Handbook of Solvents - George Wypych - ChemTech - Ventech!

578 S. Bistac, M. Brogly
Graphically this means that a plot of the DN for a series of donor solvents versus -ΔH
of their adducts formation with a given acid gives a straight line, allowing the determination
of a A and b A. By experimentally measuring the enthalpy of formation of only two adducts
for a given acid, one can predict, through the resulting a A an b A values, the enthalpy of
adduct formation of this acid with any other donor solvent for which DN is known.
Gutmann also proposes that the enthalpy of acid-base interaction could be approximated by
a two-parameters equation of the form:
AN DN
− ΔH =
AB
A B
100
[10.2.9]
where:
ΔHAB enthalpy of acid-base adduct formation
DNB donor number of the base
ANA acceptor number of the acid
The factor of 100 converts the AN value from a percentage of the SbCl5 value to a decimal
fraction. But one had to remind that on the 171 DN values reported in the literature 22
only 50 were determined precisely, i.e., calorimetrically.
10.2.1.2.6 Spectroscopic measurements: Fowkes’ approach
Fowkes 23 has proposed that for specific functional groups involved in acid-base interaction,
the enthalpy of acid-base adduct formation is related to the infrared frequency shift, Δν,of
its absorption band according to the following equation:
ΔH = k Δν
[10.2.10]
AB AB AB
where:
ΔHAB enthalpy of acid-base adduct formation
ΔνAB infrared frequency shift
kAB characteristic correlation constant between IR wavenumber shift and enthalpy
kAB is a characteristic constant of the functional group determined on the basis of compared
infrared and microcalorimetrical results of adduct formation. As an example, the latter is
equal to -0.99 kJ/mol/cm for the carbonyl group C=O. The stretching frequency of the C=O
vibration band is decreased by an amount ΔνAB proportional to the enthalpy of acid-base
bonding ΔHAB according to kAB. Such a methodology has recently been nicely confirmed not
only for polymer-solvent adduction, but also for polymer/polymer 24 and polymer/metal 25
adduction.
10.2.2 EFFECT OF POLYMER/SOLVENT INTERACTIONS ON
AGGREGATION OF STEREOREGULAR PMMA
10.2.2.1 Aggregation of stereoregular PMMA
PMMA chains are able to form aggregates in the presence of solvent 26 (in diluted solution,
concentrated solution, gel or solid). Aggregation between isotactic and syndiotactic chains,
after mixing in some solvents, leads to stereocomplexes, and self-aggregation corresponds
to the aggregation of isotactic or syndiotactic chains together. These two kinds of aggregates
result from the development of physical interactions between polymer chains. The
formation of aggregates depends mainly on the PMMA degree of stereoregularity and on
the nature of the solvent, but also on the temperature, the mixing time, and the
isotactic/syndiotactic stoichiometric ratio for stereocomplexes. 26,27 Complexing solvents fa-