PCL Chains Research Articles

Organic–inorganic hybrid brushes consisting of macrocyclic oligomeric silsesquioxane and poly(ε‐caprolactone): Synthesis, characterization, and supramolecular inclusion complexation with α‐cyclodextrin

AbstractOrganic–inorganic hybrid brushes comprised of macrocyclic oligomeric silsesquioxane (MOSS) and poly(ε‐caprolactone) (PCL) were synthesized via the ring‐opening polymerization of ε‐caprolactone (CL) with cis‐hexa[(phenyl) (2‐hydroxyethylthioethyldimethylsiloxy)]cyclohexasiloxane as the initiator. The MOSS macromer bearing hydroxyl groups was synthesized via the thiol‐ene radical addition reaction between cis‐hexa[(phenyl)(vinyldimethylsiloxy)]cyclohexasiloxane and β‐mercaptoethanol. The organic–inorganic PCL cyclic brushes were characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). These MOSS–PCL brushes were then used to prepare the supramolecular inclusion complexes with α‐cyclodextrin (α‐CD). The X‐ray diffraction (XRD) indicates that the organic–inorganic inclusion complexes (ICs) have a channel‐type crystalline structure. It is noted that the molar ratios of CL unit to α‐CD for the organic–inorganic ICs are quite dependent on the lengths of the PCL chains bonded to the silsesquioxane macrocycle. While the PCL chains were short, the efficiency of inclusion complexation was significantly decreased. The decreased efficiency could be attributed to the repulsion of the adjacent PCL chains bonded to the silsesquioxane macrocycle and the restriction of the bulky silsesquioxane macrocycle on the motion of PCL chains; this effect is pronounced with decreasing the length of the PCL chains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009

Functionalization of carbon nanotubes with biodegradable supramolecular polypseudorotaxanes from grafted-poly(ε-caprolactone) and α-cyclodextrins

Functionalization of multiwalled carbon nanotubes (MWNTs) with biodegradable supramolecular polypseudorotaxanes has been successfully performed by utilizing surface-initiated ring-opening polymerization of ε-caprolactone (CL) to yield poly(ε-caprolactone)-grafted MWNTs (MWNT- g-PCL), followed by forming inclusion complexes between grafted-PCL chains and α-cyclodextrins (α-CDs) to give α-CD-NTPCL hybrids. There are significant differences in the morphology and solubility of MWNTs before and after introduction of α-CD. Some protuberances are clearly observed for α-CD-NTPCL as compared with MWNT- g-PCL. Furthermore, the host–guest stoichiometry (monomeric unit of CL/α-CD molar ratio) for α-CD-NTPCL is much higher than that of polypseudorotaxanes consisted of linear PCL and α-CDs. This observation can be explained by a combination of several reasons including the steric hindrance of grafted-PCL, the competitive exclusion between adjacent PCL chains toward α-CD, and the addition order of α-CD as well as the host–guest feed ratio. The present methodology may open up a new opportunity toward the application of supramolecular chemistry for the chemical manipulation and processing of CNTs. Moreover, such novel supramolecular hybrids provide an entry to extend the applications of CNTs to medicine and biology fields through embedding the functional polymers and heterogeneous components.

Amphiphilic biodegradable poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) triblock copolymers: synthesis, characterization and their use as drug carriers for folic acid

Amphiphilic biodegradable poly(e-caprolactone)-poly(ethylene glycol)-poly (e-caprolactone) (PCEC) triblock copolymers have been successfully synthesized by the ring-opening polymerization of e-caprolactone (e-CL) employing SnOct as catalyst and double-hydroxyl capped PEG (DHPEG) as macro-initiator. The triblock structure and copolymer composition were conformed by FT-IR, 1H-NMR, and GPC. Using a membrane dialysis method, PCEC micelles were prepared with a core–shell type. The critical micelle concentration (CMC) of PCEC triblock copolymers was determined by fluorescence technique using pyrene as probe, and CMC values decreased with the increase of PCL chain length. From the observation of transmission electron microscopy (TEM), the morphology of polymer micelles was spherical in shape. Micelles size measured by dynamic light scattering (DLS) exhibited a narrow size distribution. Folic acid (FA) was then used as a model drug to incorporate into PCEC micelles. The diameter, drug loading, and drug release rate of PCEC micelles were influenced by the feed weight ratio of FA and copolymer, and polymer composition. In addition, in vitro release experiments of the drug-loaded PCEC micelles exhibited sustained release behavior without any burst effects and the release behavior was also affected by the pH of release media.

