polymers Article
Facile Route for Bio-Phenol Siloxane Synthesis via Heterogeneous Catalytic Method and its Autonomic Antibacterial Property Xiaoyan Pang 1 , Xin Ge 1 , Jianye Ji 1 , Weijie Liang 2 , Xunjun Chen 1 1
2
*
and Jianfang Ge 1, *
College of Chemistry and Chemical Engineering, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China;
[email protected] (X.P.);
[email protected] (X.G.);
[email protected] (J.J.);
[email protected] (X.C.). School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710072, China;
[email protected] Correspondence:
[email protected]; Tel.: +86-159-196-571-48
Received: 12 September 2018; Accepted: 11 October 2018; Published: 16 October 2018
Abstract: Eugenol, used as bio-phenol, was designed to replace the hydrogen atom of hydrogenterminated siloxane by hydrosilylation reaction under the presence of alumina-supported platinum catalyst (Pt-Al2 O3 ), silica-supported platinum catalyst (Pt-SiO2 ) and carbon nanotube-supported platinum catalyst (Pt-CNT), respectively. The catalytic activities of these three platinum catalysts were measured by nuclear magnetic resonance hydrogen spectrometer (1 H NMR). The properties of bio-phenol siloxane were characterized by Fourier transform infrared spectrometer (FT–IR), UV-visible spectrophotometer (UV) and thermogravimeter (TGA), and its antibacterial property against Escherichia coli was also studied. The results showed that the catalytic activity of the catalyst Pt-CNT was preferable. When the catalyst concentration was 100 ppm, the reaction temperature was 80 ◦ C and reaction time was 6 h, the reactant conversion rate reached 97%. After modification with bio-phenol, the thermal stability of the obtained bio-phenol siloxane was improved. For bio-phenol siloxane, when the ratio of weight loss reached 98%, the pyrolysis temperature was raised to 663 ◦ C which was 60 ◦ C higher than hydrogenterminated siloxane. Meanwhile, its autonomic antibacterial property against Escherichia coli was improved significantly. Keywords: bio-phenol siloxane; synthesis; supported platinum catalyst; autonomic antibacterial
1. Introduction A bio-phenol is a phenol that derives from natural products, for example, vegetablse, tea-leaves, and flowers. Eugenol (4-allyl-2-methoxyphenol) is one kind of bio-phenol, which is a primary constituent of plant essential oil such as clove oil, laurel oil and camphor oil and characterized by the presence of functional groups such as hydroxy group, methoxy group and allyl group. Because of this unique structure, eugenol has biological and chemical characteristics, for example, antibacterial activity, antioxidant activity thermal stability and chemical reactivity [1–4]. Eugenol is particularly widely used in the food, cosmetic, and pharmaceutical industries [5,6]. Meanwhile, eugenol was used in compound modification [7,8]. Dai [9] used eugenol in the synthesis of eugenol-based organic coatings and the results indicated that the coating showed outstanding thermal stability and excellent adhesion. Miao [10] used eugenol in the synthesis of bio-based epoxy resin and the results showed the product had outstanding comprehensive performances and high renewable carbon content. Mangeon [11] used eugenol in the synthesis of semi-interpenetrating polymer networks and used it as plasticizer of poly-(3-hydroxyalkanoate), and the results showed the compound exhibited excellent deformability. Silva [12] studied eugenol derivatives which had excellent antibacterial and antioxidant activities. Polymers 2018, 10, 1151; doi:10.3390/polym10101151
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Eugenol could replace the hydrogen atom of hydrogenterminated siloxane by hydrosilylation reaction between allyl group and silicon hydrogen group under the presence of platinum catalyst. The platinum catalysts were commonly homogeneous catalysts such as Speier’s catalyst and Karsted’s catalyst [13–15]. The homogeneous catalyst was corrosive to reactors, difficult to remove from the system and had poor selection of reaction, and thus limited the application in specific fields [16,17]. Recently, the supported platinum catalysts are attracting researchers’ interest because of excellent catalytic selectivity and their simplicity of removal [18–22]. It is notable that supported catalysts have different catalytic activities in the reaction because of the different properties of supported material. In this paper, eugenol, used as a bio-phenol, was designed to replace the hydrogen atom of hydrogenterminated siloxane by hydrosilylation reaction under the presence of alumina-supported platinum catalyst (Pt-Al2 O3 ), silica-supported platinum catalyst (Pt-SiO2 ) and carbon nanotube-supported platinum catalyst (Pt-CNT). The catalytic activities of these three catalysts were measured by nuclear magnetic resonance hydrogen (1 H NMR) spectrometer, thereby determining the preferable process conditions. The product, bio-phenol siloxane, was characterized by Fourier transform infrared spectrometer (FT–IR), ultravioler–visible (UV) spectrophotometer and thermogravimeter, and its antibacterial activity against Escherichia coli was studied. 2. Materials and Methods 2.1. Materials Eugenol of 98% purity was purchased from Guangdong Tongcai New Material Corporation (Guangzhou, China). Octamethylcyclotetrasiloxane (D4 ) and 1,1,3,3-tetramethyldisiloxane (HMMH) were obtained from Shenzhen Ji-Peng Silicon Fluoride Materials Corporation (Shenzhen, China). Macroporous cationic resin was gained from Jiangyin Nanda Synthesis Chemical Corporation (Jiangyin, China). Catalyst Pt-Al2 O3 with 3% Pt and catalyst Pt-SiO2 with 3% Pt were obtained from Hubei Xinrunde Chemical Corporation (Wuhan, China). Chloroplatinic acid was purchased from Shanghai SSS Reagent Corporation (Shanghai, China). CNT was obtained from Qinhuangdao ENO High-Tech Material Development Corporation (Qinhuangdao, China). Agar nutrient solution and Escherichia coli solution were prepared from biochemical laboratory in Zhongkai University of Agriculture and Engineering. Ethanol (AR) was supplied by Tianjin Kemiou Chemical Corporation (Tianjin, China). 