E-E-22_接枝共聚物RAFT-PS制備及其對(duì)不同液晶E7含量的PDLC電光性能影響

1、接枝共聚物RAFT-PS制備及其對(duì)不同液晶E7含量的PDLC電光性能影響秦愛林孫振孫碩汪映寒*(四川大學(xué)高分子科學(xué)與工程學(xué)院,高分子材料工程國(guó)家重點(diǎn)實(shí)驗(yàn)室,四川成都610065聚合物分散液晶(PDLC是液晶微滴分散在聚合物基體中所形成的一種新型電光復(fù)合材料。PDLC 電光性能存在的主要問題是驅(qū)動(dòng)電壓偏高、記憶效應(yīng)較強(qiáng)。影響PDLC電光性能的因素包括液晶性質(zhì)、聚合物基體的性質(zhì)、液晶與聚合物基體的相互作用等1。制備聚合物基體時(shí),綜觀所有的聚合方法,活性自由基聚合近年來受科學(xué)工作者們的廣泛關(guān)注,可逆加成-斷裂鏈轉(zhuǎn)移(RAFT聚合、原子轉(zhuǎn)移自由基聚合2(ATRP是活性聚合中的兩種聚合方法,其可聚合單體

2、范圍較廣、高分子設(shè)計(jì)能力強(qiáng)可以合成各種組成和結(jié)構(gòu)的聚合物,如均聚物、嵌段共聚物、梯度共聚物、接枝共聚物、星形聚合物、超支化聚合物等。本研究采用RAFT聚合和ATRP聚合相結(jié)合的方法制備活性接枝共聚物。首先制備接枝大分子RAFT-PS,并將其與丙烯酸甲酯(MA單體、光引發(fā)劑1104及液晶混合,利用PIPS法制備出以接枝共聚物為基體的PDLC,研究不同液晶含量對(duì)PDLC電光性能的影響。所用原料:光引發(fā)劑1104、丙烯酸甲酯(MA、偶氮二異丁腈(AIBN、四氯化碳(CCl4、苯乙烯(St、氯化鋅(ZnCl2、三氯化磷(PCl3、濃鹽酸、甲醇、四氫呋喃、1,4-丁二醇(成都科龍化工試劑廠,純度99.5

3、%,三硫酯鏈轉(zhuǎn)移劑(RAFT試劑,各結(jié)構(gòu)如圖1所示。液晶E7(TNI= 58 ,n o = 1.527 ,ne= 1.717 ,= 11.4,石家莊科潤(rùn)顯示材料有限公司。聚苯乙烯大分子RAFT試劑(RAFT-PS 的制備方法:在熔封管中加入St、RAFT試劑、AIBN,在氮?dú)獗Ｗo(hù)下進(jìn)行冷凍-抽氣-融化,循環(huán)4次以上以便除去氧氣,然后在充氮?dú)鈼l件下封管,放入預(yù)先升溫至110的油浴中,聚合反應(yīng)24 hr。反應(yīng)完成以后,用冰水冷卻,停止反應(yīng),加入少量四氫呋喃溶解產(chǎn)物,然后將其緩慢滴加到甲醇中進(jìn)行沉淀、抽濾,35真空干燥后獲得白色粉末,即為大分子RAFT-PS(M1,結(jié)構(gòu)如Fig.1所示。參照文獻(xiàn)方法

4、3用1,4-丁二醇、PCl3和濃鹽酸制備氯甲基化試劑(BCMB。然后在裝有攪拌子的單口燒瓶中按比例依次加入M1、ZnCl2和CCl4,待RAFT-PS完全溶解,用滴液漏斗將BCMB滴加到該體系中,室溫下反應(yīng)17hr。停止反應(yīng),然后將其緩慢滴加到甲醇中進(jìn)行沉淀、抽濾,35真空干燥后獲得白色粉末,即為大分子苯乙烯和對(duì)氯甲基苯乙烯的共聚物RAFT-PS-co-PCMS(M2,結(jié)構(gòu)如Fig.1所示。利用M2為大分子催化劑,采用ATRP法進(jìn)行接枝聚合物的制備:在干燥的單口燒瓶中加入St、CuCl,環(huán)六亞甲基四胺和M2,然后在充氮?dú)鈼l件下封管,放入預(yù)先升溫至110的油浴中,聚合反應(yīng)24 hr。反應(yīng)完成以后

