Miniemulsion copolymerization of methyl methacrylate and butyl acrylate in the presence of vinyl siloxane rubber

Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 9–15

Miniemulsion copolymerization of methyl methacrylate and butyl acrylate in the presence of vinyl siloxane rubber Zhang-Qing Yu∗ , Pei-Hong Ni, Jie-Ai Li, Xiu-Lin Zhu School of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215006, PR China Received 8 June 2003; accepted 15 April 2004 Available online 10 June 2004

Abstract Vinyl siloxane rubber was successfully used as the co-stabilizer in the miniemulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) initiated by ammonium persulfate. Effects of the molecular weight, vinyl content, and the amount of vinyl siloxane rubber on the kinetics and the particle morphology of the latex prepared were investigated. The rate of copolymerization was found to decrease with an increase in the molecular weight (100,000–275,000 g/mol) and the vinyl amount of the siloxane (0.1–2.0 wt.%). The highest rate of miniemulsion copolymerization was observed at the VSR amount of 1.0 g (10% based on the weight of monomers). TEM photos showed that all the siloxane was incorporated into the polyacrylate particle. This suggests that droplet nucleation mechanism was prominent in the process of the polymerization. Core-shell structure of the particle could be found in high amount of VSR recipe. 1 H NMR, and FTIR analysis demonstrated that the vinyl did participate in the reaction during the polymerization and contribute to the grafting between vinyl siloxane rubber (VSR) and polyacrylate. Extraction tests showed that the degree of grafting of the VSR to polyacrylate was increased with an increase of the vinyl content in the VSR used. © 2004 Elsevier B.V. All rights reserved. Keywords: Miniemulsion polymerization; Co-stabilizer; Vinyl siloxane; Kinetics

1. Introduction Miniemulsions are one kind of aqueous dispersions with droplet sizes between 50 and 500 nm and are opaque and of milky appearance. Generally, miniemulsions are prepared by subjecting the monomer/water mixture to high shear stress in the presence of suitable surfactant and co-stabilizer. The co-stabilizer is a highly monomer soluble, highly water insoluble material (typically long-chain alkane and alcohol), which is added to retard the diffusion of monomer from small droplets to large ones (Ostwald ripening) [1–3]. The droplet nucleation predominates in miniemulsion polymerization as most of the surfactant is absorbed to droplet surface with little surfactant available to form micelles or stabilize aqueous nucleation. Hence, in an ideal miniemulsion polymerization, no monomer transport is involved and

∗

Corresponding author. E-mail addresses: [email protected], [email protected] (Z.-Q. Yu). 0927-7757/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2004.04.055

the latex particles obtained from it have about the same size as the initial droplets [4]. It was reported that dissolving small amount of polystyrene into styrene monomer before emulsification could increase the initial stability of the miniemulsion droplets and result in an increase in the polymerization rate because of the enhanced droplet nucleation when hexadecane or cetyl alcohol was used as co-stabilizer [5–7]. Reimers and Schork [8,9] found that poly(methyl methacrylate) alone could retard the monomer diffusion of the methyl methacrylate (MMA) from the small droplets to larger droplets, therefore, imparting the MMA miniemulsion partial diffusional stability sufficiently to allow initiation of the droplets before extensive degradation occurs. The droplet nucleation was found to be dominant nucleation mechanism in the polymerization of these polymer-stabilized miniemulsions. They also found that the nucleation was more robust and less sensitive to the variations in the recipe or contamination levels, and nearly all the droplets were nucleated. The vinyl acetate emulsion co-stabilized by poly(vinyl acetate) was found to be quite unstable when poly(vinyl alcohol)