2.2. Synthesis of Bio-Phenol Siloxane CNT (2.0 g) and ethanol (35 mL) were added into a 100 mL three-necked flask equipped with a magnetic stirrer, a nitrogen inlet and a condenser. After venting nitrogen for 30 min, 15 mL chloroplatinic acid-ethanol solution was added. Then the system was heated to 75 ◦ C for 10 h. After washed and dried, the catalyst Pt-CNT was prepared successfully and the concentration of Pt was 3%. D4 (122.1 g, 0.4125 mol), HMMH (4.02 g, 0.03 mol) and macroporous cationic resin (3.78 g, 3%) were added into a 250 ml three-necked flask equipped with a magnetic stirrer, a thermometer and a reflux condenser. The system was heated to 80 ◦ C for 4 h then purified at 150 ◦ C for 4 h. The hydrogenterminated siloxane was synthesized. Hydrogenterminated siloxane (80 g, 0.02 mol) and eugenol (6.56 g, 0.04 mol) were placed in a 150-mL three-necked flask equipped with a magnetic stirrer, a nitrogen inlet, and a condenser. After venting nitrogen for 30 min, the appropriate amount of catalyst was added into the three-necked flask, and then the reaction system was heated to set temperature under nitrogen atmosphere for 6 h. Then, after centrifugation for 1 h, viscous oil was obtained. The viscous oil is bio-phenol siloxane. Figure 1 showed the scheme of synthesis of bio-phenol siloxane.
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Figure organosiloxane. Figure 1. 1. Scheme Scheme of of synthesis synthesis of of bio-phenol bio-phenol terminated terminated organosiloxane.
2.3. Nuclear Magnetic Magnetic Resonance Resonance Hydrogen Hydrogen ((11H H NMR) NMR) Spectrometer Spectrometer Analysis Analysis 2.3. Nuclear The 11H H NMR NMR spectrum spectrum were recorded on a Bruker Avance IIIHD ⅢHD 500 spectrometer (Bruker Corporation, Karlsruhe, Germany) Germany) using CDCl3 as aa solvent. The chemical chemical shifts shifts relative to solvent. The tetramethylsilane, which is used as an internal reference. The yield was calculated by the integration intensity of absorption peak of C=CH22 or or Si–H. Si–H. 2.4. Fourier Transform Transform Infrared 2.4. Fourier Infrared (FT–IR) (FT–IR) Analysis Analysis FT–IR FT–IR spectrum spectrum of of hydrogenterminated hydrogenterminated siloxane siloxane and and bio-phenol bio-phenol siloxane siloxane were were conducted conducted on on aa Perkin Elmer FT–IR spectrum 100 (Perkin-Elmer Corporation, Fremont, CA, USA) at room temperature. Perkin Elmer FT–IR spectrum 100 (Perkin-Elmer Corporation, Fremont, CA, USA) at room ◦ C for 4 h to remove moisture. Before scanning, thescanning, samples were dried in the dried drying at 80 temperature. Before the samples were incabinet the drying cabinet at 80 °C for 4 h to remove − 1 The samples were scanned within the range from 400 to 4000 cm . −1 moisture. The samples were scanned within the range from 400 to 4000 cm . 2.5. Ultraviolet–Visible (UV) Analysis 2.5. Ultraviolet–Visible (UV) Analysis UV-vis spectra were recorded on a UV-1800 UV-vis spectrophotometer (Perkin-Elmer Corporation, UV-vis spectra were recorded on a UV-1800 UV-vis spectrophotometer (Perkin-Elmer Fremont, CA, USA) within the range from 200 to 400 nm. The samples were dissolved in the ethanol. Corporation, Fremont, CA, USA) within the range from 200 to 400 nm. The samples were dissolved in the ethanol. 2.6. Thermal Analysis Thermogravimetric analyses were carried out using a Mettler Toledo TG/DTA thermal analyzer 2.6. Thermal Analysis (Mettler-Toledo AG Corporation, Columbus, OH, USA) to measure the temperature of siloxane from Thermogravimetric analyses were carried out using a Mettler Toledo TG/DTA thermal analyzer the beginning of weight loss to 100% weight loss. The experiments were performed in the range of (Mettler-Toledo AG Corporation, Columbus, OH, USA) to measure the temperature of siloxane from 40–900 ◦ C at a heating rate of 10 ◦ C/min under nitrogen atmosphere. the beginning of weight loss to 100% weight loss. The experiments were performed in the range of 40–900 °C at a heating rate of 10 °C/min under nitrogen atmosphere. 2.7. Antimicrobial Activity AntimicrobialActivity activity was measured according to a spread plate method using Escherichia coli [23]. 2.7. Antimicrobial The amounts of Escherichia coli used for the assay were optimized to better visualize the antimicrobial activityhydrogenterminated was measured according to a and spread plate method usingThe Escherichia coli effectAntimicrobial caused by eugenol, siloxane bio-phenol siloxane. agar plates [23]. Escherichia The amounts of Escherichia colithe used for the assay wereatoptimized to h. better visualize with coli were placed into biochemical incubator 35 ◦ C for 22 Optical imagesthe of antimicrobial effect caused by eugenol, hydrogenterminated siloxane and bio-phenol siloxane. The incubated plates were taken with a mobile phone. The amounts of Escherichia coli bacterial colonies agar plates withbyEscherichia coli were placed into the biochemical incubator at 35 °C for 22 h. Optical were observed manual counting. images of incubated plates were taken with a mobile phone. The amounts of Escherichia coli bacterial colonies were observed by manual counting.
