A Simple Preparation Route for Bio-Phenol MQ Silicone Resin via the Hydrosilylation Method and its Autonomic Antibacterial Property

MQ silicone resins represent a broad range of hydrolytic condensation products of monofunctional silane (M units) and tetrafunctional silane (Q units). In this work, a Bio-Phenol MQ silicone resin (BPMQ) was designed and synthesized by the hydrosilylation of hydrogen containing MQ silicone resin and eugenol in the presence of chloroplatinic acid. The structure, thermal property, and antibacterial property against Escherichia coli of the modified MQ silicone resin were investigated. The results showed that BPMQ has been prepared successfully, and the thermal stability of this modified polymer improved significantly because of the introduction of phenyl in eugenol. The temperature at the maximum degradation rate increased from 250 °C to 422.5 °C, and the residual yields mass left at 600 °C were increased from 2.0% to 28.3%. In addition, its antibacterial property against Escherichia coli was also enhanced markedly without adding any other antimicrobial agents. This improved performance is ascribed to special functional groups in the structure of eugenol. The BPMQ polymer is expected to be applied to pressure-sensitive adhesives and silicone rubber products for the biomedical field due to its reinforcing effect and antioxidant quality.


Introduction
MQ silicone resin is an organic-inorganic hybrid material with a three-dimensional structure consisting of tetra-functional siloxane (SiO 4/2 , Q units) and mono-functional siloxane (R 3 SiO 1/2 , M units). The core of MQ silicone resin is a cage-type SiO 2 (Q units) with high density, while the shell is M units with low density, and organic/inorganic groups such as methyl, aryl, vinyl, or silicon hydrogen bonds exist in M units [1][2][3]. This organic-inorganic distinctive structure gives the MQ silicone resin excellent thermal stability [4], high weather resistance [5], high chemical resistance [6], etc. MQ silicone resin can be used as a constituent of a high-temperature coating, as a tackifier for a silicone pressure-sensitive adhesive, and as a filler for liquid silicone rubber [7]. MQ silicon resin is used as a reinforcing agent in a polymer matrix, which can significantly improve the mechanical properties and thermal stability of the composites, and further improve their application value [8].
However, it is not enough to improve the mechanical properties and thermal stability of the polymers when using MQ silicone resin as a reinforcing filler. For instance, beyond improving the adhesive properties and thermal stability of adhesive, we still need to ensure the bacteriostatic and biocidal properties when MQ silicone resin is applied to silicone pressure-sensitive adhesives for

Synthesis of Bio-Phenol MQ Silicone Resin
BPMQ was prepared through a hydrosilylation reaction of HMQ and eugenol. HMQ (50.0 g), eugenol (39.1 g), and toluene (6.0 mL) were added to a 250 mL three-necked flask equipped with a nitrogen inlet, magnetic stirrer, and condenser. After venting the nitrogen for about 15 min, hydrosilylation catalyst H 2 PtCI 6 (0.3 g) was added to the flask. Then, we stirred the mixture for 5 h at 75 • C. Finally, we distilled the toluene and low boiling components at 110 • C for about 2 h to obtain the BPMQ polymer.

