In the context of optical transmission in the polymer integrated waveguides, transmission losses are a limiting factor for the development of such a technology. In this paper, we analyze the different features that cause optical losses namely intrinsic absorption of the material and light scattering in the bulk. This analysis of optical transmissions mainly in the telecom C-band (1530-1565 nm) and O-band (1260- 1360 nm) is based on measurements in bulk material and solutions. These allow to assess the limiting level of losses induced by the material itself. The results can give the intensity attenuation resulting from defects induced by the waveguide processing. It results that losses by scattering process can reach 0.1 dB/cm at 1550 nm when samples are filtered at 0.2 µm. It is slightly higher at 1320 nm but probably less than 0.2 dB/cm. Most of the optical losses are then due to the intrinsic absorption and can be around 0.7 dB/cm for PMMA, at 1550 nm. Consequently, in the case of channel singlemode waveguides, the global linear loss is higher at this wavelength, and, the additional losses are brought by imperfections of the channel both in the bulk and on the surface. This article also shows that reducing the level of C-H bonds content of the polymers down to 25x 10- 3 cm- 3 the material losses are limiting by scattering and can fall down to around 0.2 dB/cm (at 1550 nm).