Studies on the light‐focusing plastic rod. XIII. Photocopolymerization of methyl methacrylate–vinyl esters of aromatic carboxylic acid

The light‐focusing plastic rod (LFR) was prepared by the photocopolymerization of methyl methacrylate (MMA) with vinyl phenylacetate (VPAc) and vinyl benzoate (VB), using benzoyl peroxide (BPO), benzoin (BN), and benzoin methyl ether (BME) as an initiator. The LFR with high transparency and steep refractive‐index distribution was obtained using the MMA–VPAc pair and the BME. The difference in the index distributions under BPO, BN, and BME initiations was clarified in terms of the photoinitiation rate and the accompanying thermal polymerization during the photocopolymerization process. The light scattering intensity from the LFR was related to the heterogeneity of the copolymer composition and the compatibility between the M₁ and M₂ polymers. The comparison of the light scattering theory with the experimental data indicated that the much less scattering intensity from the MMA–VPAc LFR than the MMA–VB LFR should be attributed to the good compatibility between the MMA and VPAc polymers, and scarcely attributed to the index difference between the VPAc and VB polymers.