Synthesis of copolymers of 3-acryloyloxymethyl-3′-methyloxetane and 3-(2-(2-(2-methoxyethylenoxy)ethylenoxy)ethylenoxy)-3′-methyloxetane and their ionic conductivity properties

Abstract

An oxetane-derived monomer, 3-acryloyloxy-methyl-3′-methyloxetane (AMO) was prepared from the reaction of 3-hydromethyl-3-methyloxetane with acryloyl chloride. The cationic ring-opening copolymerization of AMO with another oxetane-derived monomer, 3-(2-(2-(2-methoxyethylenoxy)ethylenoxy)ethylenoxy)-3′-methyloxetane (MEMO) was conducted in CH₂Cl₂ solution using BF₃ · OEt₂/1,4-butanediol as a co-initiator. The resulting copolymers were characterized by FTIR, ¹H NMR and Gel Permeation Chromatography (GPC) analyses, and it was found that the enchained ratio of AMO in the copolymers is far lower than its feed ratio. They were crosslinked in situ via the radical polymerization of the vinyl group initiated by BPO after doping with lithium trifluoromethanesulfonimide (LiTFSI) to give rise to tough polymeric electrolyte films. The ionic conductivity was measured at varying content of AMO and different concentration of lithium salt LiTFSI by AC impedance, and a maximum ion conductivity of 1.44 × 10⁻⁵ S/cm at 30°C or 1.25 × 10⁻⁴ S/cm at 80°C was attained in the sample PAM 33 at the mole ratio of O: Li = 20. The DSC results indicated that T _g decreases with the increase of the proportion of AMO in the copolymer, well consistent with the ion conductivity trend. The TGA (thermogravimetric analysis) measurement revealed that this kind of copolymer electrolytes is more thermostable than their liquid counterparts.