Harry R. Allcock

William Penn University, Worcester, Massachusetts, United States

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Publications (439)2206.76 Total impact

  • Macromolecules 01/2015; 48(1):111-118. DOI:10.1021/ma501634b · 5.93 Impact Factor
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    ABSTRACT: 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 'N-6' 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.
    Polyhedron 01/2015; 85:429-436. DOI:10.1016/j.poly.2014.08.060 · 2.05 Impact Factor
  • Tomasz Modzelewski, Ian Hotham, Harry R. Allcock
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    ABSTRACT: A number of polyphosphazenes with negatively charged β-alanine (β-Ala) and γ-amino butyric acid (GABA) side groups were synthesized and studied for their ability to initiate the growth of hydroxyapatite (HAp) during exposure to simulated body fluid (SBF). All the polymers were hydrolytically sensitive, with the final hydrolysis rate dependent on the specific active side groups (GABA > β-Ala). These systems also underwent extensive mineralization, with calcium phosphate deposited across their entire surface during exposure to SBF (up to 115 wt % gain after 4 weeks). This degree of deposition is a major advance over previously reported polyphosphazene systems, which underwent a maximum of 27 wt % gain after immersion in SBF for 4 weeks. The extent of mineralization over the surface was monitored using environmental scanning electron microscopy (ESEM) coupled with energy dispersive X-ray spectroscopy (EDS). In addition, X-ray diffraction (XRD) was used to determine the identity of the mineralized material. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41741.
    Journal of Applied Polymer Science 12/2014; 132(13). DOI:10.1002/app.41741 · 1.64 Impact Factor
  • Jessica L. Nichol, Harry R. Allcock
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    ABSTRACT: In order for a material to be considered a potential candidate as a scaffolding substrate, it should be biodegradable to non-toxic products, and possess similar physical characteristics to those of the living tissue being replaced. Previous work centered on the direct linkage of citronellol, an anti-inflammatory molecule, to a polyphosphazene backbone. Moreover, the hydrolysis rate in that study was tuned by incorporating alanine ethyl ester co-substituent units thereby decreasing the amount of citronellol in the final polymer. By contrast, in this work citronellol was used as an ester unit linked to the carboxylic acid moiety of the amino acids glycine, alanine, valine, and phenylalanine that were in turn linked to the polymer backbone through the amino functionality. This method allowed the hydrolysis rate to be controlled via the steric hindrance generated by the amino acid ester while still providing two crosslinkable sites per repeat unit from the citronellol units. A hydrolysis study of the uncrosslinked polymers at physiological temperature showed between a 19.8 – 28.8% mass loss and between a 80.4 – 98.9% molecular weight decline after 12 weeks. The double bond in the citronellol structure also allowed polymer crosslinking by UV radiation to further control the polymer properties.
    European Polymer Journal 11/2014; DOI:10.1016/j.eurpolymj.2014.11.011 · 3.24 Impact Factor
  • Jessica L. Nichol, Ian T. Hotham, Harry R. Allcock
    Polymer Degradation and Stability 11/2014; 109:92–96. DOI:10.1016/j.polymdegradstab.2014.05.015 · 2.63 Impact Factor
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    ABSTRACT: Nanoparticles of complex architectures can have unique properties. Self-assembly of spherical nanocrystals is a high yielding route to such systems. In this study, we report the self-assembly of a polymer and nanocrystals into aggregates, where the location of the nanocrystals can be controlled to be either at the surface or in the core. These nanospheres, when surface decorated with nanocrystals, resemble disco balls thus the term nano-disco balls. We studied the mechanism of this surface loading phenomenon and found it to be Ca2+ dependent. We also investigated whether excess phospholipids could prevent nanocrystal adherence. We found surface loading to occur with a variety of nanocrystal types including iron oxide nanoparticles, quantum dots, and nanophosphors, as well as sizes (10-30 nm) and shapes. Additionally, surface loading occurred over a range of polymer molecular weights (~30-3,000 kDa) and phospholipid carbon tail length. We also show that nanocrystals remain diagnostically active after loading onto the polymer nanospheres i.e providing contrast in the case of magnetic resonance imaging for iron oxide nanoparticles and fluorescence for quantum dots. Last, we demonstrated that a fluorescently labeled protein model drug can be delivered by surface loaded nanospheres. We present a platform for contrast media delivery, with the unusual feature that the payload can be controllably localized to the core or the surface.
