OPTICAL PROPERTIES OF IPN-LIKE NETWORKS.II. POLYETHYLENE/POLY-(BUTYLMETHACRYLATE-CO-METHYLMETH­ACRYLATE) COPOLYMER SYSTEMS

IPN-like systems, made of Poly[butylmethacrylate(BMA)-co­ methylmethacrylate (MMA)] copolymers and Low Density Polyethylene (PE) networks, were synthesized by a procedure described in previous papers. The initial PE/copolymer molar ratio was kept constant1y equal to one for all the samples. Different molar BMA/MMA copoly­ mer ratios (50/50, 60/40, 80/20, 90/10 100/0) and a molar per­ centage of 1.0% of the copolymer crosslinker, l,4-Butandioldi­ methacrylate (BDDM), were used. The samples obtained were analyzed by DSC, WAXS, swelling in CCl4, and dynamic-mechanical tests. PE crystallinity was lowered by the network formation and slightly increased, whereas, the overall network density decreased, with enhanc­ ing the BMA content. Optical investigations were performed in a temperature range between room temperature (R.T.) and 180 °C, using MMA as comonomer of BMA, instead of Styrene (S), as well as a different crosslinker (BDDM instead of DVB). AlI the IPN's showed the matching-mismatching optical transi­ tion of R.I., with temperatures corresponding to a transparency condition. The larger the BMA content, in the initial reactant MMA-BMA comonomeric mixture, the higher such tempera­ tures. An analytical expression was found relating this tempera­ ture to the copolymer composition.