Polyamides interchange reactions

Amide interchange reactions of the type represented by reaction 3 in Table 5.4 are known to occur more slowly than direct amidation nevertheless, reactions between high and low molecular weight polyamides result in a polymer of intermediate molecular weight. The polymer is initially a block copolymer of the two starting materials, but randomization is eventually produced. 

As is die case for odier polycondensation reactions, internal interchange reactions are possible for ADMET, similar to diat of polyesters and polyamides.16 Interchange reactions involve a catalyst molecule on a polymer chain end reacting widi an internal double bond in another polymer chain. The result is two new polymer chains however, no change in the molecular weight distribution... 

American Society for Testing and Materials (ASTM), 242 Amic acid ammonium salt, polyimide cyclization via, 305 Amic acid formation, 301 Amidation reaction scheme, 151 Amide-amide interchange reaction, 158 Amide concentration, in polyamides, 139-141... 

Interchange reactions between two different polymers were observed in the case of polyester or polyamide, but this subject is beyond the scope of the present review. 

Similar interchange processes may occur in other condensation polymers under suitable conditions. There is ample evidence in the literature on polyamides, and on monomeric amides as well, for the occurrence of the amine-amide interchange reaction (II)... 

The susceptibility of polyesters and polyamides to interchange reactions, such as may occur in the former between a terminal hydroxyl of one molecule and an interunit ester group of another, was discussed in Chapter III. These interchange processes do not decrease the number of molecules, and hence do not affect Mnj but they might permit some molecular species to be formed in preference to others. In other words, they may conceivably bring about an alteration of the molecular size distribution. 

Hydrolysis of Copolyamide-esters (CPAEs) by Lipase (jj,). CPAEs were synthesized by the amide-ester interchange reaction between polyamide and polyester. The length of the polyamide blocks was measured after hydrolysis of ester bonds in CPAE by alkali at 30 C. The infrared spectra after hydrolyzing ester bonds on CPAEs showed that the ester bonds were almost completely removed. The molecular weight distribution of polyamide blocks was examined by GPC (Table II). The following samples were used CPAE-1 (reaction time for synthesis, 1 hr) and CPAE-2 (reaction time, U hr) composed of nylon 6 and PCL at a 50/50 molar ratio, CPAE-3 (reaction time, 1 hr) and CPAE-U (reaction time,... 

It has been established that random interchange reactions occur with polyesters and polyamides at the higli temperatures at which these thermoplastics are normally polymerized and subsequently extruded or molded. Other condensation polymers probably undergo similar shufflings of repeating units under the proper conditions. This implies that the equilibrium constant for condensation reactions like that in reaction (a) of Fig. 5-2 is independent of the sizes of the molecules which are reacting. 

Af = 90,000 and M =180,(X)0. The two polyamides are mixed in equal quantities by weight and are held at 280 C for 7 h. Interchange reactions can come to equilibrium in this time but no further polymerization could take place because condensation products were not removed from the system. What are and of the final, equilibrated system ... 

A general review of Interchange Reactions Involving Condensation Polymers describes early work on redistribution reactions in the melt blends of polyesters, polyamides, and polyester + polyamide [Kotliar, 1981],... 

PEAs were firstly obtained in 1979 from polyamides and polyesters by temperature-induced amide-ester interchange reactions. Since then, a considerable body of literature has been developed due to the noticeable characteristics and properties of the new polymers. For more detailed information on the synthesis and applications of... 

There are a number of ways that a stepwise reaction can take place. These include direct reaction, interchange, and add chloride/anhydride. Direct reactions include formation of polyesters and polyamides. Typical interchange reactions involve acetol-alcohol, amine-amide, and amine-ester. The last-named are cases in which an anhydride or acid chloride are reacted with a glycol or amine. 

Certain alkyd resins can be combined with modified polyamide resins to produce materials exhibiting a marked degree of true thixotropy when dissolved in suitable solvents. This valuable property is maintained when such products are used in the manufacture of paints. When the alkyd and polyamide are heated at elevated temperature, amide and ester interchange reactions occur that split the polyamide chains and affix the fragments to the alkyd molecule. In further reactions, the amide groups are scattered throughout the molecule. The reactions probably proceed in the following way ... 

Another type of adventitious block polymer formation occurs in the partial inter-randomization in the melt of mixtures of homopolymers such as polyesters and polyamides which can undergo ester-ester, amide-amide or ester-amide interchange reactions. 

The common condensation polymers and the reactions by which they are formed are shown in Table 1-1. It should be noted from Table 1-1 that for many of the condensation polymers there are different combinations of reactants that can be employed for their synthesis. Thus polyamides can be synthesized by the reactions of diamines with diacids or diacyl chlorides and by the self-condensation of amino acids. Similarly, polyesters can be synthesized from diols by esterification with diacids or ester interchange with diesters. 

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