Polycaprolactone (PCL) is an important polymer due to its mechanical properties, miscibility with a large range of other polymers and biodegradability. Two main pathways to produce polycaprolactone have been described in the literature: the polycondensation of a hydroxycarboxylic acid: 6-hydroxyhexanoic acid, and the ring-opening polymerisation (ROP) of a lactone: e-caprolactone (e-CL). This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems). A surprising variety of catalytic systems have been studied, touching on virtually every section of the periodic table. A detailed list of reaction conditions and catalysts/initiators is given and reaction mechanisms are presented where known. Emphasis is put on the ROP pathway due to its prevalence in the literature and the superior polymer that is obtained. In addition, ineffective systems that have been tried to catalyse the production of PCL are included in the electronic supplementary information for completeness (141 references).

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Synthesis of polycaprolactone: a review

Organocatalysis offers a number of opportunities in polymer synthesis and was among the earliest methods of catalyzing the synthesis of polyesters. In the following Perspective we attempt to highlight the opportunities and challenges in the use of organic molecules as catalysts or initiators for polymerization reactions. The ring-opening polymerization of cyclic monomers is used as a representative polymerization process to illustrate some of the features of organic catalysts and initiators and to compare them to metal-based approaches. The convergence of convenience, functional group tolerance, fast rates, and selectivities will continue to drive innovations in polymerization catalysis, and it is our perspective that organocatalysis will continue to play an important role in these developments.

Organocatalysis: Opportunities and Challenges for Polymer Synthesis

The important advances and current trends in the stereocontrolled ring-opening polymerisation of lactide are discussed in this tutorial review. Microstructures, structural characterisation methods and the properties of stereoregular poly(lactide)s are examined. The application of metal-based catalysts dominates this area although simple anionic polymerisation and organocatalytic routes that demonstrate control of the polymer tacticity are discussed.

Stereocontrolled ring-opening polymerisation of lactide

The field of tissue engineering places complex demands on the materials it uses. The materials chosen to support the intricate processes of tissue development and maintenance need to have properties which serve both the bulk mechanical and structural requirements of the target tissue, as well as enabling interactions with cells at the molecular scale. In this critical review we explore how synthetic polymers can be utilised to meet the needs of tissue engineering applications, and how biomimetic principles can be applied to polymeric materials in order to enhance the biological response to scaffolding materials (105 references).

Synthetic polymer scaffolds for tissue engineering

The review summarizes recent developments in the preparation and use of new initiators for the ring opening polymerization of lactide. The review compares different classes of initiator including metal complexes, classed according to their group in the periodic table, and carbon‐based initiators/organocatalysts. Emphasis is placed on the polymerization kinetics and the control exhibited by the different types of initiators. Where useful properties, such as high rates or stereocontrol, have been observed a more detailed examination of the initiator is provided. A further focus of the review is initiators displaying low toxicity and biocompatibility.

Biocompatible Initiators for Lactide Polymerization

Synthesis and characterization of a series of bis(oxo/thiophosphinic)diamido yttrium complexes and their application as initiators for lactide ring-opening polymerization

The syntheses of a series of bis(thiophosphinic amido) yttrium complexes are reported by the reaction of bis(thiophosphinic amine) ligands with [Y(N(SiMe3)2)3]. The complexation reactions were monitored using NMR spectroscopy and one complex was characterized by single crystal X-ray crystallography. Two substitution sites on the ligand were varied, the phosphorus substituents were phenyl, isopropyl and ethoxy groups and the diamine backbones were ethylene, trans-cyclohexylene and 2,2-dimethylpropylene groups. All the new complexes were tested as initiators for the ring opening polymerization of rac-lactide. They exhibited good polymerization control, shown by the linear fits to plots of number-averaged molecular weight (Mn) versus the percentage conversion, the close agreement between the theoretical and observed degree of polymerization (DP) and the moderate polydispersity index (PDI) values. They also showed very high polymerization rates (kapp = 2.2 × 10−4 to 1.1 × 10−2 s−1 at [lactide]0 = 1 M, [initia...

Linda M. Hodgson

Papers

Biocompatible Initiators for Lactide Polymerization

Synthesis and characterization of a series of bis(oxo/thiophosphinic)diamido yttrium complexes and their application as initiators for lactide ring-opening polymerization

A Series of Bis(thiophosphinic amido)yttrium Initiators for Lactide Ring-Opening Polymerization

Yttrium(III) complex as a highly active catalyst for lactide polymerization