【作者】 徐立新；

【导师】 杨慕杰；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2010， 博士

【摘要】 本论文通过聚合物共价/非共价修饰方法,分别将端芘基聚乙烯、超支化聚乙烯、线型短支链聚乙烯和聚苯乙烯四种聚烯烃接枝于多壁碳纳米管（MWNT）、有序介孔氧化硅（OMS）和纳米氧化钛（nm TiO₂）的表面,并对各类结构进行表征,研究它们在不同体系中的分散性能,以促进它们的相关应用。利用端芘基聚乙烯（PPE）对MWNT表面进行非共价改性,以提高MWNT的溶剂分散性能。首先将芘基引入后过渡金属催化剂Pd-Diimine的结构中,利用其在5℃、400 psi下催化乙烯“活性”聚合,制得窄分布并具有不同分子量PPE样品,然后利用制得的PPE分别在THF、庚烷和甲苯中通过超声对MWNT表面进行改性。运用GPC、GPC-LLS、¹HNMR、UV-Vis、荧光光谱、TGA、FTIR、TEM、WAXRD等对PPE的结构、体系内的非共价相互作用、MWNT的溶剂分散性能分别进行了表征,并建立了相关模型,分别就聚乙烯端基结构、分子量大小、溶剂类型及聚乙烯浓度的影响进行了讨论。结果表明:芘基已被引入聚乙烯链的一侧末端,所得PPE分子量大小可控且分布较窄（MWD:1.01-1.16）,同时含有较高的短支链密度（86-90/1000 C）;通过非共价相互作用,部分PPE已非共价接枝于MWNT表面,在THF中,同时存在π-π堆叠和CH-π作用,在庚烷中,主要为π-π堆叠作用,在甲苯中,两种作用均很微弱;经PPE改性后,MWNT在THF和庚烷中可实现单根稳定分散,其最大分散浓度分别可达812.9mg/L和230.8mg/L。利用超支化聚乙烯（HBPE）对MWNT表面进行非共价改性,以进一步提高MWNT的溶剂分散性能。首先利用催化剂Pd-Diimine的“链移走”机理,在35℃、1 atm（≈15 psi）下催化乙烯聚合制得HBPE样品,然后用其分别在THF、氯仿、庚烷和甲苯中通过超声对MWNT表面进行改性。运用TEM、HRTEM、¹HNMR、TGA、FTIR、UV-Vis、WAXRD等对MWNT的分散性能及体系内的非共价相互作用进行表征,并建立了相关模型,分别就聚乙烯链形态、聚乙烯浓度及溶剂类型的影响进行了讨论。结果表明:在THF、氯仿中,HBPE与MWNT间存在较强的非共价非特异性CH-π作用;借助上述作用,可将HBPE稳固地非共价接枝于MWNT表面,改性后的MWNT可在上述溶剂中实现高浓度稳定分散,其最大分散浓度分别达919mg/L（在THF中）和1235mg/L（在氯仿中）;在上述溶剂中,HBPE对MWNT的分散促进作用明显优于线型短支链聚乙烯（LBPE）;溶剂的类型对MWNT的分散性能有显著的影响,经HBPE改性后MWNT的分散性能满足顺序:氯仿＞THF＞甲苯或庚烷（在后两溶剂中,MWNT的分散浓度仅接近于20mg/L）。通过表面引发配位聚合机理,将线型短支链聚乙烯（LBPE）共价接枝于有序介孔氧化硅SBA15和MSUF的孔道表面,获得了有序多孔型有机/无机杂化材料PE-SBA15/PE-MSUF。首先利用偶联剂3-丙烯酰基氧基丙基三氯硅烷对SBA15/MSUF进行表面预处理以引入丙烯酰基,随后通过该基团与乙腈基Pd-Diimine催化剂进行成环反应,制得负载型催化剂Pd-SBA15/Pd-MSUF,进一步在5℃、400psi下催化乙烯使其在孔道表面引发聚合。通过氮气吸附测试、TGA、FTIR、DSC、ICP-MS等对改性前后SBA15/MSUF的结构进行了表征,同时对上述聚合的可控程度进行了考察。研究表明:借助于偶联剂,可将催化剂均匀地共价负载于SBA15/MSUF的孔道表面,所得负载型催化剂Pd-SBA15/Pd-MSUF仍保留有序多孔结构,两者的催化剂层厚分别为0.66nm和0.95nm;通过Pd-SBA15/Pd-MSUF催化乙烯聚合,可将LBPE均匀地共价接枝于孔道表面,通过对聚合时间的控制,可调节孔道表面聚乙烯层的厚度,使复合粉末PE-SBA15/PE-MSUF仍具有多孔结构;对于MSUF体系,当聚合时间达20min,所得复合粉末PE20min-MSUF仍具有一定的孔容和比表面积（分别为0.57cm³/g和141.54m²/g）。为提高nm ZiO₂在聚丙烯（PP）中的分散性能及抗紫外老化作用,利用聚苯乙烯（PS）对其表面进行共价接枝改性,并运用Friedel-Crafts（FC）烷基化反应原理对PP/（PS接枝nm TiO₂,PS-g-TiO₂）体系进行原位增容。在硅烷偶联剂改性的基础上,首先通过分散聚合工艺制得PS包覆的nm TiO₂微球（PS@TiO₂）,通过纯化进一步制得PS-g-TiO₂,随后通过熔融复合工艺分别将PS@TiO₂、PS-g-TiO₂及不同浓度的FC催化剂（AlCl₃/St）加入PP中,制得一系列PP纳米复合材料。运用TGA、FTIR、XPS、TEM、SEM、DSC及紫外加速老化测试等手段对改性后nm TiO₂的结构、nm ZiO₂的分散性能及其抗紫外老化作用进行了表征。结果表明:部分PS已共价接枝于nm TiO₂表面;通过FC催化剂（AlCl₃/St）原位增容,可进一步提高PS-g-TiO₂在PP中的分散性能,当AlCl₃浓度达1.0wt%,nm TiO₂粒子可在PP基体中实现纳米级均匀分散,同时体系的界面相容性有显著提高;通过PS接枝改性并结合FC原位增容技术,可显著提高nm TiO₂在PP中的抗紫外老化作用,同时可赋予PP纳米复合材料以更佳的耐热性能。更多还原

