Preparation, Characterization, and Flame Retardancy of Novel Rosin

Article pubs.acs.org/IECR

Preparation, Characterization, and Flame Retardancy of Novel RosinBased Siloxane Epoxy Resins Lianli Deng,†,‡ Minmin Shen,*,† Jing Yu,†,‡ Kun Wu,† and Chengyong Ha† †

Key Laboratory of Cellulose and Lignocellulosics Chemistry, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou, Guangdong, P. R. of China ‡ Graduate School of Chinese Academy of Sciences, Beijing, P. R. of China ABSTRACT: A series of novel rosin-based siloxane epoxy resins (AESE copolymers) were prepared by the reaction of ethylene glycol diglycidyl ether modified acrylpimaric acid (AP-EGDE) with poly(methylphenylsiloxane). The chemical structures of the produced epoxy resins were determined by FTIR, 1H-NMR, 13C-NMR, and epoxy equivalent weight (EEW) test. After modification, the tensile strengths of AESE (20−40) are slightly lower than that of AP-EGDE; however their breaking elongations are higher than that of AP-EGDE remarkably. TGA results reveal that the thermal stability of AESE serials is better than that of AP-EGDE due to the formation of a protective residue. The char residue of AESE increases at 700 °C with its silicon content increases. Nevertheless, there is a peak LOI value for AESE when its silicon content is 30%. Moreover, the chemical structures of char at the end of the LOI test were analyzed by FTIR. The results confirmed the formation of the protective residue. To enhance flame retardance, several approaches have been used. Traditionally, halogen-containing monomers and oligomers are used to meet the requirements in flame-retardant systems. However, halogen flame retardants can release toxic and corrosive gases as well as carcinogenic chemicals during combustion. Therefore, phosphorus-containing compounds are mostly used for replacing halogen-containing compounds. The flame-retardants containing phosphorus are low toxicity, in the case of fire, without dioxin and halogen acids, as well with low evolution of smoke. Nevertheless, the poly(phosphoric acid) formed during the thermal degradation may cause the erosion of metallic equipment in the fire locale. Consequently, some industries are cautious to apply phosphorus-containing flameretardant materials. Another way to improve the flame retardancy of polymers is the introduction of silicon content. The silicon-containing compounds show a slow burning rate without a flaming drip and no emissions of toxic smoke, and thus are regarded as environmentally friendly flame-retardants.16−19 It has been reported that incorporation of thermoplastic poly(methylphenylsiloxane) (PMPS) into the structure of DGEBA epoxy can improve not only the flexibility but also thermal stability and flame retardancy of the resins.20,21 To enhance the flame retardancy of rosin-based resin, in this study, PMPS was incorporated into rosin-based epoxy by the reaction of ethylene glycol diglycidyl ether-modified acrylpimaric acid (AP-EGDE) with siloxane. The mechanical strength, thermal stability, and flame retardancy of the resins were studied. Moreover, the chemical structure of char for the resin at the end of LOI test was analyzed by FTIR.

1. INTRODUCTION Rosin is an abundantly available natural product. The characteristic fused ring structure of rosin acids is analogous to that of some cycloaliphatic or aromatic compounds in rigidity, and makes rosin and its derivatives potential substitutes for current petroleum-based compounds in polymers. Thus, rosin has received increasing attention as a raw material for the preparation of some new polymers with specific chemical structures and valuable properties.1−9 In recent years, more and more efforts have been made to synthesize biobased epoxy from rosin and its derivatives. In Atta’s studies, epoxy binders were obtained from a reaction of epichlorohydrin with condensed products of rosin acid formaldehyde resin and kenotic adducts of rosin acid. 10,11 However, detailed information on their mechanical and thermal properties, which is the important data for new materials, was not given in those studies. Liu et al. prepared epoxy and curing agents from rosin-maleic anhydride and its derivatives such as rosinmaleic anhydride imidodicarboxylic acid (RMID), glycidyl ester of RMID.12−14 In his studies, the introduction of the hydrogenated phenanthrene ring into an epoxy or a curing agent molecule resulted in increases in glass transition temperature (Tg) and modulus at the expense of toughness. To overcome this shortcoming, Wang et al., in the same lab as Liu, incorporated a flexible chain segment into rosin-based anhydride,15 which led to an increase in the distance between cross-links in the cured resins. Consequently, the cured resin exhibits a decreased cross-link density, resulting in an increase in flexibility. The results from these studies suggested that rosin could be used as a major feedstock in place of aromatic or cycloaliphatic compounds for the synthesis of both epoxy resins and curing agents. However, to our best knowledge, all of the rosin-based epoxy resins are easily flammable and thus their applications in many fields are restricted. © 2012 American Chemical Society

