Water‐vapor permeation in semicrystalline and molten poly(octadecyl acrylate)

The water‐vapor permeability of poly(octadecyl acrylate) (PA‐18) was measured as a function of temperature in the region traversing its melting point (50 °C). The molten‐state permeability of PA‐18 is comparable to that of shorter side‐chain methacrylate polymers. Water permeability in the semicrystalline state of PA‐18 is similar to that of polyethylene at comparable crystallinity levels. The permeation switch, or change in permeability with the traversing of the melting point, for water is discussed in the context of previous results for other penetrants in this and other side‐chain crystalline polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 979–984, 2001     

The morphology of poly(vinylidene fluoride) crystallized from blends of poly(vinylidene fluoride) and poly(ethyl acrylate)

A combined optical and electron microscopical study has been carried out of the crystallization habits of poly(vinylidene fluoride) (PVF₂) when it is crystallized from blends with noncrystallizable poly(ethyl acrylate) (PEA). The PVF₂/PEA weight ratios were 0.5/99.5,5/95, and 15/85. Isothermal crystallization upon cooling the blends from the single-phase liquid region was carried out in the range 135–155°C, in which the polymer crystallizes in the α-orthorhombic unit cell form. The 0.5/99.5 blend yielded multilayered and planar lamellar crystals. The lamellae formed at low undercoolings were lozenge shaped and bounded laterally by {110} faces. This habit is prototypical of the dendritic lateral habits exhibited by the crystals grown from the same blend at high undercoolings as well as by the constituent lamellae in the incipient spherulitic aggregates and banded spherulites that formed from the 5/95 and the 15/85 blends, respectively. In contrast with the planar crystals grown from the 0.5/99.5 blend, the formation of the aggregates grown from the 5/95 blend is governed by a conformationally complex motif of dendritic lamellar growth and proliferation. The development of these aggregates is characterized by the twisting of the orientation of lamellae about their preferential b-axis direction of growth, coupled with a fan-like splaying or spreading of lamellae about that axis. The radial growth in the banded spherulites formed from the 15/85 blend is governed by a radially periodic repetition of a similar lamellar twisting/fan-like spreading growth motif whose recurrence corresponds to the extinction band spacing. This motif differs in its fan-like splaying component from banding due to just a helicoidal twisting of lamellae about the radial direction. © 1993 John Wiley & Sons, Inc.     

Electrospun cellulose acetate/poly(vinylidene fluoride) nanofibrous membrane for polymer lithium-ion batteries

The membranes for gel polymer electrolyte (GPE) for lithium-ion batteries were prepared by electrospinning a blend of poly(vinylidene fluoride) (PVdF) with cellulose acetate (CA). The performances of the prepared membranes and the resulted GPEs were investigated, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), porosity, hydrophilicity, electrolyte uptake, mechanical property, thermal stability, AC impedance measurements, linear sweep voltammetry, and charge–discharge cycle tests. The effect of the ratio of CA to PVdF on the performance of the prepared membranes was considered. It is found that the GPE based on the blended polymer with CA:PVdF =2:8 (in weight) has an outstanding combination property-strength (11.1 MPa), electrolyte uptake (768.2 %), thermal stability (no shrinkage under 80 °C without tension), and ionic conductivity (2.61 × 10^?3 S cm^?1). The Li/GPE/LiCoO₂ battery using this GPE exhibits superior cyclic stability and storage performance at room temperature. Its specific capacity reaches up to 204.15 mAh g^?1, with embedded lithium capacity utilization rate of 74.94 %, which is higher than the other lithium-ion batteries with the same cathode material LiCoO₂ (about 50 %).     

Polymer monolayers with a small viscoelastic linear regime: equilibrium and rheology of poly(octadecyl acrylate) and poly(vinyl stearate)

The equilibrium properties of monolayers of two polymers: poly(octadecyl acrylate) and poly(vinyl stearate) on water have been measured. The surface pressure (Pi) versus surface concentration (Gamma) curves indicate that the water-air interface is a poor solvent for both polymers. The thermal expansivity shows a sharp change near room temperature. This behavior is typical of a glass transition; this is the first time that such a plot is observed for Langmuir films. The Pi vs Gamma curves measured by the continuous compression method show strong anisotropy effects. They also show that the monolayer is brought into nonequilibrium states depending on the compression rate. Within the linear regime, the relaxation experiments were bimodal. The longest relaxation time strongly increases as T is decreased, which might be compatible with the high increase of viscosity in the glass transition. The oscillatory barrier experiments showed that the maximum strain of the linear regime is smaller than 3% for both monolayers. The Fourier-transform analysis of the oscillatory experiments beyond the linear regime points out the contribution of different harmonics in the response function. Oscillations in the nonlinear regime show hysteresis cycles. The results obtained indicate that some of the previously published data for these polymer monolayers correspond to nonequilibrium states.     