10

Z.-Q. Yu et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 9–15

[10] or sodium dodecyl sulfate [11] was used as surfactant, although the emulsions still behaved some characteristics of miniemulsion polymerization (nucleation of droplet). However, using PMMA or polystyrene, together with as a traditional co-stabilizer, marginal miniemulsions of vinyl acetate could be obtained and nucleation of monomer droplet becomes dominant when poly(vinyl alcohol) was used as surfactant [10]. Recently, Yu et al. [12,13] prepared the styrene miniemulsion using carboxylated polyurethane as co-stabilizer although the latter was not as efficient as hexadecane. The shelf life of the miniemulsion was influenced by not only the amount of the polyurethane but also the aqueous pH value and smaller molecular weight of the polyurethane. However, unlike the typical miniemulsion polymerization, droplet nucleation and homogeneous nucleation were found to be coexistence in this system. Silicone polymers characterize their excellent release behaviour. They are generally difficult to wet and most materials adhere poorly to them. Therefore, if they are incorporated into polyacrylate and are used as coatings, the water and staining resistance of the coating film will be improved. In this work, the influence of polymeric co-stabilizer (vinyl siloxane) on the miniemulsion copolymerization of MMA/butyl acrylate (BA) with sodium dodecyl sulfate as surfactant was investigated. The stability and the copolymerization kinetics of the MMA/BA miniemulsion co-stabilized by vinyl siloxane rubber was compared with that co-stabilized by hexadecane. Also, the effects of the vinyl content, the molecular weight, and the amount of the siloxane used on the miniemulsion polymerization were also studied. The properties of the latexes obtained were measured and evaluated.

2. Experimental 2.1. Materials Methyl methacrylate and BA were supplied by Dongfang Chemical Co. (China) and distilled in vacuum and stored in a refrigerator before use. 2,2 -azobisisobutyronitrile (AIBN) was reagent and was recrystallized from methyl alcohol. Octamethyl cyclotetrasiloxane, tetravinyl tetramethyl cyclotetrasiloxane, and dodecyl phenyl sulfonic acid were supplied by Shanghai Resin Co. (China) and used without purification. Sodium dodecyl sulfate (SDS), dodecyl sulfuric acid, hexadecane (HD), cetyl alcohol (CA), and hydroquinone were of synthetic grade and used as received. Deionized water was used throughout. 2.2. Synthesis of vinyl siloxane rubber (VSR) Vinyl siloxane rubber was synthesized by miniemulsion polymerization. SDS, dodecyl phenyl sulfonic acid, and water were added into the beaker and mixed. Predetermined amount of octamethyl cyclotetrasiloxane, tetravinyl

tetramethyl cyclotetrasiloxane, and dodecyl benzyl sulfonic acid were then added into the beaker. The mixture was stirred for 10 min at high speed with a magnetic stirrer. This pre-emulsion was then subjected to sonicating for 5 min at 60% output in pulse mode with Ultrasonic Disintegrator (CPS-2, Shanghai Branson Ultrasonic Co. China). The miniemulsion was then transferred into a four-neck flask equipped with a thermometer, mechanical stirrer, nitrogen inlet, and reflux condenser immediately. The temperature was raised to 70 ◦ C to initiate the cationic ring-open copolymerization and kept at constant until the reaction was finished by a thermostat. The latex was cooled to room temperature and precipitated by methyl alcohol. The precipitate was filtered and washed with deionized (DI) water thoroughly. The VSR obtained was dried in vacuum and its molecular weight was determined by viscosity method according to the Mark-Houwink equation [η] = KM␣ , in which [η] is the inherent viscosity of the vinyl siloxane rubber solution, M represents the molecular weight of the vinyl siloxane, K and α have the value of 8.28 × 10−3 and 0.72, respectively [14]. The inherent viscosity of the VSR toluene solution was measured with Ubbelohde viscometer. 2.3. Miniemulsion preparation and polymerization A typical recipe of miniemulsion is as follows: deionized water, 90 g; MMA, 6 g; BA, 4 g; VSR, 0.20 g; SDS, 0.2 g; and AIBN, 0.05 g (not included in the miniemulsions for the shelf life). Miniemulsions were prepared by dissolving surfactant in water and VS and AIBN in MMA and BA mixture, respectively. Oily and aqueous phases were mixed with a magnetic stirrer in high speed for 15 min. The pre-emulsion was then sonicated at 60% of output in pulse mode for 5 min (CPS-2, Shanghai Branson Ultrasonic Co. China). Immediately after sonication, the resultant miniemulsion was transferred into a 250 ml four neck flask equipped with a mechanical stirrer, nitrogen inlet and reflux condenser. The miniemulsion was purged with nitrogen for 10 min while it was heated to the reaction temperature. The polymerization temperature and the agitation speed were kept constant at 65 ◦ C and around 300 rpm, respectively. Samples were withdrawn at regular intervals, and the polymerization was quenched with adding a drop of hydroquinone ethanol solution. The conversion was determined gravimetrically. 2.4. Shelf life and droplet size of miniemulsion The shelf life of the miniemulsion was monitored by placing about 50 cm3 of sample in a capped glass tube at room temperature and observing the time necessary for a visible creaming line to appear. Two drops of a water-soluble red pigment solution were added into each sample to increase the contrast between the phases. The droplet size was measured by dynamic light scattering method (Zetasizer 3000HS, Malvern Co., UK) after diluting the miniemulsion with SDS-saturated deionized water from 20 to 10 v/v%.