    ACS Nano 09/2014; 8(9):9143-9153. DOI:10.1021/nn502730q · 12.03 Impact Factor
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    ABSTRACT: An increased focus exists on the development of materials that might serve as ligament or tendon tissue engineering scaffolds. Requirements for a suitable candidate polymer include biodegradability, biocompatibility, and elasticity. In an attempt to meet these requirements novel citronellol-containing polyphosphazenes were synthesized, characterized, and crosslinked to generate elastomers. Citronellol was chosen as a side group due to its anti-inflammatory properties in addition to the presence of a double bond in its structure to permit polymer crosslinking. Alanine ethyl ester was chosen as a co-substituent to tune hydrolysis rates without severely affecting the glass transition temperatures of the final polymers. Hydrolysis of the uncrosslinked polymers in the form of films in deionized water at 37 °C showed between ∼8 and 16% mass loss and between a ∼28 and 88% molecular weight decline over 12 weeks. Polymers were also crosslinked using ultraviolet radiation for increasing amounts of time. Preliminary mechanical testing of the homo-citronellol polymer indicated increasing modulus and decreasing tensile strength with increased crosslink density. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014
    Journal of Polymer Science Part A Polymer Chemistry 08/2014; 52(16). DOI:10.1002/pola.27236 · 3.54 Impact Factor
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    ABSTRACT: Mixed-substituent fluoroalkoxyphosphazene polymers bearing ∼15% 1H,1H,2H,2H-perfluorooctan-1-oxy or 1H,1H,2H,2H-perfluorodecan-1-oxy side groups together with trifluoroethoxy cosubstituent groups were synthesized. The low reactivity of the long-chain fluoroalkoxides and their limited solubility in organic solvents prevented higher levels of substitution. Moreover, the sodium alkoxides with two methylene residues adjacent to the oxygen proved to be unstable in solution due to elimination of NaF and precipitation of side products, and this limited the time available for chlorine replacement reactions. The resulting cosubstituent polymers were characterized by proton nuclear magnetic resonance (1H-NMR), 31P-NMR, 19F-NMR, gel-permeation chromatography, and differential scanning calorimetry. Unlike homo- or mixed-substituent fluoroalkoxyphosphazene polymers, such as [NP(OCH2CF3)2]n (a microcrystalline thermoplastic, Tg ∼ −63°C, Tm ∼ 242°C) or [NP(OCH2CF3)(OCH2(CF2)xCF2H)]n (PN-F, a rubbery elastomer, Tg ∼ −60°C, but no detectable Tm), the new polymers are gums (Tg ∼ −50°C, but no detectable Tm) with molecular weights in the 105 g/mol rather than the 106 g/mol range. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers
    Polymer Engineering and Science 08/2014; 54(8). DOI:10.1002/pen.23729 · 1.44 Impact Factor
  • Zhicheng Tian, Chen Chen, Harry R. Allcock
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    ABSTRACT: The design and assembly of new organophosphazene polymeric materials based on supramolecular “host–guest” interactions was accomplished by linkage of supramolecular coupling units to either the main-chain terminus or the side-chains of the parent phosphazene polymer. Noncovalent interactions at the main chain terminus were used to produce amphiphilic palm-tree like pseudoblock copolymers via host–guest interactions between an adamantane end-functionalized polyphosphazene and a 4-armed β-cyclodextrin (β-CD) initiated poly[poly(ethylene glycol) methyl ether methacylate] branched-star type polymer. Moreover, noncovalent interactions involving polymer side-chains were achieved between polyphosphazenes with β-CD pendant units and other polyphosphazene molecules with adamantyl moieties on the side-chains. These new organo–phosphazene structures based on noncovalent “host–guest” interactions generate new opportunities for the macromolecular modification of polyphosphazenes. The resultant materials demonstrated useful properties including self-aggregation, supramolecular gelation, and stimulus-responsive behavior.
