Nonaqueous Dispersion Formed by an Emulsion Solvent

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Non-aqueous dispersion formed by emulsion solvent evaporation method using block-random copolymer surfactant synthesized by RAFT polymerization Naofumi Ezaki, Yoshifumi Watanabe, and Hideharu Mori Langmuir, Just Accepted Manuscript • Publication Date (Web): 30 Sep 2015 Downloaded from http://pubs.acs.org on October 6, 2015

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Non-aqueous dispersion formed by emulsion solvent evaporation method using block-random copolymer surfactant synthesized by RAFT polymerization

Naofumi Ezaki*1,2, Yoshifumi Watanabe2, Hideharu Mori*1

1

Graduate School of Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan, 2RISO KAGAKU CORPORATION, 5-34-7 Shiba, Minato-ku, Tokyo 108-8385, Japan

E-mail: [email protected] E-mail: [email protected]

ACS Paragon Plus Environment

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ABSTRACT

As surfactants for preparation of non-aqueous microcapsule dispersions by the emulsion solvent evaporation method, three copolymers composed of stearyl methacrylate (SMA) and glycidyl methacrylate (GMA) with different monomer sequences (i.e., random, block, and block-random) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Despite having the same comonomer composition, the copolymers exhibited different functionality as surfactants for creating emulsions with respective dispersed and continuous phases consisting of methanol and isoparaffin solvent. The optimal monomer sequence for the surfactant was determined based on the droplet sizes and the stabilities of the emulsions created using these copolymers. The block-random copolymer led to an emulsion with better stability than obtained using the random copolymer and a smaller droplet size than achieved with the block copolymer. Modification of the epoxy group of the GMA unit by diethanolamine (DEA) further decreased the droplet size, leading to higher stability of the emulsion. The DEA-modified block-random copolymer gave rise to non-aqueous microcapsule dispersions after evaporation of methanol from the emulsions containing colored dyes in their dispersed phases. These dispersions exhibited high stability and the particle sizes were small enough for application to the inkjet printing process.


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INTRODUCTION Colorants

encapsulated

by

polymers

with

tunable

properties

and

characteristic

multidimensional architectures have prospective applications in printing,1-5 painting,6 electrophoretic ink,7-8 etc., making them attractive research targets. For application in printing, encapsulated colorants are generally used in the form of aqueous dispersions, whereas non-aqueous dispersions of encapsulated colorants are comparatively scarce. However, non-aqueous dispersions are considered to be more suitable than aqueous dispersions for use as inks for high-speed, high-volume inkjet printers for plain paper printing. The main advantage of non-aqueous dispersions is that stable paper feeding in the printer is more readily achieved with such inks as they induce less paper deformation due to pulp swelling derived from water uptake. Various methods have been reported for colorant encapsulation, including solvent evaporation,9-13

emulsion

polymerization,14-15

miniemulsion

polymerization,16-17

and

coacervation;18-19 however, most of these methods have limitations that hamper their application to industrial printing. For example, miniemulsion polymerization is limited in that only colorants that are completely dissolved or dispersed in a monomer can be used. In the case of emulsion polymerization, the efficiency of encapsulation is generally low because the production of polymer particles that do not contain any colorant cannot be avoided. In contrast, the solvent evaporation method, which is also well known as the preparation method of the spherical particles,12, 20-22 leads to less restriction of the encapsulated material and high encapsulation efficiency. This method involves evaporation of the solvent from an emulsion containing the dispersed phase composed of a volatile solvent that either dissolves or disperses the colorant. During preparation of the dispersion by this method, the surfactant used to generate the emulsion acts as the dispersant subsequent to solvent evaporation. The non-aqueous microcapsule


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dispersion is formed by evaporation of the volatile solvent from the non-aqueous emulsion, where the volatile solvent is dispersed in a non-volatile solvent. Therefore, it is necessary to find a suitable surfactant for the emulsion solvent evaporation method to generate a stable non-aqueous emulsion. Non-aqueous emulsions, in which quite a number of solvents can be used, are characteristic emulsions with a much broader range of applications.23 As the emulsifiers for non-aqueous emulsions, low molecular surfactants,10 particles,24 and polymeric surfactants11, 25-29 are generally used. Polymeric surfactants, especially block copolymers, have been frequently used as the emulsifiers for non-aqueous emulsions because the large block lengths in copolymers allow for efficient steric stabilization. For example, poly(isoprene)-b-poly(methyl methacrylate),26 poly(2-vinylpridine)-b-poly(butadiene),27

