Living Cationic Polymerization of Vinyl Ether with a Thienyl Group

To study the possibility of living cationic polymerization of vinyl ethers with a thienyl group, 2-(3-thienyl)ethyl vinyl ether (3TEVE), 2-vinyloxyethyl 2-thiophenecarboxylate (2TCVE), and 2-vinyloxyethyl 3-thiophenecarboxylate (3TCVE) were reacted with HCl/ZnCl2 in CH2Cl2 at -30 degrees C. The polymerization of 3TEVE gave only low-molecular-weight oligomer with a number-average molecular weight (M-n) of about 300 even at 100% monomer conversion. The structural analysis of the products showed that the cyclization of the carbocation with the thienyl group of 3TEVE occurred that led to chain transfer reactions. In contrast, the polymerization of the carbonyl-containing thiophene vinyl ethers 2TCVE and 3TCVE proceeded in a living manner to give high-molecular-weight polymers with narrow molecular weight distributions, (2TCVE; M-n = 14,900, M-w/M-n = 1.21, 3TCVE; M-n = 12,300, M-w/M-n, = 1.26) under the same reaction condition. H-1 NMR. and MALDI-TOF-MS analyses showed that the resulting poly(2TCVE) and poly(3TCVE) had methoxy terminals generated from the terminator.