A facile synthesis of hydrophilic poly(ε-caprolactone)-based poly(ether-ester-amide)s

Segmented poly(ether-ester-amide)s, (PEEA)s, of controlled hydrophilicity degree, based on poly(ε-caprolactone) (PCL), were synthesized according to a facile two-step procedure using α,ω-dihydroxy oligomeric PCL, 4,7,10-trioxa-1,13-tridecanediamine and macromers prepared from poly(ethylene glycol)s and adipoyl chloride. The PEEAs showed M _n values in the range 5–11.5 kDa. A PCL-type crystallinity was found by WAXS. DSC indicated T_m values (49–51 °C) close to that of PCL macromer. Single glass transitions were observed both by DSC and DMTA techniques and the T_g values (−58–−50 °C by DSC) were slightly higher than that of PCL. The water uptake was in the range 4.8–26.0 wt.-% depending on the length of the poly(ethylene glycol) segment.

Monomers used to prepare the PEEAs.     

Phase separation and phase dissolution in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

A blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile having the critical composition (80/20 PCL/SAN) was studied. This PCL/SAN blend having a lower critical solution temperature (LCST) phase boundary at 122 °C offered an excellent opportunity to investigate, firstly the kinetics of phase separation above LCST (125-180 °C), and secondly the kinetics of phase dissolution below LCST (50-115 °C). The blend underwent a temperature-jump above LCST where spinodal decomposition (SD) proceeded, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below LCST when the phase dissolution proceeded. Optical microscopy was used to observe the spinodal decomposition qualitatively while light scattering was used to characterize the phase separation and phase dissolution quantitatively. It was found that during phase dissolution the peak maximum moved towards a smaller angle (wavelength of concentration fluctuations increased) while the peak intensity decreased. This behavior was explained by a model. Also it was found that the fastest phase dissolution kinetics at 80 °C, which was characterized by an apparent diffusion coefficient, was about 10 times slower than the kinetics of phase separation at 180 °C.     

Shape-memory poly(p-dioxanone)–poly(ε-caprolactone)/sepiolite nanocomposites with enhanced recovery stress

Shape-memory poly(p-dioxanone)–poly(e-caprolactone)/sepiolite(PPDO–PCL/OSEP) nanocomposites with different OSEP nanofiber loading were fabricated by chain-extending the PPDO-diol and PCL/OSEP precursors. The precursors and the composites were characterized by1 H NMR, FT-IR, GPC, SEM and TEM.The results demonstrate that a part of PCL segments grafted on the surface of OSEP and composites display a fine dispersion of OSEP fiber in nanoscale with low OSEP content. The shape memory effect(SME) was evaluated by DMA, the results reveal that the PPDO–PCL/OSEP nanocomposites exhibit desirable shape-memory performance. The reinforcement of composites by incorporation of trace OSEP nanofiber evokes an effective improvement in shape-memory recovery stress.     

Thermal degradation of star-shaped poly(?-caprolactone)

Thermal degradation of a serials of star-shaped poly(?-caprolactone) (PCL) with well-defined arm numbers and arm length was investigated. The weight loss of star-shaped PCL during heating process showed a two-stage character, and its dependence on molecular weight and multi-armed structure was well discussed. It was found that the thermal stability could be improved not only by increasing molecular weight but also by increasing arm numbers when the molecular weight is in a certain range. Based on the analyses of pyrolytic products by ¹H NMR and TGA-FTIR, two mechanisms of thermal degradation for the random cleavage of ester bonds of PCL chains were proposed. Ester bonds were pyrolyzed into alkene and carboxyl functional groups in mechanism I while they were pyrolyzed into ketene and hydroxyl functional groups in mechanism II. The effects of multi-armed structure of star-shaped PCL on the cleavage of ester bonds of PCL chains were discussed in terms of the limitation of central “core” on mobility of each PCL arm. Combined the results of viscosity analysis with thermal analysis, it could be concluded that both thermal stability and processability of PCL materials can be improved by controlling the multi-armed structures.     

Melting of poly(ε-caprolactone) studied by step-heating calorimetry

This study demonstrates that the step-heating calorimetry, which is a kind of temperature-modulated differential scanning calorimetry, can provide valuable information on the polymer melting. Time-dependent heat flow due to the melting of lamellar crystallites in a narrow range of thickness can be directly observed, from which thickness distribution of lamellar crystallites and thickness dependence of the melting kinetics are deduced. A sample of poly(ε-caprolactone) was used as a model material of semi-crystalline polymer, which has high crystallinity (0.79) so that no recrystallization and/or reorganization occur during melting in the step-heating scan. It was revealed that superheating dependence of the melting rate coefficient increases with increasing lamellar thickness, which may be attributed to variation of the fold surface roughness with respect to lamellar thickness. Analysis based on the cylindrical nucleation model revealed much lower free energy values of lateral surface than that evaluated from crystallization behavior, suggesting that the nucleus for melting is more stable than that for crystallization.     

