Abstract
The first example of solvent-free, organocatalyzed, polymerization of 1,3-dioxolan-4-ones, used as easily accessible monomers for the synthesis of polylactic acid (PLA), is described here. An optimization of reaction conditions was carried out, with p-toluensulfonic acid emerging as the most efficient Brønsted acid catalyst. The reactivity of the monomers in the tested conditions was studied following the monomer conversion by 1H NMR and the molecular weight growth by SEC analysis. A double activation polymerization mechanism was proposed, pointing out the key role of the acid catalyst. The formation of acetal bridges was demonstrated, to different extents depending on the nature of the aldehyde or ketone employed for lactic acid protection. The polymer shows complete retention of stereochemistry, as well as good thermal properties and good polydispersity, albeit modest molecular weight.
Highlights
Following the continuous increase of plastic-made commodity manufacturing, research efforts in recent years have focused on the possibility of replacing traditional oil-based polymers with more eco-friendly materials
Given our interest in the synthesis of Polylactic acid (PLA)-based materials [24,25,26], we looked at DOXs as promising monomers for a “green” PLA-production [27,28]
Our investigation started with the selection of 1,3-dioxolan-4-one (MeDOX) 1 as monomer, known to be able to undergo polymerization through the release of volatile formaldehyde
Summary
Following the continuous increase of plastic-made commodity manufacturing, research efforts in recent years have focused on the possibility of replacing traditional oil-based polymers with more eco-friendly materials. Polylactic acid (PLA) is one of the most intriguing polymers in this category, being derived from renewable sources and, at the same time, having good biodegradability [1,2]. PLA can be synthesized either through polycondensation of lactic acid under azeotropic distillation conditions [3] or, more efficiently, through ring-opening polymerization (ROP) of lactide. Both routes usually require appropriate catalytic systems. L-lactide bulk ROP, is currently the most common and industrially exploited protocol for PLA synthesis [5], usually relying on tin(II) 2-ethylhexanoate (Sn(Oct)2 ) catalysis
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