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含嵌段共聚物的热固性树脂中纳米结构的形成

Formation of Nanostructures in Thermosets Containing Block Copolymers

【作者】 徐之光

【导师】 郑思珣;

【作者基本信息】 上海交通大学 , 材料学, 2007, 博士

【摘要】 由于高分子材料结构与性能之间的密切关系,具有纳米结构的热固性树脂的研究是高分子材料领域的一个重要课题。嵌段共聚物在热固性树脂中的应用为得到无序或者有序的纳米结构提供了便捷的途径。嵌段共聚物在热固性树脂中纳米结构的形成有两种机理:自组装机理和反应诱致微相分离机理。对于自组装机理,在固化反应前嵌段共聚物已经在热固性树脂的前驱体中自组装形成了纳米结构,这种有序或者无序的纳米结构可以通过后续的固化反应固定。这种方法中的固化反应是固定已经得到的纳米形态。自组装机理的前提是在固化反应前,嵌段共聚物在热固性树脂的前驱体中能自组装形成纳米结构。从相容性的角度来看,无论固化反应前后,需要嵌段共聚物的一个或者多个链段与热固性树脂相容,而其他的链段与热固性树脂不相容。而对于反应诱致微相分离的机理,要求在固化反应前嵌段共聚物的所有链段与热固性树脂的前驱体相容,而在反应后只有一部分链段从热固性树脂的基体中相分离出来。本论文根据热固性树脂和嵌段共聚物中链段之间的相容性和相行为,设计合成了一系列两亲性嵌段共聚物,通过嵌段共聚物与热固性树脂的共混,得到具有无序/有序纳米结构的热固性树脂。主要研究内容如下:1.含聚己内酯-b-聚(丁二烯-苯乙烯)-b-聚己内酯(PCL-b-PBS-b-PCL)嵌段共聚物的环氧树脂中反应诱致微相分离纳米结构的研究以端羟基聚(丁二烯-苯乙烯)(HTPBS)引发己内酯开环聚合得到了两亲性三嵌段共聚物PCL-b-PBS-b-PCL。将嵌段共聚物和环氧树脂共混,制备了具有纳米结构的环氧热固性树脂。进一步研究发现在固化反应前后,PCL链段和环氧树脂都是相容的;而PBS和环氧树脂前驱体之间存在最高临界相容温度(UCST),随着固化反应的进行,PBS链段发生反应诱致微相分离,在环氧热固性树脂中形成了纳米结构。2.含聚己内酯-b-聚丙烯酸丁酯(PCL-b-PBA)的环氧树脂中层状纳米结构的研究:反应诱致微相分离通过开环聚合与原子转移自由基聚合相结合的方法制备了两亲性的PCL-b-PBA嵌段共聚物。然后将嵌段共聚物与环氧树脂进行原位共混,得到了具有纳米结构的热固性树脂。用场发射扫描电镜,原子力显微镜,小角X射线散射和动态力学热分析对得到的纳米结构进行了表征。随着嵌段共聚物PCL-b-PBA含量的增加,PBA微相纳米结构逐渐从球状粒子向层状结构转变。根据固化反应前后嵌段共聚物中不同链段(PCL和PBA)与环氧树脂相容性和相行为的差异,判断这种有序的层状纳米结构是通过反应诱致微相分离产生的。3.