Fullerene End‐Capped Biodegradable Poly(ε‐caprolactone)

Fullerene capped poly(ε‐caprolactone)s (PCLs), namely single‐ and double‐fullerene end‐capped PCLs with different fullerene content, were successfully synthesized. The effect of the fullerene end on the crystallization behavior and mechanical properties of the PCL was studied. The aggregation behavior of the fullerene moieties at the end of the PCL chain was also studied. It was found that the aggregated fullerenes have two kinds of effect on the crystallization behavior of the PCL i.e., confinement effect and nucleating effect. The fullerene content shows a certain balance between the confinement effect and the nucleating effect on the crystallization rate of PCL. It was also found that the mechanical properties of the fullerene end‐capped PCLs are strongly related to the content of fullerene and the mode of end‐capping style: either single or double end‐capping.

     

Microwave‐Assisted Synthesis and Characterization of Poly(ε‐caprolactone)/Montmorillonite Nanocomposites

Poly(ε‐caprolactone) (PCL)/montmorillonite (MMT) nanocomposites were prepared by in situ ring‐opening polymerization of ε‐caprolactone in the presence of MMT modified by hydroxyl‐group containing alkylammonium cation (Cloisite®30B) in a single mode microwave oven. For the polymerization mixtures, plateaus or exothermal peaks were observed in their temperature‐time profiles and can be attributed to the heat‐generating nature of the ring‐opening polymerization. The morphologies of the nanocomposites showed a predominantly exfoliated structure. The mechanical properties of the nanocomposites were evaluated via dynamic mechanical analysis. Compared with that of the recovered PCL matrix, the mechanical properties of the PCL/Cloisite®30B nanocomposites showed obvious improvement.

     

Non‐Isothermal Crystallisation Kinetics of In Situ Prepared Poly(ε‐caprolactone)/Surface‐Treated SiO2 Nanocomposites

Poly(ε‐caprolactone)/silica nanocomposites were prepared by the in situ technique. The molecular weight of the polymer was slightly reduced on increasing the amount of filler. Most likely, the silica nanoparticles affected the action of the polymerisation catalyst. Furthermore, it was found that especially for high filler content the silica nanoparticles showed a trend to form aggregates. The non‐isothermal crystallisation of these hybrid organic/inorganic materials was studied. The crystallisation rates seemed to increase upon increasing the content of silica nanoparticles in the composites. When the silica content was above 5 wt.‐%, the molecular weight of the polymer in the hybrids decreased, and the increase in the crystallisation rates was attributed to both the nucleating effect of the nanoparticles and the lower molecular weight. The modified Avrami and Ozawa model were used to study the crystallisation kinetics. It was found that both of the models gave satisfactory results. The nucleation activity of the filler was estimated. The effective activation energy for the non‐isothermal crystallisation was calculated using the isoconversion method of Friedman and the results were compared to those from Kissinger's method. The activation energy was found to decrease upon increasing the filler content, showing that the crystallisation is favoured.

     

Synthesis and Characterization of Functionalized Crosslinkable Poly(ε‐caprolactone)

Summary: A new and rather simple method to obtain randomly crosslinked PCL is reported. PCL was previously functionalized through radical grafting of MA and GMA in the melt, using a Brabender‐like apparatus. GMA was added in order to obtain higher grafting efficiency. The structure of PCL‐g‐MAGMA was elucidated by ¹H NMR spectroscopy, and the content of grafted MA was determined by FT‐IR spectroscopy. PCL‐g‐MAGMA was successively crosslinked through reaction with HMDI. The degree of crosslinking was determined by solvent extractions with chloroform. Thermal and dynamic mechanical analysis and tensile tests were performed on plain PCL, on PCL‐g‐MAGMA and on crosslinked PCL samples.

Schematic representation of PCL‐g‐MAGMA structure.     

Polyhedral Oligomeric Silsesquioxane‐ and Fullerene‐End‐Capped Poly(ε‐caprolactone)

Novel fullerene‐ and polyhedral oligomeric silsesquioxane‐ (POSS) double end‐capped poly(ε‐caprolactone) (PCL) were successfully synthesized. The crystallization behavior of the fullerene‐ and POSS‐ double end‐capped PCL and the effect of aggregation of the POSS and fullerene moieties on the crystallization of PCL were thoroughly studied. The aggregation of the fullerene moieties has much larger confinement effect on the crystallization of PCL than that of POSS. The successful incorporation of two nano‐sized objects, that is, fullerene and POSS, into the PCL matrix may introduce their merits, so that PCL can attain multi‐functional properties.

