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Living cationic polymerization of isobutyl vinyl ether by the CF 3 CO 2 H–SnCl 4 –nBu 4 NCl system: In situ direct analysis of the growing species by 1 H, 13 C and 19 F NMR spectroscopy
Author(s) -
Katayama Hiroshi,
Kamigaito Masami,
Sawamoto Mitsuo,
Higashimura Toshinobu
Publication year - 1995
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610080411
Subject(s) - chemistry , cationic polymerization , living cationic polymerization , vinyl ether , polymerization , in situ , ether , polymer chemistry , organic chemistry , copolymer , polymer
Direct 1 H, 13 C and 19 F NMR spectroscopic analysis was carried out on the carbocationic intermediate generated in the interaction of tin(IV) chloride (SnCl 4 ) with the adduct [4, CH 3 CH(OiBu)OCOCF 3 ] of isobutyl vinyl ether (IBVE) and trifluoroacetic acid (CF 3 CO 2 H), either in the presence or in the absence of tetrabutylammonium chloride. The reactions were to mimic the living cationic polymerization of IBVE by the 4–SnCl 4 initiating system (with added nBu 4 NCl) that was also found in this study. In CD 2 Cl 2 solvent at −78°C, the 1 H and 13 C NMR analysis revealed the formation of a carbocationic intermediate [CH 3 C + H(OiBu)] that is in a rapid exchange equilibrium with the covalent counterpart 4. For the first time, the cation formation was further supported by 19 F NMR analysis on the counteranionic part (CF 3 COO − ) in 4, where, with SnCl 4 , the CF 3 group gave a broadened signal that appeared clearly downfield relative to that in the covalent form. These and other results, which are in close correlation with the corresponding polymerizations, demonstrated the following: (i) the SnCl 4 ‐assisted generation of carbocationic species from the covalent ester 4; (ii) a rapid exchange between the cation and its covalent precursor 4; (iii) the relatively high cationic concentration in the salt‐free system, where no living polymerization occurs; and (iv) the effective suppression of the cationic species in the presence of the salt, which proved to be the prime key factor for living polymerization.