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Copolymerization Behavior of β-Angelica Lactone and Styrene in the Presence of Organoaluminum Chlorides

In order to synthesize polymers containing lactone units in the backbone chains and use them as membranes, copolymerization of β-angelica lactone (β-AL) with styrene was carried out. Using α,α′-azobisisobutyronitrile at 60°C, β-AL did not copolymerize readily. In the presence of ethylaluminum sesquichloride or diethylaluminum chloride as a complexing reagent in toluene at 20°C, however, β-AL copolymerized much more readily. Spontaneous initiation took place and a copolymer containing about 50 mol% of β-AL units was obtained under the most favorable conditions. Nevertheless, it seemed unlikely that regular, highly alternating sequences could be achieved in this manner, in contrast to the well-known Lewis acid-complexed copolymerization of acrylic esters and styrene. NMR studies demonstrated that, while the binary complex between β-AL and ethylaluminum sesquichloride was formed almost instantly and completely, the ternary complex between styrene, β-AL and ethylaluminum sesquichloride had a rather low stability constant (≤0.05 dm3 mol−1) which accounts for the imperfectly alternating sequences.