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Ballistic performance, at effective strain rates of (10 4 –10 5 s −1 ), for polymeric dicyclopentadiene (pDCPD) was compared with two epoxy resin/diamine systems with comparable glass transition temperatures. The high rate response was characterized in terms of a projectile penetration kinetic energy, KE 50 , which describes the projectile kinetic energy at a velocity with a 50% probability of sample penetration. pDCPD showed superior penetration resistance, with a 300–400% improvement in ballistic energy dissipation, when compared with the structural epoxy resins. In addition, unlike typical highly crosslinked networks that become brittle at low temperatures, the improved pDCPD performance occurred over a very broad temperature range (−55 to 75 °C), despite exhibiting a glass transition temperature characteristic of structural resins (∼142 °C). In addition to the high T g , pDCPD exhibited a room temperature glassy storage modulus of 1.7 GPa, offering the potential to circumvent the common structural versus energy dissipation trade-off encountered with conventional crosslinked polymers. Quasi-static measurements suggested that the performance of pDCPD is phenomenologically related to higher fracture toughness and lower yield stress relative to typical epoxies, while molecular dynamics simulations suggest the origin is the lack of strong non-covalent interactions and the facile formation of nanoscale voids to accommodate strain in pDCPD.

The ballistic performance was examined for a series of broad glass transition temperature epoxy formulations consisting of a di-epoxy monomer crosslinked with bi-modal mixtures of both a rigid, low molecular weight diamine and a flexible, high molecular weight diamine. Interestingly, the resins did not macro-phase separate during cure, but exhibited structural and dynamic heterogeneity on a length scale of a few nanometers, as confirmed by X-ray scattering, dynamic mechanical analysis, modulus-mapped atomic force microscopy, and broadband dielectric spectroscopy. The nano-structured resins were optically transparent and demonstrated a nearly 300% increase in ballistic energy dissipation relative to the neat resins, as well as when compared to epoxy formulations composed of similar bi-modal blends that exhibited a macro-phase separated structure. The ballistic performance is found to be insensitive to sub-glass transition temperature (T g ) relaxations, but appears to be dependent on both the nano-structure and the Vogel temperature of the high T g component. The study demonstrates a new class of transparent protective materials composed of rigid and flexible components with a fine scale heterogeneous structure.

The synthesis of a series of cyclotriphosphazene and polyphosphazene ruthenium(II) compounds is reported using 2,2′:6′,2″-terpyridine (terpy) and 2,6-di(1H-pyrazol-1-yl)pyridine (bpp) pendant ligands. X-ray crystallography, UV–Vis and resonance Raman spectroscopy have been employed to gain an insight into the physical and coordination behaviour of these complexes and indicate that both the small molecule and their polymeric analogues contain coordinated Ru in an octahedral ‘N6’ environment. The results reveal a difference between the chemistry of the ruthenium(II)-bpp-terpy and ruthenium(II)-bis-terpy complexes and demonstrate a means of grafting functional groups to a polyphosphazene backbone under mild conditions.

Mossbauer and electronic absorbance spectroscopy along with variable temperature magnetic moment measurements demonstrate that a cyclotriphosphazene substituted with an iron(II)-bis-2,6-di(1H-pyrazoly-yl)pyridine moiety ( 1 ) and its polyphosphazene analogue ( 2 ) differ significantly in magnetic behaviour.

The ballistic performance of polydicyclopentadiene (pDCPD) was investigated and compared to two epoxy resins that a have similar glass transition temperature (Tg) to pDCPD. The ballistic performance of these materials (at an effective stain rate of 104–105 s−1) was characterized by determining the kinetic energy of the projectile where there is a 50 % probability that the projectile will penetrate a witness foil behind the sample (KE50). The ballistic performance of pDCPD showed a 300–400 % improvement over the structural epoxy resins. Typical, highly crosslinked epoxy networks become brittle at low temperatures, but pDCPD has a superior ballistic performance over a broad temperature range from (−55 to 75 °C), despite having a glass transition temperature of 142 °C, which characteristic of structural resins. pDCPD also exhibited a room temperature glassy storage modulus of 1.7 GPa, making pDCPD a potential structural resin that can overcome the structural vs. energy dissipation trade-off that commonly exists with some conventional crosslinked polymers. Quasi-static measurements of pDCPD when compared to epoxy resins suggested that the performance of pDCPD relates to higher fracture toughness and lower yield stress relative to typical epoxies, while molecular dynamics simulations comparing pDCPD to epoxy resins suggest that the performance of pDCPD is due to the lack of strong non-covalent interactions and the facile formation of nanoscale voids.

