Harry R. Allcock

William Penn University, Worcester, Massachusetts, United States

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Publications (547)2708.02 Total impact

  • No preview · Article · Feb 2016 · Macromolecules
  • Harry R Allcock
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    ABSTRACT: The importance of phosphorus in polymer chemistry is illustrated by the growth of the broad field of polyphosphazene science. Several hundred high polymers are now known with a phosphorus-nitrogen backbone and combinations or more than 250 different organic side groups. The properties of these polymers depend on both the character of the inorganic backbone and the structure of the organic side groups. This summary reviews the synthesis pathways to these materials, the often-unique structure-property relationships, and challenges for the future expansion of this field.
    No preview · Article · Nov 2015 · Dalton Transactions
  • Tomasz Modzelewski · Emily Wilts · Harry R. Allcock
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    ABSTRACT: New polymers with a phosphazene backbone and both 2,2,2-trifluoroethoxy- and phenoxy-functionalized cyclotriphosphazene substituents exist in three phases depending on the side group ratios. At low concentrations of the bulky substituents (up to ∼7 mol %), the polymers are semicrystalline thermoplastics, with properties that are minor variations of poly[bis(2,2,2-trifluoroethoxy)phosphazene]. However, after the incorporation of between ∼7 mol % and ∼20 mol % of the bulky cyclic trimeric side groups, the polymers lose their semicrystalline properties and become amorphous elastomers. At still higher trimer loadings (>20 mol %) the materials develop gum-like behavior. The elastomeric phase appears to be generated by interdigitation or agglomeration of the bulky aryloxy-cyclotriphosphazene side groups, which act as quasi-physical cross-links between the polymer chains. The presence of these interactions allows the materials to experience high strain values before rupture (up to 1000%), and elastic recovery of more than 85% of the original dimensions when stressed up to 60% of the break elongation over four cycles. In addition, the chemical and physical nature of the substituents on the cyclic trimeric side groups alters the physical characteristics of the polymer in a way that provides a facile method to tune the properties.
    No preview · Article · Oct 2015 · Macromolecules
  • Tomasz Modzelewski · Nichole M. Wonderling · Harry R. Allcock
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    ABSTRACT: The range of polyphosphazene-based elastomers has been expanded through the use of phenoxy or oligo-p-phenyleneoxy minor cosubstituent side groups with majority 2,2,2-trifluoroethoxy side groups. Specifically, polymers with both trifluoroethoxy and low ratios of phenoxy, p-phenylphenoxy, p-diphenylphenoxy, or p-triphenylphenoxy cosubstituents, can generate noncrystalline, noncovalently cross-linked elastomers. These are formed through the steric interactions of the oligo-p-phenyleneoxy side groups. Small-angle X-ray scattering (SAXS) analysis of polymers containing p-diphenylphenoxy or p-triphenylphenoxy cosubstituents suggests that these macromolecules contain microdomains caused by the phase separation of the trifluoroethoxy and aryloxy groups, through stacking or agglomeration of the aryloxy units, and that those serve as noncovalent cross-linking points. Moreover, annealing of the polymers at elevated temperatures (150°C) causes a decrease in the average spacing between the aryloxy aggregates and has a direct effect on the mechanical properties, similar to the toughening caused by increases in the cross-link density in conventional elastomers.
    No preview · Article · Jul 2015 · Macromolecules
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    ABSTRACT: Poly(dichlorophosphazene) is a versatile precursor material for accessing new polymeric materials via the introduction of various side groups by chlorine replacement reactions. Herein, methods are described for the synthesis of a new series of phosphazene single- and mixed-substituent high polymers containing cyclic aliphatic rings, -CnH2n-1 (where n = 4-8). These reactions were preceded by model reactions using small molecule cyclic trimeric phosphazenes. The new high polymers are amorphous, transparent, and film- and membrane-forming materials with a wide range of glass transition temperatures (-60 to +40 °C) depending on the side groups and cosubstituents. All are hydrophobic and resistant to hydrolytic breakdown. (Figure Presented).
    No preview · Article · Jul 2015 · Macromolecules
  • Zhongjing Li · Harry R Allcock
