Showing papers by "Harry R. Allcock published in 1998"

The synthesis of functional polyphosphazenes and their surfaces

Abstract: The macromolecular substitution approach for the synthesis of polyphosphazenes provides access to many different polymers. However, it precludes the use of reagents that contain two or more functional groups because such compounds would cause extensive crosslinking of the chains. This presents a problem because many of the uses for which polyphosphazenes seem ideally suited require the presence of -OH, -COOH, -NH2, -SO3H, -PR2 and other functional units in the side-chain structure. We have developed two approaches to introduce such active sites: (1) protection‐deprotection reactions; and (2) direct reactions of active reagents with the organic side-groups of non-functional poly(organophosphazenes). These methods have been applied both at the molecular level and in the form of reactions carried out only at polymer surfaces. The resultant polymers have special properties that are valuable in the microencapsulation of sensitive biological agents; in the formation of hydrophobic, hydrophilic, or adhesive surfaces; in crosslinking reactions; and in the development of solid polymer electrolytes, bio-erodible polymers, pH-triggered hydrogels, polymer blends and interpenetrating polymer networks. Overall, more than 700 different polyphosphazenes are now known, and a large number of these are functional macromolecules targeted for specific property combinations and uses. # 1998 John Wiley & Sons, Ltd.

Cation complexation and conductivity in crown ether bearing polyphosphazenes

Abstract: An attempt has been made to understand the mechanism of ionic conductivity in polyphosphazene−salt complexes by the synthesis and study of systems with crown ether side groups and salts with different cations. Amorphous phosphazene polymers, bearing either (12-crown-4)-methoxy, (15-crown-5)-methoxy, or (18-crown-6)-methoxy pendent groups, either as single-substituent polymers or mixed-substituent species in a 1:3 ratio with 2-(2-methoxyethoxy)ethoxy groups, were synthesized and characterized. The polymers in which all the side groups are crown ether units have glass transition temperatures higher than other oligo(ethyleneoxy) polyphosphazenes. They generate relatively low ionic conductivities at ambient temperatures when complexed with lithium triflate or lithium perchlorate. This suggests that the cation carries a significant part of the current in ether-type polymers. The ambient temperature ionic conductivity of the cosubstituent polyphosphazenes, as well as of poly[bis(2-(2-methoxyethoxy)ethoxy)phosph...

Polyphosphazenes with Novel Architectures: Influence on Physical Properties and Behavior as Solid Polymer Electrolytes

Abstract: Three types of polyphosphazenes with different architectures have been synthesized and characterized. The influence of the polymer architecture on solid ionic conductivity was of particular interest. The first type includes linear oligo- and polyphosphazenes with the general formula [NP(OCH2CH2OCH2CH2OCH3)2]n (MEEP) with different chain lengths. The second type consists of a series of triarmed star-branched polyphosphazenes with the general formula N{CH2CH2NH(CF3CH2O)2P[NP(OCH2CH2OCH2CH2OCH3)2]n}3 with different arm lengths. These were synthesized via the reaction of the tridentate initiator [N{CH2CH2NH(CF3CH2O)2PN−PCl3+}3][PCl6-]3 with the phosphoranimine Cl3PNSiMe3 in CH2Cl2 followed by halogen replacement with sodium (methoxyethoxy)ethoxide. The molecular weights in this system were carefully controlled by variation of the monomer-to-initiator ratios, and the effect of polymer molecular weight on solid ionic conductivity was examined. The third polymer system was designed to examine the effect of compl...

Biodegradable mixtures of polyphoshazene and other polymers

Abstract: Biodegradable polymeric compositions are provided, wherein biodegradable polyphosphazenes are combined with at least one other polymer, either in the form of a blend, a semi-interpenetrating network (semi-IPN), or an interpenetrating network IPN The side groups and composition of the polyphosphazenes are used to determine the properties of the compositions, for example, the rate and extent of degradation, and mechanical properties These are useful in biomedical applications, including controlled drug delivery and tissue regeneration, and environmental applications In the most preferred embodiment, as demonstrated by the examples, the polyphosphazenes contain hydrophobic side groups, such as p-methylphenoxy and other aromatic groups, and groups which impart hydrolytic instability, such as amino acid alkyl esters, and degrade by surface erosion A preferred example is ethyl glycinato-substituted polyphosphazene (PPHOS) with p-methylphenoxy as co-substituent These are blended with other polymers, such as PLGA, which have desirable mechanical properties but which degrade by bulk erosion, so that the blend degrades by surface erosion For the biomedical applications, FDA approved polymers, such as polymers of lactic and glycolic acids and their copolymers, are preferred Methods for making these compositions also are provided