     

Structure and Properties of Poly(ε‐caprolactone) Networks with Modulated Water Uptake

Summary: A PCL macromonomer was obtained by the reaction of PCL diol with methacrylic anhydride. The effective incorporation of the polymerizable end groups was assessed by FT‐IR and ¹H NMR spectroscopy. PCL networks were then prepared by photopolymerization of the PCL macromonomer. Furthermore, the macromonomer was copolymerized with HEA, with the aim of tailoring the hydrophilicity of the system. A set of hydrophilic semicrystalline copolymer networks were obtained. The phase microstructure of the new system and the network architecture was investigated by DSC, IR, DMS, TG, dielectric spectroscopy and water sorption studies. The presence of the hydrophilic units in the system prevented PCL crystallization on cooling; yet there was no effect on the glass transition process. The copolymer networks showed microphase separation and the α relaxation of the HEA units moved to lower temperatures as the amount of PCL in the system increased.

Ideal structure, compatible with the experimental results, for the hydrophilized poly(ε‐caprolactone) networks with modulated water uptake.     

Surface Patterning of Poly(ε‐caprolactone): Epitaxial Crystallization and Enzymatic Degradation

Surface patterning was carried out by the epitaxial crystallization of biodegradable PCL on a HOPG, and the surface morphologies were observed by atomic force microscopy. Edge‐on view lamellae were aligned along the HOPG lattice to display stripe patterns in the threefold symmetry. The intervals of stripe patterns composed of ridges and valleys increased with an increase in the crystallization temperature. Enzymatic degradation of the PCL nanopattern allowed the different depth profiles of the fringed structure. The persistence length of the nanopattern could be tuned by the molecular weight of PCL.

     

Ternary Thermosetting Blends of Epoxy Resin,Poly(ethylene oxide) and Poly(ε‐caprolactone)

Summary: The ternary thermosetting blends composed of epoxy resin, poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL) were prepared via in situ polymerization of epoxy monomers in the presence of the two crystalline polymers, PEO and PCL. DSC results showed that the binary blends of epoxy with PEO (and/or PCL) are fully miscible in the entire composition in the amorphous state. FTIR indicates that there were interchain specific interactions between the crosslinked epoxy and the linear polymers in the binary blends and the hydrogen bonding interactions between epoxy and PCL are much weaker than those between epoxy and PEO. The difference in the strength of interchain specific interactions gives rise to the competitive hydrogen bonding interactions in the ternary blends of epoxy, PEO and PCL, which were evidenced by the results of FTIR. The results of optical microscopy and DSC showed that in the ternary blends PCL component separated out with inclusion of PEO. The formation of the specific phase structures is ascribed to the competitive interchain specific interactions among the crosslinked epoxy, PEO and PCL.

Phase boundary diagram of epoxy, PEO and PCL ternary blends.     

Synthesis and Characterization of Comb‐Like Copolymers Based on Poly(ε‐caprolactone) and Poly(α‐olefin)

Comb‐like copolymers based on a polyolefin backbone of poly(10‐undecene‐1‐ol) (PUol) with poly(ε‐caprolactone) (PCL) side chains are synthesized in two steps. After synthesis of PUol by metallocene‐catalyzed polymerization, the side‐chain hydroxyl functionalities of this polar polyolefin are used as an initiator for the ring‐opening polymerization (ROP) of ε‐caprolactone (CL). In this context, copolymers with different lengths of PCL grafts are prepared. The chemical structure and the composition of the synthesized copolymers are characterized by ¹H and ¹³C NMR spectroscopy. It is shown that the hydroxyl end groups of PUol act effectively as initiating sites for the CL ROP. Size‐exclusion chromatography (SEC) measurements confirm the absence of non‐attached PCL and the expected increase in molar mass after grafting. The thermal and decomposition behaviors are investigated by DSC and thermogravimetric analysis (TGA). The effect of the length of the PCL grafts on the crystallization behavior of the comb‐like copolymers is investigated by DSC and wide‐angle X‐ray scattering (WAXS).