Isothermal crystallization kinetics of modified bamboo cellulose/PCL composites

Abstract For the purpose of utilizing bamboo cellulose and providing a theoretical basis, the isothermal crystallization kinetics of modified bamboo cellulose/poly(e-caprolactone) (MBC/PCL) composites has been investigated by differential scanning calorimetry (DSC) at different crystallization temperature (Tc). The Avrami model was applied to describe the process of isothermal crystallization. According to Hoffman–Weeks theory, the values of the equilibrium melting point ( T m 0 ) increased with an increase in the content of MBC in the composites. The spherulite growth rate, the overall crystallization rate, the activation energy and folding-surface free energy (σe) of PCL/MBC composites are markedly affected by the presence of MBC. According to Avrami theory, MBC accelerates the crystallization of PCL in the composites. However, as compared to neat PCL, all the composites of PCL/MBC had the higher σe value. This indicates that there exist constraints on the mobility of the PCL chains in the interspherulitic regions due to the presence of MBC.

New amphiphilic and pH-sensitive hydrogel for controlled release of a model poorly water-soluble drug

This paper presents the development of new pH-sensitive, amphiphilic and biocompatible hydrogels based on alginate-g-PCL, cross-linked with calcium ions to form beads, prepared for controlled delivery of poorly water-soluble drug. We have focused our study on the effect of the length of PCL chains (530 and 1250 g mol −1). Swelling profiles obtained clearly indicated that these hydrogels swell slightly (10–14%) in a simulated gastric fluid (pH 1.2), and strongly (700–1300% before disintegration) in a simulated intestinal fluid (pH 6.8). In both media, rates of swelling were lower for beads based on amphiphilic derivatives than for alginate/Ca 2+ ones due to the hydrophobic PCL grafts, and decreased when hydrophobic character increased. A model drug, theophylline, was entrapped into these hydrogels and release studies were carried out. The drug was protected in acidic fluid (only 14–20% of release for alginate-g-PCL hydrogel against 35% of release for alginate hydrogel during 350 min). The drug is released completely in neutral fluid due to ion exchanges and disintegration of the hydrogel. PCL leads to decrease in the release kinetics in SIF (2 h for alginate-g-PCL/Ca 2+ beads against 1 h for alginate/Ca 2+ beads). It was demonstrated that the establishment of clusters inside beads by intramolecular interactions between PCL grafts of 530 g mol −1 in salt media allowed to retain the drug and to slow down its release considerably.

Mg 2+-doped poly(ɛ-caprolactone)/siloxane biohybrids

Ionically conducting materials based on a poly(ɛ-caprolactone) (PCL)/siloxane organic/inorganic host framework doped with magnesium triflate (Mg(CF 3SO 3) 2) were synthesized by the sol–gel process. In this matrix short PCL chains are covalently bonded to the siliceous network via urethane linkages. In this study the salt content of samples was identified using the conventional notation n, where n indicates the number of (C( O)(CH 2) 5O) PCL repeat units per Mg 2+ ion. Xerogels with compositions ranging from n = ∞ to 1 were prepared. The only composition studied that was not entirely amorphous was that prepared with n = 1. Xerogels with n ≥ 7 are thermally stable up to at least 200 °C. The composition with the highest conductivity of the series is that with n = 34 (5.9 × 10 −9 and 9.8 × 10 −7 S cm −1 at 24 and 104 °C, respectively).

Thermoforming starch‐graft‐polycaprolactone biocomposites via one‐pot microwave assisted ring opening polymerization

AbstractA thermoformable starch‐graft‐polycaprolactone biocomposite was prepared by initiating ring‐open polymerization of caprolactone monomer onto starch under microwave irradiation. In this case, the thermoplastic and hydrophobic modification of starch could be realized by one‐pot grafting PCL, where the grafted PCL chains acted as the “plasticizing” tails of thermoforming and as the hydrophobic species of water‐resistance. The resultant biocomposites were injection‐molded as the sheets and their structure and properties were investigated by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, contact angle measurement, and tensile testing. In this case, the grafted PCL chains entangled each other, and hence contributed to the strength and elongation of biocomposites. This work provided a simple strategy of one‐pot thermoplastic and hydrophobic modification of starch, and may be applied in a continuous process of modification, compounding, and molding. Meanwhile, the resultant biocomposites containing starch are believed to have a great potential application as an environment‐friendly and/or biomedical material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

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

Thermal degradation of a serials of star-shaped poly(ɛ-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.

