Cyclic imino ethers — Polymerization chemistry and polymer characteristics

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Abstract
This paper describes recent developments in polymerization of cyclic imino ethers, 2‐oxazolines and 5,6‐dihydro‐4H‐1,3‐oxazines, which have been performed mainly in our laboratory. Cationic ring‐opening polymerizations of these two kinds of monomers gave poly(N‐acylethylenimine)s and poly(N‐acyltrimethylenimine)s, whose hydrolysis produced linear poly‐ethylenimine and poly(trimethylenimine), respectively. The mechanism of the polymerization is mainly governed by the nature of monomer and of the counter anion derived from initiator. There are two types of stable propagating species; cyclic onium species and covalent alkyl halide species. In a specific case, e.g., the polymerization of 5‐methyl‐2‐oxazoline with MeI initiator, both ionic and covalent species are involved in equilibrium and propagate concurrently. Then, a new terminology of “Electrophile Polymerization” has been proposed as a broader expression including cationic and covalent propagating species. By utilizing living nature of the cyclic imino ether polymerization, block copolymerizations between these monomers were performed. A poly(cyclic imino ether) chain becomes hydrophilic or lipophilic depending on the monomer. Product AB and ABA type block copolymers were soluble in water and showed excellent surface properties reflected by values of surface tension (γ), when A (or B) and B (or A) are hydrophilic and lipophilic. Thus, various nonionic polymer surfactants of block and graft type have been prepared from cyclic imino ethers. Finally, poly(N‐acetylethylenimine) chain showed good compatibility with poly(vinyl chloride). Cellulose diacetate and poly(vinyl chloride) are not miscible, but cellulose diacetate g‐poly(N‐acetylethylenimine) is miscible with poly(vinyl chloride), the graft chain acting as a “compatibilizer”.

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