     

Immiscible Poly(L‐lactide)/Poly(ε‐caprolactone) Blends: Influence of the Addition of a Poly(L‐lactide)‐Poly(oxyethylene) Block Copolymer on Thermal Behavior and Morphology

Summary: A binary blend of poly (L ‐lactide) (PLLA) and poly(ε‐caprolactone) (PCL) of composition 70:30 by weight was prepared using a twin screw miniextruder and investigated by differential scanning calorimetry (DSC), optical microscopy and scanning electron microscopy (SEM). Ternary 70:30:2 blends were also obtained by adding either a diblock copolymer of PLLA and poly(oxyethylene) (PEO) or a triblock PLLA‐PCL‐PLLA copolymer as a third component. Optical microscopy revealed that the domain size of dispersed PCL domains is reduced by one order of magnitude in the presence of both copolymers. SEM confirmed the strong reduction in particle size upon the addition of the copolymers, with an indication of an enhanced emulsifying effect in the case of the PLLA‐PEO copolymer. These results are analyzed on the basis of solubility parameters of the blend components.

Optical micrograph of M3EG2 blend melt quenched at 125 °C.     

Telechelic and Star‐Shaped Poly(ε‐caprolactone) Functionalized with Triethoxysilyl Groups – New Biodegradable Coatings and Adhesives

Summary: Monofunctional poly(εCL) having one CH₂OH and one CO₂CH₃ endgroup was prepared by SnOct₂ + MeOH‐initiated polymerizations of εCL at 80 °C. The CH₂OH endgroups were reacted with IPTES. In this way, poly(εCL) having one CO₂CH₃ and one TES endgroup was obtained. Poly(εCL) having two CH₂OH endgroups were prepared by means of SnOct₂ and Tetra EG or 1,4‐butanediol as coinitiators. The molecular weight distribution significantly broadened when the polymerization temperature increased from 80 to 120 °C. The OH endgroups were quantitatively functionalized by addition of IPTES. Star‐shaped poly(εCL)s having three or four OH endgroups were prepared with 1,1,1‐tris(hydroxymethyl)propane or pentaerythritol as coinitiators. All endgroups were modified with IPTES. The lengths of the poly(εCL) segments were varied via the monomer/coinitiator ratio. All functionalized oligomers were characterized by ¹H NMR spectroscopy and MALDI‐TOF mass spectrometry. Preliminary studies of film formation and adhesive properties were performed.

MALDI‐TOF mass spectrum of a poly(εCL) initiated with Sn(Oct)₂ and 1,4‐butanediol and functionalized with IPTES.     

Non‐Isothermal Crystallization of Hyperbranched Poly(ε‐caprolactone)s and Their Linear Counterpart

Summary: Three hyperbranched poly(ε‐caprolactone)s were prepared with the architectural variation in the length of linear backbone segments consisting of 5, 10, and 20 ε‐caprolactone units (accordingly given the names HPCL–5, –10, and –20, respectively) and in the number of branching points as characterized by ¹H NMR end group analyses. The non‐isothermal crystallizations of HPCLs and LPCL were performed using DSC at various cooling rates and the kinetic study was further performed by using both Ozawa and Kissinger methods. All the kinetic parameters such as the cooling functions and the apparent activation energy of crystallization indicated that HPCLs with longer linear segments and fewer number of branching points showed faster crystallization rates, whereas LPCL exhibited an intermediate rate between HPCL–10 and HPCL–20, i.e., HPCL–5 < HPCL–10 < LPCL < HPCL–20. The decrease in the crystallization rate is attributed to the presence of heterogeneous branching points in HPCLs with shorter segments, which hinders the regular chain packing to crystallize. In addition, the faster crystallization of HPCL–20 compared to LPCL was associated with the higher cooperative chain mobility in the melt.

Schematic illustrations for HPCL and LPCL.     

