Ring-Opening Polymerization of ε-Caprolactone Initiated by Natural Amino Acids

Organocatalytic Ring-Opening Polymerization of ϵ-Caprolactone with Phosphoramidimidates (PADIs) as a Bifunctional Brønsted Acid Catalyst

In this study, an organocatalytic ring-opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL) has been developed by employing PADIs as a novel and efficient acid/base bifunctional organocatalyst, which could afford metal-free poly(ϵ-caprolactone) with predictable molecular weight and narrow dispersity at a low catalyst loading under mild conditions. NMR and kinetic studies indicate that the ring-opening polymerizations of lactones catalyzed by PADIs proceed in a living and well controlled manner. Moreover, this organic Brønsted acid catalytic system could allow the synthesis of PCL with molecular weight above 60 kg/mol, as well as well-defined star polymers.

Poly(ε-caprolactones) Initiated by Chiral Compounds: A New Protocol to Support Organocatalysts

This work investigates the support of organocatalysts in polyesters, a class of polymers seldom used for this purpose. The proposal is to use the hydroxyl groups present in the structure of the chosen chiral compounds to promote the polymerization of ε-caprolactone, generating the support and anchoring the organocatalyst in a single step. A very simple method, with acid catalysis, was employed, that showed versatility in generating supported catalysts with different structures and functional groups and modulating the mass of the materials to generate specific solubility characteristics. In this way, the catalysts can be solubilized in some organic solvents, such as dichloromethane, but at the end of the reaction, they can be recovered in a heterogeneous way, through precipitation in more apolar solvents. The materials were applied as organocatalysts on an aldol addition test reaction and the product could be obtained in excellent yields and good stereoselectivity. The polymer did not show signs of degradation after the reaction, proving to be robust and suitable for use in catalysis; however, a recycling process appears to be necessary for its reuse.

Cyclodextrin-Oligocaprolactone Derivatives-Synthesis and Advanced Structural Characterization by MALDI Mass Spectrometry

Cyclodextrins have previously been proven to be active in the catalysis of cyclic ester ring-opening reactions, hypothetically in a similar way to lipase-catalyzed reactions. However, the way they act remains unclear. Here, we focus on β-cyclodextrin's involvement in the synthesis and characterization of β-cyclodextrin-oligocaprolactone (CDCL) products obtained via the organo-catalyzed ring-opening of ε-caprolactone. Previously, bulk or supercritical carbon dioxide polymerizations has led to inhomogeneous products. Our approach consists of solution polymerization (dimethyl sulfoxide and dimethylformamide) to obtain homogeneous CDCL derivatives with four monomer units on average. Oligomerization kinetics, performed by a matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) optimized method in tandem with 1H NMR, revealed that monomer conversion occurs in two stages: first, the monomer is rapidly attached to the secondary OH groups of β-cyclodextrin and, secondly, the monomer conversion is slower with attachment to the primary OH groups. MALDI MS was further employed for the measurement of the ring-opening kinetics to establish the influence of the solvents as well as the effect of organocatalysts (4-dimethylaminopyridine and (-)-sparteine). Additionally, the mass spectrometry structural evaluation was further enhanced by fragmentation studies which confirmed the attachment of oligoesters to the cyclodextrin and the cleavage of dimethylformamide amide bonds during the ring-opening process.

Synthesis of Poly(Trimethylene Carbonate) from Amine Group Initiation: Role of Urethane Bonds in the Crystallinity

Semi-crystalline poly(trimethylene carbonate) (PTMC) can be efficiently prepared by ring-opening polymerization (ROP) initiated by amine using various catalysts. More promising results were reached with the one-step process of stannous octanoate unlike the two-step one-pot reaction using TBD and MSA catalysts. The ROP-amine of TMC consists in a simple isocyanate free process to produce polycarbonate-urethanes, compatible with the large availability of amines ranging from mono- to multifunctional until natural amino acids. ROP-amine of TMC leads to urethane bonds monitored by FTIR spectroscopy. The relationship between the nature of amines and the crystallinity of PTMC was discussed through X-ray diffraction and thermal studies by DSC and TGA. The impact of the crystallinity was also demonstrated on the mechanical properties of semi-crystalline PTMC in comparison to amorphous PTMC, synthesized by ROP initiated by alcohol. The semi-crystalline PTMC synthesized by ROP-amine opens many perspectives.