Swelling behavior of poly(sodium acrylate) gels crosslinked by aluminum ions

The cylindrical poly(sodium acrylate) gel (SA gel) was synthesized in the glass capillary using aluminum ions as the crosslinker. The swelling ratio of the gel was measured after the repeated exchange of solvent (distilled deionized water, about pH 5.8). The gel exhibited two relaxation processes; at first the gel swells rapidly as exchange of water (the swelling process), then shrinks very slowly (the shrinking process). In order to reveal the microscopic structural change (especially, the formation of hydrogen bonding) by water exchange, attenuated total refraction (ATR) Fourier transform infrared (FT-IR) spectroscopy was applied to the gels with different swelling ratio. The IR absorption peaks of the gel were assigned based on those of poly(sodium acrylate) aqueous solutions at different pH. On the swelling process, the carboxyl groups were gradually protonated, and the intermolecular hydrogen bonding started to form in the gel with maximum swelling ratio. On the shrinking process, the formation of hydrogen bonding gradually increased with long-time repeated water exchange which resulted in the shrinkage of the gel. Effects of the repeated water exchange on the swelling behavior were discussed in terms of the exchange of counter ions and the formation of hydrogen bonding.     

Characteristic ratio of poly(tetrahydrofurfuryl acrylate) and poly(2-ethylbutyl acrylate)

The synthesis, characteristic ratio C_∞ and glass transition temperature (T_g) of poly(tetrahydrofurfuryl acrylate) (PTHFA) and of poly(2-ethylbutyl acrylate) (P2EBA) are reported. P2EBA has slightly lower flexibility (C_∞ = 9.2) than PTHFA (C_∞ = 8.6), mainly because of the higher bulkiness of its side group and the closer proximity to the main chain. The C_∞ results compared with the corresponding polymethacrylates show an increase in flexibility due to the absence of the α-methyl group. Comparison with poly(methyl acrylate) clearly shows the influence of the bulkiness of the side group on the chain flexibility. The lower T_g of P2EBA than that of PTHFA may be explained by the higher flexibility of the 2-ethylbutyl side group. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1589–1592, 1997     

Preparation of fluoride anion responsive poly(N-vinylcarbazole)-borane complexes

A series of novel fluoride anion responsive materials were facilely prepared by complex formation of poly(N-vinylcarbazole) with organoboron compounds in tetrahydrofuran. After addition of fluoride anion, visual color changes of fluorescence emission from green to blue were observed. The ¹¹B NMR spectra shown that poly(N-vinylcarbazole)-borane complexes were converted to poly(N-vinylcarbazole) and fluoroborate in the presence of fluoride anion. Among the obtained poly(N-vinylcarbazole)-borane complexes prepared, poly(N-vinylcarbazole)-triethylborane complex exhibited the most distinct visual changes in fluorescence emissions.     

Interaction between water and polymer chains in poly(hydroxyethyl acrylate) hydrogels

Polymer networks of different cross-linking densities were prepared by copolymerisation of hydroxyethyl acrylate and ethylene glycol dimethacrylate. The average molecular weight between cross-links as well as the polymer chain mobility were characterised by means of dynamic–mechanical spectroscopy. Equilibrium sorption isotherms and the water uptake in immersion in liquid water allowed the determination of the Flory–Huggins interaction parameter between water molecules and polymer chain segments, which decreased with the water activity in the hydrogel and increased with the cross-linking density as a consequence of the hydrophobic character of the cross-linking agent. Dynamic sorption and desorption experiments were used to determine the diffusion coefficient. Received: 11 November 1999 Accepted: 28 July 2000     

Elasticity of polymer gels: Effect of solvent quality on the shear modulus of poly(vinyl acetate) networks

The dependence of the shear modulus and of the swelling equilibrium concentration of polyvinylacetate gel homologues in equilibrium with excess isopropyl alcohol is investigated in the temperature range 30≤T≤70°C. At the theta temperature (T=52°C) the volume elastic modulus was also determined and compared with the shear modulus. The results are interpreted in terms of a free-energy function derived on the basis of the network unfolding hypothesis.     