Z.-Q. Yu et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 9–15

2.5. Particle size and its distribution of the latex The number-average sizes of latex particle were measured by laser light scattering (Sub-micro particle analyzer, Coulter LS 230) at 25 ◦ C. Standard deviation (S.V.) was used to characterize the distribution of particle size. Latex was diluted with deionized water before measuring in order to adjust the light strength suitable to the measurement condition. 2.6. Transmission electron microscopy Transmission electron microscopy (TEM) analysis was performed with a Hitachi H-600. The synthesized latexes were diluted with deionized water to about 100:1. These diluted latexes were stained for 24 h by using two drops of 1 wt.% phosphorous tungstenic acid solution in water. One drop of the stained latexes was placed on the coated side of a 200-mesh copper grid in a Petri dish. After 18–24 h of drying, the samples were ready to be analyzed. 2.7. 1 H NMR and FTIR spectroscopy 1 H NMR spectrum was recorded by an INOVA 400 (VAR-

IAN Co. USA), using deuterated chloroform as solvent. Pulse delay time was 3.0 s. Infrared analysis was completed with a Fourier Transform Infrared spectroscopy (Nicolet AVATAR 360, USA). Latex was coated on the germanium plate and dried at room temperature for 24 h. The film was dried in infrared lamp for several minutes before testing. The film together with the germanium plate was then placed on the sample support of the spectrometer to record the IR spectrum. 2.8. Degree of grafting The degree of grafting of VSR to polyacrylate was determined by solvent extraction. The extraction was performed in a Soxhlet extractor, using n-hexane as the solvent for the measurement of degree of grafting of siloxane; the mixture of acetone and methyl alcohol with a volume ratio of 3:2 was used to extract the polyacrylate and polyacrylate-grafting siloxane. The residue if existing after extraction by n-hexane and mixture solvent was considered to be high cross-linking polymer.

3. Results and discussions 3.1. Shelf life The type and amount of surfactant and co-stabilizer are pivotal to miniemulsion stability apart from the shearing intensity [15]. When a long-chain alcohol or alkane was used as co-stabilizer, a miniemulsion with dynamic stability could be obtained [4–6]. If a polymer was used alone as co-stabilizer, the shelf lives of the polymer-stabilized

11

Table 1 Effect of the co-stabilizer type and molecular weight of VSR on the shelf life of the miniemulsiona Run no.

Co-stabilizer

M/(×104 )b

Vinyl amount/ wt.%

Shelf time

D(1,0) (nm)

1 2 3 4 5 6 7 8 9 10

HD CA VSR-0 VSR-1 VSR-2 VSR-3 VSR-4 VSR-4 VSR-4 VSR-4

– – 45–50 27.5 17.3 10.5 13.1 13.1 13.1 13.1

/ / 0.20 0.5 0.5 0.5 0.5 1.0 2.0 3.0

24 day 75 h 4h 3h 2h 2h 2h 4h 3h 0.5 h

89.6 / 92.3 98.3 97.2 88.6 / / / /

a b

Amount of co-stabilizer was 0.3 g in 100 g of miniemulsion. Molecular weights of VSR.