poly(butadiene)-b-poly(ethylene

oxide),25

and

poly(butylene-co-ethylene)-b-poly(ethylene oxide)29-30 have been utilized in non-aqueous emulsions. In order to achieve further functionality and enhanced properties for inkjet inks (e.g., colorability, fixing ability, and various fastnesses), a higher ratio of the dispersed phase, small particle size, and good stability of the dispersed microcapsule are required. However, the polymeric surfactants currently employed for non-aqueous emulsions do not simultaneously fulfill these requirements. In this paper, we report the preparation of a non-aqueous microcapsule dispersion for use as an inkjet ink by using the emulsion solvent evaporation method, as illustrated in Figure 1. Initially, we demonstrate the syntheses of the copolymers consisting of stearyl methacrylate (SMA) and glycidyl methacrylate (GMA) as the polymeric surfactants. Three copolymers with different monomer sequences (i.e., random, block, and block-random sequences) are synthesized by


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reversible addition–fragmentation chain transfer (RAFT) polymerization (Scheme 1) in order to find an optimal sequence as the surfactant for the emulsion solvent evaporation method. To fulfill the aforementioned requirements of inkjet inks, the performance of these copolymers is initially evaluated in terms of the droplet size and stability after forming the non-aqueous emulsion without the colorant. Finally, non-aqueous dispersions containing the colorant are prepared using the optimal polymeric surfactants to evaluate the feasibility for application as an inkjet ink.


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Figure 1. (a) Schematic for preparation of non-aqueous dispersion by the solvent evaporation method and (b) structure of polymeric surfactants.


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Scheme 1. Syntheses of (a) random, (b) block, and (c) block-random copolymers composed of stearyl methacrylate (SMA) and glycidyl methacrylate (GMA) by reversible addition– fragmentation chain transfer (RAFT) polymerization using 2-cyano-2-propyl dodecyl trithiocarbonate (CPDTTC)

The block-random copolymers have been reported to have tunable properties such as stimuli-responsivity31-35 and exhibit characteristic behaviors of phase separations or self-assemblies.36-41 Hence, in addition to the conventional block and random copolymers, the


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block-random copolymer, poly(SMA)-b-poly(SMA-ran-GMA), was also evaluated in this study. A variety of copolymers composed of alkyl methacrylates (acrylate) and GMA have been reported.42-43 GMA is frequently employed as a functional monomer, the polarity of which is readily adjusted by modification of the epoxy group with various nucleophiles.42, 44-45 Herein, we examined the effect of modification of the GMA unit with diethanolamine (DEA) on the droplet size and stability of the emulsion, where addition of DEA to the epoxy group of the GMA unit generated three hydroxyl groups (Scheme 2). For use as inkjet inks, the preparation of non-aqueous microcapsule dispersions by the solvent evaporation method using the DEA-modified copolymer with the optimal monomer sequence was evaluated.

Scheme 2. Diethanolamine (DEA)-modification of GMA unit of the copolymers

EXPERIMENTAL SECTION Materials.

2-Cyano-2-propyl

dodecyl

trithiocarbonate

(CPDTTC,

Aldrich,

97%),

2,2'-azobis(isobutylronitrile) (AIBN, Wako Pure Chemical Industries, 98%), stearyl methacrylate (SMA, Tokyo Chemical Industry, 90%), glycidyl methacrylate (GMA, Wako Pure Chemical Industries, 95%), diethanolamine (DEA, Wako Pure Chemical Industries, 99%), Isopar M (Exxonmobil Chemical, SG = 0.7879), poly(vinylpyrrolidone) (PVP, Aldrich, average molecular


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weight 10000), and methanol (Wako Pure Chemical Industries, 99%, SG = 0.7884) were used as received. VALIFAST BLUE 1621 (modified from Colour Index (C.I.) Direct Blue 87), VALIFAST RED 1308 (dye complex), VALIFAST YELLOW 1101 (modified from C.I. Acid Yellow 42), and VALIFAST BLACK 3830 (modified from C.I. Solvent Black 27) were obtained from Orient Chemical Industries and used as received. The precise chemical structures of the dyes are not disclosed. They are industry products modified from the dyes having C.I. names and numbers, which were published by The Society of Dyers and Colourists (UK) and The American Association of Textile Chemists and Colorists (USA).

