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

More documents

Recommendations

Info

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-
Poly(macromonomers), Homo- and Copolymerization 157 efficient, high selectivity, and self-supporting properties. Poly(dimethylsiloxane) is known to have a high permeability coefficient for oxygen although its selectivity for permeants and mechanical strength are low. Kawakami et al. [102] have prepared various polymers having oligosiloxane side chains by the homopolymerization of the macromonomers. The polymer with short siloxane chains was found to be better than that with long branches in selectivity for permeation of oxygen and in mechanical strength. 6 Design of Polymeric Microspheres Using Macromonomers Polymerizations are usually carried out in a good solvent for both a monomer and its resulting polymer. When in the presence of suitable dispersants one carries out the polymerization in non-solvents, however, polymeric microspheres are produced. Much attention has been paid recently to this type of heterogeneous polymerization to afford monodisperse polymeric microspheres because of various applications in technical and biomedical fields. One of the fascinating applications of macromonomers is in the field of heterogeneous polymerization such as emulsion and dispersion systems. This was first reported for nonaqueous dispersions (NAD) by the ICI group [7]. The heterogeneous polymerization in the presence of suitable stabilizers affords submicron- to micron-sized polymeric microspheres, often of excellent monodispersity. Among a variety of methods of preparing polymeric microspheres, the macromonomer technique is unique and flexible in that the macromonomers themselves act as reactive emulsifiers or dispersants without any conventional surfactants. The macromonomers are graft-copolymerized during copolymerization and accumulate on the particle surface, so that the resulting emulsions and dispersions are very effectively sterically stabilized against flocculation. As the counterpart of NAD, a number of emulsion or dispersion systems in water or in alcoholic media have been recently developed using hydrophilic macromonomers to meet increasing concerns for environmentally friendly systems. 6.1 Dispersion Polymerization Dispersion polymerization is defined as a type of precipitation polymerization by which polymeric microspheres are formed in the presence of a suitable steric stabilizer from an initially homogeneous reaction mixture. Under favorable circumstances, this polymerization can yield, in a batch process, monodisperse, or nearly monodisperse, latex particles with a relatively large diameter (up to 15 µm) [103]. The solvent selected as the reaction medium is a good solvent for both the monomer and the steric stabilizer, but a non-solvent for the polymer being formed and therefore a selective solvent for the graft copolymer. This restriction on the choice of solvent means that these reactions can be carried out
Page 1 and 2:
142 Advances in Polymer Science Edi
Page 3 and 4:
Branched Polymers I Volume Editor:
Page 5 and 6:
Volume Editor Dr. Jacques Roovers I
Page 7 and 8:
Preface While books have been writt
Page 9 and 10:
Contents Synthesis of Branched Poly
Page 11 and 12:
Synthesis of Branched Polymers by C
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
72 N. Hadjichristidis, S. Pispas, M
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
100 N. Hadjichristidis, S. Pispas,
Page 111 and 112:
102 N. Hadjichristidis, S. Pispas,
Page 113 and 114: 104 N. Hadjichristidis, S. Pispas,
Page 137 and 138: Poly(macromonomers): Homo- and Copo
Page 139 and 140: Poly(macromonomers), Homo- and Copo
Page 163: Poly(macromonomers), Homo- and Copo
Page 187 and 188: Dendrimers and Dendrimer-Polymer Hy
Page 215 and 216:
Dendrimers and Dendrimer-Polymer Hy
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Author Index Volumes 101-142 Author
Page 239 and 240:
Author IndexVolumes 101-142 231 Dun
Page 241 and 242:
Author Index Volumes 101-142 233 Ka
Page 243 and 244:
Author Index Volumes 101-142 235 Og
Page 245 and 246:
Author Index Volumes 101-142 237 Su
Page 247 and 248:
Subject Index Addition-fragmentatio
Page 249 and 250:
Subject Index 241 Microphases 11z,
show all

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

Create successful ePaper yourself

Delete template?

Save as template?