Synthesis and Property of Water-Soluble ... - ACS Publications

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Synthesis and Property of Water-Soluble Hyperbranched Photosensitive Polysiloxane Urethane Acrylate Guonai Li,†,‡ Shengling Jiang,§ Yanjing Gao,‡ Xiaokang Liu,†,‡ and Fang Sun*,†,‡ †

State Key Laboratory of Chemical Resource Engineering, ‡College of Science, and §College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China ABSTRACT: A novel water-soluble hyperbranched photosensitive polysiloxane urethane acrylate (WHBPSUA) was synthesized, and its structure was characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, and 1H NMR. It was found that WHBPSUA possesses good compatibility with a number of acrylate monomers and deionized water. The effect of monomers on the photopolymerization kinetics of WHBPSUA was investigated by real-time infrared spectroscopy (RT-IR). The results showed that the resin that is consisted of WHBPSUA with common acrylic monomers exhibits high polymerization rate and double bond conversion. Additionally, it could form a regular image under UV irradiation through a patterned mask. More importantly, the microstructure on the surface of UV-cured WHBPSUA films was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. It is proved that the increase of the degree of crosslinking and Si content of the UV-cured WHBPSUA films leads to excellent flexibility, toughness, and heat resistance of UV-cured WHBPSUA films.

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resistance, and electric reliability of the solder resist ink.15−18 Our previous work19,20 reported the synthesis and properties of alkali-soluble linear as well as hyperbranched photosensitive polysiloxane urethane acrylate oligomers used for the solder resist ink, which have good heat resistance, flexibility, and dilute alkali-solubility. However, when they are used in solder resist ink, there is still pollution to the environment because of using alkali solution as a developer, so the water-soluble hyperbranched photosensitive polysiloxanes are expected to be present. In the present work, we continue to report our further studies on the novel water-soluble hyperbranched photosensitive polysiloxane urethane acrylate (WHBPSUA), which exhibits low viscosity, good water-solubility, high functionality, and good compatibility with acrylic monomers. The photopolymerization properties, photoimaging, mechanical, and thermal properties of WHBPSUA were evaluated. More importantly, microstructure of the UV-cured WHBPSUA films was also investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). WHBPSUA has potential application in environmentally friendly solder resist ink.

INTRODUCTION In recent decades, hyperbranched polymers have been extensively used in the photoimaging resist ink due to their excellent properties such as low viscosity, good solubility, high reactivity, and easy functionalization.1−5 The liquid photoimaging resist ink (solder resist ink) plays a very important role in the production process of the printed circuit board (PCB). To protect the environment, the manufacturing process of PCB has been constantly meliorated. Currently, lead-bearing bonding technology is replaced with lead-free bonding technology, and water developing is gradually substituted for organic solvent developing.6 The technological progress requires the solder resist ink to have a higher temperature resistance and water-solubility. In addition, the flexible printed circuit board (FPC) puts forward a higher requirement for bending resistance of the solder resist ink. Hence, much research work has been carried out on developing water-soluble resin with a high temperature resistance and excellent flexibility used for solder resist ink. Asif et al. have synthesized a waterborne hyperbranched polyester end-capped with methacrylic and salt-like groups in different ratios consisting of a multihydroxy functional aliphatic polyester core, which is used in UV curable waterborne coatings.7 Bai et al. have prepared UV curable waterborne polyurethane by modifying the conventional method of anionic aqueous polyurethane, and the UV curable films have a higher thermal stability and excellent mechanical properties.8 Bao et al. synthesized hyperbranched polyurethane acrylate through the addition of hyperbranched polyurethane end-capped by hydroxyl groups (HPU-OH) with the semiadduct urethane monoacrylate isophorone diisocyanate-2-hydroxyethylacrylate (IPDI-HEA), which is applied in UV curable waterborne coatings and inks.9 Photosensitive polysiloxanes possess good resistance to high temperature, excellent weatherability, electric reliability, and a flexible chain.10−14 Introduction of a polysiloxane chain into the solder resist ink resins could improve the flexibility, heat © 2013 American Chemical Society

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EXPERIMENTAL SECTION 2.1. Materials. Hydroxyl-terminated polysiloxane (Q43667, Mn = 2400) was obtained from Dow Corning Corp. Dimethylolpropionic acid (DMPA, AR) and triethylamine (TEA) were provided by Beijing Yili Fine Chemical Co. Isophorone diisocyanate (IPDI) was obtained from Qingdao Xinyutian Chemical Co. Dipropylene glycol diacrylate Received: Revised: Accepted: Published: 2220

