Kinetic Investigation on the Catalytic Ring-Opening (Co)Polymerization of (Macro)Lactones Using Aluminum Salen Catalysts

Abstract

The kinetic behavior of the catalytic ringopening polymerization (cROP) of a range of macrolactones, including ω-pentadecalaconte (PDL), ambrettolide (Amb), and butylene adipate (BA), and small-ring lactones, including L-lactide (LLA), ε-caprolactone (ε-CL), ε-decalactone (ε-DL), and β-butyrolactone (B-BL), using various aluminum salen complexes was investigated. The cROP rates were shown to be first order both in catalyst and in monomer. The activation energies of the polymerization of PDL and LLA in combination with aluminum salen complexes, with and without tert-butyl groups, were determined, showing that the increase in steric hindrance is negatively affecting the polymerization rate of LLA more than of PDL. Interestingly, an increase of the salen diimine bridge from ethylene to 2,2dimethyl propylene leads to a dramatic increase in rate for the polymerization of small-ring lactones, while it leaves the rate of polymerization of macrolactones practically unchanged. In order to exploit this difference in reactivity, the synthesis of blockcopolymers of ε-CL and PDL was attempted using kinetic resolution. However, all the polymers obtained over time were found to be fully random, which appeared to be the result of fast transesterification. Poly(PDL-b-CL) block copolymers were successfully synthesized applying the high reactivity of ε-CL in a sequential feed strategy. However, these block copolymers rapidly transform into fully random copolymers as a result of transesterification, which was shown to have a similar rate constant as the rate constant of the polymerization of PDL. By carefully tuning the reaction time polymers with block, gradient or random topology can be obtained.

Block Copolymers of “PE-Like” Poly(pentadecalactone) and Poly(l-lactide): Synthesis, Properties, and Compatibilization of Polyethylene/Poly(l-lactide) Blends

“…The MALDI−ToF−MS spectrum of OPL3 shows several extra signals compared to PPL5, corresponding to distributions having a combination of a PDO− and an −H The combination of the results above suggests the occurrence of the following events in the sequential feed reaction of PDL and LLA: Initially PDL is polymerized into PPDL, during which simultaneously rapid inter-and intramolecular transesterification of PPDL occurs resulting in linear and cyclic PPDL chains. 9 The formed macrocyclic PPDL will also undergo ring-opening again and it is therefore the balance between cyclization reactions and ROP reactions that will yield the equilibrium concentration of the cyclic chains. 15 After the addition of lactide, the linear PPDL chains initiate the polymerization of LLA forming the poly(PDL-block-LLA) copolymer.…”

Catalytic Ring-Opening (Co)polymerization of Semiaromatic and Aliphatic (Macro)lactones

“…The catalyst precursor, [salen]AlEt (1′), was synthesized according to literature procedures and converted into 1 by the reaction of an equivalent amount of PDOH in a solvent for 100°C. 10 1 H NMR analysis confirmed the complete conversion of 1 under these conditions. 1 H NMR spectra (CDCl 3 ) were recorded in 5 mm tubes on a Varian Mercury 400 MHz spectrometer equipped with an autosampler at ambient probe temperature.…”

Mimicking (Linear) Low-Density Polyethylenes Using Modified Polymacrolactones

“…The conversion vs time profile of Amb follows the expected pseudo-first-order reaction path based on its kinetic parameters (Figure 3a). 12 Both S1 and S2 follow a similar conversion profile as Amb. The fact that the aluminum salen catalyst is still capable of polymerizing S2 at similar rates compared to Amb means that the presence of excess alcohol does not deactivate the catalyst.…”