Polymer Bulletin, Vol.74, No.3, 857-872, 2017
Alteration of the refractive index of polyacrylate and poly(styrene-co-acrylate) films via molecular structure modification
The alteration in the refractive index (RI) of the polyacrylate and poly(styrene-co-acrylate) films was performed in order to produce a gradient index in the polymeric RI profiles. Such gradient is imperative especially in realizing the fabrication of the polymeric multilayer optical filters and the graded-refractive-index polymeric-based antireflection films. In this study, the highest RI obtained is 1.528 with the poly(styrene-co-acrylate) film which consists of 25 wt% of styrene (Sty), 70 wt% of butyl acrylate (BA) and 5 wt% of acrylic acid, with 8 wt% of divinyl benzene (DVB) which can be utilized to alter the flexibility or the hardness of the polymeric materials. Replacing Sty with methyl methacrylate (MMA) in the copolymer without DVB gives the lowest RI of 1.472 and a difference of RI of 0.056. The Sty copolymer system that contains 8 wt% of DVB has been identified to be one of the effective factors, which yields a refractive index of approximately 0.040 higher than that obtained from the PMMA copolymer system when the same amount of DVB was used. The incorporation of the DVB up to 8.5 wt% has resulted in an increase of the refractive index of approximately 0.013 in the poly(MMA-co-BA-co-AA) copolymer. The refractive index of the polyacrylate copolymer film does not change significantly with the increasing amount of up to 7 % of TMVS in both acidic and alkaline environment. The difference of the refractive index of the film under both mediums is in the order of 10(-3).
Keywords:Cross-linking;Optical waveguide;Photochemical;Refractive index;Silane treatment;UV irradiation