Micron-sized polymer particles from single poly(4-butyltriphenylamine) (PBTPA) homopolymer, binary polymer blend [PBTPA/poly(methyl methacrylate) (PMMA)], and ternary polymer blend (PBTPA/PBTPA-b-PMMA/PMMA) via a solvent evaporation method, and the surface morphologies and inside structure of resulting particles were investigated. Spherical homopolymer particles with smooth surface were resulted from PBTPA with low molecular weight. In the case of binary blends (PBTPA/PMMA = 1/1), Janus (low molecular weight) and dumbbell (high molecular weight) type morphologies were observed. The particles based on ternary blends containing PBTPA-b-PMMA showed core-shell type morphologies (PMMA; core, PBTPA; shell). Degree of engulfment of PMMArich domain increased with the content of the block copolymer. The decrease of domain size was not observed although the block copolymer had a suitable structure as a compatibilizer for the blend. It was also found that the initial concentration of polymer solution had an effect on the final morphology.
Triarylamine derivatives have been used as hole-transporting materials in organic photoconductors and electroluminescent devices [
Meanwhile, polymeric microspheres have attracted much interest and have been utilized in a number of fields. As for PAAs, we reported PBTPA microspheres [
Morphologically, controlled microspheres have been widely investigated. For conventional vinyl polymers, seeded emulsion [
In this study, the solvent evaporation method was applied to fabricate the microspheres based on PBTPA/ PMMA binary blends, and PBTPA/PBTPA-b-PMMA/PMMA ternary blends, and the relationship between the fabrication conditions and the morphologies was investigated. It is found that molecular weight of PBTPA and the concentration of original polymer solutions have a significant effect on the morphologies of the resulting particles.
Two PBTPA homopolymers with different molecular weight (PBTPA-L; Mn = 3700, and PBTPA-H; Mn = 6400) were synthesized via palladium-catalyzed C-N coupling polymerization [
A 5-mL flask equipped with a magnetic stirrer and a nitrogen inlet was charged with PBTPA-MI (0.13 g, 0.03 mmol) and CuBr (94 mg, 0.66 mmol). After the evacuation followed with backfilling of nitrogen, anisole (1 mL), distilled MMA (0.63 mL, 6.0 mmol) and N,N,N’,N”,N”-pentamethyldiethylenetriamine (PMDETA) (127 μL, 0.62 mmol) were added. Then the reaction mixture was stirred for 5 min. After five freeze-pump-thaw cycles, the flask was placed in a 100˚C oil bath for 24 h. After dilution with THF, the reaction mixture was filtered with alumina column in order to remove the copper catalyst. After concentration, the polymer was obtained by precipitation from methanol (1.70 g). Judging from GPC trace and 1H-NMR spectrum, no homopolymer was contained in the product.
Chloroform (analytical grade) was used as a volatile solvent for a solvent evaporation method. Poly (vinyl alcohol) (PVA) (Kuraray, PVA224) as a stabilizer was used as received.
A polymer solution (in chloroform, 2.5% or 5%) was dispersed in ten times volume of water containing 0.3% of PVA with a homogenizer (X520, CAT Scientific, US) to obtain 2 - 10 μm sized droplets (usually 5 min treatment).The weight ratio for the binary blend was fixed to be 1/1 (PBTPA/PMMA). In the case of ternary blends, the content of block copolymer was 10, 30 or 50 wt% keeping the weight ratio of PBTPA component to PMMA component constant (1/1). The homogenized mixture was stirred by a mechanical stirrer at 100 rpm for 24 hr to evaporated CHCl3 slowly. The resulting microspheres were washed with distilled water four times with a centrifugation process. Finally, polymer seeds dried under vacuum.
Resulting PBTPA and PBTPA-b-PMMA were characterized with 1H-NMR (ECX 300, JEOL, Japan) and GPC [
In next step, microspheres based on the binary blend PBTPA/PMMA (weight ratio 1/1) were fabricated, and the effect of molecular weight of PBTPA was investigated.
As Ge et al. discussed thermodynamically [
In order to investigate the effect of block copolymer on the surface and inside morphologies, various amount of PBTPA-b-PMMA was added to the binary blend. All ternary blend particles were fabricated keeping the weight ratio of PBTPA component to PMMA component constant (1/1), and low molecular weight PBTPA-L was utilized.
In order to investigate morphologies inside microspheres and to explore the origin of unique surface features, TEM measurements were carried out.
PBTPA homopolymer with low molecular weight (PBTPA-L) afforded spherical particles on the conditions we examined in a solvent evaporation method. On the other hand, the particles based on PBTPA with high molecular weight (PBTPA-H) were non-spherical and irregular. Unique bi-compartmental particles were obtained from binary blends with PMMA. Molecular weight dependence on the final morphologies was also observed, i.e. the particles based on PBTPA-L/PMMA and PBTPA-H/PMMA exhibited Janus and dumbbell type morphologies, respectively. This observation is reasonably explained by molecular weight dependence of the interfacial tension between two kinds of phase separated polymer solutions. Bi-compartmental morphologies were no longer observed for the particles based on ternary blends containing PBTPA-b-PMMA. Instead, the particles showed core-shell (PMMA; core, PBTPA; shell) morphologies. As the content of the block copolymer increased, the extent of engulfment of PMMA domain increased. Since physical properties such as dielectric constant and refractive index of PBTPA are considerably different from those of PMMA, the particles with various morphologies have potential applications in photonic and electronic fields.