Synthesis and Characterization of Hindered Polyphosphazenes via Functionalized Intermediates: Exploratory Models for Electro-optical Materials

Abstract: Several cosubstituent polyphosphazenes were synthesized that incorporate the nonlinear optical chromophore, disperse red 1 (DR-1), linked covalently to the polymer backbone through spacer groups. These polymers have a high chromophore loading (one DR-1 per repeat unit), have glass transition temperatures near 100 °C, and are high refractive index materials (n = ∼1.71). The syntheses were achieved via unconventional reactions that involve functionalized poly(organophosphazenes). Disperse red-1 was linked to the polymers by two different methods that generate either an ester- or an ether-linked system. Techniques such as 1H, 13C, and 31P NMR, gel permeation chromatography, differential scanning calorimetry, UV−vis spectroscopy, and optical birefringence were used to monitor the structures.

Functionalized polyphosphazenes: Polymers with pendent tertiary trialkylamino groups

Abstract: Attempts have been made to synthesize polyphosphazenes with pendent tertiary amino side units via macromolecular substitution. Incorporation of −OCH2CH2N(CH3)2, −OCH2CH2OCH2CH2N(CH3)2, and −NHCH2CH2N(CH3)2 groups was studied. Polymers in which all the side groups consisted of one type of aliphatic tertiary amino-containing unit and species that also contained 2,2,2-trifluoroethoxy or phenoxy groups as cosubstituents were examined. Related phosphazene cyclic trimers were also prepared as small molecule model systems to examine synthetic variables, characterization techniques, and hydrolytic behavior. Those phosphazenes in which the tertiary amino-containing side groups are linked to the skeleton through an aliphatic oxygen−phosphorus bond are sensitive to hydrolysis induced by the basicity of the terminal amino group. However, species in which the tertiary amino-containing units are linked to the backbone through an alkyl nitrogen−phosphorus bond are stable to water and are candidate materials for use in a...

Polyphosphazenes functionalized with sulfone or sulfoxide groups: Synthesis, characterization, and possible polymer electrolyte applications

Abstract: A method for the introduction of sulfone or sulfoxide functional groups into the side groups of polyphosphazenes has been developed This procedure involves the prior introduction of thioether-containing side groups into phosphazenes followed by oxidation of the sulfur atoms by H2O2 or m-chloroperbenzoic acid (MCPBA) This method was first explored at the level of model small molecule cyclic species as a prelude to the polymer oxidation reactions The attractive forces generated by sulfone or sulfoxide functional groups produce alkyloxy-substituted polyphosphazenes with relatively high glass transition temperatures (up to +19 °C) The potential of these materials as polymer electrolytes, both in the solid state and in systems with added propylene carbonate, was explored by means of impedance analysis conductivity studies The competition between the polymer and the solvent for lithium ions was also investigated

In vitro release of colchicine using poly(phosphazenes): the development of delivery systems for musculoskeletal use.

Abstract: A colchicine release system utilizing biodegradable poly (phosphazenes) was investigated in vitro for intra-articular administration. Polymer degradation and drug release studies were performed on colchicine-loaded poly (phosphazenes) containing either imidazotyl (I-PPHOS) or ethyl gtycinato (EG-PPHOS) side chain substituents over a 21-day period. To study the effects of an implantable colchi-cine-PPHOS delivery system on local musculoskeletal tissue in vitro, osteoblast-like cells were grown on the matrices. Colchicine release was 20% for I-PPHOS and 60% for EG-PPHOS over the 21-day period. Release appeared to proceed through a combination of diffusional and degradative mechanisms. Environmental scanning electron microscopy (ESEM) studies revealed large pores in the drug-depleted devices in contrast to the control matrices without drug, which may have contributed to the release seen, especially with ethyl glycinato-containing matrices. Cell growth on matrices containing colchicine was significant...