Characterizations and Measurements
Content of hydrogen groups in HMQ: the mass fraction of hydrogen groups in HMQ was measured via iodometric titration according to a procedure in the literature [22]. Firstly, the sample was dissolved into a 250 mL iodine flask containing a CCl 4 solution (20.0 mL) and bromo-acetic acid solution (10.0 mL). Secondly, IBr (10.0 mL) was added to the iodine flask and shaken evenly. After that, the reaction continued for about 1 h in the dark. Thirdly, KI solution (15 mL) was added into the flask and shaken for 5 min, then distilled water (40 mL) was used to wash the iodine flask. Fourth, we titrated the solution until it was light yellow with Na 2 S 2 O 3 of 0.1 mol/L, then a starch solution (1.0 mL) was added and we continued to titrate the solution until the blue coloration disappeared. In the same way, the blank experiment was carried out. The mass fraction of hydrogen groups in HMQ was determined by the following equation: where Φ is the mass fraction of hydrogen groups in HMQ (%); C is the concentration of Na 2 S 2 O 3 (mol/L); V 0 is the volume of Na 2 S 2 O 3 consumed by the blank experiment; V 1 is the volume of Na 2 S 2 O 3 consumed by the experimental group; the constant 1.008 is the molar mass of hydrogen group; the constant 0.001 is the unit conversion constant between mL with L; the constant 0.5 is the coefficient of mole balance; and M is the mass of the HMQ sample. FT-IR: The structure of the HMQ and BPMQ samples was characterized by VERTEX70 Fourier transform infrared (FT-IR) spectra (Shimadzu Corporation, Kyoto, Japan). Each sample was scanned from 450 to 4000 cm −1 and averaged over eight times. 1 H-NMR: The structures of the HMQ and BPMQ were characterized at 25 • C with an Av500 hydrogen nuclear magnetic resonance spectrometer (Bruker Corporation, Karlsruhe, Germany) at a frequency of 500 MHz. We used deuterated chloroform (CDCl 3 ) as the solvent and tetramethylsilane as an internal reference. 29 Si NMR: The 29 Si NMR analysis of the HMQ and BPMQ samples was conducted with a Bruker AVANCE AV 400 MHz spectrometer at 25 • C, with CDCl 3 as the solvent. Gel permeation chromatography (GPC): Molecular weights and molecular weight distribution of HMQ and BPMQ were determined by GPC using an Agilent 1260 infinity LC system (Agilent Technologies, Palo Alto, CA, USA), equipped with two PLgel MixedC and one PLgel Mixed-D columns and a refractive index detector. The operation was performed at 25 ± 1 • C, using HPLC-grade THF as the eluent at the flow rate of 1 mL/min and polystyrene as the molecular weight reference.
Viscosity: The viscosity of HMQ and BPMQ was measured on a Haake Mars II rotational rheometer (Haake, Karlsruhe, BW, Germany) under a steady shear flow at room temperature. The apparent viscosity was obtained at a given shear rate of 10 S −1 .
Thermogravimetric analysis (TGA): Thermogravimetric analysis was carried out on a Mettler Toledo TG thermal analyzer (Mettler Toledo, Zurich, Switzerland) at a flow rate of 20 mL/min in nitrogen, the sample was heated from 40 • C to 800 • C at a rate of 10 • C/min. Antimicrobial activity analysis: The antimicrobial activity was measured according to a spread plate method, using Escherichia coli as the bacterial strain and agar as the nutrients. Agar plates containing Escherichia coli were put into the biochemical incubator at 25 • C for 24 h. The amounts of Escherichia coli used for the experiment were optimized according to a procedure in the literature [12]. To more intuitively assess the antimicrobial effect of HMQ, PBMQ and eugenol, the same mass fractions of HMQ and BPMQ (equivalent to 20% of the weight of agar) were added to the agar plates. Likewise, we kept the amount of eugenol identical to that in BPMQ. Optical images of the cultivation plate were taken with a 12-megapixel iPhone 6s mobile phone (Apple Inc., Cupertino, CA, USA), and the number of Escherichia coli colonies was determined by manual counting.