Eutectic crystallization and hydrogen bonding interactions in polymer/surfactant blends

The unusual eutectic crystallization behavior in the poly(e-caprolactone) (PCL) and 3-pentadecylphonel (PDP) binary blends was investigated by differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. A eutectic system was found with the eutectic composition at 60 wt % PDP and the eutectic melting temperature at 35 °C. The melting process of the blend at the eutectic composition was studied by in situ FTIR. The concurrence of the melting of PCL and PDP crystallites and the sequential formation of hydrogen bonding interaction between PDP molecules and PCL chains were traced. It was also found that a further increase in temperature above the eutectic melting temperature would impair the hydrogen bonding and increase the content of nonassociated phenol hydroxyl group. The semicrystalline morphology of blends affected by the composition was also investigated.

An efficient synthetic route to well-defined theta-shaped copolymers

A series of well-defined θ-shaped copolymers composed of polystyrene (PS) and poly(ε-caprolactone) (PCL) with controlled molecular weight and narrow molecular weight distribution have been successfully synthesized without any purification procedure by the combination of atom transfer radical polymerization (ATRP), ring-opening polymerization (ROP), and the “click” chemistry. The synthetic process involves two steps: (1) synthesis of AB2 miktoarm star copolymers, which contain one PCL chain terminated with two acetylene groups and two PS chains with two azido groups at their one end, (α,α′-diacetylene-PCL) (ω-azido-PS)2, by ROP, ATRP, and the terminal group transformation; (2) intramolecular cyclization of AB2 miktoarm star copolymers to produce well-defined pure θ-shaped copolymers using “click” chemistry under high dilution. The 1H NMR, FTIR, and gel permeation chromatography techniques were applied to characterize the chemical structures of the resultant intermediates and the target polymers. Their thermal behavior was investigated by DSC. The mobility decrease of PCL chain across PS ring in the theta-shaped copolymers restricts the crystallization ability of PCL segment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2620–2630, 2009

Fluorescence study of the dynamics of a star-shaped poly(ɛ-caprolactone)s in THF: A comparison with a star-shaped poly(l-lactide)s

Molecular dynamics of 2-, 4- and 6-arm star-shaped poly(ɛ-caprolactone)s (PCLs) functionalized with pyrene at all chain ends followed by excimer formation were investigated in THF as a solvent. Dilute solutions (10−8 to 10−6molL−1) of these polymers revealed excimer emission due to the intramolecular cyclization, proceeding via chain end interaction. Time-resolved fluorescence measurements of star-shaped PCLs showed complex decay profiles of monomer and excimer fluorescence. An intensity rise component of decay profiles monitored in excimer region (500nm) was observed for star-shaped polymers due to dynamic formation of excimers. Dipyrene–PCL (2-arm) also showed partial formation of static pyrene excimers as followed from measurement of excitation spectra at ambient temperature in THF. Excimer intensity of di- and four pyrene–telechelic PCLs was found to be comparable with that of di- and four pyrene–telechelic polylactide (PLA) polyesters having similar molar masses. 6-Arm PCL showed depressed excimer formation with regard to 6-arm PLA under the otherwise identical conditions contrary to the conclusion expected from the higher flexibility of the PCL chain. Eventually, molecular dynamic simulations showed that possible explanation can be related to different conformations of 6-arm PLA versus PCL stars.

Unusual rheological properties of a new associative polysaccharide in salt media

New amphiphilic polysaccharides based on alginate-grafted-Poly (ε-caprolactone) or alg-g-PCL bearing two kinds of PCL chains with different molar masses (1250 and 530 gmol −1) with various amounts from 3% to 15% were prepared. Rheological properties in aqueous solutions of such systems have been investigated as a function of polymer concentration, added salt and temperature in semi-dilute regime. Strong hydrophobic intermolecular associations were clearly demonstrated in pure water whatever the PCL chain length and extend of modification. Increasing polymer concentration, grafting rate and/or PCL chains length can lead to a structured liquid behaviour. Rheological properties of the most organized system have been found independent to the temperature (until 60 °C). In salt media, a strong dependence of hydrophobic interactions to the length of PCL chains was observed. For M PCL = 1250 g.mol −1 the screening of charges promotes the establishment of intermolecular interactions and leads to a strong physical gel for the highest grafting rates. For M PCL = 530 g mol −1, ionic strength leads to a decrease of rheological properties when increasing grafting rate. This result may indicate an increase of hydrophobic clusters even in the entangled regime. This unusual behaviour opens the ways for the preparation of suitable hydrogels for drug release.

