Physical properties of poly(ε‐caprolactone) layered silicate nanocomposites prepared by controlled grafting polymerization

Poly(ε‐caprolactone) (PCL) chains grafted onto montmorillonite modified by a mixture of nonfunctional ammonium salts and ammonium‐bearing hydroxyl groups were prepared. The clay content was fixed to 3 wt %, whereas the hydroxyl functionality was 25, 50, 75, and 100%, obtaining an intercalated or exfoliated system. The transport properties of water and dichloromethane vapors and the mechanical properties were investigated. The mechanical and dynamic mechanical analyses showed improvement of the nanocomposite elastic modulus in a wide temperature range. Interestingly, for the higher hydroxyl contents (50, 75, and 100%), the decrease of modulus at higher temperature, due to the PCL crystalline melting, did not lead to the loss of mechanical consistence of the samples. Consequently, they revealed a measurable modulus up to 120 °C, a much higher temperature with respect to pure PCL. Water sorption was investigated in the entire activity range, and a lower sorption was observed on increasing the hydroxyl content, up to the sample with 100% hydroxyl content, which turned to be completely impermeable, even in liquid water. The sample with 75% hydroxyl content showed a threshold activity (a = 0.4) below which it was impermeable to water vapor. Also, the diffusion parameters decreased when the hydroxyl content increased, up to the 100% sample, which showed zero diffusion. The diffusion parameters of an organic vapor, dichloromethane, also exhibited a decreasing value on increasing the hydroxyl content in the nanocomposites. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1466–1475, 2004     

Gas barrier properties of poly(ε‐caprolactone)/clay nanocomposites: Influence of the morphology and polymer/clay interactions

Poly(ε‐caprolactone)/montmorillonite nanocomposites were prepared maintaining a constant inorganic content with three means: melt blending of poly(ε‐caprolactone) with natural or organomodified clays, in situ polymerization of ε‐caprolactone in the presence of organomodified clays, and initiation of ε‐caprolactone polymerization from the silicate layer with appropriate organomodified montmorillonites and activator. In this last case, the polymer chains were grafted to the silicate layers and it was possible to tune up the grafting density. The presence of clays did not modify the polymer crystallinity. It was shown that the in situ polymerization process from the clay surface improved the clay dispersion. The gas barrier properties of the different composite systems were discussed both as a function of the clay dispersion and of the matrix/clay interactions. The highest barrier properties were obtained for an exfoliated morphology and the highest grafting density. Similar evolution of the permeability and the diffusion coefficients was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 205–214, 2005     

Poly(hexamethylene terephthalate)-layered silicate nanocomposites

Nanocomposites of poly(hexamethylene terephthalate) (PHT) and montmorillonite organo-modified with alkylammonium cations bearing two primary hydroxyl functions, i.e., Cloisite^® 30B (CL30B) were synthesized. Organoclay incorporation was performed either by dispersion in the PHT matrix via melt blending or by in situ ring-opening polymerization of hexamethylene terephthalate cyclic oligomers c(HT). An additional procedure combining the two methods, preparation of a highly enriched inorganic “PHT-CL30B” nanohybrid masterbatch by in situ ring-opening polymerization and blending of the masterbatch with additional PHT was explored. The obtained nanocomposites contain 3% (w/w) of inorganics and displayed a mixture of intercalated morphology and exfoliated nanolayers as evidenced by X-ray diffraction and transmission electron microscopy. The nanocomposite obtained by the masterbatch technique exhibited a higher degree of exfoliation and displayed slightly higher glass transition temperatures, better mechanical properties and higher flame resistance. The improved results achieved with the “masterbatch route” are a consequence of the reactions occurring between the nanocomposite constituents allowing for the grafting of PHT chains onto the organoclay surface.     

Preparation of poly(ε-caprolactone)-co-poly(acrylic acid) by radiation-induced grafting

Acrylic acid was grafted onto poly(ε-caprolactone) (PCL) films by using electron beam (EB) preirradiation technique. The effect of reaction time, monomer concentration, radiation dose, time between irradiation and grafting, radiation atmosphere, and polymer crystallinity on the extent of grafting were studied. Silver and tin ions were attached to the grafted chains in order to study the grafting process. The irradiation in air was initially more rapid, but the final extent of grafting was the same when irradiated in nitrogen atmosphere. Maximum grafting extents exceeding 400% could be obtained. The optimal grafting was obtained at an acrylic acid to water ratio of 30 : 70. The grafting process could be initiated at a dose as low as 12 kGy. The grafting process proved to start at the surface and was extended into the bulk with time. The ability to form crystals was reduced as the grafting extent increased. The water uptake of the poly(ε-caprolactone)-graft-poly(acrylic acid) was increasing with increasing grafting extent, but reached a maximum of ca 100% for all grafting extents above 85%. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1805–1812, 1998     