Received: Revised: Accepted: Published: 8178

June 25, 2011 March 9, 2012 March 10, 2012 March 10, 2012 dx.doi.org/10.1021/ie201364q | Ind. Eng. Chem. Res. 2012, 51, 8178−8184

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2. EXPERIMENTAL SECTION 2.1. Materials. Acrylpimaric acid (APA) [acid number 292 mg KOH/g, 99%] was purified from acrylic-modified rosin (ARA) according to literature.8 Ethylene glycol diglycidyl ether (EGDE) with an epoxy equivalent weight of 136−137 g/mol, was purchased from Shanghai Shengying Keji Co. Methoxyfunctionalized silicone resin (DC-3074) (Mw = 1400; methoxy content = 18 wt %) was a gift from Dow Corning (Shanghai) Management Co., Ltd. Tetraisopropyl titanate (TPT) was supplied by Dorf Ketal Chemical. Methylhexahydrophthalic anhydride (MeHHPA) was purchased from Puyang Huicheng Chemical. Solvents applied in this study were all analytical grade and used directly. 2.2. Preparation of Epoxy Resins. 2.2.1. AP-EGDE, the Copolymers of Ethylene Glycol Diglycidyl Ether Modified Acrylpimaric Acid (Scheme 1). A 500-mL three-neck round-

Scheme 2. Preparation of Siloxane-Modified AP-EGDE Epoxy Resins

Scheme 1. Esterification Reaction of APA and EGDE Table 1. Epoxy Resins Produced from AP-EGDE

a

sample

AP-EGDE

AESE20

AESE30

AESE40

AESE50

AP-EGDE (%) DC-3074 (%) yield (%)

100 0

80 20 89

70 30 88

60 40 87

50 50 81a

After standing for 20 days, the produced resin conclude two layers.

2.3. Curing Procedure. Epoxy and curing agent (MeHHPA) were mixed together with 0.5 wt % (based on the weight of epoxy and curing agent) triethylamine as catalyst. The reactant mixture was transferred into two different molds for tensile and LOI tests. The curing reaction was conducted at 120 °C for 3 h then 160 °C for 3 h. The cured samples were carefully removed from the mold and used for tensile, thermal, and LOI tests. 2.4. Measurements. Infrared spectra of the prepared products were recorded in polymer/KBr pellets using an RFX65A (Analect) FTIR instrument. 1 H-NMR and 13C-NMR spectra were recorded on a DRX400 (Bruker Company, Germany) with CDCl3 solvent. The hydrochloric acid/acetone method was used to determine the epoxy equivalent weights (EEW). Samples weighing 1−1.5 g, sufficient to determine the EEW value, were used for this purpose. Tensile test was measured according to ISO 3167:1993. The apparatus used was an electric universal testing machine CMT7503 (MTS Systems Corporation). The shape of specimens used for the test was dumbbell with 25 mm radius of dimensions 75 × 3 × 5−10 mm. The tests were conducted at a speed of 5 mm/min. LOI was measured according to ISO4589. The apparatus used was a JF-3 oxygen index meter (Jiangning Analysis Instrument Company, China). Thermogravimetric analysis (TGA) was performed by a Perkin-Elmer TGA-6 Thermogravimetric Analyzer under air atmosphere. About 3 mg of samples were weighed into an alumina crucible and the profiles were recorded from 50 to 700 °C at a heating rate of 10 °C/min.

