Poly + trifluoroethanol

The intrinsic viscosity of poly(L-proline) is studied as a function of molecular weight and temperature In five commonly used solvents water, trifluoroethanol, acetic acid, propionic acid, and benzyl alcohol. The characteristic ratio is 14 in water and 18-20 in the organic solvents at 303 K, and d (in 0) / d T is negative. The theoretical rotational potential function obtained by Hopfinger and Walton for u-prolyl-L-prolyl-t-prolyl-t-proline J. Macromol. Scl. Phys. 1969, 3, 171 correctly predicts the characteristic ratio at 303 K but predicts the wrong sign for tfiln < >0) IdT. 

II. Preparative GPC Fractionation and Characterization of Poly-(methyl methacrylate) for Calibration in 2, 2, 2-Trifluoroethanol... 

In general, the synthesis of polyphosphazene polymers is unique in that, in theory, an infinite number of polymers with a variety of properties can be derived from the common polymeric intermediate, poly(dichlorophosphazene) (PNCI2), by replacing the chlorines with different nucleophiles. If the polydichlorophosphazene precursor is reacted with the sodium salts of trifluoroethanol and a mixed fluorotelomer alcohol, a poly(fluoroaIkoxyphosphazene) elastomer (FZ elastomer) is obtained. It contains a small amount of an unsaturated substituent as a curing site. The polymer is a soft gum, which can be compounded with carbon blacks and fillers and cured with sulfur or peroxides or by radiation. 

Abbreviations ASES, aerosol solvent extraction system BSA, bovine serum albumin PCA, precipitation with compressed antisolvent PLA, polylactic acid PLGA poly(lactic-co-glycolic acid) PMMA, poly(methyl methacrylate) PPG, poly(propylene glycol) RESS, rapid expansion of supercritical solution TFE, 2,2,2-trifluoroethanol. 

Abbreviations A, acetone ASES, aerosol solvent extraction system DM, dichloromethane DMF, A/,A/-dimethyl-formamide E, ethanol GAS, gas antisolvent process H, hexane HYAFF-11, hyaluronic acid benzylic ester I, isopropanol PAN, polyacrylonitrile PCA, precipitation with compressed antisolvent PCL, polycaprolactone PHB, poly(p-hydroxybutyric acid) PLA, polylactic acid PLGA, poly(lactic-co-glycolic acid) SAS, supercritical antisolvent process SEDS, solution enhanced dispersion by supercritical fluids TFE, 2,2,2-trifluoroethanol Triblock polymer, p poly(L-lactide-CO-D,L-lactide-co-glycolide)(62.5 1 2.5 25). 

Poly(vinylpyrrolidone), poly(L-proline), (+)-catechin, (-)-epicatechin, and trifluoroethanol were purchased from Sigma Chemical Co. Two of the four poly(L-proline) samples studied contained an unidentified fluorescent material that was removed with activated charcoal. A fluorescent compound in the trifluoroethanol was removed by distillation. Dr. Richard W. Hemingway kindly supplied highly purified samples of synthetic (-)-epicatechin-(4B-6)-(+)-catechin, (-)-epicatechin-(4B-8)-(+)-catechin, and (-)-epicatechin-(4B-8)-(+)-catechin decaacetate. Dioxane and 1-propanol were obtained from Aldrich Chemical Co. 

Monomers and dimers exhibit maximal emission at 314-324 nm upon excitation at 272-280 nm. Quantum yields for fluorescence, denoted by Q, are collected in Table I. Both monomers exhibit increasing fluorescence as the solvent changes from water to trifluoroethanol to dioxane. There is no significant difference in the emission of the two monomers in a common solvent. Dimers show less intense emission that do monomers. There is a further reduction in emission upon acetylation of all phenolic and aliphatic hydroxyl groups. COMPLEX FORMATION by POLY(VINYLPYRROLIDONE)... 