November 9, 2012 January 15, 2013 January 23, 2013 January 23, 2013 dx.doi.org/10.1021/ie303084w | Ind. Eng. Chem. Res. 2013, 52, 2220−2227

Industrial & Engineering Chemistry Research

Article

Scheme 1. Structure of HBP-OH

2.42 g, 0.02 mol) was added into the flask, and the reaction mixture was stirred until the absorption peak of the −NCO group in the infrared spectra disappeared. Then, IPDI (4.44 g, 0.02 mol) was added into the mixture. When the value of isocyanate reached half of the initial value, HBP-OH was added in. The reaction was stopped until the absorption peak of the −NCO group in the infrared spectra completely disappeared and the hydroxyl-terminated product (A) was obtained. In the second step, first, IPDI (4.44 g, 0.02 mol) and HEA (2.32 g, 0.02 mol) were poured into a three-necked flask equipped with a mechanical stirrer, a thermometer, and a cooler. The reaction mixture was stirred at 40 °C in the presence of DBTDL as a catalyst until the value of isocyanate had reached the theoretical one of monoisocyanate by titration. Then, the hydroxyl-terminated product (A) synthesized in the first step was added into the mixture. The reaction mixture was stirred until the absorption peak of the −NCO group in the infrared spectra disappeared. Then, the triethylamine (TEA, 2.02 g, 0.02 mol) was added. The reaction was stopped after 0.5 h. The product was purified by column chromatography. The whole process of the synthesis of WHBPSUA oligomer is shown in Scheme 2. WHBPSUA oligomers with three different structures were designed and synthesized according to the generation number of HBP-OH and named as WHB1PSUA, WHB2PSUA, and WHB3PSUA, respectively.

(DPGDA), 2-hydroxyethyl acrylate (HEA), isobornyl acrylate (IBOA), and trimethylolpropane triacrylate (TMPTA) were purchased from Beijing Dongfang Chemical Co. Photoinitiator 2-hydroxyl-2-methyl-1-phenylpropane-1-one (Darocur 1173) was obtained from Ciba Geigy Co. Dibutyltin dilaurate (DBTDL) was supplied by Shanghai Chemical Reagents Co. Polysiloxane urethane diacrylate oligomer (PSUA, Mn = 7601) and hyperbranched polyesters (HBP-OH) were synthesized by our laboratory, and the details about the experiments have been given in our previous publication.21,22 The molecular structure of HBP-OH is shown in Scheme 1. The number of branches of HB1P-OH, HB2P-OH, and HB3P-OH is 6, 12, and 24, respectively. Polyurethane acrylate OAK-27 was obtained from Ciba Geigy. 2.2. Synthesis of Water-Soluble Hyperbranched Photosensitive Polysiloxane Urethane Acrylate. The WHBPSUA was synthesized through a two-step procedure. In the first step, hydroxyl-terminated product (A) was synthesized according to the following procedure: First, Q43667 (40 g, 0.02 mol) was added in a four-necked flask equipped with a mechanical stirrer, a thermometer, and a cooler; then, IPDI (4.44 g, 0.02 mol) was added dropwise over 30 min into the flask. The reaction mixture was stirred at 50 °C in the presence of DBTDL as a catalyst until the value of isocyanate had reached the theoretical one of monoisocyanate by titration.23 Subsequently, dimethylolpropionic acid (DMPA, 2221

dx.doi.org/10.1021/ie303084w | Ind. Eng. Chem. Res. 2013, 52, 2220−2227


Article

Scheme 2. Synthesis Reaction Equation Part A of WHBPSUA

IR (KBr, cm−1): 3370 cm−1, 1520 cm−1 (N−H), 2880 cm−1, 2952 cm−1 (C−H), 1721 cm−1 (CO), 1636 cm−1 (>C C DPGDA > TMPTA. Both the Rp and DC of the WHB1PSUA system with TMPTA were the lowest. The reason

