Phosphazene monomers from the regiospecific reaction oftert-butylhydroquinone with hexachlorocyclotriphosphazene: A new composite material precursor

Abstract

ABSTRACT:A new synthesis of a phosphazene-based polymer precursor is described. tert-Butylhydroquinone was found to react with hexachlorocyclotriphosphazene in the presence of a base, 4-picoline, in cyclohexane to yield a regiospecifically substituted hexa-tert-butylcyclotriphosphazene. This reaction proceeds more rapidly to completion and in a higher yield than data previously reported for analogous cyclotriphosphazenes. Nuclear magnetic resonance spectroscopy and thermal methods (differential scanning calorimetry and thermogravimetric analysis) were employed to characterize this material, and it is observed that the bifunctional tert-butylhydroquinone substitutes only at the least hindered phenolic hydroxyl under the reported reaction conditions. This conclusion clarifies published data that suggests that without the tert-butyl substituent on the hydroquinone ring, crosslinking between phosphazene rings occurs to some extent.

Synthesis and characterization of poly{hexakis[(methyl)(4‐hydroxyphenoxy)]cyclotriphosphazene}

“…4(a)] is similar to that found for 3 and provides evidence of the presence of both bridging and nonbridging methylhydroquinone moieties. In contrast to 3 and 1 , the formation of 2 occurs with regiospecificity where the tert ‐butyl group enforces the orientation away from the phosphorus–nitrogen ring during the addition and effectively protects the remaining hydroxyl group from further reaction 18. This results in the formation of a distinct cyclotriphosphazene with a single resonance in the 31 P‐NMR spectrum with a half‐height full‐width line width of less than 4 Hz [Fig.…”

“…Hexakis[(3‐ tert ‐butyl)(4‐hydroxyphenoxy)]cyclotriphosphazene (2) was prepared as previously reported 18 . M w = (1.07 ± 0.1) × 10 3 g/mol, dn/dc = 0.138, RMS radius < 10 nm, second virial coefficient = (2.82 ± 3.0) × 10 −3 mol mL/g 2 .…”

“…3) was synthesized by reacting hexachlorocyclotriphosphazene with tertbutylhydroquinone via the one-step nucleophilic substitution method used earlier for the formation of 1. 18 The bulky nature of the tert-butyl group adjacent to one of the hydroxyl groups effectively provides enough steric hindrance that only the nonhindered hydroxyl site is available for the reaction with hexachlorocyclotriphosphazene. The result is a regiospecific substitution reaction with only discrete cyclic trimers being produced.…”

Reactions and polymerization of hexa-[3-tert-butyl-4- hydroxyphenoxy]cyclotriphosphazene: A new method for the preparation of soluble cyclomatrix phosphazene polymers

“…Syntheses of crosslinked 1 16 and neat cyclic trimer 2 17 have been reported to occur in a facile manner with high yields. Each of these cyclotriphosphazenes contains free aromatic hydroxyl groups that afford synthetic pathways to expand the chemistry of these systems.…”

“…Further work17 using the one‐step method of Femec16 examined the reaction of tert ‐butylhydroquinone with hexachlorocyclotriphosphazene where a discrete monomeric product was observed, hexa‐[3‐ tert ‐butyl‐4‐hydroxyphenoxy]cyclotriphosphazene ( 2 ; see Fig. 2).…”