Synthesis of random copolymer using CPDTTC as the CTA. The random copolymer employing CPDTTC as the chain transfer agnet (CTA) was synthesized as follows: SMA (17.3 g, 51.2 mmol), GMA (2.4 g, 17.1 mmol), CPDTTC (0.197 g, 0.57 mmol), AIBN (0.047 g, 0.28 mmol), and Isopar M (30.0 g, 38.1 mL) were placed in a round-bottom flask and the solution was purged with nitrogen gas for 10 min before sealing the reaction vessel. The reaction mixture was stirred at 80 °C for 24 h. Estimation of the monomer conversion and comonomer composition using 1H NMR (Figure S1) and size exclusion chromatography (SEC) measurements were conducted without sample purification. The SMA conversion was determined by integration of the monomer C=C-H resonance at 6.0–6.1 ppm and comparison with the sum of the CO-O-CH2 peak intensities of the polymer and monomer at 3.8–4.2 ppm. The GMA conversion was determined by integration of the monomer C=C-H resonance at 6.1–6.2 ppm and comparison with the sum of the methine peak intensities of the polymer and monomer at 3.2–3.3 ppm. The estimated SMA and GMA conversions were both 99%. The comonomer composition was determined via 1H NMR spectroscopy by comparison of the peaks corresponding to the two


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comonomers. The estimated comonomer composition was SMA:GMA = 75:25. The Mn of the prepared random copolymer was 26600 with a polydispersity index of 1.21.

Synthesis of block copolymer using poly(SMA) as the macro-CTA. Synthesis of the block copolymer employing poly(SMA) as the macro-CTA was performed as follows: SMA (19.7 g, 58.3 mmol), CPDTTC (0.224 g, 0.65 mmol), AIBN (0.053 g, 0.32 mmol), and Isopar M (30.0 g, 38.1 mL) were placed in a round-bottom flask and the solution was purged with nitrogen gas for 10 min before sealing the reaction vessel. The reaction mixture was stirred at 80 °C for 24 h. The Mn of the crude poly(SMA) was 21800 with a polydispersity index of 1.17 after 99% conversion; the crude product was used without further purification. For preparation of the block copolymer, a solution of trithiocarbonate-terminated poly(SMA) (43.8 g, 17.5 g polymer/26.3 g solvent, which corresponds to 0.57 mmol poly(SMA)), AIBN (0.047 g, 0.28 mmol), GMA (2.42 g, 17.0 mmol), and Isopar M (3.7 g, 4.7 mL) were placed in a round-bottom flask. After purging with nitrogen gas followed by sealing the vessel, polymerization was conducted at 80 °C for 24 h. The GMA conversion, as detected by 1H NMR, was 99%. The comonomer composition, determined using 1H NMR, was SMA:GMA = 75:25. The Mn of the prepared block copolymer was 27500 with a polydispersity index of 1.35.

Synthesis of block-random copolymer using poly(SMA) as the macro-CTA. Synthesis of the block-random copolymer employing poly(SMA) as the macro-CTA was performed as follows: SMA (19.6 g, 57.9 mmol), CPDTTC (0.333 g, 0.96 mmol), AIBN (0.079 g, 0.48 mmol), and Isopar M (30.0 g, 38.1 mL) were placed in a round-bottom flask and the solution was purged with nitrogen gas for 10 min before sealing the reaction vessel. The reaction mixture was stirred


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at 80 °C for 24 h. The Mn of the crude poly(SMA) (as determined by SEC) was 14700 with a polydispersity index of 1.19 after 99% conversion; the crude product was used without further purification. For preparation of the block-random copolymer, a solution of trithiocarbonate-terminated poly(SMA) (29.4 g, 11.8 g polymer/17.6 g solvent, which corresponds to 0.57 mmol poly(SMA)), AIBN (0.047 g, 0.28 mmol), SMA (5.76 g, 17.0 mmol), GMA (2.42 g, 17.0 mmol), and Isopar M (12.3 g, 15.6 mL) was placed in a round-bottom flask. After purging with nitrogen gas followed by sealing the reaction vessel, polymerization was conducted at 80 °C for 24 h. The SMA and GMA conversions, as determined by 1H NMR, were 98% and 99%, respectively. The copolymer composition was SMA:GMA = 75:25. The Mn of the prepared block-random copolymer was 21300 with a polydispersity index of 1.33. In all cases, the crude random, block, and block-random copolymers were used as polymer solutions for preparation of the emulsions or the dispersions without further purification.

