Высокомолекулярные соединения
Серия Б
ВЫСОКОМОЛЕКУЛЯРНЫЕ СОЕДИНЕНИЯ, Серия Б, 2012, том 54, № 12, с. 1748-1760
СИНТЕЗ
УДК 541.64:547.538.141
PREPARATION AND PROPERTIES OF A METHACRYLATE-CONTAINING SILICONIZED EPOXY HYBRID MONOMER AND ITS EMULSION COPOLYMERIZATION WITH STYRENE/BUTYL ACRYLATE1
© 2012 г. Hamid Javaherian Naghash, Bahman Johari, Fariba Rezaei, and Monireh Mohammadsalehi
Department of Chemistry, Shahreza Branch, Islamic Azad University, 311- 86145, Shahreza, Isfahan, Iran
e-mail: Javaherian@iaush.ac.ir Received November 29, 2011 Revised Manuscript Received April 19, 2012
Abstract—The objective of the present work was the synthesis and characterization of a methacrylate-contain-ing siliconized epoxy hybrid monomer and its emulsion copolymerization in the presence of styrene/butyl acrylate monomers. The purity and structural conformation of this monomer were ascertained from FTIR and NMR spectral studies. Thermal properties of the copolymers were investigated by using differential scanning calorimetry and thermal gravimetric analysis. The morphology of copolymers was investigated by scanning electron microscopy and then the effect of siliconized epoxy hybrid monomer concentration on the water absorption ratio was examined. The results show that the water-resistance of the terpolymer films was higher compared with the films of styrene-co-butyl acrylate copolymer.
INTRODUCTION
Polysiloxanes are widely used in various areas for their outstanding performance of high temperature resistance, weathering stability, excellent dielectric properties, as well as chemical and biological inertness [1—3]. It is therefore interesting to implant polysilox-ane to other polymer systems [4—8]. Great efforts have been made in developing polysiloxane-modified epoxy resins, which are important in coatings, adhesives, electronic and microelectronic encapsulation for excellent adhesive strength, good mechanical properties, easy to process and low cost [9—13]. On the other hand, in many industries epoxy acrylate oligomers, which introduce vinyl ester groups with carbon-carbon double bonds at the end of the epoxy resin, are generally used because of their excellent adhesive and non-yellowing properties, flexibility, hardness and chemical resistance [14-17]. Also, epoxy acrylate oligomers could be used in a wide range of viscosities and formulations in the form of single- or two-part products [18]. The epoxy backbone imparts toughness to the cured films, while the carbon-carbon and ether bonds ameliorate their chemical resistance. Their re-
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action with an acid produces hydroxyl groups, thereby introducing polarity, which can improve the wet ability of adhesive [19]. However, they generally have a linear structure. Therefore, the cross-linking of functional acrylate oligomers and monomers is needed in order to increase their thermo-mechanical stability. The advantages of functional acrylates include their good adhesion to plastics, high cross-linking density, reactivity, chemical resistance, hardness and scratch resistance. Kaczmarek and Decker [20] reported that when an adhesive is weakly cross-linked, it shows a fluid-like behavior; however, in the case of a more cross-linked adhesive, the creep resistance is greatly increased [21]. Moreover, functional acrylates cross-link occurs quickly by radical and cationic polymerizations, and their kinetics and properties have previously been investigated [22].
On the other hand, silicone epoxy methacrylate (SEMA) containing methacrylic ester groups, linked to the siloxane chain as pendant units, give the SEMA reactivity, absorptivity, coupling properties, etc [23]. This compound combines the properties of silicones with the fast cross-linking ability of methacrylates. Si-loxane-based networks have been used for metal coat-
1748
ing and for the protection of glass or optical fibers owing to their transparent nature.
In continuation of our interest on silicone containing polymers [24—30], we report the synthesis of a novel hybrid monomer SEMA, which contains epoxy, silicone and methacrylate moieties for using in the emulsion copolymerization in the presence of styrene (St), and butyl acrylate (BA) monomers. The purity and structural conformation of this monomer were ascertained from FTIR and NMR spectral studies. The thermal behavior and morphology of copolymers were also evaluated.
EXPERIMENTAL
Materials
The epoxy resin (EP) of diglycidyl ether of bisphenol A (DGEBA; epoxy equivalent = 190) was procured from Ciba Specialty Chemicals (New Delhi, India). The monomers St (Aldrich) and BA (Aldrich) were freed from the inhibitor by shaking with 10% aqueous NaOH, washing with distilled water and drying over Na2SO4. They were then distilled under reduced pressure before use and stored at —20°C to avoid thermal polymerization. Ammonium persulfate (APS), hydroxyethyl cellulose (HEC) and sodium bicarbonate (NaHCO3) were supplied by Merck, Hohenbrunn, Germany; nonionic emulsifier Nonylphe-nol polyglycolether (Arkopal N-300) a yellowish liquid with density 1.05—1.07, refractive index 1.48—1.52 and (5%) solubility and anionic surfactant sodium lau-ryl sulfate (SLS, BASF, Germany) were used as received. 1, 4-butanediol (BDO), triethylamine (TEA, Junsei), toluene, dichlorodimethyl silane (DCDMS),
cupric chloride (CuCl2) and ethylene glycol monomethyl ether (EGME) were analytically graded and were procured from Merck. 2-Hydroxyethyl methacrylate (HEMA) and tetraisoproxide titanate (TPT) were supplied from the Aldrich. Distilled water was used throughout the work.
