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The surface degradation of both linear and crosslinked polymethylmethacrylate (PMM) has been studied over the surface temperature range of 550° to 910°K by means of a hot-plate pyrolysis technique. It was demonstrated that surface gasification due to the high heat flux at the decomposing PMM surface involves a depolymerization process and surface desorption of methylmethacrylate monomer. The apparent activation energy for the linear rate of regression of the solid PMM surface (linear pyrolysis rate) was found to decrease with increasing surface temperature, approaching a limiting constant value of 11.2±0.6 kcal/mole at ∼650°K for linear PMM and at ∼770°K for crosslinked PMM. The mechanism for the surface degradation is depicted as (1) formation of monomer in the surface substrate, (2) diffusion of monomer to the surface, and (3) desorption of monomer from the surface. The linear pyrolysis rate data are correlated by means of an absolute rate theory treatment of surface decomposition. The experimental results are in good agreement with the theory.

Temperature Dependence of Osmotic Pressure of Polyvinyl Chloride 1631 of substituents about the double-bonded carbons (RsC=CHR) is reflected in the strong 12.16m band.8 The structure of the low boiling isomer is clearly indicated to be the unconjugated form, 4-methyl-4-penten-2-one, by the fact that the 0=0 band• appears at the normal unconjugated ketone position, 5.83m, and that the strong band in the 10 to 15m region occurs at 11.16m, the position associated with the R20=CHí configuration.® This result is in agreement with the Raman work of Dupont and Menut4 on a mixture of the isomers, the presence of a 1716 cm.-1 line associated with unconjugated 0=0 indicating an unconjugated form.In agreement with chemical evidence referred to in the preceding article, no appreciable concentration of enol form was present as indicated by the weakness of hydroxyl group absorption near 3.0m• The ultraviolet absorption spectra (2100 to 5000 Á.) independently lead to the same conclusion. The high-boiling isomer exhibits bands at 2310 and 3290 Á. (molar extinction coefficients 1.20 X 104 and 40.5 liters/mole cm. respectively; spectra of i-octane solutions). These bands are closely similar in position and intensity to those

SynopsisEase of processing suspension-polymerized polyvinyl chloride (PVC) is related to its ability to accept sufficient plasticizer, while remaining a dry, free-flowing powder. The successful incorporation of plasticizer, termed cold preblending or hot dryblending, depends upon basic physicochemical factors. Cold preblending corresponds to a purely geometrical filling of intraparticle pores and fissures, while hot dryblending depends additionally upon a time-dependent absorption. Quantitative laboratory tests for these two effects were developed and standardized. When applied to experimental and commercial lots of PVC and their fractions, the tests gave results which showed slight correlation with gross properties of the particles. However, intercorrelation between tests for cold preblending and hot dryblending was strong, indicating that the same factors may be responsible for both. The testa also provided good ratings of polymers for actual processing behavior. It is possible to control particle geometry via the process variables of suspension polymerization, and thence to regulate cold preblending behavior; the effects on hot dryblending are not as clear. Post-polymerization grinding markedly alters the PVC particle surfaces and can substantially improve hot dryblending capacity. Severe grinding is needed to change particle geometry enough for any large improvement of cold preblending.

Three synthetic α‐polypeptides were spread on aqueous substrates from suitable molecular solutions, and the surface areas, pressures, compressibilities, etc. measured on a horizontal film balance. On pure water spreading occurred at the best in the form of condensed films, but on aqueous solutions spreading improves with the solute concentration, especially near saturation of lyotropic compounds such as urea or potassium thiocyanate. On such substrates molecular weights (MW) and surface areas (SA) can be calculated by means of a modified van der Waals' equation. The MW and SA obtained as a function of substrate nature are found to be functionally related. The conditions and assumptions under which such a relation may be used to decide on true MW's, and their pertinence for the above polypeptide data, are discussed. Di‐ and trivalent cations in the substrate are found to increase MW's in accordance with their valence.