bottomed flask, equipped with a reflux condenser, a mechanical stirrer, and a thermometer, was charged with EGDE (156 g, 1.15 mol of the epoxy group), APA (100 g, 0.52 mol of the carboxyl group), and 0.690 g (0.3 wt % on the basis of the total weight of EGDE and APA) of triethylamine. The acidity of the system was monitored by titration with KOH ethanol solution. The temperature of the system was maintained at 110 °C until the acid number was less than 0.5 mg KOH/g. Purification of the products was carried out by washing the product with warm water for the removal of unreacted EGDE. The filtrate was then heated at 80 °C for 3 h to remove the residual water in a vacuum oven. 2.2.2. AESE, the Composites of Siloxane-Modified APEGDE (Scheme 2). In a four-necked flask (250 mL) equipped with a reflux condenser, a mechanical stirrer, and a thermometer, 70 g of AP-EGDE was heated to 120 °C. Then 30 g of siloxane oligomer (DC-3074) was added through a dropping funnel and 0.5% of TPT (based on the weight of siloxane) was added as catalyst. The reaction time was determined by the measurement of the epoxy equivalent weight (EEW). Purification of the products was carried out by washing the product with petroleum ether for the removal of unreacted DC-3074. The filtrate was then heated at 80 °C for 3 h to remove the residual water in a vacuum oven. The doses of materials in synthesis of AESE copolymers are listed in Table1. 2.2.3. Preparation of PAESE30. Seventy grams of AP-EGDE, 30 g of DC3074, and 0.5 g of triethylamine was stirred for 10 min at room temperature.

3. RESULTS AND DISCUSSION 3.1. Characterization of AP-EGDE. Figure 1 gives the FTIR spectra of APA and AP-EGDE. The disappearance of 8179

dx.doi.org/10.1021/ie201364q | Ind. Eng. Chem. Res. 2012, 51, 8178−8184

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3.2. Characterization of AESE Copolymers. Figure 4 gives the FTIR spectra of DC3074 and AESE copolymers. For AESE, the disappearance of the peak at 2846.9 cm−1 indicates the complete hydrolysis of Si−O−Me groups. The presence of epoxy groups in AESE is confirmed by the absorption bands at 914 cm−1. In Figure 2b, the diminishing of the group of CH3O−Si at 3.41 ppm can be found. At the same time, the appearance of the vital groups of CH3−Si at 0.07 ppm and Si− phenyl at 7.60, 7.33 ppm is observed. Furthermore, in Figure 3b, the disappearance of the group of CH3O−Si at 50.2 ppm is noted. At the same time, the appearance of the vital groups of CH3−Si at 0.85 ppm and Si−phenyl at 133.7, 129.8, and 127.3 ppm can be seen. These indicate the occurrence of the polycondensation reaction. The measured EEW values of the synthesized AESE copolymers are listed in Table2. The calculated values are based on the weight ratios and the experimental data agree quite well.22 This further confirms the polycondensation without opening of the epoxy ring. 3.3. Mechanical Properties of Epoxy Resins. As shown in Table 3, after chemical modification, the strength of copolymers AESE (20−40) is slightly lower than that of the unmodified resin AP-EGDE; however, its breaking elongations increase rapidly. The strength (MPa) of copolymers from 10.35 to 12.87 is observed for the increasing content of siloxane from 20 to 40 due to the increase of cross-linking density. On further increasing PMPS to 50 wt %, however, the strength value decreases due to the poor compatibility between PMPS and rosin-resin. On the other hand, the strength value of physical modification PAESE30 system is far lower than that of AESE30. This further demonstrates the transesterification of AP-EGDE with PMPS. Figure 5 shows representative tensile stress−strain curves for the epoxy resins cured with MeHHPA at different epoxy/ anhydride equivalent ratios. For the AP-EGDE system, at the epoxy/anhydride equivalent ratio of 1:1, the cured epoxy resins exhibit clear stress yield, followed by shear yielding. On further increasing the epoxy/anhydride ratio to 1:2, however, the cured resin does not display a stress yield although the tensile

Figure 1. FTIR spectra of EGDE, APA, and AP-EGDE.

