DOI: 10.1002/chem.200801659 Vacuum-UV Irradiation-Based Formation of Methyl-Si-O-Si Networks from Poly(1,1-Dimethylsilazane-co-1-ACHTUNGTRENNUNGmethylsilazane) Lutz Prager,* [a] Luise Wennrich, [a] Roswitha Heller, [a] Wolfgang Knolle, [a] Sergej Naumov, [a] Andrea Prager, [a] Daniel Decker, [b] Hubert Liebe, [b] and Michael R. Buchmeiser* [a, c] Introduction Polysilazanes are widely investigated and practically used as precursors for SiO x gas-barrier layers in packaging indus- try, [1–3] for flexible solar cells, [4, 5] for applications in electron- ics, [6] for vacuum-insulated panels, [7] and for anticorrosive protective coatings. [8, 9] Especially the inorganic oligomer perhydropolysilazane (PHPS) consisting of -SiH 2  NH- structural units has been reported as a precursor to dense and stable SiO x networks. [10–14] The most common pathway for the realization of such SiO x networks is the hydrolysis of the Si  NH bonds and the subsequent condensation of the generated silanols forming Si OSi bonds. [15, 16] At room temperature, this process proceeds slowly. It can, however, be moderately accelerated by the use of catalysts or basic reaction atmospheres. [17, 18] With the aim to avoid the slow condensation process, alternatives that use UV irradiation as the initiating step have been applied. [19–22] Employing such a technology, improved barrier properties on polymer foils, as Abstract: The vacuum-UV (VUV)-in- duced conversion of commercially available poly(1,1-dimethylsilazane-co- 1-methylsilazane) into methyl-Si-O-Si networks was studied using UV sources at wavelengths around 172, 185, and 222 nm, respectively. Time-of-flight sec- ondary ion mass spectroscopy (TOF- SIMS), X-ray photo electron spectros- copy (XPS), and Fourier transform in- frared (FTIR) measurements, as well as kinetic investigations, were carried out to elucidate the degradation pro- cess. First-order kinetics were found for the photolytically induced decom- position of the Si NH-Si network, the subsequent formation of the methyl-Si- O-Si network and the concomitant deg- radation of the Si CH 3 bond, which were additionally independent of the photon energy above a threshold of about 5.5 eV (225 nm). The kinetics of these processes were, however, depen- dent on the dose actually absorbed by the layer and, in the case of Si-O-Si formation, additionally on the oxygen concentration. The release of ammonia and methane accompanied the conver- sion process. Quantum-chemical calcu- lations on methyl substituted cyclo- ACHTUNGTRENNUNGtetrasilazanes as model compounds substantiate the suggested reaction scheme. Layers < 100 nm in thickness based on mixtures of poly(1,1-di- methylsilazane-co-1-methylsilazane) and perhydropolysilazane (PHPS) were coated onto polyethylene terephthalate (PET) foils by a continuous roll to roll process and cured by VUV irra- diation by using wavelengths < 200 nm and investigated for their O 2 and water vapor-barrier properties. It was found that the resulting layers dis- played oxygen and water vapor trans- mission rates (OTR and WVTR, re- spectively) of < 1 cm 3 m 2 d 1 bar 1 and < 4gm 2 d 1 , respectively. Keywords: barrier layers · photoly- sis · silazanes · surface chemistry · UV irradiation [a] Dr. L. Prager, Dr. L. Wennrich, R. Heller, Dr. W. Knolle, Dr. S. Naumov, A. Prager, Prof. Dr. M. R. Buchmeiser Leibniz-Institut für Oberflächenmodifizierung e.V. Permoserstraße 15, 04318 Leipzig (Germany) Fax: (+ 49) 341-235-2524 E-mail : lutz.prager@iom-leipzig.de michael.buchmeiser@iom-leipzig.de [b] Dr. D. Decker, H. Liebe Clariant Produkte GmbH Am Unisys-Park 1 65843 Sulzbach a. T. (Germany) [c] Prof. Dr. M. R. Buchmeiser Institut für Technische Chemie Universität Leipzig LinnØstraße 3, 04103 Leipzig (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200801659. Chem. Eur. J. 2009, 15, 675 – 683  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 675 FULL PAPER