Showing papers by "Harry R. Allcock published in 2019"

Synthesis, Physicochemical Analysis, and Side Group Optimization of Degradable Dipeptide-Based Polyphosphazenes as Potential Regenerative Biomaterials.

Abstract: We report the synthesis and physicochemical analysis of mixed-substituent dipeptide-based polyphosphazene polymers, poly[(glycineethylglycinato) x (phenylphenoxy) y phosphazene] (PNGEG x PhPh y ) and poly[(ethylphenylalanato) x (glycineethylglycinato) y phosphazene] (PNEPA x GEG y ), using glycylglycine ethyl ester (GEG) as the primary substituent side group and cosubstituting with phenylphenol (PhPh) and phenylalanine ethyl ester (EPA), respectively. The suitability of the cosubstituted polyphosphazenes to regenerative engineering was evaluated. The physicochemical evaluation revealed that the molecular weights, glass transition temperatures, hydrophilicity, and mechanical properties could be modulated by varying the compositions of the side groups to obtain a variety of properties. The PNEPA25GEG75 and PNGEG75PhPh25 polymers exhibited the most promising physicochemical properties. These two polymers were further subjected to in vitro hydrolysis and cell proliferation studies using poly(lactic-co-glycolic acid) (PLAGA) as a control. The hydrolysis experiments revealed that the two polymers hydrolyzed to near-neutral pH media (~5.3 to 7.0) in a relatively slow fashion, whereas a pH value as low as 2.2 was obtained for the PLAGA media over 12 weeks of degradation study. Furthermore, the two polymers showed continuous MC3T3 cell proliferation and growth in comparison to PLAGA over a 21-day culture period. These findings establish that cosubstitution of different side groups of polyphosphazenes and exploitation of the hydrogen-bonding capacity of peptide bonds in GEG offer a flexible tool that can be employed to make new and fascinating polymeric biomaterials with different and tailored properties that can suit different regenerative needs.

Hybrid Polyphosphazene–Organosilicon Polymers as Useful Elastomers

Abstract: Six high molecular weight, soluble, and stable elastomers were prepared derived from −O(CH2)3Si(CH3)3/–OCH2CF3 cosubstituted polyphosphazenes with 1–92 mol % of the organosilicon component. The surface and morphological properties are appropriate for biomaterials, soft contact printing, or other elastomeric applications. Full substitution by either side group yields thermoplastics. The syntheses were facilitated by small molecule model reactions to establish appropriate reaction conditions.

Polyphosphazenes as an Example of the Element-Blocks Approach to New Materials

Abstract: Polyphosphazenes are inorganic-organic high polymers with a backbone of alternating phosphorus and nitrogen atoms and two organic or organometallic side groups attached to each phosphorus. Most of these polymers are synthesized by macromolecular substitution reactions carried out on poly(dichlorophosphazene), (NPCl2)n. The chlorine substitution reactions involve alkoxides, aryloxides, primary or secondary amines, or a range of organometallic reagents. Structural variations are accomplished via the use of one, two, or more different nucleophiles and substituents along the polymer chain and by the employment of reagent size and reactivity to control polymer properties and emphasize specific uses. Applications have been developed for these polymers as elastomers, thermoplastics, biostable or bioerodible medical materials, fire-resistant lithium battery electrolytes, films, or foams, and gas and liquid separation membranes.

Crystal structures of three hexakis-(fluoroar-yloxy)cyclo-triphosphazenes.

Abstract: The syntheses and crystal structures of three cyclo­triphosphazenes, all with fluorinated ar­yloxy side groups that generate different steric characteristics, viz. hexa­kis­(penta­fluoro­phen­oxy)cyclo­triphosphazene, N3P3(OC6F5)6, 1, hexa­kis­[4-(tri­fluoro­methyl)­phen­oxy]cyclo­triphosphazene, N3P3[OC6H4(CF3)]6, 2 and hexa­kis­[3,5-bis(­tri­fluoro­methyl)­phen­oxy]cyclo­triphosphazene, N3P3[OC6H3(CF3)2]6 3, are reported. Specifically, each phospho­rus atom bears either two penta­fluoro­phen­oxy, 4-tri­fluoro­methyl­phen­oxy, or 3,5-tri­fluoro­methyl­phen­oxy groups. The central six-membered phosphazene rings display envelope pucker conformations in each case, albeit to varying degrees. The maximum displacement of the `flap atom' from the plane through the other ring atoms [0.308 (5) A] is seen in 1, in a mol­ecule that is devoid of hydrogen atoms and which exhibits a `wind-swept' look with all the aromatic rings displaced in the same direction. In 3 an intra­molecular C—H(aromatic)⋯F inter­action is observed. All the –CF3 groups in 2 and 3 exhibit positional disorder over two rotated orientations in close to statistical ratios. The extended structures of 2 and 3 are consolidated by C—H⋯F inter­actions of two kinds: (a) linear chains, and (b) cyclic between mol­ecules related by inversion centers. In both 1 and 3, one of the six substituted phenyl rings has a parallel-displaced aromatic π–π stacking inter­action with its respective symmetry mate with slippage values of 2.2 A in 1 and 1.0 A in 3. None of the structures reported here have solvent voids that could lead to clathrate formation.