Study of EETMOS hydrolysis and polycondensation by 29Si NMR spectroscopy. Application to optical 3D waveguides fabrication

In the last few years, ORganically MOdified SIlicates RxSi(OR)4−x (ORMOSIL) prepared by the sol–gel process were particularly attractive for the making of integrated optics. A composition based on 3-(trimethoxysilyl)propylmethacrylate (MAPTMS) has already allowed the industrial manufacturing of optical integrated devices. For this kind of material, the polymerization of the organic network is based on free radical curing under UV laser exposure. This type of polymerization has some disadvantages, in particular, it is inhibited by oxygen. To optimize the final properties, we tried to obtain waveguides with another hybrid precursor [2-(3,4 epoxycyclohexylethyltrimethoxysilane)] (EETMOS) using cationic polymerization. The main advantage of cationic polymerization is its ability to allow cure reaction in the presence of oxygen, unlike radical polymerization. We have chosen cycloaliphatic compounds because of their well known high polymerization rates. The polymerization of the organic network of this hybrid material requires a cationic photoinitiator corresponding to our LASER writing wavelength (λ = 262 nm). In this work, hydrolysis and polycondensation of EETMOS-based solution are followed by 29Si NMR. The main objective is to obtain the highest reactive multifunctional oligomer with the lowest OH groups content. The effects of pH, hydrolysis rate, HF and photoinitiator additions are studied in order to obtain the most optimized solution. Based on our results, we obtained 3D waveguides with a cross section of 5 × 5 μm2.