Solution and Solid‐State Polymerization of 2,3‐Dicyano‐5,7‐dimethyl‐6H‐1,4‐diazepine

Abstract

2,3‐Dicyano‐5,7‐dimethyl‐6H‐1,4‐diazepine (1) is polymerized to a conjugated structure in solution by both alkaline sugar reagents and butoxide in n‐butanol and in the solid state by thermal annealing. From both infrared and nuclear magnetic resonance spectra, all polymers have a similar chain repeat structure involving polymerization at one of the two cyano groups in the molecular structure of 1. Electronic spectra, gel permeation chromatography (GPC), and thermal analysis further characterize the polymers. The methyl protons of 1 are acidic, and solution polymerization is likely initiated by a delocalized anion derived from 1. This delocalized anion also provides a rationalization for polymerization at only one of the cyano groups of 1 instead of cyclopolymerization. The solid state polymerization leads to an amorphous product in a heterogeneous process. The crystal structure of 1 does not allow formation of an infinite chain. A tautomeric form of 1 likely initiates the solid state polymerization. The tautomerization creates a defect site in the crystal of 1, and the initial addition reaction is likely topochemical.

Keywords:

• Carbohydrate initiation
• Reducing sugar
• Thermal solid state polymerization
• Dimethyldiazepine tautomers

Acknowledgments

This work was supported in part by the Petroleum Research Fund under Grants 33424‐AC7 and 37138‐AC1. The Bruker 300 MHz instrument was purchased with funds partially furnished by the National Science Foundation under Grant DMR 9802866. The authors thank Professors Bruce Foxman (Brandeis U.), P. Rasmussen (U. of Michigan), and L. Tolbert (Georgia Inst. of Technology) for useful discussion. Mr. M. J. Downey furnished x‐ray powder patterns.