Molecules and oligomers

We have little information on the way low molecular weight molecules and oligomers adsorb (19). Apparently below DP s of about 100 they lie flat on the surface for concentrations up to a monolayer of segments, then seem to form thicker islands of smectic or nematic structure. Ordered condensed mono, -di, -or multi-layers are primarily the arrangements of smaller, especially amphipa-tic molecules on liquid-liquid interfaces. Polymers are too large to adsorb, in the ordinary sense, on micelles but segments of linear polymers may act as nucleation centers for micelles of small molecules which probably is one of the mechanisms for the lipid-, or detergent-, polymer interaction. 

The result is a fiber that is less crystalline and dyes more readily. The downside is an unavoidable reduction in transition temperatures, a less stable structure more prone to shrinkage, and the easier escape of dye molecules and oligomers which can deposit onto the surfaces of textile processing equipment. Depending on the level and type of comonomer used, increased problems with lightfastness or polymer degradation can also occur. 

High efficiency columns currently available for gel permeation chromatography of small molecules and oligomers provide high speed separations. The use of multiple detectors provides additional information which facilitates characterization and determination of the separated species. 

We have recently reported (1 )) the use of this technique for characterization of various compounds. Experimental data obtained for a number of compounds are shown in Figure 2. We calculated the "size factors" for a number of small molecules and oligomers. This factor is a measure of the deviation of the elution volume of a given species from the calibration curve for n-alkanes which is assigned a size factor of 1. This size factor, F, is defined to be equal to A/M, where M is the molecular weight of the compound and A is the molecular weight of a real or hypothetical n-alkane which will elute at the same retention volume as the compound. Size factors for a number of... 

After given crystallization time, the crystal suspension in the DSC cell (it should also contain molecules and oligomers) was heated from 5 °C to 105 °C at the rate of 10 or 90 °C/h. 

Interval I Particle Nucleation.—Piirma and Chang have published some very interesting results for the emulsion polymerization of styrene in the presence of an ethylene oxide-fatty alcohol condensate as surfactant. As expected, the rate of polymerization increases with increasing concentration of surfactant, but the unexpected feature is a pronounced increase in the rate of polymerization which always occurs at ca. 40% conversion. This increase is attributed to the nucleation of a new crop of particles following the release into the aqueous phase of surfactant, which was hitherto dissolved in the monomer droplets. It certainly seems to be significant that the pronounced acceleration of the polymerization occurs at approximately the conversion at which the monomer droplets are expected to disappear. Chen and Piirma have proposed that mixed micelles formed by hydrophobic association between surfactant monomer molecules and oligomers formed by aqueous-solution polymerization can provide significant numbers of loci... 

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