Poly concentration effects

In solution polymerization, monomers mix and react while dissolved in a suitable solvent or a liquid monomer under high pressure (as in the case of the manufacture of polypropylene). The solvent dilutes the monomers which helps control the polymerization rate through concentration effects. The solvent also acts as a heat sink and heat transfer agent which helps cool the locale in which polymerization occurs. A drawback to solution processes is that the solvent can sometimes be incorporated into the growing chain if it participates in a chain transfer reaction. Polymer engineers optimize the solvent to avoid this effect. An example of a polymer made via solution polymerization is poly(tetrafluoroethylene), which is better knoivn by its trade name Teflon . This commonly used commercial polymer utilizes water as the solvent during the polymerization process,... 

In the preceding section, the remarkable salt concentration effect on the acid dissociation equilibria of weak polyelectrolytes has been interpreted in a unified manner. In this treatment, the p/( ,pp values determined experimentally are believed to reflect directly the electrostatic and/or hydrophobic nature of polyelectrolyte solutions at a particular condition. It has been proposed that the nonideality term (Ap/Q corresponds to the activity ratio of H+ between the poly electrolyte phase and the bulk solution phase, and that the ion distribution equilibria between the two phases follow Donnan s law. In this section, the Gibbs-Donnan approach is extended to the equilibrium analysis of metal complexation of both weak acidic and weak basic polyelectrolytes, i.e., the ratio of the free metal ion activity or concentration in the vicinity of polyion molecules to that of bulk solution phase is expressed by the ApAT term. In Section III.A, a generalized analytical treatment of the equilibria based on the phase separation model is presented, which gives information on the intrinsic complexation equilibria at a molecular level. In Secs. B and C, which follow, two representative examples of the equilibrium analyses with weak acidic (PAA) and weak basic (PVIm) functionalities have been presented separately, in order to validate the present approach. The effect of polymer conformation on the apparent complexation equilibria has been described in Sec. III.D by exemplifying PMA. 

DER D Errico, G., Paduano, L., and Khan, A., Temperature and concentration effects on supramolecular aggregation and phase behavior for poly(propylene oxide)-f>-poly(ethylene oxide)-i-poly(propylene oxide) copolymers of different composition in aqueous mixtures, J. Coll. Interface Sci., 279, 379, 2004. 

Farrokhzad, H., H. Mobedi, J. Barzin, and A. Poorkhalil. Evaluation of polymer concentration effect on doxycycline hyclate drug release from in situ forming system based on poly (lactide-co-glycolide). 

Cui, L., Ding, Y., Li, X., Wang, Z., Han, Y. Solvent and polymer concentration effects on the surface morphology evolution of immiscible polystyrene/poly(methyl methacrylate) blends. Thin Solid Films 515(4), 2038-2048 (2006)... 

Brynda, M., Chodanowski, P. and Stoll, S. (2002). Polyelectrolyte-particle complex formation. Poly electrolyte linear charge density and ionic concentration effects. Polym.r Colloid Set, 280, 789-797. 

Nucleic acid-directed synthesis may have also been important in early peptide formation. Weber and Orgel showed that when the amino acid glycine is esterified to derivatives of adenosine (in the same manner that amino acids are bonded to tRNA in extant protein synthesis), the amino acids will form peptide bonds, resulting in cyclic Gly-Gly dipeptides [29]. Further, when poly-uracil (poly(U)) is added to the mixture, the amount of cyclic Gly-Gly formed increases about 3 times [30]. The temperature and concentration effects of the reactions suggested dependence on formation of a poly(U) hehx specifically, a triple helix of two strands of poly(U) complexed with the glycine-esterified adenosine derivatives. While the exact mechanism of peptide bond formation in this case has not been established, the increased yield of dipeptide could be due to increased local concentration/ optimal orientation of the glycine derivatives based on specific interactions between poly(U) and adenosine. 

BY2 Byun, H.-S. and Park, C., Monomer concentration effect on the phase behavior of poly(propyl acrylate) and poly(propyl methacrylate) with supercritical CO2 and... 

A. C. Ouano and R. Pecora. Rotational relaxation of chlorobenzene in poly(methyl methacrylate). 1. Temperature and concentration effects. Macromolecules, 13 (1980), 1167-1173. 

Fig. 10.5 Concentration effect on the electrospinning of poly(MEBIm-BF4) in 3/1 acetoni-tiile/DMF. Polymer concentrations (a) 2.5, (b) 5, (c) 6, tmd (d) 8 wt% (Reprinted with the permission from Chen and Elabd [42]. Copyright 2009 American Chemical Society)...

DeBruyn also determined adsorption isotherms for different salt contents, iiis results differ frem those of Van Laar and Mackor in that for high electrolyte concentrations > 0.1 TV for monovalent ions, > 0.001 N for bi- and poly-valent ions) he always found the same practically linear adsorption isotherm which would point to a constant capacity of the molecular condenser. It is not certain, however, that the complications of the sol concentration effect ( 10, p. 184) have been sufficiently avoided in his experiments. 

The molecular weight of a polymer can be controlled through the use of a chain-transfer agent, as well as by initiator concentration and type, monomer concentration, and solvent type and temperature. Chlorinated aUphatic compounds and thiols are particularly effective chain-transfer agents used for regulating the molecular weight of acryUc polymers (94). Chain-transfer constants (C at 60°C) for some typical agents for poly(methyl acrylate) are as follows (87) ... 

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