OPTICAL PROPERTIES OF IPN-LlKE NETWORKS. I. POLYETHYLENE/POLY(BUTYLMETHACRYLATE­ co-STYRENE) COPOLYMER SYSTEMS

IPN-like systems, made of Low Density Polyethylene (PE) and Poly(butylmethacrylate) (BMA)-co-styrene(S) copolymer net­ works, were synthesized by a particular procedure,described in previous papers.The initial PE/copolymer molar ratio was kept equal to one for all the samples. Different molar BMA/S ratios (50/50, 70/30, 80/20,85/15,90/10 100/0) of the copolymer and various molar percent­ tages (0.5, 1.0, 1.5, 2.0%) of the copolymer crosslinker (DVB) were used. The samples obtained were analyzed by DSC, WAXS, swelling inCCI4, dynamic-mechanical and impact tests. An accurate optical investigation was made in a temperature range going from room temperature (R.T.) up to 180°C, in order to deepen the knowledge of the optical properties of these materials, whose preliminary results were shown in a previous paper. From the experimental data, it was possible to derive an analytical expression relating the temperature, at which the IPN's become transparent, to synthetic parameters such as copolymer composition and degree of crosslinking, expressed by the initial mixture BMA/S comonomers ratio and by the amount of the DVB co-polymer crosslinker. By the use of this analytical expression, a priori designs of IPN materials with desired optical properties are made possible.