Vibrational Modes Analysis of Poly （Vinylidene Fluoride—Trifluoroethylene）

The ground State geometry and vibrational modes of poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] molecular chains have been investigated by ab initio molecular orbital calculation. The gauche bonds in P(VDF-TrFE) are introduced by TrFE monomers. The vibrational Modes are localized within all-trans segments. These results cause the infrared absorption weaker and diffused, and may be responsible for dielectric relaxation of the copolymers.     

Nonisothermal Crystallization Kinetics of Poly(ϵ-Caprolactone)/Montmorillonite Nanocomposites

Montmorillonites modified by hydroxyethylhexadecyldimethyl ammonium bromine were used to prepare poly(?-caprolactone) (PCL)/montmorillonite (MMT) nanocomposites by in situ ring-opening polymerization of ?-caprolactone. Wide-angle X-ray diffraction (WAXD) analysis illustrated that an exfoliated structure of PCL/MMT nanocomposite was obtained. The nonisothermal crystallization kinetics of poly(?-caprolactone) and PCL/MMT nanocomposite was investigated by differential scanning calorimetry (DSC) at various cooling rates. The values of half-time of crystallization (t_1/2) and crystallization rate constant (Z_c) showed that crystallization rate increased with the increase of cooling rates for both PCL and PCL/MMT nanocomposite; however, the crystallization rate of PCL/MMT nanocomposite was faster than that of PCL at a given cooling rate.     

Viscoelastic and Dielectric Behavior of Poly(1‐Butene)/Multiwalled Carbon Nanotube Nanocomposites

Linear viscoelastic properties and dielectric behavior of poly(1‐butene)/multiwalled carbon nanotube (MWCNT) nanocomposites were investigated. Dynamic mechanical analysis showed significant increase in storage modulus in the rubbery regime. The tan δ peak temperature remained constant; however, the peak intensity was lowered for the nanocomposites. In melt rheological studies the nanocomposites showed a shift in crossover frequency to the lower side, suggesting delayed relaxation of the molecular chains in the presence of MWCNT and this shift was found to depend on the content of MWCNT. The dielectric constant increased from 2.2 to 70 for the nanocomposite with 7 wt. % MWCNT. The electrical conductivity increased significantly, from 10^?15 to 10^?3 S/cm. The results of rheology and dielectric studies indicate that a percolation network is formed that is responsible for the observed changes.     

Preparation and Degradation Behaviors of Poly(L-lactide-co-glycolide-co-ε-caprolactone)/1,4-butanediamine Modified Poly(lactic-co-glycolic acid) Blend Film

Abstract

Polymer blending is an attractive method for producing new polymer materials with excellent properties. In this work the blended polymers were prepared from poly(L-lactide-co-glycolide-co-ε-caprolactone) and 1,4-butanediamine modified poly(lactic-co-glycolic acid) (PLLGC/BMPLGA). The hydrophilicity was studied by static water contact angle tests. The in-vitro degradation behaviors of the PLLGC/BMPLGA blended films were investigated during various degradation periods. The results showed that the introduction of the PLLGC reduced the hydrophilicity and degradation rate of the blended polymers while improved the tensile strength and elongation percentage. Therefore, we suggest the blends of the PLLGC and BMPLGA could supply a potential biomaterial for application in the medical field for use as tissue engineering scaffolds or drug delivery.     

Preparation and Physical Properties of Carbon Nanotubes–PVA Nanocomposites

Nanocomposite materials were prepared by incorporating multiwall carbon nanotubes (MWNTs), obtained by acetylene catalytic chemical vapor deposition (CCVD) on Co/Fe‐modified MgO, within poly(vinyl alcohol) (PVA). Before incorporation, nanotubes were oxidized to obtain better compatibilization with the polymer. It has been found that the addition of COOH‐functionalized and purified MWNTs improves the mechanical response, increases the glass transition temperature, and delays the thermal oxidation of PVA. Furthermore, the PVA crystallinity seems to be enhanced by the presence of nanotubes.     

Nonisothermal Crystallization Kinetics of Poly(ϵ-caprolactone)/Zinc Oxide Nanocomposites with High Zinc Oxide Content

Poly(?-caprolactone) (PCL)/zinc oxide (ZnO) nanocomposites (PCLZs) with high ZnO contents were prepared by using ZnO to initiate ring-opening polymerization of ?-caprolactone (?-CL). The Ozawa and Mo equations were chosen to analyze the nonisothermal crystallization kinetics of PCLZs. The results showed that the Ozawa equation was not successful while the Mo equation was successful in describing the nonisothermal crystallization kinetics of PCLZs. When the ZnO content in PCLZs was high, the effect of ZnO content on crystallization behaviors was small and the crystallization rates of PCLZs only increased slightly with the increase of ZnO content. Crystallization activation energies (E_c s) of PCLZs were estimated by Kissinger's method. The results showed that the E_c s of PCLZs with three different ZnO contents were nearly identical within the tolerance, which further demonstrated that the effect of ZnO content on crystallization behaviors was small when the ZnO content in PCLZs was high.     

