Synthesis and Characterization of Biodegradable Poly(ε‐caprolactone)‐Polyglycolide‐Poly(ethylene glycol) Monomethyl Ether Random Copolymer

Summary: Poly(ε‐caprolactone)‐polyglycolide‐poly(ethylene glycol) monomethyl ether random copolymers were synthesized from ε‐caprolactone (ε‐CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160 °C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, ¹H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG.

     

Novel biodegradable amphiphilic poly(ε‐caprolactone)/poly(N‐vinylpyrrolidone) blends via successive in situ polymerizations

In this study, biodegradable blends of poly(ε‐caprolactone) (PCL) and poly(N‐vinylpyrrolidone) (PVP) were prepared by a new strategy in the following steps: (1) free radical polymerization of N‐vinyl‐2‐pyrrolidone (NVP) in ε‐caprolactone (CL); (2) ring‐opening polymerization of ε‐caprolactone in the presence of PVP to obtain the target blends. The structure of the blends was confirmed by FTIR and ¹H NMR, and the molecular weight of PCL and PVP were determined by GPC. SEM study revealed that this polymerization method could decrease the disperse phase size and improve the interphase when compared with solution‐blending method. The phase inversion occurred when PVP content was 15–20 wt %. Subsequently, the PCL sphere dispersed in PVP matrix and its size decreased with the increase of PVP content. The contact angle results showed that PVP has a profound effect on hydrophilic properties of PCL/PVP blends. PCL/PVP blends are believed to be promising for drug delivery, cell therapy, and other biomedical applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Biodegradable poly(vinyl alcohol)‐graft‐ poly(ε‐caprolactone) comb‐like polyester: Microwave synthesis and its characterization

Poly(vinyl alcohol)‐initiated microwave‐assisted ring opening polymerization of ε‐caprolactone in bulk was investigated, and a series of poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) copolymers were prepared, with the degree of polymerization (DP) of PCL side chains and the degree of substitution (DS) of PVA by PCL being in the range of 3–24 and 0.35–0.89, respectively. The resultant comb‐like PVA‐g‐PCL copolymers were confirmed by means of FTIR, ¹H NMR, and viscometry measurement. The introduction of hydrophilic backbone resulted in the decrease in both melting point and crystallization property of the PVA‐g‐PCL copolymers comparing with linear PCL. With higher microwave power, the DP of PCL side chains and DS of PVA backbone were higher, and the polymerization reaction proceeded more rapidly. Both the DP and monomer conversion increased with irradiation time, while the DS increased first and then remained constant. With initiator in low concentration, the DP and DS were higher, while the monomer was converted more slowly. Microwaves dramatically improved the polymerization reaction in comparison of conventional heating method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3973–3979, 2007     

Functionalization of multi‐walled carbon nanotubes with poly(ε‐caprolactone) using click chemistry

Multi‐walled carbon nanotubes (MWNTs) were covalently functionalized with poly(ε‐caprolactone) (PCL) using click chemistry. First, chlorine moiety‐containing PCL was synthesized by the copolymerization of α‐chloro‐ε‐caprolactone with ε‐caprolactone monomer using ring opening polymerization, and further converted to azide moiety‐containing PCL. The alkyne‐functionalized MWNTs were prepared with the treatment of p‐amino propargyl ether using a solvent free diazotization procedure. The covalent functionalization of alkyne‐derived MWNTs with azide moiety‐containing PCL was accomplished using Cu(I)‐catalyzed [3+2] Huisgen dipolar cycloaddition click chemistry. The PCL‐functionalization of MWNTs was confirmed by the measurements of Fourier transform infra‐red, NMR, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Asymmetric penta‐armed poly(ε‐caprolactone)s with short‐chain phosphazene core: synthesis,characterization, and in vitro degradation

A novel hydroxyl‐terminated short‐chain penta‐armed phosphazene was prepared. This penta‐armed compound was studied as an initiator for the synthesis of asymmetric penta‐armed poly(ε‐caprolactone)s in the presence of stannous octoate. The effect of molar ratio of monomer to initiator was investigated. Thermal analysis revealed that the penta‐armed poly(ε‐caprolactone)s possessed lower melting point and crystallinity than linear ones. The penta‐armed poly(ε‐caprolactone)s with long chain‐length exhibited higher onset decomposition temperature and maximum decomposition temperature than linear ones owing to the presence of the phosphazene core. The in vitro degradation of linear and penta‐armed PCL was performed in phosphate buffer solution at 37 and 55 °C. Copyright © 2005 Society of Chemical Industry     

