PCL Arms Research Articles

Synthesis and characterization of new biodegradable comb‐dendritic triblock copolymers

AbstractA series of well‐defined dumbbell‐shaped triblock copolymers consisting of linear poly(ethylene glycol) (PEG) and comb‐like poly(ε‐caprolactone) (PCL) with varied PCL arm lengths have been synthesized via the sequential preparation of different generation terminal dendronized PEG and ring‐opening polymerization of ε‐caprolactone. The copolymers were characterized using Fourier transform infrared, 1H NMR and 13C NMR spectroscopy and gel permeation chromatography. Differential scanning calorimetry was performed to measure the glass transition temperature, melting point and degree of crystallinity and the PEG segment and PCL segment crystallization temperatures. The crystallization of the copolymers was also studied using X‐ray diffraction. The dumbbell‐shaped copolymers were further used to construct microspheres using a double emulsion method. Scanning electron microscopy and dynamic light scattering results showed the size of the microspheres was about 2 to 4 µm and the size distribution was quite narrow. Copyright © 2012 Society of Chemical Industry

Synthesis of a new multiarm star polymer based on hyperbranched poly(styrene) core and poly(ε‐caprolactone) arms and its use as reactive modifier of epoxy thermosets

AbstractA well‐defined multiarm star copolymer poly(styrene)‐b‐poly(ε‐caprolactone) (PSOH‐b‐PCL) with an average number of PCL arms per molecule of 60 has been prepared. 4‐Chloromethyl styrene (4‐CMS) was polymerized by means of atom transfer radical polymerization (ATRP) to obtain a hyperbranched poly(styrene) with chlorines as terminal groups. Subsequently, chlorines were substituted by reaction with diisopropanolamine (DIPA) to give the hydroxyl‐ended derivative. Finally, the hydroxyl‐ended hyperbranched poly(styrene) has been used as a macroinitiator core to polymerize ε‐caprolactone by means of cationic ring‐opening polymerization so as to obtain the star copolymer. In a second step, PSOH‐b‐PCL was used as reactive modifier of diglycidylether of bisphenol A formulations cured by 1‐methyl imidazole (1‐MI) obtaining nanostructured thermosets. The curing process was studied by dynamic scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). By rheometry, the effect of this new polymer topology on the complex viscosity (η*) of the reactive mixture and on the gelation process was also analyzed. The thermomechanical characteristics of the modified materials were determined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Novel macrothiols for the synthesis of a structurally comprehensive dendritic library using thiol–ene click chemistry

In the last decades, the fabrication of ordered nano- and microporous structures has attracted increasing interest due to their specific properties and multiple possible applications in electronics, as templates or in the biological field. The development of such materials has been favored by the introduction of the simple breath-figure templating method in the 1990’s. In order to fully exploit the potential of these porous materials, the use of advanced functional molecules as precursors is essential. One suitable class of molecules is the well-defined linear-dendritic hybrids (LD hybrids) family. The structural variations, multiple end-groups and possible amphiphilicity of these molecules are significant advantages that could lead to highly sophisticated functional materials with potential usage in biology. Therefore, this project was directed towards the synthesis of advanced LD hybrids and the evaluation of their ability to form ordered functional porous films.A degradation and toxicity study was initially conducted on polyester-based 2,2-bis(methylol)propionic acid (bis-MPA) dendrimers under physiological conditions to support the potential usage of these molecules for biological purposes. The materials were found to undergo a relatively fast depolymerization process at pH 7.5. Moreover, the initial dendrimer and its decomposition products were proven to be non-toxic for immune competent cells, allowing for the utilization of these molecules for biological applications.A linear-dendritic-linear hybrid library was successfully synthesized from biocompatible poly(ethylene glycol) (PEG), poly(e-caprolactone) (PCL) and bis-MPA building blocks using a combination of ring-opening polymerization (ROP)and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The materials, consisting of one long PEG block connected to the focal point of the dendron and several PCL arms attached at its periphery, were used to construct ordered porous films using the breath figure method. The polymeric architecture strongly affected the ordering of the films with a more regular morphology obtained from a more flexible polymer. Changing the semi-crystalline PCL to amorphous polylactide (PLA) also permitted the formation of porous arrays. Interestingly, films obtained from inverted structures possessing one long PCL block and several short PEG chains, also presented a regular morphology. Moreover they could be activated to exhibit multiple surface hydroxyl groups.To increase the number of orthogonal synthetic methodologies available for the preparation of advanced macromolecules, high molecular weight dendritic macrothiols were synthesized. These molecules were efficiently coupled to a number of core molecules via thiol-ene coupling, generating a comprehensive library of dendritic materials. This approach represents an attractive alternative to the commonly used, but potentially toxic, CuAAC.Exploiting the obtained results, a final LD hybrid was synthesized from atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA) derivatives and thiol-ene coupling (TEC) with macrothiols. This macromolecule was successfully utilized to form functional ordered porous arrays and the availability of peripheral alkyne functional groups was demonstrated by efficient coupling with fluorescent Rhodamine-B. The HEMA-backbone allowed for the introduction of cross-linkable azide groups that were used to significantly improve the thermal stability of the films from 50 °C to 200 °C. These materials have the potential to be used in applications such as catalysis, in medicine and as sensors.

