Pendant groups fine‐tuning thermal gelation of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) aqueous solution

Novel poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) bearing pendant hydrophobic γ‐(carbamic acid benzyl ester) groups (PECB) and hydrophiphilic amino groups (PECN) were synthesized based on the functionalized comonomer γ‐(carbamic acid benzyl ester)‐ε‐caprolactone (CABCL). The thermal gelation behavior of the amphiphilic copolymer aqueous solutions was examined. The phase transition behavior could be finely tuned via the pendant groups, and an abnormal phenomenon occurred that the sol–gel transition temperature shifted to a higher temperature for PECB whereas a lower temperature for PECN. The micelles percolation was adopted to clarify the hydrogel mechanism, and the effect of the pendant groups on the micellization was further investigated in detail. The results demonstrated that the introduction of γ‐(carbamic acid benzyl ester) pendant groups significantly decreased the crystallinity of the copolymer micelles whereas amino pendant groups made the micelles easy to aggregate. Thus, the thermal gelation of PEG/PCL aqueous solution could be finely tuned by the pendant groups, and the pendant groups modified PEG/PCL hydrogels are expected to have great potential biomedical application. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2571–2581     

Synthesis and hydrolysis behaviour of poly(ester anhydrides) from polylactone precursors containing alkenyl moieties

Hydroxyl-group functional polylactones were prepared and converted to acid- terminated polyesters in a reaction with a series of alkenylsuccinic anhydrides containing 8, 12, or 18 carbons in their alkenyl chains. These polyester precursors were then linked into higher molecular weight poly(ester anhydrides) containing alkenyl moieties in their polyester blocks. The hydrolysis behaviour of the poly(ester anhydrides) was found to depend on the thermal properties of the polyester precursors. For poly(ester anhydrides) prepared from low molecular weight prepolymers with thermal transitions below 37 degrees C, the presence of hydrophobic alkenyl chains in the polyester precursors slowed the rate of weight loss. Poly(ester anhydrides) prepared from higher molecular weight prepolymers showed the opposite weight-loss behaviour; i.e., the crystallinity and thermal transitions of the alkenyl chain-containing poly(ester anhydrides) were low, and the weight loss was faster than for poly(ester anhydrides) without the alkenyl chains. The differences in length of the alkenyl chain, as such, had little effect on the hydrolysis behaviour and thermal properties of the poly(ester anhydrides).     

Hydrolytic degradation of poly(ε‐caprolactone) with different end groups and poly(ε‐caprolactone‐co‐γ‐butyrolactone): characterization and kinetics of hydrocortisone delivery

Asymmetric telechelic α‐hydroxyl‐ω‐(carboxylic acid)‐poly(ε‐caprolactone) (HA‐PCL), α‐hydroxyl‐ω‐(benzylic ester)‐poly(ε‐caprolactone) (HBz‐PCL), and an asymmetric telechelic copolymer α‐hydroxyl‐ω‐(carboxylic acid)‐poly(ε‐caprolactone‐co‐γ‐butyrolactone) (HA‐PCB) were synthesized by ring‐opening polymerization of ε‐caprolactone (CL). CL and CL/γ‐butyrolactone mixture were used to obtain homopolymers and copolymer respectively at 150°C and 2 hr using ammonium decamolybdate (NH₄) [Mo₁₀O₃₄] (Dec) as a catalyst. Water (HA‐PCL and HA‐PCB) or benzyl alcohol (HBz‐PCL) were used as initiators. The three polylactones reached initial molecular weights between 2000 and 3000 Da measured by proton nuclear magnetic resonance (¹H‐NMR). Compression‐molded polylactone caplets were allowed to degrade in 0.5 M aqueous p‐toluenesulfonic acid at 37°C and monitored up to 60 days for weight loss behavior. Data showed that the copolymer degraded faster than the PCL homopolymers, and that there was no difference in the weight loss behavior between HA‐PCL and HBz‐PCL. Caplets of the three polylactones containing 1% (w/w) hydrocortisone were placed in two different buffer systems, pH 5.0 with citrate buffer and pH 7.4 with phosphate buffer at 37°C, and monitored up to 50 days for their release behavior. The release profiles of hydrocortisone presented two stages. The introduction of a second monomer in the polymer chain significantly increased the release rate, the degradation rate for HA‐PCB being faster than those for HBz‐PCL and HA‐PCL. At the pH studied, only slight differences on the liberation profiles were observed. SEM micrographs indicate that hydrolytic degradation occurred mainly by a surface erosion mechanism. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Poly(ε-caprolactone-co-δ-valerolactone) with Pendant Carboxylic Functional Groups

