Improved Route to Linear Triblock Copolymers by Coupling with Glycidyl Ether-Activated Poly(ethylene oxide) Chains

Poly(ethylene oxide) block copolymers (PEO(z) BCP) have been demonstrated to exhibit remarkably high lithium ion (Li(+)) conductivity for Li(+) batteries applications. For linear poly(isoprene)-b-poly(styrene)-b-poly(ethylene oxide) triblock copolymers (PI(x)PS(y)PEO(z)), a pronounced maximum ion conductivity was reported for short PEO(z) molecular weights around 2 kg mol(−1). To later enable a systematic exploration of the influence of the PI(x) and PS(y) block lengths and related morphologies on the ion conductivity, a synthetic method is needed where the short PEO(z) block length can be kept constant, while the PI(x) and PS(y) block lengths could be systematically and independently varied. Here, we introduce a glycidyl ether route that allows covalent attachment of pre-synthesized glycidyl-end functionalized PEO(z) chains to terminate PI(x)PS(y) BCPs. The attachment proceeds to full conversion in a simplified and reproducible one-pot polymerization such that PI(x)PS(y)PEO(z) with narrow chain length distribution and a fixed PEO(z) block length of z = 1.9 kg mol(−1) and a Đ = 1.03 are obtained. The successful quantitative end group modification of the PEO(z) block was verified by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). We demonstrate further that with a controlled casting process, ordered microphases with macroscopic long-range directional order can be fabricated, as demonstrated by small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has already been shown in a patent, published by us, that BCPs from the synthesis method presented here exhibit comparable or even higher ionic conductivities than those previously published. Therefore, this PEO(z) BCP system is ideally suitable to relate BCP morphology, order and orientation to macroscopic Li(+) conductivity in Li(+) batteries.