Showing papers by "Harry R. Allcock published in 1996"
TL;DR: A degradable 3-dimensional osteoblast cell-polymer matrix designed as a construct for skeletal tissue regeneration and found to be suitable for use as a bioerodible scaffold for regeneration of skeletal tissue.
Abstract: Current methods for the replacement of skeletal tissue in general involve the use of autografts or allografts. There are considerable drawbacks in the use of either of these tissues. In an effort to provide an alternative to traditional graft materials, a degradable 3-dimensional (3-D) osteoblast cell–polymer matrix was designed as a construct for skeletal tissue regeneration. A degradable amino acid containing polymer, poly[(methylphenoxy)(ethyl glycinato) phosphazene], was synthesized and a 3-D matrix system was prepared using a salt leaching technique. This 3-D polyphosphazene polymer matrix system, 3-D-PHOS, was then seeded with osteoblast cells for the creation of a cell–polymer matrix material. The 3-D-PHOS matrix possessed an average pore diameter of 165 μm. Environmental scanning electron microscopy revealed a reconnecting porous network throughout the polymer with an even distribution of pores over the surface of the matrix. Osteoblast cells were found attached and grew on the 3-D-PHOS at a steady rate throughout the 21-day period studied in vitro, in contrast to osteoblast growth kinetics on similar, but 2-D polyphosphazene matrices, that showed a decline in cell growth after 7 days. Characterization of 3-D-PHOS osteoblast-polymer matrices by light microscopy revealed cells growing within the pores as well as on surface of the polymer as early as day 1. This novel porous 3-D-PHOS matrix may be suitable for use as a bioerodible scaffold for regeneration of skeletal tissue. © 1996 John Wiley & Sons, Inc.
193 citations
TL;DR: In this paper, a new method for the synthesis of poly(dichlorophosphazene) at ambient temperatures is described, which involves the initiation of Cl3PNSiMe3 with small amounts of PCl5 in CH2Cl2 to yield poly(Dichloropeptazene), (NPCl2)n, with narrow polydispersities.
Abstract: A new method for the synthesis of poly(dichlorophosphazene) at ambient temperatures is described It involves the initiation of Cl3PNSiMe3 with small amounts of PCl5 in CH2Cl2 to yield poly(dichlorophosphazene), (NPCl2)n, with narrow polydispersities The molecular weight of poly(dichlorophosphazene) was controlled by altering the ratio of monomer to initiator The polymer chains were found to be active after chain propagation since further addition of monomer resulted in the formation of higher molecular weight polymer Integration of 1H and 31P NMR spectra of these reactions revealed that the polymerization follows first-order reaction kinetics with respect to monomer concentration Active polymer chains may be quenched or end-capped by the addition of trace quantities of Me2(CF3CH2O)PNSiMe3 or (CF3CH2O)3PNSiMe3 Furthermore, PBr5, SbCl5, and Ph3C[PF6] were also found to be effective initiators in CH2Cl2 at room temperature
162 citations
TL;DR: In this paper, a series of solid polymer electrolyte materials based on the poly(organophosphazene) system has been designed and synthesized, which contain linear or branched oligoethyleneoxy side chains.
Abstract: A new series of solid polymer electrolyte materials based on the poly(organophosphazene) system has been designed and synthesized. The new polymers contain linear or branched oligoethyleneoxy side chains. The polymers were characterized by 31P, 13C, and 1H-NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and elemental analysis. The ambient temperature (25 °C) ionic conductivities of the polymers complexed with lithium triflate were measured by complex impedance analysis. The polymers that bear linear oligoethyleneoxy side chains [NP{O(CH2CH2O)nCH3}2], have low glass transition temperatures that range from −84 to −75 °C. These polymers have properties that are similar to those of the classical counterpart poly[bis(2-(2-methoxyethoxy)ethoxy)phosphazene. They have low dimensional stabilities and undergo viscous flow even at room temperature. The polymers with branched oligoethyleneoxy side chains (podands) have similar glass transition temperatures, in the range of −82 to −...
