Optical rotation measurements polymers

Marvel, Dec, and Cooke [J. Am. Chem. Soc., 62 (3499), 1940] have used optical rotation measurements to study the kinetics of the polymerization of certain optically active vinyl esters. The change in rotation during the polymerization may be used to determine the reaction order and reaction rate constant. The specific rotation angle in dioxane solution is a linear combination of the contributions of the monomer and of the polymerized mer units. The optical rotation due to each mer unit in the polymer chain is independent of the chain length. The following values of the optical rotation were recorded as a function of time for the polymerization of d-s-butyl a-chloroacrylate... 

Conformations of the polymers were studied by CD and optical rotation measurements. Poly-L-lysine is known to exist in disordered, helical and -conformation, depending on the temperature, pH of the system and the solvent used. The side chain of the polymer has a significant effect on the backbone conformation. At neutral pH, poly-L-lysine exists in a random coil structure while at pH above 10, the e-amino group becomes a neutral form and the polymer undergoes transition to a helical structure. In order to elucidate the effect of base substituents on the conformation of poly-L-lysine, CD spectra of the copolymer were measured. 

Another important factor for the polymer conformation is the solvent effect. As the usual solvents for the copolymers in question are DMSO and DMF, which have absorption in the UV region, CD spectral measurements are impossible. However, the optical rotation measurements and analyses using the Moffitt-Yang equation give the Moffitt parameter bo for the copolymers (Table 21). Hie parameter is known to be related to the helix content of poly-(a-amino acids). The b0 value of polycarboben-... 

Novozym 435-catalyzed KRP of racemic 4-MeCL was applied by Xiao et al. to prepare chiral crosslinked particle. By letting the conversion in the KRP of 4-MeCL proceed to 50% or 91%, poly ((.S )- and poly((rac)-4-MeCL), respectively, were obtained. The R-enantiomer of 4-MeCL could be recovered from the polymerization mixture that afforded poly((S)-4-MeCL), and was subsequently polymerized with Novozym 435 to poly((R)-4-MeCL) (Scheme 11.22). GPC analysis confirmed that molecular weights of the polymers were almost identical (Mn around 3kgmoT PDI around 1.5 after precipitation) and optical rotation measurements revealed opposite signs for poly((S)- and poly((R)-4-MeCL) while... 

C. S. Marvel, J. Dec, and H. G. Cooke, Jr. [/ Am. Chem. Soc., 62, 3499 (1940)] employed optical rotation measurements to study the kinetics of polymerization of vinyl-1-phenylbutyrate. In dioxane solution the specific rotation angle represents a linear combination of contributions from the monomer proper and those of the polymerized monomer units. The contribution of the polymerized units can be viewed as independent of chain length. The reaction takes place in a constant-volume system and may be viewed as irreversible. The stoichiometry of the reaction may be viewed as A -I-Pjj Pn+i where A represents the monomer and P the polymer. The following data are characteristic of this reaction. 

To find out, if there is a correlation between the content of the network junctions and the helical content of the mixture, we have combined kinetic measurements of the mechanical and optical properties. For this reason we have constructed a special measuring cell for the simultaneous detection of the complex shear modulus and the optical rotation of polymer/solvent systems, e.g. gelatin/water up to 4 wt.% of gelatin. 

The optical rotatory dispersion of poly-(+)-l-methyl-benzyl-methacry ate has been measured between 320 and 230 raft. The optical activity for polymer and model has values of the same sign and of the same order of magnitude, but the isotactic polymer seems to have a larger [M] than the syndiotactic and the atactic polymers [K. J. Liu, J. S. Lignowski, R. Ullman ACS Polymer Preprints, 6, 904 (1965)]. Optically active N-methyl-N-methylbenzyl-acrylamide and N-(n-propyl)-N-methylbenzyl-acrylamide have been polymerized by Kaiser and Schulz and the optical rotation dispersion between 589 raft and 365 raft has been... 

