Heterogeneous ring‐opening polymerization of lactones for biomedical applications

Abstract

Catalysis of the ring‐opening reaction of L‐lactide and ε‐caprolactone to form the corresponding biodegradable polyesters is frequently performed using organometallic compounds such as tin(II) 2‐ethylhexanoate, which operates by a living, coordination insertion mechanism. For biomedical applications, non‐toxic calcium salts have been researched but these rarely approach the same efficiency. The use of heterogeneous immobilized catalysts offers an alternative approach, but competing reactions such as transesterification affect the final molecular weight and polydispersity. The formation of hybrid materials by using silica as the initiation site offers the prospect of biomaterials with novel properties. Copyright © 2009 Society of Chemical Industry

Isoconversional kinetic analysis of ring-opening polymerization of ε-caprolactone: Steric influence of titanium(IV) alkoxides as initiators

“…The activation energies, E a , of the bulk ROP of ε-CL initiated by the four Ti(IV) alkoxides (1)(2)(3)(4) were determined from the non-isothermal DSC data by the three isoconversional methods of Friedman, KAS and OFW. The plots of ln (dα/dt), ln(β/T 2 ) and ln β against 1/T based on these methods are shown in Figs.…”

“…Biodegradable and biocompatible poly(ε-caprolactone) (PCL) is a well-known aliphatic polyester which has attracted considerable attention in recent years due to its potential use in biomedical and pharmaceutical applications [1][2][3]. Ring-opening polymerization (ROP) of ε-CL has been widely used to produce PCL via a coordinationinsertion mechanism [4,5].…”

Bulk solvent-free melt ring-opening polymerization (ROP) of L-lactide catalyzed by Ni(II) and Ni(II)–Ln(III) complexes based on the acyclic Salen-type Schiff-base ligand

“…The PLLA polymer is usually prepared by the ring-opening polymerization (ROP) of L-lactide from diverse catalysts [4], both in solution polymerization and in bulk solvent-free melt polymerization. In spite of the well-established achievements in solution polymerization [5], commercially, the ROP of L-lactide is most commonly carried out with the bulk solvent-free melt polymerization [6], which exhibits advantages over solution polymerization: (i) no solvent is required; (ii) it is less vulnerable to impurity levels and unwanted side reactions; (iii) it is often useful for the large-scale production of PLLAs [7]. As to the needed catalysts for the bulk solvent-free melt ROP of L-lactide, two kinds of typical catalysts have been reported: one is the metal complexes containing the characteristic initiators (alkoxide), and the ROP mechanism is the same as that in solution polymerization, and generally recognized to proceed via the reaction pathway shown in Scheme 1, involving the attack of a characteristic group on the ketonic group of a coordinated L-lactide molecule [8]; the other is metal complexes (Cu 2+ , Ni 2+ or Zn 2+ salicylaldimine complexes [9], Ag + or Au + N-heterocyclic carbene complexes [10]) or metal-free compounds [11] lacking those normal initiators, while the excellent control of the bulk polymerization could be well achieved from the molecular design of diverse catalysts and the selectivity of reaction conditions.…”

A tetranuclear [Zn 4 (L) 2 (OAc) 3 (OH)] complex based on the Salen-type Schiff-base ligand H2L for effective bulk solvent-free melt ring-opening polymerization (ROP) of l -lactide

“…

Bulk solvent-free melt procedure Isotactic PLLA Through the self-assembly of the typical Salen-type Schiff-base ligand H 2 L (H 2 L = N,N′-bis(salicylidene)cyclohexane-1,2-diamine) and an excess of Zn(OAc) 2 ·2H 2 O in the presence of Et 3 N, a new tetranuclear complex [Zn 4 (L) 2 (OAc) 3 (OH)] (1) with multiple active species and self-owned normal initiators was obtained and shown to efficiently catalyze the bulk solvent-free melt ring-opening polymerization (ROP) of L-lactide, giving the uniformly isotactic poly-L-lactides (PLLAs).Poly-L-lactide (PLLA) mostly synthesized from the ring-opening polymerization (ROP) of L-lactide with diverse catalysts [1], due to good biodegradability and biocompatibility, is currently of interest because of its potential applications in pharmaceuticals [2] and biomedicine [3]. Commercially, the bulk solvent-free melt ROP procedure is commonly carried out, despite the well-established achievements from the solution polymerization with metal complexes containing alkoxide [4] or alkyl and ROH [5] as the catalysts, which should be attributed to its solvent-free "green" synthesis and suitability for a large-scale production.

…”

“…Poly-L-lactide (PLLA) mostly synthesized from the ring-opening polymerization (ROP) of L-lactide with diverse catalysts [1], due to good biodegradability and biocompatibility, is currently of interest because of its potential applications in pharmaceuticals [2] and biomedicine [3]. Commercially, the bulk solvent-free melt ROP procedure is commonly carried out, despite the well-established achievements from the solution polymerization with metal complexes containing alkoxide [4] or alkyl and ROH [5] as the catalysts, which should be attributed to its solvent-free "green" synthesis and suitability for a large-scale production.…”