Gas transport in poly(alkoxyphosphazenes)

The permeability of four structurally related poly(alkoxyphosphazenes), three isomers of poly(dibutoxyphosphazenes) (PBuP), and poly(di-neopentyloxyphosphazene) (Pneo-PeP), to 13 gases has been determined by the time-lag method. Systematic variations in chemical structure have shown a large effect of side chains on permeabilities and permselectivities. The permeability of poly(di-n-butoxyphosphazene) (Pn-BuP) is of the order of 10^?8 cm³ (STP) cm/(cm² s cmHg) for many gases, and the value for a large gas is higher than that for a smaller one. For small gases such as He and H₂, poly(di-sec-butoxyphosphazene) (Ps-BuP) is as permeable as Pn-BuP, but its diffusivities for larger gases such as Xe and C₃H₈ are about one order lower than those of Pn-BuP. While the permselectivity of Pn-BuP is determined by the solubility, that of Ps-BuP depends on both the diffusivity and solubility factors. The property of poly(diisobutoxyphosphazene) (Pi-BuP) is intermediate between them. These polymers are constitutionally identical, and the only difference is the arrangements of carbons in the side groups. As the side chains become bulky, the permeability decreases, whereas the permselectivity increases. Further decreases of diffusivity and then permeability are observed for Pneo-PeP, whose side groups have one more methyl group than does Pi-BuP. But the solubility data are not much different from other three polymers and the diffusivity factor becomes more significant in permselectivity. The diffusivity depends on the polymer structure much more than does the solubility. The relationships between chemical structure and gas diffusivity and solubility are discussed.     

Gas transport in poly(vinyl cyclohexanecarboxylate)

Low-pressure gas permeation measurements were performed on poly(vinyl cyclohexanecarboxylate) to evaluate its transport characteristics. The transport data of CO₂, O₂, N₂, He, and Ar, were presented as a function of temperature ranging from 15 to 85°C. The apparent transport parameters were determined by the time lag method above and below the glass transition temperature and they were compared with other polymers of similar chemical structures. The side chain of the polymer has a bulky cyclohexyl group, which seemed to increase gas diffusivity. The activation energy for diffusion seemed to be related with the polarity of side chain. The relationships between gas diffusivity, physical properties, and chemical structure were qualitatively discussed in comparison with the data on poly(vinyl benzoate) and poly(vinyl acetate).     

Gas transport in poly(vinyl benzoate)

The transport parameters of nine gases (O₂, N₂, CO₂, He, Ne, Ar, Kr, Xe) through poly(vinyl benzoate) (PVB) have been measured by the time lag method above and below the glass transition temperature, T_g The results are compared with the related data of poly(vinyl acetate) (PVAc) by Meares and discussed as the effect of replacement of the methyl group by a phenyl group in the side chain of PVAc. Small molecules, such as H₂, He, and Ne, diffuse more easily through PVAc than PVB, but the tendency is reversed for the larger gases. The activation energy for diffusion is proportional to the squares of the Lennard–Jones diameters of the gases below the T_g. On the other hand, above the T_g, linear relation is obtained to the cubes of the diameters. Solubility behavior is discussed by comparing the heats of solution for PVB and PVAc.     

Gas transport properties of MgO filled poly(1-trimethylsilyl-1-propyne) nanocomposites

Magnesium oxide (MgO) nanoparticles were dispersed via solution processing in poly(1-trimethylsilyl-1-propyne) (PTMSP) to form polymer nanocomposites. Transmission electron microscopy was used to determine the extent of particle aggregation in the composites. Both nanocomposite density and CO₂, CH₄, N₂, and H₂ permeability were influenced by nanoparticle loading. Nanocomposite densities were markedly lower than predicted by a two phase additive model. For example, in films containing 75 nominal volume percent MgO, the polymer-particle composite density was 68 percent lower than expected based on an additive model. At this loading, gas permeability coefficients were, depending on the gas, 17-50 times higher than in unfilled PTMSP at similar conditions. The changes in permeability with particle content were interpreted in terms of measured changes in gas solubility with particle content and diffusion coefficients calculated from the permeability and solubility data.     

Gas transport properties of crown-ether methacrylic polymers: poly(1,4,7,10-tetraoxacyclododecan-2-yl) methyl methacrylate

Polymer membranes were prepared by radical polymerization of the 1,4,7,10-(tetraoxacyclododecan-2-yl) methyl methacrylate (CR4MA) monomer and a small quantity of a cross-linking agent ethyleneglycoldimethacrylate. High vacuum pressure techniques were used to evaluate oxygen and helium transport through these membranes at temperatures below and above its glass transition temperature, between 0 and 50 °C. The apparent values of both the permeability and diffusion coefficients are unusually low because of the high packing degree of these polymeric membrane materials. The results obtained were also compared with those determined for polymer membranes derived from their open chain counterparts, the polymer derivatives from methacrylate monomers with a number of oxyethylene units in the ester residue variable between 2 and 6, and with a set of other polymers.     