Structural Analysis
HMQ was synthesized first via hydrolysis and a condensation reaction. To determine the additional amount of HMQ needed for a further reaction, the content of hydrogen groups in HMQ was measured by chemical titration. The results showed that the mass fraction of hydrogen in HMQ was 0.5%. Then, BPMQ was prepared via the hydrosilylation reaction of HMQ and eugenol, using H 2 PtCl 6 as an additional catalyst. Theoretically, this reaction of Si-H and vinyl is in the molar ratio of 1:1, but to overcome side effects caused by the lively reaction of Si-H in HMQ, a slightly excess molar ratio of HMQ to eugenol was used to promote the reaction more completely, and a molar ratio of 1.02:1 of the value of Si-H/-CH=CH 2 was chosen in this reaction [23]. The preparation routes of HMQ and BPMQ are shown in Figure 1. The structures of HMQ and BPMQ were characterized by FT-IR. As shown in Figure 2, in the curve of HMQ, the sharp peaks at 2960 and 2903 cm −1 are assigned to the stretching vibration of C-H group on Si-CH3. The strong absorption peak at 2140 cm −1 is attributed to Si-H stretching vibration in the molecular structure of HMQ [24]. In addition, the sharp peaks at 1418, 1260, and 841 cm −1 are ascribed to the characteristic absorption peaks of Si-CH3, while the peak located at 1080 cm −1 is a characteristic symmetric stretching absorption peak of Si-O-Si. These indicate that HMQ has been synthesized successfully [25]. In the curve of PBMQ, the broad peak at 3550 cm −1 corresponds to the stretching vibration of phenol hydroxyl. The characteristic absorption peaks at 3060 and 3010 cm −1 are ascribed to the stretching vibration of the C-H group on phenyl [26], while the peaks at 1610 and 1520 cm −1 are C-C stretching vibration of benzene. The peak at 1370 cm −1 corresponds to C-H in C-CH3, which was introduced from eugenol. Moreover, the characteristic absorption peak of Si-H at 2140 cm −1 has disappeared, and the symmetric stretching vibrations of C-H on Si-CH2 formed during the hydrosilylation at 2850 cm −1 were found. These indicate that BPMQ has been prepared successfully through the hydrosilylation reaction of HMQ and eugenol. The structures of HMQ and BPMQ were characterized by FT-IR. As shown in Figure 2, in the curve of HMQ, the sharp peaks at 2960 and 2903 cm −1 are assigned to the stretching vibration of C-H group on Si-CH 3 . The strong absorption peak at 2140 cm −1 is attributed to Si-H stretching vibration in the molecular structure of HMQ [24]. In addition, the sharp peaks at 1418, 1260, and 841 cm −1 are ascribed to the characteristic absorption peaks of Si-CH 3 , while the peak located at 1080 cm −1 is a characteristic symmetric stretching absorption peak of Si-O-Si. These indicate that HMQ has been synthesized successfully [25]. In the curve of PBMQ, the broad peak at 3550 cm −1 corresponds to the stretching vibration of phenol hydroxyl. The characteristic absorption peaks at 3060 and 3010 cm −1 are ascribed to the stretching vibration of the C-H group on phenyl [26], while the peaks at 1610 and 1520 cm −1 are C-C stretching vibration of benzene. The peak at 1370 cm −1 corresponds to C-H in C-CH 3 , which was introduced from eugenol. Moreover, the characteristic absorption peak of Si-H at 2140 cm −1 has disappeared, and the symmetric stretching vibrations of C-H on Si-CH 2 formed during the hydrosilylation at 2850 cm −1 were found. These indicate that BPMQ has been prepared successfully through the hydrosilylation reaction of HMQ and eugenol. The structures of HMQ and BPMQ were characterized by FT-IR. As shown in Figure 2, in the curve of HMQ, the sharp peaks at 2960 and 2903 cm −1 are assigned to the stretching vibration of C-H group on Si-CH3. The strong absorption peak at 2140 cm −1 is attributed to Si-H stretching vibration in the molecular structure of HMQ [24]. In addition, the sharp peaks at 1418, 1260, and 841 cm −1 are ascribed to the characteristic absorption peaks of Si-CH3, while the peak located at 1080 cm −1 is a characteristic symmetric stretching absorption peak of Si-O-Si. These indicate that HMQ has been synthesized successfully [25]. In the curve of PBMQ, the broad peak at 3550 cm −1 corresponds to the stretching vibration of phenol hydroxyl. The characteristic absorption peaks at 3060 and 3010 cm −1 are ascribed to the stretching vibration of the C-H group on phenyl [26], while the peaks at 1610 and 1520 cm −1 are C-C stretching vibration of benzene. The peak at 1370 cm −1 corresponds to C-H in C-CH3, which was introduced from eugenol. Moreover, the characteristic absorption peak of Si-H at 2140 cm −1 has disappeared, and the symmetric stretching vibrations of C-H on Si-CH2 formed during the hydrosilylation at 2850 cm −1 were found. These indicate that BPMQ has been prepared successfully through the hydrosilylation reaction of HMQ and eugenol. The molecular formulas of HMQ and BPMQ and 1 H NMR spectra of HMQ and BPMQ are shown in Figure 2. In the 1 H NMR spectra curve of HMQ, only two chemical shifts of protons can be observed.
