Synthesis of Unsaturated (Co)polyesters from Ring-Opening Copolymerization by Aluminum Bipyridine Bisphenolate Complexes with Improved Protonic Impurities Tolerance

Abstract

Synthesis of unsaturated polyesters (UPES) via ring-opening copolymerization (ROCOP) of maleic anhydride (MAH) and epoxides still remains a great challenge, because the reported catalytic systems generally showed low catalytic activity or complete deactivation at low catalyst concentration and exhibit poor tolerance to protonic impurities. In this work, we synthesized a series of bipyridine bisphenolate aluminum (BpyBph-Al) complexes and used these complexes to catalyze the MAH/ epoxide copolymerization for synthesis of UPES. UPES with perfectly alternating structure could be synthesized using BpyBph-Al complexes without onium salt as cocatalyst, and the catalytic activities seem to be dependent on the steric and electronic effects of the ligands as well as the leaving ability of the axial group. The catalytic activities were further increased in the binary catalysts consisting of a BpyBph-Al as Lewis acid and an onium salt as a Lewis base. Compared with salen-Al/onium salt and typical Lewis pairs, the BpyBph-Al/onium salt binary system exhibited a completely maintained catalytic activity even when the [epoxide]/ [MAH]/[catalyst pair] feed ratio was high up to 25 000:5000:1 ([catalyst pair] = 0.004 mol %). In addition, BpyBph-Al/onium salt exhibited better tolerance to protonic impurity than salen-Al/onium salt and Lewis pairs. The catalytic activity was slightly decreased (about 15%) in the presence of 100 equiv (relative to catalyst) of external-added maleic acid, while a substantial decrease in activity or complete deactivation was observed in the ROCOPs catalyzed by salen-Al/onium salt and Lewis pairs. These features of BpyBph-Al/onium salt further allowed UPES synthesis by using commercial MAH without any purification as a comonomer. The maleic acid residuals in the commercial MAH could serve as a chain transfer agent (CTA), and UPES polyols with uniform −OH chain ends were obtained via reversible-deactivation chain transfer reaction. Chain extension could be initiated by the active alkoxide end when adding the second cyclic anhydride after the full conversion of MAH, finally producing ABA-type triblock copolymers.

Simple yttrium salts as highly active and controlled catalysts for the atom-efficient synthesis of high molecular weight polyesters

“…S47–S53†), in agreement with prior reports for ROCOP catalyst systems containing excess chain transfer agents. 41,42 For example, Williams et al have previously reported a smooth transition from bi-modal molecular weight distribution to monomodal upon incremental addition of diol chain transfer agent equivalents (5 to 10 equiv.) to the ROCOP of cyclohexene oxide and phthalic anhydride using aluminum o -vanillin catalysts.…”

General Approach to Silica-Supported Salens and Salophens and Their Use as Catalysts for the Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide

“…Ligand 13a was also reacted with copper(II) acetate to afford copper(II) complex 22f and with vanadium(V) oxychloride to afford vanadium(V) complex 22g . Between them, complexes 22a–g include examples of salen/salophen complexes for which soluble analogues are known to be four-, 31 five-, 32 and six-coordinate. 33 …”

Group 13 salphen compounds (In, Ga and Al): a comparison of their structural features and activities as catalysts for cyclic carbonate synthesis

“…This compound is well described in the literature and has found a variety of applications. 19 The lack of ready availability of similar M-alkyl reagents for Ga and In led us to search for other routes for the synthesis of [GaCl(salphen)] and [InCl(salphen)]. A salt-metathesis using K[N(SiMe 3 ) 2 ] reported by Williams and co-workers 15 for synthesis of their [InCl(salphen)] complex could be readily transferred and furnished good yields for preparation of these salphen complexes.…”