Suzuki–Miyaura Catalyst-Transfer Condensation Polymerization for the Synthesis of Polyphenylene with Ester Side Chain by Using Stable, Reactive 1,1,2,2-Tetraethylethylene Glycol Boronate (B(Epin)) Monomer

Abstract

Suzuki–Miyaura catalyst-transfer condensation polymerization (CTCP) of 4-bromo-2,5-dihexyloxycarbonylphenylboronic acid ester (2) as an acceptor monomer was investigated. The polymerization of the boronic acid pinacol ester (Bpin) monomer (2a) was first conducted in the presence of t Bu3P-ligated tolyl–Pd-Br initiator 1 and CsF/18-crown-6 as a base, affording mainly polymers with H/H ends. We thought that the unsuccessful CTCP of 2a might be due to (1) poor catalyst transfer from the donor initiator unit to the acceptor monomer unit, (2) strong coordination of the Pd catalyst to the alkoxycarbonyl groups on successive repeat units, or (3) nonplanarity of the π-face of the backbone owing to the steric effect of the alkoxycarbonyl groups in the repeat unit. However, model reactions showed that the Pd catalyst successfully underwent intramolecular catalyst transfer, ruling out these possibilities. We then replaced 2a with B(Epin) monomer 2b, which is more stable than 2a. In the polymerization of 2b, the M n value increased in proportion to the monomer conversion and feed ratio of [2b]0/[1]0 and the molecular weight distribution remained narrow. The matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrum showed a series of peaks due to the polymer with Tolyl/H ends. After end-capping of the polymer with 4-methoxyphenylboronic acid, the 1H NMR spectrum exhibited signals of both end groups. These results indicate that the polymerization of 2b proceeded according to the CTCP mechanism.

Low-Pressure Preparative Size-Exclusion Chromatography: from Narrow Disperse Polymer to Monodisperse Oligomer Batches

“…In this work, the recent advances of catalytic C–C cross-coupling polycondensation protocols toward versatile catalyst-transfer variants will be exploited . More precisely, the polymerization of difunctionalized monomers bearing complementary functional groupsdenoted as A/B in the followingenables a chain-growth mechanism that leads to heterotelechelic polymers with narrow dispersity values ( Đ ), tunable degrees of polymerization ( n ) set by the initiation conditions at the α-terminus, ,, as well as capping of the ω-terminus using monofunctionalized reagents. ,, Corroborated by the recent mechanistic insights, the Suzuki-Miyaura catalyst-transfer polymerization (SCTP) was recently extended to a broad variety of electron-rich and electron-deficient monomers, for the preparation of hyperbranched polymer-analogous molecules, to exploit the end-group chemistries in postpolymerization reactions, as well as to prepare controlled nanoribbon precursors, e.g., via commercially available Buchwald-type Pd G3 precatalysts . In essence, the typical SCTP conditions will be slightly adapted to maintain the focus on the complementing separation stage.…”