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3. Results and Discussions 3. Results and Discussions 3.1. Analysis Analysis of of Catalytic Catalytic Activity Activity 3.1. 3.1.1. Catalytic Catalytic Activity Activity of of Pt-Al Pt-Al22O 3.1.1. O33 Table 11 shows shows the the effect effect of ofreaction reactiontemperature temperature on onactivity activityof ofthe thecatalyst catalystPt-Al Pt-Al2 2O O33 when when the the Table amount of of catalyst catalyst was was 100 100 ppm. ppm. The The reaction reaction time time was was set set to to 66 hh in in all all experiments. experiments. As As shown shown in in the the amount Table 1, 1, when when the the reaction reaction temperature temperature was was 80 80 ◦°C, the product product was was stratified stratified and and this this explains explains the the Table C, the existence of of unreacted unreacted eugenol eugenol which which was was yellowish. yellowish. By By raising temperature, the the degree degree existence raising the the reaction reaction temperature, of reaction reaction improved, improved, and and the the yellowing yellowing degree degree of of product product also also enhanced, enhanced, which of which was was detrimental. detrimental. When the the temperature temperature was was increased increased to to 160 160 ◦°C, the product product turned turned into into yellow yellow turbid turbid liquid. liquid. As As the the When C, the ◦ result shows, shows, the the preferable preferable temperature temperature for for catalyst catalyst Pt-Al Pt-Al22O O33 was sample A-2 A-2 was was result was 100 100 °C C and and the the sample preferable. Figure Figure 2a 2a shows shows the the 11H of sample sample A-2. A-2. As 2a shown, the signals preferable. H NMR NMR spectrum spectrum of As the the Figure Figure 2a shown, the signals at 5.9, 5.9, 5.1, 5.1, and and 4.7 4.7 ppm ppm were were corresponding corresponding to toC=CH–, C=CH–, –C=CH –C=CH22 and and Si–H Si–H group. group. The of the the at The ratio ratio of integration intensity intensity of these three three signals signals is is 1:2:1, 1:2:1, which which matched matched well well with with the the value value calculated calculated integration of these according to to the the structure. structure. This This indicated indicated that that the the reaction reactionsystem systemstill stillhad hadunreacted unreactedC=CH–, C=CH–,–C=CH –C=CH22 according and Si–H group and the yield was 36% by calculating the integration intensity of signal of the and Si–H group and the yield was 36% by calculating the integration intensity of signal ofSi–H the group. Table 2Table shows the effect catalyst concentration on the activity catalyst 2O3 when Si–H group. 2 shows theof effect of catalyst concentration on the of activity of Pt-Al catalyst Pt-Al2the O3 ◦ C. 2As reaction was 100 °C. As100 Table shown, the when catalyst was increased when thetemperature reaction temperature was Table when 2 shown, theconcentration catalyst concentration was 1H NMR spectrum to 500 ppm, still turbid liquid (Sample Figure 2b Figure shows 2b theshows increased to the 500 product ppm, thewas product was still turbid liquidA-10). (Sample A-10). the 1 H NMR of sample of A-10 and we can seewe the signals of signals unreacted C=CH–, –C=CH 2 and Si–H2 group. Thegroup. yield spectrum sample A-10 and can see the of unreacted C=CH–, –C=CH and Si–H was yield 76%. As the turbidity productofdemonstrated the reaction degree of system. When the The wasknown, 76%. As known, theof turbidity product demonstrated the reaction degree of system. yield was highwas as possible, product was was revealed It that therevealed catalyst Pt-Al 2O3 When the as yield as high the as possible, the transparent. product wasIt transparent. was that the had a low catalytic activity in this hydrosilylation reaction between eugenol and hydrogenterminated catalyst Pt-Al O had a low catalytic activity in this hydrosilylation reaction between eugenol and 2 3 siloxane. hydrogenterminated siloxane. Table 1. Effect Effect of of reaction reaction temperature temperature on on activity activity of of catalyst. catalyst. Table 1. Samples Samples
Catalys (ppm) Catalys (ppm)
◦ C) Temperature((°C) Temperature
A-1 A-1 A-2 A-2 A-3 A-3 A-4 A-4 A-5 A-5
100 100 100 100 100 100 100 100 100 100
80 80 100 100 120 120 140 140 160 160
Appearance Appearance Stratified, the bottom layer was unreactive Stratified, the bottom layer was unreactive eugenol eugenol Not stratified, as colorless turbid liquid Not stratified, colorless turbid liquid Not stratified, as as pale yellowish turbid liquid NotNot stratified, as pale yellowish turbid liquid stratified, as yellowish turbid liquid Not stratified, asas yellowish turbidliquid liquid Not stratified, yellow turbid Not stratified, as yellow turbid liquid
Yield Yield(%) (%) -36 36---
