Copolymerization of styrene and methyl methacrylate photosensitized by a methyl methacrylate‐triethylaluminium complex

We have re‐examined the copolymerization of methyl methacrylate (MMA) and styrene in the presence of triethylaluminium at 273°K under visible light following recent claims that it was an alternating system. We applied gel‐permeation chromatography to establish that the polymers had monomodal distributions and could be regarded as coherent samples for analysis. Proton and 13C‐NMR spectroscopy were used to determine the composition and structure of the copolymers and investigate the presence of complexes in the comonomer solutions. We found that the polymers produced are not strictly alternating. In the absence of excess, uncomplexed MMA, the system is a radical copolymerization of styrene and a 1:1 MMA‐AlEt3 complex with reactivity ratios such that there is a strong tendency for styrene (S) and MMA (M) units to alternate. The alternating SMS triads were predominantly isotactic. Significant proportions of SSS, MMM and MMS triads could be detected.