嵌段共聚物的拓扑结构对热固性树脂纳米结构的影响合成了四臂星型嵌段共聚物fa(PCL-b-PS)4。将嵌段共聚物与环氧树脂共混固化,得到了具有纳米结构的热固性树脂。研究结果表明,含有四臂星型嵌段共聚物fa(PCL-b-PS)4的环氧树脂能形成层状纳米结构,这与含有线型两嵌段共聚物PCL-b-PS的环氧树脂能形成简单立方纳米结构完全不同。FTIR和DSC数据证明,环氧树脂的前驱体能穿过星型嵌段共聚物的外围PS链段而进入内部,使PCL链段与环氧树脂基体间形成了强烈的分子间相互作用,从而得以使PCL链段与环氧树脂基体保持相容。根据PS链段和PCL链段与环氧树脂在固化前后相容性的差别,证明这种纳米结构形成的原因是PS链段在固化反应的过程中发生反应诱致微相分离的结果。4.含聚己内酯-b-聚二甲基硅氧烷-b-聚己内酯(PCL-b-PDMS-b-PCL)嵌段共聚物的交联环氧树脂中自组装纳米结构的研究用双端羟基聚二甲基硅氧烷(HTPDMS)为引发剂引发己内酯开环聚合得到了两亲性的三嵌段聚合物PCL-b-PDMS-b-PCL,然后与环氧树脂共混制备了具有纳米结构的环氧热固性树脂。透射电子显微镜,原子力显微镜和小角X射线散射结果均证实当嵌段共聚物的含量为10 wt %时,形成直径为10~20 nm的球形PDMS微相,当嵌段共聚物的含量大于20 wt %时,形成蠕虫状的PDMS微相。根据固化反应前后嵌段共聚物中PCL链段和PDMS链段与环氧树脂之间的相容性,判断这种纳米结构的形成机理属于自组装机理。5.聚己内酯-b-聚二甲基硅氧烷-b-聚己内酯(PCL-b-PDMS-b-PCL)与线型环氧树脂共混体系的表面性能与结构的研究三嵌段共聚物PCL-b-PDMS-b-PCL和聚酚氧共混制备了二元共混物,FTIR和DSC结果表明嵌段共聚物中的PCL链段和聚酚氧是相容的。研究发现,当嵌段共聚物的含量为10 wt %时,共混物的表面接触角显著增加,而且随着嵌段共聚物含量的增加,共混体系的表面接触角增加,表面张力下降。XPS结果表明,这种现象是由于嵌段共聚物中的低表面能的PDMS链段向共混物表面迁移的结果。通过SAXS数据可以证明嵌段共聚物在共混体系中发生了微相分离,形成了纳米结构,而通过共混物表面的不同摩擦力可以证明嵌段共聚物在共混物的表面也发生了相分离。6.含聚氧化乙烯-b-聚苯乙烯(PEO-b-PS)嵌段共聚物的酚醛树脂中自组装形成的有序纳米结构的研究通过原子转移自由基聚合的方法合成了两亲性嵌段共聚物PEO-b-PS。然后将嵌段共聚物PEO-b-PS与线型酚醛树脂共混,研究证明嵌段共聚物在酚醛树脂中自组装形成了长程有序的纳米结构,并用SAXS研究了自组装形成的纳米结构在酚醛树脂固化反应前后形态的变化情况。结果证实,当嵌段共聚物的含量达到40 wt %后,PS球状粒子按照六边圆柱型均匀排布在整个环氧树脂基体中。根据固化反应前后,嵌段共聚物中PEO链段和PS链段与酚醛树脂之间相容性和相行为的差异,可以证明这种长程有序纳米结构是通过嵌段共聚物在酚醛树脂中的自组装形成的。