Ultrahigh strain rate performance in a series of model amine cured epoxy resins was investigated as a function of the glass transition temperature (Tg) of the cured polymer network, where the network Tg was systematically varied through the monomer stiffness, structure, and size. The high rate response was characterized in terms of a projectile penetration velocity, V50BL(P) (ballistic limit, protection criteria), which describes the projectile velocity with a 50% probability of sample penetration. One factor that dictates the ballistic performance of the epoxy networks, at effective rates of 104–105 s−1, is the difference between the measurement temperature and the glass transition temperature of the network. Sub-Tg relaxations did not have a measurable effect on ballistic performance, and neither did the monomer structure and functionality outside of the influence of the resin Tg, while off-stoichiometric (excess amine) formulations improved V50BL(P) slightly with high Tg epoxies. The results have implications in protective materials for military, aerospace, transportation, and construction industries, where high strain rate insults from airborne debris, high rate collisions, and natural events are increasingly considered during product design.

Two new cyclotriphosphazene ligands with pendant 2,2':6',2″-terpyridine (Terpy) moieties, namely, (pentaphenoxy){4-[2,6-bis(2-pyridyl)]pyridoxy}cyclotriphosphazene (L(1)), (pentaphenoxy){4-[2,6-terpyridin-4-yl]phenoxy}cyclotriphosphazene (L(2)), and their respective polymeric analogues, L(1P) and L(2P), were synthesized. These ligands were used to form iron(II) complexes with an Fe(II)Terpy(2) core. Variable-temperature resonance Raman, UV-visible, and Mössbauer spectroscopies with magnetic measurements aided by density functional theory calculations were used to understand the physical characteristics of the complexes. By a comparison of measurements, the polymers were shown to behave in the same way as the cyclotriphosphazene analogues. The results showed that spin crossover (SCO) can be induced to start at high temperatures by extending the spacer length of the ligand to that in L(2) and L(2P); this combination provides a route to forming a malleable SCO material.

Two new polyphosphazene ligands containing 1,10-phenanthrolin-2-olate (L1) and 2,2ʹ-bipyridine-6-olate moieties (L2) with 5,5ʹ-di-tert-butylbiphenyl-2,2ʹ-bis(olate) co-substituents were synthesised and then reacted with Fe(Pyridine)4(NCS)2. Variable temperature Mossbauer and electronic absorbance spectroscopies were used to establish the physical behaviour of the new iron-polyphosphazenes. By attaching two bidentate ligands to a geminal phosphorus atom a pseudo tetradentate ligand can be formed that prevents cross-linking when iron is coordinated to the polyphosphazene.

