Polymer association

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. 

A consequence of tacticity/stereoregularity is the production of regular helical coiling of the polymer chain. Helical coiling is a secondary structure for synthetic polymers associated with the primary structure of the tactic sequence. Using IR spectroscopy, it has been possible to assign some unique bands to... 

Poly(ethylene oxide) (PEO), 10 665, 673-674 13 540, 542-543, 731. See also Ethylene oxide polymers association reactions of, 10 682 behavior in solution, 10 685 commercial block copolymers, 7 648t crystallinity of, 10 690 as a flocculating agent, 11 630-631 low molecular weight, 14 259 oxidation of, 10 682 in paper manufacture, IS 117 preparation of, 20 462 Polyethylene oxide chains, in cationic surfactants, 24 147... 

A concept along similar lines was recently developed to account for the auto-accelerated character of the polymerization of carboxylic monomers and of acrylonitrile. Accelerated propagation is assumed to occur in oriented monomer-polymer association complexes. This conclusion is reached on the basis of kinetic evidence and the investigation of molecular associations present in these systems. 

Abstract. Auto-accelerated polymerization is known to occur in viscous reaction media ("gel-effect") and also when the polymer precipitates as it forms. It is generally assumed that the cause of auto-acceleration is the arising of non-steady-state kinetics created by a diffusion controlled termination step. Recent work has shown that the polymerization of acrylic acid in bulk and in solution proceeds under steady or auto-accelered conditions irrespective of the precipitation of the polymer. On the other hand, a close correlation is established between auto-acceleration and the type of H-bonded molecular association involving acrylic acid in the system. On the basis of numerous data it is concluded that auto-acceleration is determined by the formation of an oriented monomer-polymer association complex which favors an ultra-fast propagation process. Similar conclusions are derived for the polymerization of methacrylic acid and acrylonitrile based on studies of polymerization kinetics in bulk and in solution and on evidence of molecular associations. In the case of acrylonitrile a dipole-dipole complex involving the nitrile groups is assumed to be responsible for the observed auto-acceleration. 

Fluorescence resonance energy transfer has also been used for ionic strength measurements.(95) Fluorescein labeled dextran (donor) and polyethyleneimine-Texas Red (acceptor) were placed behind a dialysis membrane. The polymer association is ionic strength dependent and the ratio of intensities (F o/Fw) was used as the measured parameter. Since both the donor and acceptor are fluorescent, this kind of sensor may allow expand the sensitive ionic strength range by shifts in observation wavelength, as was discussed for pH probe Carboxy SNAFL-2 (see Section 10.3). 

On the basis of the above experimental results, the expected conformations of polymer-surfactant complexes at the oil-water interface are depicted in Fig. 2.19. In case I, the added polymer associates with excess surfactants present in the bulk solution, but the complexes prefer to remain in the bulk phase. Alternately, the polymer-surfactant complexes are unable to displace the adsorbed surfactant molecules from the liquid-liquid interface. Irrespective of the amount of polymer-surfactant concentration in the bulk, the experimental decay length values remain comparable to the Debye lengths, corresponding to the concentration of ion species in the bulk solution (Eq. (2.11)). This means that the force profile is... 

Abbreviations, generally initials in capital letters, are also employed to describe polymers. Table 3 contains a listing of some of the more widely used abbreviations and the polymer associated with the abbreviation. 

Figure 20-23 (a) Surface plasmon resonance spectrum of sensor coated with molecularly imprinted polymer that selectively binds NAD+. (b) Response of sensor to four similar molecules shows largest response to NAD+, which was the template for polymerization. [From O. A. Raitman. V. I. Chegel, a B. Kharitonov. M. Zayats. E. Katz, and I. Winner. Analysis of NAD(P) and NAD(P)H Cofactors by Means of Imprinted Polymers Associated with Au Surfaces A Surface Plasmon Resonance Study. Anal. CNm. Ada 2004,504. 101.]... 

For instance, it has been shown for PEO (oligomer) — PMA (polymer) interaction that the reaction heat calculated per monomer unit does not depend on the DP of the oligomer26). Then the probability of oligomer-polymer association is... 

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