Designing and Characterization of Poly(L-Lactide)/Poly(ϵ-Caprolactone) Multiblock Copolymers

A series of poly(L-lactide)/poly(?-caprolactone) (PLA/PCL) biodegradable multiblock copolymers was synthesized by a two-step process and characterized. Ring-opening polymerization was used to prepare a series of HO-PLA-PCL-PLA-OH copolymers initiated by hydroxyl-terminated PCL. Then the triblock copolymers and 1,6-hexamethylene diisocyanate (HDI) were reacted with different copolymer/HDI weight ratios. Consequently, a series of PLA/PCL multiblock copolymers with designed molecular chain structure was obtained. Gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and ¹H NMR were used to characterize these copolymers and the results showed that the designed PLA/PCL copolymers had been synthesized. Dynamic mechanical analysis (DMA) was applied to characterize their thermal properties. Stress–strain curves showed that a PLA/PCL copolymer with adjustable mechanical properties had been achieved.     

Rheological Characterization of Poly(3,3′-Diaminodiphenylsulfone Terephthaloylchloride) Solutions in Dimethylsulfoxide

Steadyshear and oscillatory shear rheological measurements were performed to characterize the solution rheological behavior of poly(3,3′-diaminodiphenylsulfone terephthaloylchloride) (P(3,3′-DDS-TPC)) in dimethyl sulfoxide (DMSO). The effects of temperature, concentration, and weight-average molar mass () on the rheological properties were investigated. From the temperature dependence of zero-shear viscosity, the flow activation energies, E_η, of P(3,3′-DDS-TPC)/DMSO solutions were calculated. Both the overlap concentration, C*, and the entanglement concentration, C_e, were determined from the concentration dependence of the specific viscosity η_sp. All the P(3,3′-DDS-TPC) solutions, we studied, can be separated into three regimes: the dilute, semidilute-unentangled, and entangled regime with slopes of 1, 1.3, and 3.9, of concentration versus η_sp plots, respectively, which are consistent with scaling predictions for flexible polymers in a good solvent.     

A Study on Properties of Poly(vinyl chloride)/Poly(α-methylstyrene-acrylonitrile) Binary Blends

Blends of poly(vinyl chloride) (PVC) and poly(α-methylstyrene-acrylonitrile) (α-MSAN) with variable composition of 0 to 100 wt% were prepared by melt mixing. Properties of binary blends were extensively studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), heat distortion temperature (HDT), mechanical properties, melt flow rate (MFR), and scanning electron microscope (SEM). A single glass transition temperature (T_g ) was observed by DSC and DMTA, indicating miscibility between PVC and α-MSAN. The results of ATR-FTIR indicated that specific strong interactions were not present in the blends and the miscibility was due to interaction between –CN and PVC. With increasing amount of α-MSAN, considerable increase occurred in HDT, flexural strength, and flexural modulus compared with reverse s-shaped decrease in impact strength and elongation at break. Synergism was observed in tensile strength and MFR. No phase separation was observed in SEM photographs, indicating miscibility between PVC and α-MSAN. In addition, morphology of the impact-fractured surfaces, including roughness and non-fused particles, correlated well with the mechanical properties and MFR.     

Preparation and Rheological Characteristics of Ethylene‐Vinyl Acetate Copolymer/Organoclay Nanocomposites

Ethylene‐vinyl acetate copolymer (EVA) with 40 wt.% vinyl acetate content (EVA40)/organoclay nanocomposites were prepared using a melt intercalation method with several different clay concentrations (2.5, 5.0, 7.5, and 10.0 wt.%). X‐ray diffraction confirmed the formation of exfoliated nanocomposite in all cases with disappearance of the characteristic peak corresponding to the d‐spacing of the pristine organoclay. Transmission electron microscopy studies also showed an exfoliated morphology of the nanocomposites. Morphology and thermal properties of the nanocomposites were further examined by means of scanning electron microscopy (SEM) and thermo gravimetric analysis (TGA), respectively. Rheological properties of the EVA40/organoclay nanocomposites were investigated using a rotational rheometer with parallel‐plate geometry in both steady shear and dynamic modes, demonstrating remarkable differences with the clay contents in comparison to that of pure EVA40 copolymer.     