The first successful experiments were reported by Schwab [16] Cu, Ni and Pt on quartz HI were used to dehydrogenate racemic 2-butanol 23. At low conversions, a measurable optical rotation of the reaction solution indicated that one enantiomer of 23 had reacted preferentially (eeright-handed quartz gave the opposite optical rotation it was deduced that the chiral arrangement of the crystal was indeed responsible for this kinetic resolution (for a review see [8]). Later, natural fibres like silk fibroin H5 (Akabori [21]), polysaccharides H8 (Balandin [23]) and cellulose H12 (Harada [29]) were employed as chiral carriers or as protective polymer for several metals. With the exception of Pd/silk fibroin HS, where ee s up to 66% were reported, the optical yields observed for catalysts from natural or synthetic (H8, Hll. H13) chiral supports were very low and it was later found that the results observed with HS were not reproducible [4],... 

The polymer obtained from 1,5-hexadiene using 6.22 and MAO has measurable optical rotation. Why ... 

Polymer molecules in solution can be found in many different geometric conformations, and there exist a variety of experimental methods (e.g., viscosity, light scattering, optical rotation) for obtaining information about these conformations. In this experiment, the measurement of optical rotation will be used to study a special type of conformational change that occurs in many polypeptides. 

Usually, the chiroptical properties of highly cross-linked polymers cannot be measured. The asymmetry of the empty cavities can be deduced from their excellent racemate resolution ability, but under special conditions it can also be directly detected by optical activity measurements [41]. For this, the polymer is suspended in a solvent that has the same refractive index as the polymer, a technique which was developed for other types of insoluble polymers. The values of molar optical rotation thus determined are shown in Table 4.3. 

If we compare the value (—61.7°) for a polymer prepared from 1 (calculated for the molar content of 1), still containing the template, with the value —448.9° for the template monomer 1, it becomes apparent that the molar optical rotation value is considerably decreased as a result of polymerisation. This can have several causes, one being the influence of the polymer matrix. Its effect can be determined by removing the optically active template la. If the boronic acids are then converted with ethylene glycol to the corresponding achiral ester, the polymer shows a positive molar rotation [M] °546 = -1- 110.0°. Apparently, in P-E the imprints generated in the polymer make a positive contribution to the optical rotation value. Measuring the optical rotation in the solid phase allows the... 

As seen in Figure 5.IB, the polymer forms a layered structure below the transition point, showing a well-developed system of SAXS peaks. Moreover, the ORD measurements (see Figure 5.2) exhibit drastic growth of the optic rotation in the IsoSm phase towards shorter wavelengths, in contrast to the proper isotropic melt of the same polymer above the transition point, suggesting some helix-like superstructural ordering in the mesophase with a pitch below 300 nm. That hypothesis was further supported with CD, dielectric spectroscopy, and UV-vis spectroscopy data. " Tlie critical importance of chirality for the formation of the IsoSm phase is also confirmed by... 

Fig. 29 Schematic drawing of the ultrafiltration system for the measurement of the dissociation kinetics of polymer ICs. Concentrations of CD both in the filtrate and the retentate were determined from the optical rotations of the solutions...

The template 7a can be split off by water or methanol to an extent of up to 95% (Scheme 2-5). The accuracy of the steric arrangement of the binding sites in the cavity can be tested by the ability of the polymer to resolve the racemate of the template, namely of phenyl-a-D,L-mannopyranoside. Therefore the polymer is equilibrated in a batch procedure with a solution of the racemate under conditions under which rebinding in equilibrium is possible. The enrichment of the antipodes on the polymer and in solution is determined by measuring the specific optical rotation and the separation factor a, i.e., the ratio of the distribution coefficients of the D and L compounds between polymer and solution, is calculated. After extensive optimization of the procedure, a values between 3.5 and 6.0 were obtained [10]. This is an extremely high selectivity for racemic resolution that cannot be reached by most other methods. 

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