engleski

Characteristic vibrations of siloxane structures in different phases

As a part of our study of polymerization process of aminopropylsilanetriol (APST) we investigated the behavior of the APST dissolved in water under low pressure (approximately 5 mbar) by Raman spectroscopy. It has been already noticed that the polymerized structure of APST depends significantly on the temperature at which the condensation took place. At the same time the speed of evaporation of water could also play important role in forming different polymer structures. In order to distinguish between these two influences, the glass tubes with solution were connected to the vacuum pump and exposed to the low pressure of app. 5 mbar for one to three hours. The samples with different concentrations of water were then left to polymerize under atmospheric conditions. In order to determine the starting water content, the samples were weighted after being exposed to the low pressure and at the end of the condensation process. Raman spectra of vapor, solutions and of condensed samples were recorded. Structure developments were also monitored under mid-magnification optical microscope. In the Raman spectra of vapor above the solution we observed the bands of water molecules and those characteristic for APST molecule. The spectra of solutions show the change in distribution of water clusters present in different solutions. Concentration of dimmers and trimmers is increasing with decreasing content of water. On the other hand, the same condition favors formation of gauche conformation of propyl chain in APST molecules. Spectra of APST polymer obtained from 25% solution show presence of water. In the spectra of samples that were exposed to the low pressure, and then left to condensate, no presence of water was observed. The accelerated decrease of water content favors the gauche conformation of propyl chains and hinders the formation of siloxane ladder structure in APST polymer. In slowly polymerized structures some water remains, participating in formation of layers by forming hydrogen bonds between ladders.

propylsilanetriol ; polymerization ; conformations ; ladder

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