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

Abstract

Front Cover: In article number 1900306, Ulrich S. Schubert and co‐workers show that Sr(OiPr)2 is a highly active catalyst/initiator for the ring‐opening polymerization of lactide and various lactones, producing polyesters with excellent end‐group fidelity. The catalyst is promising for applications in implant production because strontium is beneficial for bone regeneration.

Phenoxy imine NOON complexes of heavy alkaline earth ions for the ring-opening polymerisation of cyclic esters

“…It was considered that these pro-ligand signals were an indication of catalyst decomposition as it is difficult to categorically eliminate the possibility of a low concentration of protic impurities, however, they were observed not to increase over the course of the polymerisation and were therefore interpreted as being consistent with a possible anionic mechanism. At all temperatures, the GPC traces of the PLA produced using complex 2 were bimodal; similar observations were made by Schubert and co-workers when employing strontium iso-propoxide as a catalyst, 49 and also Mountford et al for the bimetallic strontium DBP system. 41 This bimodality may result from different initiating species in solution (i.e.…”

“…44,48 The bimodal nature of the molecular weight distributions can be rationalised by the presence of both linear and cyclic PLA and the presence of different initiating species as a consequence of catalyst speciation (vide infra). 41,49,50 The experimental molecular weights however, are slightly lower than the previously documented range for the polymerisation of 500 eq. using Ca, Sr and Ba systems (67 000-74 100 gmol −1 ).…”

Gram Scale Synthesis of Dual-Responsive Dendritic Polyglycerol Sulfate as Drug Delivery System

“…In order to find optimal conditions for the synthesis of the copolymers, a wide scope of catalysts were screened. Thus far, a variety of catalysts has been studied for the ROP of caprolactones and oxiranes including Lewis acids such as Sn(oct) 2 , strontium isporopoxide (Sr(OiPR) 2 ), Mg(HMDS) 2 and organocatalysts such as 1,8-diaza-[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and diphenyl phosphate (DPP) [ 27 , 28 , 29 ]. In our group, the synthesis of dPG-PCL copolymers was reported recently, utilizing Sn(oct) 2 as a suitable catalyst [ 30 ].…”

Synthesis of Poly(δ-caprolactone) via Bis(phenolate) Rare-Earth Metal Complexes Mediated Ring-Opening Polymerization and Its Chemical Recycling

“…3,4 As a biobased monomer that can be obtained from renewable resources, 5,6 the ROP of δ-caprolactone (δCL) has been largely underexplored compared to its unsubstituted counterpart δ-valerolactone and structural isomer ε-caprolactone, probably due to its poor polymerizability. 7 Although a few catalysts including Candida antarctica lipase, 8,9 triphenyl bismuth, 10,11 diphenyl phosphate, 12,13 strontium isopropoxide, 14 1,5,7-triazabicyclo [4.4.0]dec-5-ene (TBD)/alcohol, 15,16 and alkali metal alkoxides 17 have been employed for the homopolymerization or copolymerization of δCL, these polymerization systems still face challenges, such as low monomer conversion, broad molecular weight distribution, and harsh polymerization condition. On the other hand, examples for the chemical recycling of the corresponding poly(δcaprolactone) (PδCL) are rather limited.…”

“…Renewable monomers derived from bioresources and chemically recyclable polymers have gained increasing attention to addressing the crisis arising from depleting fossil sources and environmental concerns. , Among the large family of synthetic polymers, the synthesis of polyesters via ring-opening polymerization (ROP) of cyclic esters and their chemical recycling to pristine monomers have gained tremendous momentum in recent years. , As a biobased monomer that can be obtained from renewable resources, , the ROP of δ-caprolactone (δCL) has been largely underexplored compared to its unsubstituted counterpart δ-valerolactone and structural isomer ε-caprolactone, probably due to its poor polymerizability . Although a few catalysts including Candida antarctica lipase, , triphenyl bismuth, , diphenyl phosphate, , strontium isopropoxide, 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD)/alcohol, , and alkali metal alkoxides have been employed for the homopolymerization or copolymerization of δCL, these polymerization systems still face challenges, such as low monomer conversion, broad molecular weight distribution, and harsh polymerization condition. On the other hand, examples for the chemical recycling of the corresponding poly­(δ-caprolactone) (PδCL) are rather limited.…”