Four amphiphilic block copolymers polyisobutylene-block-poly(methacrylic acid) (IB
m
-MAA
n
;
m = 70−134, n = 52−228) were synthesized and transferred into aqueous medium at pH 10−12. Their
structure in solution was characterized by fluorescence correlation spectroscopy (FCS), static and dynamic
light scattering (SLS, DLS), analytical ultracentrifuge (AUC), and by transmission electron microscopy
(TEM) with freeze-fracturing and staining techniques. DLS data, AUC sedimentation traces, and TEM
images indicate at least two different kinds of particles. TEM shows spherical micelles; however, especially
for polymers with larger hydrophobic blocks, additional particles are observed. FCS shows extremely
low critical micelle concentrations (cmc < 0.3 mg/L). The main part of the particles consists of micelles
with diameters from 15 to 50 nm, built by 130−200 block copolymer molecules. Aggregation numbers
and diameters are consistent with a model recently proposed by Förster et al. (J. Chem. Phys. 1996, 104,
9956−9970). The packing densities are determined from the hydrodynamic diameters and the aggregation
numbers; they vary between 6 and 32%. For large hydrophobic block lengths additional structures are
found, in most cases with a narrow size distribution. The origin of these structures is discussed.
Laser light scattering (LLS) was employed to monitor the microemulsion-like polymerization
processes by using poly(methyl methacrylate)-b-poly(methacrylic acid) (P(MMA-b-MAA)) block copolymers
with different block lengths (MMA58-b-MAA57, MMA67-b-MAA217, and MMA32-b-MAA69) or sodium dodecyl
sulfate (SDS) surfactant as dispersants. A combination of static and dynamic light scattering techniques
(SLS and DLS) was used to monitor the microemulsion-like systems before, during, and after
polymerization. The polymerization of MMA (methyl methacrylate) was found to occur first in the
dispersing aqueous medium, and then it was transferred inside the micellar cores to continue the
polymerization process, which is similar to the homogeneous nucleation mechanism found when using
small-molecule surfactants as dispersants. Depending on the hydrophobicity of the micellar cores, a
rearrangement of micellar chains was found to take place during the different stages of the polymerization
process. The similarities and differences of the dispersants between SDS surfactant micelles and P(MMA-b-MAA) block copolymer micelles are discussed. The polymerization of n-BA in micellar solution was
also studied and compared with that of MMA.
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