Ring-expansion cationic cyclopolymerization of divinyl ethers: synthesis of macrocyclic cyclopolymers with 8- and 13-membered rings

Abstract

Herein, a ring-expansion cationic cyclopolymerization leading to the formation of macrocyclic cyclopolymers is reported. 4,4-Bis(vinyloxymethyl)cyclohexene (1), 5,5-bis(vinyloxymethyl)-2-bicyclo[2,2,1]heptane (2), 1,2-bis(vinyloxyethoxy)benzene (3) and 1,2-bis(2-vinyloxyethoxy)-3,5-di-tert-butylbenzene (4) were polymerized in toluene at 0 °C. A hemiacetal ester-incorporated cyclic initiator was used in conjunction with SnBr4 as a Lewis acid activator in the presence of 2,6-di-tert-butylpyridine (DTBP) and 1,4-dioxane was used to suppress uncontrolled initiation by adventitious proton impurities. All synthesized cyclopolymers (Cyclic-Poly(1), Cyclic-Poly(2), Cyclic-Poly(3) and Cyclic-Poly(4)) were ring-shaped, with number-average molecular weights of 5000–13,000 and respective degrees of cyclization of 98.2%, 98.9%, 96.0% and 98.0%. Except for Cyclic-Poly(3), all the macrocyclic cyclopolymers had a high degree of cyclization exceeding 98%. Cyclic-Poly(1), Cyclic-Poly(2) and Cyclic-Poly(4) were soluble in solvents up to 100% monomer conversion, whereas Cyclic-Poly(3) was partially insoluble in the later stages of polymerization (>65% monomer conversion). The glass transition temperature (Tg) was 127, 178, 98 and 136 °C for Cyclic-Poly(1), Cyclic-Poly(2), Cyclic-Poly(3) and Cyclic-Poly(4), respectively. The Tgs of the cyclic cyclopolymers were higher than those of the corresponding linear cyclopolymers. Divinyl ethers 1, 2, 3 and 4 caused ring-expansion cationic cyclopolymerization with a hemiacetal ester-incorporated cyclic initiator in conjunction with SnBr4 to yield cyclic Poly(1), Poly(2), Poly(3) and Poly(4), respectively. High degree of cyclization of cyclopolymerization (>~98%) was necessary to obtain these macrocyclic cyclopolymers of well-defined structure quantitatively. The Tgs of these macrocyclic cyclopoly(divinyl ether)s were higher than those of the corresponding linear cyclopoly(divinyl ether)s.