Shear Effect on Morphology of Poly(Butylene Terephthalate)/Poly(Styrene‐co‐Acrylonitrile) Blends

Abstract

The shear flow effect on the morphology of poly(butylene terephthalate)(PBT)/poly(styrene‐co‐acrylonitrile)(SAN) was studied by a parallel plate type shear apparatus. In PBT/SAN = 20/80 blend, particle size of dispersed domains was governed by both break‐up and coalescence processes, and it was much affected by shear rate. The minimum particle size was observed at a certain shear rate. This phenomenon can be explained by the shear matching effect of PBT and SAN; that is, the viscosity ratio of PBT to SAN changed with shear rate and the finest morphology was obtained at the appropriate viscosity ratio. Similar behavior was also observed for PBT/SAN = 70/30 (PBT was the matrix), even though the particle size was larger than that of PBT/SAN = 20/80. For PBT/SAN = 10/90 blend, the sample showed a complicated appearance during shearing. A translucent region correlated to the fine morphology was observed more than twice with increasing shear rate. This phenomenon could not be explained by the viscosity matching effect only. It was affected by small changes in the balance of breaking‐up and coalescence effects.     

Non‐isothermal Melt Crystallization Kinetics for Poly(ethylene 2,6‐naphthalate) (PEN)/Montmorillonite Nanocomposites Prepared by Melt Intercalation

The nonisothermal crystallization behaviors for poly(ethylene 2,6‐naphthalate) (PEN) and poly(ethylene 2,6‐naphthalate) (PEN)/montmorillonite nanocomposites prepared by melt intercalation were investigated using differential scanning calorimetry (DSC). The Jeziorny, Ozawa, Ziabicki, and Kissinger models were used to analyze the experimental data. Both the Jeziorny and the Ozawa models were found to describe the nonisothermal crystallization processes of PEN and PEN/montmorillonite nanocomposites fairly well. The results obtained from the Jeziorny and the Ozawa analysis show that the montmorillonite nanoparticles dispersed into PEN matrix act as heterogeneous nuclei for PEN and enhance its crystallization rate, accelerating the crystallization, but a high‐loading of montmorillonites restrain the crystal growth of PEN. The analysis results from the Ziabicki and the Kissinger models further verify the dual actions stated above of the montmorillonite nanoparticles in PEN matrix.     

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). III. Rheological Kinetics of Cross‐Linking Reaction

Abstract

The kinetics of the thermally activated cross‐linking reaction of poly(vinyl methyl ether) (PVME) were investigated rheologically by evaluating the viscoelastic material functions such as elastic storage modulus, G′, viscous loss modulus, G″ and complex dynamic viscosity, η*, during the curing process, both isothermally and nonisothermally. The isothermal kinetics reaction was described using a phenomenological equation based on the Malkin and Kulichikhin model, which was predicated originally for the isothermal curing kinetics of thermosetting polymers followed by differential scanning calorimetery (DSC) and was found to be applicable for rheokinetic reactions as well. An excellent representation of the data was obtained using this model; the rate of the reaction was found to be second order regardless of the temperature, which is in good agreement with literature data. The temperature dependence of the cross‐linking rate constant was described by an Arrhenius plot with an apparent activation energy equal to 60–62 kJ mol^?1, in reasonable agreement with the value obtained previously from the temperature dependence of gel time, t _gel. The nonisothermal kinetics reaction rate was described by a model that included the classical rate equation, the Arrhenius equation, and the time–temperature relationships. The apparent activation energy obtained nonisothermally was found to be frequency independent and equal to 72 kJ mol^?1, in very good agreement with the value obtained isothermally from the temperature dependence of t _gel in part II.     

Synthesis and Characterization of Novel Poly(1‐Naphthylamine)‐Montmorillonite Nanocomposites Intercalated by Emulsion Polymerization

Nanocomposites of montmorillonite (MMT) with poly(1‐naphthylamine) (PNA) is investigated for the first time by emulsion polymerization using three different oxidants. Polymerization of PNA was confirmed by Fourier transformation infrared (FT‐IR) as well as UV‐visible spectra. The in situ intercalative polymerization of PNA within MMT layers was confirmed by FT‐IR, X‐ray diffraction, conductivity; scanning electron microscopy (SEM) as well as transmission electron microscopy studies. X‐ray diffraction revealed intercalated as well as exfoliated structures of PNA/MMT nanocomposites, which were compared with the reported polyaniline‐MMT nanocomposites. It was found that the increase in the concentration of PNA in the interlayer galleries of MMT led to destruction of the layered clay structure resulting in exfoliation of the nanocomposite. Conductivity of the nanocomposites was found to be in the range of 10^?3 to 10^?2 S cm^?1 which was found to be higher than the ones reported for polyaniline‐clay nanocomposites as well as PEOA‐OMMT nanocomposites at similar concentrations of intercalated species. The morphology of PNA/MMT nanocomposites was found to be governed by the nature of the oxidant used.     