5、,用冰水冷卻,停止反應(yīng),加入少量四氫呋喃溶解產(chǎn)物,然后將其緩慢滴加到甲醇中進(jìn)行沉淀、抽濾,35真空干燥后獲得白色粉末,即為帶有接支鏈的大分子RAFT-PS(M3,基金項(xiàng)目:國(guó)家自然科學(xué)基金(No. 50773045;留學(xué)回國(guó)人員啟動(dòng)基金*通訊聯(lián)系人:汪映寒,主要從事液晶取向材料、液晶/聚合物復(fù)合材料等的研究與開發(fā)。E-mail:prof_wangpaper結(jié)構(gòu)如Fig.1所示。用M3、可聚合單體MA、光引發(fā)劑1104配制成溶液,將其與液晶E7混合,形成均相溶液后,用毛細(xì)管吸取樣品灌入ITO導(dǎo)電玻璃制備的液晶盒,盒厚為20m。然后將該液晶盒置于紫外光下固化3hr,即可制得不同液晶E7含量的以接枝

6、共聚物為基體的PDLC。具體配方如表1所示。ClH2CO2Cl BCMB (chloromethoxylbutaneNNNNHexamethylenetetramineSOCCCH33CH33HOOCTrithiocarbonate*HCH2C CHH2CHCH2CHH2C*M1 ( macro RAFT-PS, Mw=7689 ;Mn=6198;PDI=1.24*HCH2C CHH2CHCH2C CHH2CCH2CH2ClCH2CH2ClM2 (chloromethylated macro RAFT-PS*HCH2C CHH2CHCH2C CHH2C*CH2CH2CH2CH2M3 (Mw=1

7、65,760 ; Mn=79,388 ;PDI=2.08 Chains of StFig.1. Chemical structures of the compoundsTab. 1 The composition of polymer dispersed liquidcrystal prepared with various contents of liquid crystal E7sample liquid crystal E7(weight ratio MI:MA (weight ratio1 30% 5:952 40% 5:953 50% 5:954 60% 5:955 70% 5:95

8、用偏光顯微鏡(POM觀察PDLC膜的微觀形貌;利用改裝過的TU-1810紫外可見分光光度計(jì)(北京普析通用儀器有限公司生產(chǎn)測(cè)試電光性能(測(cè)定波長(zhǎng)設(shè)為550nm,以空氣作參比。各項(xiàng)電光性能參數(shù)的定義分別是:飽和電壓(Vsat 為透光率達(dá)到T90時(shí)所施加的電壓,其中90min max min=9T T T T+(-0%,T max 為最大透光率,Tmin為最小透光率;對(duì)比度CR是Tmax與Tmin的比值。聚合物的分子量用凝膠滲透色譜(GPC法測(cè)定。 a b c d eFig.2 Polarized optical micrographs of polymer/liquid crystal films

9、 of different concentration of liquid crystal E7:(a30%; (b 40%; (c 50%; (d 60%; (e 70%.Fig.2是液晶E7含量分別為30%、40%、50%、60%和70%時(shí)所制備的PDLC薄膜的偏光顯微鏡(POM照片。從Fig.2可以看出,當(dāng)E7含量由30%增加到70%時(shí),PDLC薄膜的液晶微滴分布越來越均勻,且液滴的粒徑越來越小,在PDLC體系中隨著液晶含量的增加,活性大分子M3的相對(duì)濃度降低,進(jìn)而形成分子量更大的聚合物基體,而較大的分子量有利于液晶凝結(jié)為液滴的形態(tài),所以使得PDLC 膜中的液晶微滴逐漸減小且越來越均勻。