Figure 2. 2. Nuclear Nuclear magnetic magnetic resonance resonance hydrogen hydrogen ((11H of sample sample A-2 A-2 (a) (a) and and A-10 A-10 (b). (b). Figure H NMR) NMR) spectrum spectrum of
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Table 2. Effect of catalyst concentration on activity of catalyst. Samples
Samples A-6 A-6 A-7 A-7 A-8 A-8 A-9 A-9 A-10 A-10
Table 2. Effect of catalyst of catalyst. Catalyst (ppm) Temperature (°C) concentration on activity Appearance Catalyst (ppm) 50 50 100100 100100 200 500200 500
◦ Temperature 100( C)
100 100100 100100 100 100100 100
Stratified, the bottom layer was unreactive Appearance eugenol Stratified, the bottom layer was unreactive eugenol Not stratified, as colorless turbid turbid liquid liquid Not stratified, as colorless Not stratified, as colorless turbid liquid Not stratified, as colorless turbid liquid Not stratified, as colorless turbid liquid Not stratified, stratified, as as colorless colorless turbid turbid liquid liquid Not Not stratified, as colorless turbid liquid
Yield (%) Yield (%)
- - - 76 76
3.1.2. Catalytic Activity of Pt-SiO2 3.1.2. Catalytic Activity of Pt-SiO2 Table 3 shows the effect of reaction temperature on activity of catalyst Pt-SiO2 when the amount ◦ C, the Tablewas 3 shows the effect of reaction on activity of 100 catalyst Pt-SiO 2 when the amount of catalyst 100 ppm. We knew that astemperature the temperature exceeded product would be turn ◦ of catalyst was 100 ppm. We knew that as the temperature exceeded 100 °C, the product would be into yellow, so the temperature was setting at range of 60–100 C. As Table 3 shown, when temperature ◦ ◦ turn into yellow, so the temperature was setting at range of 60–100 °C. As Table 3 shown, was 60 C, the solution was stratified. When the temperature increased to 100 C, the solutionwhen had 1 temperature was 60 °C, the solution was stratified. When the temperature increased to 100 °C, the turned into yellowish (Sample B-3). Figure 3a is the H NMR spectrum of sample B-3 and its yield 1H NMR spectrum of sample B-3 solution had turned into yellowish (Sample B-3). Figure 3a is the was 66% by calculating the integration intensity of signal of Si–H group. Table 4 shows the effect ◦ and its yield was 66% by calculating integration intensity of signal of Si–H group. Table 4 shows of catalyst concentration on activity the of catalyst Pt-SiO 2 when the reaction temperature was 80 C. the effect of catalyst concentration on activity of catalyst Pt-SiO 2 when the reaction temperature was As Table 2 shown, when the catalyst concentration was increased to 200 ppm, the product was colorless 1 Hincreased 80 °C. As Table 2 shown, when the catalyst was to 200 ppm, the product and slight transparent liquid (Sample B-7). concentration Figure 3b is the NMR spectrum of sample B-7 andwas its 1 colorless and slight transparent liquid (Sample B-7). Figure 3b is the H NMR spectrum of sample Byield was 80% by calculating the integration intensity of signal of Si–H group. It was revealed that 7 and its yield was 80% by calculating the integration intensity of signal of Si–H group. It was revealed catalyst Pt-SiO2 had a higher catalytic activity than catalyst Pt-Al2 O3 in this hydrosilylation reaction. thatcatalytic catalyst activity Pt-SiO2ofhad a higher catalytic activity than catalyst Pt-Al2O3 in this hydrosilylation But catalyst Pt-SiO 2 was not high enough to meet production requirements. reaction. But catalytic activity of catalyst Pt-SiO2 was not high enough to meet production requirements. Table 3. Effect of reaction temperature on activity of catalyst. Samples
Table 3.Temperature Effect of reaction temperature onAppearance activity of catalyst. Catalyst (ppm) (◦ C)
Yield (%)
Samples B-1 B-1 B-2 B-3 B-2 B-3
Catalyst 100(ppm) 100 100 100 100 100
Yield- (%) -66 66
Temperature (°C) Stratified, the bottomAppearance 60 layer was unreactive eugenol 60 Stratified, the bottom was turbid unreactive eugenol 80 Not stratified, as layer colorless liquid 100 Not stratified, as yellowish, little turbid transparent 80 Not stratified, as colorless liquidliquid 100 Not stratified, as yellowish, little transparent liquid
Table 4. Effect of catalyst concentration on activity of catalyst. Table 4. Effect of catalyst concentration on activity of catalyst. Samples Samples B-4 B-4 B-5 B-5 B-6 B-6 B-7 B-7
Catalyst (◦ C)(°C) Appearance Catalyst (ppm) Temperature Temperature Appearance (ppm) 10 80 Not stratified, as colorless turbid liquid 10 80 Not stratified, as colorless turbid liquid 50 80 Not stratified, as colorless turbid liquid 50 80 Not stratified, as colorless turbid liquid 100 stratified, as colorless turbid liquid 100 80 80 NotNot stratified, as colorless turbid liquid Not stratified, as colorless, slight transparent 200 80 80 Not stratified, as colorless, slight transparent liquid 200 liquid
Figure 3. 1 H NMR spectrum of sample B-3 (a) and B-7 (b). Figure 3. 1H NMR spectrum of sample B-3 (a) and B-7 (b).
