Molecular weight effects aggregation

The existence of aggregates is evidenced by virial coefficients wh ch are lower than the theoretical values, for the measured M,. This is because the second virial coefficient decreases with increasing molecular weight. Supermolecular aggregates appear to have very high effective molecular weights. 

This unusual variation of N with emulsifier concentration suggests that the monomer droplets were a locus for particle nucleation, which was demonstrated by the particles as small as 20nm formed by emulsification of 20% aqueous poly-p-sodium styrene sulfonate solutions under the same conditions. Moreover, the interfacial tension between 20% aqueous p-sodium styrene sulfonate and o-xylene containing dissolved Span 60 was O.OOlO.Ol dynes/cm. Emulsion droplets as small as 20nm could compete effectively as a locus for particle nucleation with the monomer-swollen micelles (cmc in benzene 0.0022 gm/cc micelle molecular weight 52800 aggregation number 94 (55)). Thus both the micelles and the monomer droplets are loci for particle nucleation. 

The observed molecular weight suggests that this polymer associates into a dimer in CHCI3, but that this aggregation is effectively blocked by small amounts of DMF. The particle lengths are not quite in the 2 1 ratio indicative of end-to-end association, but the increase in length is sufficiently large to make such a mechanism worthy of additional study. 

The methodology for preparation of hydrocarbon-soluble, dilithium initiators is generally based on the reaction of an aromatic divinyl precursor with two moles of butyUithium. Unfortunately, because of the tendency of organ olithium chain ends in hydrocarbon solution to associate and form electron-deficient dimeric, tetrameric, or hexameric aggregates (see Table 2) (33,38,44,67), attempts to prepare dilithium initiators in hydrocarbon media have generally resulted in the formation of insoluble, three-dimensionally associated species (34,66,68—72). These precipitates are not effective initiators because of their heterogeneous initiation reactions with monomers which tend to result in broader molecular weight distributions > 1.1)... 

The above observation is significant, Theoretical considerations 102,103,104), as well as some experimental studies 105,106), revealed an effect of excluded volume on the rates and equilibria of polymeric reagents. For example, the equilibrium constant of dissociation of high molecular weight aggregates (MW > 1(f) such as... 

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