Complex formed in the system hydrophobically modified polyethylene glycol/methylated α-cyclodextrin/water. An NMR diffusometry study

In aqueous solutions hydrophobically modified polyethylene glycol (HM-PEG) forms a transient polymer network held together by intermolecular hydrophobic associations. In the present investigation we have used NMR-diffusometry to study how the addition of methylated α-cyclodextrin (M-α-CD) influences the polymer network. The addition of M-α-CD resulted in an increased mean self-diffusion of HM-PEG, DHM-PEG, which is referred to a degradation of the polymer network when hydrophobic associations are disrupted due to complex formation between the hydrophobic groups of HM-PEG and M-α-CD. Addition of small amounts of M-α-CD results in a dramatic increase in DHM-PEG. Upon further addition of M-α-CD the increase in DHM-PEG is less dramatic and at excess M-α-CD, DHM-PEG levels off and equals the mean self-diffusion coefficient for unmodified PEG with the same molecular weight. The suggested interpretation is that the addition of the first molecules of M-α-CD mainly reduces the probability for hydrophobic associations inter-connecting different clusters of polymer micelles whereas at higher M-α-CD concentrations a disengagement of the individual clusters into separate HM-PEG molecules becomes important.