Yield Yield(%) (%) -8080
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3.1.3. Catalytic Activity of Pt-CNT 3.1.3. Catalytic Activity of Pt-CNT Table 5 shows the effect of reaction temperature on activity of catalyst Pt-CNT when the amount Table 5 shows the effect of reaction temperature on activity of catalyst Pt-CNT when the amount of catalyst was 100 ppm and the temperature was set at a range of 60–100 ◦ C. As Table 5 shows, of catalyst was 100 ppm and the temperature was set at a range of 60–100 °C. As Table 5 shows, when when temperature was 60 ◦ C, the solution was colorless and a slightly transparent liquid. When the temperature was 60 °C, the solution was colorless and a slightly transparent liquid. When the temperature increased to 80 ◦ C, the solution was a colorless transparent liquid (Sample C-2). Figure 4 temperature increased to 80 °C, the solution was a colorless transparent liquid (Sample C-2). Figure is the 1 H NMR spectrum of sample C-2. As Figure 4 shown, the signals at 5.9, 5.1, and 4.7 ppm had 4 is the 1H NMR spectrum of sample C-2. As Figure 4 shown, the signals at 5.9, 5.1, and 4.7 ppm had nearly disappeared which were corresponding to C=CH–, –C=CH2 and Si–H group. The yield was 97% nearly disappeared which were corresponding to C=CH–, –C=CH2 and Si–H group. The yield was by calculating the integration intensity of signal of the Si–H group. Table 6 shows the effect of catalyst 97% by calculating the integration intensity of signal of the Si–H group. Table 6 shows the effect of concentration on activity of catalyst Pt-CNT when the reaction temperature was 80 ◦ C. By decreasing catalyst concentration on activity of catalyst Pt-CNT when the reaction temperature was 80 °C. By the catalyst concentration, the reaction degree declined. Combined with the analysis above, it was decreasing the catalyst concentration, the reaction degree declined. Combined with the analysis shown that the catalytic activity of catalyst Pt-CNT was preferable compared with catalyst Pt-Al2 O3 above, it was shown that the catalytic activity of catalyst Pt-CNT was preferable compared with and catalyst Pt-SiO2 in this hydrosilylation reaction between eugenol and hydrogenterminated siloxane. catalyst Pt-Al2O3 and catalyst Pt-SiO2 in this hydrosilylation reaction between eugenol and This was because the CNT had a larger specific surface area and thus had a better contact with the hydrogenterminated siloxane. This was because the CNT had a larger specific surface area and thus reactants. Meanwhile, when catalyst Pt-CNT was used 4 times after recyling, it also had a high catalytic had a better contact with the reactants. Meanwhile, when catalyst Pt-CNT was used 4 times after activity and the yield was still more than 90%. recyling, it also had a high catalytic activity and the yield was still more than 90%. Table 5. Effect of reaction temperature on activity of catalyst. Table 5. Effect of reaction temperature on activity of catalyst Samples
Samples C-1 C-1 C-2 C-2 C-3 C-3
Catalyst (ppm)
Catalyst (ppm) 100 100 100 100 100 100
Temperature (◦ C)
Temperature (°C) 60 60 80 80 100 100
Appearance
Appearance
Not stratified, stratified, as liquid Not as colorless colorlessand andslight slighttransparent transparent liquid Not stratified, as colorless transparent liquid Not stratified, as colorless transparent liquid Not stratified, as yellowish and slight transparent liquid
Not stratified, as yellowish and slight transparent liquid
Yield (%)
Yield (%) -97 97 -
Table 6. Effect of catalyst concentration on activity of catalyst. Table 6. Effect of catalyst concentration on activity of catalyst Samples
Samples C-4 C-4 C-5 C-5 C-6 C-6
Catalyst (ppm)
Catalyst (ppm) 30 30 50 50 100 100
Temperature (◦ C)
Temperature (°C) 80 80 80 80 80 80
Appearance
Appearance
Not transparent liquid Not stratified, stratified,asascolorless colorlessand andslight slight transparent liquid Not stratified, as colorless and slight transparent liquid Not stratified, as colorless and slight transparent liquid Not stratified, as colorless transparent liquid
Not stratified, as colorless transparent liquid
Yield (%)
Yield (%) --97 97
Figure 4. 4. 11H Figure H NMR NMR spectrum spectrum of of sample sample C-2. C-2.