    Macromolecules 01/2014; 47(3). DOI:10.1021/ma500020p · 5.93 Impact Factor
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    ABSTRACT: Synthetic bone grafts that promote the natural mineralization process are excellent candidates for the repair and replacement of bone defects. In this study, a series of phosphoester and phosphonic acid containing polyphosphazenes were examined for their ability to mineralize hydroxyapatite (HAp) during exposure to a solution of simulated body fluid (SBF) for a period of four weeks. Although all the polymers showed an initial mineralization response, the amount of deposition and the time scale were dependent upon the side group chemistry of the polymers. After exposure to SBF for one week, all polymers mineralized HAp. After three weeks in SBF, polymers containing phosphoester substituents showed no significant change, with a weight gain of <1%, while polymers containing phosphonic acid substituents underwent a significant increase in the amount of mineralized HAp, with weight gains between 5-10%. The morphology of mineralized features was observed with Environmental Scanning Electron Microscopy (ESEM). However, due to the structural complexity of the mineralized polymers, the identity of the mineralized phase could not be definitively identified using traditional characterization techniques such as energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), or X-ray photoelectron spectroscopy (XPS). Time-of-flight secondary ion mass spectrometry (ToF-SIMS), a technique not previously explored for this type of application, successfully reveals details of the chemistry associated with the mineralized phase not possible to achieve with XRD analysis.
    RSC Advances 01/2014; 4(38):19680. DOI:10.1039/c3ra47205a · 3.71 Impact Factor
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    ABSTRACT: Phosphazene polymers with N-linked and O-linked amino acid side groups are of biomedical interest, especially for their ability to bioerode under physiological conditions. Polyphosphazenes containing serine and threonine substituents, which contain two different functional sites for attachment to a polyphosphazene backbone (N- and O-terminus), were synthesized using an improved technique, and their hydrolysis behavior was investigated. In aqueous media the solid polymers yield hydrolysis products phosphate, ammonia, the amino acid, and ethanol and have the potential to be used in several different biomedical applications ultimately determined by their hydrolysis behavior. A hydrolysis study in deionized water revealed that all the polymers are hydrolytically sensitive, regardless of the type of linkage to the polyphosphazene backbone, although the hydrolysis rates may be different. Polymers with amino acid ester side groups linked through the N-terminus underwent solid phase hydrolysis between 16 and 60 % within a 6-week period. This is the fastest reported solid state hydrolysis of any amino acid ester substituted polyphosphazene. The mechanism of hydrolysis is by bulk erosion as monitored by environmental scanning electron microscopy. Polymers with the amino acid units linked through the O-terminus are soluble in water; thus their solid state erosion profile in aqueous media could not be determined. However, 31P NMR spectroscopy confirmed their hydrolytic sensitivity in aqueous solution and the formation of phosphorus-containing oligomeric species, the concentrations of which increased during the 6-week hydrolysis period. Complete hydrolysis did not occur within 6 weeks. The O-linked species are possible starting points for bioerodible hydrogel formation.
    Journal of Inorganic and Organometallic Polymers and Materials 01/2014; 24(1). DOI:10.1007/s10904-013-9989-4 · 1.08 Impact Factor
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    ABSTRACT: Cross-linking in metallo-polyphosphazenes can be prevented by attaching two bidentate donors in a geminal fashion to the phosphorus atoms in the polymer chain.
    Inorganic Chemistry Communications 01/2014; DOI:10.1016/j.inoche.2014.10.011 · 2.06 Impact Factor
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    ABSTRACT: A homologous series of fire-retardant oligoalkyleneoxy-phosphates was synthesized for evaluation as electrolyte media for dye sensitized solar cells (DSSCs) and lithium-batteries. Unoptimized DSSC electrolyte formulations for DSSCs achieved ionic conductivities as high as 5.71×10-3 S∙cm-1, and DSSC test-cell efficiencies up to 3.6% as well as Voc, Jsc and ff up to 0.81 V, 8.03 mA∙cm-2 and 0.69 respectively. Poly(bis-(2-(2-methoxyethoxy)ethoxy)phosphazene) based Li+ conducting gel-electrolytes plasticized with the best performing phosphate had conductivities as high as 9.9×10-4 S∙cm-1 at 30 °C. All the compounds have boiling points higher than 197 °C. The results show that the viscosity, glass transition temperatures, and conductivity of the compounds are dependent mainly on the length of the longest alkyleneoxy chain.
