Strontium Isopropoxide: A Highly Active Catalyst for the Ring‐Opening Polymerization of Lactide and Various Lactones

Abstract

Commercially available strontium isopropoxide represents a suitable catalyst/initiator for the ring‐opening polymerization (ROP) of lactide (LA), ε−caprolactone, δ−valerolactone, δ−caprolactone, and δ−decalactone. Well‐defined polyesters are accessible via the solution polymerization of lactide in toluene with a [LA]:[Sr] ratio of 100:1 at room temperature with or without the addition of dodecanol as coinitiator. Kinetic studies and detailed analysis by means of matrix‐assisted laser desorption ionization mass spectrometry reveal pseudo‐first‐order kinetics of the ROP as well as excellent endgroup fidelity of the polylactide (PLA) with isopropyl and dodecyl α‐endgroups. Both isopropanolate moieties as well as the coinitiator each initiate PLA chains, enabling the synthesis of PLA with tailored molar mass. The polymerization of ε−caprolactone and δ−valerolactone confirms the high catalyst activity, which causes quantitative monomer conversion after 1 min polymerization time but broad molar mass distributions. In contrast, the catalyst is well suited for the ROP of the less reactive δ−caprolactone and δ−decalactone. Although kinetic studies reveal initially bimodal molar mass distributions, polyesters with dispersity values Ð < 1.2 and unimodal molar mass distributions can be obtained at moderate to high monomer conversions.

Rapid and Controlled Ring-Opening (Co)Polymerization of Bio-Sourced Alkyl-δ-Lactones To Produce Recyclable (Co)Polyesters and Their Application as Pressure-Sensitive Adhesives

“…To the best of our knowledge, the ROPs of alkyl-δ-lactones bearing different alkyl substituents have been only investigated using diphenyl phosphate (DPP) as the catalyst. 36,37 Schneiderman and Hillmyer systematically investigated the effects of substituent length on their polymerization kinetics and thermodynamics for a series of alkyl-δ-lactones. 36 Nevertheless, the ROPs of alkyl-δ-lactones suffered from a slow polymerization rate.…”

“…Moreover, the thermal and mechanical properties of resultant poly(alkyl-δ-lactone)s can be tailored by adjusting the length of alkyl substituents. Despite these advantages, in contrast to their unsubstituted counterpart δ-valerolactone, only limited examples reported the ROPs of alkyl-δ-lactones, especially for those with long alkyl substituents. ,− Recently, we successfully achieved the “living”/controlled (co)polymerization of δ-caprolactone (δ-CL) to produce chemically recyclable poly(δ-caprolactone) (PδCL) and thermoplastic elastomers . In this contribution, we further investigated the effects of alkyl substituent length on their polymerization thermodynamics and kinetics as well as the properties of resultant poly(alkyl-δ-lactone)s. Rapid and controlled bulk ROPs of three alkyl-δ-lactones bearing with different pendent alkyl groups were achieved in the presence of an organobase/urea binary catalyst to produce closed-loop recyclable polyesters that can be recycled back to pristine monomers with high yields (>96%).…”

Sourcing, thermodynamics, and ring-opening (co)polymerization of substituted δ-lactones: a review

“…More recently, strontium isopropoxide was used as the initiator/catalyst with or without n -dodecanol as a co-initiator for the ROP of δ-HL and δ-DL at RT. 95 It is shown to have better activity than lanthanum isopropoxide for δ-HL, as 82% conversion and a molar mass of 5000 g mol −1 can be reached in 15 min using a co-initiator at a δ-HL concentration of 4 mol L −1 in toluene. Furthermore, a dispersity of 1.16 was obtained.…”

Chemically Recyclable Thermoplastic Polyurethane Elastomers via a Cascade Ring-Opening and Step-Growth Polymerization Strategy from Bio-renewable δ-Caprolactone

“…Although a range of different catalysts have been tried, the preparation of PδCL with well-defined terminal groups and controlled molecular weight remains as a challenge, which is necessary for the preparation of polyurethanes. Meanwhile, the previously reported ROP conditions did not fulfill the criteria of green chemistry, which suffered from high catalyst loadings, excess use of solvents, long reaction time, and/or toxic metal residues. − In this contribution, we first realized the “living”/controlled ROP of δCL to produce telechelic PδCL diol by judicious selection of a combination of an organobase and urea as a catalyst at room temperature in bulk. Moreover, thermoplastic polyurethane elastomers (TPUs) were then prepared via a one-pot strategy by cascade ROP of δCL and subsequent step-growth polymerization of PδCL diol precursors with diisocyanate under solvent-free conditions.…”