Synthesis of Bis-hydroxybutoxydimethyl Silane (BHBDMS)
The BHBDMS has been synthesized according to Liaw [31] and Naghash [32]. Briefly dichlorodimeth-ylsilane 3.62 ml, 30 mmol was added drop-wise to a well-stirred slurry mixture of 1,4-butanediol (5.30 ml, 60 mmol), anhydrous triethylamine (2 g, 5%), and 30 ml fresh distilled toluene at —5°C in a 100 ml three-necked flask which was dried, purged with nitrogen, and fitted with a magnetic stirrer and a condenser. After the addition, the mixture was heated under reflux temperature and was continuously stirred for 24 h. The colour of the slushy mixture was white at first, and then it gradually turned slightly yellow. Then, the mixture was cooled to room temperature. The white byproduct triethylhydroammonium chloride salt was filtered off quickly to minimize contamination of the product by hydrolysis when the salt was exposed to moisture. The viscous crude product was recovered after removing the solvent using an evaporator. The crude product was then dissolved in chloroform and filtered. The solvent of the filtrate was removed and the residue was finally dried in a vacuum at 50°C. The final product was viscous pale yellow oil. Yield = 5 g, 80%. The reaction path is given in Scheme 1.
CH3
I 3
HO-CH2CH2CH2CH2—OH + Cl-Si-Cl
CH3
TEA, Toluene 24 h reflux
CH3 I 3
ho-(ch2)4—o-Si-o—(ch2)4—OH CH3
Scheme 1. Preparation of BHBDMS.
Synthesis of BHBDMS Containing Epoxy Resin
Epoxy (DGEBA) resin was pre-activated at 120°C for 30 min. The pre-activated epoxy (DGEBA) resin and BHBDMS in 4:1 (100 g: 25 g) ratio was taken into a three-necked flask fitted with a magnetic stirrer, thermometer and nitrogen inlet. 0.02 g of phosphoric acid was added. The reaction
mixture was continuously stirred on a magnetic stir-rer at 30°C for 45 min. The progress of the reaction was monitored by thin layer chromatography, by the determination of epoxy equivalent and hydroxyl value at regular intervals. The structure of siloxane-modified epoxy resin was further confirmed by FTIR, 1H-NMR and 13C-NMR spectral analysis. The reaction path is given in Scheme 2.
CK3
O
CK3
K o i
O-K2 / N + KO—(CK2)4—O—Si—O—(CK2)4_ OK
CK
3
H3PO4
O
=4 CK3/=
CK3
I
, , C .,., ,—, OK
/Л K2 / \ I У \ K2 I K2
C—)~C\. /—O—C—C—C-O—(CK2)4—O—Si-O-(CK2)4-OK
- CK3 --K CK3
Scheme 2. Synthesis of BHBDMS type epoxy resin.
Synthesis of Silicone Epoxy Methacrylate (SEMA) Monomer
SEMA monomer was synthesized from the reaction ofBHBDMS containing epoxy resin with 2-hydroxyeth-yl methacrylate. In a 500 ml four-necked round bottom flask fitted with Dean Stark assembly, 57.6 g (0.1 mol) of modified epoxy resin, 0.5 g of TPT, 0.5 g of cupric chloride (CuCl2) and 60—70 ml of toluene were taken. To
this, 13 g ofHEMA (0.1 mol) was added drop wise maintaining temperature at 80°C. After complete addition, the reaction mixture was heated to 120°C under stirring till calculated amount of water was collected through Dean Stark apparatus. Use of TPT promotes the desirable condensation between OH-groups of epoxy resin and HEMA. The yield based on HEMA was 90%. The reaction path is given in Scheme 3.
120°C, CuCl2, TPT Toluene -KO, 2h
Scheme 3. Synthesis of silicone epoxy methacrylate (SEMA) monomer.
Determination of Epoxy Equivalent
Epoxy resins are characterized by two or more epoxy groups in the structure [33]. To cure an epoxy resin with a suitable hardener, accurate estimation of epoxy groups is crucial. Epoxy equivalent (the amount of resin that contains one mole of epoxy) is determined by a standard titration method using hydrogen bromide solution in acetic acid. Briefly about 100 mg of anhydrous sodium carbonate, 20 ml of chlorobenzene and 10 ml of glacial acetic acid are taken in an Erlenmeyer flask and magnetically stirred until all the carbonate dissolves. Four drops of 0.1% solution of crystal violet in acetic acid are added. The purple-colored solution
is titrated with hydrogen bromide solution (prepared by diluting about 6 ml of commercial reagent with 250 ml of acetic acid). The titre value is noted at the blue—green end point. About 300 mg of epoxy sample is titrated in a similar way. A blank titration is also carried out without any sample. The epoxy equivalent (Z) is calculated from the following formula: Z = W x 53 x x V/(Vs — V0) x Wp, where W, Wp are the weig
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