【作者】 薛小强；

【导师】 朱秀林；

【作者基本信息】 苏州大学 ， 高分子化学与物理， 2010， 博士

【摘要】 偶氮苯聚合物既具有偶氮苯基团的光致顺反异构化活性,又具有高分子材料优异的力学性能和加工性能,在液晶材料、光信息存储材料及非线性光学材料等许多领域都具有广泛的应用,近年来引起了研究工作者极大的关注。因此,探索并设计具有新颖结构和优异性能的偶氮苯聚合物成为高分子化学和材料领域的重要课题之一。本论文主要从聚合物合成设计的角度出发,设计并合成了结构新颖的偶氮苯聚合物,研究聚合物独特的光学性能。研究内容具体包括:(1).合成了新型含偶氮苯基团的二硫代氨基甲酸酯,苯乙基-N, N’-(4-偶氮苯基)苯基二硫代氨基甲酸酯(PPADC)。将其作为RAFT试剂,成功用于丙烯酸甲酯的RAFT聚合,聚合过程显示出“活性”/可控的特征:聚合呈现一级动力学特征,聚合物分子量随转化率的提高而线性增加,且聚合物分子量分布指数较小。然而,由于PPADC中N原子孤对电子与硫羰基相互作用依旧很强,降低了二硫键活性,使其在类似条件下不能对苯乙烯单体实现活性可控聚合。同时,结果显示PPADC可以作为ATRP假卤素引发剂用于引发苯乙烯的聚合,实现了对聚合过程的控制。对所获得端基含二硫代氨基甲酸酯结构片段的聚合物利用核磁、紫外和红外等手段进行了表征,证实了这些过程的活性特征。另外,还考察了端基含偶氮苯聚合物(PS和PMA)溶液的光致异构化性能。经测定聚合物PS,PMA和PPADC的在氯仿溶液中的光致异构化速率常数kexp分别为0.00733 s-1,0.00515 s-1和0.00651 s-1,聚合物链对偶氮苯光致异构化速率没有明显的影响。(2).首先利用RAFT聚合技术,制备了端基含α-炔基和偶氮苯基团的聚苯乙烯(PS)和端基含ω-叠氮基团的聚醋酸乙烯酯(PVAc);随后,用Cu(Ι)催化体系,进行聚合物端基上叠氮和炔基的“Click”化学反应,成功合成了分子量可控的嵌段共聚物PS-b-PVAc,实现了链段中间含偶氮苯功能基团聚合物的制备。经过GPC,核磁谱图和红外谱图对制备的嵌段共聚物PS-b-PVAc的结构进行了证实。得到的嵌段聚合物具有高的偶氮苯端基功能化度,窄的分子量分布。对含该嵌段共聚物PS-b-PVAc光致反-顺异构化和热致顺-反异构化行为进行了研究,发现聚合物的光致反-顺异构化速率常数(kexp)和热致顺-反异构化速率常数(kH)分别为0.0027 s-1,2.2×10-4 s-1,其中嵌段共聚物的光致反-顺异构化速率比均聚物PS (kexp= 0.0047 s-1)的速率慢很多,嵌段共聚物中的偶氮苯结构易受到聚合物链的阻碍而影响异构化速率。(3).利用偶氮苯马来酰亚胺(MAB)和苯乙烯(St)为交替共聚单体,α-二硫代萘甲酸异丁腈酯(CPDN)为RAFT链转移试剂,AIBN为引发剂,在1, 4-二氧六环溶液中进行RAFT聚合,合成了光响应的偶氮苯交替共聚物聚(偶氮苯马来酰亚胺-alt-苯乙烯) (PMSts),聚合过程显示出“活性”/可控的特征。利用红外、紫外和核磁等测试手段,对PMSt进行了表征,证实了聚合物的交替结构。另外,在聚合体系中加入二乙烯基单体,4, 4’-双马来酰亚胺二苯甲烷,制备了高分子量的超支化偶氮苯共聚物。所有偶氮苯聚合物都能溶解于大部分有机溶剂,成膜性好,具有高的玻璃化转变温度(Tg = 174 ~ 250 oC)以及良好的耐热性(Td >320 oC)。得到的偶氮苯交替共聚物PMSt可以用于表面起伏光栅的制备。其衍射效率最高达到3.4 %。此外,聚合物形成的光栅具有高的热稳定,能在150 oC环境中保持不变,高于玻璃化转变温度时可以顺利擦除。(4).成功合成了新型四唑偶氮苯单体MACA,并利用RAFT聚合技术成功合成了分子量可控的均聚物(PMACA)和嵌段聚合物(PMACA-b-PMMA)。利用核磁共振氢谱、凝胶色谱、红外谱图等测试方法对聚合物进行结构表征,表明聚合物分子量可控,较低的分子量分布指数(Mw/Mns <1.30)。同时聚合物的热性能和结晶性能通过差示扫描量热法(DSC)和广角X射线衍射(WAXD)进行了研究,结果表明偶氮苯聚合物具有较好热稳定性(Tg = 133-141 oC),并以无定形态存在。此外偶氮苯嵌段共聚物在365 nm光照下异构化较为特殊:光照前期,偶氮苯反式含量略有增加,可能由于四唑基团对偶氮苯基团有一定的影响。光照三分钟后,反式结构吸收峰开始减弱,其反式结构向顺式转变,同时反式偶氮苯吸收峰发生红移现象。循环伏安法也能发现光照后偶氮苯的氧化峰发生了明显的位移,偶氮苯聚合物溶液的氧化还原行为受紫外光照射调控。(5).利用“Cilck”化学技术成功合成了主链含三氮唑的偶氮苯聚合物PEAPA,利用核磁共振、凝胶色谱(GPC)、红外光谱仪器等方法对聚合物进行了结构表征。获得的聚合物PEAPA相对于不含杂环的主链偶氮苯聚合物PDHA (Tg = 109 oC, Td = 278 oC),具有更好的耐热性和热稳定性,如PEAPA1:Tg = 134 oC, Td = 357 oC,表明三氮杂环基团对偶氮苯聚合物的热稳定有很大的提高。通过差示扫描量热法(DSC)和广角X射线衍射(WAXD)显示聚合物具有一定的结晶性能。此外,研究了该偶氮苯聚合物在DMF溶液中的光致顺反异构化及其热回复行为。(6).高温下利用1, 3-偶极环加成聚法制备出高分子量的主链型偶氮苯聚合物PEHPA2。聚合物PEHPA2显示出良好的溶解性和成膜性。利用核磁对聚合物进行了结构表征,结果发现偶氮苯聚合物PEHPA2中含有78 %的1, 4-式和22 %的1, 5-式两种三唑环的区域异构体,另外,偶氮苯聚合物PEHPA2的热稳定达330 oC,表明三唑杂环基团引入到聚合物主链,可提高偶氮苯聚合物的耐热性。同时研究了偶氮苯聚合物PEHPA2的光致异构化性能,其一阶速率常数ke为0.010 s-1。此外,聚合物PEHPA2旋涂成膜,激光雕刻成表面起伏光栅(SRG),其槽深约74 nm,衍射效率约0.82 %。更多还原

【Abstract】 Polymers bearing azobenzene moieties (azobenzene polymers) combine the unique optical trans-cis-trans isomerization behavior of azobenzene and the good processability and mechanical properties of polymer materials. These azobenzene polymers can be potentially applied in fascinating photo-responsive variations, such as liquid crystal displays, optical data storage, nonlinear optical materials and so on, which have attracted increasing attention in the past few years. Therefore, develop and design of new azobenzene polymers with the novelty structure and excellent optical activity has been an important assignment for polymer chemistry.In this thesis, we designed and synthesized a series of azobenzene polymers with the novel structures. Their trans-cis isomerization and so caused properties change were investigated. The detailed researches were summarized