3.2. FT–IR Analysis 3.2. FT–IR Analysis For aabetter of of thethe difference between hydrogenterminated siloxane and bio-phenol betterunderstanding understanding difference between hydrogenterminated siloxane and bioterminated siloxanesiloxane (Sample(Sample C-2), Fourier transform infraredinfrared spectroscopy was employed to identify phenol terminated C-2), Fourier transform spectroscopy was employed to their functional groups. Figure 5 shows the FTIR spectrum of hydrogenterminated siloxane (a) and identify their functional groups. Figure 5 shows the FTIR spectrum of hydrogenterminated siloxane bio-phenol terminated siloxane (b). In (b). bothIncurves, an absorption peak peak appeared at 2900, 13001300 and (a) and bio-phenol terminated siloxane both curves, an absorption appeared at 2900, −1 corresponding −1 1050 cm to C–H stretching vibration, C–H in-plane bending vibration and Si–O–Si and 1050 cm corresponding to C–H stretching vibration, C–H in-plane bending vibration and Si–O– stretching vibration in turn. curve a characteristic peak appeared at 2200 cm−1 was corresponding Si stretching vibration in In turn. Ina,curve a, a characteristic peak appeared at 2200 cm−1 was to Si–H stretching in the molecular of hydrogenterminated siloxane. In curve b, corresponding to vibration Si–H stretching vibration structure in the molecular structure of hydrogenterminated siloxane. In curve b, the absorption peak of Si–H had disappeared, and two new characteristic peaks appeared at 3500 and 1500 cm−1 corresponding to O–H and benzene stretching vibration, which were
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the absorption peak of Si–H had disappeared, and two new characteristic peaks appeared at 3500 and −1 corresponding Polymers 2018, 10, x FOR PEER 7 of 10 1500 cm toREVIEW O–H and benzene stretching vibration, which were derived from eugenol. Polymers 2018, 10, x FOR PEER REVIEW 7 of 10 It was indicated that the eugenol was connected to hydrogenterminated siloxane and bio-phenol derived from eugenol. It was indicated that the eugenol was connected to hydrogenterminated terminated was synthesized successfully. derived siloxane from eugenol. It was indicated that the eugenol was connected to hydrogenterminated siloxane and bio-phenol terminated siloxane was synthesized successfully. siloxane and bio-phenol terminated siloxane was synthesized successfully. a ab b
a a b b
C-H C-H
Si-H Si-H
C-H C-H Si-O-Si Si-O-Si
-OH -OH
4000 4000
3000 2000 3000 Wavenumber 2000 (cm-1)
1000 1000
-1
Wavenumber (cm )
Figure 5. Fourier transforminfrared infrared (FT–IR) (FT–IR) spectrum siloxane (a) and Figure 5. Fourier transform spectrumofofhydrogenterminated hydrogenterminated siloxane (a) and Figure 5. Fourier transform infrared (FT–IR) spectrum of hydrogenterminated siloxane (a) and biophenol terminated siloxane (b). biophenol terminated siloxane (b). biophenol terminated siloxane (b).
3.3.Analysis UV Analysis 3.3. UV
3.3. UV Analysis After the atoms absorb photons, the outer electrons transition from the ground state to the AfterAfter the atoms absorb photons, the outer electrons transition from thethe ground state to the excited theDifferent atoms absorb photons, outer ways electrons transitionand from ground state to the excited state. structures havethe different of transition different wavelength range state.excited Different structures have different ways of transition and different wavelength range of absorbed state. light. Different structures spectrophotometer have different waysisofcommonly transition used and different wavelength range of absorbed A UV-visible to identify the conjugated light.ofAabsorbed UV-visible spectrophotometer is commonly used to identifyused the conjugated olefin and aromatic light. A UV-visible spectrophotometer is commonly to identify the conjugated olefin and aromatic hydrocarbon in the molecular structure according to wavelength range of hydrocarbon inaromatic theFigure molecular structure according tostructure wavelength range of wavelength absorbed light. 6 olefin andlight. hydrocarbon in the molecular according to rangeFigure of absorbed 6 shows the UV spectrum of hydrogenterminated siloxane (a) and bio-phenol absorbed light. Figure 6 shows the UV spectrum of hydrogenterminated siloxane (a) and bio-phenol shows the UV spectrum of hydrogenterminated siloxane (a) and bio-phenol terminated siloxane (b). terminated siloxane (b). As Figure 6 shown, in curve b, a new characteristic absorption tail appeared terminated siloxane (b). As nm Figure 6 shown, in curveto b,absorption a new characteristic absorption tail appeared As Figure shown, in to curve b, awere new characteristic tail appeared at the range of 240 to at the 6range of 240 280 corresponding benzene absorption tail, which were derived at the range of 240 to 280 nm were corresponding to benzene absorption tail, which were derived 280 nm were corresponding benzene absorption tail, analysis which were derived from eugenol. Combined from eugenol. Combined to with the FT–IR spectroscopy above, it was demonstrated that the from eugenol. Combined to with the FT–IR spectroscopy analysis above, it was demonstrated that was the eugenol was connected hydrogenterminated siloxane and bio-phenol terminated siloxane with the FT–IR spectroscopy analysis above, it was demonstrated that the eugenol was connected to eugenol wassuccessfully. connected to hydrogenterminated siloxane and bio-phenol terminated siloxane was synthesized hydrogenterminated siloxane and bio-phenol terminated siloxane was synthesized successfully. synthesized successfully.