The characteristic peaks at about 0-0.15 ppm corresponded to the protons on -CH 3 of terminal M units, and the signal at 4.71 ppm was attributed to the proton peaks of Si-H. Compared with HMQ, except for the characteristic signals of protons on -CH 3 , it multiple different signals of proton peaks are seen in the 1H NMR spectra of BPMQ. The chemical shifts at 6.71, 6.53, and 6.17 ppm belong to the chemical shifts of protons in phenyl region [27]. The signals at about 5.39 and 3.72 ppm are the characteristic absorption peaks for phenol hydroxyl and ortho-methoxy of eugenol, respectively [28]. In addition, the chemical shift at 0.42-0.63 ppm was assigned to the proton peaks of C-CH 3 , and the characteristic peak at 1.70-1.79 ppm corresponded to the proton of tertiary carbon (C-H). However, strong signals for the protons of the Si-CH 2 CH 2 CH 2 -Si groups were also observed at chemical shifts of 1.01-1.13, 1.41-1.55, and 2.19-2.25 ppm, which indicated that the hydrosilylation of HMQ and eugenol was carried out as a result of α-addition and β-addition products, dominated by β-addition [8,29]. Meanwhile, the chemical shifts of Si-H occurring at 4~5 ppm and vinyl of eugenol at 5~6 ppm were not found. This proved that the reaction was complete and BPMQ was prepared successfully.
The structure of HMQ and BPMQ were also determined by 13 C NMR spectra, as shown in Figure 3c; in the curve of HMQ, only a single chemical shift was found at about −1~0.8 ppm, assigned to the carbon atoms of silicon methyl. In the curve of BPMQ, the expected chemical signals for carbon atoms in the phenyl moiety corresponded to about 109~144 ppm. The characteristic peak for ortho-methoxy of eugenol was at 54 ppm, the carbon atoms' characteristic absorption peaks of methyl in tertiary carbon (CH 3 ) were at about 13 ppm, and characteristic signals of the tertiary carbon (CH) at 16 ppm. In addition, chemical shifts for Si-CH 2 CH 2 CH 2 -Si at 19~20 and 23~24 ppm have also been found. This further illustrated that BPMQ has been synthesized successfully through the hydrosilylation reaction of the Markovnikov and Anti-Markovnikov rule [30]. The molecular formulas of HMQ and BPMQ and 1 H NMR spectra of HMQ and BPMQ are shown in Figure 2. In the 1 H NMR spectra curve of HMQ, only two chemical shifts of protons can be observed. The characteristic peaks at about 0-0.15 ppm corresponded to the protons on -CH3 of terminal M units, and the signal at 4.71 ppm was attributed to the proton peaks of Si-H. Compared with HMQ, except for the characteristic signals of protons on -CH3, it multiple different signals of proton peaks are seen in the 1H NMR spectra of BPMQ. The chemical shifts at 6.71, 6.53, and 6.17 ppm belong to the chemical shifts of protons in phenyl region [27]. The signals at about 5.39 and 3.72 ppm are the characteristic absorption peaks for phenol hydroxyl and ortho-methoxy of eugenol, respectively [28]. In addition, the chemical shift at 0.42-0.63 ppm was assigned to the proton peaks of C-CH3, and the characteristic peak at 1.70-1.79 ppm corresponded to the proton of tertiary carbon (C-H). However, strong signals for the protons of the Si-CH2CH2CH2-Si groups were also observed at chemical shifts of 1.01-1.13, 1.41-1.55, and 2.19-2.25 ppm, which indicated that the hydrosilylation of HMQ and eugenol was carried out as a result of α-addition and β-addition products, dominated by β-addition [8,29]. Meanwhile, the chemical shifts of Si-H occurring at 4~5 ppm and vinyl of eugenol at 5~6 ppm were not found. This proved that the reaction was complete and BPMQ was prepared successfully.
