Solvent effect poly

Effect of Solvents. The most commonly used solvents in poly(amic acid) preparation are dipolar amide solvents such as DMAc and NMP. 

The auto-acceleration effect appears most marked with polymers that are insoluble in their monomers. In these circumstances the radical end becomes entrapped in the polymer and termination reactions become very difficult. It has been suggested that, in thermodynamic terms, methyl methacrylate is a relatively poor solvent for poly(methyl methacrylate) because it causes radicals to coil while in solution. The termination reaction is then determined by the rate at which the radical ends come to the surface of the coil and hence become available for mutual termination. 

Klooster, N. Th. M., van der Trouw, F. Mandel, M. (1984). Solvent effects in polyelectrolyte solutions. 3. Spectrophotometric results with (partially) neutralised poly(acrylic acid) in methanol and general conclusions regarding these systems. Macromolecules, 17, 2087-93. 

Solvent Effects in the Sn Spectra of Poly(TBTM/MMA). Samples of poly(MMA/TBTM) synthesized by the free-radical copolymerization of the appropriate monomers were solutions in benzene with approximately 33% solids (weight to volume). The particular formulation chosen as representative of the class contained a 1 1 ratio of pendant methyl to tri-n-butyltin groups. In preparing the dry polymer, the benzene was removed in vacuo with nominally 5% by weight residual solvent. 

We have reported the first example of a ring-opening metathesis polymerization in C02 [144,145]. In this work, bicyclo[2.2.1]hept-2-ene (norbornene) was polymerized in C02 and C02/methanol mixtures using a Ru(H20)6(tos)2 initiator (see Scheme 6). These reactions were carried out at 65 °C and pressure was varied from 60 to 345 bar they resulted in poly(norbornene) with similar conversions and molecular weights as those obtained in other solvent systems. JH NMR spectroscopy of the poly(norbornene) showed that the product from a polymerization in pure methanol had the same structure as the product from the polymerization in pure C02. More interestingly, it was shown that the cis/trans ratio of the polymer microstructure can be controlled by the addition of a methanol cosolvent to the polymerization medium (see Fig. 12). The poly(norbornene) prepared in pure methanol or in methanol/C02 mixtures had a very high trans-vinylene content, while the polymer prepared in pure C02 had very high ds-vinylene content. These results can be explained by the solvent effects on relative populations of the two different possible metal... 

V, is the molar volume of polymer or solvent, as appropriate, and the concentration is in mass per unit volume. It can be seen from Equation (2.42) that the interaction term changes with the square of the polymer concentration but more importantly for our discussion is the implications of the value of x- When x = 0.5 we are left with the van t Hoff expression which describes the osmotic pressure of an ideal polymer solution. A sol vent/temperature condition that yields this result is known as the 0-condition. For example, the 0-temperature for poly(styrene) in cyclohexane is 311.5 K. At this temperature, the poly(styrene) molecule is at its closest to a random coil configuration because its conformation is unperturbed by specific solvent effects. If x is greater than 0.5 we have a poor solvent for our polymer and the coil will collapse. At x values less than 0.5 we have the polymer in a good solvent and the conformation will be expanded in order to pack as many solvent molecules around each chain segment as possible. A 0-condition is often used when determining the molecular weight of a polymer by measurement of the concentration dependence of viscosity, for example, but solution polymers are invariably used in better than 0-conditions. 

The effective dielectric function of poly electrolyte solutions remains as a mystery, demanding a better understanding of structure of solvent surrounding poly electrolyte molecules. 

An unstable analogue of prostaglandin, PGE, formulated in a poly butadiene polymeric matrix, was placed in a SFE cell and extracted with C02/formic acid (95 5) at 15°C Extraction was continued for 60 min and then the extract was collected in hexane/ethanol (2 1) at 0"C. The advantages of the SFE method were that the solvent effected simultaneous cleavage of the polymer-prostaglandin bond without instability problems and with improved mass transfer enabling good recovery from the polymer matrix. 

Table II. Solvent Effect on Yields of Poly (Cyclohexyl Methyl) Silane.

To avoid any complications caused by the intermolecular association, Goodman (78) reinvestigated the optical rotation of the peptides in dimethyl formamide, since in this medium the specific rotation is independent of concentration. From the latter study it was concluded that at 25° C the spontaneous helix formation of poly-y-methyl-L-glutamate in dimethyl formamide is occurring at the critical range of 7—9 units. Extension of these studies (73 b, 79) led to a better understanding of temperature and solvent effects upon the helix-coil transition of oligomeric polypeptides. 

Sengwa, R.J., Solvent effects on microwave dielectric relaxation in poly(ethylene glycols), Polym. Int., 1998, 45, 43. 

Since n-alkanes are good solvents for poly (dimethylsiloxane), the adjacent dimethylsiloxane chains may not interpenetrate, as a result of excluded volume effect. Thus, the shape of a dimethylsiloxane chain may be represented by a prolate ellipsoid with y as the minor axis. The major axis h may be calculated by equating the volume of ellipsoid to (y/2)2(h/2) to (s2)3/2. The h value so calculated agreed reasonably well with the value of <5. Therefore, the shape of the stabilizing dimethylsiloxane chain should be close to an ellipsoid. 

Yu TL, Lu W-C, Liu W-H et al (2004) Solvents effect on the physical properties of semi-dilute poly(Ar-isopropyl acryl amide) solutions. Polymer 45 5579-5589... 

Dewey, T. G., and Turner, D. H. (1980). Laser temperature jump study of solvent effects on poly (adenylic acid) stacking. Biochemistry 19, 1681-1685. 

If interactions of an electrostatic nature have some effect on the relative stability of trans and gauche rotational isomers, it seems reasonable to expect an effect of solvent, though perhaps small, on the factor a. Such effects on the conformations of small molecules are well known [see Mizushima (14,188) and Wada (259)]. The relatively high value of a for poly(methyl methacrylate), as discussed in paragraph (iv) above, may be due to electrostatic interactions, and it is therefore appropriate to search for a solvent effect here. No such effect was found by Marchal and Lapp (175) in their measurements of the apparent dipole moment of the polymer in various solvents as compared with that of the model monomeric compound, methyl isobutyrate. They concluded that to within experimental error (about 3%) the unperturbed dimensions were independent of the solvent. More recently a very small solvent effect on the dipole moment of the isotactic polymer has been reported by Salovey (223a). 

Table 13. Solvent effect on the formation of the complex of poly(methacrylic acid) (PMAA) with poly(N-vinyl-2-pyrrolidone) (PVPo) linked by hydrogen bonds...

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