3D laser scanning confocal microscopy of siloxane-based <Emphasis Type="Italic">comb</Emphasis> and double-<Emphasis Type="Italic">comb</Emphasis> polymers in PVDF-HFP thin films

Currently, atomic force microscopy is the preferred technique to determine roughness on membrane surfaces. In this paper, a new method to measure surface roughness is presented using a 3D laser scanning confocal microscope for high-resolution topographic analysis and is compared to conventional SEM. For this study, the surfaces of eight samples based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) host polymer with different liquid interpenetrating components were analyzed. Polymethylhydrosiloxane, triethylene glycolallylmethylether, (3,3,3-trifluoropropyl)methylcyclotrisiloxane (D₃-C₂H₄CF₃), polysiloxane-comb-propyloxymethoxytriglycol (PSx), polysiloxane-comb-propyl-3,3,3-trifluoro (PSx-C₂H₄CF₃), poly[bis(2-(2-methoxyethoxy) ethoxy) phosphazene, or poly[bis(trifluoro)ethoxy] phosphazene was chosen as interpenetrating compound to investigate the impact of comb and double-comb-structured polymer backbones, as well as their dipolar or fluorous residues on the PVDF-HFP-miscibility. Different phases of the constituting ingredients were identified via their thermal properties determined by DSC. Additionally, the COSMO-RS method supported the experimental results, and with regard to computed σ-profiles, new modified structures for polysiloxane and polyphosphazene synthesis were suggested.     

Synthesis and characterization of soluble multi-walled carbon nanotube/poly(organophosphazene) composites

Poor solubility of carbon nanotubes (CNTs) in water and organic solvents offers a significant problem for their applications. Macromolecules can be suitable solubilizing agents and a structural component of composite materials for CNTs. Several polymers were tested for the preparation of CNT dispersions. In this study, a poly[(4-pyridineoxy)(phenoxy)phosphazene] (3) was prepared by sequential treatment of poly(dichlorophosphazene) (2) with sodium 4-pyridineoxy and sodium phenoxide in THF. Multi-walled carbon nanotube/poly(organophosphazene) composites (f-MWCNT/PZS) with different feed ratios [R_feed = 1:1, 1:3, 1:5 and 1:10 (w/w)] were obtained by the treatment of the functionalized multi-walled carbon nanotube (f-MWCNT) with the protonated poly(organophosphazene) (PZS). Excellent dispersions of the f-MWCNT/PZS nanocomposites in water and common organic solvents were achieved. The influence of feed ratio on polymer coating and the stability of composites were investigated by thermal gravimetric analysis (TGA). f-MWCNT/PZS_1:5 nanocomposite was characterized by ³¹P, ¹H NMR, FTIR, XRD, EDX and Raman Spectroscopy. The morphologic characterizations of f-MWCNT/PZS_1:5 were carried out by HRTEM and SEM methods.     

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.     

Effects of alkyl substitution on the physical properties and gas transport behavior in selected poly(R-phenoxyphosphazenes)

A systematic preparation of alkyl substituted phenoxyphosphazene polymers was performed and their gas transport properties determined. In this study, phosphazenes substituted with 4-methylphenol, 4-ethylphenol, and 4-isopropylphenol are reported. An additional polymer substituted with 4-tert-butylphenoxy-1-ethanol also was synthesized in this work. Data derived for these materials, including chemical, thermal and gas transport characterization, were compared to previous reports discussing poly[bis-phenoxyphosphazene] and its analog with tert-butyl substitution: poly[bis-(4-tert-butylphenoxy)phosphazene]. The tert-butyl moiety influences orderly chain packing, presumably through steric hindrance that can influence aromatic π-stacking. For the new poly[(alkylphenoxy)phosphazenes], semicrystallinity is maintained and the added steric bulk serves to decrease the polymer glass transition temperature (Tg) and increase both permeability and selectivity for the gas pairs: O₂/N₂ and CO₂/CH₄. Removal of the tert-butyl moiety from the immediate vicinity of the backbone through a flexible spacer serves to depress the Tg as compared to poly[bis-(4-tert-butylphenoxy)phosphazene], but provides no performance enhancement for gas transport.     