Gas transport in poly[bis(trifluoroethoxy)phosphazene]

The gas transport parameters of 14 gases in poly[bis(trifluoroethoxy)phosphazene] were determined at temperatures ranging from about 12 to 45°C by the time-lag method. The phosphazene polymer demonstrated a high diffusivity; rather high crystallinity was expected, though. The permeation data determined were between polydimethylsiloxane and low-density polyethylene. The most interesting characteristic shown over the course of experimentation is that poly[bis(trifluoroethoxy)phosphazene] has significantly high solubility for CO₂, as compared to other gases. The polar side groups—i.e., the electron-withdrawing trifluoroethoxy parts—which should contribute specific interaction with CO₂, were shown to be stronger than their interaction with the polar N₂O molecule. The sorption behavior is compared with those of other rubbery polymers, while phosphazene polymer characteristics are also discussed.     

Gas permeation properties of poly(2,5-dialkyl-p-phenyleneethynylene) membranes

Dipropynylbenzenes with alkyl groups (CH₃C ≡ CRC₆H₂RC≡CCH₃, R=n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, 1a–c, respectively) were polymerized with Mo(CO)₆ to afford solvent-soluble poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c). The polymers (2a–c) had high molecular weight over 3×10⁴, and gave free-standing membranes by solution casting method. According to thermogravimetric analysis (TGA), these poly(p-phenyleneethynylene)s showed high thermal stability (T₀ ≥380 °C). The densities of membranes of poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c) were 0.936–0.965, and their fractional free volume (FFV) were relatively large (ca. 0.14–0.15). The oxygen permeability coefficients (PO₂) of membranes of 2a–c were 4.88, 7.06, and 16.6 barrers, respectively.     

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997     

Gas transport in poly(vinyl-p-isopropylbenzoate): Comparison and correlation with some other poly(vinyl esters)

Gas permeability in poly(vinyl-p-isopropylbenzoate) (PVp-i-PrB) was determined by a timelag method. The transport properties were discussed from comparison with the permeability data of other poly(vinyl esters), which were studied previously. All these polymers are structurally related, and the size of a side group or the position of its substituent was changed systematically. The isopropyl group of PVp-i-PrB is attached at the para position of a phenyl ring and is the largest in size. As a result gas diffusivity and therefore permeability were increased. The effect of the substituent on gas diffusivity was explained as it increases the interchain and intrachain distances. The discussion was supported from the comparison of the density data between PVp-i-PrB and other poly(vinyl esters). The diffusion coefficients of six glassy poly(vinyl esters) were correlated at their T_g and good correlations were shown to the free volume and its fraction. On the other hand, gas solubility was little affected by the change of an alkyl group on a phenyl ring. The solubility data of PVp-i-PrB and poly(vinyl benzoate) were shown to be clearly correlated with the critical properties of the penetrants. © 1995 John Wiley & Sons, Inc.     

Some properties of poly(3-hydroxybutyrate)–poly(3-hydroxyvalerate) blends

The melting, crystallization and dynamic mechanical behaviour of blends of bacterially produced poly[D (–)-3-hydroxybutyrate] (PHB) and poly[D (–)-3-hydroxyvalerate] (PHV) have been investigated. Results showed that melt-pressed PHB–PHV blends contained phase-separated domains in the melt which subsequently crystallized as PHB and PHV type spherulites respectively. The two melting regions detected by DTA related to separate melting of PHB and PHV crystallites, which were almost unaffected by the blend composition. The mechanical behaviour of a random copolymer of PHB/HV was compared with that of a blend of almost the same composition, and found to be markedly different.     

Measurement of transport properties of poly(methylmethacrylate-co-methacrylic acid) ion-containing membranes

Several membranes prepared from poly(methylmethacrylate-co-methacrylic acid) and its Li⁺ and Zn²⁺ ionomers were tested for NaCl, creatinine and urea permeability. The permeabilities of the membranes were explained on the basis of pore contents determined from their scanning electron microscope micrographs. All the membranes showed higher permeabilities during the first 2 hours of experimentation. Introduction of Zn²⁺ ions into the copolymer as crosslinking agent did not have much effect on the membrane properties but the properties of the copolymer were modified.     

