AbstractThe cationic copolymerization of isobutylene and β‐pinene (2(10)‐pinene) yields random copolymers which exhibit interesting physical properties. E.g., high molecular weight copolymers containing isobutylene/β‐pinene in the ratio of 90/10 and 97/3 are sulfur‐vulcanizable ozone‐resistant elastomers. Copolymer synthesis was accomplished with Friedel‐Crafts halides e.g., C2H5AlCl2, BF3, etc. using ethyl chloride diluent at low temperatures. The structure of the copolymers was determined by NMR spectroscopy. The reactivity ratios of isobutylene and β‐pinene are stongly affected by temperature, however, are much less sensitive to the particular Lewis acid used. Interestingly, with C2H5AlCl2, the individual reactivity ratios become equal to unity below ca. −100°C, i.e., the copolymerization becomes azeotropic.The mechanism of cationic olefin polymerizations induced by various alkylaluminum compounds has been investigated by model reactions. The rate of the reactions. The rate of the reaction equation image is strongly affected by the nature of the (CH3)3CX and the CH3X solvent (X=Cl, Br. I). Unexpectedly, the sequence of rates of this reaction was found to be (CH3)3CCl>(CH3)3CBr>(CH3)3Cl. Further, an intensive study of the 2,4,4‐trimethyl‐1‐pentene/(CH3)3Al/(CH3)3CCl model system gave a series of important mechanistic insights. E.g., if an alkylaluminum compound having a β‐hydrogen in respect to aluminum is used as the coinitiator e.g., (C2H5)3Al, [(CH3)2CHCH2]3Al, etc., rapid hydridation terminates the reaction:
Read full abstract