Polyethyleneoxide times

Diacyllipid-polyethyleneoxide conjugates have been introduced into the controlled drug delivery area as polymeric surface modiLers for liposomes (Klibanov et al., 1990). Being incorporated into the liposome membrane by insertion of their lipidic anchor into the bilayer, such molecules can ster-ically stabilize the liposome against interaction with certain plasma proteins in the blood that results in signiLcant prolongation of the vesicle circulation time. The diacyllipid-PEO molecule itself represents a characteristic amphiphilic polymer with a bulky hydrophilic (PEO) portion and a very short but extremely hydrophobic diacyllipid part. Typically, for other PEO-containing amphiphilic block... 

The relaxation time obtained in this manner is about 0.1 seconds for polyethyleneoxide and 0.4 seconds for polyacrylamide. Measurements at different solvent viscosities gave that the relaxation time scales about linearly with the solvent viscosity. 

Although polyethyleneoxide is a bad stabilizer for colloidal noble metals, it appeared possible to prepare rather stable colloidal gold solutions in toluene with polystyrene/polyethyleneoxide block copolymers by reduction of LiAuCU. When polymer/salt complexes were allowed to approach their equilibrium during longer times, a more homogeneous distribution of gold salt in the micelles resulted in more narrow particle size distributions. 

Fig. 29. Proton spin-lattice relaxation time of polyethyleneoxide (PEO) melts as a function of the frequency [49]. The data refer to the molecular weight independent chainmode regime II (low-mode-number limit) and regime III influenced by intersegment dipolar interactions [154]...

Fig. 36a, b. Deuteron spin-lattice relaxation times of deuterated polyethyleneoxide (PEG) (a) and polybutadiene (PB) (b) as a function of the frequency [156]... 

Fig. 42. Time-dependent diffusion coefficient measured in a polyethyleneoxide melt (M =5,000,000) at 353 K as a function of the diffusion time [12]. The data were evaluated according to Eq. 27. The Rouse relaxation time Tr and the tube disengagement time predicted by the tube/reptation model based on the neutron scattering value of the ratio (R ee)/M = 1.01x10 ° m mol/g [179, 180] are indicated. The broken line represents the power law D(t)(xr which, according to the tube/reptation model, should appear in the time interval above Tr as limit (III)de and not below (see Table 1). The time range where this power law appears and the value for Zr estimated on the basis of the tube/reptation model are not consistent with each other. The plateau of the experimental data for f 0.1 s is due to flip-flop spin diffusion which physically limits the detection of molecular displacements by NMR diffusometry...

The effect is also evident in Fig. 42 referring to a polyethyleneoxide melt with an extremely large molecular weight, Mw=5,000,000. The time-depen-dent diffusion coefficient was evaluated in the low wave number approximation, Eq. 27, according to R t))=6D(t)t. The time-independent plateau appearing at times t 0.1 s was shown to be due to flip-flop spin diffusion [10, 12]. 

Fig. 44. Echo attenuation curves for polyethyleneoxide, M = 11,200, confined to PHEMA pores at 80 °C as a function of the squared wave number, k, for different diffusion times. The solid lines represent a fit of Eqs. 76-79 to the experimental data. The tube diameter is found to be a=(9 l) nm as the only fitting parameter. Other parameter values such as N=MJ853, Do=9.66x10 ° m /s, and =8.38x10 ° m were taken from the literature [180, 187]...

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