Effect of Thermal History on Structural Changes in Melt‐Intercalated Poly(ε‐caprolactone)/Organoclay Nanocomposites Investigated by Dynamic Viscoelastic Relaxation Measurements

Poly(ε‐caprolactone) (PCL) nanocomposites were prepared using two different types of organically modified nanosilicates by melt intercalation with an internal mixer. Dynamic mechanical analysis revealed possible structural changes in the nanocomposites even during the small deformation occurring during shear oscillatory measurements, as evidenced by a V‐shaped modulus change in the plot of the dynamic storage modulus as a function of stepwise increased temperature. X‐ray diffraction patterns were recorded at different simulated temperatures during the various stages of dynamic measurements. The X‐ray data indicate that the structural changes can be ascribed to a further intercalation of the PCL matrix chains into the silicate layers. This further intercalation is a consequence of the heat treatment during the dynamic mechanical measurements. Furthermore, there is a considerable vertical shift in addition to the horizontal shift in the higher temperature regime, which allows the mapping of a master curve through the application of the time‐temperature superposition principle to the dynamic storage and the loss modulus data obtained at various isothermal temperatures. The present study is also concerned with the relative molecular mobility of both PCL nanocomposites in the given experimental conditions considering the Williams‐Landel‐Ferry (WLF) equation and the Arrhenius relationship between the horizontal shift factor and the activation energy of flow. Moreover, the extent of the vertical shift as a function of temperature made it possible to determine the apparent activation energy of the further intercalation of PCL into the silicate layers. This intercalation is caused by the additional exposure to heat during the dynamic mechanical measurements after mixing, which led to a comparison of the relative diffusivity of the PCL matrix in the two nanocomposites.

Dynamic shear storage moduli G′ of PCLOC25A and PCLOC30B as a function of temperature with increase increments of 20 °C from 60 to 260 °C. The G′ data were obtained from isothermal frequency sweep G′(ω) data at ω = 1 rad · s^?1 at the corresponding temperatures.     

A single active site metal center of neodymocene chloride for the ring‐opening polymerization of ε‐caprolactone

A germyl‐bridged lanthanocene chloride, Me₂Ge(^tBu‐C₅H₃)₂LnCl (Ln = Nd; (Cat‐ Nd ), was prepared and successfully used as single catalyst to initiate the ring‐opening polymerization of ε‐caprolactone (ε‐CL) for the first time. Under mild conditions (60°C,[ε‐CL]/[Ln] = 200, 4 h), Cat‐ Nd efficiently catalyzes the polymerization of ε‐CL, giving poly(ε‐caprolactone) (PCL) with high molecular weight (MW) (>2.5 × 10⁴) in high yield (>95%). The effects of molar ratio of [ε‐CL]/Cat‐Nd, polymerization temperature and time, as well as solvent were determined in detail. When the polymerization is carried out in bulk or in petroleum ether, it gives PCL with higher MW and perfect conversion (100%). The higher catalytic activity of this neodymocene chloride could be ascribed to the bigger atom in the bridge of bridged ring ligands. Some activators, such as NaBPh₄, KBH₄, AlEt_3, and Al(i‐Bu)₃, can promote the polymerization of ε‐CL by Cat‐ Nd, which leads to an increase both in the polymerization conversion and in the MW of PCL. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1212–1217, 2012     

Ring‐opening polymerization of ε‐caprolactone by a new yttrium complex: Y[2,2′‐ethylidene‐bis(4,6‐di‐tert‐butylphenoxy)]2(ethylene glycol dimethyl ether)Na(ethylene glycol dimethyl ether)3

