Preparation of Phenylsiloxane Films VIA Solution Deposition Techniques
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PREPARATION OF PHENYLSILOXANE FILMS VIA SOLUTION DEPOSITION TECHNIQUES E.W.
Burkhardt*,
R.R. Burford**,
and J.H.
Deatcher*
*Akzo Chemicals Inc., Livingstone Ave., Dobbs Ferry, NY 10522 **Chisholm Institute of Technology, Department of Chemistry, East Caulfield,
Victoria,
Australia,
3145
ABSTRACT Thin films (i-I0 thick) can be spin coated on a variety of substrates from formulations containing polyphenylsiloxanes and alkylsilicates. These films may be cured either thermally or photochemically, yielding films with good adherence to the substrate. The combination of photolysis and thermolysis results in changes in the film hardness characteristics. The use of a mask during photocuring results in films which may be developed in either a positive or negative fashion. The preparation of various formulations along with film curing processes will be discussed. INTRODUCTION Silsesquioxanes (R-SiO0. 5 ) are interesting materials in that they possess both organic and inorganic properties. These materials have been the object of investigation for use in areas such as interlayer dielectrics [1-3], modifiers for glassy materials [4,5], and protective coatings for low earth orbit environments [6-8]. The solubility of silsesquioxane oligomers is dependent in part upon the nature of the organic group present, the size of the polymer chain, and also the degree of crosslinking (free hydroxyl content). We have found polyphenylsilsesquioxane (Wacker brand SY-430) to be a useful component in formulations for the spin deposition of siloxane films. Our goal was to develop systems which would exhibit film characteristics such as good adhesion to a variety of substrates, planarity, increased thickness without cracking, flexibility, and variable curing methods. EXPERIMENTAL Description of reagents and systems prepared The systems consist of mixtures of SY-430 with a variety of alkylsilicates. SY-430 [9] is a phenylsilsesquioxane oligomer with an average molecular weight of 1700, containing -5 wt% free hydroxyl groups and a softening point of 50 0 C. SY-430 is known to react with a number of functional organic groups through its free -OH groups and is thermally stable up to temperatures of 450 0 C. Alkylsilicates used include tetraethylorthosilicate (TEOS), triethoxyvinylsilane (TEVS), and triethoxyphenylsilane (TEPS). A nomenclature system has been developed in order to quickly identify the systems as to their composition. In some cases, SY-430 is dissolved in an organic solvent such as toluene or l-methoxy-2-propanol, followed by addition of Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
768
tetraethylorthosilicate (TEOS). This system is given the designation "a". The weight ratio of SY-430 to TEOS can vary from 10:1 to 3:1, with a 6:1 ratio giving the best results. The weight ratios of solvent to SY-430 and TEOS can vary depending on the film thickness desired. A minimum solvent:SY-430:TEOS ratio for good films is about 10:6:1, generally a ratio of 15:6:1 is used. Systems can also be prepared without orga
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