Controlled Cationic Polymerization of Lactide

Abstract

The combination of trifluoromethanesulfonic acid (as a catalyst) and a protic reagent (such as water, 2-propanol, or 1-pentanol as an initiator) efficiently initiates the cationic polymerization of lactide in dichloromethane solution at room temperature. Polylactides (PLAs) with molar masses up to 20 000 were obtained via an activated-monomer mechanism. 1 H NMR spectroscopy and electrosprayionization mass spectrometry of PLA oligomers demonstrated the quantitative incorporation of the protic initiator in the polymer chains and showed that transesterification reactions did not occur to a significant extent. The controlled character of the polymerization was indicated by the linear relationships of the number-average molar mass vs monomer conversion and monomer-to-initiator ratio. Kinetic measurements revealed a first-order dependence on monomer concentration. Moreover, no noticeable epimerization of the stereogenic carbon atom was observed in these polymerization conditions, as deduced from 1 H NMR analysis of a poly(L-lactide) sample.

Ring-opening polymerization of lactides by (pyrazol-1-ylmethyl)pyridine Zn(II) and Cu(II) complexes: Kinetics, mechanism and tacticity studies

“…The -OH end groups could originate from adventitious water molecules that are capable of initiating hydrolysis of the polymer chain. These results are in agreement with those reported by Pilone et al 43 and Bourissou et al 34 in which water molecules hydrolyzed the polymer end chains. From these data, the polymerization reactions by complexes 1-4 can thus be said to proceed through coordination insertion mechanism followed by hydrolysis of the acetate and complex end groups.…”

“…20 The narrow PDIs coupled with the relatively high Mw observed in L-LA polymerization indicate absence/minimum transesterification reactions. 33,34 However, low molecular weights of poly(D,L-LA) is consistent with the occurrence of intramolecular transesterification reactions. 34 The narrow PDIs achieved for complexes 1-4 bearing acetate groups is in fact unusual as most acetate complexes give broad PDI in comparison to the alkoxide initiators.…”

“…33,34 However, low molecular weights of poly(D,L-LA) is consistent with the occurrence of intramolecular transesterification reactions. 34 The narrow PDIs achieved for complexes 1-4 bearing acetate groups is in fact unusual as most acetate complexes give broad PDI in comparison to the alkoxide initiators. 35 The nature of the metal centre also showed significant influence on the polymer molecular weight.…”

Desenvolvimento de biocompósitos de poli(L-ácido láctico) (PLLA) com serragem de madeira

“…O poli(L-ácido láctico) (PLLA) vem recebendo cada vez mais atenção de ambas as comunidades científicas e industriais, uma vez que atualmente tem o maior potencial comercial como um plástico versátil biodegradável feito a partir de materiais agrícolas renováveis, como milho ou batatas fermentados [10,11]. Com base na sua biodegradabilidade e biocompatibilidade, o poli(ácido láctico) (PLA) é amplamente utilizado na medicina, engenharia de tecidos e alguns outros campos da vida civil, como libertação controlada de fármacos, compostos implantáveis, dispositivos para fixação óssea, embalagens de papel, revestimentos, sistemas de libertação prolongada para pesticidas e fertilizantes e embalagens [12][13][14].…”

Mechanism of propagation in the cationic polymerization of L,L‐lactide

“…More recently, a series of papers appeared describing cationic homo-and copolymerization (mostly with e-caprolactone) of L,L-lactide in the presence of alcohols or diols, that is, at the conditions when activated monomer (AM) mechanism operates. [12][13][14][15] Cationic polymerization of L,L-lactide catalyzed by strong acids in the presence of diols leads to polymers terminated at both ends with hydroxyl group. Because in such process, protic acid acts as a catalyst and HOA group containing compound is an initiator, molecular weight can easily be controlled by adjusting [L,L-lactide] 0 /[HOA] 0 ratio.…”