научная статья по теме STRUCTURE AND PROPERTIES OF NOVEL FLUORINATED POLYACRYLATE LATEX PREPARED WITH REACTIVE SURFACTANT Физика

Текст научной статьи на тему «STRUCTURE AND PROPERTIES OF NOVEL FLUORINATED POLYACRYLATE LATEX PREPARED WITH REACTIVE SURFACTANT»

Высокомолекулярные соединения

Серия Б

ВЫСОКОМОЛЕКУЛЯРНЫЕ СОЕДИНЕНИЯ, Серия Б, 2011, том 53, № 12, с. 2166-2172

ПОЛИМЕРИЗАЦИЯ

УДК 541.64:542.952

STRUCTURE AND PROPERTIES OF NOVEL FLUORINATED POLYACRYLATE LATEX PREPARED WITH REACTIVE SURFACTANT1 © 2011 г. L. J. Chen a and F. Q. Wu b

a School of Chemical Engineering and Materials Science, Zhejiang University of Technology,

Hangzhou 310032, China bIntertek Testing Services, Hangzhou 310052, China e-mail: chenlj@zjut.edu.cn Received April 18, 2011 Revised Manuscript Received July 2, 2011

Abstract—The novel fluorinated polyacrylate latex was successfully prepared by emulsion polymerization of perfluorononylene allyl ether, butyl acrylate and methyl methacrylate initiated by potassium persulfate in water and emulsified with the reactive surfactant. Films of the novel fluorinated polyacrylate latex were prepared by coating the latex directly on the clean glass sheet and allowed to dry at 80°C in the bake oven. The characteristics of the film such as hydrophobicity and glass transition temperature were studied; its structure was investigated by FTIR spectrometry and NMR. The influence of the fluorinated monomer content on the emulsion polymerization and performance of the latex were also studied. It was shown that the hydrophobicity and glass transition temperature of the latex are improved when the fluorinated monomer is introduced to copolymerize with other monomers, however, the stability of emulsion polymer and the conversion rate is decreased with the increase of its content.

INTRODUCTION

Fluorine-containing polymers are particularly attractive and useful due to their unique properties including high thermal, chemical, aging and weather resistance; low dielectric constants, refractive index, surface energy and flammability; excellent inertness to solvents, hydrocarbons, acids, alkalis and moisture adsorption as well as interesting oil and water repellency due to the low polarizability and the strong electronegativity of the fluorine atom [1—7]. Consequently, fluorine-containing polymers have wide applications in modern technologies ranging from building, automotive and aerospace industries to optics and microelectronics [8, 9]. Up to now, the investigations on fluorine-containing polymers latex, especially on fluorine-containing polyacrylate latex attract attention of researchers. There are mainly two methods for obtaining the fluorine-containing polyacrylate latex: (1) to prepare fluorinated polyacrylate latex with fluorine-

1 Статья печатается в представленном авторами виде.

containing acrylate and acrylate monomers [10—20]; (2) to introduce fluorine-containing structure via using the reaction characteristic of the epoxy group [21]. Usually, the conventional non-reactive surfactants are used as emulsifiers for preparing the fluorinated polyacrylate latex in the above two methods. However, the conventional surfactants can migrate during the course of film-forming, which have a negative effect on the properties of the latex. Besides, conventional surfactants can desorb, which can lead to many drawbacks of the latex, such as generation of gel at high shear rate, poor freeze-thaw stability, mechanical stability and storage stability. The reactive surfactants for emulsion polymerization have been examined recently, and the reports have highlighted two advantages of reactive surfactants: (a) hydrophobicity of the film of the latex is improved [14, 19]; (b) reactive surfactants exhibit an efficient steric hindrance [22—24]. Thus, the reactive surfactants will be important emulsifiers in the field of emulsion polymerization [25]. Reactive surfactants can copolymerize with the adsorbed ma-

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trix and be bonded onto the surface of the matrix permanently. They can emulsify the matrix and be a part of the matrix.

Sodium 2-hydroxy-3-(methacryloyloxy) propane-1-sulfonate (HMPS), which is the copolymerized stabilizer with good properties, can be copolymerized with other vinyl group monomers, e.g., acrylate, vinyl acetate and styrene because the C=C bond in the

HMPS has high reactivity. In the present paper, using the intermediate perfluoro nonene and 3-allyl alcohol as the staring reactants (see Scheme 1), we would like to report the convenient method to synthesize new fluorinated polyacrylate latex by the emulsion polymerization technique with the reactive surfactant (see Scheme 2). The emphasis is put in the present work on the structure and the properties of the novel fluorinated polyacrylate latex.

C9F18 + HOCH2-CH=CH

Acid binding agent

!2

Solvent

c9f17o—ch2-ch=ch2

Scheme 1. Synthesis of perfluorononylene allyl ether using perfluoro nonene and 3-allyl alcohol as staring reactants

O

O

nC9F17O-CH2-CH=CH2 + mH2C=CH—C-O-C4H9 + oH2C=C"C-QCH3

CH3

O

+ ¿H2C=C-C-O-CH2-CH-CH2SO3Na

h3C Oh

CH3 I 3

Copolymerization

CH3

H2C"C-H- H2C C

oc9f17-ch2

I

C=O

I

0

1

C4H9

I

C=O

OCH3

p

C=O

I

0

Ch2

1 2

OH-CH-CH2SO3Na Scheme 2. Synthesis pathway of fluorinated polyacrylate latex

EXPERIMENTAL

BA and MMA were distilled under reduced pressure prior to polymerization. HMPS was of industrial grade and purchased from Foshan Kodi Gas Chemical Industry Co., LTD. Potassium persulfate and sodium bicarbonate were used as received. The water used in this experiment was distilled followed by deionization.

