Thermodynamic characterization of interpenetrating polymer networks of poly (carbonate-urethane) and poly (methyl methacrylate)

Crosslinked poly (methyl methacrylate) and poly (carbonate-urethane) as well as full interpenetrating network on their base (IPN) were characterized by precise heat capacity measurements in the temperature interval 1.2–150 K. As judged by the positive sign of the excess Gibbs free energy in the whole temperature interval above 30 K, the apparently single-phase state of IPN is thermodynamically unstable; however, its kinetic stability is ensured by permanent chamical crosslinks prohibiting the incipient phase separation. © 1994 John Wiley & Sons, Inc.     

Proteinases immobilized on poly(vinyl alcohol) cryogel: novel biocatalysts for peptide synthesis in organic media

Covalent immobilization of subtilisin and thermolysin on cryogel of poly(vinyl alcohol) was carried out. The biocatalysts obtained are characterized by high stability in water and in DMF—MeCN mixtures of various compositions. The synthetic efficiency of immobilized subtilisin in the multiple iterative synthesis of the peptide Z—Ala—Ala—Leu—Phe—pNA was examined in organic mixtures of different solvent compositions. Immobilized subtilisin exhibits high synthetic activity in organic media. A series of N-acylated p-nitroanilides of tetrapeptides of the general formula Z—Ala—Ala—Xaa—Yaa—pNA (Z is benzyloxycarbonyl, Xaa = Leu, Lys, or Glu; Yaa = Phe or Asp; pNA = 4-NO₂—C₆H₄NH-) were synthesized in 70—98% yields using immobilized subtilisin as a biocatalyst without activation and protection of the ionogenic groups of polyfunctional amino acids. Immobilized thermolysin in a DMF—MeCN mixture catalyzed the formation of the peptide Z—Ala—Ala—Leu—pNA, which was obtained in 90% yield (during 1 h). It was demonstrated that the biocatalyst can be used repeatedly and that it retained activity after storage in an aqueous buffer during 6 months.     

Thermodynamic characterization of carbon black-filled rubbers

Unfilled and carbon black-filled samples of synthetic isoprene- and butadiene-methylstyrenebased rubbers were characterized by precise heat capacity measurements in the temperature interval 4.2–300 K. Both unfilled samples proved to behave in an essentially fracton-like way in the temperature interval 6–30 K. The excess thermodynamic quantities derived from the smoothed data suggested that the thermodynamic state of the elastomeric phase in the filled rubbers was intrinsically unstable.     

Low temperature heat capacity of heterocyclic polymer networks

The predicted crossover to a fractal-like vibrational regime above 8–10 K was apparently proved by precise measurements of heat capacity of a series of cross-linked heterocyclic polymers.