Abs Abs
1.5 1.5
a ab b
1.0 1.0
benzene absorption tail benzene absorption tail
0.5 0.5 0.0 0.0 200 200
250 250
300
λ (nm)300 λ (nm)
350 350
Figure 6. Ultraviolet–visible (UV) spectrum of hydrogenterminated siloxane (a) and bio-phenol
Figure 6. Ultraviolet–visible (UV) spectrum spectrum of siloxane (a) and bio-phenol Figure 6. Ultraviolet–visible (UV) of hydrogenterminated hydrogenterminated siloxane (a) and bio-phenol terminated siloxane (b). terminated siloxane terminated siloxane (b).(b). 3.4. Thermal Analysis 3.4. Thermal Analysis 3.4. Thermal Analysis For providing evidence about effect of eugenol on enhancing the thermal stability of siloxane, For providing evidence abouteffect effect of eugenol eugenol on enhancing thethe thermal stability of siloxane, For providing evidence of on enhancing thermal stability of siloxane, the ratio of weight loss wasabout measured. Figure 7 shows the thermogravimetric analysis (TGA) curves the ratio of weight loss was measured. Figure 7 shows the thermogravimetric analysis (TGA) curves the ratio of weight loss was measured. Figure 7 shows the thermogravimetric analysis (TGA) curves of hydrogenterminated siloxane (a) and bio-phenol terminated siloxane (b). In curve a, the first stage of hydrogenterminated siloxane (a) and bio-phenol terminated siloxane (b). In curve a, the first stage of weight loss was volatile water the bio-phenol range of 80–120 °C and the second (b). stageIn was mainly the first of hydrogenterminated siloxane (a)atand terminated siloxane curve a, the of weight loss was volatile water at the siloxane. range of When 80–120the °C ratio and◦ the second loss stagereached was mainly the hydrogenterminated weight stagedecomposition of weight lossofwas volatile water at the range of 80–120 Cofand the second stage98%, wasthe mainly decomposition of hydrogenterminated siloxane. the ratio of weight loss as reached 98%, thea pyrolysis temperature was 603 °C. In curve b, theWhen first When stage ofthe weight loss was same as curve the decomposition of hydrogenterminated siloxane. ratio of weight loss reached 98%, pyrolysis temperature was 603 °C. In curve b, the first stage of weight loss was as same as curve a
the pyrolysis temperature was 603 ◦ C. In curve b, the first stage of weight loss was as same as curve a
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and the second stage was the decomposition of siloxane and residual eugenol. The third stage of weight lossand was decomposition of bio-phenol terminated siloxane. WhenThe thethird ratiostage of weight loss themainly secondthe stage was the decomposition of siloxane and residual eugenol. of Polymers 2018, 10, x FOR PEER REVIEW 8 of 10 ◦ ◦ reached temperature was of 663bio-phenol C whichterminated was 60 C siloxane. higher than hydrogenterminated weight98%, loss the waspyrolysis mainly the decomposition When the ratio of siloxane. It was demonstrated that the introduction of eugenol had enhanced the thermal stability weight loss reached 98%, the pyrolysis temperature was 663 °C which was 60 °C higher than and the second stage was the decomposition of siloxane and residual eugenol. The third stage of of hydrogenterminated siloxane. It was demonstrated that the introduction of eugenol had enhanced siloxane because of the benzene structure in the eugenol. weight loss was mainly the decomposition of bio-phenol terminated siloxane. When the ratio of theweight thermalloss stability of siloxane because of the benzene structure in the eugenol. reached 98%, the pyrolysis temperature was 663 °C which was 60 °C higher than hydrogenterminated siloxane. It was demonstrated that the introduction of eugenol had enhanced 100 the thermal stability of siloxane because of1 the benzene structure inathe eugenol.
b
Weight (%) Weight (%)
80 100 60 40 20 0
b
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a b
60
a b
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3 a
40 20 0
200 0
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Temperature (℃) 0
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Figure Thermogravimetricanalysis analysis(TGA) (TGA)curves curves of ofhydrogenterminated hydrogenterminated siloxane Figure 7. 7. Thermogravimetric siloxane(a) (a)and and biobio-phenol Temperature (℃) phenol terminated siloxane (b). terminated siloxane (b). Figure 7. Thermogravimetric analysis (TGA) curves of hydrogenterminated siloxane (a) and bio-
Antimicrobial Activitysiloxane (b). 3.5.3.5. Antimicrobial Activity phenol terminated
Figure 8 shows optical images of the antimicrobial activities of control group (a), eugenol (b), Figure 8 shows optical images of the antimicrobial activities of control group (a), eugenol (b), 3.5. Antimicrobial Activity hydrogenterminated siloxane (c) and bio-phenol terminated siloxane (d). In this assay, agar was used hydrogenterminated siloxane (c) and bio-phenol terminated siloxane (d). In this assay, agar was as nutrient solution andoptical the Escherichia colithe was used as model to evaluate the antimicrobial activity.