Takashi Fukutomi

Synthesis and properties of microgel bearing a mercapto group

Vinylbenzyl S-thioacetate (1) was prepared from thioacetic acid and chloromethylstyrene. Although bulk polymerization of 1 afforded a crosslinked polymer, solution polymerization in chlorobenzene afforded a corresponding soluble polymer. The S-thioacetate group did not react during the radical polymerization of 1. Bulk copolymerization of 1 with styrene afforded a soluble copolymer when the feed ratio of 1 was lower than 30 mol %. Soap-free emulsion copolymerization of 1, St, divinylbenzene, and 2-hydroxyethyl methacrylate (66 : 28 : 1 : 5) was carried out in water using 2,2′-azobis (N,N′-dimethyleneisobutyramidine) dichloride as an initiator to afford uniform spherical microgel 2, whose average diameter was 135 nm. Aminolysis of 2 with an excess amount of butylamine in the presence of sodium tetrahydridoborate followed by treatment with hydrochloric acid resulted in complete removal of the acetyl group to give a slightly distorted spherical microgel (MG-SH) bearing mercapto group. The average diameter of MG-SH was 165 nm. Trans-esterification of p-nitrophenyl acetate (3) in the presence of triethylamine was efficiently accelerated by the addition of MG-SH. The radical polymerization of methyl methacrylate (MMA) in the presence of suspended MG-SH in chlorobenzene afforded the MMA-grafted microgel. Although MG-SH is a crosslinked gel, it acts as a soluble polymer bearing mercapto group.

Crosslinking of the inner poly(methyl methacrylate) core of poly(α-methylstyrene-b-methyl methacrylate) micelles in selective solvent: 1. Effect of solvent selectivity

The crosslinking reaction of poly(methyl methacrylate) cores in poly(α-methylstyrene-b-methyl methacrylate) micelles was carried out in mixed solvents of benzene and cyclohexane. In suitable solvent core-corona type particles were obtained for block copolymers with sufficiently high molecular weight and α-methylstyrene content > 39%. The particle size became a minimum at a benzene/cyclohexane ratio of 37–46 (v/v) which depended on the nature of the block copolymers. The particle size increased drastically when the solvent compositions deviated from this region. When the molecular weight of the block copolymer was < 2 × 104, inter-micelle crosslinking took place under the experimental conditions of this study, even when the α-methylstyrene content was very high.

Orientation on microdomains of diblock copolymers

Abstract Well defined poly(styrene- block -isoprene) and poly(styrene- block -2-vinylpyridine) diblock copolymers were prepared by sequential anionic addition. Films were fabricated by casting these diblock copolymer solutions on a Teflon sheet by varying the casting conditions. Morphological results of these ultrathin sections were obtained on a transmission electron microscope. The surface characterization of poly(styrene- block -2-vinylpyridine) film was carried out by X-ray photoelectron microscopy. Both surface and bulk morphologies of these diblock copolymer films (about 50 wt% polystyrene blocks) showed an interesting tendency, namely that alternating lamellar structures of two microphases were oriented with their interface parallel to the surface that contacts air.

Microphase separation and crystallization of crystalline-amorphous type block copolymer—2. microstructure of crystalline part

Abstract The crystallization of poly[tetrahydrofuran (THF)-b-isoprene (crystalline segment-amorphous segment) was studied by transmission electron microscopy (TEM), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and small angle X-ray diffraction (SAXS). It was found by TEM observation that the amorphous part of poly(tetrahydrofuran) (PTHF) mostly existed near the PIP domains with a small radius of curvature. The crystallite core size of PTHF (determined from GPC data, 110 A) was smaller than that of homo-PTHF (184 A). It was found by TEM, DSC and SAXS that the PTHF domain was composed of three layers viz. crystallite layer, semicrystalline layer and crystallite layers. These results suggest that the crystallization of PTHF proceeded near the interface and the PTHF chains were arranged perpendicularly to the interface. Crystallization of PTHF in the block copolymer film is therefore different from that of homo-PTHF.

