Polymer size effects

As in SEC, the surface chemistry of the HdC gels should be similar to that of the mobile phase and the solute. Otherwise, the retention time may increase as with the nonsize exclusion effects. However, the tolerance of PCHdC for a poorer mobile phase is better than SEC. The polymer size under 0 conditions has been studied using PCHdC (19). 

Another advantage of HdC is its generosity in terms of mobile-phase selection. The polymer size and solution properties of a polymer can be studied using HdC, especially OTHdC, in almost any solvent. In SEC, by comparison, the packing material and mobile phase have to be selected to prevent the nonsize exclusion effect. Because the instrumentation of HdC is similar to SEC, and the packing material and columns have become available commercially, this technique will gain in popularity. 

Karthaus, O., Okamoto, K., Chiba, R. and Kaga, K (2002) Size effect of cyanine dye J-aggregates in micrometer-sized polymer Domes . Int. J. Nanosci., 1, 461—464. 

In the case of polymer blends, the fractionated crystallization phenomenon that has been widely reported for many polymer systems can not be attributed to simple size effects. For instance, in Fig. 1, one could argue that the different exotherms originated in the crystallization of different droplet populations that have diverse average diameters. This cannot be the case, since the droplet distribution is monomodal and a smooth variation in heat... 

The first section, Chemical Reactions on Polymers, deals with aspects of chemical reactions occurring on polymers—aspects relating to polymer size, shape, and composition are described in detail. One of the timely fields of applications comprises the use of modified polymers as catalysts (such as the immobilization of centers for homogeneous catalysis). This topic is considered in detail in Chapters 2, 3, 8, 9, and 11 and dealt with to a lesser extent in other chapters. The use of models and neighboring group effect(s) is described in detail. The modification of polymers for chemical and physical change is also described in detail in Chapters 2 (polystyrene) 4 (polyvinyl chloride) 5 (polyacrylic acid, polyvinyl alcohol, polyethyleneimine, and polyacrylamide) 6 (polyimides) 7 (polyvinyl alcohol) 8 (polystyrene sulfonate and polyvinylphosphonate) 10 (polyacrylamide) and 12 (organotin carboxylates). 

It should also be noted that ternary and higher order polymer-polymer interactions persist in the theta condition. In fact, the three-parameter theoretical treatment of flexible chains in the theta state shows that in real polymers with finite units, the theta point corresponds to the cancellation of effective binary interactions which include both two body and fundamentally repulsive three body terms [26]. This causes a shift of the theta point and an increase of the chain mean size, with respect to Eq. (2). However, the power-law dependence, Eq. (3), is still valid. The RG calculations in the theta (tricritical) state [26] show that size effect deviations from this law are only manifested in linear chains through logarithmic corrections, in agreement with the previous arguments sketched by de Gennes [16]. The presence of these corrections in the macroscopic properties of experimental samples of linear chains is very difficult to detect. 

The second approach uses multiple detectors (Figure 3.13), allowing a double extrapolation to zero concentration and zero angle with the data forming what is called a Zimm plot (Figure 3.14). The extrapolation to zero angle corrects for finite particle size effects. The radius of gyration, related to polymer shape and size, can also be determined from this plot. The second extrapolation to zero concentration corrects for concentration factors. The intercepts of both plots are equal to /M . 

The typical effect of initiator chain transfer [Baysal and Tobolsky, 1952] can be seen graphically in Fig. 3-6. The decrease of polymer size due to chain transfer to initiator is much less than indicated from the Ci values because it is the quantity Ci[I]/[M], which affects Xn (Eq. 3-109b). The initiator concentrations are quite low (10 4 I0 2 M) in polymerization, and the ratio [I]/[M] is typically in the range 10 3-10 s. 

Intraparticle diffusion limits rates in triphase catalysis whenever the reaction is fast enough to prevent attaiment of an equilibrium distribution of reactant throughout the gel catalyst. Numerous experimental parameters affect intraparticle diffusion. If mass transfer is not rate-limiting, particle size effects on observed rates can be attributed entirely to intraparticle diffusion. Polymer % cross-linking (% CL), % ring substitution (% RS), swelling solvent, and the size of reactant molecule all can affect both intrinsic reactivity and intraparticle diffusion. Typical particle size effects on the... 

Pigments such as titanium dioxide (n = 2.5) with n values which are higher than that of the polymer are effective opacifiers. The opacity is also related to the size of the pigment particles. 

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