Preparation of pH-sensitive star-shaped aliphatic polyesters as precursors of polymersomes

This article reports on the synthesis of a new pH-sensitive amphiphilic A2B mikto-arm star-shaped aliphatic copolyester [with A = poly(e-caprolactone) and B = tertiary amine-bearing poly(e-caprolactone)] with two hydrophobic arms and one hydrophilic arm when protonated at pH = 5.5. First, the ring-opening polymerization of e-caprolactone (eCL) was initiated by an aliphatic diol substituted by an alkyne. The copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) was use to convert the alkyne into a hydroxyl group prone to initiate the ring-opening copolymerization of γ-bromo-e-caprolactone (γBreCL) and eCL. After the substitution of the bromide atoms into azide functions, the N,N-dimethylprop-2-yn-1-amine was grafted onto the azide bearing PCL arm by CuAAC, with the purpose to make the B arm hydrophilic at low pH. The precursors of the A2B copolymers were characterized by 1H NMR, SEC, and MALDI-TOF. As expected, the A2B copolyester was soluble into water at pH = 5. The formation of polymersomes in water at pH 5 was assessed by DLS and TEM analyses. The effects of the architecture and the molecular weight of the A2B copolymers on the formation of polymersomes were investigated. Moreover, the versatility of our approach was demonstrated by the synthesis of an AB2 star-shaped copolyester. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Calixarene‐centered amphiphilic A2B2 miktoarm star copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol): Synthesis and self‐assembly behaviors in water

AbstractNovel calixarene‐centered amphiphilic A2B2 miktoarm star copolymers composed of two PCL arms and two PEG arms with calix[4]arene as core moiety were synthesized by the combination of CROP and “click” chemistry. First, a heterotetrafunctional calix[4]arene derivative with two hydroxyl groups and two alkyne groups was designed as a macroinitiator to prepare calixarene‐centered PCL homopolymers (C4‐PCL) by CROP in the presence of Sn(Oct)2 as catalyst at 110 °C. Next, azide‐terminated PEG (A‐PEG) was synthesized by tandem treating methoxy poly(ethylene glycol)s (mPEG) with 4‐chlorobutyryl chloride and NaN3. Finally, copper(I)‐catalyzed cycloaddition reaction between C4‐PCL and A‐PEG led to A2B2 miktoarm star copolymer [C4S(PCL)2‐(PEG)2]. 1H NMR, FT‐IR, and SEC analyses confirmed the well‐defined miktoarm star architecture. These amphiphilic miktoarm star copolymers could self‐assemble into multimorphological aggregates in water. The calix[4]arene moieties with a cavity <1 nm on the hydrophilic/hydrophobic interface of these aggregates may provide potential opportunities to entrap guest molecules for special applications in supermolecular science. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Synthesis and characterization of two-armed poly(ɛ-caprolactone) polymers initiated by the Schiff's base complexes of copper(II) and nickel(II)