Microparticles of Lamivudine-Poly-ε-Caprolactone Conjugate for Drug Delivery via Internalization by Macrophages

The past decade may be considered as revolutionary in the research field focused on the physiological function of macrophages. Unknown subtypes of these cells involved in pathological mechanisms were described recently, and they are considered as potential drug delivery targets. The innate ability to internalize foreign bodies exhibited by macrophages can be employed as a therapeutic strategy. The efficiency of this uptake depends on the size, shape and surface physiochemical properties of the phagocyted objects. Here, we propose a method of preparation and preliminary evaluation of drug-polymer conjugate-based microspheres for macrophage targeted drug delivery. The aim of the study was to identify crucial uptake-enhancing parameters for solid, surface modified particles. A model drug molecule-lamivudine-was conjugated with poly-ε-caprolactone via ring opening polymerization. The conjugate was utilized in a solvent evaporation method technique to form solid particles. Interactions between particles and a model rat alveolar cell line were evaluated by flow cytometry. The polymerization product was characterized by a molecular weight of 3.8 kDa. The surface of the obtained solid drug-loaded cores of a hydrodynamic diameter equal to 2.4 µm was modified with biocompatible polyelectrolytes via a layer-by-layer assembly method. Differences in the internalization efficiency of four particle batches by the model RAW 264.7 cell line suggest that particle diameter and surface hydrophobicity are the most influential parameters in terms of phagocytic uptake.

Enzymatic Synthesis of Amino Acids Endcapped Polycaprolactone: A Green Route Towards Functional Polyesters

ε-caprolactone (CL) has been enzymatically polymerized using α-amino acids based on sulfur (methionine and cysteine) as (co-)initiators and immobilized lipase B of Candida antarctica (CALB) as biocatalyst. In-depth characterizations allowed determining the corresponding involved mechanisms and the polymers thermal properties. Two synthetic strategies were tested, a first one with direct polymerization of CL with the native amino acids and a second one involving the use of an amino acid with protected functional groups. The first route showed that mainly polycaprolactone (PCL) homopolymer could be obtained and highlighted the lack of reactivity of the unmodified amino acids due to poor solubility and affinity with the lipase active site. The second strategy based on protected cysteine showed higher monomer conversion, with the amino acids acting as (co-)initiators, but their insertion along the PCL chains remained limited to chain endcapping. These results thus showed the possibility to synthesize enzymatically polycaprolactone-based chains bearing amino acids units. Such cysteine endcapped PCL materials could then find application in the biomedical field. Indeed, subsequent functionalization of these polyesters with drugs or bioactive molecules can be obtained, by derivatization of the amino acids, after removal of the protecting group.

Influence of Chain Length on the Self-Assembly of Poly(ε-caprolactone)-Grafted Graphene Quantum Dots

The multifarious applications of graphene quantum dots (GQDs) necessitate surface modifications to enhance their solution processability. Herein, we report the synthesis and self-assembly of GQDs grafted with poly(ε-caprolactone) (PCL) of different degrees of polymerization (3, 7, 15, and 21) produced from ring-opening polymerization. Optical and morphological studies unveil the transformation of the assemblies from J-aggregates to H-aggregates, accompanied by an alteration in morphology from toroid to spheroid to rodlike structures with increasing chain length of PCL. Functionalized GQDs with lower chain lengths of PCL at higher concentration also assemble into liquid-crystalline phases as observed from birefringent textures, which are later correlated to the formation of columnar hexagonal (Col_h) mesophases. However, no such behavior is observed at higher chain lengths of PCL under identical conditions. Therefore, it is evident that the variation in the PCL chain length plays a crucial role in the self-assembly, which is primarily triggered by the van der Waals force between the polymer chains dictating the π stacking of GQDs, resulting in different self- aggregated behavior.

Precise Polymerization of a Highly Tumor Microenvironment-Responsive Nanoplatform for Strongly Enhanced Intracellular Drug Release

The importance of achieving a high content of responsive groups of drug carriers is well-known for achieving rapid intracellular drug release; however, very little research has been published on this subject. Here, we present an entirely new strategy to synthesize a highly reduction-sensitive polymer-drug conjugate with one disulfide bond corresponding to each resultant copolymer through a precise ring-opening polymerization of ε-caprolactone that is initiated by a monoprotected cystamine. Simultaneously, the anticancer drug doxorubicin is chemically conjugated to the polymer via pH-responsive hydrazone bonds, which effectively prevent premature drug release in the blood circulation. The 3-aminophenylboronic acid (PBA) targeting ligands endow an active-targeting ability that significantly prompts the specific internalization of nanocarriers by tumor cells and thus results in excellent cytotoxicity against tumor cells. The concept of precise polymerization is put forward to achieve multifunctional nanocarriers for the first time. This study is expected to inspire the development of a highly environment-responsive nanoplatform for drug delivery in future clinical applications.