10、Fig.3是液晶E7含量分別為30%、40%、50%、60%和70%時(shí)所制備的PDLC的電光性能曲線。從Fig.3中可以很容易看出,液晶E7含量由30%增加到70%時(shí),開態(tài)透光率呈遞增趨勢(shì)。PDLC的開態(tài)透光率與液晶微滴和聚合物基體之間的折射率的匹配程度有關(guān)4,而施加電壓使PDLC處于開態(tài)時(shí),隨著液晶E7含量的增加,液晶微滴的折射率趨于與聚合物基體的折射率相匹配,因而PDLC呈現(xiàn)出 Fig.3 Electro-optical curves of PDLC prepared with Fig.4 V sat of PDLC with various liquid crystal various

11、liquid crystal E7 contents E7 contents更高的開態(tài)透光率。Fig.4是液晶E7含量分別為30%、40%、50%、60%和70%時(shí)所制備的PDLC的飽和電壓Vsat的變化曲線。從Fig.4可以看出隨著PDLC體系中液晶E7含量的增加,PDLC的飽和電壓呈現(xiàn)遞減的趨勢(shì),即從最初的48.62V降低至39.88V。PDLC的Vsat與聚合物基體和液晶微滴之間錨定能的強(qiáng)弱有關(guān),液晶微滴與聚合物之間的錨定能越強(qiáng),則PDLC的Vsat就越高。這該實(shí)驗(yàn)體系中,隨著液晶含量的增加,較少的聚合物中分散著更多的液晶微滴,即液晶微滴的密度增大使得液晶和聚合物基體的相互作用降低。主要

12、參考文獻(xiàn)1 竇艷麗, 張萬喜, 秦創(chuàng)業(yè)等. 聚合物分散液晶膜J. 化學(xué)進(jìn)展,2006,19:1400.2 唐燕春, 艾長(zhǎng)軍, 馬敬紅等. 原子轉(zhuǎn)移自由基聚合機(jī)理及其應(yīng)用J. 合成技術(shù)及應(yīng)用,2007,22:38.3 申艷玲,楊云峰,高保嬌,朱勇.高分子學(xué)報(bào), 2007,6:559.4 J. He, B. Yan, S. Wang, Y. Yu, X Wang, Y. Wang. J. Polym Sci Polym Chem. 2007,45: 4144.Synthesis of graft polymer with RAFT-PS and effect of concentration of

13、 E7 on electro-optical properties of polymer dispersed liquid crystalQIN Ai-lin, Sun Zhen, Sun Shuo, WANG Yi ng-ha nCollege of Polymer Science and Engineering, State Key Laboruary of Polymer Materials and Engineering,Sichuan University, Chengdou 610065, ChinaABSTRACT: Molecular weight and structures

14、 of polymer are the important factors that affect electro-optical properties of polymer dispersed liquid crystal (PDLC. It is difficult to control structures and molecular weight of polymer by conventional polymerization methods. The higher the molecular weight of polymer, the higher the driving vol

15、tage of PDLC. Besides, the ON-State transmittance of PDLC is determined by the match between the refraction index of polymer matrix and that of droplets of liquid crystal. Through proper designing of polymer structure can we realize well match between the refraction index of polymer matrix and that

16、of droplets of liquid crystal and thus improve the ON-State transmittance of PDLC. In this study, PDLC films were prepared by photopolymerization induced phase separation (PIPS with living graft macromolecule, synthesized by reversible addition-fragmentation transfer (RAFT and atom transfer radical polymerization (ATRP in sequential steps.The living graft macromolecule was called graft RAFT-PS. The effects of liquid crystal E7 concentration on morphologies, transmittance, saturated voltage (V sat were studied. It is found that the radius of the liquid crystal droplet of PDLC decreased wi