PREPARATION OF STAR-BRANCHED POLYMERS WITH CYCLOTRIPHOSPHAZENE CORES

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene was prepared by the reaction of hexachlorocyclotriphosphazene with the sodium salt of 4-hydroxybenzaldehyde and subsequent reduction of aldehyde groups to alcohol groups by using sodium borohydride. The bromination reaction was carried out by using hydrobromic acid-sulfuric acid to give hexakis[p-(bromomethyl)phenoxy]cyclotriphosphazene. This compound was employed in initiating polymerization of 2-methyl-2-oxazoline to produce six-armed, star-branched polymers. Monofunctional initiator, N3P3(OC6H5)5(OC6H4-p-CH2Br), was also prepared and used for initiating the polymerization of 2-methyl-2-oxazoline to result in linear polymers. Molecular weights and DP's per an arm of the polymers were determined by gel permeation chromatography and H-1 NMR, respectively. The molecular weight of the linear polymer measured by GPC was much higher than that of the star-branched polymer when their molecular weights determined by H-1 NMR were nearly same. The linear polymer (DP = 31) with a bulky hydrophobic head and a hydrophilic chain exhibited nonionic surfactant behavior, forming micelles above a polymer concentration of about 0.1% by weight. The star-branched polymers had a hydrophobic core and hydrophilic branches. The surface tension of the aqueous solution of the star-branched polymer (DP = 13.4 per branch) decreased very slowly as polymer concentration increased, and any evidence for forming micelles was not observed. N-Acetyl groups of star-branched polymers were removed by hydrolysis under acidic conditions to give the polymers with N-protonated poly(ethylenimine) branches.