    ACS Applied Materials & Interfaces 12/2013; 5(24). DOI:10.1021/am403924t · 5.90 Impact Factor
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    ABSTRACT: 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.
    Inorganic Chemistry Communications 11/2013; 37:158-161. DOI:10.1016/j.inoche.2013.09.056 · 2.06 Impact Factor
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  • Zhicheng Tian, Chen Chen, Harry R. Allcock
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    ABSTRACT: Biodegradable poly(organophosphazenes) containing side chains of various oligo(ethylene glycol) methyl ethers (mPEGs) and glycine ethyl ester units were synthesized and characterized. Novel supramolecular-structured hydrogel systems based on the inclusion complex between the mPEG grafted polyphosphazenes and α-cyclodextrin were prepared in aqueous media. The gelation time depended on the length of the mPEG side chains, the molar ratio between mPEG repeat units and α-cyclodextrin, and the concentration of the polymeric gel precursors. The rheological measurements of the supramolecular hydrogels indicate a fast gelation process and flowable character under a large strain. The hydrogel systems demonstrate unique structure-related reversible gel–sol transition properties at a certain temperature due to the reversible supramolecular assembly. The formation of a channel-type inclusion complex induced gelation mechanism was studied by DSC, TGA, 13C CP/MAS NMR, and X-ray diffraction techniques. The strong potential of the system for injectable drug delivery applications was explored with the use of bovine serum albumin as a model protein for in vitro release studies. All the supramolecular hydrogels studied showed disintegration by dethreading of the α-cyclodextrin. Polymers with longer poly(ethylene glycol) side chains had better stability and slower protein release profiles. The molecular weights of the polymers were monitored by GPC to show the biodegradability of the hydrogel system.
    Macromolecules 04/2013; 46(7):2715-2724. DOI:10.1021/ma4004314 · 5.93 Impact Factor
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    ABSTRACT: A series of novel polyphosphazene ionomers with short chain poly(ethylene oxide) (PEO) moieties, bound ammonium cations, and free iodide anions were previously synthesized. Ion dynamics during anion conduction of the ionomers were studied by dielectric relaxation spectroscopy (DRS). These polyphosphazenes provide interesting conductive materials to study because of their low glass transition temperature, high segmental mobility, and high ion content. Analysis of DRS results provides static dielectric constant, conducting ion mobility, and conducting ion content for the materials. An increase in the length of the alkyl group extending from the polymer-bound ammonium cation increases conductivity and conducting ion concentration due to new steric interactions weakening ion-ion associations that restrict segmental mobility. By placing ether oxygens in the short alkyl group a large increase in conductivity and a decrease in the glass transition temperature is observed due to strong associations between the cation and ether oxygen lone pairs.
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    ABSTRACT: Novel polyphosphazenes containing the fluoroquinolone antibiotic substituents, ciprofloxacin or norfloxacin, were synthesized and characterized. Nano/microfibers of several selected polymers were prepared by an electrospinning technique. The sensitivity to hydrolysis, pH behavior, and antibiotic release profile of all the polymers as films and the selected polymers as nano/microfibers were investigated. The hydrolysis release behavior was further studied by an in vitro antibacterial test against E. coli. Protection and deprotection reactions of ciprofloxacin and norfloxacin were carried out before and after polymer synthesis to prevent cross-linking of multi-functional reagents with polymers. No more than 25 mol% of antibiotics can be introduced to poly(dichlorophosphazene) which was synthesized by a thermal ring opening polymerization of hexachlorocyclotriphosphazene. Various amino acid ethyl esters (glycine, alanine, and phenylalanine) were linked to the polymers as co-substituents to increase the solubility as well as to control the rate of antibiotic release. Depending on the polymer compositions, 5–23% weight loss and 4–30% antibiotic release were observed in a six week hydrolysis study at 37 °C. The corresponding nano/microfibers showed a much faster degradation and antibiotics release due to a substantially larger surface area. The in vitro antibacterial tests showed an antibacterial effect as long as ciprofloxacin or norfloxacin was released from the polymers. Meanwhile, all the polymers gave a near-neutral hydrolysis environment with the pH ranging from 5.9 to 6.8.
