The photodegradation of segmented polyurethanes based on methylene 4, 4′‐diphenyldiisocyanate (MDI) is shown to be dependent on the physical structure of the polymer. As the hard segment content of the polyurethane is increased, the photodegradation efficiency is lowered. In particular, the extent of the photolytic decomposition is inversely dependent on the degree of hydrogen bonding in the aryl carbamate groups in the polyurethane backbone. Utilizing appropriate model compounds for comparison, the formation of the ortho photo‐Fries rearrangement product, as detected by fluorescene spectroscopy, is also shown to be dependent onthe degree of hydrogen bonding. In general, the restrictive mobility imposed by hydrogen bonding is a critical factor which must be considered in the photochemistry of segmented polyurethanes.

SynopsisThe ability of aromatic amines to accelerate the photoinitiated polymerization of multifunctional acrylates in the presence of oxygen is shown to be dependent on the structure of the amine.For N, N-dimethylaniline, a rapid oxygen-scavenging process which proceeds by a radical-chain mechanism accounts for the large polymerization rate increase. Conversely, aniline cannot sustain an oxygen-scavenging process and inhibits the polymerization of air-saturated monomers. In general, the degree of rate enhancement and/or inhibition of the aromatic amines investigated is subject to the amine concentration.

Fluorescence analysis has been employed as an analytical technique to elucidate the photolysis mechanism of several aromatic diisocyanate‐based polyurethanes in solution. Based on a comparison with model arylmonocarbamates and arylbiscarbamates, the photo‐Fries rearrangement and cleavage‐type products found for the small‐model arylcarbamates were also identified for the photolyzed polyurethanes in solution. Viscosity and absorbance change results for photolysis of both air and nitrogen‐saturated polyurethane solutions are consistent with a general two‐step mechanism for the photolysis of aromatic diisocyanate‐based polyurethanes.

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SynopsisPolymerization of styrene in gel-like emulsions (concentrated emulsions which have a volume fraction of monomer greater than 0.74), by using sodium dodecylsulfate as emulsifier and small amounts of water, was carried out with an oil-soluble initiator, AIBN. Both higher conversions and higher molecular weights of the polymer were obtained as compared to the polymerization in bulk. The higher "rigidity" of the monomer in the interior of the cells of the gel is responsible for the increased rate of polymerization and molecular weight. The polymer particles thus obtained have diameters in the range of 0.1 to 0.3 pm, depending upon the conditions of preparation of the gel. The effects of the concentration of the initiator, the concentration of surfactant, the monomer volume fraction, termperature, and ionic strength of the aqueous solution have been investigated.