characteristic peak for COOH group of APA at 2661 and 1698 cm−1 can be found. At the same time, the appearance of signal for ester groups at 1727 cm−1 (AP-EGDE) was noted. The results show that the reaction between APA and EGDE occurred. Moreover, the presence of epoxy group is confirmed by the absorption bands observed at 1256, 912, and 840 cm−1. The 1H NMR of AP-EGDE is shown in Figure 2a. The peak at 10−12 ppm, characteristic of COOH groups, disappeared. The oxirane group shows its individual proton at 2.79 and 2.61 ppm (2H) for O−CH2 and 3.16 ppm (1H) for O−CH of the oxirane ring. In Figure 3a, the appearance of the resonance signals for ester group at 179.70 and 176.14 ppm are observed. At the same time, the disappearance of the resonance signals for COOH group at 186.22 and 184.94 ppm8 is noted. The results further support the formation of the AP-EGDE copolymer. Furthermore, the presence of the epoxy group in structure of AP-EGDE is verified by the resonance signals at 44.99 and 51.63 ppm. The acid number was less than 0.5 mgKOH/g at the end of the reaction. This can also verify the esterification reaction of APA and EGDE. The measured EEW value of AP-EGDE is 481 g/mol and its calculated value is 464 g/mol. The calculated value and the experimental data agree quite well. This further confirms the esterification reaction of APA and EGDE.

Figure 2. 1H-NMR spectra of (a) AP-EGDE and (b) AESE30. 8180

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Figure 3. 13C-NMR spectra of (a) AP-EGDE and (b) AESE30.

Figure 5. Tensile properties of the various epoxy systems.

Figure 4. FTIR spectra of AP-EGDE, DC-3074, and AESE copolymers.

strength is rapidly increased. This is caused by the excess hydroxyl group of the AP-EGDE. At the epoxy/anhydride equivalent ratio of 1:2, the excess hydroxyl can also react with MeHHPA. As a result, the tensile strength for the cure system increases due to its cross-linking density increase. However, in the system of the AESE, most hydroxyl of AP-EGDE reacted with methoxy group of PMPS and there left few hydroxyls reacted with MeHHPA. The cured resin of AESE30 exhibits a weak strength when the epoxy/anhydride ratio is 2:1. 3.4. Thermal Stability of Epoxy Resins. The thermal behavior of the polymers was evaluated by TGA. TG curves of DC-3074, AP-EGDE, AP-EGDE2, AESE20, AESE30, AESE40, and AESE50 under air atmosphere are presented in Figure 6. The onset degradation temperature of samples which was evaluated by the temperature of 5 wt % weight loss (T−5%) and the solid residue left at 700 °C were obtained from the TG curve. The temperature of the maximum weight loss rate (Tmax) of samples was obtained from the DTG curve. These data are shown in Table 4. The temperature of 10, 15, 20,..., and to 95 wt % weight loss can be also obtained from the TG curve of different samples, and then temperature differential of degradation (ΔT) between modified resins and AP-EGDE at the same weight loss can be obtained. As a result, the relation figure of ΔT and weight loss (WL) is concluded (Figure 7).

Table 2. EEW Values of AESE sample EEW (calculated value)a (g/mol) EEW (experimental value) (g/mol) a

APEGDE

AESE20

AESE30

AESE40

AESE50

481

601

687

801

962

481

645

714

952

1190

Based on the EEW of AP-EGDE.

Table 3. Mechanical Properties of Cured Epoxy Resins

sample

epoxy/ curing agenta

AP-EGDE AESE20 AESE30 AESE40 AESE50 PAESE30 AP-EGDE2 AESE302

1:1 1:1 1:1 1:1 1:1 1:1 1:2 1:2

a

tensile strength (MPa) 15.6 10.4 11.4 12.9 3.1 1.16 29.6 1.64

± ± ± ± ± ± ± ±

0.5 0.7 0.8 0.8 0.3 0.1 0.4 0.1

breaking elongation (%) 35.3 129.4 68.7 53.9 93.44 89.5 11.4 244.3

± ± ± ± ± ± ± ±

4.2 10.1 4.9 5.1 8.9 6.3 2.2 10.2

breaking strength (MPa) 14.1 9.4 10.3 11.6 2.1 0.6 29.6 1.36

± ± ± ± ± ± ± ±

0.7 0.7 0.5 0.6 0.2 0.1 0.4 0.2

Epoxy group/anhydride group. 8181

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Figure 6. TGA (a) and DTG (b) curves for the samples.

