Monomer-Isomerization Polymerization of 3-Methyl-3-(phthalimidomethyl)oxetane with Two Different Ring-Opening Courses

Abstract

The cationic polymerization of 3-methyl-3-(phthalimidomethyl)oxetane (1) afforded two kinds of polymers. One was a polyacetal, i.e., poly{oxy(8,9-benzo-4-methyl-7-oxo-2,6-oxazabicyclo[4.3]nona-8-ene-1,4-diyl)methylene} (3), produced at 50 °C and below, and the other was a polyether, i.e., poly[oxy(2-methyl-2-phthalimidomethyltrimethylene)] (4), produced at 80 °C and above. This new polymerization with the two ring-opening courses was accompanied by the monomer-isomerization process of 1 to give 5,6-benzo-1-methyl-8,11,3-dioxazatricyclo[5.2.2.03,7]undeca-5-en-4-one (2). The cyclic acetal 2, therefore, functioned as the real monomer, and either single or double ring-opening polymerization took place to give 3 or 4, respectively, depending on the reaction temperature. The strain of 2 for ring-opening is discussed on the basis of the result of X-ray structure analysis. The single ring-opening process of 2 was an equilibrium polymerization having the standard enthalpy and entropy changes in dichloromethane equal to −15.8 kJ mol-1 and −46.0 J mol-1 K-1, respectively, and the ceiling temperature (T c) equal to 70.1 °C for 1 mol L-1 solution. The critical temperature, where the structure of the product polymer changed, was related to a T c calculated for the conditions employed (59.1 °C for polymerization in 0.83 mol L-1 dichloromethane solution). Therefore, 3 was successfully transformed to 4 with a thermal latent catalyst at a higher temperature than the T c through the ring-closure depolymerization of 3 to 2 followed by the repolymerization of 2 in the double ring-opening manner. When 1 was polymerized in a temperature step-down mode, a block copolymer with the 3-4 sequence was prepared from the single monomer. Moreover, 1 was copolymerized with a nonisomerizable oxetane, accompanying the monomer isomerization of 1.

Cationic Monomer-Isomerization Polymerization of Oxetanes Having an Ester Substituent, to Give Poly(orthoester) or Polyether

“…The values of k i are a factor of 10 -1 to 10 -2 smaller than those reported for the isomerization of cyclic imide-substituted oxetanes under the same conditions. [8,9] However, 1 was sufficiently reactive to permit the isomerization even at -78 8C (run no. 2).…”

“…The initial reaction probably begins with the coordination of Lewis acid E to the oxetanyl oxygen atom of 1. [8,9] In oxonium A thus generated, the ester carbonyl oxygen atom is readily accessible to the electrophilic carbon atom. Consequently, the intramolecular nucleophilic attack (isomerization) is entropically preferred to the intermolecular nucleophilic attack of 1 or 2 (polymerization).…”

“…For instance, bicyclic acetals produced from oxetane imides in situ entered into either a single-or double-ring-opening polymerization depending on temperature, to give polyacetals or polyethers, respectively. [8,9] This was a typical example showing that structurally isomeric polymers were produced from a single monomer with complete selection. Consequently, the starting oxetanes polymerized cationically through greatly different processes than the conventional ring-opening polymerization.…”

“…Thus, this new mode of polymerization involving such an isomerization has been termed "monomer-isomerization polymerization". [8] In this paper, we report the cationic monomer-isomerization polymerization of oxetanes having an ester group, such as benzoate (1 a and 1 c) and butyrate (1 b), as represented in Scheme 2. Our previous results certainly promise the isomerization of 1 to [2.2.2]bicyclic orthoesters (2) and the polymerization of 2 to poly(orthoester) (3) and polyether (4).…”

Catalytic reactions of oxetanes with protonic reagents and aprotic reagents leading to novel polymers

“…Furthermore, Motoi and coworkers recently reported that the isomerization and polymerization of oxetanes proceeded smoothly using acid catalysts, affording the polyethers and polyacetals. [33][34][35][36][37][38] However, there has been no report concerning the reactions of oxetanes except for these cationic isomerization and polymerizations. Since more than 15 years ago, we have considered that oxetanes might react with various reagents similarly using appropriate catalyst to epoxides as mentioned earlier.…”