118 citations
TL;DR: A series of mixed-substituent poly(organophosphazenes) with ethyleneoxy side groups has been synthesized in this paper, which possess multiple electron-donor coordination sites that can form complexes with metal salts and generate solid electrolyte behavior.
Abstract: A series of mixed-substituent poly(organophosphazenes) with ethyleneoxy side groups has been synthesized. These polymers possess multiple electron-donor coordination sites that can form complexes with metal salts and generate “solid electrolyte” behavior. The polymers were characterized by 31P, 1H, and 13C NMR spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and elemental analysis. All the mixed-substituent polymers have low glass transition temperatures, from −70 to −56 °C, as well as at least one melting transition. Several polymer−lithium triflate complexes were examined by impedance analysis. The maximum conductivities for these polymers ranged from 1.6 × 10-6 to 3.9 × 10-5 S cm-1.
81 citations
TL;DR: The hydrogels had higher equilibrium degrees of swelling in basic than in acidic buffer solutions, and polymers with a higher loading of the ionic side group showed higher swellability than those with a lower loading of this side group.
80 citations
TL;DR: A series of poly(alkyl ether)phosphazenes were synthesized and their lower critical solution temperatures (LCST) were examined in water at concentrations from 0.1 to 30.0 wt %.
Abstract: A series of poly[(alkyl ether)phosphazenes] was synthesized and their lower critical solution temperatures (LCST) were examined in water at concentrations from 0.1 to 30.0 wt %. The polymers synthesized were poly[bis(2,3-dimethoxypropanoxy)phosphazene], poly[bis(2,3-bis(2-methoxyethoxy)propanoxy)phosphazene], poly[bis(2,3-bis(2-(2‘-methoxyethoxy)ethoxy)propanoxy)phosphazene], poly[bis(2,3-bis(2-(2‘-(2‘‘-dimethoxyethoxy)ethoxy)ethoxy)phosphazene], and poly[bis(2-(2‘-methoxyethoxy)ethoxy)phosphazene]. All the polymers examined showed LCST behavior. The LCST values were approximately 44.0, 38.0, 49.5, 61.5, and 65.0 °C, respectively. Cross-linked polymer films were examined as hydrogels in water at various temperatures and showed a rapid decrease in volume and weight as the temperature was raised through the LCST. The change in LCST was also examined as a function of increasing ionic strength in the presence of NaCl. A linear decrease in LCST was detected as a function of increasing ionic strength. The entha...
68 citations
TL;DR: A series of mixed-substituent poly(organophosphazenes) with the general structure {NP[OCH2CH2OCH 2CH 2OCH 3]x[O(CH2)yCH3]2-x}n, where x = 1 and y = 2−9 was synthesized as mentioned in this paper.
Abstract: A series of mixed-substituent poly(organophosphazenes) with the general structure {NP[OCH2CH2OCH2CH2OCH3]x[O(CH2)yCH3]2-x}n, where x = 1 and y = 2−9 was synthesized These polymers are candidates for use as solid polymeric, ionic conduction media The polymers were characterized by 1H, 13C, and 31P nuclear magnetic resonance spectroscopy, gel permeation chromatography, elemental microanalysis, infrared spectroscopy, and differential scanning calorimetry The polymers were complexed with LiSO3CF3 and ambient temperature (25 °C) ionic conductivity studies were performed with the use of complex impedance analysis The effect of changes in the length of the alkyl component of the alkoxy groups on conductivity was examined A maximum conductivity as a function of the concentration of lithium triflate was found for each system The conductivity decreased with an increase in the alkyl group side-chain length These polymers were compared to the polyphosphazene single-substituent polymer [NP(OCH2CH2OCH2CH2OCH3)2]
68 citations
TL;DR: High inulin loading increased the levels of initial drug burst release and resulted in higher levels of ultimate drug release as measured at 25 days, indicating that PPHOS polymers can predictably release macromolecules such as inulin.
59 citations
TL;DR: In this paper, the authors examined the thermal stability and compressive strength of a composite material comprised of hydroxyapatite (HAp, Ca10-x(HPO4)x(PO4)6-x (OH)2-x) and the polyphosphazene poly[bis(carboxylatophenoxy)phosphasene].