The main aims of the work reported here were to synthesize and characterize a new 2,2′‐ethylidene‐bis(4,6‐di‐tert‐butylphenol) (EDBPH₂)‐based bimetal yttrium complex, Y(EDBP)₂(DME)Na(DME)₃ (1c; where DME is ethylene glycol dimethyl ether), which was employed as an efficient initiator for the ring‐opening polymerization of ε‐caprolactone (ε‐CL). From single‐crystal X‐ray diffraction, the solid structure of this new bimetal initiator was well established. Experimental results show that 1c initiates the ring‐opening polymerization of ε‐CL to afford poly(ε‐CL) with a narrow molecular weight distribution (M_w/M_n = 1.09–1.36, 65 °C). Based on an in situ NMR study, a plausible coordination–insertion mechanism is then proposed. The bimetal complex 1c can be used as an initiator for the ring‐opening polymerization of ε‐CL with some living characteristics. A study of the mechanism reveals that DME displacement in 1c by ε‐CL is involved in the initiation process and the propagation may proceed through three pathways by Na? O insertion or Y? O insertion. Copyright © 2009 Society of Chemical Industry     

Poly(vinyl pyrrolidone‐co‐vinyl acetate)‐graft‐poly(ε‐caprolactone) as a compatibilizer for cellulose acetate/poly(ε‐caprolactone) blends

Poly(vinyl pyrrolidone‐co‐vinyl acetate)‐graft‐poly(ε‐caprolactone) (PVPVAc‐g‐PCL) was synthesized by radical copolymerization of N‐vinyl‐2‐pyrrolidone (VP)/vinyl acetate (VAc) comonomer and PCL macromonomer containing a reactive 2‐hydroxyethyl methacrylate terminal. The graft copolymer was designed in order to improve the interfacial adhesiveness of an immiscible blend system composed of cellulose acetate/poly(ε‐caprolactone) (CA/PCL). Adequate selections of preparation conditions led to successful acquisition of a series of graft copolymer samples with different values of molecular weight ( ), number of grafts (n), and segmental molecular weight of PVPVAc between adjacent grafts (M_n (between grafts)). Differential scanning calorimetry measurements gave a still immiscible indication for all of the ternary blends of CA/PCL/PVPVAc‐g‐PCL (72 : 18 : 10 in weight) that were prepared by using any of the copolymer samples as a compatibilizer. However, the incorporation enabled the CA/PCL (4 : 1) blend to be easily melt‐molded to give a visually homogeneous film sheet. This compatibilizing effect was found to be drastically enhanced when PVPVAc‐g‐PCLs of higher and M_n (between grafts) and lower n were employed. Scanning electron microscopy revealed that a uniform dispersion of the respective ingredients in the ternary blends was attainable with an assurance of the mixing scale of several hundreds of nanometers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of fullerene grafted poly(ε‐caprolactone)

The fullerene grafted poly(ε‐caprolactone) (PCL) was successfully synthesized with a graft efficiency of 80%. The fullerene moieties grafted onto the PCL chain aggregate into 1–2 μm particles so that a physical pseudo‐network is formed. Because of the existence of the network structure, the fullerene grafted PCL film can retain its shape at much higher temperatures than that of pure PCL film, as observed in dynamic mechanical tests. It shows a hydrophobic gelling behavior in chloroform solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Transesterification in homogeneous poly(ε‐caprolactone)–epoxy blends

Transesterification has been investigated in poly(ε‐caprolactone) (PCL)–epoxy blends. In the hot melt process, the hydroxyl on diglycidyl ether of bisphenol‐A (DGEBA) monomers is too low to give a noticeable transesterification reaction. In the postcure process, model reactions reveal that the hydroxyls from a ring‐opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular weight decrease and its distribution becomes broader. Nuclear magnetic resonance spectra reveal that fraction of the tertiary hydroxyls converts to secondary hydroxyls. In the cured DGEBA–3,3′‐dimethylmethylene‐di(cyclohexylamine)–PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and result in the lower T_g observed in the differential scanning calorimetry thermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 75–82, 1999     

Preparation of poly(ε‐caprolactone)/poly(ε‐caprolactone‐co‐lactide) (PCL/PLCL) blend filament by melt spinning

Poly(ε‐caprolactone)/poly(ε‐caprolactone‐co‐lactide) (PCL/PLCL) blend filaments with various ratios of PCL and PLCL were prepared by melt spinning. The effect of PLCL content on the physical properties of the blended filament was investigated. The melt spinning of the blend was carried out and the as spun filament was subsequently subjected to drawing and heat setting process. The addition of PLCL caused significant changes in the mechanical properties of the filaments. Crystallinity of blend decreased with the addition of PLCL as observed by X‐ray diffraction (XRD) and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) revealed that the fracture surface becomes rougher at higher PLCL content. It may be proposed that PCL and PLCL show limited interaction within the blend matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Crystallization behavior of poly(ε‐caprolactone)/layered double hydroxide nanocomposites

