The miscibility of polyester/nitrocellulose blends was investigated by differential scanning calorimetry and Fourier‐transform infrared (FTIR) spectroscopy. Two nitrocelluloses (NC) derived from wood and having different nitrogen contents (12.62 and 13.42%) were used. On the basis of the glass transition temperature criterion, poly(ϵ‐caprolactone) (PCL), poly(valerolactone), poly(ethylene adipate), and poly(butylene adipate) are miscible with nitrocellulose, whereas poly(α‐methyl α‐propyl β‐propiolactone) and poly(α‐methyl β‐proiolactone) are immiscible. The Tg versus composition curves of PCL/NC blends do not follow a monotone function but exhibit a singular point at a critical PCL volume fraction of 0.51 for NC‐1342 and 0.45 for NC‐1262 in agreement with Kovacs' theory. A shift of 17 cm‐1 of the carbonyl stretching band was observed with PCL/NC blends and is taken as evidence for hydrogen bonding interaction between the PCL carbonyl group and NC hydroxyl group. The frequency difference between the free hydroxyl absorbance and the absorbances of the hydrogen‐bonded species was found to be 85 cm‐1 in pure NC and 125 cm‐1 in PCL/NC blends; it indicates that the average strength of this interaction is stronger than the corresponding self‐associated hydrogen bonding in pure NC. The presence of a dipole‐dipole interaction between the nitrate‐ester groups of NC and the carbonyl groups of the polyesters is reported. The relative strength of the hydrogen bonding and dipole‐dipole interactions is discussed and correlated with polymer miscibility.

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'HOMME, G r o v e de recherche sur les m c m m~c u l e s , Lldpartement de chi&, Universitd Laval, Q&bec (Qu4bec) Canada GlK 7P4 synopsis The nonisothermal decomposition of nitrocellulose (NC) films cast from acetone, tetrahydrofuran, and ethyl acetate was followed Using Fourier transform infrared (FI'IR) spectroscopy. NC samples were derived from wood (two samples) and from cotton (four samples) and their nitrogen content ranged from 12.6 to 13.5%. Kinetic parameters such as activation energies and preexponential factors were calculated using the curvefitting treatment initially proposed by Eisenreich and Pfd and the FI'IR relative absorbance intensity of two functional groups (i.e., C = O and NO,). The experimental data were best described by a first-order autocatalytic equation with activation energies equal to 178 and 175 kJ/mole for the two steps of the autocatalytic reaction. No variation in activation energy was observed between the different NC samples, whatever their nitrogen content and vegetal origin, or the solvent used to cast films. The extinction coe5uent of the hydroxyl groups of NC was also determined Using a modified Beer-Lambert equation and used to calculate precisely their nitrogen content.

Extensive Raman measurements have been made on calf thymus chromatin, core chromatin, the (H3,H4)/DNA complex, and isolated DNA. The results indicate that the alpha-helical content of the nucleosomal histones gradually increases as they form the heterocomplexes that lead to the formation of the octameric nucleosome core. The secondary structure of the latter is not modified as it binds to DNA. The spectra indicate that the DNA essentially retains its B conformation in nucleosomes, although slight changes probably occur in the ribose-phosphate backbone. No specific interactions between the nucleosomal histones and DNA can be established from the spectra, but histone H1 possibly interacts selectively with the thymine bases.