Binary blends based on poly(vinyl chloride) and multi-block copolymers containing poly(ϵ-caprolactone) and poly(ethylene glycol) segments

Binary blends based on poly(vinyl chloride) (PVC) were prepared both by casting from tetrahydrofuran (THF) and by mixing in the melt form, in a discontinuous mixer, PVC and multi-block copolymers containing poly(ϵ-caprolactone) (PCDT) and poly(ethylene glycol) (PEG) segments. PCDT-PEG copolymers were synthesized using a polycondensation reaction where the α,ω-bis-chloroformate of an oligomeric poly(ϵ-caprolactone) diol terminated (PCDT) and oligomeric PEG were employed as macromonomers. For comparison purposes, blends PVC with starting oligomers as well as with mixtures containing a typical low molecular plasticizer, dioctylphthalate (DOP), were also prepared. The copolymer miscibility was studied by differential scanning calorimetry (DSC) and FT-IR spectroscopy. The blend morphology was investigated by polarized light microscopy (PLM). A higher miscibility with PVC was observed for copolymers compared to PEG.     

Thermal degradation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ϵ-caprolactone) or poly(ethylene glycol)

Thermodegradative investigations of two classes of multi-block copolymers containing poly(D,L-lactic-glycolic acid) (PLGA) and either poly(ethylene glycol) (PEG) or poly(ϵ-caprolactone) diol-terminated (PCDT) segments were performed. In particular, the influence of the type and length of the segments as well as of the molar ratio between the D,L-lactic acid (LA) and glycolic acid (GA) residues was investigated at 180°C in air by viscometry, FT-IR analysis and isothermal thermogravimetry. The thermal oxidative degradation of these materials is largely affected by the LA/GA ratio, a higher LA content generally imparting higher stability. The FT-IR analysis suggests that, depending on the composition of the PLGA segments, degradative processes are triggered which can lead to a preferential degradation of the blocks.     

High temperature pyrolysis of poly(phenylene vinylene)s with poly(ε-caprolactone) or polystyrene side chains

Journal of Thermal Analysis and Calorimetry - High temperature pyrolysis studies of poly(phenylene vinylene)s PPVs with lateral substituents poly(ε-caprolactone) (PPV–PCL) or...     

Accelerated degradation behaviour of poly(?-caprolactone) via melt blending with poly(aspartic acid-co-lactide) (PAL)

Poly(?-caprolactone) (PCL) has many favourable attributes for tissue engineering scaffold applications. A major drawback, however, is its slow degradation rate, typically greater than 3 years. In this study PCL was melt blended with a small percentage of poly(aspartic acid-co-lactide) (PAL) and the degradation behaviour was evaluated in phosphate buffer solution (PBS) at 37 °C. The addition of PAL was found to significantly enhance the degradation profile of PCL. Subsequent degradation behaviour was investigated in terms of the polymer's mechanical properties, molecular weight (M_w), mass changes and thermal characteristics. The results indicate that the addition of PAL accelerates the degradation of PCL, with 20% mass loss recorded after just 7 months in vitro for samples containing 8 wt% PAL. The corresponding pure PCL samples exhibited no mass loss over the same time period. In vitro assessment of PCL and PCL/PAL composites in tissue culture medium in the absence of cells revealed stable pH readings with time. SEM studies of cell/biomaterial interactions demonstrated biocompatibility of C₃H₁₀T_1/2 cells with PCL and PCL/PAL composites at all concentrations of PAL additive.     

Controlled-release and antibacterial studies of doxycycline-loaded poly(ε-caprolactone) microspheres

The objective of the present study is to achieve doxycycline’s maximum therapeutic efficacy. Doxycycline-loaded poly(ε-caprolactone) microspheres were prepared by water-in-oil-in-water (w/o/w) double emulsion solvent evaporation technique with different formulation variables such as concentrations of drug and polymer. The effects of these variables on surface morphology, particle size distribution, encapsulation efficiency, and in vitro release behavior were examined. To observe the nature of microspheres, X-ray diffraction studies were carried out. The release data obtained were determined using various kinetic models and Korsmeyer–Peppas model showed an acceptable regression value for all compositions. Antibacterial efficiency of doxycycline-loaded poly(ε-caprolactone) microspheres were assessed by determining Minimum Inhibition Concentration (MIC) by standard tube dilution method against four standard pathogenic strains. The in vitro drug release studies were carried out in phosphate buffer solution (pH 7.2). The results showed marked retardation of doxycycline release and higher percentage of polymer gave longer drug release profile. This may definitely provide a useful controlled-release drug therapy and also prove to be effective over a long period of time (76 h).     