Two-armed poly(ɛ-caprolactone) (TAPCL) polymers were successfully synthesized via the ring opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL) using the Schiff's base complexes [Cu(SAEE) 2] ( 1) and [Ni(SAEE) 2] ( 2), which have two hydroxyl functional groups, as the two-site initiators and tin(II) 2-ethylhexanoate (Sn(Oct) 2) as the catalyst in bulk at 115 °C. The Schiff's base complexes ( 1 and 2) were synthesized by utilizing the concentrated template synthesis method starting from salicyl aldehyde, 2-(2-aminoethoxy) ethanol and related metal acetate salts. The synthesized TAPCL polymers were characterized by GPC, FTIR, UV–vis, and electron paramagnetic resonance (EPR). The molecular weights of TAPCL polymers linearly increased with increasing molar ratio of the monomer to the initiator. The results obtained from FTIR, UV–vis, and EPR studies indicated that TAPCL polymers had the Schiff's base complexes at the junction point of PCL arms. The crystallization behavior of TAPCL was studied by using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Thermal behavior of TAPCL was also investigated by thermogravimetrical analysis (TGA).

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.

Synthesis and characterization of well‐defined polystyrene and poly(ε‐caprolactone) hetero eight‐shaped copolymers

AbstractWell‐defined hetero eight‐shaped copolymers composed of polystyrene (PS) and poly(ε‐caprolactone) (PCL) with controlled molecular weight and narrow molecular weight distribution were successfully synthesized by the combination of ring‐opening polymerization, ATRP, and “click” reaction. The synthetic procedure involves three steps: (1) preparation of a tetrafunctional PS and PCL star copolymer with two PS and two PCL arms using the tetrafunctional initiator bearing two hydroxyl groups and two bromo groups; (2) synthesis of tetrafunctional star copolymer, (α‐acetylene‐PCL)2(ω‐azido‐PS)2, by the transition of terminal hydroxyl and bromo groups to acetylene and azido groups through the reaction with 4‐propargyloxybutanedioyl chloride and NaN3 respectively; (3) intramolecular cyclization reaction to produce the hetero eight‐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 resulted intermediates and the target polymers. Their thermal behavior was investigated by DSC, and their crystallization behaviors of PCL were studied by polarized optical microscopy. The decrease in chain mobility of the eight‐shaped copolymers restricts the crystallization of PCL and the crystallization rate of PCL is slower in comparison with their corresponding star precursors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6496–6508, 2008

Amphiphilic Core−Shell Nanocarriers Based On Hyperbranched Poly(ester amide)-star-PCL: Synthesis, Characterization, and Potential as Efficient Phase Transfer Agent

Amphiphilic biodegradable star-shaped polymer was conveniently prepared by the Sn(Oct)2-catalyzed ring opening polymerization of epsilon-caprolactone (CL) with hyperbranched poly(ester amide) (PEA) as a macroinitiator. Various monomer/initiator ratios were employed to vary the length of the PCL arms. (1)H NMR and FTIR characterizations showed the successful synthesis of star polymer with high initiation efficiency. SEC analysis using triple detectors, RI, light scattering, and viscosity confirmed the controlled manner of polymerization and the star architecture. Because of the hydrophilic PEA core and hydrophobic PCL shell, the obtained star polymers displayed inverted unimolecular micellar structure confirmed by dynamic light scattering. Three water soluble dyes, congo red, methyl orange, and bromophenol blue, were used to investigate the host-guest behavior of the micelles. It proved that the core-shell unimolecular reverse micelles were able to transport polar dyes from water to the organic phase with a high efficiency of up to 22.6 dyes per polymer, indicating a great potential of the micelles as drug carriers. The influence of arm length and core size on the load efficiency of the nanocarrier was also evaluated.