T−5% increases from 301.4 to 325.9 °C. Nevertheless, further increasing the content of PMPS to 50%, T−5% for AESE50 (315.6 °C) is lower than that of AESE40 due to the poor compatibility between PMPS and rosin-resin. The result agrees on the tensile test. Due to the transesterification of AP-EGDE with PMPS, the chemically modified system (AESE30) has higher cross-link density than the physically modified system (PAESE30). Therefore, it can be also observed in Table4 that T−5% of AESE30 is higher than that of PAESE30. With the increase of weight loss, it can be observed in Figure 7 that temperature differential of degradation (ΔT) between modified resins and AP-EGDE reduces. This indicates that PMPS, which could decompose at a low temperature, is decomposing. It is reported that the composition of siloxane at lower temperature can form a silicone-containing group. In the presence of silicone-containing group, a protective residue was formed and can act as a thermal insulation with excellent thermal stability.8 As a result, further increasing weight loss, ΔT between modified resins and AP-EGDE enlarges greatly due to the formation of the protective residue. It is also indicated from Figure 7 that the degradation temperature of AESE40, AESE50, and PAESE30 at the low temperature is higher than that of AESE20 and AESE30. The char yield at 700 °C increases from 0% (pure rosin-based resin) to 24.76% (AESE50). The char yield for modified resins increased significantly comparing with the calculated value of residue. This further demonstrates that the introduction of PMPS produces a protective layer and improves the thermal degradation. 3.5. Limiting Oxygen Index (LOI) Measurement of Epoxy Resins. Figure 8 shows the LOI value of the cured systems. It can be seen that the introduction of the siloxane leads to the increase of the LOI values of cured samples. Moreover the LOI values of AESE copolymers (chemically modified) are higher than that of PAESE30 (physically modified). The LOI value of AESE30 (30.2%) is the highest among the samples. It is interesting that char yields for AESE50 and AESE40 are more than that for AESE30, but the LOI values of AESE40 and AESE50 are lower than that of AESE30. The reason may be that the decomposition temperature at low temperature for AESE40 and AESE50 is too high to form a thick residue which can act as a protective layer. 3.6. Analysis of the Char Residue. FTIR spectra of char residue of AESE30 and PAESE30 are shown in Figure 9. Compared with AESE30 cured system, the absorption of Si−O at the range of 1000 to 1200 cm−1 is still strong, while the other absorptions such as C−H, CO, Si−phenyl are diminishing in Figure 9b and 9c. In other words, the siloxane-containing group

Table 4. TG and DTG Data of the Cured Systems sample

T−5% (°C)

Tmax (°C)

residue (%) (700 °C)

calculated value of residue (%) (700 °C)a

AP-EGDE AP-EGDE2 DC-3074 AESE20 AESE30 AESE40 AESE50 PAESE30

251.3 276.2 179.8 301.4 303.2 325.9 315.6 294.3

391.6 399.5 324.9 398.5 398.4 402 399.4 411.8

0 0 25.59 8.22 13.36 18.53 24.76 16.2

0 0 25.59 4.19 6.34 8.71 11.21 6.34

a

Based on the residue of DC-3074 and AP-EGDE and the loss of silicon for AESE copolymers is ignored.

Figure 7. Temperature differential of degradation as a function of weight loss.

