142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

156 K. Ito, S. Kawaguchi
5.3
Some Properties of Graft Copolymers
Amphiphilic graft copolymers are conveniently synthesized by copolymerization
of a hydrophobic monomer with a hydrophilic macromonomer and vice
versa. The resulting copolymers are of great interest from the point of view of
their surface active properties.
Amphiphilic graft copolymers synthesized by HEMA with PSt macromonomer
were found to form a micellar aggregate in methanol by 1 H NMR analysis
[93, 94]; the spectrum of HEMA-rich graft copolymer (85% of HEMA content)
in CD 3 OD showed only peaks due to PHEMA segments, expected from their
conformations like that shown in Fig. 1f. On addition of CDCl 3 to the solution of
the graft copolymer, peaks ascribed to polystyrene segments also appeared, corresponding
to the expected conformation with both segments expanded or
coiled like in Fig. 1b. These data clearly indicate that the PSt segments, insoluble
in methanol, constitute a micelle core which behaves as a solid on the NMR time
scale. Consequently, their resonance peaks were too broad to be observed. The
reverse phenomenon was observed in the case of polystyrene-rich graft copolymer
(72% of PSt content); in the NMR spectrum measured in CDCl 3, only the
peaks due to the PSt segments were observed, indicating the formation of a micelle
with a PHEMA core surrounded by PSt segments. The conformation of the
micelle is shown in Fig. 1d. In parallel to this line, some papers about surfactant
properties of various kinds of graft copolymers have been reported [95, 96].
Control of surface properties of polymers is very important in technical fields
such as coatings, adhesives, films, and fibers. Among various surface modification
techniques, surface accumulation of graft copolymers is a convenient and
promising method for the surface control. Yamashita et al. [97] investigated the
surface activity of graft copolymers prepared from perfluoroalkylethyl acrylate
and PMMA macromonomer in PMMA films, prepared by the solvent cast method.
A very small amount of the graft copolymer was sufficient to improve the
anti-wettability of PMMA films, as evaluated by contact angle of a water or dodecane
droplet. Fluorine- [98], silicon- [99], PMMA-[100], and poly(2-methyl-2oxazoline)-containing
[96] graft copolymers have been prepared and studied
with respect to their properties as a surface modifier.
The polymer composites have been investigated in order to achieve various
functions and properties enhancements. In blending polymer materials, compatibility
between the respective polymers becomes very important to affect the
properties of the resulting polymer blend. In immiscible cases, the graft copolymers
are often used as a compatibilizer. Poly(styrene-g-MMA) prepared by a
macromonomer technique was reported to be an effective compatibilizer for
blending between PSt and PVC; elongation and tensile strength of the composite
containing the graft copolymer are superior to those without the compatibilizer
[101].
Recently, much attention has been paid to selective gas permeable membranes.
The basic requirements for these membrane are a high permeability co-