Miscibility and ferroelectric behavior in blends of poly(vinylidene fluoride/trifluoroethylene) and poly(vinyl acetate)

The blend system containing a poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)] copolymer (68/32 mol %) and poly(vinyl acetate) (PVAc) was miscible from the results of differential scanning calorimetry (DSC) studies that exhibit the presence of a single, composition‐dependent glass transition temperature (T_g) and a strong melting point depression for the semicrystalline P(VDF/TrFE) component. However, differences between the DSC and dielectric measurements, which showed a separate P(VDF/TrFE) T_g peak, suggests that the P(VDF/TrFE)/PVAc blends are actually partially miscible. Because of the lower dielectric constant of PVAc and the reduced sample crystallinity caused by the addition of PVAc, both the dielectric constant and the remanent polarization of the copolymer blends decrease with increasing PVAc content. The presence of a small amount of PVAc stabilized the anomalous ferroelectric behavior of ice–water‐quenched P(VDF/TrFE), and the blend portrayed normal polarization reversal behavior after adding only 1 wt % PVAc. The piezoelectric response suggests small changes with an increasing number of poling cycles. It is believed that PVAc affects the D‐E hysteresis behavior at the interface between crystalline and amorphous phases, although much work remains to be done to confirm this hypothesis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 927–935, 2003     

Calorimetric study of free-radical polymerized poly(p-biphenyl acrylate) and poly(p-cyclohexylphenyl acrylate)

DSC traces and specific heat data for poly(p-diphenyl acrylate) (PPBA) and poly(p-cyclohexylphenyl acrylate) (PPCPA) obtained by radical polymerization are reported. The results indicate the existence of a definite ordered phase and of a reversible firstorder solid–liquid transition in both polymers although x-ray diffraction studies showed that they are not crystalline in the conventional sense. The extent of the ordered phase present in each polymer is calculated, and the problems involved in such determination by thermal measurements are discussed. On the basis of the experimental results reported here in conjunction with the x-ray data, models are proposed for the morphology of these polymers.     

Swelling of poly(methacrylic acid) gels and adsorption of L-lysine and its polymer on the gels

Poly (methacrylic acid) gels (PMAA gels) of various degrees of crosslinking were prepared and the dissociation behavior of these gels was examined; the swelling behavior was investigated as a function of the solution pH values. A reentrant phenomenon of swelling was observed and interpreted based on the Flory-Huggins equation and the Donnan equilibrium formula. Moreover, adsorption of L-lysine, oligo(L-lysine)s (Lys-n,n=3, 9, and 19) and poly(L-lysine) onto PMAA gels from aqueous solutions was investigated under different conditions of pH and concentration of adsorbate. The adsorption ratio of L-lysine onto PMAA gel is dependent on both the pH of solution and the degree of crosslinking. In a pH range between 8 and 9, the protonated form of L-lysine is strongly adsorbed on the PMAA gel by electrostatic interactions. Oligomers and polymer of L-lysine are adsorbed in a somewhat different way from the monomeric L-lysine. In addition, the desorption behavior of L-lysine from PMAA gels by a change in pH was also investigated.     

Equilibrium study of polymer–polymer complexation of poly(methacrylic acid) and poly(acrylic acid) with complementary polymers through cooperative hydrogen bonding

The degree of linkage, θ, defined as the ratio of the binding groups to the total of potentially interacting groups and the stability constant K of the polymer–polymer complexes in the systems poly(methacrylic acid)–poly(ethylene glycol), poly(acrylic acid)–poly(ethylene glycol), and poly-(methacrylic acid)–poly(vinyl pyrrolidone) in aqueous and aqueous alcohol media were determined as a function of temperature by potentiometric titration. It was found that θ and K are strongly dependent on chain length, temperature, and medium and that hydrophobic interaction is a significant factor in the stabilization of the complexes. The enthalpy and entropy changes and the cooperativeness parameter of the systems were calculated. A mechanism for the complexation in terms of cooperative interaction was proposed.     

Hollow nanoparticles via stepwise complexation and selective decomplexation of poly(ethylene imine)

The preparation of hollow nanoparticles with amino groups on the inner side via the stepwise complexation and selective decomplexation of poly(ethylene imine) is presented.     