In this paper, aliphatic polyesters functionalized with pendant carboxylic groups were synthesized via several steps. Firstly, substituted cyclic ketone, 2‐(benzyloxycarbonyl methyl)cyclopentanone (BCP) was prepared through the reaction of enamine with benzyl‐2‐bromoacetate, and subsequently converted into the relevant functionalized δ‐valerolactone derivative, 5‐(benzyloxy carbonylmethyl)‐δ‐valerolactone (BVL) by the Baeyer‐Villiger oxidation. Secondly, the ring‐opening polymerization of BVL with ε‐caprolactone was carried out in bulk using stannous octoate as the catalyst to produce poly(ε‐caprolactone‐co‐δ‐valerolactone) bearing the benzyl‐protected carboxyl functional groups [P(CL‐co‐BVL)]. Finally, the benzyl‐protecting groups of P(CL‐co‐BVL) were effectively removed by H₂ using Pd/C as the catalyst to obtain poly(ε‐caprolactone‐co‐δ‐valerolactone) bearing pendant carboxylic acids [P(CL‐co‐CVL)]. The structure and the properties of the polymer have been studied by Nuclear Magnetic Resonance (NMR), Fourier Infrared Spectroscopy (FT‐IR) and Differential Scan Calorimetry (DSC) etc. The NMR and FT‐IR results confirmed the polymer structure, and the ¹³C NMR spectra have clearly interpreted the sequence of ε‐caprolactone and 5‐(benzyloxycarbonylmethyl)‐δ‐valerolactone in the copolymer. When the benzyl‐protecting groups were removed, the aliphatic polyesters bearing carboxylic groups were obtained. Moreover, the hydrophilicity of the polymer was improved. Thus, poly(ε‐caprolactone‐co‐δ‐valerolactone) might have great potential in biomedical fields.     

Reactive blending of functional polysiloxanes with poly(butylene terephthalate): Clarification of reaction mechanisms and kinetics from a model compound study

We clarify the reaction mechanisms and kinetics in melt‐reacted blends consisting of functional polysiloxanes and poly(butylene terephthalate) (PBT) with a model compound study. As models for polysiloxanes, we have selected two monodisperse ω‐functionalized siloxane oligomers with Si? H and Si? vinyl moieties. To mimic PBT, we have chosen low molecular weight compounds representative for in‐chain and end‐functional groups of the polymer; ester, carboxylic acid, alcohol, and vinyl. Uncatalyzed and platinum‐catalyzed reactions have been performed in sealed vials. Reaction products have been characterized by gradient polymer elution chromatography, Fourier transform infrared spectroscopy, and size exclusion chromatography. PBT functional groups reactive toward functional siloxane oligomers at high temperatures in the presence and absence of a catalyst have been identified, and an estimate of relative reaction kinetics has been provided. We suggest reaction mechanisms compatible with our results and with literature data. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1952–1961, 2002     

Covalent VEGF protein immobilization on resorbable polymeric surfaces

Vascular endothelial growth factor type protein (VEGF), a potent angiogenic effector molecule, was successfully covalently immobilized onto the surfaces of the resorbable polymers poly(L‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) through a three‐step strategy. The surfaces were first covalently grafted with poly(acrylic acid) using non‐destructive and solvent free vapor‐phase grafting. A diamine spacer was coupled to the carboxylic acid pendant groups on the graft chains using EDC/NHS chemistry and VEGF was finally covalently attached to the amine linkers. The chemistry and topography of the modified substrates were quantitatively and qualitatively verified with XPS, ATR‐FTIR, UV–VIS, SEM, and ELISA. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel biodegradable epoxy‐modified polyurethane elastomers