Core-shell type multiarm star poly(ε-caprolactone) with high molecular weight hyperbranched polyethylenimine as core: Synthesis, characterization and encapsulation properties

Core-shell type multiarm star copolymers with poly(ε-caprolactone) (PCL) as shells and hyperbranched polyethylenimine (PEI) as core have been successfully prepared by the Sn(Oct) 2 catalyzed ring-opening polymerization of ε-caprolactone (CL) using high molecular weigh PEIs directly as macroinitiators. The initiation efficiency is in the range of 91–95% for PEI with M n = 10 4 (PEI10K) and only around 60% for PEI with M n = 2.5 × 10 4 (PEI25K), leading to star polymers with an average arm number in the range of 155–276. The thermal property of the obtained multiarm star polymers were also investigated by DSC. The melting and crystallization temperatures of the star polymers increase as the PCL arm length increases when the PEI core is fixed. The fusion enthalpy, crystalline enthalpy and degree of crystallinity values of the star polymers with PEI10K core are less than those with PEI1.8K core. Due to the polarity difference between PCL arm and PEI core, the resulting multiarm star polymers can act as inverted micellar nanocapsules capable of extracting and encapsulating water soluble guests. Increasing the size and polarity of the hydrophilic PEI core of the star nanocapsules are two effective ways to enhance their hydrophilic guest encapsulation capacity. Increasing the hydrophobic PCL arm length can increase the molar ratio, whereas reduce the weight ratio of the encapsulated hydrophilic guests to the star nanocapsules. Unexpectedly, the obtained nanocapsules can entrap the bigger size hydrophilic congo red guests more than the smaller size methyl orange.

Crystallization behavior and micelle formation of star-shaped amphiphilic block copolymer based on dendritic poly(ether-amide)

The star-shaped amphiphilic block copolymer (DPEA-PCL-PEG) was prepared through ring opening polymerization of ε-caprolactone (CL) initiated by hydroxyl end-capped dendritic poly(ether-amide) (DPEA-OH), then coupling with monomethoxy-terminated poly(ethylene-glycol) (PEG) via an esterification process. The molecular structure was verified by FT-IR, 1H NMR and gel permeation chromatography (GPC). The number average molecular weight of the PCL arm was calculated to be about 1910 g mol −1 by 1H NMR analysis. The number average molecular weight of the copolymer was determined to be 74,020 with the molecular weight distribution of 1.15 by GPC. The DSC and X-ray diffraction analysis indicated that the copolymer possesses double melting and crystallization peaks, attributed to PCL and PEG segments in DPEA-PCL-PEG. The corresponding melting and crystallization temperature, and value of crystallinity are much lower than that of their individual homopolymers. The copolymer easily formed the core–shell structural nanoparticles as micelles in water with a lower critical micelle concentration of 5.524 mg l −1.

Core–shell‐type multiarm star polyethylenimine‐block‐poly(ε‐caprolactone): Synthesis and guest encapsulation potential

AbstractNovel multiarm star copolymers with poly(ϵ‐caprolactone) (PCL) as the arms and hyperbranched polyethylenimine (HPEI) as the core have been successfully prepared by the tin(II) 2‐ethylhexanoate catalyzed ring‐opening polymerization of ϵ‐caprolactone (CL) with HPEI used directly as a macroinitiator. Not only primary but also secondary amine groups of HPEI participate in initiating the ring‐opening polymerization of CL with almost 100% initiation efficiency. The average degree of polymerization of the PCL arms can be controlled by the feed ratio of the monomers to the initiating sites. Because of the polarity difference of the PCL arms and HPEI core, the obtained multiarm star polymers display an inverted micellar structure with potential extraction and encapsulation of water‐soluble guests. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4165–4173, 2006

Single crystal morphology of star-branched polyesters with crystallisable poly( ε-caprolactone) arms

