No abstract

synopsisThe mechanism of film formation was studied with respect to the flocculation phenomenon. It was observed that almoet all latices would air-dry to a point at which coagulation of the latex particlee had juat occurred and beyond which the wet film was no longer redispersible in water. Thia flocculation point was sharp and could be detected visually or by immersing the film in water. Two methods have been devised t o measure the solids at which incipient flocculation occurred: croseeection method, and cone method. The floc point was found to be about 5Q-60% for B model acrylic latex depending on the soap present in the dispersion. After flocculation had occurred, further drying would lead to different 6lm properties depending on the hardnesa of the particles, the rate of drying, the substrate, and the degree of croeslinking.

The degrees of crosslinking of three post‐gelation high‐conversion copolymers were measured by γ‐irradiation, extraction, and swelling experiments. The copolymers containing 0.2, 0.5, and 1.0 mole‐% of the crosslinker were prepared by suspension polymerization at 60°C. with a free‐radical catalyst. The degree of effective chemical crosslinking for the parent copolymers was calculated by correlating irradiation dose with extractables data after Shultz and the efficiencies of effective crosslinking were 40, 35, and 27% for the three copolymers, respectively. Based on related data by other workers, the low effective crosslinking efficiencies were due partly to incomplete polymerization of some crosslinkers on both ends and partly to wastage of crosslinks by intramolecular cyclization. On correlating the extractables data with the backbone molecular weight of the irradiated and extracted gels after Horikx, similar crosslinking efficiencies were obtained. A new technique has been shown to obtain the latter information by hydrolyzing the copolymer with 80% sulfuric acid under specific conditions and reesterifying the hydrolyzed intermediate with diazomethane. The effective chemical crosslinking of the irradiated and extracted gels, (ve)ir, were calculated from the crosslinking efficiency and extractables data. The degree of effective crosslinking, (ve)sw, for the parent as well as the irradiated gels were calculated from swelling data by means of Flory's swelling equation. It was found that the apparent value of (ve)sw for a given polymer decreased when a better solvent was used in the swelling. This finding was interpreted to be due to failure to correct the polymer‐solvent interaction parameter X1, that was used in the swelling equation, for concentration dependence. The aim of this work was to ascertain the validity of the swelling equation with respect to the prediction of (ve)sw. On comparing (ve)ir with (ve)sw, the latter being determined in benzene (X1 = 0.439), the ratios (ve)sw/(ve)ir for the three parent copolymers were between 9 and 10. A large part of the discrepancy was believed to be due to the presence of permanent chain entanglements which acted like physical crosslinks. (ve)sw/(ve)ir for the corresponding irradiated and extracted gels decreased sharply, and all appeared to approach an apparent common limit of about two at large irradiation doses. The theoretical limit should be one. Since the theory of rubber elasticity by James and Guth would require the limit of (ve)sw/(ve)ir to be 0.5 by the present scheme, Flory's theory on which the swelling equation was based seemed to be preferable. This work, however, could not distinguish Flory's theory from a slightly different theory by Hermans.

Copolymerizations of methacrylic anhydride and a variety of common types of vinyl monomers were conducted in bulk and in solution at 60–80° with benzoyl peroxide catalyst. The copolymers were characterized by conversion, solubility in hot dimethyl sulfoxide, elementary analysis, and infrared spectroscopy. A copolymer composition equation was derived for a special divinyl–vinyl system in which the divinyl monomer would cyclize extensively during polymerization and give rise to soluble, although perhaps branched, copolymers. The results showed that both soluble and insoluble copolymers were obtained, depending on the comonomer used and experimental conditions under which the copolymerization was carried out. In general, soluble copolymers were formed under the following conditions: (a) the less reactive the comonomer in free radical copolymerizations; (b) the greater the dilution; (c) the greater the difference in the moles of the two components in charge; and (d) the lower the conversion. According to reactivity ratio determinations and a comparison with published data, the anhydride ring radical behaved like a methyl methacrylate radical. The key step which led to gelation was believed to be “ring interruption” by the comonomer (CH2 = CHR): The question why methacrylic anhydride does not gel in homopolymerization, however, still remains unresolved.

The free‐radical polymerization of four acrylic anhydrides—methacrylic anhydride, acrylic anhydride, acrylic methacrylic anhydride, and acrylic propionic anhydride—under a variety of conditions has been studied. The polymers and their polyacid and polyester derivatives were characterized by solubility, infrared spectroscopy, and x‐ray diffraction. Methacrylic anhydride could be polymerized in bulk and in hydrocarbon solvents from −50°C. to 80°C. to give soluble, linear cyclopolymers in high conversions. In a polar solvent such as dimethyl sulfoxide, gelation would result at high monomer concentrations and at high conversions. Acrylic anhydride, however, appeared to become crosslinked more readily; soluble polymers could be obtained only by polymerization in nonpolar solvents. Most of the previous and somewhat conflicting results on the cyclopolymerization of these two monomers can now be reconciled by the present findings. The physical properties of cast poly(methacrylic anhydride) suggest that it has a stiff backbone with hindered functional groups and that the monomer itself was perhaps intramolecularly associated. Some improvements in the aqueous hydrolysis of poly(methacrylic anhydride) and in the esterification of the derived polyacid by diazomethane were described. By these refinements, poly(methyl methacrylate), derived from a −50°C. poly(methacrylic anhydride), had previously been shown to possess a novel, mixed syndiotactic and syndioduotactic (++−−++−−) configuration. Acrylic methacrylic anhydride could be cyclopolymerized very much like methacrylic anhydride. The polyacid and polyester derived from this unsymmetrical anhydride are expected to have unique structures; the acrylic or methacrylic units in the derivatives do not occur more than twice in succession. Acrylic propionic anhydride, when homopolymerized, readily changed to a soluble polymer and an unidentified, immiscible liquid. Its soluble copolymer with methyl methacrylate, however, could be crosslinked by heating. An intramolecular and intermolecular disproportionation reaction was postulated to explain these two interesting observations, respectively.