Biodegradable polyurethane elastomers with the potential for applications in medical implants were synthesized from the reaction of epoxy‐terminated polyurethane prepolymers (EUPs) with 1,6‐hexamethylenediamine as a curing agent. EUPs were themselves prepared from the reaction of glycidol and isocyanate‐terminated polyurethanes made from different molecular weights of poly(ε‐caprolactone) (CAPA) and 1,6‐hexamethylene diisocyanate. All materials were characterized by spectroscopic methods. The curing conditions were optimized by gel content measurements. The curing kinetic and kinetic parameters were determined from differential scanning calorimetry measurements. The effects of changing the crosslink density and crystallinity of elastomers via the alteration of the CAPA polyol molecular weight on the physical, mechanical, and degradation properties of the final elastomeric polymers were examined fully. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2985‐2996, 2005     

Preparation of Porous Poly(ε‐caprolactone) Structures

Porous poly(ε‐caprolactone) structures have been prepared by leaching of compression moulded salt‐containing polymer precipitates. Coagulation takes place when a PCL solution containing dispersed water‐soluble salt particles is precipitated into an excess of non‐solvent. Porous scaffolds are obtained after leaching of the compression moulded polymer‐salt precipitate. This process yields scaffolds with a very homogeneous pore morphology and independent control of pore size and porosity.     

Poly(ε‐caprolactone)‐Based Organogels and Hydrogels with Poly(ethylene glycol) Cross‐Linkings

Summary: The reaction of triphosgene with poly(ethylene glycol) yielded poly(ethylene glycol) dichloroformate. This difunctional cross‐linker was allowed to react with poly(ε‐caprolactone) bearing carbanionic sites obtained by activation with lithium diisopropylamide. The reaction resulted in the cross‐linking of poly(ε‐caprolactone) chains by poly(ethylene glycol) segments, giving copolymer networks that gel in both organic and aqueous media.

Schematic of the PCL‐g‐PEG copolymers synthesized here.     

Synthesis and Characterization of Star‐Shaped Diblock Poly(ε‐caprolactone)/Poly(ethylene oxide) Copolymers

Summary: Star‐shaped hydroxy‐terminated poly(ε‐caprolactone)s (ssPCL), with arms of different lengths, were obtained by ring‐opening polymerization (ROP) of ε‐caprolactone initiated by pentaerythritol, and were condensed with α‐methyl‐ω‐(3‐carboxypropionyloxy)‐poly(ethylene oxide)s ( = 550–5 000) to afford four‐armed PCL‐PEO star diblock copolymers (ssPCL‐PEO). The polymers were characterized by ¹H and ¹³C NMR spectroscopy and size‐exclusion chromatography (SEC). The melting behavior of ssPCLs was studied by differential scanning calorimetry (DSC). X‐ray diffraction and DSC techniques were used to investigate the crystalline phases of ssPCL‐PEOs.

The part of the synthesis of four‐armed star‐shaped diblock poly(ε‐caprolactone)‐poly(ethylene oxide) copolymers as described.     

Epoxy resins from rosin acids: synthesis and characterization

A series of multifunctional cycloaliphatic glycidyl ester and ether epoxy resins were synthesized by reaction of condensed rosin acid‐formaldehyde resins with epichlorohydrin. The chemical structure of the produced resins was determined by IR and ¹H‐NMR analysis. The molecular weight of the produced resins was determined by gel permeation chromatography (GPC). A series of poly‐ (amide‐imide) hardeners were prepared from condensation of Diels–Alder adducts of rosin acid‐maleic anhydride and acrylic acid with triethylene tetramine and pentaethylene hexamine. These amines were also condensed with Diels–Alder adducts of rosin ketones. The curing exotherms of the produced epoxy resins with poly(amide‐imide) hardeners were investigated. The data of mechanical properties, solvent and chemical resistance indicate the superior adhesion of the cured epoxy resins. Copyright © 2004 John Wiley & Sons, Ltd.     

