Polyamides molecular weight determination

Condensation polymers such as polyesters and polyamides are especially well suited to this method of molecular weight determination. For one thing, the molecular weight of these polymers is usually less than for addition polymers. Even more pertinent to the method is the fact that the chain ends in these molecules consist of unreacted functional groups. Using polyamides as an example, we can readily account for the following possibilities ... 

The molecular weights of fatty polyamides generally encompass the range of 3000-15,000. Anderson and Wheeler (10) evolved a relationship for number-average molecular weight determined by end-group analysis and viscosity so that molecular weight can be... 

The molecular weights were estimated by applying the Mark-Houwink relationship [r/ = KMa. The intrinsic viscosity [r/ was determined in m-cresol at 20°C. The values for K in the literature vary from 1.35 to 18.10 x 10-4 and the a values vary from 0.654 to 0.96 for polyamide-cresol systems. 

Dissolution/reprecipitation processes were evaluated for the recycling of poly-epsilon-caprolactam (PA6) and polyhexamethyleneadipamide (PA66). The process involved solution of the polyamide in an appropriate solvent, precipitation by the addition of a non-solvent, and recovery of the polymer by washing and drying. Dimethylsulphoxide was used as the solvent for PA6, and formic acid for PA66, and methylethylketone was used as the non-solvent for both polymers. The recycled polymers were evaluated by determination of molecular weight, crystallinity and grain size. Excellent recoveries were achieved, with no deterioration in the polymer properties. 33 refs. 

The molecular weights of the polymers before and after irradiation were followed by GPC to determine changes in the molecular weights of the polyamides. It was found that photolysis of the polymer resulted in polymer chain scission, leading to the appearance of oligomers containing thymine bases at the end of the molecules. 

Thus the Endgroup analysis method is quite useful for the determination of the Molecular weight of the polymers that possesses endgroups which can be determined precisely by some analytical reaction. In addition to Polyamides and polyesters, where the Endgroup analysis method is commonly used, the method can also be used for polysaccharides. 

The molecular weight of the grafted chain of polyacrylic acid, determined by acid hydrolysis, is of the order of 10000. The product differs markedly from the original polyamide in electrochemical properties. As a confirmation of a radical mechanism, radical acceptors prevented the reaction (see Fig. 5). The possibility of a minor and competitive ionic mechanism was also considered. 

K 8 Korshak, V. V., and S. A. Palova Determination of molecular weights of polyamides from viscosity of their solutions in cresol and methanol. Izvest. Akad. Nauk. S.S.S.R. 1955, 1107. 

R4 Rusznak, I., I. GAczy and A. Ady The viscometric determination of the molecular weight of super polyamides in aqueous chloralhydrate. Textiltechn. 7. 490 (1956). 

The properties of nylon block copolymers are determined to the greatest extent by the ratio of polyol to polyamide. Other factors which play an important role are polyol type, polyol molecular weight, coupler-activator type and reactant ratios as well as the polymerization conditions. 

In order to determine the effects of a given monomer on polyamide permeation properties, data obtained from copolymers where the monomer of interest was diluted by another diamine or diacid were often used. It is assumed that the OPV data for copolymers are weighted averages of the OPV data for the constituent homopolymers. The use of copolymers was necessitated by several reasons. It was often too difficult to form the homopolymer of interest with high enough molecular weight to allow formation of cohesive films. In other cases, the homopolymer was semi-crystalline, which, as will be described in the next paragraph, is undesirable for this study. 

Number-average molecular weights may be determined by use of a Mechrolab vapor pressure osmometer, utilizing a solution of polyamide resin in chloroform at 37 °C. The procedure is described in detail by Pasternak et al. (. Typical molecular weight values for ethylenediamine-based polyamides with varying viscosities are listed in Table I. Viscosities of the melts were determined by utilizing a Brookfield viscometer. Model RVF, at 160 °C with a No. 3 spindle at 20 rpra. 

Some molecular weights of this type of polyamide resin are listed in Table II. Viscosity was determined at 150 °C by utilizing a Brookfield viscometer, Model RVF, No. 3 spindle at 20 rpms. If... 

Tokura et al.49 synthesized a polyamide of the Perlon type (40) starting from a 6-O-carboxymethyl-D-glucosamine derivative as monomer.This compound was obtained by carboxylmethylation of chitin with monochloroacetic acid, followed by hydrolysis of the glycosidic linkage. Hie molecular weight (Mw 15,000) of the resulting water-soluble polyamide 40 was determined by gel-permeation chromatography and electrophoresis (Scheme 11). 

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