Synthesis and polymerization of methyl 3‐methylenecyclobutene‐1‐carboxylate and dimethyl 3‐methylenecyclobutene‐1,2‐dicarboxylate

Abstract

SynopsisThe two title monomers were synthesized. In both cases the key cyclobutane intermediates were obtained by cycloaddition of allene to acrylonitrile or chloromaleic anhydride. These two new monomers proved to be highly reactive in free radical polymerization, and each polymerized spontaneously in air at room temperature. Linear polymers were prepared in dimethyl sulfoxide solution at 35" with AIBN and UV light. At higher temperatures crosslinking became a problem in some instances. The structure of the polymers derived from 1,4 polymerization in the diene portion of the monomers was confirmed by '3c-NMR, 'H-NMR and I R spectra. Copolymers were prepared with methyl methacrylate, styrene, and p-methoxystyrene and were always rich in the methylenecyclobutene monomers used. Films of homopolymers and copolymers codd be cast from chloroform solution.

Bicyclobutanes and cyclobutenes: Unusual carbocyclic monomers

“…α‐Chlorination of the intermediate 3‐methylenecyclobutane‐1‐carbonitrile followed by dehydrochlorination led to 3‐methylenecyclobutene‐1‐carbonitrile 32. Analogous chemistry formed the corresponding methyl ester:33 Similarly, the cycloaddition of allene to chloromaleic anhydride yielded the cycloadduct shown; conversions to diacid and dimethyl ester were followed by dehydrochlorination to form dimethyl 3‐methylene‐1‐cyclobutene‐1,2‐dicarboxylate:33 4‐Chloro‐1,2‐butadiene reacted with acrylonitrile at 210–225 °C to yield 2‐chloromethyl‐3‐methylenecyclobutane‐1‐carbonitrile:34 Potassium t ‐butoxide in ether gave a reactive nitrile monomer originally thought to be 3‐methylenebicyclo‐[2.1.0]‐pentane‐1‐carbonitrile 34. However, at the suggestion of Cheves Walling, we reexamined it and found that it was in fact 3‐methylene‐2‐methylcyclobutene‐1‐carbonitrile, which was formed via dehydrochlorination and isomerization to the conjugated structure 35…”