    02/2013; 4(6). DOI:10.1039/C2PY21064A
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    ABSTRACT: The synthesis and characterization of novel poly (CTFE-g-oligoEO) graft copolymers [chlorotrifluoroethylene (CTFE) and ethylene oxide (EO)] are presented. First, vinyl ether monomers bearing oligo(EO) were prepared by transe-therification of x-hydroxyoligo(EO) with ethyl vinyl ether catalyzed by a palladium complex in 70–84% yields. Two vinyl ethers of different molecular weights (three and 10 EO units) were thus obtained. Then, radical copolymerization of the above vinyl ethers with CTFE led to alternating poly(CTFE-alt-VE) copolymers that bore oligo(OE) side chains in satisfactory yields (65%). These original poly(CTFE-g-oligoEO) graft copolymers were characterized by 1 H, 19 F, and 13 C NMR spec-troscopy.
    Journal of Polymer Science Part A Polymer Chemistry 02/2013; 51(4):977. DOI:10.1002/pola.26463 · 3.25 Impact Factor
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    ABSTRACT: This report describes the surface morphology and wetting behavior of one aryl and three fluorous polyphosphazenes: poly[bis(2,2,2-trifluoroethoxy)phosphazene], PTFEP, 1, poly[bis(para-fluorophenoxy)phosphazene] 2, poly[bis(meta-trifluoromethylphenoxy)phosphazene] 3, and poly(diphenoxyphosphazene) 4. Thermal analysis confirms high thermal stability for these polyphosphazenes. With phenyl side chains, 2–4 are particularly stable with T5% >400 °C. Surface morphology via tapping mode atomic force microscopy (TM-AFM) and dynamic contact angles (DMA) are correlated with composition and crystallinity estimated by differential scanning calorimetry (DSC). The resulting structure property relationships define trends in processability, hydrophobicity and oleophobicity. Compared to 1, 3, and 4 poly[bis(para-fluorophenoxy)phosphazene] 2 is noteworthy by virtue of a high melting point (179 °C), high crystallinity (ΔHf, 30.2 J/g), and a moderate molecular weight. The remaining polyphosphazenes in this group have Tm <100 °C. Heats of fusion (J/g) are in the order 1 (29.4) ≈ 2 (30.2) > 3 (17) >> 4 (4.0). High molecular weights for 3 and 4 (>103 kDa) would make melt processability problematic. Thus 1 or 2 has a favorable combination of properties, with 2 favored for many applications due to a higher Tm. In summary, for performance and processing, high Tm, and resistance to water and hydrocarbons poly[bis(para-fluorophenoxy)phosphazene], 2 is attractive. This finding suggests other para-substituted phenyl phosphazenes are worth further study.
    Polymer 02/2013; 54(3):1123–1129. DOI:10.1016/j.polymer.2012.12.063 · 3.77 Impact Factor

Publication Stats

8k Citations
2,206.76 Total Impact Points

Institutions

  • 1983–2015
    • William Penn University
      Worcester, Massachusetts, United States
  • 1977–2014
    • Pennsylvania State University
      • • Department of Chemistry
      • • Department of Biology
      University Park, Maryland, United States
  • 1999–2010
    • The University of Calgary
      • Department of Chemistry
      Calgary, Alberta, Canada
  • 2006
    • Drexel University
      • Department of Chemical and Biological Engineering
      Filadelfia, Pennsylvania, United States
  • 2003
    • University of Virginia
      Charlottesville, Virginia, United States
    • Inha University
      • Department of Polymer Science and Engineering
      Chemulpo, Incheon, South Korea
  • 2002
    • Edison Pharmaceuticals
      Mountain View, California, United States
    • Northwestern University
      • Department of Chemistry
      Evanston, Illinois, United States
    • Energy Institute
      Londinium, England, United Kingdom
    • University of Bayreuth
      Bayreuth, Bavaria, Germany
  • 1998–2002
    • Massachusetts Institute of Technology
      • • Department of Biology
      • • Department of Chemical Engineering
      Cambridge, Massachusetts, United States
  • 2000
    • University of Toronto
      • Department of Chemistry
      Toronto, Ontario, Canada
  • 1988
    • Park University
      Parkville, Missouri, United States