Star-branched polymers consisting of poly( ε-caprolactone) (PCL) attached to third generation dendrimer, hyperbranched and dendron cores have been studied together with linear PCL analogues. The degree of polymerisation of the PCL arms of the star-branched polymers ranged from 14 to 81. Single crystals were grown from dilute solution and studied by transmission electron microscopy. Single crystals of linear PCL were multilayer hexagons with flat or slightly curved {110} and {100} faces. These single crystals were larger along [010] than along [100]. Single crystals of star-branched PCL showed the same basic shape, but with many crystallographic and irregular steps on the lateral crystal faces. The width of the micro-faces was typically 100–300 nm. These single crystals were more extended along [100] than along [010]. It is proposed that the high fold surface free energy and the constrained character of the star-branched polymers favour the formation of steps on the growth faces. Globular polycrystalline aggregates were also observed. They originated from a more concentrated polymer phase following phase separation of the solution. In the case of the star-branched polymers, lamellar branching was observed with a 30° angle between the crystals arms.

Crystal structure, melting behaviour and equilibrium melting point of star polyesters with crystallisable poly( ε-caprolactone) arms

Star polymers consisting of poly( ε-caprolactone), PCL, attached to third generation dendrimer, hyperbranched and dendron cores have been studied by differential scanning calorimetry and wide-angle X-ray scattering. The degree of polymerisation of the PCL arms of the star polymers ranged from 14 to 81. The crystal unit cell was the same for the star polymers as for their linear PCL analogues. The star polymers showed a lower degree of crystallinity than the linear PCL, suggesting that the dendritic cores imposed restriction on PCL crystallisation. Slow heating of rapidly cooled samples led to crystal rearrangement—a gradual increase in melting point with decreasing heating rate and recrystallisation followed by additional high temperature melting. The tendency for crystal rearrangement was less pronounced in star polymers based on dendrimer or hyperbranched cores, suggesting that the dendritic cores constitute an obstacle to crystal rearrangement. The star polymers showed higher equilibrium melting points than the linear PCL analogues. It is suggested that covalent attachment of the PCL arms to the dendritic core reduced the positional freedom and the entropy of the melt with respect to that of linear PCL.

Crystallization Behavior and Morphology of Star Polyesters with Poly(ϵ‐Caprolactone) Arms

Star polymers consisting of poly(ϵ‐caprolactone), (PCL), grafted onto third generation dendrimer, which had hyperbranched and dendron cores, were studied by polarized light microscopy together with reference linear PCL. The degree of polymerization of the PCL arms in the star polymers ranged between 14 and 81. The star polymers exhibited a greater tendency than the linear polymers to form spherulites. It is suggested that the preference of the star polymers for forming spherulites is due to the presence of amorphous material—dendritic cores and PCL cilia—between crystal lamellae that generates the necessary pressure to force the lamellae to diverge at lamellar branch points. The linear growth rate data followed a single crystallization regime. The fold surface free energy was higher for the star polymers than for their linear analogs. It is proposed that the presence of the large and rigid dendritic cores on the fold surfaces of the star polymer crystals increases the fold surface energy.

Adsorption of triarm starblock copolymers based on polystyrene, poly(ethylene oxide) and poly(ϵ-caprolactone) at the solid-solution interface

Triarm starblock copolymers of ABC type and AB diblock copolymers, where A, B and C are respectively poly(ethylene oxide) (PEO), polystyrene (PS) and poly(ϵ-caprolactone) (PCL) blocks, having molecular weights in the range 24 700–260 000, were prepared by anionic polymerization in tetrahydrofuran. The copolymer adsorption onto titanium dioxide particles in toluene was studied in the concentration range 0.1–30 g dm −3. The proton NMR experimental results indicate that the copolymers were adsorbed by titanium dioxide via the PEO block. For the diblock copolymer the measured maximum adsorbed amount Γ and the surface density σ were larger than those observed for the corresponding star copolymer. For star copolymers having the same number of repeat units of PS and PEO blocks ( N PS and N PEO) Γ and σ were found to increase with decreasing size of PCL block N PCL. Furthermore, the estimated average spacing Σ between the adsorbed chains was found to increase with N PCL, indicating that in the adsorbing layer the PCL arms were close together and stretched.