Polyacrylonitrile of molecular weight 130,000 has been pyrolyzed under nitrogen, between 200° and 320°. The predominant gaseous products are hydrogen cyanide and ammonia; the rates of formation of these have been measured, and at 270° for example, after 300 minutes, only 10% of the available nitrogen is lost. A liquid distillate containing nitriles, amines, and unsaturated groups was also obtained. Using infrared absorption measurements, it was found that the nitrile groups of the polymer disappear as heating progresses, and CN linkages appear. As heating is continued, evidence for aromatization is found. These experimental facts indicate ring formation to be an important reaction; the heat‐stable residues are considered to be mainly fused pyridine systems.
synopsisMonolayer balance techniques have been used to study "two-dimensional" polymerization of monomolecular films of octadecyl methacrylate and a divinyl ester. Polymerizations were initiated with ultraviolet radiation, and reaction rates and properties of the product evaluated from surface pressure-area isotherms. The polymerization rate of the acrylate in argon is linear up t o 70% conversion; the product obtained in this way exhibits an isotherm which may reflect the packing and orientation of the starting monolayer. Rate data for the divinyl system-the product of which should be a sheetlike, two-dimensional analog of a network system-exhibit no unusual features.
The electronic environment about the main chain atoms in polystyrenes has been varied systematically by introducing electronegative or electropositive substituents (H3C, CH3O, Br, Cl, NC, and O2N groups) in the p‐position of the ring. Energy yields for γ‐initiated H2 formation and crosslinking, both a measure of the radiation sensitivity of the backbone, were determined above and below Tg from (1) mass spectrometric examination of the decomposition gases and (2) molecular weight changes. For most of the polymers, it is concluded that the backbones of p‐substituted polystyrenes are more radiation stable than that of polystyrene, and that main chain macroradicals formed early in the reaction are responsible for the major changes observed, i.e., hydrogen evolution and crosslinking. The role of the p‐substituent on the latter effects is interpreted qualitatively in terms of the contribution by the substituent to the resonance stability of these intermediate polymer radicals. In the case of poly‐p‐bromo‐ and poly‐p‐chlorostyrene, the inordinately high sensitivity to crosslinking and the absence of halogen atoms in the decomposition gases suggest the importance of a chain reaction in the radiation chemistry of these molecules.
Vinyl stearate has been polymerized by 1000 kv. electrons with field intensities ranging from 1.0 × 103 to 20 × 103 rep per second; the polymers are considered to be branched. A discontinuity of reaction rate and molecular weight with respect to temperature was noted in the vicinity of monomer melting point, and it is suggested that in this temperature region, the diffusion constant for propagation is easily affected. A linear relationship between field intensity and polymerization rate, and a constancy in molecular weight with varying field intensities, at constant total dose, indicated that polymerization occurs in “volume elements.”
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