Odd—even effect

In principle, the odd-even effect can be explained from the differences in the packing arrangement of the... 

PTT, with three methylene units in its glycol moiety, is called an odd-numbered polyester. It is often compared to the even-numbered polyesters such as PET and PBT for the odd-even effect on their properties. Although this effect is well established for many polycondensation polymers such as polyamides, where the number of methylene units in the chemical structures determines the extent of hydrogen bonding between neighboring chains and thus their polymer properties, neighboring chain interactions in polyesters are weak dispersive, dipole interactions. We have found that many PET, PTT and PBT properties do not follow the odd-even effect. While the PTT heat of fusion and glass transition temperature have values between those of PET and PBT, properties such as modulus... 

In general, properties that are additive and could be estimated by group contribution methods, such as density and heat of fusion, tend to follow the order of PET, PTT and PBT properties dependent on the conformational arrangement of the methylene units, such as modulus, show an odd-even effect, at least among these three polyesters. 

PTT has three dynamic mechanical viscoelastic relaxations [61, 62], a, (j and Y (Figure 11.9). The 70°C a-relaxation is the glass transition. In a study on the effect of methylene sequence length on aromatic polyester viscoelastic properties, Farrow et al. [63] reported a PTT a-relaxation as high as 95 °C. They also found that Tg of this series of aromatic polyesters did not show any odd-even effects, which was later confirmed by Smith et al. [64],... 

Figure 5.9 Cyclic voltammograms of MBPm SAMs on Au/mica recorded in 0.5 m KOH at a scan rate of 20 mV/s. The dotted line highlights the odd-even effect in the desorption peak. Arrows in MBPl curve indicate CV scan direction. Samples were prepared at 295 K.

E.J. Knust, C. Kupfernagel, G. Stocklin, Long chain [ F]-fatty acids for the study of regional metabolism in heart and liver odd-even effects of metabolism in mice, J. Nucl. Med. 20 (1979) 1170-1175. 

The polymerization of lactones with the methyl substituent at different positions showed identical enantiopreferences in the polymerization reactions (Scheme 8b) as observed for the hydrolysis reaction (Fig. 10a) [26]. Also in this case, the alternating orientation of the methyl group from 3- to 5-MeCL in the faster reacting enantiomer suggested an odd-even effect. Comparison of the initial rate constants showed that the polymerization of 5-MeCL proceeded the fastest ki = 5h ), whereas 3-MeCL... 

The conformational characteristics of dimethyl esters of dicarboxylic acids are studies by the NMR and dipole moment method. Conformational energies of the internal CH2-CH2 bonds are determined from the observed 1H-1H vicinal coupling constants. Preferred conformations around the C-C bond are elucidated from the RIS analysis of dipble moments. With the RIS parameters thus established, the orientational correlation between the terminal ester groups is examined. The analysis provides the reason why the odd-even effect in the dipole moment is moderate, and attenuates rapidly with n in the ct.co-diester series. 

The prospensity for the formation of bends in the flexible spacer in polyesters containing naphthyl units is examined by the study of the fluorescence of a series of diesters. The dependence of the degree of intramolecular excimer formation on the length of the aliphatic spacer, under circumstances where the dynamics of rotational isomerism in the flexible spacer is suppressed, is evaluated by extrapolation of the measurements to infinite viscosity n. The extrapolated results exhibit an odd-even effect, with the more intense excimer emission being observed when the number of methylene groups is odd. The odd-even effect is rationalized by an RIS analysis of the diesters. 

Fluorescence is measured in dilute solution of model compounds for polymers of 2,6-naphthalene dicarboxylic acid and eight different glycols. The ratio of excimer to monomer emission depends on the glycol used. Studies as functions of temperature and solvent show that, in contrast with the analogous polyesters in which the naphthalene moiety is replaced with a benzene ring, there can be a substantial dynamic component to the excimer emission. Extrapolation to media of infinite viscosity shows that in the absence of rotational isomerism during the lifetime of the singlet excited state, there is an odd-even effect In the series in which the flexible spacers differ in the number of methylene units, but not in the series in which the flexible spacers differ in the number of oxyethylene units. 

The fluorescence of the a,co-diesters of HO(CH2)mOH, m 2-6, and 1-naphthoic acid is characterized in dilute solution in solvents of different viscosity. An equilibrium RIS analysis can rationalize the observation of the odd-even effect and the occurrence of the maximum at m = 5. 

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