidization increases with the content of carboxylic groups. ... 

A termination is often purposefully induced to obtain functional end groups. Carboxyl, hydroxyl, and thiol end groups can be produced in this way ... 

Apart from fatty acids, straight-chain molecules containing other hydrophilic end groups have been employed in numerous studies. In order to stabilize LB films chemical entities such as tlie alcohol group and tlie metliyl ester group have been introduced, botli of which are less hydrophilic tlian carboxylic acids and are largely unaffected by tlie pH of tlie subphase. 

Aqueous caprolactam is polymerized alone and in the presence of sebacic acid (S) or hexamethylenediamine (H).t After a 24-hr reaction time, the polymer is isolated and the end groups are analyzed by titrating the carboxyl groups with KOH in benzyl alcohol and the amino groups with p-toluenesulfonic acid in trifluoroethanol. The number of milliequivalents of carboxyl group per mole caprolactam converted to polymer, [A ], and the number of milliequivalents of amino groups per mole caprolactam converted to polymer, [B ], are given below for three different runs ... 

One of the most sensitive tests of the dependence of chemical reactivity on the size of the reacting molecules is the comparison of the rates of reaction for compounds which are members of a homologous series with different chain lengths. Studies by Flory and others on the rates of esterification and saponification of esters were the first investigations conducted to clarify the dependence of reactivity on molecular size. The rate constants for these reactions are observed to converge quite rapidly to a constant value which is independent of molecular size, after an initial dependence on molecular size for small molecules. The effect is reminiscent of the discussion on the uniqueness of end groups in connection with Example 1.1. In the esterification of carboxylic acids, for example, the rate constants are different for acetic, propionic, and butyric acids, but constant for carboxyUc acids with 4-18 carbon atoms. This observation on nonpolymeric compounds has been generalized to apply to polymerization reactions as well. The latter are subject to several complications which are not involved in the study of simple model compounds, but when these complications are properly considered, the independence of reactivity on molecular size has been repeatedly verified. 

Low molecular weight liquid nitrile rubbers with vinyl, carboxyl or mercaptan reactive end groups have been used with acrylic adhesives, epoxide resins and polyesters. Japanese workers have produced interesting butadiene-acrylonitrile alternating copolymers using Ziegler-Natta-type catalysts that are capable of some degree of ciystallisation. 

Polymers with an antiplatelet agent of 5-(6-carboxyl-hexyl) l-(3-cyclohexyl-3-hydroxyropyl) hydantoin as an end group were synthesized by esterifying the hydantoin molecule with a haloalcohol, such as CCI3CH2OH or BrCH2CH20H, and using the product as coinitiator with... 

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. 

Scheme 1 The proposed acid/amine and anhydride/ amine reaction between carboxylic groups/anhydride groups on modified polyolefins and amine end groups on Nylon-6.

Stearic acid is a member of the group called fatty acids. These are hydrocarbon chains (chains made of repeated units of a carbon atom and two hydrogen atoms) with a carboxyl group at one end. A carboxyl group is the COOH in the chemical formula. It is what turns the hydrocarbon chain into an organic acid. 

The presence of a large number of chain-ends in the fully synthesized dendrimer molecules makes them highly soluble and also readily miscible, for example with other dendrimer solutions. The solubility is controlled by the nature of the end-groups, so that dendrimers with hydrophilic groups, such as hydroxyl or carboxylic acid, at the ends of the branches are soluble in polar solvents, whereas dendrimers with hydrophobic end-groups are soluble in non-polar solvents. The density of the end-groups at the surface of the dendrimer molecule means that they have proportionately more influence on the solubility than in linear polymers. Hence a dendritic polyester has been shown to be more soluble in tetrahydrofuran than an equivalent linear polyester. 

Ethoxylation of the carboxylic acid end groups of aliphatic polyesters significantly changes the biodegradation rate as well as the crystallinity of these materials (41). 

The choice of the alcohol permits manipulation of the structure of the polymer. Water and monohydric alcohols afford linear chains with carboxylic acid and ester end groups, respectively. Polyhydroxy initiators afford a route to ester end-blocked star and comb polymers (Fig. 4) (47). 

This behavior is consistent with an autocatalytic process, whereby the liberated carboxylic end groups catalyze the cleavage of additional ester groups (Eq. 3) ... 

An implication of the kinetic analysis presented in Sec. IV.A is that the rate of chain scission of polyesters can be retarded by endcapping to reduce the initial carboxylic acid end-group concentration. Alternatively, the rate may be increased by acidic additives that supplement the effect of the carboxy end groups. The first expectation was confirmed by partial ethanolysis of high molecular weight... 

Huffman, K. R., and Casey, D. J., Effect of Carboxylic end groups on hydrolysis of polyglycolic acid, J. Polym. Sci. 

These were prepared by efficiently interhnking pairs of carboxyl end groups in fibers extruded from tetra-chain and from octachain poly- -caproamides (see p. 

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