Synthesis and characterization of novel segmented polyurethane/clay nanocomposite via poly(ε-caprolactone)/clay

A novel segmented polyurethane/clay (PU/clay) nanocomposite based on poly(caprolactone), diphenylmethane diisocyanate, butanediol, and poly(caprolactone)/clay prepolymer was synthesized as evidenced by FTIR and X-ray diffraction studies. Poly(caprolactone)/clay (PCL/clay) prepolymer was first synthesized in a nanocomposite form as confirmed by X-ray diffraction. X-ray diffraction study showed that PU/clay contained crystalline structure due to the presence of PCL/clay. In mechanical properties, about 1.4% PCL/clay in PU/clay resulted in a large increase in the elongation of PU/clay. However, when the amount of PCL/clay was 4.2%, the elongation of PU/clay was reduced drastically. This behavior indicated that PU/clay can be transformed from an elastomer to a thermoplastic material as the amount of PCL/clay in PU/clay increased. Additionally, the lap shear stress of PU/clay was at least three times that of neat PU as a result of the PCL/clay component. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2225–2233, 1999     

Rheological properties and crystallization behavior of multi‐walled carbon nanotube/poly(ε‐caprolactone) composites

Multi‐walled carbon nanotube/poly(ε‐caprolactone) composites (PCLCNs) were prepared by melt compounding. The rheology, nonisothermal crystallization behavior, and thermal stability of PCLCNs were, respectively, investigated by the parallel‐plate rheometer, differential scanning calorimeter, and TGA. Cole–Cole plots were employed successfully to detect the rheological percolation of PCLCNs under small amplitude oscillatory shear. PCLCNs present a low percolation threshold of about 2–3 wt % in contrast to that of clay‐based nanocomposites. The percolated nanotube network is very sensitive to the steady shear deformation, and is also to the temperature, which makes the principle of time‐temperature superposition be invalid on those percolated PCLCNs. Small addition of nanotube cannot improve the thermal stability of PCL but can increase crystallization temperature remarkably due to the nucleating effect. As the nanotube is much enough to be percolated, however, the impeding effect becomes the dominant role on the crystallization, and the thermal stability increases to some extent. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3137–3147, 2007     

Equilibrium thermal behavior and morphology of organophilic montmorillonite/poly(ε‐caprolactone) nanocomposites

With differential scanning calorimetry, we have demonstrated a peculiar behavior under equilibrium conditions of neat poly(ε‐caprolactone) and its organophilic montmorillonite nanocomposites. In particular, in the determination of the equilibrium melting temperature by the extrapolation of the data of the melting temperature (T_m) versus the crystallization temperature (T_c), a bimodal trend has been observed. At the lower T_c's, the data of T_m follow a constant trend, whereas at the higher ones, the usual increasing trend has been obtained. Morphological observations by atomic force microscopy (AFM) have provided evidence of two different crystalline morphologies for the lower and higher T_c ranges. Moreover, AFM has shown that the thermal treatments strongly influence the clay dispersion in the polymer matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 22–32, 2006     

Mechanical and dynamic viscoelastic properties of hydroxyapatite reinforced poly(ε-caprolactone)

Poly(ε-caprolactone)/hydroxyapatite (PCL/HA) composites as potential bone substitutes were prepared by melt-blending. The melting, crystallization and glass transition temperatures deduced from differential scanning calorimetery and dynamic mechanical thermal analysis (DMTA) were all changed by the addition of HA, suggesting an interaction at the interface of these two phases. Quasi-static mechanical testing shows that the yield strength and Young's modulus of PCL were increased by the addition of the reinforcement filler, HA. Dynamic viscoelastic properties were investigated using DMTA and an advanced rheometric expansion system. The results show that both the storage modulus and viscous modulus are enhanced by HA, and the PCL composite melts still behave like pseudo-plastic liquid.     

Complex formation of poly(ε-caprolactone) with cyclodextrin

Poly(ε-caprolactone) was found to form inclusion complexes with α-cyclodextrin to give crystalline compounds. The complexes are stoichiometric one-to-one (cyclodextrin: monomer unit) compounds. The yields of the complexes decreased with increasing the molecular weight of the polymer. They were characterized by IR, ¹H NMR, ¹³C CP/MAS NMR, and X-ray diffraction. The inclusion modes are discussed.     

Intramolecular interactions in poly(styrene-co-acrylonitrile)/poly(ε-caprolactone) blends

Specific interactions in blends of poly(ε-caprolactone) (PCL) and poly(styrene-co-acry-lonitrile) (SAN) were studied as a function of copolymer composition and blend ratio by using Fourier-transform infrared spectroscopy (FTIR). It was shown that miscibility occurred within a certain range of copolymer compositions because the presence of PCL reduced the thermodynamically unfavorable repulsion between styrene and acrylonitrile segments in the random copolymer. This effect was observed in terms of a shift to higher frequencies in the 700 cm^-1 γ-CH out-of-plane deformation vibration absorption of styrene and in the approximately 2236 cm^?1 C?N stretching frequency band in acrylonitrile segments. Specific intermolecular interactions between SAN and PCL were not observed in this study. © 1993 John Wiley & Sons, Inc.     

