Transitions pendant group effects

Comparison of the UV spectrum of polystyrene in the 2600 A region with that of toluene shows a close relationship in terms of both extinction coefficients and vibronic fine structure. The effect of para substituents is most conveniently characterized by the shift in the band corresponding to the a0-o transition. The comparison of substituent effects on the electronic excited states of thepara substituted polystyrenes parallels those for the corresponding para substituted toluenes. Such a correlation would only be expected if the tr - n transitions were effectively localized within a given pendant group of the polymer system. This conclusion is reinforced by the observation that polystyrene and toluene show similar shake up structure in their ESC A spectra with respect to both band profiles and intensities (when due... 

The size of the pendant group does not effect the glass transition, DMP results, fg, or values. 

As for nematic phases, if the pendant group occupies a recess in the structure such that its full broadening effect is not operative, an increase in Sc thermal stability can arise, e.g. in 5-subsitututed 6- -alkoxy-2-naphtholic acids. The increase in T[Sc N] is larger than that for T[N->I], showing again that dipole interactions play a role in enhancing the thermal stability of the Sc transition. 

No effort is made to accoimt for the concentration-dependent effect on the glass-transition temperature of P4VP due to nickel acetate trihydrate pendant groups coordinated to the lone pair of electrons on nitrogen in the pyridine ring. This bulky sidegroup effect becomes more important when the nickel concentration exceeds 33 mol% and approaches 50 mol%. 

Nickel acetate trihydrate pendant groups in the para-position of the pyridine ring could affect the glass transition temperature of P4VP. If this type of coordination occms for nickel acetate concentrations below 35 mol%, then this effect is contained in the parameter p. 

In monosubstituted vinyl polymers and at least some other classes of polymers, flexible pendant groups reduce the glass transition of the polymer by acting as internal diluents, lowering the frictional interaction between chains. The total effect is to reduce the rotational energy requirements of the backbone. 

In practice TMA is mostly used for measurement of the glass transition temperature by measuring CLTE and on occasion volume expansion. Therefore, it is appropriate to review those chemical factors (effects of pendant groups, molecular mass, tacticity, crystallinity, crosslinking, etc.) that have the largest influence on the glass transition temperature and the expansion of a polymer. 

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