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RESULTS AND DISCUSSION 3.1. GPC of WHBPSUA. The molecular weight and molecular weight distribution of the WHBPSUA have been analyzed by GPC, and the results are shown in Table 1. The GPC instrument was calibrated using multiple linear polystyrene standards. The values of molar masses of hyperbranched polymers, which are obtained by GPC measurements, are generally lower than their true values because linear polymers have a much larger hydrodynamic volume than the corresponding branched polymers of the same molar mass.16 Table 1. Molecular Weight Distribution and Polydispersity of WHBPSUA oligomer

Mn

Mw

Mw/Mn

WHB1PUSA WHB2PUSA WHB3PUSA

5070 7386 8226

15570 18715 22465

3.07 2.53 2.73 2223



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Figure 2. Effect of the structure of the oligomers on photopolymerization kinetics. System composition: oligomer/DPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

Figure 4. Effect of the content of DPGDA on photopolymerization kinetics of the WHB 1 PSUA system. System composition: (WHB1PSUA + DPGDA)/photoinitiator 1173 = 100/0.1 (wt %).

60, and 50/50, respectively. The mixtures were stirred for 10 min and stored for 24 h at room temperature prior to a visual observation of the clarity degree of the mixtures. It was found that WHBPSUA exhibits a good compatibility with the acrylic monomers at the weight ratio investigated, which can enhance the miscibility of the constituents in coatings, and the newly synthesized polymer could dissolve in deionized water easily, and completely, which demonstrates WHBPSUA had excellent water solubility. The dynamic mechanical thermal analysis (DMTA) is utilized to investigate the dynamic mechanical behavior of the UV-cured films. The glass transition temperature (Tg) of material can be detected as the relaxation peak of the loss factor (tan δ). DMTA thermograms of UV-cured films of WHBPSUA (see Figure 5 and Figure 6) showed that the systems of WHBPSUA with HEA, HDDA, DPGDA, and TMPTA, respectively, have only one glass transition temperature, which further proved the good compatibility of WHBPSUA with acrylic monomers. As shown in Figure 5, the intensity of damping peaks increased according to the following sequence, HEA > HDDA ∼ DPGDA > TMPTA. It may be because the degree of crosslinking of the system increased with an increase of monomer functionality. The system containing monofunctional monomer possessed much better flexibility than the others. Meanwhile, there was an obvious decrease in Tg (from 70.18 to 60.24 °C) and an increase in the intensity of damping peaks along with an increasing number of branches of WHBPSUA, as shown in Figure 6. It could be ascribed to enhancement of the content of polysiloxane with high flexibility in WHBPSUA molecule, which is caused by the increase of the number of branches of WHBPSUA. 3.5. Surface Morphology Analysis by Scanning Electron Microscope (SEM). The surface morphology of each UV-cured film of WHBPSUA was observed. As shown in Figure 7, as an increasing the number of branches of WHBPSUA oligomer, the surface morphology of the UVcured films became dense. It may be because the degree of cross-linking of the system increased with the increase in the number of branches of WHBPSUA oligomer. The surface morphology of UV-cured films of WHB1PSUA with HEA,

Figure 3. Effect of monomers on photopolymerization kinetics of WHB1PSUA. System composition: WHB1PSUA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

is that three-dimensional gel structure forms more easily in the system with TMPTA, leading to that fact the uncured double bonds trapped in the polymeric networks cannot polymerize further. The effect of the ratio of the WHB1PSUA to monomer DPGDA on photopolymerization kinetics of WHB1PSUA is shown in Figure 4. When the ratio increased from 20/80 to 80/ 20, the DC increased regularly, but the change of Rp was irregular. It can be explained by the viscosity of the resin, and the concentration of double bonds. As more WHB1PSUA was added, the viscosity of the resin became higher and high viscosity often accelerates the polymerization. Meanwhile, the concentration of double bonds of the resin became lower, leading to a small rate of polymerization. As a result of the two aspects, the Rp of the resin changed irregularly. 3.4. Compatibility of WHBPSUA with Monomers and Solubility in Deionized Water. WHBPSUA was mixed with monomers HEA, HDDA, DPGDA, TMPTA, and deionized water, respectively, with the weight ratio of 20/80, 30/70, 40/ 2224



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Figure 5. (a) DMTA of WHB1PSUA system with HEA and HDDA. (b) DMTA of WHB1PSUA system with DPGDA and TMPTA. System composition: WHB1PSUA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

Figure 6. DMTA of the WHBPSUA system with DPGDA. The cured film composition: WHBPSUA/DPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

Figure 8. SEM images of the syetem of WHB1PSUA with different monomers. The cured film composition: WHB1PSUA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %: (a) HEA, (b) IBOA, (c) DPGDA, (d) TMPTA.