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    ABSTRACT: Red, green, and blue dye molecules were linked covalently to polyphosphazenes to generate soluble, film-forming materials appropriate for the formation of patterned tricolor filters for possible use in liquid crystalline and other display devices or in camera sensors. The mono-functional dyes, a red [1-[(E)-(4-nitrophenyl)diazenyl]-2-naphthol], a green tetraphenylporphyrin [5-(4-hydroxyphenyl)-10, 15, 20-tetraphenylporphyrin], and a blue toluidine blue dye, were employed as representative chromophores. The cosubstituents employed include 2,2,2-trifluoroethoxy with and without aryloxy groups, or cyclopentanoxy groups. The optical densities were varied by adopting several dye to cosubstituent side group ratios. These dyes are models for a wide range of different chromophores that can be linked to polyphosphazene chains.
    No preview · Article · May 2015 · ACS Applied Materials & Interfaces
  • Zhicheng Tian · Chen Chen · Harry R. Allcock
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    ABSTRACT: This work is an investigation of the influence of bulky fluoroalkoxy side groups on the properties of polyphosphazenes. A new series of mixed-substituent high polymeric poly(fluoroalkoxyphosphazenes) containing trifluoroethoxy and branched fluoroalkoxy side groups was synthesized and characterized by NMR and GPC methods. These polymers contained 19-29 mol % of dibranched hexafluoropropoxy groups or 4 mol % of tribranched tert-perfluorobutoxy groups which serve as regio-irregularities to reduce the macromolecular microcrystallinity. The structure-property correlations of the polymers were then analyzed and interpreted by several techniques: specifically by the thermal behavior by DSC and TGA methods, the crystallinity by wide-angle X-ray diffraction, and the surface hydrophobicity/oleophobicity by contact angle measurements. Ultraviolet cross-linkable elastomers were prepared from the new polymers through the incorporation of 3 mol % of 2-allylphenoxy and photoirradiation. The mechanical properties and the elastomeric deformation-recovery behavior were then monitored by varying the time of ultraviolet irradiation. Side reactions detected during the synthesis of the high polymers, such as side group exchange reactions and α-carbon attack, were analyzed via use of a cyclic trimer model system. The new polyphosphazenes with branched fluorinated side groups expand the scope of phosphazene-related materials and provide an understanding of the effect of different side group geometries on the overall properties of the fluoroelastomers.
    No preview · Article · Mar 2015 · Macromolecules
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    ABSTRACT: Anion conducting polyphosphazene ionomer analogues of poly[bis(methoxyethoxyethoxy)phosphazene] (MEEP) were synthesized and their iodide transport properties studied. Polymer bound cations were quaternized with either short alkyl or short ether oxygen chains. X-ray scattering reveals a low q peak near 4 nm–1 arising from the backbone–backbone spacing between polyphosphazene chains, an ion-related peak at 8 nm–1, and a peak at 15 nm–1 corresponding primarily to the amorphous halo of the PEO side chains. Because of the short spacing of the intermediate q peak, the ions are proposed to exist mostly in isolated ion pairs or small aggregates. First-principles calculations combined with dielectric spectroscopy suggest that less than 10% of the ions are in isolated pairs while the remainder participate in quadrupoles or other small aggregates. These ionomers display high values for the high frequency dielectric constant, ε∞ (highest value ε∞ = 11), due to atomic polarization of the iodide anion. These MEEP-based ionomers have room temperature dc conductivity of order 10–6 S cm–1 and show potential for application in iodide conducting solar cells if the segmental mobility could be increased.
    No preview · Article · Jan 2015 · Macromolecules
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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.
    No preview · Article · Jan 2015 · Polyhedron
  • 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.
    No preview · Article · Dec 2014 · Journal of Applied Polymer Science
  • 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.
    No preview · Article · Nov 2014 · European Polymer Journal
  • Jessica L. Nichol · Ian T. Hotham · Harry R. Allcock
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    ABSTRACT: Hydrolytically sensitive polymers that degrade into benign products are of interest as biomedical materials. The aim of this study was to determine the properties and hydrolytic characteristics of both poly(diethoxyphosphazene) and related derivatives with both ethoxy and hydrophobic co-substituent groups in a near-1:1 M ratio such as 2,2,2-trifluoroethoxy, phenoxy, or p-methylphenoxy units. These hydrophobic cosubstituents served as models for bioactive counterparts. The hydrolytic sensitivity of the ethoxyphosphazene units was so pronounced that even hydrophobic or bulky O-linked co-substituents failed to counteract the hydrolysis behavior during a twelve-week hydrolysis study. This work illustrates a pathway for the development of a new class of useful bioerodible polymers.