Characterization of bi-layered magnetic nanoparticles synthesized via two-step surface-initiated ring-opening polymerization

A versatile strategy to integrate multiple functions in a polymer based material is the formation of polymer networks with defined nanostructures. Here, we present synthesis and comprehensive characterization of covalently surface functionalized magnetic nanoparticles (MNPs) comprising a bi-layer oligomeric shell, using Sn(Oct)2 as catalyst for a two-step functionalization. These hydroxy-terminated precursors for degradable magneto- and thermo-sensitive polymer networks were prepared via two subsequent surface-initiated ring-opening polymerizations (ROPs) with ω-pentadecalactone and ε-caprolactone. A two-step mass loss obtained in thermogravimetric analysis and two distinct melting transitions around 50 and 85°C observed in differential scanning calorimetry experiments, which are attributed to the melting of OPDL and OCL crystallites, confirmed a successful preparation of the modified MNPs. The oligomeric coating of the nanoparticles could be visualized by transmission electron microscopy. The investigation of degrafted oligomeric coatings by gel permeation chromatography and 1H-NMR spectroscopy showed an increase in number average molecular weight as well as the presence of signals related to both of oligo(ω-pentadecalactone) (OPDL) and oligo(ε-caprolactone) (OCL) after the second ROP. A more detailed analysis of the NMR results revealed that only a few ω-pentadecalactone repeating units are present in the degrafted oligomeric bi-layers, whereby a considerable degree of transesterification could be observed when OPDL was polymerized in the 2nd ROP step. These findings are supported by a low degree of crystallinity for OPDL in the degrafted oligomeric bi-layers obtained in wide angle X-ray scattering experiments. Based on these findings it can be concluded that Sn(Oct)2 was suitable as catalyst for the preparation of nanosized bi-layered coated MNP precursors by a two-step ROP.

Organophosphate-catalyzed bulk ring-opening polymerization as an environmentally benign route leading to block copolyesters, end-functionalized polyesters, and polyester-based polyurethane

To expand the potential of an organophosphate catalyst, ring-opening polymerization of cyclic esters, cyclic ester-ether, and cyclic carbonate was demonstrated under bulk conditions.

Supramolecular, prodrug-based micelles with enzyme-regulated release behavior for controlled drug delivery

Supramolecular, prodrug-based micelles (SMPMs) with enzyme-induced drug release behavior were engineeredviahost–guest interaction of camptothecin carrying PCL and α-cyclodextrin.

1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

The ring-opening polymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) under solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO₂) as precatalyst is described. Linear and star-branched polyesters were synthesized by successive use of benzyl alcohol, ethylene glycol, glycerol and pentaerythritol as initiator alcohols, and the products were fully characterized by ¹H and ¹³C{¹H} NMR spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). BMIM-2-CO₂ acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation, either by heating under vacuo (method A) or by addition of NaBPh₄ (method B). Possible catalytic and deactivation mechanisms are proposed.

Organic Catalysis for Ring-Opening Polymerization

Organic catalysis in ring-opening polymerization (ROP) has become a powerful alternative to more traditional metal-based catalysts. The field has developed to a point at which there are not only excellent low cost and easy to use organocatalysts for day-to-day polymerizations, but the ability to precisely control the synthesis of advanced polymer architectures and ROP monomers that are extremely challenging to polymerize with other catalysts now exists. This viewpoint article will highlight the key advances in organocatalyst design with the aim of encouraging the wider application of organic catalysts in ROP.

Synthesis and properties of a star-shaped poly(ϵ-caprolactone)-ibuprofen conjugate

A series of novel star-shaped poly(ϵ-caprolactone) (PCL) biodegradable polyesters were synthesized through ring-opening polymerization of ϵ-caprolactone in the presence of a poly(amidoamine) (PAMAM) dendrimer initiator. The polymers (PAMAM/PCLs) were obtained with a high yield (92%) and a number-average molecular weight of up to 14 000 g/mol. The nonlinear structure of PAMAM/PCLs was confirmed by nuclear magnetic resonance, gel-permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. Thermal analysis indicated that the star-shaped PAMAM/PCLs had a melting point, degree of crystallinity, glass transition temperature and maximum decomposition temperature all lower than those of linear PCL. Ibuprofen (IBU), a popular non-steroidal anti-inflammatory drug, was co-valently (ester) bonded to the PAMAM/PCL molecules using the DCC/DMAP coupling method (DCC, N,N'-dicyclohexylcarbodiimide; DMAP, 4-(dimethylamino)pyridine). A high drug content (33.1 mol%) in the conjugate was obtained. The in-vitro drug-release profiles of IBU from the PAMAM/PCL/IBU conjugate were examined and found adequate for drug-carrier applications of our star-shaped polymers.

