Lactide Cyclopolymerization Kinetics, X-ray Structure, and Solution Dynamics of (^tBu-SalAmEE)Al and a Cautionary Tale Of Polymetalate Formation

Abstract

The complex ( t Bu-SalAmEE)Al ( t Bu-SalAmEEH 3 = N , N -bis(3,5-di-tert-butyl-2-hydroxybenzyl)-2-(2aminoethoxy)ethanol, 1) catalyzes the ring-expansion polymerization of lactide to form cyclic poly(lactide) (cPLA). The X-ray structure of 1 was determined, its polymerization kinetics were examined and its interactions with Lewis bases were observed. The data from these experiments are consistent with a coordination−insertion mechanism whose rate-determining step is catalyst rearrangement by loss of a hemilabile, datively bound, bridging ligand ether. cPLA was examined by thermogravimetric analysis and found more stable than its linear counterpart. In the course of these studies, we unexpectedly observed the formation of polymetalate (AlMe( t Bu-SalAmEE)-AlMe 2 ) 2 (6), which was characterized (X-ray, EA, and 1 H and 13 C NMR).

Recent progress on the synthesis of cyclic polymers via ring‐expansion strategies

“…The polymerization also proceeded in toluene, though higher activity was observed in melt polymerizations conducted at 130 °C. The mechanism of the polymerization was investigated in further detail by the same group in 2013 . Kinetic analyses showed the rate‐determining step to be the rearrangement of the alumatrane catalyst to form the substrate‐bound complex 3 (Fig.…”

Cyclic Polyester Formation with an [OSSO]‐Type Iron(III) Catalyst

“…[4] Indeed, av ery high degree of control over the polymerization process has been achieved, which offerst he possibility to obtain polymers with predictable molecular weights, compositions,a nd microstructures. Actually, the number of reports in which the production of cAPEs by means of aw ell-defined metal complex is described is limited, [24] and mosti nvolve the use of Al- [25][26][27] and Zn-based catalysts. [6] Different approaches have been proposed for the production of cyclic polymers, [7] andnotable examples have been reported in literature.…”

“…[8] However,t he formation of cyclic polyesters remains a challenge. Actually, the number of reports in which the production of cAPEs by means of aw ell-defined metal complex is described is limited, [24] and mosti nvolve the use of Al- [25][26][27] and Zn-based catalysts. Indeed,t he biodistribution of cyclic aliphatic polyesters (cAPEs)i sd ifferent from that of linear APEs, [10] which offers an opportunity to develop new drug deliverys ystems.…”

“…Indeed,t he biodistribution of cyclic aliphatic polyesters (cAPEs)i sd ifferent from that of linear APEs, [10] which offers an opportunity to develop new drug deliverys ystems. Actually, the number of reports in which the production of cAPEs by means of aw ell-defined metal complex is described is limited, [24] and mosti nvolve the use of Al- [25][26][27] and Zn-based catalysts. Fe complexes activei nt he ROP of cyclic esters are limited, [11][12][13][14][15][16][17][18][19][20][21][22][23] and no examples have been reported that produce cAPEs.…”

“…[8,[25][26][27] Indeed,i tw as not possible to assigna ny of the observed peaks to al inear chain with initiating groups of any nature (eitherf rom Cl of 1 or PO). This analysisr evealed that the formation of cyclic poly(lactic acid) (cPLA) occurred, which justifies the discrepancy betweent he estimated and observed M n values( Figures S9 and S10 in the Supporting Information).…”