A series of small phosphazene ligands with pendant 6-phenyl-2,2′-bipyridyl moieties, namely L1 [N3P3(OPh)5(OPhbpyPh)], L2 [N3P3(biph)2(OPhbpyPh)2], L3 [N3P3(tBubiph)2(OPhbpyPh)2], L4 [N3P3(biph)2(OPhbpyPh)Cl] and L5 [N3P3(biph)2(OPhbpyPh)(OPh)] [OPhbpyPh = 4-(4-phenoxy)-6-phenyl-2,2′-bipyridine, OPh = phenoxy, biph = 2,2′-oxybiphenyl and tBubiph = 4,4′-di-tert-butyl-2,2′-oxybiphenyl], have been used to synthesise the new cyclometallated palladium(II) and platinum(II) complexes [(L1-H)PdCl], [(L1-H)PtCl], [(L1-H)(PdCl)2], [(L3-H)(PdCl)2], [(L4-H)PtCl], [(L5-H)PtCl] and the rhenium(I) complex [L5Re(CO)3Cl]. Single-crystal X-ray diffraction analysis was performed on the free ligand L2 and the palladium complexes [(L1-H)PdCl] and [(L3-H)(PdCl)2]. In both PdII complexes, the metal centre lies in a distorted square-planar geometry with an “N2CCl” donor set confirming the cyclopalladation. The ligand pendant arms are involved in intermolecular stacking interactions with adjacent molecules. A polyphosphazene (L6) with 4-tert-butylphenoxy (OtBuPh) and the potential donor OPhbpyPh as pendant groups was prepared and used to synthesise metallopolymers with ReI and PtII. Spectroscopic and computational studies were conducted to compare the discrete complexes with the polymers with similar metal pendants as well as to model compounds in the literature. By using UV/Vis and resonance Raman spectroscopic techniques it was found that very few deviations from known metal chromophores exist for both the triphosphazene- and polyphosphazene-based complexes. The transient resonance Raman spectra of the PtII complexes revealed a ligand radical anion signature associated with the N2C unit.

Polyphosphazenes are a class of hybrid organic–inorganic polymers that have good solubility in classical organic solvents and are thermo-oxidatively stable. Over the years, poly(dichlorophosphazene) has been used as a macromolecular intermediate to yield a number of polymers which can be hydrophobic or superhydrophobic. This review deals with several classical hydrophobic polyphosphazenes such as poly(bis-2,2,2-trifluoroethoxyphosphazene), species with siloxane containing substituents and phosphazene graft polymers. Poly(phosphazophosphazenes) and phenoxy-substituted polyphosphazenes are some of the more recent polymers that have been examined for their hydrophobic character. Processing methods such as electrospinning can enhance the hydrophobicity of polyphosphazenes to move them into the realm of superhydrophobic materials. Many polymers which are only borderline hydrophobic can now be converted into superhydrophobic materials by the use of environmental plasma treatment.

We report here the first examples of poly(organophosphazenes) with side groups derived from the purines guanine and adenine and the pyrimidine cytosine. Polymers with these purines or pyrimidines as the only side groups proved difficult to synthesize by macromolecular substitution techniques because of the insolubility of the intermediate products. Therefore, cosubstitution reactions of the poly(dichlorophosphazene) with glycine ethyl ester, alanine ethyl ester, or diethylene glycol methyl ether, followed by the respective purine or pyrimidine, were utilized. Each pair of side groups was incorporated into the polyphosphazene in a 1:1 ratio. 31P NMR spectroscopy verified the replacement of all the chlorine atoms, while 1H and 13C NMR techniques confirmed the presence and ratio of the different side group. DRIFT spectroscopy indicated that the attachment of the purines or pyrimidines was via the primary amino functionality. Glass transition temperatures ranged from −28 to −15 °C for the mixed-substituent po...

The nontoxic, neutral degradation products of amino acid ester polyphosphazenes make them ideal candidates for in vivo orthopedic applications. The quest for new osteocompatible materials for load bearing tissue engineering applications has led us to investigate mechanically competent amino acid ester substituted polyphosphazenes. In this study, we have synthesized three biodegradable polyphosphazenes substituted with side groups, namely, leucine, valine, and phenylalanine ethyl esters. Of these polymers, the phenylalanine ethyl ester substituted polyphosphazene showed the highest glass transition temperature (41.6 degrees C) and, hence, was chosen as a candidate material for forming composite microspheres with 100 nm sized hydroxyapatite (nHAp). The fabricated composite microspheres were sintered into a three-dimensional (3-D) porous scaffold by adopting a dynamic solvent sintering approach. The composite microsphere scaffolds showed compressive moduli of 46-81 MPa with mean pore diameters in the range of 86-145 microm. The 3-D polyphosphazene-nHAp composite microsphere scaffolds showed good osteoblast cell adhesion, proliferation, and alkaline phosphatase expression and are potential suitors for bone tissue engineering applications.