Characterization of an antimicrobial poly(lactic acid) film prepared with poly(ε‐caprolactone) and thymol for active packaging

Antimicrobial active films based on poly(lactic acid) (PLA) were prepared with poly(ε‐caprolactone) (PCL) and thymol (0, 3, 6, 9, and 12 wt%) by solvent casting methods. The films were characterized by thermal, structural, mechanical, gas barrier, and antimicrobial properties. Scanning electron microscopy analysis revealed that the surface of film became rougher with certain porosity when thymol was incorporated into the PLA/PCL blends. Thymol acted as plasticizers, which reduce the intermolecular forces of polymer chains, thus improving the flexibility and extensibility of the films. The addition of PCL into the pure PLA film decreased the glass transition temperature of the films. The presence of thymol decreased the crystallinity of PLA phase, but did not affect the thermal stability of films. Water vapor barrier properties of films slightly decreased with the increase of thymol loading. The antimicrobial properties of thymol containing films showed a significant activity against Escherichia coli and Listeria monocytogenes. The results indicated the potential of PLA/PCL/thymol composites for applications in antimicrobial packaging. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation and characterization of biodegradable poly(lactic acid)‐ block‐poly(ε‐caprolactone) multiblock copolymer

Biodegradable copolymers of poly(lactic acid)‐block‐poly(ε‐caprolactone) (PLA‐b‐PCL) were successfully prepared by two steps. In the first step, lactic acid monomer is oligomerized to low molecular weight prepolymer and copolymerized with the (ε‐caprolactone) diol to prepolymer, and then the molecular weight is raised by joining prepolymer chains together using 1,6‐hexamethylene diisocyanate (HDI) as the chain extender. The polymer was carefully characterized by using ¹H‐NMR analysis, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The results of ¹H‐NMR and TGA indicate PLA‐b‐PCL prepolymer with number average molecular weights (M_n) of 4000–6000 were obtained. When PCL‐diols are 10 wt%, copolymer is better for chain extension reaction to obtain the polymer with high molecular weight. After chain extension, the weight average molecular weight can reach 250,000 g/mol, as determined by GPC, when the molar ratio of –NCO to –OH was 3:1. DSC curve showed that the degree of crystallization of PLA–PCL copolymer was low, even became amorphous after chain extended reaction. The product exhibits superior mechanical properties with elongation at break above 297% that is much higher than that of PLA chain extended products. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,characterization, and degradation of poly(ethylene‐b‐ε‐caprolactone) diblock copolymer

Poly(ethylene‐b‐ε‐caprolactone) (PE‐b‐PCL) diblock copolymers were synthesized by ring‐opening polymerization (ROP) of ε‐caprolactone (CL) with α‐hydroxyl‐ω‐methyl polyethylene (PE‐OH) as a macroinitiator and ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] as a catalyst. Polymerization was conducted in bulk (130–150°C) with high yield (87–97%). Block copolymers with different compositions were obtained and characterized by ¹H and ¹³C NMR, MALDI‐TOF, SAXS, and DSC. End‐group analysis by NMR and MALDI‐TOF indicates the formation of α‐hydroxyl‐ω‐methyl PE‐b‐PCL. The PE‐b‐PCL degradation was studied using thermogravimetric analysis (TGA) and alkaline hydrolysis. The PCL block was hydrolyzed by NaOH (4M), without any effect on the PE segment. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Ring Opening Polymerization of a New Functional Lactone, α‐Iodo‐ε‐caprolactone: A Novel Route to Functionalized Aliphatic Polyesters

A new functional lactone, α‐iodo‐ε‐caprolactone (αIεCL), was synthesized from ε‐caprolactone by anionic activation using a non‐nucleophilic strong base (lithium diisopropylamide) followed by an electrophilic substitution with iodine chloride. Ring‐opening (co)polymerizations of the resulting monomer with ε‐caprolactone were carried out using tin 2‐ethylhexanoate as a catalyst in toluene at 100 °C. Homopolymerization of αIεCL was achieved, and poly(αIεCL) was fully characterized by SEC, ¹H NMR and elemental analysis. Random copolymerizations of αIεCL with εCL were controlled with experimental molecular weights close to the theoretical values, narrow molecular weight distributions and a good agreement between experimental and theoretical molar compositions of αIεCL.

     

Synthesis of Novel Star Shaped Poly(ε‐caprolactone) Utilizing Fullerene as the Molecular Core

Summary: The synthesis of star shaped poly(ε‐caprolactone) (PCL) with a fullerene molecular core (s‐PCLF) was successfully achieved by the ring‐opening polymerization of ε‐caprolactone with fullerenol as the initiator. Through NMR and GPC analysis, the average number of arms of PCL on each fullerene core was estimated to be 2–3.

Fullerenol (left) and PCL star polymer (right) in THF.     