On the Contributions to the Materials Science Aspects of Phosphazene Chemistry by Professor Christopher W. Allen: The One-Pot Synthesis of Linear Polyphosphazenes

Summary The wide range of applications for the phosphazene compounds has stimulated a major research effort involving several industrial, academic, and national laboratories over the past 40 years. One of Professor Allen’s research areas was to establish fundamental synthetic methods for the commercial preparation of phosphazene polymers, investigate their properties, and develop useful products. In this paper we review some of the materials science aspects of Professor Allen’s research including recent advances on the preparation and polymerization of Cl₃PNP(O)Cl₂. This work, in particular, has led to a route for the “one-pot” synthesis of stable linear poly(organophosphazenes) as demonstrated through the formation of poly[bis-(2-methoxyethoxyethoxy)phosphazene] (MEEP) and a phosphazene heteropolymer (HPP) containing a balance of hydrophilic and hydrophobic components that allow for control and molecular affinities. The authors would like to dedicate this paper to Professor Christopher W. Allen in honor of his significant contributions to phosphazene chemistry. Furthermore, the authors thank him for his counsel and friendship in the development of the “one pot” phosphazene synthesis discussed in this paper.     

Photochemical behavior of poly(organophosphazenes). X. Photo-cross-linking phenomena in poly[bis(4-isopropylphenoxy)0.8 (4-benzoylphenoxy)1.2 phosphazene]

The synthesis and photochemical behavior both in solution and in the solid state of poly[bis(4-isopropylphenoxy)_0.8 (4-benzoylphenoxy)_1.2 phosphazene] is described. The main reaction of this material under illumination with light of a wavelength longer than 340 nm is the intramolecular abstraction of an hydrogen atom by the excited benzophenone substituent from the 4-isopropylphenoxy moiety geminally substituted on the same phosphorus of the phosphazene chain. In this way highly reactive radical species are produced which induce very efficient photo-cross-linking of the phosphazene copolymer and insolubilization. The efficiency of this process in the solid state is examined in view of the potential application of this material as a polyphosphazene-based negative photoresist.     

Photochemical behavior of poly(organophosphazenes). X. Photo-cross-linking phenomena in poly[bis(4-isopropylphenoxy)0.8 (4-benzoylphenoxy)1.2 phosphazene]

The synthesis and photochemical behavior both in solution and in the solid state of poly[bis(4-isopropylphenoxy)_0.8 (4-benzoylphenoxy)_1.2 phosphazene] is described. The main reaction of this material under illumination with light of a wavelength longer than 340 nm is the intramolecular abstraction of an hydrogen atom by the excited benzophenone substituent from the 4-isopropylphenoxy moiety geminally substituted on the same phosphorus of the phosphazene chain. In this way highly reactive radical species are produced which induce very efficient photo-cross-linking of the phosphazene copolymer and insolubilization. The efficiency of this process in the solid state is examined in view of the potential application of this material as a polyphosphazene-based negative photoresist.     

Synthesis,Characterization, Hydrolytic Degradation,and Biocompatibility of Poly[bis(lactic acid ester)phosphazenes)]

New biodegradable polyphosphazenes containing lactic acid ester side groups were synthesized via a route of macromolecular substitution. Their biodegradability and biocompatibility were studied in vitro. The polymers showed the fastest hydrolysis in the basic solution, followed by the acidic and then the neutral solution. The rate of these polymers' degradation decreased in the order of poly[bis(ethyl lactato)phosphazene] > poly[bis(propyl lactato)phosphazene] > poly[bis(butyl lactato)phosphazene]. The possible degradation pathways were discussed. MTT assays indicated that these polymers had good biocompatibility against HepG2 and K562/VCR cells. Due to good biodegradability and biocompatibility, these polyphosphazenes may be promising for biomedical applications.     

Synthesis and characterization of polyphenylaminophosphazene and fluorinated polyarylaminophosphazene

Two polyarylaminophosphazenes, poly[bis(phenylamino)phosphazene] (PBAP) and poly[bis(p‐trifluoroethoxyphenylamino)phosphazene] (PBTAP), were successfully synthesized by ring‐opening polymerizations and nucleophilic substitution reactions. Their chemical structures, thermal properties, and surface properties were investigated by NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and water contact angles (WCA). The results indicate that the glass‐transition temperature (T_g), thermal stability, and WCAs of PBAP and PBTAP presented obviously differences; this suggested that PBTAP possessed the lower T_g and higher contact angle than PBAP. This was attributed to the influence of trifluoroethoxy at the para position of aniline. TGA measurements indicated that PBAP possessed a higher thermal stability than PBTAP; this was attributed to the strong electron‐withdrawing influence of the trifluoroethoxy. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42542.     

