Complexes of Poly[Sodium(Sulfamate/Carboxylate)Isoprene] ... 89aggregation concentration (cac) which is much lower than the surfactant
critical micelle concentration (cmc).
In this chapter we use light scattering methods to determine the size and
aggregation state of linear anionic polyelectrolyte poly[sodium (sulfamate/
carboxylate)isoprene] (SCPI) in the presence of the cationic surfactant
dodecyltrimethylammonium bromide (DTMAB). Fluorescence spectroscopy
and electrophoretic light scattering reveal the formation of hydrophobic
domains within the polyelectrolyte aggregates and the reduction of their
charge caused by the surfactant binding. The aggregation morphology, charge
and hydrophobicity depend as expected on the relative concentrations of the
individual species. Additionally though, dilution of the complexes-containing
solutions leads to tunable hydrophobicity of the aggregates.
EXPERIMENTAL SECTION
2.1. Materials and Sample Preparation
The SCPI polyelectrolyte was prepared by a post-polymerization
functionalization reaction on a polyisoprene (PI) homopolymer precursor. The
PI precursor was synthesized by living anionic polymerization high vacuum
techniques.^ Consequently, the PI precursor was transformed to SCPI by
reaction of the isoprene double bonds with chlorosulfonyl isocyanate (CSI,
from Acros), followed by basic hydrolysis of the lactam intermediate with
NaOH [7]. Thus sodium sulfamate and sodium carboxylate groups are
introduced in the same isoprene monomeric unit.
SCPI is an intrinsically flexible hydrophobic polyelectrolyte due to its
polyisoprene backbone.^13 C-NMR and FTIR analysis give proof of the
presence of the sodium sulfamate and sodium carboxylate groups on the SCPI
chains. Potentiometric titrations and elemental analysis, show that the extent of
functionalization is 68 mole %, which is in accord with^13 C-NMR data.
Therefore, due to the presence of unfunctionalized PI segments, the SCPI
polyelectrolyte chain retains some hydrophobic character. The molecular
structure of the SCPI is presented in Scheme 1.