Abstract: We have examined the thermal stability and compressive strength of a composite material comprised of hydroxyapatite (HAp, Ca10-x(HPO4)x(PO4)6-x(OH)2-x) and the polyphosphazene poly[bis(carboxylatophenoxy)phosphazene]. The HAp is synthesized in the presence of the polyphosphazene utilizing dicalcium phosphate dihydrate (DCPD), CaHPO4·2H2O, and tetracalcium phosphate (TetCP), Ca4(PO4)2O, as the inorganic precursors. Calcium from the inorganic precursors participates in the formation of a polymeric network via ionic cross-linking through the pendent carboxylate groups. The degree of cross-linking of the polyphosphazene and its bonding to the HAp increases the overall thermal stability and changes the mode of failure of the final composite material.The thermal behavior of the polyphosphazene in its protonated, sodium salt, and calcium cross-linked forms was examined utilizing (1) thermogravimetric analysis at temperatures between 50 and 1000 °C, (2) electron impact mass spectrometry up to 550 °C, and (3) isot...
35 citations
TL;DR: A number of new poly(organophosphazenes) have been synthesized which bear 2-butenoxy or 4-allyloxyphenylphenoxy side groups as mentioned in this paper.
Abstract: A number of new poly(organophosphazenes) have been synthesized which bear 2-butenoxy or 4-allyloxyphenylphenoxy side groups. Co-substituent groups included trifluoroethoxy, phenoxy, or benzyloxyphenoxy groups. Species with 4-allyloxyphenylphenoxy units underwent Si--H coupling to linear silanes or siloxanes to extend the side groups and form hybrid phosphazene/organosilicon polymers. A number of these polymers are rubbery elastomers which are readily cross-linked by heat or light. Seven of the mixed-substituent, cross-linked polymers were incorporated into interpenetrating polymer networks (IPN's) with polystyrene, poly(methyl methacrylate), polyacrylonitrile, poly(acrylic acid) and poly(dimethylsiloxane). The phase compatibility characteristics of the IPN's were assessed by DSC, TEM, FT-IR spectroscopy, and 1H and 31P NMR spectroscopy data.
27 citations
TL;DR: In this paper, the authors investigated the low temperature formation of a hydroxyapatite-polyphosphazene polymer composite likely to be biocompatible in the presence of CaHPO4·2H2O, Ca4(PO4)2O.
Abstract: The present study was undertaken to investigate the low temperature formation of a hydroxyapatite-polyphosphazene polymer composite likely to be biocompatible. The temperature range studied (25 to 60°C) was selected to bracket physiological temperatures. The composite precursors consisted of CaHPO4·2H2O, Ca4(PO4)2O, and poly[bis(sodium carboxylatophenoxy)phosphazene]. The results indicate that a synergistic relationship exists in the formation of a polyphosphazene network and hydroxyapatite (HAp) matrix phase during composite synthesis. Calcium from the HAp precursors participates in the formation of a Ca crosslinked polymeric network which influences the rate of HAp formation and its morphology. The mechanistic paths taken during composite formation were followed by determining variations in the concentration of species in solution (at physiological temperature), rates of heat evolution, and microstructural development. These analyses indicate that the polymer controls the kinetics of hydroxyapatite formation and the composite microstructure. Low reaction temperatures and a high proportion of polymer facilitate the formation of a highly interconnected composite. The presence of the polyphosphazene allows a metastable calcium phosphate solution to persist for extended periods prior to the formation of hydroxyapatite. The degree of supersaturation and the length of the induction period increase with an increase in polyphosphazene content. The temperature dependence of these induction periods obeyed an Arrhenius relationship.
TL;DR: The first phosphazenes with adamantyl side groups were synthesized in this article, and they have a slightly puckered phosphazene ring due to the steric bulk of the adamantanamino side group.
Abstract: The first phosphazenes with adamantyl side groups have been synthesized. Hexakis(adamantanamino)cyclotriphosphazene, octakis(adamantanamino)cyclotetraphosphazene, and poly[bis(adamantanamino-co-trifluoroethoxy)phosphazene] have been prepared. The single-crystal X-ray structure of the cyclic trimer has been solved. This compound has a slightly puckered phosphazene ring due to the steric bulk of the adamantanamino side group.
