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Use of titanocalix[4]arenes in the ring opening polymerization of cyclic esters

journal contribution
posted on 06.02.2020 by Ziyue Sun, Yanxia Zhao, Orlando Santoro, Mark Elsegood, Elizabeth Bedwell, Khadisha Zahra, Alex Walton, Carl Redshaw

The known dichloride complexes [TiCl2L(O)2(OR)2] (type I: R = Me (1), n-Pr (2) and n-pentyl (3); L(OH)2(OR)2 = 1,3-dialkyloxy-p-tert-butylcalix[4]arene), together with the new complexes {[TiL(O)3(OR)]2(mu-Cl)2}∙6MeCN (R = n-decyl (4∙6MeCN), and [Ti(NCMe)Cl(L(O)3(OR)]∙MeCN (type II: R = Me, 5∙MeCN) are reported. Attempts to prepare type II for R = n-Pr and n-pentyl using [TiCl4] resulted in the complexes {[TiL(O)3(On-propyl)]2(mu-Cl)(mu-OH)} 6∙7MeCN and {[TiL(O)3(On-pentyl)]2(mu-Cl)(mu-OH)}∙7.5MeCN (7∙7.5MeCN), respectively; [TiCl4(THF)2] resulted in a co-crystallized THF ring-opened product [Ti(NCMe)(μ3-O)L(O)4TiCl(O(CH2)4Cl)]2 - 2[TiCl(NCMe)(L(O)3(On-Pr))]∙11MeCN (8∙11MeCN). Type I and II complexes have been screened for their ability to act as catalysts in the ring opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL), delta-valerolactone (delta-VL), omega-pentadecalactone (omega-PDL) and rac-lactide (r-LA), both with and without benzyl alcohol present and either under N2 or in air. The copolymerization of epsilon-CL with delta-VL and with r-LA has also been investigated. For the ROP of epsilon-CL, all were highly active (>99% conversion) at 130 oC over 24 h both under N2 and in air, whilst over 1h, for the type I complexes the trend was 3>2>1 but all were poor (≤12% conversion). By contrast, 5 over 1h at 130 oC was highly active (85% conversion). At 80oC, the activity trend followed the order 5 ≈ 4 > 3 > 2 > 1. For delta-VL, at 80 oC the activity trend 5 ≈ 4 > 1 > 2 > 3 was observed. ROP of the larger omega-PDL was only possible using 5 at 130 oC over 24 h with moderate activity (48 % conversion). For r-LA, only low molecular weight products were obtained, whilst for the co-polymerization of epsilon-CL with delta-VL using 5, high activity was observed at 80 oC affording a polymer of molecular weight > 23,000 and with equal incorporation of each monomer. In the case of epsilon-CL/r-LA co-polymerization using 5 either under N2 or air, the polymerization was more sluggish and only 65% conversion of CL was observed and the resultant co-polymer had 65:35 incorporation. Complex 5 could also be supported on silica, however this system was not as active as its homogeneous counterpart.Finally, the activity of these complexes is compared to that of three benchmark species.

Funding

Shaanxi Province for the 100 Talents Award

EPSRC National Crystallography Service at Southampton (UK)

EPSRC Mass Spectrometry Service, Swansea (UK)

EPSRC for an Overseas Travel Grant (EP/R023816/1)

UKRI Creative Circular Plastic grant (EP/S025537/1)

History

School

  • Science

Department

  • Chemistry

Published in

Catalysis Science & Technology

Volume

10

Pages

1619-1639

Publisher

Royal Society of Chemistry (RSC)

Version

AM (Accepted Manuscript)

Publisher statement

This paper was accepted for publication in the journal Catalysis Science & Technology and the definitive published version is available at https://doi.org/10.1039/C9CY02571E.

Acceptance date

25/01/2020

Publication date

2020-01-27

Copyright date

2020

ISSN

2044-4753

eISSN

2044-4761

Language

en

Depositor

Dr Mark Elsegood. Deposit date: 5 February 2020

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