miniemulsion ranged from hours to days, which was not as stable as the miniemulsion created with HD or CA [8–13,16–20]. Shelf lives of the miniemulsions stabilized by HD, CA, and VSR with different molecular weights in Table 1 showed that VSR is not a good co-stabilizer as CA or HD. The results indicated that stability of the polymer-stabilized miniemulsion was increased with molecular weight of the VSR used, and the shelf lives of the polymer-stabilized miniemulsions was not longer than 4 h. However, the cream line was very blurred. The appearance of bottom phase was very turbid and milky similar to the observations in the vinyl acetate miniemulsion co-stabilized with poly(vinyl acetate) [10] and in the styrene miniemulsion co-stabilized with carboxylated polyurethane [12]. The effect of the amount of VSR on the shelf life seems more complicated. As seen in Table 1, the shelf life of the miniemulsion was increased from 2 to 4 h when the amount of VSR was increased from 0.5 to 1.0 g. However, the shelf life of the miniemulsion co-stabilized with VSR was shortened when more VSR was incorporated into it. This could be attributed to the less effectiveness in mini-emulsifying process caused by the higher viscosity of the monomer mixture and the bigger droplet size at higher VSR content. The initial droplet sizes of the miniemulsion with 0.5, 1.0, and 2.0 g of the VSR of molecular weight of 131,000 were 132.1, 366.7, and 504.6 nm, respectively. The evolution of the droplet size of the miniemulsion prepared with 1.0 and 2.0 g of the VSR was given in Fig. 1. It could be seen from Fig. 1 that the miniemulsion with 1.0 g of VSR was more stable than that with 2.0 g of VSR. The droplet size of the miniemulsion was measured after the miniemulsion was diluted with SDS-saturated DI water and kept static without stirring. 3.2. Kinetic analysis A plot of conversion–time of the miniemulsion polymerizations co-stabilized with HD, VSR-3, and VSR-0 was

12

Z.-Q. Yu et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 9–15

100

500

Droplet size (nm)

80

conversion/%

600

400

300

60 4

10.5*10 4 17.3*10 4 27.5*10

40 20 0

200

0

20

40

60

80 100 120 140 160 180 200

t/min 100 0

15

30

45

60

75

90

105

120

135

150

Time (min)

Fig. 1. Profiles of droplet size of the miniemulsion prepared with 1.0 g (䊏) and 2.0 g (䊉) of VSR of molecular weight of 131,000 with time.

shown in Fig. 2. VSR-3 was synthesized in our lab with 0.5% of vinyl and 1.05 × 105 of molecular weight. VSR-0 was industrial product (supplied by Shanghai resin Co.) with 0.20% of vinyl and 4.5–5.0 × 105 of molecular weight. The results showed that the polymerization rate of the miniemulsion co-stabilized by HD was higher than that by VSR. This is in line with the results of shelf life mentioned above. However, the miniemulsion prepared with industrial product (VSR-0) had the lowest rate of polymerization among them, although it has a longer shelf life than miniemulsion co-stabilized by VSR-3. This might be attributed to the impurities possibly existing in the industrial product and the higher molecular weight of VSR-0 (reference to Fig. 3). The particle sizes of the latexes resulting from HD, VSR-3 and VSR-0 were 89.6, 93.1, and 92.3 nm respectively. Fig. 3 gives the curves of conversion–time of the miniemulsion polymerization with different molecular weight of VSR as co-stabilizer. The highest rate of the polymerization was found in the miniemulsion prepared with VSR of molecular weight of 105,000 g/mol. The miniemulsion prepared with VSR of molecular weight of 275,000 g/mol had the lowest rate of polymerization among the three of miniemulsions. The rate of miniemulsion co-stabilized with VSR of molecular weight of

Fig. 3. Effect of the molecular weight of the VSR on miniemulsion polymerization kinetics.

