Handbook of Solvents - George Wypych - ChemTech - Ventech!

272 Ligia Gargallo and Deodato Radic
the nitrile ester group interaction and an extensive polymer solvation becomes possible. According
to Prolongo et a1., 44 the number of methylene units or length of the n-alkyl chain is
very important for reaching cosolvency when the second liquid is an ester (acetate). Another
factor G E of the acetonitrile + acetate mixtures is larger for long alkyl chains such as in
pentyl acetate, favors cosolvency.
In the majority of cases, the cosolvent mixtures for PMMA contain either CCl 4 73,77,80,81
or acetonitrile 13,42-44,67 as one of the liquid components. A study of the mixture formed by
these two liquids and a comparison with the results obtained in the other cosolvents studied
before has been also reported. 84 The total sorption of the coil (PMMA) was calculated from
second virial coefficient and intrinsic viscosity data. According to these authors,
acetonitrile can interact favorably with the ester group of PMMA and is unfavorable with its
methylene backbone. The role of these opposing interactions and of liquid order in
acetonitrile are taken into account to explain the dilute solution properties of PMMA in this
cosolvent system. 84
On the other hand, in the case of PMMA, in powerful cosolvents, a small proportion of
liquid 2, added to the polymer/liquid 1 solution, is enough to produce a large decrease in the
phase separation temperature (T p). 64
Katime et al. 85 have studied the influence of cosolvency on stereo-complex formation
of isotactic and syndiotactic PMMA. The formation of PMMA stereo-complex has been attributed
to the interactions between the ester group of the isotactic form and the α-methyl
group of the syndiotactic form. 86
The stereo-complex was obtained at different compositions of the cosolvent mixtures
acetonitrile/carbon tetrachloride, acetonitrile/butyl chloride and butyl chloride/carbon tetrachloride.
The results show a high yield of complex formation in pure solvents and when
approaches its solvency maximum a decrease of the yield of stereo-complex was observed,
indicating that the interactions are impeded. 85
The dilute solution viscosity of PMMA in the cosolvent mixture formed by
acetonitrile (MeCN) and 1-chloro-n-butane (ClBu) at 25°C has been studied. 42,87 The
cosolvent effect in this system is extremely large. It has been observed a large increase in the
hydrodynamic volume of the macromolecule in solution, 42,17 and a step depression in the
critical temperature of phase separation (UCST). 64,88 The quantitative determination of the
magnitude of these effects has been reported. 42,64,88 Horta et al., 71 have compared a relative
capacities of temperature and of cosolvent mixing on expanding the macromolecular coils
and the tendency of the polymer to associate in poor solvents. They have also shown that
there is a connection which relates the dependencies of [η] on temperature and solvent composition
with the depression in critical temperature (UCST) caused by cosolvency. 71 The action
of the cosolvent was much more effective in expanding the macromolecule than
temperature was. 71 These authors have concluded that the comparison between the temperature
and solvent composition variations of [η] allows for a correct prediction of the
cosolvent depression of the UCST. The comparison between cloud points and [η] - T gives,
in general, inconsistent results, but the combination of [η] - T and [η]-φcompensates such
inconsistency and establishes a valid link between T c and [η].
It was found that when the cosolvent power of the binary mixture increases, the
complexing capacity decreases. These results were explained by taking into account the excess
Gibbs free energy, G E , and the order of the liquid.