SynopsisCopolymerization of 2-hydroxyethyl methacrylate with methacrylamide or acrylamide and a crosslinking agent in the presence of water or other diluents yielded transparent hydrogels with a varying degree of swelling and varying sorption properties. The equilibrium degree of swelling increases with increasing content of amide groups and exhibits a maximum at ca. 60 wt-% methacrylamide. The temperature dependence of swelling at 25-50°C changes from negative to positive with growing content of methacrylamide in the copolymer. The effect of the introduction of the amide groups can be interpreted by a weakening of the extent of hydrophobic interactions and by an increase in the role played by the hydrogen bonds. A t the same time, the swelling-in effect of the salting-in anions decreases and the sensitivity to the sorption of metal cations increases. The increasing content of methacrylamide is reflected in an increase in the modulus, tensile strength, and elongation-at-break in gels swollen to the same degree. In gels swollen in water to equilibrium, the positive effect of methacrylamide units is compensated for by the negative effect of the increasing degree of swelling, so that the mechanical properties of these gels do not depend too much on the composition of the copolymer. The increasing content of acrylamide in the copolymer strongly raises the degree of swelling, which is reflected in poorer mechanical properties compared to poly(2-hydroxyethyl methacrylate).
By using the method of free torsion vibrations, a detailed dependence was determined of the temperature position and the height of the secondary (β) loss maximum of alkali‐polymerized polycaprolactam upon the concentration of water in the range of 0 < PA < 1.3, where PA is the number of moles of water per mole of monomer units of the portions accessible to the sorption of water. The increase in the secondary loss maximum and the decrease in the height of the low‐temperature loss maximum due to the effect of water in the concentration range 0 < PA < 0.5 is interpreted as consequence of a transformation of the corresponding relaxation processes; subsequent increase in the water content then exhibits only little influence on the height of both the maxima. The β relaxation process is attributed to kinetic units containing amide groups which, owing to interaction with molecules of water, are more firmly bonded to neighboring molecules than the amide groups of a dry polymer. The secondary loss maximum arises also because of the effect of caprolactam monomer and of some low molecular weight amides, being markedly shifted to higher temperatures with the decreasing molecular weight of the amide.
SynopsisThe dynamic relaxation behavior of a model two-phase system, poly(2-hydroxyethyl methacry1ate)-glass beads, was studied by means of a freely oscillating torsional pendulum. The effect of the filler content on the storage and loss moduli of the composites could be described in terms of the modified Kerner equation in complex form. At temperatures below the glass transition temperature of the matrix, the agreement between experimental and theoretical data was satisfactory after correction for thermally induced stress due to different thermal expansion coefficients of matrix and filler. In the presence of filler, the capacity of the matrix to store and dissipate energy increases, but the character of molecular motions underlying the dispersions observed is preserved because the temperature of the dispersions remains unchanged. The effect of water on the dynamic relaxation behavior of composites is primarily reflected in changes in the shape of the temperature dependence of the dissipating capacity of the matrix. The data allow the conclusion to be drawn that the chain mobility a t the interphase boundary does not decrease and that no additional frictional mechanisms appear.
The method of free torsional vibrations was used to determine the temperature dependence of the storage and loss shear modulus of poly(2‐hydroxyethyl methacrylate) samples swollen with ethylene glycol, formamide, n‐propanol, and water. The measurements included the glassy region (starting with temperatures from −130 to −190°C) and the main (α) transition from the glassy to the rubberlike state. At a volume fraction of the low molecular weight compound vd > 0.2, the above systems exhibit, besides the α dispersion, only the secondary (βSW) dispersion, which is generally attributed to the relaxation motions of the hydroxyethyl groups of the side chains interacting with molecules of the diluent. If no separation of the diluent in a second phase occurs at the measurement temperatures, the temperatures of both dispersions decrease with increasing vd and approach the glass transition temperature of the low molecular weight compound. The concentration dependences of the dispersion temperatures were described by an equation derived elsewhere for the concentration dependence of the glass transition temperature. The results indicate that molecules of the diluent contribute significantly to the intensity of the βSW transition and simultaneously affect its limiting temperatures (for vd = 1 and vd = 0). Specific differences among the systems described above appear only at those temperatures where same of the low molecular weight compound separates into a crystalline or glassy phase.
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