The structure of HMQ and BPMQ were also determined by 13 C NMR spectra, as shown in Figure 3c; in the curve of HMQ, only a single chemical shift was found at about −1~0.8 ppm, assigned to the carbon atoms of silicon methyl. In the curve of BPMQ, the expected chemical signals for carbon atoms in the phenyl moiety corresponded to about 109~144 ppm. The characteristic peak for ortho-methoxy of eugenol was at 54 ppm, the carbon atoms' characteristic absorption peaks of methyl in tertiary carbon (CH3) were at about 13 ppm, and characteristic signals of the tertiary carbon (CH) at 16 ppm. In addition, chemical shifts for Si-CH2CH2CH2-Si at 19~20 and 23~24 ppm have also been found. This further illustrated that BPMQ has been synthesized successfully through the hydrosilylation reaction of the Markovnikov and Anti-Markovnikov rule [30].  13 C NMR spectrum of HMQ and BPMQ. 29 Si NMR spectra were a useful tool to reflect the skeleton structure of the organic silicone polymer. Figure 4 presents the 29 Si NMR spectra of HMQ and BPMQ. In the curve of HMQ, the signal at about -110 ppm corresponds to the Q (SiO4/2) units. Chemical shifts at about −5.0 and 11.8 ppm were assigned to M(R3SiO1/2) and H M(R1R2SiO1/2) units, respectively [31]. Compared with the 29 SiNMR spectra curve of HMQ, the characteristic peak for H M(R1R2SiO1/2) units at about −5 ppm  13 C NMR spectrum of HMQ and BPMQ. 29 Si NMR spectra were a useful tool to reflect the skeleton structure of the organic silicone polymer. Figure 4 presents the 29 Si NMR spectra of HMQ and BPMQ. In the curve of HMQ, the signal at about -110 ppm corresponds to the Q (SiO 4/2 ) units. Chemical shifts at about −5.0 and 11.8 ppm were assigned to M(R 3 SiO 1/2 ) and H M(R 1 R 2 SiO 1/2 ) units, respectively [31]. Compared with the 29 SiNMR spectra curve of HMQ, the characteristic peak for H M(R 1 R 2 SiO 1/2 ) units at about −5 ppm could not be found, and peaks at about 15 ppm for Si-CH 2 CH 2 CH 2 -Si of M units appeared, which indicated that Si-H in HMQ had been consumed completely and the BPMQ was prepared successfully.   The molecular weights of HMQ and BPMQ are listed in Table 1. The weight average molecular weights of HMQ and BPMQ were 2000 and 2600 dal.mol −1 , respectively. The average molecular weights of HMQ and BPMQ were 1400 and 1800 dal.mol −1 , respectively, with a similar polydispersity index of 1.43 and 1.44. Obviously, the molecular weights of BPMQ were slightly higher than those of HMQ, which can be attributed to the introduction of the eugenol micromolecule. Moreover, this slight change in molecular weights indicates that side reactions such as self-condensation of HMQ or dehydrogenation of HMQ and BPMQ barely existed in the system.

Viscosity Analysis
The effect of the introduction of eugenol was investigated by a viscosity analysis of HMQ and BPMQ. As depicted in Table 1, the dynamic viscosity of BPMQ was 455 mpa.s at room temperature, which was a little higher than that at 440 mpa.s for HMQ. The viscosity of polymers is related to their molecular weight, so a higher molecular weight generally results in higher viscosity under the same condition [32]. This slight viscosity increase for the polymer reflects a limited increase in their molecular weight and almost no side effects in this reaction.