【Abstract】 The study on the nanostructured thermosets is an important topic in the polymer materials because of the relation between the structure and property of polymer. The application of block copolymers in thermosets provides a convenient way for obtaining disordered and/or ordered nanostructures. It is recognized that the formation of nanostructures can be carried out via self-assembly or reaction-induced microphase separation mechanisms of amphiphilic block copolymers in thermosets.In the protocol of self-assembly, self-organized nanostructures are formed prior to curing and these disordered and/or ordered nanostructures are further locked in with the subsequent curing reaction. And for the self-assembly, some self-assembly nanostructured morphologies are formed in the precursor of thermosets before curing reaction. One subchain of the block copolymer is miscible with thermosets while the others are not miscible with the matrix before and after curing reaction. For the formation of nanostructures via reaction-induced microphase separation mechanism, it is required that all the subchains of the block copolymer are miscible with precursors of thermosets before curing whereas only a part of subchains were phase-separated from the matrix of thermosets after curing.We designed and sythesized a series of amphilic block copolymers according to the structures of the thermosets and miscibility between block copolymer and thermosets. And disordered and/or ordered nanostructured thermosets were obtained by the mixtures of block copolymer and thermosets. The main researches are as follows:1. Study on the nanostructure in epoxy thermosets containing poly(ε-caprolactone)-b- poly(butadiene-styrene)-b-poly(ε-caprolactone) (PCL-b-PBS-b-PCL): an evidence of reaction-induced microphase separationThe block copolymer PCL-b-PBS-b-PCL was synthesized by the ring-opening polymerization ofε-caprolactone. The triblock copolymer was further mixed with epoxy resin to prepare nanostructured epoxy thermosets. Further study illustrated that PCL subchains were miscible with epoxy after and before curing while PBS subchains and diglycidyl ether of bisphenol A (DGEBA) had the upper critical solution temperature (UCST). Then PBS subchains occurred reaction-induced microphase separation during curing reaction and formed nanostructures in epoxy thermosets.2. Lamellar nanostructures in epoxy thermosets containg poly(ε-caprolactone)-b-poly(butyl acrylate) (PCL-b-PBA) via reaction-induced microphase separationThe diblock copolymer PCL-b-PBA was synthesized via the ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The diblock copolymer was incorporated into epoxy thermosets to access the nanostructures in the thermosets. The nanostructures were investigated by means of field-emission scanning electron microscope (FESEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA). It was found that depending on the concentration of the diblock copolymer in the thermosets, the nanostructures changed from spherical particles to lamellar objects of PBA nanophases. In terms of the miscibility of the PCL/PBA subchains of the block copolymer with epoxy resin after and before curing reaction, it was judged that the nanostructures were formed via the mechanism of reaction-induced phase separation.3. Effect of topological structures of block copolymers on nanostructures in thermosetsThe four arms star-shape block copolymer fa(PCL-b-PS)4 was synthesized. Then the star-shape block copolymer was mixed with epoxy resin and the nanostructures were obtained. The results showed that the lamellar nanostructures were formed in epoxy thermosets containing four arms shar-shape block copolymer fa(PCL-b-PS)4 while the lattice with simple cubic nanostructures were in epoxy thermosets containing diblock copolymer PCL-b-PS. FTIR and DSC results illustrated that the precursor of epoxy (DGEBA) could rip into the outer PS subchains and come into the inner PCL subchains of the star-shape block copolymer. This resulted in the miscibility of PCL subchains and epoxy matrix. In terms of the miscibility of the PCL/PS subchains of the block copolymer with epoxy resin after and before curing reaction, it was judged that the lamellar nanostructures were formed via reaction-induced phase separation.4. Study on the self-assembly nanostructures in the cross-linked epoxy thermosts containing poly(ε-caprolactone)-b-poly(dimethylsiloxane)-b-poly(ε-caprolactone)The triblock copolymer PCL-b-PDMS-b-PCL was synthesized via the ring-opening polymerization ofε-caprolactone in the presence of dihydroxypropyl-terminated PDMS (HTPDMS) initiator, and was incorporated into epoxy resin and the nanostructured thermosets were successfully obtained. The morphology of the epoxy thermosets containing PCL-b-PDMS-b-PCL triblock copolymers were investigated by means of atomic force microscopy, transmission electronic microscopy and small angle X-ray scattering. The spherical PDMS microphase with the diameter as 10-20 nm was dispersed in epoxy thermosets containing 10 wt % block copolymer; and wormlike PDMS microphase was formed when the content of block copolymer more than 20 wt %. The formation was judged to follow the self-assembly mechanism in terms of the difference in miscibility of the PDMS and PCL subchains with epoxy resin after and before curing reaction.5. Study on the surface properties and structures of the triblock copolymer PCL-b-PDMS-b-PCL and linear epoxy resin mixturesThe binary polymer blends were obtained by mixing triblock copolymer PCL-b-PDMS-b-PCL and Phenoxy. FTIR and DSC results illustrated that PCL blocks in the triblock copolymer are miscible with Phenoxy. The contact angle of Phenoxy blends containing 10 wt % triblock copolymer was significantly increased and the contact angles increased with increasing the content of triblock copolymer while the surface free energy decreased. XPS results showed that the PDMS block aggregated on the surface to minimize the surface free energy of the polymer blends. Microphase separation of the triblock copolymer occurred in binary Phenoxy blends and phase separation on the surface of the Phenoxy blends was proved by atom force microscope via the different friction force of the surface of the polymer blends.6. Study on the self-assembly ordered nanostructures in phenolic resin containing poly(ethylene oxide)-b-poly(styrene) (PEO-b-PS) diblock copolymerThe diblock copolymer PEO-b-PS was synthesized by ATRP. Then the PEO-b-PS diblock copolymer was used to incorporate into phenolic resin to afford the long-range ordered nanostructured phenolic resin by self-assembly. And the changes of the nanostructures in phenolic resin before and after curing reaction were studied by SAXS. The results showed that the PS microdomains arranged into hexagonal cylinder when the content of PEO-b-PS diblock copolymer was 40 wt %. In views of the difference in miscibility and phase behavior for the blends of the PEO/PS subchains of the diblock copolymer with phenolic resin after and before cuing, the formation of the ordered nanostructures was judged to be via the mechanism of self-assembly.

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