嵌段共聚物的合成及其改性環(huán)氧樹脂性能研究

1、嵌段共聚物的合成及其改性環(huán)氧樹脂性能研究 何尚錦,王小兵,郭先芝,石可瑜,杜宗杰,張寶龍*南開大學化學系,天津300071關鍵詞:環(huán)氧樹脂 嵌段共聚物 原子轉移自由基聚合 增韌 CH 3CH COOC 2H 5CH 2CH COOCH 2CH 2CH 2CH 3CH 2C CH 3COOCH 3CH 2C CH 3COOCH 2CH CH 2OBr n x y m a b c d環(huán)氧樹脂具有許多優(yōu)異的化學和機械性能,在電子、汽車和航天航空等工業(yè)得到廣泛的應用。但由于其交聯密度較高,使得固化后環(huán)氧樹脂的沖擊韌性較低。多年來,國內外科研工作者為了提高環(huán)氧樹脂的韌性,進行了大量的卓有成效的工作1-5

2、。本文采用原子轉移自由基聚合方法合成了含有環(huán)氧基團的嵌段共聚物BMG ,聚丙烯酸丁酯-b -聚(甲基丙烯酸甲酯-co -甲基丙烯酸縮水甘油酯,并對其結構進行了表征。在此基礎上,利用動態(tài)力學分析儀(DMA 、沖擊試驗及掃描電鏡對此共聚物改性的環(huán)氧樹脂E-51/DDM 固化體系的性能和形態(tài)結構進行了系統的表征。嵌段共聚物BMG 的合成分為兩步:首先合成大分子引發(fā)劑聚丙烯酸丁酯PBA -Br ,反應在無水無氧條件下進行,引發(fā)劑為2-溴丙酸乙酯,催化劑為溴化亞銅,配體為 2,2-聯吡啶,所使溶劑為苯甲醚。然后以產物PBA -Br 為引發(fā)劑,進一步引發(fā)甲基丙烯酸甲酯(MMA 和甲基丙烯酸縮水甘油酯(GM

3、A共聚,制備了含有環(huán)氧基團的嵌段共聚物BMG ,其結構如圖1所示。Figure 1. Chemical structure of BMG聚合物分子量的計算采用了文獻6中有關PBA 的Mark-Houwink 參數:k=0.000074,a=0.75。從表1中看出,嵌段共聚物的PDI 小于1.4,顯示出聚合反應具有活性聚合的特點。另外,根據嵌段共聚物中各單體相應的1H NMR 特征吸收峰(BA,質子a,4.0ppm ;MMA ,質子b ,3.6ppm ;GMA ,質子c 和d,3.2-2.6ppm的積分面積,可以計算出嵌段共聚物的化學組成,結果列于表1中。為考察嵌段共聚物BMG 對環(huán)氧樹脂的改性

4、效果,本文選擇了環(huán)氧樹脂E-51(環(huán)氧值0.51/4,4-二氨基二苯基甲烷DDM 體系作為研究對象。試樣的固化程序為1h/100o C+2h/160o C 。表2列出了各固化體系的DMA 和沖擊試驗結果。DMA觀察結果表明,各固化體系皆顯示,'和松弛轉變峰。松弛為體系的主轉變,對應于玻璃化轉變,'松弛與由環(huán)氧固化網絡的不完善有關。對于空白體系,出現在低溫的松弛轉變峰是由-CH2CH(OH-CH2N-鏈段引起的7。由于嵌段共聚物中PBA段與環(huán)氧體系不相容,在固化體系中形成相分離,而PBA的玻璃化轉變溫度約為-55o C,因此對于BMG改性體系來說,在-50o C附近出現的寬的吸收

5、峰應為PBA的玻璃化轉變與環(huán)氧體系的松弛轉變的疊加。另外,從表3可見,BMG的加入使得體系的室溫模量稍有降低,而玻璃化溫度則變化不大。為了考察嵌段共聚物的結構與其增韌效果的關系,保持嵌段共聚物的加量不變(每100份E-51加10份BMG,利用沖擊試驗機對各體系的沖擊強度進行了測試,結果列于表2中。從表中數據可以看出,改性劑BMG中PBA鏈段過短或過長,增韌效果均較差,如BMG1,共聚物中的PBA鏈較短,相分離所形成的橡膠顆粒尺寸較小,斷裂過程難以形成空穴而誘發(fā)塑性形變,致使韌性較低。只有當共聚物中PBA與pMMA-co-GMA鏈段長短比例適中(BMG2,BMG5和BMG6,而且GMA含量達到一

