Ring-opening polymerization of lactones and lactides with Sn(IV) and Al(III) initiators
2002 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 35, no 5, 1556-1562 p.Article in journal (Refereed) Published
A theoretical study is presented of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and glycolide with Sn(II) and Al(III) alkoxide initiators (SnMe3MeO, SnMe2-(MeO)(2), and AlMe2MeO). The B3LYP density functional method has been used to perform the quantum chemical calculations. A coordination-insertion mechanism is presented with two principal reaction steps. First, the alkoxide of the initiator performs a nucleophilic attack on the carbonyl carbon, and the carbonyl bond is broken. An intermediate is formed at this point, where the former carbonyl oxygen of the monomer is coordinated to tin via an alkoxide bond, while the carbonyl carbon assumes a sp(3) bonding geometry. The second step involves the acyl-oxygen cleavage of the monomer. For all three initiators it was found that the transition state involving the breaking of the carbonyl double bond (TS1) represented the highest point on the potential energy surface for DXO. For glycolide, however, the transition state of the acyl-oxygen cleavage (TS2) was the least stable structure. The reaction barriers were calculated to 17.1 kcal/mol for DXO/SnMe3MeO, 18.7 kcal/mol for glycolide/SnMe3MeO, 14.3 kcal/mol for DXO/SnMe2(MeO)(2), 14.5 kcal/mol for glycolide/SnMe2(MeO)(2), 13.6 kcal/mol for DXO/AlMe2MeO, and 9.3 kcal/mol for glycolide/AlMe2MeO. Both electronic and steric properties of the monomer affect the reaction barriers. It was found that the more electrophilic initiators polymerized cyclic esters faster.
Place, publisher, year, edition, pages
2002. Vol. 35, no 5, 1556-1562 p.
density-functional theory, effective core potentials, gaussian basis functions, atomic basis sets, first-row atoms, molecular calculations, epsilon-caprolactone, cyclic esters, aluminum alkoxides, tin(ii) octoate
IdentifiersURN: urn:nbn:se:kth:diva-21344DOI: 10.1021/ma011653iISI: 000174036600014OAI: oai:DiVA.org:kth-21344DiVA: diva2:340042
QC 201005252010-08-102010-08-10Bibliographically approved