A study of phase separation of crystalline and miscible polymer blends. Poly(ε-caprolactone)/poly(styrene-co-acrylonitrile)

The phase separation of a crystalline and miscible polymer blend, poly(ε-caprolactone) /poly(styrene-co-acrylonitrile) (PCL/SAN), has been studied by differential scanning calorimetry (DSC), using a SAN containing 28.3% of acrylonitrile units. Several phenomena can be associated with the occurrence of phase separation depending upon the composition of the mixture. Following annealing at high temperatures, below and above the phase separation temperature T_c, three cases can be distinguished. In Case I, there is no sign of crystallization during quenching and DSC scanning, but a melting peak is observed at T_c, and above. In Case II, there is no crystallization on quenching but it does occur during the DSC run; the shift of the crystallization peak can then be related to T_c. In Case III, there is crystallization on quenching, and additional crystallization during the DSC run; the change of area of the crystallization peak is indicative of T_c. From these observations, the phase diagram of the system was determined. © 1993 John Wiley & Sons, Inc.     

Synthesis,characterization, and kinetics studies of organic soluble photosensitive copolyimide

A copolyimide synthesized from 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, 3,5-diaminobenzoic acid, and 2,3,5,6-tetramethyl-p-phenylene diamine was found to be soluble in N-alkyl substituted amides. An organic soluble photosensitive polyimide was obtained by further reaction of the copolyimide with methacrylic acid glycidyl ester. After adding Michler's ketone, the UV spectra absorbance near 360 nm of the copolyimide decreased rapidly upon the irradiation of mercury lamp. Using benzoic acid and methacrylic acid glycidyl ester as model compounds and N, N-dimethylbenzylamine as catalyst, the mechanism of reaction between the carboxylic group of the copolyimide and epoxy group of methacrylic acid glycidyl ester in N-methyl-2-pyrrolidone was found to have two competitive reactions, namely the auto-catalytic and the catalytic reactions. The apparent rate constants of each reaction were determined. Comparison of apparent rate constants between the model compound and the polymer reaction system are also reported.     

Poly(γ‐glutamic acid) esters with reactive functional groups suitable for orthogonal conjugation strategies

We report on a series of novel poly(γ‐glutamic acid) (PGGA) esters, in which the chemical structure and composition, and the molecular weight are systematically changed. Modification of PGGA of microbial origin, used either as the sodium salt or in the free acid form, by means of alkylation with highly reactive bromides under S_N2 conditions, affords copolymers with an essentially random microstructure. These reaction conditions are applied iteratively to achieve full esterification, obtaining allyl or propargyl ester functionalities within the polymer backbone, diluted with inert functional groups, such as benzyl, ethyl, or hexyl ester functionalities. The copolymers have been characterized regarding their chemical structure and thermal and bulk properties using nuclear magnetic resonance, thermogravimetry, differential scanning calorimetry, and X‐ray diffraction techniques. We demonstrate that allyl and propargyl ester groups can be efficiently transformed using click chemistries, such as thiol‐ene or copper(I)‐catalyzed azide–alkyne cycloaddition reactions; such efficient conjugation strategies will be required to transform the native bacterial biopolymer into a material with tailored properties for bulk scale or biomedical applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ternary blends of phenoxy/SAN/poly(-ε-caprolactone)

The compatibilizing effect of poly(ε-caprolactone) (PCL) on the blends of two immiscible polymers, poly(hydroxy ether of bisphenol A) (phenoxy) and poly(styrene-co-acrylonitrile) (SAN) has been investigated. The phase behavior of the ternary blends was affected by the AN content in the SAN copolymers and a maximum miscible region was observed at 19.5 wt % of AN. The effect of AN content on the phase behavior of the ternary blends was interpreted in terms of the relative magnitude of the segmental interaction energy densities, which were obtained by combining a melting point depression and an extended binary interaction model. When a small amount of PCL was added to the phenoxy/SAN blends, the phase morphology showed a finer phase dispersion, indicating that the interfacial tension between the phenoxy and SAN is considerably reduced. However, the improvement in tensile properties was limited despite the morphological change with the PCL content. From the results of the DSC measurements, SEM, and tensile testing, it was understood that the PCL acted as a compatibilizer for the immiscible phenoxy/SAN blends. © 1994 John Wiley & Sons, Inc.