Solution properties of poly(methyl acrylate) and (1:1) poly(styrene-co-methyl acrylate)

Poly(methyl acrylate) (PMA) and 1:1 poly(styrene-co-methyl acrylate) (PSMA) were prepared by solution and bulk polymerization, respectively. The copolymer was analyzed with NMR to ascertain its composition and microstructure. The solution properties of unfractionated PMA and fractionated PSMA in ethyl acetate were investigated by light-scattering and viscosity techniques at 35°C. Narrow composition heterogeneity as revealed from the light-scattering measurements in different solvents justified the use of a single solvent for the copolymer characterization. The equations relating the limiting viscosity number to molecular weight, the molecular dimension to molecular weight, etc., were found for homopolymer and copolymers in ethyl acetate at 35°C. In the evaluation of the Flory constant K for the unperturbed state by methods based on Flory-Fox-Schaefgen, Kurata-Stockmayer, and Stockmayer-Fixman expressions, only the first method gave a value for PMA in ethyl acetate, consistent with that obtained in other solvents, whereas similar values of K were obtained by the three methods for PSMA in ethyl acetate. The studies indicate reduced thermodynamic interaction for PSMA–ethyl acetate compared to PMA–ethyl acetate, but increased steric effect in the copolymer compared with the homopolymer.     

Poly(methyl acrylate)/poly(hydroxyethyl acrylate) sequential interpenetrating polymer networks. Miscibility and water sorption behavior

Sequential poly(methyl acrylate)/poly(hydroxyethyl acrylate) interpenetrating polymer networks with different poly(hydroxyethyl acrylate) contents were prepared by free radical polymerization of hydroxyethyl acrylate inside the previously polymerized poly(methyl acrylate) network. Differential scanning calorimetry on dry samples shows that the interpenetrating polymer networks exhibit phase separation, and no differences are found between the glass transition temperatures of the two phases present in the interpenetrating polymer network and those of the pure components. Thermally stimulated depolarization current experiments were used to study the influence of water sorption on the mobility of the different molecular groups in the poly(hydroxyethyl acrylate) phase of the interpenetrating polymer network. Isothermal water sorption of the interpenetrating polymer networks and pure poly(methyl acrylate) and poly(hydroxyethyl acrylate) networks is analyzed with different theories to compare the behavior of the poly(hydroxyethyl acrylate) phase in the interpenetrating polymer networks with that of the pure poly(hydroxyethyl acrylate) network. Diffusion coefficients of water in the interpenetrating polymer networks are obtained by means of dynamic sorption experiments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1587–1599, 1999     

Miscibility of poly(vinyl chloride) with poly(methyl-co-hexyl acrylate) and poly(methyl-co-2 ethyl hexyl acrylate)

The miscibility and phase behavior in blends of PVC with poly(methyl-co-hexyl acrylate)[MHA] and poly(methyl-co-2 ethyl hexyl acrylate)[MEH] were studied. It was found that PVC is miscible with MHA copolymers having a HA volume fraction from 0.30 to 0.92 and MEH copolymers having an EH volume fraction from 0.30 to 0.83 at 100°C. By applying the mean field theory to the phase diagrams of these blend systems, segmental interaction parameters which represent the binary interaction between different monomer units were estimated. The calculated values reflect the fact that the miscibility window observed for PVC/MHA and PVC/MEH blend systems was attributed to the effect of repulsion between different monomer units within the copolymer. To investigate the effect of specific interaction on the miscibility for these blend systems, an attempt was also made to describe the blend interaction parameter as a function of polar group concentration in the acrylate copolymer. The blend interaction parameter values exhibit a u-shaped curve as a function of the weight fraction of C?O group in the copolymer, and the lowest blend interaction parameter value appears at about 0.24 C?O weight fraction.     

Conformational effect of silica-supported poly(octadecyl acrylate) on molecular-shape selectivity of polycyclic aromatic hydrocarbons in RP-HPLC.

Poly(octadecyl acrylate) with a terminal reactive group was synthesized by radical telomerization in various solvents. The polymers were grafted onto porous silica for use in RP-HPLC, and the molecular recognition ability was investigated along with the selectivity for the structural isomers of polycyclic aromatic hydrocarbons. The mechanism of selectivity was also investigated with differential scanning calorimetry and NMR spectroscopic observations.     

Interpenetrating polymer networks of poly(2,6-dimethyl-1,4 phenylene oxide) and poly(urethane acrylate). I

Simultaneous full and pseudo- interpenetrating polymer networks of poly(2,6-dimethyl-1,4 phenylene oxide) (PPO) and a poly(urethane acrylate) (PUA) have been synthesized and characterized by differential scanning calorimetry, ultimate mechanical properties, and electron microscopy. No evidence of phase separation was detected in both the full and pseudo- PPO/PUA networks. The networks exhibited a single glass transition temperature at all the compositions studied. A maximum in tensile strength to break was observed at 25 PPO/75 PUA composition by weight percent.     

Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)

The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by a dilute probe polymer in the presence of a matrix polymer and a small molecule solvent.