Linear Polyphosphazenes Research Articles

Effects of naphthoxy side groups on functionalities of linear polyphosphazenes: Fluorescence, ion response and degradability

Polyphosphazenes with different substitution rates of β-naphthoxy side groups are synthesized through ring opening polymerization of hexachlorocyclotriphosphazene (HCCP), subsequent nucleophilic substitution by β-naphthol in organic solutions. The concentration and solvent effects, ions response, solid-state fluorescence and degradability of these polymers are investigated. It is found that the peaks in excitation spectra redshift with the increase of polymer concentration, and gradually stronger interaction of polymer molecules results in different concentration effects at λex = 300 nm and λex = 355 nm, respectively. It demonstrates that the fluorescence intensity of polymer solution enhance by increasing the polarity of solvents, and iron ions could quench fluorescence of polymer solutions. Moreover, the fluorescence intensities of polyphosphazenes containing β-naphthoxy side groups in solid-state is stronger than those in solution. The highest fluorescence intensities of those in both solid and solution is those polymers with 90% substitution rate of naphthoxy side groups. However, the polymers with lower substitution rate of naphthoxy side groups are degradable easily in acid medium.

Synthesis of hybrid crosslinked polyphosphazenes and investigation of their properties

Novel organic/inorganic hybrid polyphosphazenes were prepared by free radical UV copolymerization of linear polyphosphazenes and vinyl monomers. In this work, linear polyphosphazenes grafted by allyl amino and n-butylamino groups have been synthesized via nucleophilic substitution reaction at an anhydrous and anaerobic atmosphere. By regulating the molar ratio of allyl amino and n-butylamino groups, five different linear polyphosphazenes were prepared. The hybrid polyphosphazenes have been crosslinked using the linear polyphosphazenes and vinyl monomers including styrene, methyl methacrylate, and lauryl methacrylate as intermediates via free radical UV copolymerization. By changing the quantity of vinyl monomers participating in the crosslinking reaction, series of hybrid polyphosphazene membranes were obtained. The linear polyphosphazenes have been characterized by Nuclear magnetic resonance, Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), Differential scanning calorimeter, Dynamic mechanical analyzer and Drop Shape Analysis (DSA). The hybrid polyphosphazenes have also been studied via FTIR, TGA and DSA. The test results proved that the linear polymers were successfully synthesized. Moreover, the water contact angles showed that the hybrid crosslinked polyphosphazenes had a better hydrophobicity and thermal stability than the linear polyphosphazenes and the hydrophobicity of hybrid membranes have a regular changing tendency with the quantities of UV-monomers and ratio of allylamino. The initial decomposition temperatures of the hybrid polymers also had a regular change due to the difference and quantities of vinyl monomers.

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

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.

Revisiting the Electronic Structure of Phosphazenes

Natural bond orbital (NBO) and topological electron density analyses have been used to investigate the electronic structure of phosphazenes [N3P3R6] (R = H, F, Cl, Br, CH3, CF3, N(C2H4); 2R = O2C6H4), [N4P4Cl8], and H[NPCl2]4H. Using the former, the two most likely phosphazene bonding alternatives, negative hyperconjugation and ionic bonding have been critically evaluated. Ionic bonding, as suggested by topological analysis, was found to be the dominant bonding feature, although contributions from negative hyperconjugation are necessary for a more complete bonding description. Substituent effects on the P-N bond have been assessed and cases of bond length alternation have been rationalized using this combined bonding model, which supersedes previous models involving d-orbital participation, leading to an explanation for the observed bond length alternation found in some linear polyphosphazenes. In addition, common aromaticity indicators, nucleus independent chemical shifts (NICS) and para-delocalization indices (PDI), have been determined for the cyclophosphazenes.

Novel micro-crosslinked poly(organophosphazenes) with improved mechanical properties and controllable degradation rate as potential biodegradable matrix

As biodegradable materials, linear polyphosphazenes undergo rapid hydrolysis degradation but exhibit poor mechanical properties. Blending with biodegradable polyesters or inorganic particles strengthen their mechanical properties but give rise to slower degradation rate. To balance the mechanical properties and the degradation rate, micro-crosslinked polyphosphazenes were synthesized in this study. Their glass transition temperatures, mechanical properties, and in vitro degradation behavior were investigated. 2-Hydroxyethyl methacrylate (HEMA) was firstly attached to the side chain along with glycine ethyl ester to prepare co-substituted poly(organophosphazene) with pendant ethenyl substituents. The co-substituted poly(organophosphazene) was blended with HEMA or acrylic acid (AA) followed by a free radical polymerization to prepare micro-crosslinked poly(organophosphazenes). The resulting crosslinked polymers showed two separate glass transition temperatures depending on the HEMA or AA feed. Incorporation of crosslinking affected the mechanical properties positively. Crosslinked poly(organophosphazenes) showed an approximately 11–17 fold increase in terms of modulus of elasticity when compared to the linear counterpart. In vitro degradation tests indicated that HEMA-crosslinked polymers hydrolyzed at a retarded rate while AA-crosslinked polymers hydrolyzed at a moderate rate compared to linear polymers.

Gel electrolytes from co-substituted oligoethyleneoxy/trifluoroethoxy linear polyphosphazenes

Four new co-substituted linear phosphazene polymers have been synthesized with controlled ratios of oligoethyleneoxy (MEEP-type) and trifluoroethoxy side groups. The polymers were synthesized as models for gel electrolyte systems with more dimensional stability than can be achieved by MEEP-type electrolytes alone. The conductivity is significantly influenced by the ratios of the two side groups and by the concentration of small-molecule organic additives. Insights are suggested into the mechanism of ionic conduction within polyphosphazene gels.

Synthesis of Norbornenyl Telechelic Polyphosphazenes and Ring-Opening Metathesis Polymerization Reactions

Mono- and ditelechelic linear polyphosphazenes, functionalized with a norbornene end group, were synthesized through the termination of living poly(dichlorophosphazene) with norbornenyl phosphoranimines. These materials were employed as macromonomers for the synthesis of graft copolymers via the ring-opening metathesis polymerization (ROMP) of the terminal norbornenyl component. Norbornenyl monotelechelic polyphosphazenes with various molecular weights yielded un-cross-linked graft copolymers when subjected to ROMP. The ditelechelic polyphosphazenes yielded branched or cross-linked materials due to the multiple reactive sites. In addition, the 5-norbornene-2-methoxy phosphoranimine was polymerized via ROMP to yield materials that consisted of a polynorbornene backbone with phosphoranimine pendent side groups.

Self‐assembling with formation of mesogenic polymer structures in non‐mesogenic species

AbstractThe trivial statement that liquid crystals are formed on the base of either mesogenic organic molecules or molecules with amphiphilic structure may be applied to polymers as well. But at the same time it became clear that polymer LC world in certain sense is richer than the low‐molecular one and more and more one finds mesophase and LC polymers based on non‐mesogenic macromolecules. Linear polyphosphazenes, polysiloxanes, some ladder polymers etc. exhibit mesophase behavior in absence of any mesogenic groups in their structure.