Thermal Property
The weight loss of HMQ and BPMQ was measured to evaluate the effect of eugenol on enhancing the thermal stability of BPMQ. Figure 5 presents the TG and DTG curves of the samples. Two degradation stages were observed in the overall thermal degradation of HMQ in nitrogen. The first stage is likely due to the degradation of organic groups (M units) of HMQ at the range of 100-410 °C. The temperature at the maximum degradation rate of HMQ in this step was 250 °C. The second degradation stage of HMQ was in the temperature range of 410-600 °C, which could be attributed to the decomposition of the Si-O network structure in Q units of HMQ [4,32]. HMQ has almost finished degradation when the temperature reaches 600 °C, and possesses residual yields of 2.0%. Three degradation steps were found in the overall thermal decomposition of BPMQ. The first step is mainly due to the degradation of some smaller molecules, such as toluene reagent, small The molecular weights of HMQ and BPMQ are listed in Table 1. The weight average molecular weights of HMQ and BPMQ were 2000 and 2600 dal.mol −1 , respectively. The average molecular weights of HMQ and BPMQ were 1400 and 1800 dal.mol −1 , respectively, with a similar polydispersity index of 1.43 and 1.44. Obviously, the molecular weights of BPMQ were slightly higher than those of HMQ, which can be attributed to the introduction of the eugenol micromolecule. Moreover, this slight change in molecular weights indicates that side reactions such as self-condensation of HMQ or dehydrogenation of HMQ and BPMQ barely existed in the system.

Viscosity Analysis
The effect of the introduction of eugenol was investigated by a viscosity analysis of HMQ and BPMQ. As depicted in Table 1, the dynamic viscosity of BPMQ was 455 mpa.s at room temperature, which was a little higher than that at 440 mpa.s for HMQ. The viscosity of polymers is related to their molecular weight, so a higher molecular weight generally results in higher viscosity under the same condition [32]. This slight viscosity increase for the polymer reflects a limited increase in their molecular weight and almost no side effects in this reaction.

Thermal Property
The weight loss of HMQ and BPMQ was measured to evaluate the effect of eugenol on enhancing the thermal stability of BPMQ. Figure 5 presents the TG and DTG curves of the samples. Two degradation stages were observed in the overall thermal degradation of HMQ in nitrogen. The first stage is likely due to the degradation of organic groups (M units) of HMQ at the range of 100-410 • C. The temperature at the maximum degradation rate of HMQ in this step was 250 • C. The second degradation stage of HMQ was in the temperature range of 410-600 • C, which could be attributed to the decomposition of the Si-O network structure in Q units of HMQ [4,32]. HMQ has almost finished degradation when the temperature reaches 600 • C, and possesses residual yields of 2.0%. Three degradation steps were found in the overall thermal decomposition of BPMQ. The first step is mainly due to the degradation of some smaller molecules, such as toluene reagent, small amounts of volatile water, and residual eugenol at the range of 50-220 • C. The second decomposition step of BPMQ can be observed at the temperature range of 220-490 • C, and is also mainly ascribed to the degradation of M units in BPMQ. Meanwhile, the temperature at the maximum degradation rate of BPMQ in this stage was 422.5 • C, which was far higher than that (250 • C) for HMQ. This is likely due to the introduction of a benzene structure in the eugenol [33]. Moreover, BPMQ has almost finished degradation at about 600 • C, similar to the temperature at the maximum degradation of HMQ. This demonstrates that HMQ and BPMQ have the similar structure. Simultaneously, the residual yields of BPMQ at 600 • C was 28.3%, which was about 26.3% higher than that of HMQ. It was concluded that the introduction of eugenol can enhance the thermal stability of HMQ. amounts of volatile water, and residual eugenol at the range of 50-220 °C. The second decomposition step of BPMQ can be observed at the temperature range of 220-490 °C, and is also mainly ascribed to the degradation of M units in BPMQ. Meanwhile, the temperature at the maximum degradation rate of BPMQ in this stage was 422.5 °C , which was far higher than that (250 °C) for HMQ. This is likely due to the introduction of a benzene structure in the eugenol [33]. Moreover, BPMQ has almost finished degradation at about 600 °C, similar to the temperature at the maximum degradation of HMQ. This demonstrates that HMQ and BPMQ have the similar structure. Simultaneously, the residual yields of BPMQ at 600 °C was 28.3%, which was about 26.3% higher than that of HMQ. It was concluded that the introduction of eugenol can enhance the thermal stability of HMQ.

