Conformational energies have been determined by Fourier transform infrared (FT IR) spectroscopy for isotactic, atactic, and syndiotactic PMMA's and the results have been compared with rotational isomeric state (RIS) calculations. Results for syndiotactic PMMA by FT IR (2000 cal/mol) are in good agreement with RIS calculations (1900 cal/mol), but FT IR results for isotactic PMMA indicate a lower conformational energy (700 cal/mol). Conformational energies for the side chain vary from 700 to 900 cal/mol with tacticity.Conformational contributions to the specific heat change at the glass temperature are calculated and compared with experimental results and previous analyses. The constancy of AH/RTg predicted by the Gibbs-DiMarzio theory is found not to hold. AH/RTg varies from 1.2 to 2.6 with tacticity. Other factors, such as the conformation and packing of side chains, must influence the glass transition process.

In an attempt to clarify the criteria satisfied at the glass transition (Tg) the effect of pressure on Tg of polyvinyl acetate has been measured by dielectric and volumetric techniques. Dielectric constant and loss has been measured as a function of temperature (25–120°C.), pressure (0–3300 atm.) and frequency (0.06–10 kcycles/sec.). At fixed frequency the temperature at which ε″max occurs increases with pressure by 0.022°C. atm. and this value is identified with (∂Tg/∂P). The In τD (where τD is dielectric relaxation time) is linear in the pressure. This dependence of In τD on pressure is different from the dependence of In τD on (T − Tg), which can be described by the WLF equation. By assuming f = (f0 + αfΔT)/(a + bP) and using the free volume model, we find In ap = bP/(f0 + αfΔT). If a = 1, f0 = 0.025; then the calculated value of b is 3.1 × 10−4 atm., and 1/b = 3.2 × 103 atm. is the same order of magnitude as an internal pressure. Volume measurements were made by the piston displacement method and by use of an Instron tester for recording force and length. The change in compressibility at Tg was used to follow ∂Tg/∂, and ∂Tg/∂P = 0.021°C./atm. in good agreement with the dielectric measurements. It was found that the volume of the sample at the same final pressure is smaller when compressed at high temperature than at low temperatures. In other words, vitrification at high temperatures and pressures produces a more dense sample than can be achieved by compression at low temperatures and seems to be a property of many glass forming systems. These results and other examples were used to show that the application of thermodynamic equations, namely ∂Tg/∂P = TgVΔα/ΔCp, to the glass transition is justified.

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2657that the amino acids are zwitterions and that glycine6 has an entropy of ionization of -8.9 e.u., but these acids must have much smaller dipole moments owing to smaller charge separations than the above classes of acids. Thus, it appears probable that the pyridinecarboxylic acids exist in solutions principally in nonzwitterionic form, contrary to the conclusion of Millero, etal.The heat capacities of atactic polystyrene and of amorphous and partially crystalline isotactic polystyrene have been measured from 300 to 520'K. and, in the case of the atactic sample, in the low-temperature region also. The results show that molecular configuration in itself has only a minor effect on bulk thermodynamic properties, and that the partially crystalline material obeys a two-phase additive model reasonably well. Residual entropies and enthalpies for the amorphous polymer were calculated as a function of temperature and related to current theories of glass formation.(2) G. Natta, P. Conadini, and I. W. Bassi, Numo Cimento, Sup& 1 , 15, 68 (1960).

Specific heat data for isotactic, atactic, and syndiotactic PMMA from 80 to 445 K are reported. The specific heats of the three polymers are monotonic functions of temperature and are the same within 1% from 80 to 300 K. Glass transition temperatures of 318, 378, and 388 K are observed for isotactic, atactic, and syndiotactic PMMA, respectively, with small differences in ACp. In the liquid the isotactic polymer has a slightly higher specific heat. Only the isotactic polymer could be prepared in the crystalline state by solvent treatment and yielded crystals with a maximum melting point of 435 K. From the calculated entropy of the crystalline and amorphous isotactic polymer, a residual entropy at of 2.5 eu is found. Extrapolation of ASt to zero leads to Tg -= 33 K and T2 = 285 K. In addition, the calorimetrically determined difference in entropy between PMMA stereoisomers was found to be 3 eu. The calculated conformational contributions to this difference were about 0.5 eu from rotational isomeric state calculations and volume effects. Thus additional intermolecular and/or intramolecular factors contribute to the entropy.