Structure and properties of new thermoforming bionanocomposites based on chitin whisker‐graft‐polycaprolactone

AbstractThermoformable bionanocomposites of chitin whisker‐graft‐polycaprolactone (CHW‐g‐PCL) were synthesized by initiating the ring‐opening polymerization of caprolactone monomer onto the CHW surface under microwave radiation. In this case, the “graft from” strategy contributed to long and dense “plasticizing” PCL tails onto the CHW surface as the key of thermoforming, and, therefore, such bionanocomposites were injection‐molded as the sheets with a structure of cocontinuous phase mediated with the entanglement of grafted PCL chains. The structure and properties of the molded CHW‐g‐PCL sheets were investigated by FTIR, XRD, SEM, DSC, DMTA, contact angle measurement, and tensile test. With an increase of the PCL content in CHW‐g‐PCL, the strength and elongation as well as the hydrophobicity of the nanocomposites increased at one time. This is the first report on the thermoformable polymer‐grafted nanocrystal derived from natural polysaccharide. Moreover, such new bionanocomposites with good mechanical performances could have great potential applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Simultaneous enhancement of the strength and elongation of polycaprolactone: The role of chitosan‐graft‐polycaprolactone

AbstractPolycaprolactone (PCL) is a basic substance for biomedical materials and especially for scaffolds in tissue engineering. To improve the performance of PCL‐based materials, we filled a PCL matrix with a biocompatible polysaccharide‐grafted PCL, chitosan‐g‐polycaprolactone (CS‐g‐PCL). The results showed that the strength, elongation, and Young's modulus of the resultant composites were simultaneously enhanced in contrast with those of neat PCL. The structures of the PCL/CS‐g‐PCL blends were investigated with Fourier transform infrared, X‐ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and scanning electron microscopy, and the effects of the chitosan (CS) content in CS‐g‐PCL and the CS‐g‐PCL content in the blends on the mechanical properties and structures of the blends were examined. The rigidity of CS chains and the increasing crystallinity induced by the nucleation of CS‐g‐PCL contributed to the enhancement of the strength, whereas the cocontinuous interfacial structure and improved miscibility between CS and PCL matrix mediated with grafted PCL chains greatly enhanced the elongation of the composite materials. This work presents a strategy for enhancing the mechanical performance of PCL as a biomaterial. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A Novel Thermoformable Bionanocomposite Based on Cellulose Nanocrystal‐graft‐Poly(ε‐caprolactone)

AbstractThis is the first report on a thermoformable bionanocomposite based on a natural nanocrystal and formed by grafting long polymer chains onto the surface of microcrystalline cellulose. For the cellulose nanocrystal‐graft‐poly(ε‐caprolactone), the “graft from” strategy contributed to long and dense “plasticizing” PCL tails onto the CN surface as the key of thermoforming. The grafted PCL chains shielded the hydrophilic surface of CN and, hence, showed high water‐resistance. Moreover, a strategy for developing new bionanocomposite materials based on natural nanocrystals has been presented.magnified image

Reactive Processing of Cellulose Acetate/Corn Starch Biodegradable Composite Materials and their Characterization

Simultaneous grafting of poly(e-caprolactone) (PCL) onto cornstarch as well as cellulose diacetate (CDA) and their composite machining were tried and succeeded by reactive processing using a twin screw extruder to result in plasticization of CDA, and at the same time, to obtain water-resistant and highly biomass-containing biodegradable composite materials. The properties of the composites obtained were examined through solvent fractionation, FT-IR, 1H NMR, tensile test, thermal flow test, SEM observation, water absorption test and biodegradability test. It was demonstrated that the composite materials containing maximum 60% cornstarch and maximum 70% biomass could be produced by the reactive processing method and they have good tensile property, processability, water resistance, and biodegradability. Especially the materials of which matrix polymer, PCL grafted CDA (PCL-g-CDA) in the degree of molar substitution range, 1.72–1.84 showed desirable biodegradability, having a certain induction period before rapid degradation, being attributable to the strong interaction between cornstarch and PCL-g-CDA, which is caused by somewhat long PCL chains grafted on both starch granules and CDA molecules. Furthermore, it was found that starch could accelerate the biodegradation rate of the matrix polymer, associating with starch degradation because of increase in surface area for microbial attack and its naturalization.

