Synthesis and Topological Trapping of Cyclic Poly(alkylene
phosphates)
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Abstract
The zwitterionic ring-opening polymerization
of 2-isopropoxy-2-oxo-1,3,2-dioxaphospholane
(iPP) with <i>N</i>-heterocyclic carbenes (NHC) generates
poly(alkylene phosphate)s with molecular weights of <i>M</i><sub>n</sub> = 55000–202000 Da. MALDI-TOF mass spectrometry
provided clear evidence for cyclic poly(alkylene phosphate)s (poly(iPP))
for lower molecular weight fractions (<i>m</i>/<i>z</i> ≤ 3000). The cyclic topology of the higher molecular weight
fractions was inferred by trapping of poly(iPP) in cross-linked 2-hydroxyethyl
methacrylate (HEMA) hydrogels. Cross-linked HEMA hydrogels were generated
in the presence of a high molecular weight (<i>M</i><sub>n</sub> = 202000 Da) poly(iPP) generated from the zwitterionic ring-opening
polymerization of iPP with the NHC 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene <b>2</b>. Extraction of the resulting gel with methanol for 11 days
revealed that 36% of the poly(iPP) was retained in the gel, whereas
a linear poly(iPP) was completely extracted under similar conditions.
The retention of the poly(iPP)s in the gels is attributed to topological
trapping of the cyclic poly(iPP) in the cross-linked network