    No preview · Article · Nov 2014 · Polymer Degradation and Stability
  • Tomasz Modzelewski · Harry R. Allcock
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    ABSTRACT: We report the synthesis and characterization of a new linear polyphosphazene architecture in which rigid, bulky side units provide the possibility of interdigitation with their counterparts on neighboring chains to generate noncovalent cross-links and distinct elastomeric properties. The bulky side groups are cyclotriphosphazene rings substituted with trifluoroethoxy groups connected to the main chain via aryloxy spacers. These bulky units are distributed along the polymer backbone and separated from each other by trifluoroethoxy units linked directly to the main chain. Compared to the well-known poly[(bis-2,2,2-trifluoroethoxy)phosphazene], [NP(OCH2CF3)(2)](n), which is a microcrystalline film- and fiber-forming polymer, several of the new materials are elastomers with properties that arise partly from interactions of the protruding cydotriphosphazene side units with those on nearby polymer chains. Specific elastomers are capable of regaining up to 89% of their original shape when elongated to high strain (up to 1000%) over four elongation cycles and show even longer elongations at break (>1600%). The overall physical properties depend on the ratios of the cyclic trimeric side units to main chain linked trifluoroethoxy side groups. The polymers were characterized using H-1, P-31 NMR, DSC, TGA, X-ray diffraction, GPC, and stress strain techniques.
    No preview · Article · Oct 2014 · Macromolecules
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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.
    Preview · Article · Sep 2014 · ACS Nano
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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
    No preview · Article · Aug 2014 · Journal of Polymer Science Part A Polymer Chemistry
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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
    No preview · Article · Aug 2014 · Polymer Engineering and Science
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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.
    Preview · Article · Apr 2014 · RSC Advances
  • 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.
    No preview · Article · Jan 2014 · Macromolecules
  • Harry R. Allcock
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    ABSTRACT: Polyphosphazenes are macromolecules with a chain of alternating phosphorus and nitrogen atoms and with two (usually) organic side groups linked to each phosphorus. Although the earliest poly(organophosphazenes) were essentially linear polymers each bearing only one type of side group along the chain, research in our program in recent years has widened the scope to include mixed-substituent polymers with two or more different side groups, block copolymers, comb structures, stars, and dendrimers, all with a wide variety of different properties. In addition, supramolecular systems have also been synthesized including vesicles, microspheres, and a variety of composite systems. This review provides a summary of these developments together with an introduction to the widening array of developing uses. Copyright (c) 2013 John Wiley & Sons, Ltd.
    No preview · Article · Jan 2014 · ChemInform
  • Nicole L. Morozowich · Ryan J. Mondschein · Harry R. Allcock
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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. Graphical Abstract
    No preview · Article · Jan 2014 · Journal of Inorganic and Organometallic Polymers and Materials

Publication Stats

16k Citations
2,708.02 Total Impact Points


  • 1978-2015
    • William Penn University
      Worcester, Massachusetts, United States
  • 1966-2015
    • 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
  • 2002
    • Energy Institute
      Londinium, England, United Kingdom
  • 2000
    • University of Toronto
      • Department of Chemistry
      Toronto, Ontario, Canada
  • 1997
    • Bloomsburg University
      • Department of Chemistry and Biochemistry
      Блумсбург, Pennsylvania, United States
  • 1993
    • University of Bayreuth
      Bayreuth, Bavaria, Germany
  • 1991-1992
    • Edison Pharmaceuticals
      Mountain View, California, United States
  • 1990-1991
    • Massachusetts Institute of Technology
      • • Department of Chemical Engineering
      • • Department of Biology
      Cambridge, Massachusetts, United States
    • University of California, Los Angeles
      • Department of Electrical Engineering
      Los Ángeles, California, United States
  • 1988
    • Park University
      Parkville, Missouri, United States