Addition of DEA to GMA unit of the copolymer. Addition of DEA to the epoxy groups of the copolymer was conducted as follows (as a representative example): a solution of the block-random copolymer (30.0 g, 12.0 g polymer/18.0 g solvent, which corresponds to 0.34 mmol block-random copolymer), DEA (1.05 g, 10.0 mmol, corresponding to [DEA]/[GMA unit] = 0.98), and Isopar M (1.58 g, 2.0 mL) were placed in a round-bottom flask. The reaction mixture was stirred under ambient atmosphere at 120 °C for 3 h. The reaction mixture was used for preparation of the emulsions or the dispersions without further purification. To determine the amination degree (Eq. 1) by elemental analysis, the reaction mixture was purified by reprecipitation in acetone and separated by centrifugation (14000 rpm, 1 min) and decantation.


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The resulting product was dried at 50 °C for 4 h under vacuum. The amination degree of this copolymer, which was calculated using Equation 1, was 89%. A high degree of amination was also confirmed by 1H NMR measurements (Figure S2). Amination degree % =

[ !] [#$! !]

(1)

The same procedure was employed for modification of the random and block copolymers.

Preparation of non-aqueous emulsion and dispersion without colorant. Preparation of the non-aqueous emulsion was conducted as follows (as a representative example): an Isopar M solution containing the 40 wt% DEA-modified block-random copolymer (1.88 g) and Isopar M (11.9 g, 15.1 mL) was placed in a glass beaker. A mixture of methanol (7.88 g, 10.0 mL) and PVP (3.38 g) was added to the Isopar M solution of the surfactant (3 wt% relative to the sum of the methanol and Isopar M solutions). The emulsion was obtained by pulse ultrasonic irradiation (10 s irradiation, 5 s pause) for 15 min using an ultrasonic processor (SONICS, VC750 model) at 40% amplitude under cooling with ice water. The droplet size was measured immediately after preparation. The non-aqueous emulsion was directly employed for preparation of the non-aqueous dispersion using the solvent evaporation method. A part (16.0 g) of the prepared emulsion (methanol/PVP/Isopar M/surfactant = 31.5/13.5/52.0/3.0 by weight) was transferred to a glass test tube. The non-aqueous dispersion was obtained via evaporation of methanol from the emulsion by bubbling with Ar gas at 40 °C for 3 h.

Preparation of non-aqueous microcapsule dispersion with colorant. The non-aqueous dispersion of the colorant encapsulated by PVP was prepared using a procedure similar to that


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used for preparation of the non-aqueous dispersion without colorant. The representative example is as follows: an Isopar M solution containing the DEA-modified block-random copolymer (1.88 g, 40 wt% surfactant) and Isopar M (11.9 g, 15.1 mL) was placed in a glass beaker. A mixture of methanol (7.88 g, 10.0 mL), PVP (2.63 g), and a dye (0.75 g) was added to the Isopar M solution containing the surfactant. The emulsion was obtained by pulse ultrasonic irradiation (10 s irradiation, 5 s pause) for 15 min using an ultrasonic processor at 40% amplitude while cooling with ice water. A part (16 g) of the obtained emulsion (methanol/PVP/dye/Isopar M/surfactant = 31.5/10.5/3.0/52.0/3.0 by weight) was transferred to a glass test tube. The non-aqueous microcapsule dispersion was obtained via evaporation of methanol from the emulsion by bubbling with Ar gas at 40 °C for 3 h.

Instrumentation. 1H NMR (500 MHz) spectra were recorded using a Bruker AVANCE III instrument. The Mn and Mw/Mn values were estimated by SEC at 40 °C using a Shimadzu HPLC Prominence system equipped with refractive index detector. The column sets consisted of a crosslinked polymer-based gel column (Shodex KF-804) and a guard column (Shodex KF-G). The system was operated at a flow rate of 1.0 mL/min using THF as the eluent. Polystyrene standards were employed for calibration. Dynamic light scattering (DLS) was performed using a nano Partica SZ-100 (Horiba) instrument. For DLS measurements, the emulsions and the dispersions were diluted by a factor of 5 and 50, respectively, using Isopar M. Scanning electron microscopy (SEM) observations were conducted with an Hitachi-hightech SU8010 system. Elemental analyses were carried out on a PerkinElmer 2400 CHNS/O analyzer. The interfacial tension was measured at room temperature (25 ± 1 °C) by the pendant drop method using a Teclis Tracker tensiometer; the methanol phase containing 3 wt% PVP

(relative to the total


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weight of the methanol phase) was injected into the Isopar M phase containing 3 wt% polymeric surfactant (relative to the total weight of the Isopar M phase). For quantification of the interfacial rheological property, the interfacial area of the drop was oscillated at a frequency of 0.1 Hz using a strain of 10%. UV and visible absorbance spectra were measured using a Shimadzu UV-2450 spectrophotometer at 0.001 wt% dye concentration.

