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Polymers 2018, 10(10), 1105; https://doi.org/10.3390/polym10101105

Mechanistic Insights of BHT-Mg-Catalyzed Ethylene Phosphate’s Coordination Ring-Opening Polymerization: DFT Modeling and Experimental Data

1
M.V.Lomonosov Moscow State University, Chemistry Department, 1-3 Leninskie Gory, Moscow 119991, Russia
2
A.V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninsky Pr., Moscow 119991, Russia
3
Joint-stock company “Institute of petroleum refining and petrochemistry”, 12 Iniciativnaya Str., Ufa, Republic of Bashkortostan 450065, Russia
*
Author to whom correspondence should be addressed.
Received: 25 September 2018 / Revised: 3 October 2018 / Accepted: 4 October 2018 / Published: 6 October 2018
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Abstract

Poly(ethylene phosphates) are promising polymers for use in biomedical applications. Catalytic ring-opening polymerization (ROP) of cyclic ethylene phosphate monomers (CEPMs) is the most effective approach for obtaining these polymers. The mechanism of coordination ROP of CEPMs remains unclear. We report, for the first time, the results of DFT modeling of CEPM ROP. In these calculations by Gaussian-09 program package with the B3PW91/DGTZVP basis set, we explored methyl ethylene phosphate (MeOEP) ROP catalyzed by dimeric and monomeric catalytic species derived from heteroleptic complex [(BHT)Mg(μ-OBn)(THF)]2 (Mg1, BHT = 2,6-di-tert-butyl-4-methylphenolate). Analysis of the reaction profiles for the binuclear and mononuclear reaction mechanisms allowed us to conclude that the ROP of MeOEP is preferentially catalyzed by mononuclear Mg complexes. This estimation was confirmed by comparative polymerization experiments using MeOEP and traditional monomers ε-caprolactone (εCL), racemic lactide (rac-LA), and l-lactide (l-LA) initiated by Mg1. ROP of MeOEP proceeds at an extremely high rate due to the substantially lower activation barrier calculated for mononuclear mechanism in comparison with that of cyclic esters that polymerize without the dissociation of BHT-Mg binuclear species. We also demonstrated the use of MeOEP as a "monomerization" agent in the synthesis of MeOEP-lactide block copolymers. Comparison of the multiple acceleration of l-LA ROP after MeOEP prepolymerization and formation of atactic PLA blocks in rac-LA polymerization with the heterotactic PLA formation during Mg1-catalyzed homopolymerization also confirmed the mononuclear nature of the polyphosphate-containing catalytic particles. View Full-Text
Keywords: ring-opening polymerization; ethylene phosphate; lactide; DFT; magnesium phenoxide ring-opening polymerization; ethylene phosphate; lactide; DFT; magnesium phenoxide
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Nifant’ev, I.; Shlyakhtin, A.; Kosarev, M.; Karchevsky, S.; Ivchenko, P. Mechanistic Insights of BHT-Mg-Catalyzed Ethylene Phosphate’s Coordination Ring-Opening Polymerization: DFT Modeling and Experimental Data. Polymers 2018, 10, 1105.

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