Banded Spherulitic Morphology in Blends of Poly (propylene fumarate) and Poly(ϵ‐caprolactone) and Interaction with MC3T3‐E1 Cells

The thermal properties, morphological development, crystallization behavior, and miscibility of semicrystalline PCL and its 25, 50, and 75 wt% blends with amorphous PPF in spin‐coated thin films crystallized at various crystallization temperatures (T_c) from 25 to 52 °C are investigated. The surface roughness of PPF/PCL (?_PCL = 75%) films increases with increasing T_c and consequently the adsorption of serum proteins is also increased. No significant variance is found in surface hydrophilicity or in mouse MC3T3‐E1 cell attachment, spreading, and proliferation on PPF/PCL (?_PCL = 75%) films crystallized isothermally at 25, 37, and 45 °C, because of low ridge height, nonuniformity in structures, and PPF surface segregation.     

Synthesis of a Poly(vinyl alcohol)‐Based Graft Copolymer Having Poly(ε‐caprolactone) Side Chains by Solution Polymerization

Poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) was synthesized by ring‐opening polymerization of ε‐caprolactone with poly(vinyl alcohol) in the presence of tin(II) 2‐ethylhexanoate as a catalyst in dimethyl sulfoxide. The relationship between the reaction conditions of the solution polymerization and the chemical structure of the graft copolymer was investigated. The degree of substitution (DS) and degree of polymerization (DP) of the PCL side chains were roughly controlled by varying the reaction periods and feed molar ratios of the monomer and the catalyst to the backbone. PVA‐g‐PCL with a PCL content of 97 wt.‐% (DP = 22.8, DS = 0.54) was obtained in 56 wt.‐% yield. The graft copolymer was soluble in a number of organic solvents, including toluene, tetrahydrofuran, chloroform, and acetonitrile, which are solvents of PCL. The molecular motion of the graft copolymer from ¹H NMR measurements appears to be restricted to some extent at 27–50°C, however the ¹H NMR signal intensities measured at temperatures higher than ca. 50°C reflect the actual chemical structure of the graft copolymer as determined by elemental analysis. The graft copolymer having a short PCL side chain (DP = 4.4, DS = 0.15) was amorphous. The melting temperature of a sample with relatively high PCL content (DP = 22.8, DS = 0.54) was observed at 39°C. Thermogravimetric analysis revealed that the thermal stability of PVA was improved by introducing PCL side chains. The surface free energies of the air‐side of a graft copolymer film, as calculated by Owens' equation using contact angles, were comparable to that of PCL homopolymer.     

Poly(ε‐caprolactone) and Pluronic Diol‐Containing Segmented Polyurethanes for Shape Memory Performance

A series of novel segmented linear and crosslinked polyurethanes (PUs) are synthesized from poly(ε‐caprolactone) (PCL) (25 kg mol^?1), methylene diphenyl diisocyanate (MDI), and various polyether diols (Pluronic (PLU) and polyethylene glycol (PEG)). The basic structures of the highly deformable PUs are PLU/PEG–MDI–PCL–MDI–PLU/PEG and PLU–MDI–PCL–MDI–PLU, respectively. The linear and crosslinked PUs are characterized. Changes in the tensile behavior are attributed to the effects of compositional variables and alterations in the crosslink density. Additional information on the morphology of the segmented PUs is deduced from differential scanning calorimetry, as well as transmission and scanning electron microscopy investigations. Both the linear and the crosslinked PUs exhibit a broad rubbery plateau above the melting temperature of the crystalline PCL phase, which is highly beneficial for shape memory function. This work highlights that the chemical build‐up of soft segments containing high‐molecular‐weight crystallizable chain units is a proper tool to tailor the morphology and mechanical properties of PUs, and thus also their shape memory properties.

     

Real‐Time Observations of Oriented Crystallization of Poly(ε‐caprolactone) Thin Film,Induced by an AFM Tip

Atomic force microscopy (AFM) was used for modifying the surface structures of poly(ε‐caprolactone) (PCL) thin film. Oriented growth of PCL crystals at a desired area of the film surface was induced by scanning with a strong, normal load. PCL crystals were first grown edge‐on from the induction line and then their orientation changed to flat‐on at a lamellar length. The effects of molecular weight, crystallization temperature, scanning rate, and normal load on the AFM‐tip‐induced crystallization were examined. The growth kinetics of lamellar crystals in the AFM‐tip‐induced crystallization was the same as that in spherulitic crystallization. It was found that the formation of precursors strongly depends on the applied tip load and is facilitated when the applied load is higher than a threshold.