Polymer-layered silicate nanocomposites based on poly(ε-caprolactone)

Poly(ε-caprolactone) nanocomposites based on montmorillonite modified with hexadecyltrimethylammonium bromide (M-HTAB) were prepared by the in situ polymerization technique. As a result, nano-structured PCL/M-HTAB systems were obtained. It was found that the molecular weight of PCL decreased with an increase in silicate content in the system. Within the investigated range of molecular weight, crystallization behavior of poly(ε-caprolactone) was affected only by the presence of M-HTAB. A silicate loading of higher than 10 wt.% reduced both crystallinity degree and the crystallization rate of PCL. The structure of obtained intercalated nanocomposites depended on the amount of montmorillonite in the systems. The periodicity of clay layers, estimated by X-ray diffraction, was found to be high at increased silicate loading in the nanocomposite. Since PCL and SAN are miscible, an attempt was made to use PCL/M-HTAB systems as a modifier for SAN matrix. Apparently, a quantity as small as 0.66 wt.% of M-HTAB in such blends induced a clear increase in material stiffness. An increase of Young's modulus of more than 40% in comparison to neat SAN was observed at 5.65 wt.% silicate loading.     

Ring-opening metathesis polymerization of new α-norbornenyl poly(ε-caprolactone) macromonomers

Poly(ε-caprolactone) (PCL) macromonomers capped by a polymerizable norbornene end-group have been synthesized and (co)polymerized by ring-opening metathesis with formation of graft copolymers and polymacromonomers. α-Norbornenyl PCL macromonomers have been synthesized by ring opening polymerization (ROP) of ε-caprolactone (εCL) initiated by 2-diethylaluminoxymethyl-5-norbornene. Copolymerization of these PCL macromonomers with norbornene and polymerizable derivatives has been catalyzed by the [RuCl₂(p-cymene)]₂ PCy₃/(trimethylsilyl)diazomethane complex yielding a series of poly(norbornene)-graft-poly(ε-caprolactone) copolymers. These new graft copolymers have been characterized by a set of analytical methods, i.e., SEC, ¹H-NMR, FTIR, DSC, and TGA. Furthermore, PCL macromonomers have been polymerized into high molecular weight comb chains of narrow molecular weight distribution (M_w/M_n = 1.10) within high yields (90%). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2447–2455, 1999     

Phase behavior of modified montmorillonite– poly(ϵ‐caprolactone) nanocomposites

The thermal behavior and overall isothermal crystallization kinetics of a series of organophilic modified montmorillonite–poly(?‐caprolactone) nanocomposites were investigated. In general, the thermal behavior was influenced more by the type of dispersion than by the clay content. For nanocomposites in which silicate platelets were predominantly dispersed in the polymer matrix to give exfoliated structures, the thermal properties were improved with respect to those of neat poly(?‐caprolactone), whereas in those cases in which simply intercalated structures were attained, the thermal properties regularly decayed as the clay content increased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1321–1332, 2004     

Organic–inorganic hybrid diblock copolymer composed of poly (ε‐caprolactone) and poly(MA POSS): Synthesis and its nanocomposites with epoxy resin

Organic–inorganic hybrid diblock copolymers composed of poly(ε‐caprolactone) and poly(MA POSS) [PCL‐b‐P(MA POSS)] were synthesized via reversible addition‐fragmentation chain transfer polymerization of 3‐methacryloxypropylheptaphenyl polyhedral oligomeric silsesquioxane (MA POSS) with dithiobenzoate‐terminated poly(ε‐caprolactone) as the macromolecular chain transfer agent. The dithiobenzoate‐terminated poly(ε‐caprolactone) (PCL‐CTA) was synthesized via the atom transfer radical reaction of 2‐bromopropionyl‐terminated PCL with bis(thiobenzoyl)disulfide in the presence of the complex of copper (I) bromide with N,N,N′,N″,N″‐pentamethyldiethylenetriamine. The results of molecular weights and polydispersity indicate that the polymerizations were in a controlled fashion. The organic–inorganic diblock copolymer was incorporated into epoxy to afford the organic–inorganic nanocomposites. The nanostructures of the organic–inorganic composites were investigated by means of transmission electron microscopy and dynamic mechanical thermal analysis. Thermogravimetric analysis shows that the organic–inorganic nanocomposites displayed the increased yields of degradation residues compared to the control epoxy. In the organic–inorganic nanocomposites, the inorganic block [viz., P(MA POSS)] had a tendency to enrich at the surface of the materials and the dewettability of surface for the organic–inorganic nanocomposites were improved in terms of the measurement of surface contact angles. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Transport and mechanical properties of blends of poly(ϵ‐caprolactone) and a modified montmorillonite‐ poly(ϵ‐caprolactone) nanocomposite