pH-responsive star-shaped functionalized poly(ethylene glycol)-b-poly(ε-caprolactone) with amino groups

Functional star-shaped 4-arm poly(ethylene glycol)-b-poly[(ε-caprolactone-co-γ-amino-ε-caprolactone)] (4-arm PEG-b-P(CL-co-ACL) was synthesized through ring-opening polymerization. The structure of the copolymer was confirmed by ¹H NMR, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). To further understand the copolymers, the difference of the conversion rate between ε-caprolactone (CL) and γ-(carbamic acid benzyl ester)-ε-caprolactone (CABCL) and the detailed deprotection condition were studied. The thermal property of the copolymer was analyzed by WAXR and differential scanning calorimetry (DSC), which demonstrated that the thermal property could be well adjusted. The pH-responsive behavior of the copolymers was studied in detail by dynamic light scattering (DLS), pH titration, and pyrene fluorescence methods, which indicated that it could form micelles and exhibit pH responsibility. Moreover, the copolymer was nontoxic and had good biocompatibility according to the results by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay.     

Preparation and characterization of microspheres based on blend of poly(lactic acid) and poly(ɛ-caprolactone) with poly(vinyl alcohol) as emulsifier

In this paper, microspheres were prepared by oil-in-water (o/w) emulsion solvent evaporation method. Biodegradable polymer such as blend of poly (lactic acid) (PLA) and poly(?-caprolactone) (PCL) with certain compositions and characteristics was used to prepare the microspheres with poly(vinyl alcohol) (PVA) as an emulsifier. This study observed the microspheres particle’s size distribution at various concentrations of PVA (1%, 1.5%, 2%, and 2.5% PVA). The PVA volume variations effects during the process (50, 100, 150, 200, and 250 mL) were also observed. The blend of PLA and PCL is formed only by physical interaction between them. This can be seen from the FTIR spectrum which shows both PLA and PCL component. The microspheres physical size and appearance were observed by optical microscope (MO). The overall results of this study showed that the formula which used 50–150 mL of 2.5% polyvinyl alcohol produced the microspheres with the most uniform size distribution.     

Hydrophobicities of poly(ε-caprolactone) oligomers functionalized with different succinic anhydrides

Different succinic anhydrides were used for modification of hydrophobicities of linear and star-shaped poly (ε-caprolactone) oligomers with different molecular weights. Hydroxyl-terminated poly(ε-caprolactone) oligomers were acid-functionalized either with succinic anhydride (SAH) or with alkenylsuccinic anhydrides (ASAs) containing 8 or 18 carbons in their alkenyl chains. Hydrophobicities of the linear and corresponding star-shaped oligomers were investigated by immersion studies and by water contact angle measurements. In comparison with SAH functionalized oligomers, alkenyl chain containing oligomers showed lower thermal transitions and higher hydrophobicities. In addition, oligomers with 18 carbons alkenyl chain showed considerably higher hydrophobicities than corresponding oligomers with 8 carbon alkenyl chain.     

Development of orientation during electrospinning of fibres of poly(ε-caprolactone)

We explore the influence of a rotating collector on the internal structure of poly(ε-caprolactone) fibres electrospun from a solution in dichloroethane. We find that above a threshold collector speed, the mean fibre diameter reduces as the speed increases and the fibres are further extended. Small-angle and wide-angle X-ray scattering techniques show a preferred orientation of the lamellar crystals normal to the fibre axis which increases with collector speed to a maximum and then reduces. We have separated out the processes of fibre alignment on the collector and the orientation of crystals within the fibres. There are several stages to this behaviour which correspond to the situations (a) where the collector speed is slower than the fibre spinning rate, (b) the fibre is mechanically extended by the rotating collector and (c) where the deformation leads to fibre fracture. The mechanical deformation leads to a development of preferred orientation with extension which is similar to the prediction of the pseudo-affine deformation model and suggests that the deformation takes place during the spinning process after the crystals have formed.     

Viscoelastic behaviors of poly(ε-caprolactone)/attapulgite nanocomposites

Nanocomposites based on biodegradable poly(ε-caprolactone) (PCL) and attapulgite (AT) were prepared by solution blend. The morphology and rheological behaviors of the blends were examined. SEM observation showed that AT nano-rods were well dispersed in the PCL matrix in a nanometer scale at low AT content and a severe aggregation would happen at high AT content. The rheological behaviors of the polymer/fibrous clay nanocomposite samples were investigated by an Advanced Rheometric Expansion System with parallel plate geometry. The effects of AT content on the viscoelastic behaviors of the PCL/AT nanocomposites were also confirmed by rheological analysis. The apparent activation energies of flow were calculated by the Arrhenius equation.     