TL;DR: In this paper, the behavior of nonlinear optical groups linked to a polyphosphazene chain was studied by solid-state NMR spectroscopy, and a series of poly(organophosphazenes) was prepared with the general stru
Abstract: The behavior of nonlinear optical (NLO) groups linked to a polyphosphazene chain was studied by solid-state NMR spectroscopy A series of poly(organophosphazenes) was prepared with the general stru
TL;DR: In this article, two methods have been developed for the controlled formation of carboxylic acid units at the surfaces of aryloxyphosphazene high polymers.
Abstract: Two methods have been developed for the controlled formation of carboxylic acid units at the surfaces of aryloxyphosphazene high polymers. The first involves a permanganate-induced oxidation of p-methylphenoxy side groups, with the surface density of carboxylic acid units being controlled by the ratio of p-methylphenoxy to phenoxy groups along the polymer chains. The second approach involves a base-induced hydrolysis of carboxylate ester functions at the para-positions of surface aryloxy side groups. In this method the surface density of carboxyl units is controlled by the reaction conditions, especially by the temperature and the solvent for the base. The same ester functions were converted to alcohol moieties by surface reductions using lithium aluminum hydride in diethyl ether. The surface structures before and after these reactions were studied by a combination of contact angle measurements, X-ray photoelectron spectroscopy, scanning electron microscopy with X-ray microanalysis, and ATR-IR spectroscopy.
TL;DR: In this paper, a series of cyclic phosphazenes and a linear short-chain phosphazene have been synthesized as models for the preparation of the corresponding high polymers, and their structures confirmed by a variety of techniques including 1H and 31P NMR spectroscopy, elemental analysis and differential scanning calorimetry.
Abstract: A series of new cyclic phosphazenes and a linear short-chain phosphazene have been synthesized as models for the preparation of the corresponding phosphazene high polymers. Several of the high polymers were also prepared. The small molecule compounds were characterized by a combination of 31P NMR, mass spectrometry and elemental analysis. The crystal and molecular structures of N3P3(OC6H4R-4)6(R = CH3, OH, OPh or OCH2Ph), N4P4(OC6H4OPh-4)8 and OP(OC6H4But-4)2NP(OC6H4 But-4) were investigated by single-crystal X-ray diffraction techniques. High polymers, [NP(OC6H4R-4)2]n, (R = OPh, OCH2Ph or But), [NP(OC6H4CPh3-4)1.5Cl0.5]n, and [NP(OCH2C6H4OCH2Ph-4)2]n were also prepared and their structures confirmed by a variety of techniques including 1H and 31P NMR spectroscopy, elemental analysis and differential scanning calorimetry.
TL;DR: In this paper, the triphenylsiloxy-substituted cyclotriphosphazenes, N3P3Cl5OSiPh3, gem-N3P 3Cl4(OSIPh3)2, N 3P3CL4(OPh)6, and N 3 P3CL5OPh5OSIph3, have been synthesized.
Abstract: The triphenylsiloxy-substituted cyclotriphosphazenes, N3P3Cl5OSiPh3, gem-N3P3Cl4(OSiPh3)2, N3P3(OSiPh3)6, and N3P3(OPh)5OSiPh3, have been prepared. The synthesis of gem-N3P3Cl4(OSiPh3)2 involves the reaction of (NPCl2)3 with Ph3SiONa to form the intermediates gem-N3P3Cl4(OSiPh3)2(ONa) and gem-N3P3Cl4(ONa)2, which yield gem-N3P3Cl4(OSiPh3)2 when treated with Ph3SiCl. The compounds N3P3Cl5OSiPh3 and N3P3(OSiPh3)0 are formed by the condensation reactions of N3P3Cl5OBun and N3P3(OBun)6, respectively, with Ph3SiCl. The compound N3P3(OPh)5OSiPh3 is synthesized by the reaction between N3P3(OPh)5Cl and Et3SiONa to first give the intermediate N3P3(OPh)5ONa, which yields N3P3(OPh)5OSiPh3 when reacted with Ph3SiCl. The structural characterization and properties of these compounds are discussed. The crystal and molecular structure of gem-N3P3Cl4(OSiPh3)2 has been investigated by single-crystal X-ray diffraction techniques. The crystals are monoclinic with the space group P21/c with a = 16.850(8), b = 12.829(4), c = 18.505(15) A, and β = 101.00(6)° with V = 3927 A3 and Z = 4. © 1996 John Wiley & Sons, Inc.