Poly(?‐caprolactone) (PCL)/layered double hydroxide (LDH) nanocomposites were prepared successfully via simple solution intercalation. The nonisothermal melt crystallization kinetics of neat PCL and its LDH nanocomposites was investigated with the Ozawa, Avrami, and combined Avrami–Ozawa methods. The Ozawa method failed to describe the crystallization kinetics of the studied systems. The Avrami method was found to be useful for describing the nonisothermal crystallization behavior, but the parameters in this method do not have explicit meaning for nonisothermal crystallization. The combined Avrami–Ozawa method explained the nonisothermal crystallization behavior of PCL and its LDH nanocomposites effectively. The kinetic results and polarized optical microscopy observations indicated that the addition of LDH could affect the mechanism of nucleation and growth of the PCL matrix. The Takhor model was used to analyze the activation energies of nonisothermal crystallization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structure and Mechanical Properties of Poly(lactic acid) Filled with (Starch nanocrystal)‐graft‐poly(ε‐caprolactone)

Poly(ε‐caprolactone) (PCL) was grafted to the surface of starch nanocrystals (StN) via microwave‐assisted ROP. The resultant nanoparticles were then incorporated into a poly(lactic acid) matrix to produce fully‐biodegradable nanocomposites with good mechanical properties. A loading level of 5 wt.‐% StN‐g‐PCL resulted in simultaneous enhancements of strength and elongation. The StN‐g‐PCL self‐aggregated as rubbery microparticles to enhance the elongation by ca. 10‐fold over that of neat PLA. Meanwhile, the grafted PCL chains were miscible with PLA and formed a stress‐transferring interface to the StN, providing a reinforcing function.

     

Functionalization and Compatibilization of Poly(ε‐caprolactone) Composites with Cellulose Microfibres: Morphology,Thermal and Mechanical Properties

A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.

     

Evaluation of the Degree of Exfoliation in Poly(ε‐caprolactone)/Organoclay Nanocomposites Based on Viscoelastic Relaxation

Poly(ε‐caprolactone) nanocomposites, PCLOC25A and PCLOC30B, with organoclays (OCs) having nonpolar and polar organic modifiers, respectively, were prepared by the melt mixing method and additional heat treatment. WXRD analysis revealed that both nanocomposites were exfoliated, irrespective of the OC polarity. However, WXRD failed to show the degree of exfoliation of the nanocomposites, because the d₀₀₁ peaks disappeared. Thus, dynamic mechanical analysis (DMA) was carried out to compare the degree of exfoliation of the PCL nanocomposites. From DMA, PCLOC30B showed higher elasticity, storage moduli, viscosity, and activation energy than PCLOC25A, indicating that PCLOC30B had a more exfoliated structure than PCLOC25A. This is due to the polar interaction in PCLOC30B, as verified by the plots of a_T versus temperature. Thus, it was confirmed that DMA provides an alternative approach to evaluating the degree of exfoliation of nanocomposites.

     

Preparation and characterization of electrospun poly(ε‐caprolactone)–pluronic–poly(ε‐caprolactone)‐based polyurethane nanofibers

In this study, amphiphilic poly(ε‐caprolactone)–pluronic–poly(ε‐caprolactone) (PCL–pluronic–PCL, PCFC) copolymers were synthesized by ring‐opening copolymerization and then reacted with isophorone diisocyanate to form polyurethane (PU) copolymers. The molecular weight of the PU copolymers was measured by gel permeation chromatography, and the chemical structure was analyzed by ¹H‐nuclear magnetic resonance and Fourier transform infrared spectra. Then, the PU copolymers were processed into fibrous scaffolds by the electrospinning technology. The morphology, surface wettability, mechanical strength, and cytotoxicity of the obtained PU fibrous mats were investigated by scanning electron microscopy, water contact angle analysis, tensile test, and MTT analysis. The results show that the molecular weights of PCFC and PU copolymers significantly affected the physicochemical properties of electrospun PU nanofibers. Moreover, their good in vitro biocompatibility showed that the as‐prepared PU nanofibers have great potential for applications in tissue engineering. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43643.     