173,000 g/mol was between the two miniemulsions. The particle size of the latexes (shown in Table 1) became bigger when the molecular weight of the VSR increased. This means that the smaller the molecular weight of the VSR, the higher the polymerization rate. Therefore, homogeneous nucleation also played some effect during the polymerization according to the shelf life data in Table 1. This is also not in line with the results reported by Reimers and Schork [9] in the PMMA-stabilized MMA miniemulsion. They found that most efficient co-stabilizer for MMA miniemulsion was the PMMA with a moderate molecular weight (350,000 g/mol). The amount of the VSR used in the miniemulsion polymerization was shown in Fig. 4 when the reaction condition and the other components were kept constant. The molecular weight of the VSR used was 131,000 g/mol. The shelf life of the miniemulsion prepared with 0.5, 1.0, 2.0, and 3.0 g of the VSR above is 2.0, 3.0, 2.5, and 0.5 h, respectively. It can be seen that the rate of copolymerization was accelerated when the amount of the VSR was increased from 0.5 to 1.0 g. While the rate of copolymerization was decreased, the amount of the VSR was continued to increase thereafter. The results are consistent with the initial droplet sizes prepared with different amount of VSR shown in Table 1, which resulted from two reciprocal effects of the VSR in the miniemulsion preparation. First, the hydrophobic VSR suppresses the transportation of the monomer from the small droplets to large droplets and endows the

100

60 HD VSR-3 VSR-0

40 20

conversion/%

conversion/%

100

80 80 60 0.5g 1.0g 2.0g 3.0g

40 20

0 0

20

40

60

80 100 120 140 160 180 200

t/min Fig. 2. Effect of co-stabilizer type on the miniemulsion polymerization kinetics.

0 0

20

40

60

80 100 120 140 160 180 200

t/min Fig. 4. Effect of the VSR amount on miniemulsion polymerization.

Z.-Q. Yu et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 9–15 100

100

b

80

c a

60 0.0% 0.1% 0.5% 2.0%

40 20

% Transmittance

conversion/%

80

13

60 40 20

0 0

20

40

60

80 100 120 140 160 180 200

t/min Fig. 5. Effect of the vinyl amount of the VSR on miniemulsion polymerization.

stability of the miniemulsion. Meanwhile, the viscosity of the monomer solution was increased when more VSR was added and dissolved into monomer. The latter might reduce the mini-emulsifying effect of the sonication process and resulted in a miniemulsion with bigger droplets and then decreased the rate of polymerization. The coincidence between the polymerization rate and the shelf life of the miniemulsion suggests that droplet nucleation plays dominant role during polymerization. The effect of the vinyl content of the siloxane on the miniemulsion copolymerization was showed in Fig. 5. The molecular weights are 159,000, 131,000, 105,000, and 178,000 g/mol for the VSR with vinyl content of 0.0, 0.10, 0.50, and 2.00 wt.%, respectively. It was found from Fig. 5 that all of the polymerization rates of miniemulsions co-stabilized with VSR containing vinyl were higher than that co-stabilized by VSR without vinyl. Comparing the polymerization rates of miniemulsion prepared with 2.0% vinyl group content and without vinyl group in the VSR, it could be seen that the existence of vinyl in the VSR could accelerate the rate of polymerization. The higher polymerization rates of the miniemulsion prepared by VSR containing 0.1 and 0.5% vinyl group may be contributed to

0 3000

2500

2000

1500

Wavenumbers/cm

1000

-1

Fig. 7. IR spectrums of the different products (a) polyacrylate; (b) the remainder of the polyacrylate with VSR as co-stabilizer after n-hexane extraction; and (c) polyacrylate with VSR as co-stabilizer.

