A series of new poly(siloxane) and poly(silazane) derivates were synthesized by cationic ring opening mass copolymerization of the cyclic monomers octamethylcyclotetrasiloxane and hexamethylcyclotrisilazane, obtaining poly[(dimethylsiloxane)-co-(dimethylsilazane) ] copolymers with different concentrations of the comonomer units. The molar masses of the soluble fractions of the copolymers and of the macrocycles generated in the copolymerization reaction medium, were determined by gel permeation chromatography. Thermogravimetric analysis shows that poly(dimethylsiloxane) is more stable than the copolymers and the homopolymer poly(dimethylsilazane). Differential scanning calorimetry of poly(dimethylsilazane) presents a melting endotherm, indicating that this homopolymer is crystalline. The copolymers were characterized by FT-IR and ¹H and 13C NMR spectroscopy.. The polymers were thermally cured and pyrolysed, obtaining ceramic powder. The morphology of the ceramic powder, studied by scanning electronic microscopy, corresponds to highly uniform spherical particles. The ceramic material was characterized by FT-IR. It was shown that these cyclic monomers copolymerize and that they constitute pre-polymer precursors of the powdered ceramic material since the products have Si, C, N and O atoms

The thermogravimetric analysis resulted to be an analytical technique, very illustrative that allowed us to determine the thermal stability, molecular structure and the formation process of cross-linked structures, in the synthesis of poly(methylsiloxane). Poly(methylsiloxane) was synthesized by cationic ring-opening polymerization of the cyclic monomer 1, 3, 5, 7-tetramethylcyclotetrasiloxane. A series of polymers were obtained by varying polymerization times. The initial and maximum decomposition temperatures increase to higher polymerization time until constant values are reached. At short polymerization time mainly linear polymers are formed with small fraction of cross-linked structures. At higher polymerization time partial and total cross-linked polymers are obtained. Formation of cross-linked structures stabilizes thermically the whole polymeric matrix, being the stability proportional to the cross-linking degree. The thermogravimetric analysis allowed us to formulate a method to determine the cross-linking degree of these polymers. FT-IR analysis showed the existence of the absorption band of variable intensity, corresponding to the vibration of the Si-H bond, in all the studied polymers. FT-IR spectra of the residual ceramic powder obtained by pyrolysis showed the typical absorption bands of these materials. The characterization of the polymers was also carried out by thermomechanical analysis. Kinetic decomposition parameters such us pre-exponential factors, decomposition reaction orders and activation energies were determined by thermogravimetry.

Complexation between acyclovir (ACV), an antiviral drug used for the treatment of herpes simplex virus infection, and beta-cyclodextrin (beta-CD) was studied in solution and in solid states. Complexation in solution was evaluated using solubility studies and nuclear magnetic resonance spectroscopy (¹H-NMR). In the solid state, X-ray diffraction, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and dissolution studies were used. Solubility studies suggested the existence of a 1:1 complex between ACV and beta-CD. ¹H-NMR spectroscopy studies showed that the complex formed occurs with a stoichiometry ratio of 1:1. Powder X-ray diffraction indicated that ACV exists in a semicrystalline state in the complexed form with beta-CD. DSC studies showed the existence of a complex of ACV with beta-CD. The TGA studies confirmed the DSC results of the complex. Solubility of ACV in solid complexes was studied by the dissolution method and it was found to be much more soluble than the uncomplexed drug.