The structural characterization and transport properties of blends of a commercial high molecular weight poly(?‐caprolactone) with different amounts of a montmorillonite‐poly(?‐caprolactone) nanocomposite containing 30 wt % clay were studied. Two different vapors were used for the sorption and diffusion analysis—water as a hydrophilic permeant and dichloromethane as anorganic permeant—in the range of vapor activity between 0.2 and 0.8. The blends showed improved mechanical properties in terms of flexibility and drawability as compared with the starting nanocomposites. The permeability (P), calculated as the product of the sorption (S) and the zero‐concentration diffusion coefficient (D₀), showed a strong dependence on the clay content in the blends. It greatly decreased on increasing the montmorillonite content for both vapors. This behavior was largely dominated by the diffusion parameters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1118–1124, 2002     

Biodegradable highly porous interconnected poly(ε-caprolactone)/poly(L-lactide-co-ε-caprolactone) scaffolds by supercritical foaming for small-diameter vascular tissue engineering

Biodegradable ?4 mm tubular porous poly(ε-caprolactone)/poly(L-lactide-co-ε-caprolactone) (PCL/PLCL) scaffolds are fabricated successfully via one-step microcellular supercritical carbon dioxide foaming process. The effect of blending ratio on the rheology, pore structures, mechanical property, wettability, and biocompatibility of PCL/PLCL blends tubular scaffold are reported. Rheological results show that PCL matrix and PLCL dispersed phase has good compatibility. The melt strength of PCL can be enhanced obviously by adding PLCL. With an increase of PLCL content from 10 to 30 wt%, the pore size increases from 7.6 to 24.9 μm due to the homogeneous nucleation effect. The maximum open-cell content can reach 77% for PCL/PLCL foamed sample. Cyclical tensile and compliance tests show that few content of dispersed PLCL (10–20 wt%) improves the flexibility and recoverability. Cell viability results demonstrate that human umbilical vein endothelial cells (HUVECs) cultured on all PCL/PLCL porous scaffolds exhibit a typical spindle-like cell morphology. Moreover, HUVECs have a higher density and spreading areas on surface of 10% PLCL scaffold. The results gathered in this paper may open a new perspective for the fabrication of small-diameter vascular tissue engineering scaffold.     

Preparation and properties of poly(vinyl alcohol)–vermiculite nanocomposites

A vermiculite (VMT) dispersion in water was blended with aqueous poly(vinyl alcohol) (PVA). The properties of the PVA–VMT nanocomposites greatly depended on the preparation procedure because of the chemical reactions and physical interactions involved. The samples were prepared in two steps to investigate the properties of the PVA–VMT nanocomposites. The VMT was first pretreated and delaminated with hydrochloric acid. The delaminated VMT was then added to the PVA solution with various mixing times. The structure and properties of the films were investigated. From X‐ray diffraction and transmission electron microscopy, the VMT layers were found to be well dispersed individually in the PVA–VMT blends. The effect of the VMT content on the thermal behavior of the PVA–VMT blends was also studied with differential scanning calorimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 749–755, 2003     

Synthesis and conjugation of a triiodohydroxylamine for the preparation of highly X‐ray opaque poly(ε‐caprolactone) materials

To address a need for highly X‐ray opaque biodegradable materials, a series of poly(ε‐caprolactone) derivatives were prepared using oxime post‐polymerization modification to conjugate two different iodinated hydroxylamines. These materials were synthesized with up to 32 wt. % iodine content and demonstrated improved X‐ray contrast relative to both the ketone precursors and previously reported monoiodinated materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 787–793     

Synthesis of poly(γ-methoxypropylmethylsilylene) and poly(γ-methoxypropylmethylsilylene-co-di-n-hexylsilylene)

The synthesis of γ;-methoxypropylmethyldichlorosilane, and its subsequent polymerization and copolymerization with di;-n;-hexyldichlorosilane through the reductive coupling with sodium has been accomplished. The resulting polymers contain methyl ether side groups that allow further synthetic transformations on the polysilane backbone. For poly (γ;-methoxypropylmethylsilylene) these groups impart solubility characteristics different than typical alkyl and aryl substituted polysilanes. These new polymers and copolymers have been characterized by GPC and ¹H-, ¹³C-, and ²⁹Si-NMR. © 1994 John Wiley & Sons, Inc.     

Isothermal crystallization kinetics of poly(3‐hydroxybutyrate)/layered double hydroxide nanocomposites

Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006