as the following:(1) A novel azobenzene-containing dithiocarbamate, 1-phenylethyl N, N’-(4-phenylazo)phenylphenyldithiocarbamate (PPADC), was successfully synthesized. PPADC was used as RAFT agent, the reversible addition-fragmentation chain transfer (RAFT) polymerization was well controlled in the case of MA. However, there was the slightly ill-controlled in the case of St, which was affected by a less reactive double bond due to the delocalization of the nonbonded electron pair on the nitrogen with the thiocarbonyl group. Interestingly, the polymerization of St could be well-controlled when using PPADC as the initiator via atom transfer radical polymerization (ATRP) technique. The obtained polymer was characterized by 1H NMR analysis, ultraviolet absorption, FT-IR spectra analysis and chain-extension experiments. The polymerizations by RAFT and ATRP system were both well controlled. Furthermore, the photoresponsive behaviors of azobenzene-terminated poly(methyl acrylate) (PMA) and polystyrene (PS) were similar to PPADC. The isomerization rate constants (kexps) of PPADC, PMA and PS were 0.00651 s-1, 0.00515 s-1 and 0.00733 s-1, respectively.(2) The well-defined block copolymers, poly(vinyl acetate)-b-poly(styrene)s (PS-b-PVAc) containing middle azobenzene moiety were successfully synthesized by a combination of RAFT and“Click”chemistry. This novel method provided an efficient way to prepare middle functionalized block copolymer: firstly,α-alkyne and azobenzene chromophore terminated poly(styrene) (PS), andω-azido-terminated poly(vinyl acetate) (PVAc) were designed via RAFT technology. Secondly,‘‘Click’’reaction was performed using the combination of CuBr and PMDETA as catalyst system. Thus, well-controlled block copolymer poly(vinyl acetate)-b-poly(styrene) (PS-b-PVAc) was obtained. Block copolymers (PS-b-PVAc) were demonstrated by GPC, 1H NMR, FT-IR spectra and differential scanning calorimetry (DSC) analysis. Furthermore, the trans-cis-trans isomerization of PS-b-PVAc was also observed in chloroform solution. The ke and kH of PS-b-PVAc was 0.0027 and 2.2×10-4 s-1, respectively.(3) The well-defined photo-responsive alternating copolymer containing azobenzene chromophore, poly(4-(N-maleimido)azobenzene-alt-styrene) (PMSt) was successfully synthesized from the copolymerization of 4-(N-maleimido)azobenzene (MAB) and styrene (St) via RAFT polymerization using CPDN as the RAFT agent and AIBN as an initiator in 1,4-dioxane solution. The copolymerization was well controlled, which showed polymers with controlled molecular weight and narrow molecular weight distribution. The alternating structure of the copolymers PMSts were characterized by 1H NMR, 13C NMR, UV-vis absorption and FT-IR. Furthermore, The highly branched azobenzne copolymers with high molecular weight were successfully obtained after adding N, N-4,4-diphenylmethyenebismaleimide (BMI) into the polymerization system. The copolymers showed high glass transition temperature (Tg = 174 ~ 250 oC) and decomposition temperature (Tg = 174 ~ 250 oC). On irradiation with a linearly polarized Kr+ laser beam, the diffraction efficiency of SRG decreased along with increasing the molecular weight of polymer film. For the same polymer, film with high thickness showed high SRG diffraction efficiency. The formed SRG on PMSt1 film was stable even at 150 oC due to the high Tg of PMSt1.