嵌段共聚物的合成及其改性環(huán)氧樹(shù)脂性能研究_圖文

1、嵌段共聚物的合成及其改性環(huán)氧樹(shù)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(kāi)大學(xué)化學(xué)系,天津300071關(guān)鍵詞:環(huán)氧樹(shù)脂 嵌段共聚物 原子轉(zhuǎn)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(shù)脂具有許多優(yōu)異的化學(xué)和機(jī)械性能,在電子、汽車(chē)和航天航空等工業(yè)得到廣泛的應(yīng)用。但由于其交聯(lián)密度較高,使得固化后環(huán)氧樹(shù)脂的沖擊韌性較低。多年來(lái),國(guó)內(nèi)外科研工作者為了提高環(huán)氧樹(shù)脂的韌性,進(jìn)行了大量的卓有成效的工作1-5

2、。本文采用原子轉(zhuǎn)移自由基聚合方法合成了含有環(huán)氧基團(tuán)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(duì)其結(jié)構(gòu)進(jìn)行了表征。在此基礎(chǔ)上,利用動(dòng)態(tài)力學(xué)分析儀(DMA 、沖擊試驗(yàn)及掃描電鏡對(duì)此共聚物改性的環(huán)氧樹(shù)脂E-51/DDM 固化體系的性能和形態(tài)結(jié)構(gòu)進(jìn)行了系統(tǒng)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(yīng)在無(wú)水無(wú)氧條件下進(jìn)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(lián)吡啶,所使溶劑為苯甲醚。然后以產(chǎn)物PBA -Br 為引發(fā)劑,進(jìn)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(tuán)的嵌段共聚物BMG ,其結(jié)構(gòu)如圖1所示。Figure 1. Chemical structure of BMG聚合物分子量的計(jì)算采用了文獻(xiàn)6中有關(guān)PBA 的Mark-Houwink 參數(shù):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(yīng)具有活性聚合的特點(diǎn)。另外,根據(jù)嵌段共聚物中各單體相應(yīng)的1H NMR 特征吸收峰(BA,質(zhì)子a,4.0ppm ;MMA ,質(zhì)子b ,3.6ppm ;GMA ,質(zhì)子c 和d,3.2-2.6ppm的積分面積,可以計(jì)算出嵌段共聚物的化學(xué)組成,結(jié)果列于表1中。為考察嵌段共聚物BMG 對(duì)環(huán)氧樹(shù)脂的改性

4、效果,本文選擇了環(huán)氧樹(shù)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(duì)象。試樣的固化程序?yàn)?h/100o C+2h/160o C 。表2列出了各固化體系的DMA 和沖擊試驗(yàn)結(jié)果。DMA觀察結(jié)果表明,各固化體系皆顯示,和松弛轉(zhuǎn)變峰。松弛為體系的主轉(zhuǎn)變,對(duì)應(yīng)于玻璃化轉(zhuǎn)變,松弛與由環(huán)氧固化網(wǎng)絡(luò)的不完善有關(guān)。對(duì)于空白體系,出現(xiàn)在低溫的松弛轉(zhuǎn)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(zhuǎn)變溫度約為-55o C,因此對(duì)于BMG改性體系來(lái)說(shuō),在-50o C附近出現(xiàn)的寬的吸收峰應(yīng)為PBA的玻璃化

5、轉(zhuǎn)變與環(huán)氧體系的松弛轉(zhuǎn)變的疊加。另外,從表3可見(jiàn),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(jié)構(gòu)與其增韌效果的關(guān)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(yàn)機(jī)對(duì)各體系的沖擊強(qiáng)度進(jìn)行了測(cè)試,結(jié)果列于表2中。從表中數(shù)據(jù)可以看出,改性劑BMG中PBA鏈段過(guò)短或過(guò)長(zhǎng),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(guò)程難以形成空穴而誘發(fā)塑性形變,致使韌性較低。只有當(dāng)共聚物中PBA與pMMA-co-GMA鏈段長(zhǎng)短比例適中(BMG2,BMG5和BMG6,而且GMA含量達(dá)到一定的比例,可與環(huán)氧網(wǎng)

6、絡(luò)形成較多的交聯(lián)點(diǎn),方可獲得較好的增韌效果。同時(shí),沖擊試驗(yàn)數(shù)據(jù)得到了掃描電鏡(SEM觀測(cè)結(jié)果的證實(shí)。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(duì)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(jié)構(gòu)具有很大的差別。由于BMG1中與環(huán)氧樹(shù)脂不相容的PBA段較短,相應(yīng)的SEM照片中未見(jiàn)明顯相分離;而對(duì)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(guān)。BMG5改性體系的斷裂面則較粗糙,體系顯示出較高的沖擊強(qiáng)度。Table 1. Data of block copolymer BMGM(GPC PDI (GPC%Cop

7、olymers 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 at 20 o C(

8、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-51+26 g DDM

9、+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(xiàn)1 A. J. Kinloch, S. J. Shaw, D. A. Tod, D. L. Hunston, Polymer, 1983, 24: 13552 A. Bonnet, J. P. Pascault, H. Sautereau, Macromolecules, 1

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11、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 propertie

12、s 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 cross-link

13、ed 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 system and

14、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 epoxy thermose

15、ts 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 che