Synthesis and properties of star oligo/poly(trimethylene carbonate)s with cholic acid moieties as cores

Star oligo/poly(trimethylene carbonate)s with cholic acid moieties as cores were synthesized by ring-opening polymerization of trimethylene carbonate (TMC) initiated by cholic acid with hydroxyl groups. The molecular weights of the star oligomers/polymers were controlled by adjusting the feed ratio of the initiator cholic acid to the monomer TMC. The star oligo/poly(trimethylene carbonate)s were characterized by Fourier transform infrared spectroscopy (FT-IR), (1)H nuclear magnetic resonance spectroscopy ((1)H-NMR) and combined size-exclusion chromatography and multiangle laser light scattering (SEC-MALLS) analysis. The water contact angles of the star oligo/poly(trimethylene carbonate)s were measured. Using 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, the star oligo/poly(trimethylene carbonate) was proved to have a low cytotoxicity. A microsphere drug-delivery system based on a star polymer was fabricated and its in vitro drug release property was studied.

Biodegradable soy protein isolate-based materials: a review

Recently, there is an increasing interest of using bio-based polymers instead of conventional petroleum-based polymers to fabricate biodegradable materials. Soy protein isolate (SPI), a protein with reproducible resource, good biocompatibility, biodegradability, and processability, has a significant potential in the food industry, agriculture, bioscience, and biotechnology. Up to now, several technologies have been applied to prepare SPI-based materials with equivalent or superior physical and mechanical properties compared with petroleum-based materials. The aim of this review is focused on discussion of the advantages and limitations of native SPI as well as the bulk and surface modification strategies for SPI. Moreover, some applications of SPI-based materials, especially for food preservation and packaging technology, were discussed.

Structure-Processing-Property Relationship of Poly(Glycolic Acid) for Drug Delivery Systems 1: Synthesis and Catalysis

Till date, market is augmented with a huge number of improved drug delivery systems. The success in this area is basically due to biodegradable polymers. Although conventional systems of drug delivery utilizing the natural and semisynthetic polymers so long but synthetic polymer gains success in the controlled drug delivery area due to better degradation profile and controlled network and functionality. The polyesters are the most studied class group due the susceptible ester linkage in their backbone. The Poly(glycolic Acid) (PGA), Poly(lactic acid) (PLA), and Polylactide-co-glycolide (PLGA) are the best profiled polyesters and are most widely used in marketed products. These polymers, however, still are having drawbacks which failed them to be used in platform technologies like matrix systems, microspheres, and nanospheres in some cases. The common problems arose with these polymers are entrapment inefficiency, inability to degrade and release drugs with required profile, and drug instability in the microenvironment of the polymers. These problems are forcing us to develop new polymers with improved physicochemical properties. The present review gave us an insight in the various structural elements of Poly(glycolic acid), polyester, with in depth study. The first part of the review focuses on the result of studies related to synthetic methodologies and catalysts being utilized to synthesize the polyesters. However the author will also focus on the effect of processing methodologies but due some constraints those are not included in the preview of this part of review.

Ring-opening polymerization of epsilon-caprolactone initiated by the antitumor agent doxifluridine

A novel 5'-deoxy-5-fluorouridine-poly(epsilon-caprolactone) (5'-DFUR-PCL) polymer was synthesized from the antitumor agent doxifluridine (5'-DFUR) by the ring-opening polymerization of epsilon-caprolactone (epsilon-CL) using Sn(II) 2-ethylhexanoate (Sn(Oct)2) as the catalyst. The structure and molecular weight of these polymers were further elucidated by proton nuclear magnetic resonance and gel-permeation chromatography. The results revealed that the molecular weights of the 5'-DFUR-PCL polymers were close to the theoretical values calculated from the epsilon-CL to 5'-DFUR molar ratios and their recovery yields were as high as 90%. Two mechanisms of epsilon-CL polymerization initiated by Sn(Oct)2 were proposed involving either a single or two 5'-DFUR molecules. This study has provided an efficient method for the preparation of 5'-DFUR-PCL polymers. These novel 5'-DFUR-PCL polymers can be applied as drugs on carriers without the need for the coating or grafting processes associated with drugs in drug delivery and have great potential for cancer therapy.