RESULTS AND DISCUSSION Synthesis of polymeric surfactants. To determine the optimal sequence of SMA and GMA for the surfactant for use in the emulsion solvent evaporation method, three copolymers with different monomer sequences (i.e., random, block, and block-random) were synthesized (Scheme 1). All polymerizations were conducted in Isopar M, which is an industrial solvent comprising an isoparaffin mixture, because the resulting copolymer solutions were directly used for the following emulsification without purification. Since Isopar M has been used as a solvent for electrophoretic ink,46 it is also considered to be a promising solvent for use in inkjet inks owing to its relatively high boiling point (about 220 °C), low viscosity, and low toxicity to humans. The SMA/GMA ratio in the feed, the molecular weight of the poly(SMA) macro-CTAs, and the monomer-to-CTA ratio were adjusted in order to obtain copolymers having similar comonomer compositions and molecular weights. The comonomer composition of SMA:GMA = 75:25 was selected to enhance the solubility of these copolymers in the Isopar M phase according to the Bancroft rule,47 which led to the formation of a continuous phase solubilizing a surfactant. The experimental conditions and the results are summarized in Table 1. Initially, the random copolymer was synthesized via the RAFT process using CPDTTC as the CTA, as shown in Scheme 1a. The SEC peak (Figure S3a) of the obtained copolymer was


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symmetrical and unimodal, corresponding to a narrow molecular weight distribution (Mw/Mn = 1.21) and a quite high conversion (SMA 99%, GMA >99%), indicating that copolymerization was well controlled. Secondly, the block copolymer containing a SMA homoblock and a GMA homoblock was synthesized by RAFT polymerization using trithiocarbonate-terminated poly(SMA)89 (Mn = 21800, Mw/Mn = 1.17) as the macro-CTA (Scheme 1b). Figure S3b shows the SEC chromatograms of the starting macro-CTA and the resulting block copolymer. A shift in the SEC trace toward higher molecular weight was observed, while maintaining low polydispersity (Mw/Mn = 1.35), indicating block formation. Thirdly, the block-random copolymer containing a homoblock of SMA and a heteroblock composed of SMA and GMA was synthesized by RAFT polymerization using trithiocarbonate-terminated poly(SMA)59 (Mn = 14700, Mw/Mn = 1.19) as the macro-CTA (Scheme 1c). The obtained copolymer was characterized by high conversion (SMA 98%, GMA 99%) and a narrow molecular weight distribution (Mw/Mn = 1.33). Figure S3c shows a clear shift of the SEC trace toward higher molecular weight, indicating formation of a block-random structure. The comonomer composition (SMA:GMA = 75:25) of the three copolymers was the same and the molecular weights (Mn = 21000–27000) were similar, whereas the monomer sequences were different (Table 1).

Performance of the copolymers as the surfactant. For the emulsion solvent evaporation method, the surfactant must be capable of creating a stable emulsion with a small droplet size, thereby leading to the formation of a microcapsule dispersion with a small particle size and good


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dispersion stability. The droplet sizes and stabilities of the emulsions prepared using each of the three GMA-based copolymers with different monomer sequences as the polymeric surfactant (Table 2) were preliminarily evaluated for selection of a suitable monomer sequence. Initially, the experiments were conducted without the colorant because of the difficulty in evaluating the stability of the colored emulsions by visual observation. Emulsification was conducted by ultrasonication of the mixture of methanol and PVP with Isopar M containing 3 wt% polymeric surfactant (relative to the total weight of the emulsion) (Figure 1). Dispersed and continuous phases of the emulsion were formed by methanol containing PVP and Isopar M, respectively. The solubility of methanol to Isopar M measured by gas chromatography was 2.6 g/L. PVP was selected as a shell material for encapsulating the colorant. PVP is expected to suppress aggregation of the colorant during evaporation of methanol because of the binding affinity toward azo dyes.48 When emulsification was conducted using the block or block-random copolymers, the obtained emulsions were stable without unfavorable phase separation over 1 week. In contrast, when the random copolymer was used for the emulsification, the emulsion was unstable, resulting in phase separation within several hours. The droplet size of the emulsion employing the block-random copolymer was 615 nm, which was apparently smaller than that obtained by using the block copolymer (>1200 nm). These results suggest that the block-random sequence of the polymeric surfactant composed of SMA and GMA is the most effective for generating a stable emulsion with a small droplet size.