the effect of vinyl group and the lower molecular weight of VSR (reference to Fig. 3). 3.3. Particle morphology and grafting Fig. 6 showed the TEM photos of the latex particles prepared by the miniemulsions co-stabilized by 0.0, 0.20 and 2.0 g of VSR containing 0.10 wt.% of vinyl. As can be seen in Fig. 6(B) and (C), no bare siloxane particle was found in TEM photos although phase separation was observed to some extent in the particle containing VSR. VSR, considered to be a highly hydrophobic polymer, could not diffuse out of the droplet, through the aqueous phase, and arrive at the reactive loci if the micelle nucleation mechanism was predominant in polymerization process. The fact that all the siloxane was incorporated into polyacrylate particle showed that droplet nucleation mechanism was prevailing in the process of the miniemulsion polymerization. When the amount of the VSR used was multiplied, the phase separation was found to become more obvious and its particle size distribution became wider. This suggested that the grafting degree

Fig. 6. TEM photographs of latexes prepared by miniemulsion polymerization with different amounts of VSR (A) 0.0, (B) 0.2, and (C) 2.0 g.

14

Z.-Q. Yu et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 9–15

Table 2 Effect of vinyl amount in VSR on the degree of grafting of siloxane Sample no.

Vinyl amount/wt.%

Sample weight/g

Residual weight after hexane extraction/g

Extract of hexane

Degree of grafting/%

1 2 3

0.10 0.50 2.00

1.0877 1.0907 0.9889

0.9165 0.9220 0.8455

0.1712 0.1687 0.1434

5.75 7.38 13.17

Residual weight after mixture of acetone and methyl alcohol (volume ratio 2:3) extraction was 0 for all three samples and was not included in the table. The theoretic amount of VSR in the latex was 16.7%.

of the polyacrylate onto VSR was not big enough to avoid the incompatibility between them. The 1 H NMR analysis demonstrated that vinyl peak of the VSR spectrum disappeared in the spectrum of the latex copolymer (the spectrum were not given here). This manifested that the vinyl group in the siloxane did join the reaction and consumed during the miniemulsion polymerization. The FTIR analysis was also used to confirm the occurrence of graft reaction between the VSR and polyacrylate during polymerization. Fig. 7(b) and (c) depict the FTIR spectra of the polyacrylate with VSR as co-stabilizer before and after the hexane extraction. As a comparison, FTIR spectrum of polyacrylate co-stabilized with HD was given in Fig. 7(a). The interesting peaks are 800 and 1261/cm, which belong to the antisymmetric stretch vibration and bending vibration of carbon silicon bond in the Si(CH3 )2 group of VSR chain. It was found that the peaks of 800 and 1261/cm did exist in the polyacrylate co-stabilized with VSR after extraction from hexane although the strength of absorption was lessened greatly. This means that the part of the VSR did graft into polyacrylate chains during miniemulsion polymerization, although the degree of graft was not very high. Effect of the vinyl content in the VSR used as co-stabilizer on the degree of graft was investigated by solvent extraction when keeping a constant amount of VSR in miniemulsion preparations. Hexane is a good solvent for polysiloxane and polysiloxane grafted with small amount of polyacrylate. Mixture of acetone and methanol (volume ratio equals 3:2) is considered as a good mixture solvent for polyacrylate and polyacrylate containing little polysiloxane. High cross-linking polymer would be left, if existed, as residue after extraction. The latex film prepared was subjected to the extraction of hexane and the mixture solvent in sequence. The degree of grafting of siloxane was calculated as: Degree of grafting Weight of siloxane grafted to polyacrylate = × 100 Total weight of siloxane added Results of extraction experiments showed that no residue was left after the extraction of hexane and the mixture solvent in sequence. This indicated that no high cross-linking polymer was formed during the miniemulsion polymerization. Results in Table 2 indicated that the residue after extraction by hexane was reduced; in other words, more VSR moieties were incorporated into the polyacrylate chain when the vinyl amount of the VSR was increased. Therefore, the

degree of grafting of VSR to polyacrylate became higher with an increase in the vinyl amount in VSR.