Miscibility of block copolymers of poly(ε‐caprolactone) and poly(ethylene glycol) with poly(3‐hydroxybutyrate) as well as the compatibilizing effect of these copolymers in blends of poly(ε‐caprolactone) and poly(3‐hydroxybutyrate)

Atactic poly(3‐hydroxybutyrate) (a‐PHB) and block copolymers of poly(ethylene glycol) (PEG) with poly(ε‐caprolactone) (PCL‐b‐PEG) were synthesized through anionic polymerization and coordination polymerization, respectively. As demonstrated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) measurements, both chemosynthesized a‐PHB and biosynthesized isotactic PHB (i‐PHB) are miscible with the PEG segment phase of PCL‐b‐PEGs. However, there is no evidence showing miscibility between both PHBs and the PCL segment phase of the copolymer even though PCL has been block‐copolymerized with PEG. Based on these results, PCL‐b‐PEG was added, as a compatibilizer, to both the PCL/a‐PHB blends and the PCL i‐PHB blends. The blend films were obtained through the evaporation of chloroform solutions of mixed components. Excitingly, the improvement in mechanical properties of PCL/PHB blends was achieved as anticipated initially upon the addition of PCL‐b‐PEG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2600–2608, 2001     

Nanoporous Low Dielectric Cyclosiloxane Bearing Polysilsesquioxane Thin Films Templated by Poly(ε‐caprolactone)

Summary: Dielectric cyclosiloxane bearing polysilsesquioxanes (CS‐PSSQs) were prepared by acid catalyzed polymerization using 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane. The molecular weight, and content of the functional end‐groups of the CS‐PSSQs were found to be dependent on the process parameters, such as the molar ratio of water and catalyst to the ? OCH₃ group of the silane monomer, the amount of solvent, and the poly(ε‐caprolactone) (PCL) content, etc. Based on these CS‐PSSQ prepolymers, nanoporous organic/inorganic hybrid thin films were fabricated by spin‐coating mixtures of these prepolymers with star‐shaped PCL on the silicon substrate, and subsequently heating them at 150 and 250 °C for 1 minute each and then at 420 °C for 1 hour. A dielectric constant as low as 2.28 was achieved for the nanoporous PCL/CS‐PSSQ (3:7 v/v) film, along with low moisture absorption in ambient and water conditions, primarily due to the presence of hydrophobic moieties such as ethylene and methyl groups of the polymer and nano‐sized hydrophobic pores inside the matrix, resulting in the film having stable dielectric properties. Moreover, the PCL/CS‐PSSQ (3:7 v/v) nanohybrid film revealed a nanoporous structure containing ca. 1.52 nm of average‐sized mesopores, as measured by the N₂ adsorption method. The CS‐PSSQ‐only film showed high mechanical strengths having an elastic modulus and hardness of 6.64 and 0.88 GPa, respectively, for the 7 500 Å thick film and 2.41 and 0.38 GPa, respectively, for the PCL/CS‐PSSQ (3:7 v/v) film. In addition, the crack velocity of the CS‐PSSQ‐only film was found to be ca. 10^?11 m · s^?1 in ambient conditions and an aqueous environment, probably due to the enhanced hydrophobicity and mechanical toughness of the incorporated methyl group, siloxane unit and ethylene moieties in the polymer matrix.

     

Synthesis and characterization of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) triblock copolymers with dibutylmagnesium as catalyst

Two series of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) triblock copolymers were prepared by the ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) and dibutylmagnesium in 1,4‐dioxane solution at 70°C. The triblock structure and molecular weight of the copolymers were analyzed and confirmed by ¹H NMR, ¹³C NMR, FTIR, and gel permeation chromatography. The crystallization and thermal properties of the copolymers were investigated by wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results illustrated that the crystallization and melting behaviors of the copolymers were depended on the copolymer composition and the relative length of each block in copolymers. Crystallization exothermal peaks (T_c) and melting endothermic peaks (T_m) of PEG block were significantly influenced by the relative length of PCL blocks, due to the hindrance of the lateral PCL blocks. With increasing of the length of PCL blocks, the diffraction and the melting peak of PEG block disappeared gradually in the WAXD patterns and DSC curves, respectively. In contrast, the crystallization of PCL blocks was not suppressed by the middle PEG block. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009