Ring-Opening Polymerization of ε-Caprolactone in Supercritical Carbon Dioxide

Ring-Opening Dispersion Polymerization of ʟ-Lactide with Polylactide Stabilizer in Supercritical Carbon Dioxide

Non-fluorous triblock copolymers of poly(l-lactide)-block-hydroxypropyl-terminated poly(dimethyl siloxanes)-block-poly(l-lactide) (PLLA-HTPDMS-PLLA) with two different molecular weights in the range of 4800 to 6500 Da, were prepared by changing the ratio of HTPDMS to l-lactide (L-LA), and were used as stabilizers for the ring-opening dispersion polymerization (RODP) of L-LA to prepare poly(l-lactide) (PLLA) in supercritical carbon dioxide (ScCO2). The experimental results showed that the prepared non-fluorous triblock copolymers were very effective as new stabilizers for the RODP and fine powders of PLLA were obtained. The structure of the stabilizers and PLLA were characterized by 1H NMR and FTIR spectroscopy. The morphology of PLLA was investigated by scanning electron microscopy (SEM). The effects of the CO2-philic/lipophilic segment lengths of the stabilizers on the RODP were explored. The effects of the stabilizer concentration on the polymerization yield, molecular weight, and morphology of PLLA were investigated.

Ultrasound-Assisted Enzymatic Synthesis of Poly-ε-Caprolactone: Kinetic Behavior and ReactorDesign

Lipase-mediated, ultrasound-assisted synthesis of poly-ε-caprolactone was investigated. It was found that ultrasound irradiation helped to improve the rate constant of poly-ε-caprolactone chain propagation (kp) at high initial monomer (ε-caprolactone) concentration. The enhancement of kp ranged from 34% to 46% at 22.5–18.0 M initial monomer concentration, respectively. In a system proned to time-dependent mass-transfer limitation due to polymer chain extension, the acoustic effects could have also allowed the reaction to continue longer compared to non-sonicated process until it became impossible at highly elevated reaction mixture viscosity(>2,000 times increase from initial viscosity). Consequently, it also helped to improve monomer conversion. In a continuous flow polymerization system, a plug flow reactor system is recommended due to its lowest volume for maximum conversion compared to a continuously stirred tank reactor system.

Synthesis of polycaprolactone: a review

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: epsilon-caprolactone (epsilon-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).

Branched Pentablock Poly(L-lactide-co-∊-caprolactone) Synthesis in scCO2

Pentablock poly(L-lactide-co-∊-caprolactone) (PLLA/PCL), with a central fluorinated segment and four PLLA/PCL side chains was synthesized by sequential ring-opening polymerization (ROP) with stannous octoate catalyst in an environmentally benign and clean medium, scCO2. Copolymers of PLLA and PCL are extensively researched for biomedical applications. Fluorinated hydrocarbons are similarly promising for biomedicine, and especially for oxygen-carrying substitute applications. Initially, a fluorinated reactive triblock stabilizer (prepolymer, PCL-FLKT-PCL) with inner fluorinated segment and PCL side chains was synthesized in bulk from a tetraol fluorinated alcohol (FLKT) with a 99% conversion. The prepolymer was then utilized for the synthesis of copolymers in scCO2, where PLLA segments were successively incorporated to the ends of the prepolymer, forming a pentablock structure with four polyester side chains. Reactions were carried out at 75°C and 4000-4500 psi. Solubility studies of the prepolymer and the pentablock copolymer in scCO2 showed effective solubilization at the reaction temperature and pressure. The molecular weights of the products were measured with the aid of gel permeation chromatography; the prepolymer and the copolymer possessed average number molecular weights (Mn) in the range of 13 000 and 24 000 (for 96% conversion of LLA), respectively. Low poly-dispersity indexes were obtained: 1.34 for the prepolymer and 1.08-1.34 for the pentablock copolymer. Material characterization was carried out by 1H NMR, 13C NMR, 19F NMR, differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and scanning electron microscopy (SEM).

Copolymerization ofD,L-lactide and glycolide in supercritical carbon dioxide with zinc octoate as catalyst

The objective of the study is the development of a new technique based on supercritical technology for the production of bioabsorbable polymeric microparticles containing pharmaceutical principles, for their use in the controlled release of medicines. For this purpose, the ring-opening copolymerization of D,L-lactide and glycolide in supercritical carbon dioxide, using zinc(II) 2-ethylhexanoate (ZnOct2) as catalyst, was studied. The polymer obtained with ZnOct2 has similar characteristics to that obtained with stannous octoate (SnOct2), the conventional catalyst used up to now for this kind of polymerization process. Experiments were performed at various reaction times, pressures, and stirring rates. The most outstanding result was found by varying the stirring rate, where particles forming agglomerates seem to be obtained at the greater agitation levels.

Impact of silicone-based block copolymer surfactants on the surface and bulk microscopic organization of a biodegradable polymer, poly(epsilon-caprolactone)

Two amphiphilic AB block copolymers, containing a highly compatible poly(epsilon-caprolactone) (PCL) block connected to a poly(dimethylsiloxane) (PDMS) block having a low surface energy, are synthesized and characterized in terms of their dispersion in a presynthesized PCL matrix. X-ray photoelectron spectroscopy, contact angle measurements, atomic force microscopy, and optical microscopy are used to describe the evolution of the surface chemical composition, as well as the surface and bulk morphology of the PCL/copolymer blends as a function of the nature and weight surface free energy and the dispersion of the copolymers in the blends, leading to important modifications of the bulk and the surface morphology. These differences are interpreted in terms of the impact of the block copolymers on the semicrystalline polymer structure and related properties in the prospect of using the surfactants to improve the synthesis of PCL in supercritical CO(2).