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The GMA units in the synthesized polymeric surfactants are presumed to have higher affinity towards the methanol phase than the Isopar M phase because of the relatively polar epoxy group of GMA. It is expected that modification of the epoxy group with a compound having highly polar groups should enable adsorption of the surfactant onto the interface more easily, resulting in generation of a more stable emulsion with a smaller droplet size. On the basis of these assumptions, DEA was selected as the modifier. Modification with DEA leads to the generation of three hydroxyl groups via addition to the epoxy group (Scheme 2). Initially, the effect of DEA-modification of the block-random copolymer on the emulsion properties was investigated by varying the [DEA]/[GMA unit] ratio in the feed (Table S1). The block-random copolymer with over 80% of the epoxy groups modified afforded small emulsion droplets (99

34500

21300

1.33

75:25

a

Calculated by 1H NMR in CDCl3. b(Mn,theory) = (MW of SMA) × [SMA]0/[CTA]0 × (conv. of SMA) + (MW of GMA) × [GMA]0/[CTA]0 × (conv. of GMA) + (MW of CTA). cMeasured by SEC using PSt standards in THF. dMacro-CTA = poly(SMA)89 (Mn(SEC) = 21800, Mw/Mn = 1.17) prepared with CPDTTC. eMacro-CTA = poly(SMA)59 (Mn(SEC) = 14700, Mw/Mn = 1.19) prepared with CPDTTC.


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Table 2. Droplet sizes and stabilities of emulsionsa prepared with random, block, and block-random copolymers composed of SMA and GMA with or without DEA-modification Copolymer

Aminationb

Droplet sizec

type

(%)

(nm)

GMA-based random

0

NDf

−

GMA-based block

0

1207

+

GMA-based block-random

0

615

+

DEA-modified randome

82

200

−

DEA-modified blocke

91

774

+

DEA-modified block-randome

89

205

+

Stabilityd

a

Composed of methanol/PVP/Isopar M/surfactant = 31.5/13.5/52.0/3.0 by weight. bEstimated by elemental analysis. cMeasured by DLS immediately after preparation. dVisual examination 1 day after preparation; “+” stable; “−” unstable with phase separation. eThe GMA-based copolymers were modified by DEA. fNo detectable emulsion.


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Table 3. Tension and modulus of the interface between the PVP-containing methanol phase and Isopar M phase employing polymeric surfactants with different monomer sequencesa Copolymer

Interfacial tensionb

Interfacial modulusc

type

(mN/m)

(mN/m)

No surfactant

1.16 ± 0.03

0.47 ± 0.05

DEA-modified randomd

0.60 ± 0.05

0.24 ± 0.01

DEA-modified blockd

1.16 ± 0.07

0.69 ± 0.04

DEA-modified block-randomd

0.21 ± 0.01

0.67 ± 0.03

GMA-based block-random

1.38 ± 0.03

0.70 ± 0.04

a

Methanol phase: 3 wt% PVP, Isopar M phase: 3 wt% polymeric surfactant. bValues are means ± standard deviations measured by the pendant drop method at over five times. cValues are means ± standard deviations measured by the oscillating droplet technique at over five times. d The GMA-based copolymers were modified with DEA.


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Table 4. Sizes and stabilities of non-aqueous dispersions without or with black dye, stabilized by DEA-modified random, block, or block-random copolymers composed of SMA and GMAa

Copolymer type

Aminationb

Without colorant Particle sizec

(%)

With colorant d

Particle sizec

Stability (nm)

Stabilityd

(nm)

Random

82

154

−

NDe

NDe

Block

91

467

+

NDe

NDe

Block-random

89

165

+

164

+

a

Prepared from emulsions composed of methanol/PVP/dye/Isopar M/surfactant = 31.5/13.5-10.5/0-3.0/52.0/3.0 by weight. bEstimated by elemental analysis. cMeasured by DLS just after preparation. dVisual examination 1 day after preparation; “+” stable; “−” unstable with sedimentation. eNo data.


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For Table of Contents Use Only

Non-aqueous dispersion formed by emulsion solvent evaporation method using block-random copolymer surfactant synthesized by RAFT polymerization

Naofumi Ezaki*1,2, Yoshifumi Watanab2, Hideharu Mori*1


39

Nonaqueous Dispersion Formed by an Emulsion Solvent

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