4. Conclusions Vinyl siloxane rubber was successfully used as costabilizer in the MMA/BA miniemulsion copolymerization, although the miniemulsion co-stabilized by vinyl siloxane rubber was not as stable as that co-stabilized by HD. The rate of copolymerization was found to decrease with the increase in the molecular weight and the vinyl amount of the siloxane used in the range of 100,000–275,000 g/mol and 0.1–2.0 wt.%, respectively. The rate of miniemulsion copolymerization was accelerated when the amount of VSR was increased from 0.5 to 1.0 g, whereas, the rate of miniemulsion copolymerization was reduced when the amount of VSR was increased from 1.0 to 3.0 g. TEM photos showed that all the siloxane was included in the particle of final polyacrylate latex and indicated that the droplet nucleation mechanism was prominent during the miniemulsion copolymerization. Phase separation was found to occur in some particles of the latex. The results of 1 H NMR and FTIR analyses demonstrated that the vinyl did participate in the reaction during the polymerization and contribute to the grafting between VSR and polyacrylate. Solvent extraction tests showed that the grafting degree of VSR onto polyacrylate was increased with an increase of the vinyl content in the VSR used.

Acknowledgements This research was supported by the National Natural Science Foundation of China (Grant 20276044) and the Natural Science Foundation of the Educational Department of Jiangsu Province (00KJB150002).

References [1] J. Delgado, M.S. El-Aasser, J.W. Vanderhoff, J. Polym. Sci.: Part A: Polym. Chem. 24 (1986) 861. [2] J. Delgado, M.S. El-Aasser, C.A. Silebi, J.W. Vanderhoff, J. Guillot, J. Polym. Sci.: Part B: Polym. Phys. 26 (1988) 1495. [3] K. Fontenot, F.J. Schork, J. Appl. Polym. Sci. 49 (1993) 633. [4] K. Landfester, N. Bechthold, F. Tiarks, M. Antomietti, Macromol. 32 (1999) 5222.

Z.-Q. Yu et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 9–15 [5] C.M. Miller, E.D. Sudol, C.A. Silebi, M.S. El-Aasser, Macromolecules 28 (1995) 2754. [6] P.J. Blythe, B.R. Morrison, K.A. Mathauer, E.D. Sudol, M.S. El-Aasser, Langmuir 16 (2000) 898. [7] P.J. Blythe, A. Klein, E.D. Sudol, M.S. El-Aasser, Macromolecules 32 (1999) 6952. [8] J. Reimers, F.J. Schork, J. Appl. Polym. Sci. 59 (1996) 1833. [9] J. Reimers, F.J. Schork, J. Appl. Polym. Sci. 60 (1996) 251. [10] I. Aizpurua, J.I. Amalvy, M.J. Barandiaran, Colloids Surf. A: Phys. Eng. Asp. 166 (2000) 59. [11] S. Wang, F.J. Schork, J. Appl. Polym. Sci. 54 (1994) 2157. [12] Z.Q. Yu, D.Y. Lee, I.W. Cheong, J.S. Shin, Y.J. Park, J.H. Kim, J. Appl. Polym. Sci. 87 (2003) 1933. [13] Z.Q. Yu, D.Y. Lee, I.W. Cheong, J.S. Shin, Y.J. Park, J.H. Kim, J. Appl. Polym. Sci. 87 (2003) 1941.

15

[14] S.M. Xin, Y.L. Wang (Eds.), Synthesis Technology and application of Organic Silicone, Publishing Company of Chemical Engineering, Beijin, 2001. [15] K. Fontenot, F.J. Schork, Ind. Eng. Chem. Res. 32 (1993) 373. [16] S.T. Wang, F.J. Schork, G.W. Poehlein, J.W. Gooch, J. Appl. Polym. Sci. 60 (1996) 2069. [17] X.Q. Xu, F.J. Schork, J.W. Gooch, J. Polym. Sci.: Part A: Polym. Chem. 37 (1999) 4159. [18] J.G. Tsavalas, J.W. Gooch, F.J. Schork, J. Appl. Polym. Sci. 75 (2000) 916. [19] J.W. Gooch, H. Dong, F.J. Schork, J. Appl. Polym. Sci. 76 (2000) 105. [20] H. Kawahara, T. Goto, K. Ohnishi, H. Ogura, H. Kage, Y. Matsuno, J. Appl. Polym. Sci. 81 (2001) 128.