Amino end-terminated poly(l-lactic acid), poly(trimethylene carbonate), and polycaprolactone were synthesized via ring-opening polymerization techniques. The amino terminus was used to form a covalent link to poly(dichlorophosphazene), itself synthesized using a living cationic polymerization. The chlorine atoms in the polyphosphazene blocks were subsequently replaced by trifluoroethoxy groups. This is the first reported synthesis of block copolymers of polyphosphazenes linked to polyesters or polycarbonates. The molecular structure of each copolymer was established using multinuclear NMR techniques. Molecular weight analysis was used to provide confirmatory evidence that the two polymers chains were covalently linked. Thermal analysis results showed evidence that in the solid state the two blocks were phase-separated because the parent thermal transitions were detectable for each copolymer.

Currently employed bone tissue engineered scaffolds often lack the potential for vascularization, which may be enhanced through the incorporation of and regulated release of angiogenic factors. For this reason, the objective here was to fabricate and characterize protein-loaded amino acid ester polyphosphazene (Pphos)-based scaffolds and evaluate the novel sintering method used for protein incorporation, a method which will ultimately allow for the incorporation of proangiogenic agents. To test the hypothesis, Pphos and their composite microspheres with nanocrystalline hydroxyapatite (Pphos-HAp) were fabricated via the emulsion solvent evaporation method. Next, bovine serum albumin (BSA)-containing microsphere matrices were created using a novel solvent-non-solvent approach for protein loading. The resulting protein (BSA) loaded circular porous microsphere based scaffolds were characterized for morphology, porosity, protein structure, protein distribution and subsequent protein release pattern. Scanning electron microscopy revealed porous microsphere scaffolds with a smooth surface and sufficient level of sintering, illustrated by fusion of adjacent microspheres. The porosity measured for the poly(ethyl phenylalanato:glycinato)phosphazene (PNPhGly) and poly(ethyl phenylalanato:glycinato)phosphazene-hydroxyapatite (PNPhGly-HAp) scaffolds were 23 +/- 0.11% and 18 +/- 4.02%, respectively, and within the range of trabecular bone. Circular dichroism confirmed an intact secondary protein structure for BSA following the solvent sintering method used for loading and confocal microscopy verified that FITC-BSA was successfully entrapped both between adjacent microspheres and within the surface of the microspheres while sintering. For both Pphos and their composite microsphere scaffolds, BSA was released at a steady rate over a 21 day time period, following a zero order release profile. HAp particles in the composite scaffolds served to improve the release profile pattern, underscoring the potential of HAp for growth factor delivery. Moreover, the results of this work suggest that the solvent-non-solvent technique for protein loading is an optimal one that will allow for future development of angiogenic factor-loaded Pphos matrices with the capacity to invoke neovascularization.

The first poly(organophosphazenes) with iodinated side groups for possible use as radio-opaque biomaterials are reported. Depending on the types of side groups present, these polymers may be biostable or bioerodible. Single-substituent polymers with 4-iodophenoxy or 4-iodophenylanaline ethyl ester units as the only side groups were prepared. Although a single-substituent polymer with 3,5-diiodotyrosine ethyl ester groups was difficult to synthesize, probably because of steric hindrance, mixed-substituent polymers that contained the non-iodinated ethyl esters of glycine, alanine, or phenylalanine plus a corresponding iodinated substituent could be synthesized. 31P, 1H, and 13C NMR spectroscopy techniques were used to follow the linkage of the side groups to the phosphazene skeleton and to establish the ratios of the different side groups. Hydrolysis of the iodo-amino acid/non-iodinated amino acid side group species in deionized water at 37 °C followed a bulk hydrolysis profile, with the rates dependent on the structure of the side groups. The effectiveness of these polymers as X-ray opaque materials was examined by the use of the poly(organophosphazenes) and conventional organic polymers as filters for copper Kα or rhenium–tungsten–molybdenum radiation. The phosphazene polymers that contained iodine in the side groups were opaque to X-rays, whereas the conventional organic polymers were essentially transparent to the same radiation.