Nanosized Micelles Self-Assembled from amphiphilic dextran- graft-methoxypolyethylene glycol/poly(ε-caprolactone) copolymers

A series of amphiphilic copolymers, dextran- graft-methoxypolyethylene glycol/poly(ε-caprolactone) (Dex- g-mPEG/PCL) were synthesized by grafting both PCL and mPEG chains to dextran, and subsequently the micellar self-assembly behavior of resultant copolymers was investigated. PCL was designed by using Fmoc-protected valine other than organometallic catalyst as the initiator to ring-opening polymerize ε-caprolactone (CL) in view of the safety demand as well as the extra application potential resulting from –NH 2 group introduced after Fmoc deprotection. All the copolymers were characterized by 1H NMR, FT-IR and GPC measurements. The prepared copolymers are capable of self-assembling into nanosized spherical micelles in aqueous solution with the diameter of around 100–200 nm determined by TEM image and DLS measurement. The critical micellar concentration (CMC) of the graft copolymers is in the range of 10–100 mg/L determined by the fluorescence robe technique using pyrene. The result also indicated that the CMC of self-assembled micelles could be adjusted by controlling the degree of substitution of mPEG and PCL, and these micelles may find great potential as drug carriers in biomedical fields.

Self-assembly behavior of hepta(3,3,3-trifluoropropyl) polyhedral oligomeric silsesquioxane-capped poly(ɛ-caprolactone) in epoxy resin: Nanostructures and surface properties

The organic–inorganic amphiphile, hepta(3,3,3-trifluoropropyl) polyhedral oligomeric silsesquioxane (POSS)-capped poly(ɛ-caprolactone) (POSS-capped PCL) was synthesized via the ring-opening reaction of ɛ-caprolactone, which was initiated by 3-hydroxypropylhepta(3,3,3-trifluoropropyl) polyhedral oligomeric silsesquioxane (POSS) with stannous (II) octanoate [Sn(Oct)2] as the catalyst. The organic–inorganic nanocomposites were prepared via the in situ polymerization of epoxy monomers in the presence of the POSS-capped PCL. The atomic force microscopy (AFM) shows that the organic–inorganic hybrids possess the nanostructures. In view of the miscibility of the sub-components of the organic–inorganic amphiphile [i.e., PCL chains and POSS cages] with epoxy after and before curing reaction, the formation of the nanostructures in the thermosets followed the mechanism of self-assembly. The surface properties of the organic–inorganic nanocomposites were investigated by means of static contact angle measurements and X-ray photoelectronic spectroscopy (XPS). It is demonstrated that the improvement in surface hydrophobicity was ascribed to the enrichment of the POSS cages on the surface of the materials.

Crystallization Behavior of Poly(ε‐caprolactone) Grafted onto Cellulose Alkyl Esters: Effects of Copolymer Composition and Intercomponent Miscibility

AbstractGraft copolymers of CA and CB with PCL were prepared at compositions rich in PCL. Kinetic DSC data were analyzed in terms of a folded‐chain crystallization formula expanded for a binary mixing system of amorphous/crystalline polymers. The order of crystallization rates was plain PCL > CA‐g‐PCL (DS = 2.98) > CB‐g‐PCL (DS = 2.1–2.95) > CA‐g‐PCL (DS = 2.1–2.5), and the fold‐surface free energy of the PCL crystals obeyed the reverse order. POM revealed a generally tardy growth of spherulites for all the graft copolymers. The slower crystallization process may be ascribed primarily to the compulsory effect of anchoring PCL chains onto the semi‐rigid cellulose backbone. Intercomponent miscibility of the CA/PCL and CB/PCL pairs was also taken into consideration.magnified image

Advancing the Solid State Properties of Metallo‐Supramolecular Materials: Poly(ε‐caprolactone) Modified π‐Conjugated Bis(terpyridine)s and their Zn(II) Based Metallo‐Polymers

AbstractA set of rigid π‐conjugated bis(terpyridine) macroligands with poly(ε‐caprolactone) (pCL) on their side chains was synthesized and investigated. The introduced pCL chains gave rise to enhanced processability and film‐forming properties of the materials. Blue photoluminescence with high quantum yields was observed in dilute solution and in the solid state, indicating that intermolecular aggregation of the π‐conjugated systems was effectively suppressed. The macroligands were further used for coordination with zinc(II) ions leading to new metallo‐polymers with high solubility, improved film‐forming behavior and promising photophysical properties with respect to potential OLED applications.magnified image