The swelling curves of 6μ films of low conversion homopolymers and copolymers of acrylamide (AM) and N‐isopropylacrylamide (NIPAM) were obtained in water by an optical microscope technique. Poly(AM) swelled appreciably faster than poly(NIPAM) but there was no apparent correlation between overall swelling rate and copolymer composition. A 57/43 (mole %) AM–NIPAM copolymer swelled fastest. Sequence distribution calculations indicated that its backbone structure tended toward comonomer alternation, which might reduce the extent of hydrogen bonding in the film. The amount of water sorbed during swelling, as approximated from increasing film thickness, was proportional to the square root of time and agreed well with previous work in the literature. Homopolymer films from runs of ca. 50% conversion consistently swelled slower than their low conversion counterparts, probably due to branching and increased entanglements. Heating also promoted slower film swelling due to a tightening of the film structure and/or a low degree of imidization. Monomer reactivity ratios and Alfrey‐Price Q and e values for NIPAM were calculated. Cloud points of 5% aqueous solutions of the copolymers were measured and found to decrease with increasing NIPAM content.

Polyacrylylglycinamide (PAG) and its thermally reversible aqueous gels have been investigated and comparisons made with gelatin. For unfractionated PAG homopolymers in 2M NaCNS at 25°C, the Mark‐Houwink‐Sakurada equation is [η] = 1.16 × 10−3 M̄n0.52. The Huggins k′ value is found to be about 0.9 and the Flory‐Huggins polymer‐solvent interaction parameter, 0.49. A theoretically calculated value of Kθ is very close to the experimental one and it is for this reason and the observed μ and M̄n exponent values that 2M NaCNS at 25°C approaches being a θ solvent for PAG. A thermodynamic approach based on equilibrium swelling and modulus measurements indicates that a single thermally reversible crosslink in a gelatin gel involves numerous peptide backbone units, whereas in PAG gels a crosslink perhaps involves only one residue from each of two chains. These results complement the very high exothermic heat of gelation crosslinking, δHc, for gelatin compared to PAG. ΔHc has been measured on PAG samples of different DP and found to be independent of chain length. Similar measurements on acrylylglycinamide copolymers and terpolymers containing basic and acidic groups produce no change in δHc so that coulombic forces do not appear to be significant. Data are also included relating to the density of PAG, its glass transition and thermal decomposition temperature, the tensile modulus of equilibrium‐swelled PAG films in water and the chain‐transfer constant of methanol with the acrylylglycinamide free radical.

SynopsisThe high-resolution carbon-13 NMR spectrum of hydroxyethylcellulose (HEC) with about 2.5 moles of ethylene oxide (MS 2.5) average substitution per anhydroglucose ring (AHG) is presented. From models, the CMR chemical shifts for all of the different carbon atoms are assigned. Direct measurement of the relative intensities of the CMR signals for certain carbon atoms in HEC permits rapid and accurate computation of (1) the average chain length of poly(ethy1ene oxide); (2) the degree of substitution of ethylene oxide, and (3) the average relative degree of substitution of the alcohol groups on the AHG ring.

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Nylon 66 and nylon 6 yarns were exposed in air, nitrogen, and vacuum to temperatures from 136 to 215OC. for periods from 5 min. to 17.5 hr. The moisture absorption of both fibers is reduced by the exposure independently of the presence of oxygen or of antioxidant. This is ascribed to secondary crystallization. Siultaneuusly, the electrical resistivity is increased. The breaking strength is reduced by exposure in the presence of oxygen anlesa the polymer contains antioxidant. The extent of oxidative cleavage was measured by the viscosity-average molecular weight of nylon 66. Simultaneously, a reduction of the amine endgroup content waa observed. It occurs only in the presence of oxygen and approaches a limit indicating that some amine groups are not subject to elimination. If oxygen is absent or the polymer protected by antioxidant, the Sorption of hydrochloric acid is reduced by the exposure. Only 80% of the amine groups in the unexposed and 55% in the exposed nylon participate in acid binding a t pH 2.5. The rate constants of cleavage as manifested by a,, and of the process leading to disappearance of amine groups were determined for nylon 66. The activation energies were calculated 40 and 36 Kcal./mole, respectively.increases.