Gas transport in poly(n-alkyl acrylate)/poly(m-alkyl acrylate) blends

Poly(n-alkyl acrylate)s can have side chains that crystallize independently of the main chain; side-chain length can thus be used as a tunable parameter to control the gas permeability of membranes. The gas permeation response of poly(n-alkyl acrylate) and poly(m-alkyl acrylate) blends as a function of temperature is reported for varying side-chain lengths, n and m, and blend composition in the semi-crystalline and molten states. Macroscopic homogeneity is observed for a small range of n and m where |n − m| ≤ 2-4 methylene units. Thermal analysis indicates that the blend components crystallize independently of one another; however, crystallization is hindered by the presence of the other component. Permeation responses of the blends investigated in some cases exhibited two distinct permeation jumps or increases at the melting temperature of each component. Blends with continuous permeation responses but higher effective activation energies of permeation (i.e., more thermally responsive) were observed for some blends over the temperature of interest for membranes to be used for modified atmosphere packaging.     

Electron transport properties of polyaniline composite films containing poly(3‐hydroxybutyric acid)

Polyaniline (PANI) composites containing poly(3‐hydroxybutyric acid) (PHB) were synthesized via in situ deposition technique. The oxidative polymerization of aniline hydrochloride was carried out by dissolving different weight percentages (10 wt%, 20 wt%, 30 wt%, 40 wt%, and 50 wt%) of PHB using ammonium persulfate as an oxidant. The as‐synthesized composites were characterized using Fourier‐transform infrared spectroscopy and X‐ray diffraction pattern. The surface morphology of the resulting composites was studied using transmission electron microscopy. The temperature‐dependent direct current conductivity of the synthesized composite films was measured, and the activation energy responsible for the conductivity was examined. Incorporation of the biodegradable polymer, PHB, during the preparation of new PANI composites significantly increased the conductivity of the resulting composites. POLYM. COMPOS., 34:1655–1662, 2013. © 2013 Society of Plastics Engineers     

Survey on transport properties of liquids,vapors, and gases in biodegradable poly(3-hydroxybutyrate) (PHB)

The transport properties of carbon dioxide, water, and different organic solvents in bacterial poly(3-hydroxybutyrate) (PHB) at 30°C were investigated. CO₂ sorption was measured by the gravimetric method using a recording microbalance at subatmospheric pressures. Results were adequately interpreted in terms of Henry's law. Organic solvent and water permeabilities for both vapors and liquid were measured using a gravimetric cell. The data were interpreted in different terms depending on the units in which permeability was measured. Most of the solvent-polymer systems showed the typical time-lag plot, but in liquid permeation experiments, some anomalous behaviors were observed, with a transient period of rapid permeation at the beginning of the experiment before reaching the steady state. The transport properties of PHB were compared with those of other polymers, either from synthetic or biodegradable origin. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1849–1859, 1997     

Charge transport properties of poly(N-vinylimidazole) containing [Os(N)6]2+/3+ moieties

The rate of charge transport of electrodes modified with osmium containing poly(N-vinylimidazole) has been examined as a function of the nature of the contacting electrolyte solution and of temperature. Heterogeneous electron transfer from the electrode into the polymer film has also been investigated. The charge transport parameters show that the nature of the electrolyte anion and its concentration have a large impact on the polymer morphology. In sulfuric acid the films appear significantly swollen, hydrated, and porous, while in perchlorate-containing solutions they are rather compact. Activation energies for the rate-determining step of charge transport show that, depending on the electrolyte, segmental chain motion or ion movement represents the rate-limiting process.     

Electronic properties of poly(thiophene-3-methyl acetate)

The electronic structure of poly(thiophene-3-methyl acetate) has been investigated using UV–vis absorption spectroscopy and quantum mechanical calculations. Experimental measures in chloroform solution indicate that the π-conjugation length increases with the polymer concentration, which is reflected by the red shift of the absorbance peak of the π-π* transition. On the other hand, the energy required for the π-π* transition has been found to decrease with the volatility of the solvent for concentrated polymer solutions, even though the influence of the solvent is very small for dilute solutions. Quantum mechanical calculations indicate that the interactions between the π-conjugated backbone and the methyl acetate side groups are very weak. On the other hand, the lowest energy transition predicted for an infinite polymer chain that adopts the anti-gauche and all-anti conformations is 2.8 and 1.9 eV, respectively. Finally, measurements on spin-casted nanofilms reflect that the π-π* transition energy increases with the thickness, which has been attributed to the distortion of the molecular conformation. In spite of this, the energy gap obtained for the thinnest film (1.52 eV) is significantly smaller than that determined for dilute and concentrated chloroform solutions (2.56 and 2.09 eV, respectively).     