(b), Figure 8 shows images of antimicrobial activities of control group (a), eugenol used as nutrient solution andthat the Escherichia coli was used as model to evaluate the antimicrobial In hydrogenterminated Figure 8a, it was shown bacterial colonies within siloxane (c) the and Escherichia bio-phenol coli terminated siloxane (d).grew In thisquickly assay, agar wasthe used activity. In Figure 8a, it was shown that the Escherichia coli bacterial colonies grew quickly within incubation time of 24 h.and In Figure 8b, the presence eugenol resulted in almost visible Escherichia as nutrient solution the Escherichia coli was of used as model to evaluate theno antimicrobial activity. thecoli incubation time of 24 h. In Figure 8b, the presence of eugenol resulted in almost no visible andshown eugenolthat hadthe an outstanding antimicrobial activity. grew Compared with Figurethe Inbacterial Figure colonies 8a, it was Escherichia coli bacterial colonies quickly within Escherichia coli bacterial hadin an outstanding antimicrobial activity. Compared 8c,d, the amount ofof Escherichia coliand bacterial colonies the agar plate with presence of bio-phenol incubation time 24 colonies h. In Figure 8b,eugenol the presence of eugenol resulted inthe almost no visible Escherichia terminated siloxane was less than the one with hydrogenterminated siloxane at the same incubation with Figure 8c,d, the amount of Escherichia coli bacterial colonies in the agar plate with the presence coli bacterial colonies and eugenol had an outstanding antimicrobial activity. Compared with Figure of time. It was indicated the introduction of eugenol had strengthened the antimicrobial activity bio-phenol terminated siloxane was less than the one hydrogenterminated siloxane at of the same 8c,d, the amount of that Escherichia coli bacterial colonies inwith the agar plate with the presence of bio-phenol siloxane because of the characteristic structure of eugenol. The phenolic hydroxyl group was the main terminated was less than the one with hydrogenterminated siloxane at the same incubation time.siloxane It was indicated that the introduction of eugenol had strengthened theincubation antimicrobial functional group that plays antimicrobial activity. Thehad ortho-methoxy group could enhance the of time. was indicated that introduction of eugenol the antimicrobial activity activity of It siloxane because ofathe the characteristic structure of strengthened eugenol. The phenolic hydroxyl group was antibacterial activity. Meanwhile, the antibacterial activity may also be related to the electrical, siloxane because of the characteristic structure of eugenol. The phenolic hydroxyl group was the main the main functional group that plays a antimicrobial activity. The ortho-methoxy group could enhance hydrophobic and spatial structure of bio-phenol siloxane It was shown thatcould the bio-phenol functional group that plays a antimicrobial activity. The[24]. ortho-methoxy group enhance the thesiloxane antibacterial activity.antimicrobial Meanwhile,activity the antibacterial activity of may also be related to the electrical, had autonomic without the addition antimicrobial agents. antibacterial activity. Meanwhile, the antibacterial activity may also be related to the electrical,
hydrophobic and spatial structure of bio-phenol siloxane [24]. It was shown that the bio-phenol hydrophobic and spatial structure of bio-phenol siloxane [24]. It was shown that the bio-phenol siloxane had autonomic antimicrobial activity without the addition of antimicrobial agents. siloxane had autonomic antimicrobial activity without the addition of antimicrobial agents.
Figure 8. Optical images of agar plates characteristic of the antimicrobial activities of the control group (a), eugenol (b), hydrogenterminated siloxane (c) and bio-phenol siloxane (d). Figure 8. Optical imagesof of agar characteristic of the activitiesactivities of the control group Figure 8. Optical images agarplates plates characteristic ofantimicrobial the antimicrobial of the control (a), eugenol (b), hydrogenterminated siloxane (c) and bio-phenol siloxane (d). group (a), eugenol (b), hydrogenterminated siloxane (c) and bio-phenol siloxane (d).
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4. Conclusions Compared with catalyst Pt-Al2 O3 and catalyst Pt-SiO2 , we found the catalytic activity of catalyst Pt-CNT was preferable, because catalyst Pt-CNT has larger specific surface area and catalytic selectivity in this hydrosilylation reaction between eugenol and hydrogenterminated siloxane. When the catalyst concentration was 100 ppm, the reaction temperature was 80 ◦ C and reaction time was 6 h, the yield reached 97% and bio-phenol terminated siloxane was synthesized successfully. Meanwhile, when catalyst Pt-CNT was used 4 times after recycling, it also had a high catalytic activity and the yield was still more than 90%. After modification with eugenol, the thermal stability of the obtained bio-phenol terminated siloxane had improved. For bio-phenol siloxane, when the ratio of weight loss reached 98%, the pyrolysis temperature was raised to 663 ◦ C which was 60 ◦ C higher than hydrogenterminated siloxane. Its antibacterial property against Escherichia coli was improved significantly. Without the addition of antimicrobial agents, the bio-phenol siloxane had autonomic antimicrobial activity because of special functional groups in the structure. Bio-phenol siloxane is expected to be applied to polymer modification, because it will enhance the thermal stability, weather resistance, hydrophobicity, and antibacterial and antioxidant qualities of the compounds. Author Contributions: Conceptualization, J.G. and X.C.; Methodology, X.G.; Software, J.J.; Validation, X.P.; Formal Analysis, X.P.; Investigation, X.P.; Resources, J.G.; Data Curation, W.L.; Writing-original Draft Preparation, X.P.; Writing-review and Editing, X.P.; Visualization, J.G.; Supervision, X.G.; Project Administration, J.G.; Funding Acquisition, J.G. Funding: This work was funded by the Special Funds for Applied Science and Technology Research and Development of Guangdong Province, No. 2015B090925022; and Guangdong Public Welfare Fund and Ability Construction Project, No. 2016A010103037; and Graduate Science and Technology Innovation Fund of Zhongkai University of Agriculture and Engineering, No. KJCX2018007. Acknowledgments: The authors wish to thank the Zhongkai University of Agriculture and Engineering for financial support. Conflicts of Interest: The authors declare no conflict of interest.
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