In Figure 6, it is observed that the siloxane (DC-3074) could decompose at a low temperature. The DTG curve for modified resins shows a similar trend with AP-EGDE in Figure 6b. Moreover, their thermal stability is improved greatly by the introduction of siloxane. In Table 4, the T−5% for modified resins is higher than that of DC-3074 and AP-EGDE. There may be two reasons for this: first, unlike the small molecular siloxane, such as phenyltrimethoxysilane and phenyldimethoxysilane,18,23,24 PMPS segment can absorb more thermal energy and dissipate thermal energy through its flexible siloxane structure.20,23 Thus the T−5% of AESE copolymers is higher than that of pure rosin-based resin. Second, fuse of rosin causes the higher T−5% of modified resins compared with DC3074. The effect of the content of PMPS on T−5% for AESE copolymers has been investigated. With the increase of the content of PMPS from 20% to 40%, 8182

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EGDE. On the other hand, the surface of AESE20 and AESE30 residue is covered with an expanded char network. The residue left by AESE40 and AESE50 is mainly formed of thin black char, and the char is better than that of PAESE30 in protecting the underlying materials. After the burning, AESE20 and AESE30 can form a blacker and thicker char compared with other cured resins.

4. CONCLUSIONS An ethylene glycol diglycidyl ether-modified acrylpimaric acid (AP-EGDE) and PMPS modified AP-EGDE (AESE) were synthesized. The chemical structures were confirmed using 1HNMR, 13C-NMR, and FTIR. The tensile tests indicate the epoxy/anhydride equivalent ratio and the content of silicone could influence the cross-link density of epoxy, and therefore influence the mechanical properties. The mechanical property of AESE40 is the best in the silicone-modified copolymers. It can be found from TGA data that AESE copolymers exhibit excellent thermal stability. The mass of residual char increases with the silicon content. The LOI results suggest that incorporation of silicon enhances the flame retardance. However, the LOI value does not increase with the char yield content. The LOI value of AESE30 is highest (30.2%) among samples. The chemical structure of char at the end of LOI test was analyzed by FTIR. Based on the above results, it can be concluded that AESE can form a protective residue at high temperature or burning which acts as thermal insulation and preventing gas evolution, and achieve ultimate improvement on the thermal stability and flame restardant. These results suggest that resins from rosin, as an abundantly available natural material, could be used as biobased epoxy, and that the application of rosin-based resin is extended by the introduction of siloxane.

Figure 8. LOI values of the cured systems: a, AR-EGDE; b, AREGDE2; c, AESE20; d, AESE30; e, AESE302; f, AESE40; g, AESE50; h, PAESE30.

Figure 9. IR spectra of AESE30 cured system (a), PAESE30 charred layer after combustion (b), and AESE30 charred layer after combustion (c).

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

is retained on the surface during the combustion, while the carbon-containing group is diminished. The above results confirm the formation of the carbon−silicon residue on the surface of the polymer. It is reported that a good char can prevent the heat transfer and flame spread, and thus protect the underlying materials from further burning.25 Photographs of residue chars of AP-EGDE and its modified system at the end of the LOI test are shown in Figure 10. There is almost no residue left at the end of LOI test for pure rosin-resin AP-

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for financial support by grant 2008GA780001 from the State Torch Plan and 2007AA100704 from the State High-tech Research and Development Plans (863 Program).

Figure 10. Residue chars of AP-EGDE and its modified system at the end of LOI test. 8183

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(24) Mercado, L. A.; Reina, J. A.; Galia, M. Flame retardant epoxy resins based on diglycidyloxymethylphenylsilane. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 5580. (25) Wu, K.; Song, L.; Wang, Z. Z.; Hu, Y. Preparation and characterization of double shell microencapsulated ammonium polyphosphate and its flame retardance in polypropylene. J. Polym. Res. 2009, 16, 283.