Dielectric Relaxations and Structures of Nanoclay in Solution Cast Poly(Ethylene Oxide)– Montmorillonite Clay Nanocomposites

The relative complex dielectric function, electric modulus and alternating current electrical conductivity spectra and complex impedance plane plots of aqueous solution cast poly(ethylene oxide)–montmorillonite clay (PEO–MMT) nanocomposite films were investigated over the frequency range 20 Hz to 1 MHz at ambient temperature. The intercalated and exfoliated structures of nanoclay dispersed in PEO matrix were recognized by the significant change in real part of dielectric function with clay concentration in the range 0%–20 wt%. The relaxation times corresponding to PEO chain segmental motion and ionic conduction relaxation processes were used to explore the interactions compatibility between PEO molecules and the dispersed MMT clay nanoplatelets and their effect on PEO chain dynamics. Real part of conductivity spectra of these nanocomposites over five decades of frequency has nonlinear behavior, which is influenced by the MMT clay concentration. The complex impedance plane plots confirm the bulk properties of these nanocomposites over the experimental frequency range.     

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). II. Rheological Behavior at the Gel Point

Abstract

Isothermal time evolution measurements at different constant temperatures (170°C, 180°C, and 190°C) over a wide range of frequency for the thermal cross‐linking process of poly(vinyl methyl ether), PVME, have been investigated rheologically. At the onset of cross‐linking (t _onset) the elastic storage modulus, G′, increases abruptly. The magnitude of the elevation in G′ and the value of t _onset were found to be temperature‐dependent. Similar behavior was observed for both the viscous loss modulus, G″ and the complex dynamic viscosity, η*; however, the value of G″ shows a very low sensitivity to the cross‐linking process compared to G′ and η* at the same experimental conditions. The gel point, t _gel, was evaluated from the point of intersection in plots of tan δ vs. curing time for different constant shear frequencies. At the gel point tan δ is no longer frequency‐dependent, and all curves cross‐over, indicating the validity of the Winter–Chambon criterion. The value of t _gel obtained from the coincidence of G′ and G″ was about 10 min longer than that determined from tan δ vs. t, indicating that the crossover of G′ and G″ is not be considered as a general method for evaluation of t _gel. The value of the apparent activation energy of gelation determined from the temperature dependence of t _gel was 74 kJ mol^?1 in good agreement with literature values for other different systems. At the gel point G′ and G″ showed a power law with shear frequency, i.e., G′ ～ G″ ～ ω _n with critical exponents equal to 0.64 and 0.75, respectively, in close agreement with the percolation theory (n = 2/3). The zero shear viscosity, η₀, and the equilibrium shear modulus, G _eq, can also be expressed in power low scaling functions with the relative distance from the gel point, ? i.e., η₀ ～ ?^?k and G _eq ～ ? ^z with k = 1.3 and z = 2.4 in good agreement with the predicted values based on the percolation theory.     

Poly(acrylamide‐co‐acrylic acid)/Poly(vinyl pyrrolidone) Polymer Blends Prepared by Dispersion Polymerization

The structure and properties of a three‐component system, a poly(acrylamide‐co‐acrylic acid)/poly(vinyl pyrrolidone) [P(AM‐co‐AA)/PVP] polymer blend prepared by dispersion polymerization, were studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the resulting P(AM‐co‐AA) microspheres with diameters between 200–300 nm were well‐dispersed in the PVP matrix. Fourier transform infrared spectra (FTIR) showed that intermolecular hydrogen bonding interaction occurred between the dispersed phase and the continuous phase. The mechanical properties of P(AM‐co‐AA)/PVP polymer blends were also determined. With different mass ratios of acrylamide to acrylic acid, it was found that the blends had better mechanical properties with increased AA content.     

Preparation and Characterization of Poly(L-lactide-co-glycolide-co-ε-caprolactone)/Nano-biaoactive Glass-Nano-β-tricalcium Phosphate Composite Scaffolds

Abstract

Polymeric/ceramic composite scaffolds that are biocompatible and biodegradable are widely used for tissue engineering applications. In this work a series of poly(L-lactide-co-glycolide-co-ε-caprolactone)/nano-biaoactive glass-nano-β-tricalcium phosphate composite scaffolds were successfully fabricated and the influences of the inorganic content and freezing temperature on the physical properties were studied. The composite scaffolds with various inorganic contents showed an interconnected pore structure with irregular shapes. The composite scaffolds had a porosity that was reduced with increasing inorganic content and decreasing freezing temperature. The incorporation of inorganic fillers and decreasing freezing temperature improved the mechanical properties of the hybrid scaffolds. By appropriate control of these two factors (10.0?wt% content of NBAG and β-TCP with freezing at ?30?°C) a suitable composite scaffold was prepared as a potential bone tissue engineering implant.