     

Synthesis of hydroxytelechelic ε‐caprolactone/poly(ethylene terephthalate) co‐oligomers, 1

In the presence of ethylene glycol, poly(ethylene terephthalate) (PET) undergoes chain scissions with the formation of α,ω‐hydroxyl oligomers, through classical transesterification by alcoholysis. ε‐Caprolactone was subsequently added on the hydroxyl end groups of PET oligomers by ring‐opening polymerization at different molar ratios of ε‐caprolactone to PET oligomers. The chemical structure of the products was investigated by size exclusion chromatography, ¹H NMR spectroscopy, and differential scanning calorimetry. A large majority of these products are soluble in common organic solvents. The thermal and ¹H NMR analyses reveal that the transesterification between base units of PET oligomers and ε‐caprolactone during the synthesis is always present whatever the reaction conditions. This phenomenon leads to copolymers having thermal properties different from those of PET. However, some co‐oligomers present the interest of keeping properties close to those of PET. The main purpose of this study was the synthesis of PET co‐oligomers that are soluble in some organic solvents that would make their use easier, and so that they can be used further as hard segment precursers for polycondensation reactions.

Ring‐opening polymerization of ε‐caprolactone onto hydroxytelechelic oligomers of PET.     

Synthesis of Functional Poly(ε‐caprolactone)s via Living Ring‐Opening Polymerization of ε‐Caprolactone Using Functionalized Aluminum Alkoxides as Initiators

The new aluminum compounds 1–3 modified by unsaturated alcohol, Me_3−n Al(O(CH₂)₄OCHCH₂)_n (n = 1 ( 1 ), 2 ( 2 ), 3 ( 3 )), are synthesized and investigated by multinuclear (¹H, ¹³C, ²⁷Al) NMR spectroscopy. The compounds 1 – 3 initiate living ring‐opening polymerization of ε‐caprolactone in bulk at 40–80 °C to afford polyesters with controlled molecular weight (M _n up to 35 000 g mol⁻¹) and relatively narrow molecular weight distribution (M _w/M _n < 1.8). Among initiators studied here, aluminum trialkoxide shows the highest activity, whereas aluminum dialkoxide is a less active. In all cases, the fragment of unsaturated alcohol is transferred to the end of the polymeric chain with high degree of functionality (>85%) yielding macromonomers. These macromonomers are copolymerized with maleic anhydride to give poly(vinyl ether‐co‐maleic anhydride)‐g‐poly(ε‐caprolactone) graft copolymers.

     

Synthesis and Characterisation of Poly[oligo(ε‐caprolactone)L‐malate‐graft‐poly(L‐lactide)]

Graft copolyesters with a PCL backbone and PLLA side chains were successfully prepared in three steps avoiding transesterification. First ε‐caprolactone was polymerised with 1,6‐hexane diol as initiator to obtain hydroxytelechelic oligo(ε‐caprolactone)s. These diols were then subjected—in the second step—to polycondensation with L ‐malic acid yielding in linear poly[oligo(ε‐caprolactone)L ‐malate] having secondary hydroxyl functions in the side chain. For both reactions scandium triflate Sc(OTf)₃ was used as a catalyst. In the third step various amounts of L ‐lactide were grafted from the polymer backbone using Zn(oct)₂ as catalyst. The successful reaction was confirmed by NMR and SEC (size exclusion chromatography) analysis. Further the thermal properties of the graft copolymers with different graft lengths were determined via differential scanning calorimetry.

     

Preparation and Properties of Degradable Shape Memory Material Based on Partial α‐Cyclodextrin–Poly(ε‐caprolactone) Inclusion Complex

A series of supramolecular degradable inclusion complex (IC) films were formed by threading α‐cyclodextrin (α‐CD) molecules over poly(ε‐caprolactone) (PCL) according to the designed ratio of α‐CD–PCL. Due to containing both α‐CD–PCL inclusion crystallites and uncovered PCL crystallites, the resulting supramolecular α‐CD–PCL IC partial films displayed a shape memory effect. The properties of the materials were investigated by ¹H NMR, X‐ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and swelling measurement. It was found that the casting temperature and solvent have great influence on the formation and properties of the α‐CD–PCL partial ICs. The modes of complexes on different conditions were proposed. In addition, the introduction of inclusion structure accelerates the degradation of materials strongly.