Reaction of methyl thioglycolate with chloromethylstyrene microgel : Preparation of core-shell-type microgel by chemical modification

A uniform spherical polychloromethylstyrene (PCMS) microgel whose average diameter was 2.3 μm was prepared by dispersion copolymerization of chloromethylstyrene and divinylbenzene in ethanol–DMSO (25/3 v/v) in the presence of polyvinylpyrrolidinone. When the PCMS microgel was treated with an excess amount of methyl thioglycolate (MTG) in the presence of 1,8-diazabicylco[5.4.0]undec-7-ene (DBU) at room temperature in THF for 4 h, sulfenylated microgel was obtained. The introduction ratio of MTG corresponded well to the amount of DBU used. A transmission electron microscope (TEM) photograph and thermal analysis of the PCMS microgel partially modified by MTG showed that it had a core–shell structure, that is, an MTG-modified shell and an unchanged core. Since the reaction of the chloromethyl group and MTG was a diffusion-limited one, MTG was introduced into the PCMS microgel from the outer side layer by layer. The PCMS microgel in which 52% of the MTG was introduced was treated with an excess amount of pyridine in DMAc at 50°C for 48 h followed by acid-catalyzed hydrolysis in dioxane–water at 80°C for 48 h to give a zwitterionic microgel that formed a stable suspension.

Crosslinking of the inner poly(methyl methacrylate) core of poly(α-methylstyrene-b-methyl methacrylate) micelles in selective solvent: 2. Effect of polymer concentration

Abstract Core-corona type microgels composed of poly(methyl methacrylate) core and poly(α-methylstyrene) corona were synthesized from poly(α-methylstyrene-b-methyl methacrylate) in benzene/cyclohexane mixtures with varying polymer concentration. It was possible to synthesize soluble core-corona type microgels from the block copolymer with a small degree of polymerization ( DP ) in concentrated solution, when the micelle system turned from ‘open associated’ (stepwise associated) to ‘closed associated’ (mass action type) with increase of the polymer concentration. In the ‘open associated’ systems, the increase of the polymer concentration was the cause of inter-micelle crosslinking due to macrogelation and anomalization of the shape of the products.

Phase separation in binary block copolymer blends

Abstract The well defined poly(styrene(S)-b-isoprene(I)) and poly(S-b-2-vinylpyridine(2VP)) diblock copolymers were prepared by sequential anionic addition. Binary poly(S-b-I)/poly(S-b-2VP) diblock copolymer blend films were prepared by solution casting, varying the volume fraction of the three-block sequences. Morphological results were obtained by transmission and scanning electron microscopy (TEM and SEM). The three-phase separated microdomains formed depended strongly on the volume fraction of binary block sequences and casting conditions.

Influence of graft copolymer structure on the dimensions and morphology of core-corona type microgels

Abstract Several types of poly(vinyl chloride)- graft -poly(α-methylstyrene) (P(VC- g -MeSt)) graft copolymers whose branch numbers and branch lengths are different, were crosslinked with a dianionic dimer of 1,1-diphenylethylene in a mixed solvent of tetrahydrofuran (good solvent for PVC and PMeSt) and cyclohexane (non-solvent for PVC). The crosslinked products were characterized using gel permeation chromatography and electron microscopy. A microphased core-corona type microgel was synthesized when the graft copolymer has a small number of long branches. The size distribution of the crosslinked products became broad with increase in the branch number of the graft copolymer. The average number of graft copolymers per microphased core-corona type microgel was calculated from the electron micrographs to be 12.5.

Connection of poly(methyl methacrylate) microgel particles dispersed in poly(vinyl alcohol) matrix by seed polymerization

Poly(methyl methacrylate) microgels covered with poly(hydroxyethyl methacrylate) thin layer was dispersed in poly(vinyl alcohol) matrix. Homogeneous and regular arrangement of the microgel particles was suggested by Bragg diffraction for the films prepared by varying the PVA/microgel ratio (from 6/4 to 3/7 (w/w)). It was proved that the regular arrangement and connection of the microgels by seeded polymerization in poly(vinyl alcohol) were possible.

The microgel formation by crosslinking reaction of primary polymer

Abstract The crosslinking reaction of primary polymers under the influence of potentials was studied by computer simulation. Under the predominant action of repulsive potential, macrogelation did not appear and the products remained as a sol (microgel). With increasing repulsive potential, the particle size descended and the final size distribution became narrow (Pw/Pn = 1·06; Pw, weight average degree of polymerization; Pn, number average degree of polymerization). By the simulation according to a diffusion limited aggregation model with distant repulsive potential and short distant weak attractive potential, round and dense particles were obtained. In the crosslinking reaction of partially quaternized poly (4-vinylpyridine) (q-P4VP), the size of the particles declined and the size distribution became narrow with the quaternization degree of q-P4VP. This result agrees with that of the simulation.