Grafting reactions onto poly(organophosphazenes). VIII. Grafting kinetics, surface properties, thermal and dynamic mechanical characterization of phosphazene grafted copolymers containing poly(vinyl acetate) and poly(vinyl alcohol)

In this paper we report the light-induced grafting kinetics of vinyl acetate onto three poly(organophosphazene) films, i.e., poly[bis(4-methylphenoxy) phosphazene], poly[bis(4-ethylphenoxy)phosphazene], and poly[bis(4-secbutylphenoxy)phosphazene], and the characterization of the poly(organophosphazene)-g-poly-vinylacetate materials and the poly(organophosphazene)-g-poly-vinylalcohol copolymers, derived from hydrolysis of the previous ones. The reactivity of poly(organophosphazenes) was found to be directly dependent on the different crystallinity content. The modification of the surface properties was studied by SEM analysis and DCA measurements. The higher the grafting pereentage, the higher the roughness of surface and the lower the receeding contact angle. DSC analysis revealed that the crystallizability of poly(organophosphazene)-g-poly-vinylacetate decreases as the grafting percentage increases. Finally, DMTA measurements confirmed the presence of polyvinylacetate after grafting and its disappearance and the simultaneous increase in thermomechanical stability after hydrolysis.Presented at the 1st Italian Workshop on Cyclo- and Poly(phosphazene) Materials. February 15–16, 1996, at the CNR Research Area in Padova, Italy.     

Grafting reactions onto poly(organophosphazenes). IV. Light-induced graft copolymerization of organic polymers containing free acid or basic functionalities onto poly[bis(4-benzylphenoxy)phosphazene]

The light-induced graft copolymerization of acrylic acid, methacrylic acid, and 4-vinylpyridine onto poly[bis(4-benzylphenoxy)phosphazene] films to prepare new grafted phosphazene copolymers containing acid and basic functionalities is reported. The process was carried out in monomer/methanol mixtures in the presence of benzophenone or benzoin ethyl ether as photosensitizers by selective excitation of these last species. The yield of the grafting processes was evaluated as a function of the monomer concentration in the reaction medium, type of photoinitiator, and characteristics of the grafted organic monomers. The acid functions inserted in poly[bis(4-benzylphenoxy)phosphazene]-g-poly(meth)acrylic acid grafted copolymers, and the basic groups of the poly[bis(4-benzylphenoxy)phosphazene]-g-poly-4-vinylpyridine substrates were allowed to interact with basic and acid dyes, respectively, to form permanently colored polymeric films. The photoactivity of these films as substrates for the photosensitized production of singlet oxygen was tested. © 1995 John Wiley & Sons, Inc.     

Degradation of poly[bis(ethylamino)phosphazene] in aqueous solution

Three polymers of poly[bis(ethylamino)phosphazene] (PBEAP) containing different amounts of the residual P–Cl moieties, which had been hydrolyzed into P OH in the following sample purification processes, were prepared by substitution of the chlorines on poly(dichlorophosphazene) with ethylamine. Only the polymer which had the highest side-chain content of ethylamino groups (ca. 93°_o) had a film-forming ability and a crystalline nature. The hydrolytic degradation of PBEAP in acidic solutions was investigated using the solution viscosity data obtained as a function of standing time. Acetic acid, 0.5 and 1N, pure acetic acid, and 2.2.2-trifluoroethanol were used as solvents. The degradation was composed of random breaking processes along the polymer chain, especially at the-N=P(OH)₂-and-N=P(OH)(NHC₂H₅)-units, and an unzippering-like breaking process which was started at the chain ends produced by the former random breaking. The random breaking caused an abrupt decrease in viscosity at the beginning of the degradation, and on the contrary, the unzippering-like breaking appeared as a gradual decrease in viscosity at the later stages of degradation. The total rate of degradation depended on the concentration of the ethylamino groups.     

A Novel Inorganic Polymer as Cathode Material for Secondary Lithium Batteries

Summary: This paper introduces a new inorganic poly(phosphazene disulfide) material. With unique element composition and molecular structure, the polymer has noncombustible safety and preferable conductivity. When used as cathode material for rechargeable lithium batteries, the polymer's first discharge capacity is as high as 467.9 mAh · g^?1, which can be retained at 409.9 mAh · g^?1 after 60 repeated cycles. Therefore, it has a great application potential in the field of lithium batteries.

Replacement of the Cl atoms by S? S groups by refluxing Na₂S₂ and linear poly(dichloro‐phosphazene).     