6、定的比例,可與環(huán)氧網絡形成較多的交聯點,方可獲得較好的增韌效果。同時,沖擊試驗數據得到了掃描電鏡(SEM觀測結果的證實。從圖2可以看出,未改性體系的斷裂面非常光滑,屬于典型的脆性斷裂。對于BMG1和BMG3改性體系,雖然它們的增韌效果相似,但其斷裂面形態(tài)結構具有很大的差別。由于BMG1中與環(huán)氧樹脂不相容的PBA段較短,相應的SEM照片中未見明顯相分離;而對于BMG3改性體系,相分離形成的橡膠顆粒雖然很明顯,增韌效果不佳可能與界面相互作用力較小有關。BMG5改性體系的斷裂面則較粗糙,體系顯示出較高的沖擊強度。Table 1. Data of block copolymer BMGM(GPC PD

7、I (GPC%Copolymers N PBA N PMMA N PGMA PBA(wtnBMG1 20 84 9 21 8400 - BMG2 47 90 10 37 18500 1.19 BMG3 141 36 5 81 19200 1.13 BMG4 91 15 3 85 18200 1.33 BMG5 91 104 11 49 33800 1.19 BMG6 91 142 18 41 39200 1.25Table 2. Mechanical properties of the cured blends with block copolymersFormulation T (o CE

8、at 20 o C(GPa Impact strength(J/m 2100 g E-51+26 g DDM168.5 3.01 583 100 g E-51+26 g DDM+10 g BMG1166.1 3.42 700 100 g E-51+26 g DDM+10 g BMG2173.5 3.23 1032 100 g E-51+26 g DDM+10 g BMG3162.9 2.68 540 100 g E-51+26 g DDM+10 g BMG4166.6 2.48 600 100 g E-51+26 g DDM+10 g BMG5166.6 2.69 1271 100 g E-5

9、1+26 g DDM+10 g BMG6 165.3 2.78 1091 abc dFigure 2. SEM micrographs of the cured epoxy thermosets modified with block copolymers (a neat, (b BMG1, (c BMG3, and (d BMG5.參考文獻1 A. J. Kinloch, S. J. Shaw, D. A. Tod, D. L. Hunston, Polymer, 1983, 24: 13552 A. Bonnet, J. P. Pascault, H. Sautereau, Macromo

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11、, J. Bai, K. Shi, B. Zhang, Polymer, 2001, 42: 9641Synthesis of Block Copolymers for Modification of Epoxy Thermosets Shangjin He, Xiaobing Wang, Xianzhi Guo, Keyu Shi, Zongjie Du, Baolong Zhang* Department of Chemistry, Nankai University, Tianjin 300071 ABSTRACT: Epoxy resin provides many excellent

12、 properties and is widely utilized in the automotive, electronics, aviation industry. However, the inherent brittleness of the cured network resulting from its high crosslinking density restricted its use as structural materials.Many attempts have been made to overcome the brittleness of the highly

13、cross-linked epoxy networks. In this paper, poly(n-butyl acrylate-b-poly(methyl methacrylate-co-glycidyl methacrylate (BMG diblock copolymers incorporating epoxy-reactive functionality in one block have been synthesized through copper-mediated atom transfer radical polymerization (ATRP in solution s

14、ystem and used as modifiers for model epoxy resin E-51 cured with 4,4-diaminodiphenyl methane (DDM. The polydispersity indices (PDIs of the polymers calculated from GPC traces were found to be small, suggesting the living nature of the polymerization. Properties and morphologies of the modified epox

15、y thermosets were investigated by impact testing machine, dynamic mechanical analysis (DMA and scanning electron microscopy (SEM. The results reveal that the additionof block copolymers leaves the glass transition temperature of the blends relatively unchanged and a little decrease of storage modulus at room temperature. Toughening effect is dependent on the ch