Anionically prepared poly(ε-caprolactam-co-ε-caprolactone) and poly(ε-caprolactam-co-δ-valerolactone) copolymers: Thermal and mechanical properties

Thermal and representative physico-mechanical properties of newly prepared poly[(ε-caprolactam)-co-(ε-caprolactone)] and poly[(ε-caprolactam)-co-(δ-valerolactone)] copolymers were studied. The copolymers were synthesized by anionic polymerization of ε-caprolactam activated by isocyanate end-capped oligomeric aliphatic polyesters designated as the macroactivators (MAs). Type, concentration and molecular weight of the MAs were varied, which resulted in copolymers with different structure and properties. The impact of the new MAs used in this study on the glass transition temperature and the melting temperature of poly-ε-caprolactam was investigated by DSC. DMTA was used to analyze the effect of copolymerization on the storage modulus (E^′) and tan δ of poly-ε-caprolactam. Conventional and high-resolution TGA data revealed that all the synthesized polyesteramides possess good thermal stability. Mechanical properties were studied by notched impact and tensile testing. According to the experimental data the impact toughness increase with the MA content, being six time higher compared to the poly(ε-caprolactam) in the best situation. Water absorption was also considered in relation to the composition of the copolymers.     

Hydrolytic and microbial degradation of multi-block polyurethanes based on poly(?-caprolactone)/poly(ethylene glycol) segments

Biodegradable amphiphilic multi-block poly(ether-ester-urethane)s were prepared by one-step bulk polycondensation of PEG and PCL macro-diols and HMDI. For biomedical or environmental applications of the proposed materials, one of the critical steps is the study of the degradation characteristics under physiological or environmental conditions. Different ratios of PEG/PCL and molecular weights of the resultant copolymers allowed for tuning their hydrophilicity, as evaluated by water uptake measurements. The swelling results were further supported by microgravimetric measurements performed by QCM-D. In vitro hydrolytic biodegradation was carried out under different conditions (i.e., in phosphate buffer solution - with and without Lipase). Total mineralization in the presence of microorganisms from a sample of river water was observed to follow different kinetics, depending upon the composition and the molecular weight of the copolymer.     

Synthesis and micellar characterization of thermosensitive amphiphilic poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) block copolymers

Poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) (PCL-b-PVCL) block copolymers were synthesized as new biocompatible, thermosensitive, amphiphilic block polymers by a combination of ring-opening polymerization and reversible addition–fragmentation chain transfer (RAFT) polymerization, and their thermosensitive micellar behavior was examined. The PCL macro-chain-transfer agent was first synthesized by converting the end group of PCL-OH to O-ethyl xanthate, which was subsequently used for the RAFT polymerization of N-vinylcaprolactam. The critical micelle concentration of PCL-b-PVCL (M _n,NMR?=?56,300?g/mol, polydispersity index?=?1.18) was 0.026?mg/mL. The mean diameter of the PCL-b-PVCL micelles determined by transmission electron microscopy was 55?±?25?nm. The PCL-b-PVCL micelles exhibited repetitive aggregation and dispersion during reversible cooling and heating cycles between 20 and 40?°C due to the thermosensitive behavior of the PVCL shell. Overall, the PCL-b-PVCL block copolymers have potential applications in thermosensitive drug delivery applications.     

Diselenide-containing poly(ε-caprolactone)-based thermo-responsive hydrogels with oxidation and reduction-triggered degradation

Herein, novel multi-responsive injectable polyester hydrogels were reported based on the diselenide-containing poly(ε-caprolactone) copolymers ((mPEG-PCL-Se)₂). The (mPEG-PCL-Se)₂ solution remained a free-flowing state at ambient temperature but spontaneously turned into a semisolid hydrogel upon heating to physiologic temperature. The phase transition temperature was examined to be dependent on the composition and aqueous concentration of the copolymers. More importantly, the thermo-responsive hydrogels were endowed with oxidation and reduction-triggered degradation by the incorporation of diselenide groups. Accordingly, the degradation of poly(ε-caprolactone)-based hydrogels was greatly improved and the rate of degradation was well regulated by the concentration of hydrogen peroxide (H₂O₂) or glutathione (GSH). This superior stimuli-responsive degradation could lead to an enhanced drug release of encapsulated drug (Doxorubicin, DOX). Thus the oxidation and reduction-triggered degradable diselenide-containing poly(ε-caprolactone) hydrogels would offer great potential for the controlled drug delivery.