Dielectric relaxation of polyorganophosphazenes

Dielectric relaxation spectra of poly(bis-trifluoroethoxy phosphazene) (PBFP), poly(bis-n-propoxy phosphazene) (PBPP), and poly(bis-n-propylamino phosphazene) (PBPAP) were measured in wide temperature and frequency regions, and the -relaxation caused by micro-Brownian motion of segments in the rubbery state and the -relaxation due to the local motions of the polymer in the glassy region were observed. The dielectric spectra of PBFP at temperatures higher than the rubbery region exhibited a mesophase transition at 358 K. From conformation analysis according to the two-site model, it has been elucidated that the mechanism for -relaxation of these samples is hindered internal rotation of the side groups.     

Co‐electrospun composite nanofibers of blends of poly[(amino acid ester)phosphazene] and gelatin

Electrospinning is known as a simple and effective fabrication method to produce polymeric nanofibers suitable for biomedical applications. Many synthesized and natural polymers have been electrospun and reported in the literature; however, there is little information on the electrospinning of poly[(amino acid ester)phosphazene] and its blends with gelatin. Composite nanofibers were made by co‐dissolving poly[(alaninoethyl ester)_0.67(glycinoethyl ester)_0.33phosphazene] (PAGP) and gelatin in trifluoroethanol and co‐electrospinning. The co‐electrospun composite nanofibers from different mixing ratios (0, 10, 30, 50, 70 and 90 wt%) of gelatin to PAGP consisted of nanoscale fibers with a mean diameter ranging from approximately 300 nm to 1 µm. An increase in gelatin in the solution resulted in an increase of average fiber diameter. Transmission electron microscopy and energy dispersive X‐ray spectrometry measurements showed that gelatin core/PAGP shell nanofibers were formed when the content of gelatin in the hybrid was below 50 wt%, but homogeneous PAGP/gelatin composite nanofibers were obtained as the mixing ratios of gelatin to PAGP were increased up to 70 and 90 wt%. The study suggests that the interaction between gelatin and PAGP could help to stabilize PAGP/gelatin composite fibrous membranes in aqueous medium and improve the hydrophilicity of pure PAGP nanofibers. Copyright © 2009 Society of Chemical Industry     

Synthesis and characterization of multiblock semi-crystalline hydrophobic poly(ether ether ketone)–hydrophilic disulfonated poly(arylene ether sulfone) copolymers for proton exchange membranes

Multiblock copolymers based on alternating segments of telechelic phenoxide terminated hydrophilic fully disulfonated poly(arylene ether sulfone) (BPS100) and decafluorobiphenyl (DFBP) terminated hydrophobic poly(arylene ether ketimine) (PEEKt), were synthesized from the hydrophilic and ketimine-protected amorphous hydrophobic telechelic oligomers by nucleophilic coupling reactions. After film formation from DMSO, the copolymer was acidified, which converted the ketimine to semi-crystalline ketone segments and the sulfonate salts to disulfonic acids. A semi-crystalline phase with a T_m of 325 °C was confirmed. The semi-crystalline multiblock copolymer membranes were tough, ductile and solvent resistant. Fundamental properties as proton exchange membranes (PEMs) showed enhanced conductivities under fully hydrated and reduced humidity conditions. These multiblock copolymers exhibited low in-plane anisotropic swelling behavior, in contrast to the random copolymers.     

One‐Pot Substitution Approach for the Syntheses of Nonfunctional and Functional Poly[(amino acid ester)phosphazene] Biomaterials

Biodegradable polyphosphazenes are important class of biomaterials. Their preparation typically requires specialized setup, inert conditions, and cumbersome and multiple processes. This work focuses on the synthesis of both nonfunctional and novel functional poly[(amino acid ester)phosphazene]s using a simplified thermal ring opening polymerization in air, followed by one‐pot ( 1P ) room temperature substitution, also in air. While some hydrolysis was inevitable under such conditions, purified materials with lower polydispersity indices than previously reported and acceptable yields were successfully and reproducibly obtained. The poly[(amino acid ester)phosphazene]s developed in this work are based on l ‐alanine, l ‐phenylalanine, and l ‐methionine with l ‐glutamic acid to render them functionality. Characterization of these synthesized materials demonstrated that the 1P substitution was successful in developing mono‐ and co‐substituted poly[(amino acid ester)phosphazene]s. Cytotoxicity studies on 2D films showed the materials to be compatible with NIH‐3T3 fibroblasts while confocal imaging of cells showed a well‐spread morphology with abundant F‐actin within the cytoskeleton. The l ‐phenylalanine‐based poly[(amino acid ester)phosphazene]s also showed significantly enhanced cell viability over tissue culture polystyrene at days 1 and 3 of cultivation (p < 0.01). Overall, this study has shown that poly[(amino acid ester)phosphazene]s can be obtained with acceptable yields and straightforward reaction conditions, leading to materials suitable for broader biomedical applications.