Perfluorononylene allyl ether (PFAE) was prepared according to Scheme 1. Triethylamine and 3-al-lyl alcohol were introduced into a three-necked flask with the stirrer. Acetone was then added into the flask and was agitated for 5 min with the stirrer. Perfluoro nonene was added dropwise within 3 h at room temperature. The reaction continued for 5 h after perfluoro nonene was dripped completely. The resulting mixture was dissolved in 2.5% HCl solution to separate the mixture. The lower layer was washed with 5% HCl solution and then with the distilled water. The obtained liquid was dried with Na2SO4. Finally, the liquid was purified further with reduced pressure distillation. FTIR spectrum of PFAE is shown on Fig. 1. As is seen, 1613 cm-1 is the characteristic stretching peaks of C=C bond; 1428 cm-1, 966 cm-1 and 753 cm-1 are

the stretching and flexural vibration peak of C—H bond; 1230 cm-1 is the characteristic stretching peak of C-F bond; 1030 cm-1 is the stretching vibration peak of C-O bond; 719 cm-1 is the rocking vibration of -CH2.

T, % 100

80 60 40

20

3500 2500 1500 500

Wavenumbers, cm-1

Fig. 1. FTIR spectrum of PFAE.

0

7 5 3

Fig. 2. *H-NMR of PFAE.

1 ppm

9

Figure 2 represents the *H-NMR of PFAE. *H-NMR (CDCl3, 5, ppm): 5.90-5.82 (1H, CH), 5.37-5.28(2H, CH2), 4.52-4.29(2H, CH2).

The results obtained confirmed that PFAE had been prepared.

In copolymerization we used the mixture of monomers, which consisted of16.00 g BA, 8.00 g MMA and varying amount of PFAE. A homogeneous aqueous solution containing 110.0 g de-ionized water, 0.90 g NaHCO3 and 2.00 g HMPS was charged into a 250 ml four-neck flask equipped with reflux condenser, mechanical stirrer, dropping funnels and heated with the water bath. The stirring speed was maintained at 200 rpm throughout the runs. The reaction temperature was increased to 80°C within 30 min. An initiator solution containing 0.18 g potassium persulfate and 6.0 g de-ionized water and a monomer mixture containing 4.00 g BA and 2.00 g MMA were charged to the reactor to form the seed latex within 15 min. The seeded polymerization was continued for an additional 10 min. At that point, the rest of initiator solution and mixed monomers was added slowly to the reactor using two separate dropping funnels. The feeding time for the initiator and the monomer emulsion stock solutions were 3.5 and 3.0 h, respectively. After the feed

T, % 100

95 90 85

80 -

75 4000

3000

2000

1000

Wavenumbers, cm 1 Fig. 3. FTIR spectrum of latex.

was completed, the temperature was raised to 90 °C and maintained for another 30 min to increase monomer conversion. The latex was then cooled to below 40°C, and NH4OH (25 wt. %) was added to increase the pH to about 8.0. Finally, the mixture in the flask was cooled and filtered. Thus, the latex was obtained.

FTIR spectrometric analyzer (Thermo Nicolet AVATAR370, USA) was used to analyze the chemical structures of the latex films. *H-NMR and 19F-NMR spectra were recorded with Bruker AVANCE 500MHz (Switzerland) spectrometer. CDCl3 was used as internal reference for chemical shift of and 19F. The amount of coagulum was measured by collecting the solid deposited on the reactor walls and stirrer, and by the residual of filtered latex. It is expressed as the weight of coagulum per total weight of monomer added. Conversion rate was determined by the mass difference of a sample taken before and after evaporation of the liquid phase. The sample was dried completely, and the residual polymer was weighed. The contact angle between film and water was determined with the DataPhysics contact angle meter (0CA-20, Germany) at room temperature. DSC (DSC Q100, USA) was applied to determine the glass transition temperature of the film of the latex. The heating temperature was in the range from -40 to 100°C. The heat rate was 10 K/min. The film of latex is obtained from coating the latex on the clean glass and drying for 2 h at 80 °C in the bake oven. In the case, the water and un-reacted monomers were removed completely.

RESULTS AND DISCUSSION

Figure 3 shows the FTIR spectrum of the latex which was synthesized by emulsion polymerization with reactive surfactant. 2957 and 2873 cm-1 were the characteristic stretching peaks of C—H (CH3,CH2); 1731 cm-1 was stretching vibration of C=0; 1455 cm-1 was distortion vibration of -COO-; 1237 cm-1 was the stretching vibration of C-F bond. 1164 and 1067 cm-1 were the characteristic absorption peaks of SO3Na. 843 cm-1 was the stretching vibration absorption peak of C=O in the acrylic group. FTIR

-40 -60 -80 -100 -120 -140 -160 -180 ppm

Fig. 4. 19F-NMR of latex.

spectr

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