Association phenomena in carboxyl‐containing polymers

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Abstract
Gelation effects were studied as a function of pH for the following polymeric materials: alginic acid, poly(methyl acrylate co acrylic acid), poly(ethyl acrylate co acrylic acid), and phthalated ethylcellulose. The effects of various addenda were also studied. The results suggest a gelation mechanism for all the polymers which consists of a balance of repulsive force interactions due to ionization of carboxyl groups, and of attractive force interactions due to hydrogen bonding. The groups involved in hydrogen‐bonding interactions are deduced. The melting points of phthalated ethylcellulose and poly(ethyl acrylate co acrylic acid) gels were obtained as a function of concentration and plots of log c versus reciprocal absolute temperature of melting gave linear curves. The heat of reaction for the formation of crosslinks was −8 ± 0.4 kcal./mole crosslinks. This is much lower than values obtained for gelatin gels and suggests that a single crosslink contains 1–2 hydrogen bonds.