Kinetic Study of Thermal Degradation of Polydimethylsiloxane: The Effect of Molecular Weight on Thermal Stability in Inert Atmosphere

RuaIgaj A,Sebenik U,Krajnc M

doi:10.4172/2471-9935.100024

Abstract

Thermal degradation of polydimethylsiloxane (PDMS) of different molecular weights in inert and oxygen atmosphere is studied and discussed in detail. PDMS samples of different molecular weights were prepared by anionically initiated ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion. The molecular weight of PDMS drastically affected the shape of TGA curve at higher temperatures when thermogravimetric (TGA) measurements were performed in the inert atmosphere. The thermal stability of PDMS decreased with increasing the average molecular weight of the sample, which could be explained by prevailing unzipping mechanism at lower molecular weights over intramolecular and intermolecular redistribution, which were more important at higher molecular weights. On the other hand, experiments in oxygen atmosphere showed zero effect of polydimethylsiloxane molecular weight on its thermal stability. In addition, a kinetic model describing the thermal degradation of PDMS in inert atmosphere as a function of PDMS molecular weight was proposed. The proposed kinetic model was composed of diffusion-limited kinetics step related to evaporation rates of the degradation products and of rate-determined step related to the formation of cyclic degradation products. As a result of mathematical modeling by fitting the calculated data to experimental data kinetic parameters were derived properly.

Highlights

One of the technically most important advantages of polysiloxanes is their superior thermal stability if compared to the other polymeric materials
When building kinetic model we focused on two main effects: degradation of polydimethylsiloxane and evaporation of the formed molecules
The results in inert atmosphere showed better thermal stability of samples with lower molecular weights, which we explained by different mechanisms of thermal degradation of PDMS

Summary

Introduction

One of the technically most important advantages of polysiloxanes is their superior thermal stability if compared to the other polymeric materials. Their applicability exhibits over the wide temperature range. Beside the high thermal stability, polysiloxanes possess low electrical conductivity and a large degree of main-chain flexibility. For that reason their value is recognized in different areas, namely automotive industry, metallurgy, electronics and medicine, used as in a form of lubricants, high temperature stable fluids, elastomers or adhesives. The main drawback of obtained emulsions is their emulsifier and initiator residues content, which can affect polysiloxane thermal stability [4,6,7,8,9,10,11]

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Results

Conclusion