Antibacterial Property
The antimicrobial activity is displayed in Figure 6, showing the blank group (a), HMQ (b), eugenol (c) and BPMQ (d). In the experiment, the antimicrobial activity was assessed by choosing Escherichia coli as a template and agar as the nutrient solution. In order to more intuitively assess the antimicrobial effect of HMQ, PBMQ, and eugenol, the same mass fraction of HMQ and BPMQ was added to the agar plates; simultaneously, we kept the amount of eugenol identical to that in BPMQ. It can be observed that the agar culture dish of the blank experiment was almost completely covered in Escherichia coli colonies after incubation for one day (Figure 6(a)). Similarly, the agar culture dish with the presence of 20 wt % HMQ was also completely covered in Escherichia coli colonies after 24 h (Figure 6 (b)), which illustrated that HMQ has almost no antimicrobial activity. In addition, there were almost no visible Escherichia coli colonies on the culture dish containing 20 wt % eugenol (Figure 6(c)), which indicates that eugenol exhibits superior antibiotic activity. Compared with Figure 6(a), 6(d), the number of Escherichia coli colonies in the agar culture dish containing the same amount of BPMQ was far lower than in the control group and the one with HMQ. This shows that the introduction of eugenol enhanced the antimicrobial activity of HMQ due to the unique structure (containing phenolic hydroxyl and an ortho-methoxy group) of eugenol [34,35]. Moreover, according to some reports, the antibacterial activity of bio-phenol siloxane may be related to the electrical, hydrophobic, and spatial network structure [12,36]. The result shows that BPMQ had favorable autonomic antimicrobial activity.

Antibacterial Property
The antimicrobial activity is displayed in Figure 6, showing the blank group (a), HMQ (b), eugenol (c) and BPMQ (d). In the experiment, the antimicrobial activity was assessed by choosing Escherichia coli as a template and agar as the nutrient solution. In order to more intuitively assess the antimicrobial effect of HMQ, PBMQ, and eugenol, the same mass fraction of HMQ and BPMQ was added to the agar plates; simultaneously, we kept the amount of eugenol identical to that in BPMQ. It can be observed that the agar culture dish of the blank experiment was almost completely covered in Escherichia coli colonies after incubation for one day (Figure 6a). Similarly, the agar culture dish with the presence of 20 wt % HMQ was also completely covered in Escherichia coli colonies after 24 h (Figure 6b), which illustrated that HMQ has almost no antimicrobial activity. In addition, there were almost no visible Escherichia coli colonies on the culture dish containing 20 wt % eugenol (Figure 6c), which indicates that eugenol exhibits superior antibiotic activity. Compared with Figure 6a,d, the number of Escherichia coli colonies in the agar culture dish containing the same amount of BPMQ was far lower than in the control group and the one with HMQ. This shows that the introduction of eugenol enhanced the antimicrobial activity of HMQ due to the unique structure (containing phenolic hydroxyl and an ortho-methoxy group) of eugenol [34,35]. Moreover, according to some reports, the antibacterial activity of bio-phenol siloxane may be related to the electrical, hydrophobic, and spatial network structure [12,36]. The result shows that BPMQ had favorable autonomic antimicrobial activity.

Conclusions
Bio-Phenol MQ silicone resin was prepared through a hydrosilylation reaction of hydrogen containing MQ silicone resin and eugenol. Compared to the unmodified MQ silicone resin, the thermal stability of this modified polymer improved significantly because of the introduction of phenyl in eugenol. The temperature at the maximum degradation rate rose from 250 • C to 422.5 • C, and the residual yields at 600 • C were increased from 2.0% to 28.3%. In addition, its antibacterial property against Escherichia coli was also enhanced markedly without adding other antimicrobial agents. The bio-phenol MQ silicone resin had autonomic antimicrobial activity due to special functional groups in the structure of eugenol. This modified polymer is expected to be applied to pressure-sensitive adhesives and silicone rubber products for the biomedical field because of its reinforcing effect and antioxidant quality.