     

Polyphosphazene membranes. II. Solid-state photocrosslinking of poly[(alkylphenoxy)(phenoxy)phosphazene] films

The solid-state UV photocrosslinking mechanism and the properties of dense crosslinked films composed of poly [(methylphenoxy)(phenoxy)phosphazene], poly[(ethylphenoxy)(phenoxy)phosphazene], and poly[(isopropylphenoxy)(phenoxy)phosphazene] were investigated, where the alkyl substituent was in either the meta- or para-position. Solution-cast films containing dissolved benzophenone photoinitiator (at a concentration of 1–25 mol %) were crosslinked at either 25 or 70°C. The ordering of benzophenone disappearance during polymer irradiation was methylphenoxy > ethylphenoxy > isopropylphenoxy, indicating that the rate controlling step for photoinitiator disappearance was the consumption of benzophenone, either by benzopinacole formation (with the creation of a polymer crosslink) or by reaction of a benzophenone-derived ketyl radical with a polymer macro-radical. The presence of such a ketyl adduct in crosslinked ethylphenoxy/phenoxy and isopropylphenoxy/phenoxy phosphazene films was verified by solid-state NMR. The ordering of crosslinked polymer swelling (for a given initial benzophenone concentration) when films were equilibrated in dimethylacetamide (DMAc) was isopropylphenoxy/phenoxy > ethylphenoxy/phenoxy > methylphenoxy/phenoxy, indicating that steric effects of the alkyl group were playing a role during crosslink formation. The methylphenoxy/phenoxy phosphazenes were the best materials for crosslinking; the glass transition temperature increased by approximately 25°C (from −15 to 10°C) and the film swelling (in DMAc) decreased from infinity (complete solubilization) to 35% as the benzophenone concentration was increased from 0 to 25 mol %. © 1998 John Wiley & Sons, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America.

J Appl Polym Sci 68:827–836, 1998     

XPS and DSC Studies of Solution Cast Polystyrene/Poly(organophosphazene) Blends. I. Polystyrene/Poly(phenoxy)phosphazene

Blends of polystyrene (PS) with poly(phenoxy)phosphazene (PPN) were studied by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). A third component, poly(2,6-dimethyl-1,4-phenylene ether) (PPE), was added with the aim of increasing compatibility of the blends. T _g values did not vary in the PS/PPN blends, indicating that the components are substantially incompatible. The addition of PPE did not change the situation much even though some compatibility between PPN and PPE was detected. XPS on the cast films showed that only PPN was present at the surface. The surface composition of the blends was found to be dependent on the preparation technique.     

Polyphosphazene membranes. IV. Polymer morphology and proton conductivity in sulfonated poly[bis(3‐methylphenoxy)phosphazene] films

The microstructure of sulfonated poly[bis(3‐methylphenoxy)phosphazene] was studied using wide‐ and small‐angle X‐ray diffraction. A reflection peak, attributed to the presence of ionic clusters, was observed in the small‐angle X‐ray diffraction patterns of hydrated and dry polymers with an ion‐exchange capacity (IEC) ≥0.6 mmol/g. The Bragg spacing from the ionic cluster structure was about 30 Å for the nonhydrated polymer and 50 to 90 Å for fully hydrated films. The effects of IEC, cation form of the polymer, temperature, and polymer water content on the cluster structure were investigated. The specific proton conductivity of water‐swollen, sulfonated poly[bis(3‐methylphenoxy)phosphazene] films at 25°C increased with increasing IEC, with a maximum conductivity of 0.1 S/cm at a polymer ion‐exchange capacity of 1.6 mmol/g. The water‐content percolation threshold for conductivity was between 17.5 and 25 vol %, and decreased with polymer IEC. The temperature dependence of proton conductivity for 1.2 mmol/g IEC poly[bis(3‐methylphenoxy)phosphazene] membranes exhibited Arrhenius behavior with an apparent activation energy of 27.8 and 36.7 kJ/mol for crosslinked and noncrosslinked polymers, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 49–59, 2001