IBOA, DPGDA, and TMPTA, respectively, is also presented in Figure 8. The same phenomenon was observed when the degree of monomer functionality increased. It also can be explained by the degree of cross-linking of the system. 3.6. Surface Element Analysis by X-ray Photoelectron Spectroscopy (XPS). The Si content in the UV-cured films was measured using XPS. Figure 9 showed that Si content of the cured product was different and increased in the following order, WHB3PSUA > WHB2PSUA > WHB1PSUA. It further indicated that the quantity of flexible polysiloxane was enhanced with an increase in the number of branches of

WHBPSUA in the photosensitive system. Moreover, the polysiloxane content of the UV-cured films has a marked influence on their physical properties. 3.7. Property of Photoimaging. The mixture of WHBPSUA, DPGDA, and Darocur 1173 was cured under UV irradiation through a patterned mask. Then, after development in deionized water, a resist pattern was formed (see Figure 10). The part which was not irradiated by

Figure 7. SEM images of different WHBPSUA oligomers system. The cured film composition: oligomer/DPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %: (a) WHB1PSUA, (b) WHB2PSUA, (c) WHB3PSUA. 2225



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than 7% at 300 °C and was far lower than that of the OAK-27 (25.76%), resulting from the high cross-linking density and the stability of the Si−O bond. As an increasing the number of branches of WHBPSUA oligomer, the elongation percentage of the WHBPSUA system was increased. This is mainly ascribed to a great quantity of flexible polysiloxane chains, which is caused by the increase in the number of branches of WHBPSUA.

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CONCLUSIONS A novel environmentally friendly water-soluble hyperbranched photosensitive polysiloxane urethane acrylate (WHBPSUA) has been synthesized and characterized adequately by FTIR, 1H NMR, and GPC analyses. The photopolymerization properties of WHBPSUA systems were investigated by RT-IR. WHBPSUA exhibits excellent compatibility with a number of acrylate monomers. The functionality, concentration, and viscosity of the monomer have great influence on the polymerization kinetics of WHBPSUA systems. The resin that is consisted of WHBPSUA with common acrylate monomers exhibits high polymerization rate and double bond conversion. Especially, the WHBPSUA system could dissolve in deionized water easily and completely. Therefore, it would be energy-saving and environmentally friendly in industrial applications. The resin that is consisted of WHBPSUA with common acrylate monomers could form a regular image under UV irradiation through a patterned mask. The cured film of the resin possesses excellent flexibility, toughness, and heat resistance. WHBPSUA with these properties has prospective application in solder mask and photosensitive coating.

Figure 9. Results of photoelectron counts versus binding energy of Si in different WHBPSUA oligomers.

ultraviolet light could dissolve easily and completely in deionized water. The WHBPSUA was capable of securing the accuracy of pattern.

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Figure 10. Appearance of cured film of the WHBPUSA system with image. The cured film composition: WHBPSUA/DPGDA = 50/50 (wt %); photoinitiator 1173, 0.07 wt %.

Corresponding Author

*Tel.: +86-10-64449336. E-mail: [email protected].

3.8. Properties of UV-Curing Film. The properties of UVcured film of WHBPSUA have been measured such as those listed in Table 2 and compared with properties of the OAK-27

Notes

The authors declare no competing financial interest.

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Table 2. Properties of WHBPSUA Cured Filma

ACKNOWLEDGMENTS The financial support from National Natural Science Foundation of China (Grant No. 50873011 and Grant No. 51273014) is gratefully acknowledged.

value items tensile strength (MPa) elongation percentage (%) pencil hardness weight loss (%, 300 °C)

WHB1PSUA WHB2PSUA

WHB3PSUA

OAK27

45.49

44.15

41.62

5.09

13.90

15.30

17.60

9.48

5H 6.77

5H 6.63

6H 6.56

2H 25.76

AUTHOR INFORMATION

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REFERENCES

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Composition of the cured film: oligomers/DPGDA/Darocur 1173 = 50/50/0.1 (wt %). a

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Synthesis and Property of Water-Soluble ... - ACS Publications

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