Poly rotational isomerism

Fig. 18. Staggered rotational isomeric states of the CH—CH bond of threodiisotactic poly(l,2-dimethyltetramethylene)...

A theoretical investigation of the use of NMR lineshape second moments in determining elastomer chain configurations has been undertaken. Monte Carlo chains have been generated by computer using a modified rotational isomeric state (RIS) theory in which parameters have been included which simulate bulk uniaxial deformation. The behavior of the model for a hypothetical poly(methylene) system and for a real poly(p-fluorostyrene) system has been examined. Excluded volume effects are described. Initial experimental approaches are discussed. 

G. D. Smith, D. Y. Yoon, and R. L. Jaffe, Macromolecules, 26, 5213 (1993). A Third-Order Rotational Isomeric State Model for Poly(oxyethylene) Based upon Ab Initio Electronic Structure Analyses of Model Molecules. 

The validity of this dynamic model can be justified by the fact that in polystyrene and other carbon-chain polymers of the type (—CH2—CHR—) (poly(p-chlorostyrene), poly(methyl acrylate) or poly(vinyl acetate)), containing no methyl groups bonded directly to the main chain, rotational isomerization with 17 5—6 Kcal/mol (in the time interval of r 10 — 10 s in solvents with ij 0.01 P) can occur ... 

Figure 3 shows a plot of the fluorescence maximum for poly(n-propyl methyl silylene) in hexane vs. sin ir/2(N + 1) using a defect energy of 1650 calories/mole. Although the ag eement here seems good, the uncertainty in location of the fluorescence maximum is large as the band broadens near room temperature and may disguise a real nonlinearity. Nevertheless, this result lends credibility to the rotational isomeric state model for thermochromism in these polysilylenes. 

NMR chemical shift prediction by quantum chemical calculation and the 7-gauche effect method has become a useful approach for stereochemical assignment of vinyl polymers. Recently C NMR assignments based on 7-effect and the rotational isomeric model were demonstrated successfully for a series of polyolefins, poly(l-pentene) to poly(l-octene).188... 

The modulation technique mentioned above has been used to identify triplet excimers in 1,2-benzanthracene and 1,2 3,4-dibenzanthracene at high solute concentrations167 and the differences between luminescence from naphthalene in fluid solution in the temperature range 353—173 and naphthalene in a rigid solution at 77 have been ascribed to phosphorescence from a triplet excimer.168 Excimer formation in solid poly-(2-vinylnaphthalene) and polystyrene is found to be dependent on the temperature at which the film is cast, and a statistical model based on the rotational isomeric state approximation has been used to formulate an expression for the fraction of excimer sites in the solid systems.168 Kinetic equations for dimer formation and decay, based on the statistical mechanics of ideal gases, have been obtained. These equations, derived from the N-atom von Neumann equation, take into account both bimolecular and termolecular equations.157 158 160... 

Sasanuma, Y., H. Kato, and A. Kaito. 2003. Conformational analysis of poly(di- -butylsilane), poly(di-M-hexylsilane), and poly(methyl- -propylsilane) by a rotational isomeric state scheme with molecular dynamics simulations. J Phys Chem B 107 11852. 

Atactic poly(methyl methacrylate)-Q FTIR spectroscopic analysis of the conformational energy differences between rotational isomeric states is presented. [32]... 

Table 1.5 summarizes the studies on cyclics of poly(di-methyl siloxane) and derivatives, and Table 1.6, those of other polymers. In these tables, refers to the molar cyclization equilibrium constant and RIS, to the rotational isomeric state scheme to analyze chain conformations. 

Cyclization studies have also been carried out on the chemical copolymers poly(ethylene, dimethylsiloxane) and poly(styrene, dimethylsilox-ane). Numerous intramolecular interactions need to be taken into account in a chemical copolymer. Consequently, the results on the copolymers have been given only a preliminary interpretation in terms of rotational isomeric state theory. Cyclization calculations have also been carried out for poly(dihydrogensiloxane) [-SiH O-], but at present there are no experimental data available for comparison with theory. 

Curro, J. G. Mark, J. E., A Non-Gaussian Theory of Rubberlike Elasticity Based on Rotational Isomeric State Simulations of Network Chain Configurations. II. Bimodal Poly(dimethylsiloxane) Networks. J. Chem. Phys. 1984, 80, 4521-4525. 

The work described here is concerned with the effect of the ethyl group at the 3-position of the pyrrolidine ring on the ordered helical array and the mutarotation when compared with unsubstituted poly-L-proline. An examination of the space-filling models of poly-trans-3-ethylproline indicates the existence of two different forms. The rotational isomerism of the side chain ethyl group shows that the carbonyl group is literally locked on one side, which suggests that mutarotation processes may be hindered. 

Chain structure departs from tgt and changes to ttt when PEO is blended with poly(methyl methacrylate) (88). The structure of adsorbed PEO chains in the air-solution interface was found to be very different from the disordered structure expected for the solution state (89-91). In fact, the vibrational bands for these adsorbed chains have characteristics similar to those in the crystalline state (90). Various theoretical studies have led to quite different results for chain conformations of PEO (62,92-98). Because of differences in the local dielectric environment, different sets of rotational isomeric states need be considered. 

Conformational Analysis.— The major effort in this area has been directed towards empirical correlations of chemical shift and conformation. Tonelli and co-workers have examined the stereosequence dependence of C chemical shifts in polypropylene (PP) poly(vinyl chloride) (PVC), and polystyrene (PS) using the rotational isomeric-state scheme of polymer statistical mechanics. The structural variation of C shifts was shown to correlate well with the occurrence of three-bond gauche (y) interactions between carbon atoms together with y interactions between carbon and chlorine atoms in PVC and ring-current shifts in PS. It has been... 

Conformation and Chemical Shifts.—Chemical shifts have been correlated with conformation for H shifts in polystyrene and poly(vinyl chloride) and C shifts in model compounds of polypropylene. In all these papers, the chemical shift is related empirically to the occurrence of three- and four-bond steric interactions, similar to those used in the rotational isomeric state treatment of polymer statistical mechanics, " and the shift is expressed as a sum of compositional and conformational increments. The origin of the shielding contributions (magnetic anisotropy, electric field effects, etc.) is not stated, except for polystyrene in which the magnetic anistropy of the aromatic rings are incorporated... 

Experimental measurements of the dipole moment and its temperature coefficient of the polyoxides poly(trimethylene oxide) polyftetramethylene oxide) and poly(decamcthylene oxide), and poly(l,3-dioxolane) are in general agreement with estimates obtained by rotational isomeric state treatments. In the latter case, an alternating copolymer of formaldehyde and ethylene oxide, the appropriate intramolecular interactions were obtained from studies of the homopolymers the matrix calculation provides the proper statistical mechanical average, in contrast to simply taking a mean. 

Riande et al. (21,22) synthesized the cis and tmns isomers of PCDS as well as the trans isomer of poly(l,4-cyclohexylenedimethylene adipate) (PCDA), and studied their polarity by measurements of dielectric constants and dipole moments. They observed that the trans isomer exhibited lower polarity than the cis one, and that the dipole moment decreased with the number of methylene groups of the diacid unit. The configurational properties of the two PCDS isomers were comparatively examined, both experimentally and theoretically, using the rotational isomeric state model. 

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