(4) A novel methacrylate monomer containing azobenzene chromophore and tetrazole moiety, 4′-(2-methacryloxyethyl)methylamino-4- (5-chlorotetrazol-1-yl)azobenzene (MACA), was synthesized and polymerized to form homopolymers (PMACA) and block copolymers (PMMA-b-PMACA) via reversible addition-fragmentation chain transfer (RAFT) polymerization. The structures of these polymers were characterized by 1H NMR spectroscopy and FT-IR spectra, and gel permeation chromatography (GPC) characterization, which indicated that polymers with controlled molecular weights and narrow molecular weight distributions (Mw/Mns <1.30). Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) results indicated these polymers were amorphous. Furthermore, the photoisomerization of azobenzene polymers was investigated, it should be indicated that in the beginning period of irradiation (3 minutes), the absorption (430 nm) of trans-form azobenzene slightly increased upon UV irradiation, which may due to the bulky tetrazole substitution on the azobenzene. After UV irradiation of 3 minutes, the trans- form content of azobenzene was increased irradiation time of 365 nm UV light. Furthermore, during the tran-cis isomerization, the absorption peak at 430 nm was a“red-shift”peak from 413 to 513 nm. The electrochemical behavior of polymers in solution before and after UV irradiation was investigated using the cyclic voltammetry (CV), the oxidation peak in CV curve obviously shifted to 0.6V. The electrochemical behavior can be adjusted by the UV irradiation, which may find their applications in photo electronic materials.(5) A novelα-azide andω-alkyne A-B type azobenzene monomer, 3’-enthynylphenyl[4-(4-azidobutoxy)phenyl]azobenzene (EAPA), was synthesized and used to generate a novel polymer via step-growth polymerization using“Click”chemistry. The structure of the resultant main-chain azobenzene polymer, PEAPA, was characterized by GPC, 13C-NMR, ultraviolet and FT-IR spectra. Thermal stability and crystallinity of PEAPA powder was studied by TGA and WAXD. The obtained linear main-chain azobenzene polymer PEAPA containing 1, 2, 3-triazol group showed a good thermal stability and crystallinity, for example: PEAPA1, Tg = 134 oC, Td = 357 oC, which was due to the introduction of the triazole ring in the polymer backbone. Comparing the rate constant of trans-cis photoisomerization of monomer EAPA (ke = 0.022 s-1), the corresponding value of PEAPA was much slower (ke = 0.0088 s-1). The reason was considered due to sterically hindering effect of the main-chain configuration and the triazole group in PEAPA2. However, the cis-trans thermal isomerization behavior of PEAPA2 (7.4×10-4 s-1) was similar to EAPA’s (5.4×10-4 s-1).(6) The main-chain azobenzene polymer PEHPA2 was obtained through thermal 1, 3-dipolar cycloaddition technique. All of these polymers showed high thermally resistance (Td above 330 oC). The polymer PEHPA2 showed good solubility in common organic solvents due to the formation of regiorandom structures, and the 1,4-regioisomeric ratios (F1,4, F1,4’) of PEHPA2 were calculated to be 78 % from NMR spectrum of PEHPA2. The photo-induced trans-cis isomerization of the polymers in CHCl3 solution was examined, and the photoisomerization rate constant was 0.010 s-1. The film prepared from PEHPA2 showed efficient surface relief gratings (SRGs) formation ability. The diffraction efficiency from SRG with film thickness of 465 nm was measured to be about 0.82 %.更多还原