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.
Highlights
Poly(ethylene phosphates), or PEPs are a prospective group of biocompatible polymers with controlled hydrophilicity and biodegradability
Basis set, we explored methyl ethylene phosphate (MeOEP) Ring-opening polymerization (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)
ROP, we found that a stable chelate complex that is similar to MI-4 was rac-lactide ROP, we found that a stable chelate complex that is similar to MI-4 was formed during formed the first ring-opening
Summary
Poly(ethylene phosphates), or PEPs are a prospective group of biocompatible polymers with controlled hydrophilicity and biodegradability. Ring-opening polymerization (ROP) of cyclic ethylene phosphate monomers (CEPMs) is an efficient method for the preparation of PEPs (Scheme 1a) [10,11,12,13,14,15]. We demonstrated the high efficiency of BHT-Mg (BHT = 2,6-di-tert-butyl-4-methylphenolate) alkoxy complexes (Mg1, Scheme 1b) in the ROP. 22 of BHT-Mg (BHT = 2,6-di-tert-butyl-4-methylphenolate) alkoxy complexes (Mg1, Scheme 1b) in the ofROP ethylene phosphates with the formation linear and of branched [16,17,18].polymers. Complexes with the formula Mg1 (R' = Et, Bn) are effective in the ROP of traditional monomers, esters our recent paperIn[20], reported results of an experimental theoretical studyand of which[19].
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