In a suitably chosen mixed solvent system, such as acetic acid and 1-propanol (21), a sharp reversible transition between Form I and Form II can be achieved with a small change in solvent composition. Measurements of optical activity provide a convenient way to follow the transition in dilute solution. There are large changes in optical activity because Forms I and II are helices of opposite handedness. The left panel in Figure 3 depicts the reversible transition that is detected by circular dichroism measurements in mixtures of trifluoroethanol and 1-propanol. Form II is the only conformation present in trifluorethanol. A solution of poly(L-proline) in 35 65 trifluoroethanol 1-propanol exhibits the same circular dichroism pattern as does a solution where the solvent is pure trifluoroethanol. However, further addition of 1-propanol produces a dramatic change in the circular dichroism. At 20 80 trifluoroethanol 1-propanol the circular dichroism pattern is that characteristic of Form I. Data in Figure 3 do not extend beyond 10 90 trifluoroethanol 1-propanol because of the low solubility of poly(L-proline) in 1-propanol. 

The right panel in Figure 3 depicts 1/1(0) for (+)-catechin in mixtures of trifluoroethanol and 1-propanol that contain poly(L-proline) at a concentration of 0.90 mg/ml. In pure trifluoroethanol 1/1(0) is slightly less than one. At the opposite extreme of solvent composition, I/l(0) is greater than one and increases over a period of several days. The greatest sensitivity of 1/1(0) to solvent composition occurs near 25 75 trifluoroethanol 1-propanol, which is where the Form I - Form II interconversion is detected by circular dichroism. Measurements of the fluorescence of (+)-catechin in the mixed solvents, but in the absence of poly(L-proline), show no unusual dependence of emission on solvent. 

Fig. 3. CD and absorption spectra of poly(Pro) in trifluoroethanol. Curve a represents a close approximation to the poly(Pro) I CD spectrum with the maximum recorded less than 20 min after dissolution. Curve b was recorded about 1 hr after dissolution. Curve c, representing poly(Pro) II, was recorded 19 hr after dissolution. Curve a was run at 10 min with a 10-fold larger path length. Curves d and e are the absorption spectra, run at 15 min (form I) and 19 hr (form II), respectively. [Reprinted with permission from Bovey and Hood (1967). Copyright 1967 John Wiley Sons, Inc.]...

Figure 3. CD spectra of poly-trans-3-ethyl-D-proline. In trifluoroethanol, ( —...

TFA Trifluoroacetic acid TFE Trifluoroethanol HA Hydroxyapatite filler PEO Poly(ethylene oxide) PANi Polyaniline (emeraldine base) BDI Diisocyanatobutane DCM Dichloromethane DMAC Dimethylacetamide THE Tetrahydrofuran HEA Hexafluoroacetone HEP l,l,l,3,3,3-Hexafluoro-2-Propanol D Eiber diameter. The silk is isolated from cocoons of silkworm B. mori and degummed. The silk derived has an average molecular weight of around 9 x 10 (g/mol). 

Fig. 9.11 Circular dichroism spectra of double-stranded poly[d(G-C)] in three different helical forms [65]. Dotted curve, B form (10 mM phosphate) dashed curve, A form (0.67 mM phosphate, 80% trifluoroethanol) solid curve, Z form (10 mM phosphate, 2 M NaC104). The ordinate scale is the mean difference between the molar extinction coefficients for left- and right-circularly polarized light (e — 8 ), with molarity referring to the concentration of nuclotide base pairs...

Fig.43. TheCDat22 Cofpoly[d(G-C)]-poly[d(G-C)] as 7 the B-form, in 0.01 M sodium phosphate buffer, pH 7, 2 the A-form, in 0.67 mM sodium phosphate buffer, 80% 1,1,1-trifluoroethanol, and 3 the Z-form, in 0.01 M sodium phosphate buffer, 2 M sodium perchlorate [85R1].

We therefore carried out a series of studies on the circular dichroism spectrum of poly(i -oxypropylene) in a number of solvents in the vacuum ultraviolet region under the cooperation with W.C. Johnson, Oregon State University. In the circular dichroism(CD) spectra of poly(/ -oxypropylene), two CD bands were observed for cyclohexane, acetonitrile, and trifluoroethanol(TFE) solutions. 

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