A pure sample of an oligo(ethylene glycol) (OEG), tetrapentaconta(ethylene glycol) (H0-(CH2CH20)54H (OEG54)), has been prepared by stepwise synthesis coupled with preparative size exclusion chromatography (SEC) used as a separation method. The purity of the OEG54 sample has been checked by analytical SEC and differential scanning calorimetry. Furthermore, the molecular weights (MW) of the OEG54 sample and a pure sample of octadeca(ethylene glycol) (OEG18) previously prepared have been determined by mass spectroscopy, light scattering (LS), vapor pressure osmometry, 13C NMR, and NMR. The observed MW values of the OEG samples are in good agreement with those expected from their chemical formulas. In particular, fairly good agreements observed in LS and NMR measurements show that these pure OEG samples can be used as ideal MW standard samples.
A good correlation between the ortho-positronium (o-Ps) pick-off annihilation lifetime and the free volume, computed as the difference between the specific volume at room temperature and that at 0 K, is reported for molecular liquids and polymers. Bondi’s group contribution approach was employed for estimating the specific volume at 0 K. The o-Ps lifetimes in molecular solids, such as phenanthrene deviate considerably from the correlation. It is suggested that a bubble may be formed around Ps in liquids and polymers, but not in the low-molecular-weight crystalline solids. A correlation is presented between the diffusion coefficients of Ar and the lifetimes of o-Ps in both liquids and polymers.
ABSTRACT:The solution properties of a pure oligoethylene glycol, i.e., octadecaethylene glycol (OEG 18), in acetonitrile have been studied by light scattering and small-angle X-ray scattering (SAXS) measurements. No strong downturn at small angles have been observed in the Zimm plot of light scattering data, indicating that OEG18 molecules disperse molecularly in solution. The weight-average molecular weight Mw ( =833) obtained by light scattering measurements is in good agreement with the expected molecular weight M ( = 810.9) of OEG 18. The radius of gyration (S 2 ) 112 ( =9.6±0.4A) has been determined bySAXS, yielding the characteristic ratio Cn=4.8 ±0.4.KEY WORDS Poly(ethylene oxide)/ Oligoethylene Glycol/ Light Scattering / Small-Angle X-Ray Scattering/ Radius of Gyration/ Characteristic Ratio/ Poly(ethylene oxide) (PEO) is a simple polymer with unusual properties. 1 One of the characteristic features of PEO is that the polymer tends to aggregate in various solvents. Elias and Lys 2 pointed out that PEO aggregates in some solvents and light scattering data show a strong downturn at small angles in Zimm plots for PEO in methanol, 3 dimethylformamide,4 and water,5 indicating the presence of some aggregates in these good solvents.To discuss unperturbed chain dimensions of polymers, the characteristic ratio en= (R 2 ) 0 /nl2 is often used, where (R 2 ) 0 is the unperturbed mean-square end-to-end distance, n the number of skeletal bonds, and l2 the average of the square of their length. 6 The value of en can be estimated from the unperturbed mean-square radius of gyration (S 2 ) 0 ( = (R 2 ) 0 /6 for large n) obtained by a scattering method such as light scattering, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS In our previous study, we described a method for preparing a pure oligoethylene glycol, i.e., octadecaethylene glycol (OEG 18). 8
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