Particular thermal properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) oligomers

Telechelic hydroxylated poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s (PHBV-diols) were synthesized by transesterification with ethylene glycol, which could be used as the macromonomers for synthesis of block copolymers. PHBV-diols owned particular thermal properties. PHBV-diols had much lower the melting temperatures (T _m s) and better thermal stability than original PHBV. With the decrease of molecular weight, T _m s of PHBV-diols decreased gradually and maximum degradation temperatures (T _max s) increased gradually. T _max -T _m of PHBV-diol could increase by 57.9 °C in comparison with original PHBV. It was meaningful that PHBV block in the block copolymers based on PHBV-diol owned the good thermal stability and low melting temperature of its precursor PHBV-diol, which widened greatly the melt-processing window of PHBV. In addition, thermal degradation kinetics was studied by Ozawa method, the integration method and Kissinger method. The results showed that the thermal degradation of original PHBV and PHBV-diols proceeded by at least two steps including a random degradation process and subsequent thermal degradation process due to the auto-accelerated degradation reaction.     

Particular thermal properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) oligomers

A novel electroactive polyamide with alternating amino-capped aniline pentamer and azo groups in the main chain was synthesized via a four-step synthetic procedure. The characteristics of the obtained polyamide were studied in detail by Fourier-transform infrared (FTIR) spectra, nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). The thermogravimetric analysis (TGA) was used to evaluate its thermal characteristics, and the result showed the as-synthesized polymer had a good thermal stability. Besides, the electrochemical behavior of the polyamide was checked by cyclic voltammetry (CV) and the mechanism of electrochemical oxidation process was well studied. Furthermore, UV–vis spectra were used to monitor the doping process and photoisomerization process of the polyamide. Ratifying results were obtained in the investigation on dielectric properties of the as-synthesized polymer. The dielectric constant was greatly increased by treating the conjugated oligoaniline segments with hydrochloric acid.     

Water transport properties in poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) biopolymers

Water sorption and diffusion have been investigated in poly(3‐hydroxybutyrate) (PHB) and three poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) copolymers [P(HB‐HV)] by means of a Cahn electromicrobalance. Permeability of these samples have been determined using a gravimetric permeation cell. Two experimental setups were used for the gravimetric sorption measurements, under dynamic and static conditions, respectively. The differences observed in the results obtained using these techniques are discussed. The sorption measurements have evidenced the tendency of water molecules to form aggregates or clusters in the polymer. In addition, the static sorption method revealed the potential of PHB and P(HB‐HV) to undergo molecular relaxations, eventually leading to a partial desorption of the previously sorbed water after an induction period. The clustering effect was adequately described by the polycondensation model. On the other hand, the interpretation of the diffusivity in terms of mobility coefficients has revealed a competition between a plasticization effect and clustering. As a whole, water transport properties in PHB and its copolymers can be considered to be very close in magnitude to those of common thermoplastics such as PVC and PET. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 455–468, 1999     

Blends of bacterial poly(3-hydroxybutyrate) and a poly(epichlorohydrin-co-ethylene oxide) copolymer: thermal and CO2 transport properties

In this work the miscibility and the carbon dioxide transport properties of a bacterial, isotactic poly(3-hydroxybutyrate) (iPHB) and its blends with a copolymer of epichlorohydrin and ethylene oxide (ECH-co-EO) have been studied. Blends were prepared by solution/precipitation. The aim to obtain miscible blends of iPHB with a rubbery second component (such as the ECH-co-EO copolymer) is to have mixtures with glass transition temperatures below room temperature. In these conditions, the iPHB chains not involved in the crystalline regions retain its mobility. This mobility seems to be necessary for the attack of microorganisms and the corresponding biodegradability.Miscibility is the general rule of these mixtures, as shown by the existence of a single glass transition temperature for each blend and by the depression of the iPHB melting point. The interaction energy density stabilising the mixtures, calculated using the Nishi-Wang treatment, was similar to those of other polymer mixtures involving different polyesters and poly(epichlorohydrin) (PECH) and ECH-co-EO copolymers. The so-called binary interaction model has been used in order to simulate the evolution of the interaction energy density with the ECH-co-EO copolymer composition. Previously reported experimental data on blends of iPHB with PECH and poly(ethylene oxide) (PEO) have been used to quantify the required segmental interaction energy densities.In the determination of the CO₂ transport properties of the mixtures, only iPHB rich blends containing up to 40% of copolymer were considered. The effect of the ECH-co-EO copolymer is to increase the sorption and the diffusion of the penetrant (and, consequently, the permeability) with respect to the values of the pure iPHB. This is primarily due to the reduction of the global crystallinity of the blends and to the low barrier character of the ECH-co-EO copolymer. Sorption data can be reasonably reproduced using an extension of the Henry's law to ternary systems.