TL;DR: A review of recent progress in this new field can be found in this paper, with a focus on polyphosphazenes, a relatively new class of inorganic backbone polymers which rival many organic systems in their molecular structural diversity and property variations.
Abstract: Most of the polymers that have been synthesized and studied over the past 50 years are organic macromolecules. However, many advantages exist for the development of polymers with inorganic backbones. The first major class of inorganic backbone polymers to be developed widely were the polytorganosiloxanes] (silicones), and these now are the subject of broad industrial and fundamental interest. Polyphosphazenes are a relatively new class of inorganic backbone polymers which rival many organic systems in their molecular structural diversity and property variations. They constitute only the second group of inorganic-organic polymers to be developed extensively. An emerging field of research involves an attempt to create a new area of polymer science at the interface between these two subjects, by the synthesis of hybrid organophosphazene organosilicon systems. This review is a summary of recent progress in this new field.
TL;DR: In this article, the incorporation of inorganic elements into a polymer structure should broaden the range of properties accessible in polymeric substances, and many elements other than carbon could form part of a macromolecular backbone.
Abstract: Most known polymers are organic macromolecules derived either from living organisms or from petrochemical monomers. However, in principle, many elements other than carbon could form part of a macromolecular backbone, and the incorporation of ‘inorganic’ elements into a polymer structure should broaden the range of properties accessible in polymeric substances.1
TL;DR: In this article, the synthesis of polyphosphazene−siloxane polymers was described, which contain polyphazene backbone and [(N-methylamino)propyl] side groups, in ratios of 1:1 and 1:3 with trifluoroethoxy, 2-(2-methoxyethoxy)ethoxy or p-methylphenoxy cosubstituents.
Abstract: The synthesis of new hybrid polyphosphazene−siloxane polymers is described. These polymers contain a polyphosphazene backbone and [(N-methylamino)propyl]siloxane side groups, −N(Me)(CH2)3SiMe2OSiMe3 or −N(Me)(CH2)3SiMe2OSiMe2OSiMe3, in ratios of 1:1 and 1:3 with trifluoroethoxy, 2-(2-methoxyethoxy)ethoxy, or p-methylphenoxy cosubstituents. The synthetic method utilized allows the polymer properties to be tuned by variations in the cosubstituent ratios. The polymers were characterized by 31P, 13C, and 1H NMR, differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and elemental analysis. The percent loading of siloxane-containing side groups and the nature of the cosubstituents were correlated to the glass transition temperatures. The glass transition temperatures ranged from −83 to −22 °C. The longer, trisiloxane-containing units generated lower glass transition temperatures than did the analogous polymers with disiloxane-containing side groups. Several polymers were further characte...
Patent•
07 Mar 1996
TL;DR: The following ionically conductive polyphosphazenes have been synthesized: as discussed by the authors, where m = 0 - 3, n ∩ 15,000, R = (CH2)3CH3, where m ranges from 2 to 9.
Abstract: The following ionically conductive polyphosphazenes have been synthesized: A) [NP(OCH2CH(CH2O(CH2CH2O)mR)(OCH2CH2)mR)2]n where m = 0 - 3, n ∩ 15,000, R = CH3, and where m = 1, n ∩ 15,000 R = (CH2)3CH3; B) [NP(O(CH2CH2O)mCH3)2]n; C) [NP(OR)x(OCH2CH2OCH2CH2OCH3)y]n, where n = 15,000, x and y are approximately 1 and R is equivalent to O-(CH2)m-CH3 where m ranges from 2 to 9; D) polyphosphazenes bearing crown ether sidegroups.