REFERENCES

(1) Penczek, P.; Matynia, T. Synthesis of glycidyl esters of maleopimaric acid. Rocz. Chem. 1975, 49, 1939. (2) Atta, A. M.; Elsaeed, A. M.; Farag, R. K.; El-Saeed, S. M. Synthesis of unsaturated polyester resins based on rosin acrylic acid adduct for coating applications. React. Funct. Polym. 2007, 67, 549. (3) Atta, A. M.; El-Saeed, S. M.; Farag, R. K. New vinyl ester resins based on rosin for coating applications. React. Funct. Polym. 2006, 66, 1596. (4) Atta, A. M.; Nassar, I. F.; Bedawy, H. M. Unsaturated polyester resins based on rosin maleic anhydride adduct as corrosion protections of steel. React. Funct. Polym. 2007, 67, 617. (5) Bicu, I.; Mustata, F. Polymers from a levopimaric acidacrylonitrile Diels-Alder adduct: Synthesis and characterization. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 6308. (6) Bicu, I.; Mustata, F. Crosslinked polymers from resin acids. Angew. Makromol. Chem. 1996, 234, 91. (7) Bicu, I.; Mustata, F. Ketone derivatives of diels-alder adducts of levopimaric acid with acrylic acid and maleic anhydride: Synthesis, characterization, and polymerization. J. Appl. Polym. Sci. 2004, 92, 2240. (8) Bicu, I.; Mustata, F. Polymers from a levopimaric acid-acrylic acid Diels-Alder adduct: Synthesis and characterization. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 5979. (9) Mustata, F.; Bicu, I. Diels-Alder polymers from resinic acids. J. Polym. Eng. 2005, 25 (3), 217−237. (10) Atta, A. M.; Mansour, R.; Abdou, M. I.; El-Sayed, A. M. Epoxy resins from rosin acids: synthesis and characterization. Polym. Adv. Technol. 2004, 15, 514. (11) Atta, A. M.; Mansour, R.; Abdou, M. I.; El-Sayed, A. M. Synthesis and characterization of tetra-functional epoxy resins from rosin. J. Polym. Res. 2005, 12, 127. (12) Liu, X. Q.; Xin, W. B.; Zhang, J. W. Rosin-based acid anhydrides as alternatives to petrochemical curing agents. Green Chem. 2009, 11, 1018. (13) Liu, X. Q.; Xin, W. B.; Zhang, J. W. Rosin-derived imide-diacids as epoxy curing agents for enhanced performance. Bioresour. Technol. 2010, 101, 2520. (14) Liu, X. Q.; Zhang, J. W. High-performance biobased epoxy derived from rosin. Polym. Int. 2010, 59, 607. (15) Wang, H. H.; Liu, X. Q.; Liu, B.; Zhang, J. W.; Xian, M. Synthesis of rosin-based flexible anhydride-type curing agents and properties of the cured epoxy. Polym. Int. 2009, 58, 1435. (16) Mercado, L. A.; Galia, M.; Reina, J. A. Silicon-containing flame retardant epoxy resins: Synthesis, characterization and properties. Polym. Degrad. Stab. 2006, 91, 2588. (17) Kuan, C. F.; Yen, W. H.; Chen, C. H.; Yuen, S. M.; Kuan, H. C.; Chiang, C. L. Synthesis, characterization, flame retardance and thermal properties of halogen-free expandable graphite/PMMA composites prepared from sol-gel method. Polym. Degrad. Stab. 2008, 93, 1357. (18) Cheng, X. E.; Shi, W. F. UV-curing behavior and properties of tri/di(acryloyloxyethyloxy) phenyl silane used for flame-retardant coatings. Prog. Org. Coat. 2010, 69, 252. (19) Hamdani, S.; Longuet, C.; Perrin, D.; Lopez-Cuesta, J. M.; Ganachaud, F. Flame retardancy of silicone-based materials. Polym. Degrad. Stab. 2009, 94, 465. (20) Lin, S. T.; Huang, S. K. Thermal degradation study of siloxaneAGEBA epocy copolymers. Eur. Polym. J. 1997, 33, 365. (21) Lin, S. T.; Huang, S. K. Synthesis and impact properties of siloxane-DCEBA epoxy copolymers. J. Polym. Sci., Part A: Polym. Chem. 1996, 34, 1907. (22) Lin, S. T.; Huang, S. K. Preparation and structural determination of siloxane-modified sulfone-containing epoxy resins. J. Polym. Sci., Part A: Polym. Chem. 1996, 34, 869. (23) Wang, W. J.; Perng, L. H.; Hsiue, G. H.; Chang, F. C. Characterization and properties of new silicone-containing epoxy resin. Polymer 2000, 41, 6113. 8184

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