【Abstract】 Four different types of polyolefins,including pyrene-end-capped polyethylene （PPE）,hyperbranched polyethylene（HBPE）,linear short-branched polyethylene（LBPE） and polystyrene（PS）,were covalently/noncovalently grafted onto the surface of multi-walled carbon nanotubes（MWNT）,organized mesoporous silica（OMS）,and nano-sized titanium dioxide（nm TiO₂）,respectively,to promote their applications as functional nanomaterials.The structure of the modified nanoparticles was characterized and their dispersibility in different system was investigated.The surface of MWNT was noncovalently modified with a range of narrow-distributed pyrene-end-capped polyethylenes（PPE）to improve its dispersibility in solvent.A pyrene group was first introduced into an acetonitrile Pd-Diimine complex, a typical late-transition-metal catalyst used for olefin coordination polymerization,and then a series of PPE samples were synthesized via "living" ethylene polymerization with the obtained pyrene-functionalized Pd-Diimine as a catalyst at a temperature of 5℃and an ethylene pressure of 400 psi.The functionalization of MWNT with PPE was subsequently carried out by ultrasonication in tetrahydrofuran（THF）,heptane,and toluene,respectively.The structure of the prepared PPE samples,the interactions between PPE and MWNT,and the dispersibility of MWNT in solvent were characterized through GPC、GPC-LLS、¹HNMR、UV-Vis、Fluorescent spectra、TGA、FT-IR、TEM、WAXRD etc.The influence of various factors on dispersibility of MWNT was also discussed including end-group type of polyethylene,molecular weight of PPE, and solvent used etc.It was confirmed that each polyethylene chain is functionalized with an end-capped pyrene group and the pyrene-end-capped polyethylenes have controllable average molecular weight with narrow moleculhear weight distribution （MWD）of 1.01-1.16 and higher short-branch density of 86-90/1000 C.The stronger noncovalent interaction between PPE and MWNT was confirmed,which was attributed to bothπ-πstacking and CH-πinteraction in THF,whereas mainlyπ-πstacking in heptane.A few PPE chains had been noncovalently grafted to the surface of MWNT via above noncovalent interactions between PPE and MWNT,which led to a higher dispersibility of MWNT both in THF（up to 812.9 mg/L）and in heptane（up to 230.8 mg/L）. To further enhance its dispersibility in solvent,the surface of MWNT was noncovalently functionalized using HBPE,which could be conveniently synthesized from commercially abundant ethylene via one-step chain walking polymerization.The HBPE was first synthesized by ethylene polymerization with the acetonitrile Pd-Diimine complex as a catalyst at a temperature of 35℃and an ethylene pressure of 1 atm（≈15 psi）,and then the surface modification of MWNT with HBPE was conducted by ultrasonication in THF,chloroform,heptane,and toluene,respectively.The dispersibility of MWNT in solvent and the interactions between HBPE and MWNT were characterized through a series of methods,including TEM、HRTEM、¹HNMR、TGA、FT-IR、UV-Vis、WAXRD etc.The influence of solvent type,HBPE chain topology,and mass ratio of HBPE to MWNT on MWNT dispersibility was discussed via a theoretical model.It was found that the HBPE could be steadily grafted to the surface of MWNT both in THF and chloroform by means of the stronger noncovalent nonspecific CH-πinteraction between HBPE and MWNT.The HBPE was found to effectively exfoliate MWNT bundles to form stable MWNT dispersions both in THF and chloroform at surprisingly high concentrations（up to 919 mg/L in THF and 1235 mg/L in chloroform）.It was also found that solvent type had a notable influence on MWNT dispersibility,which increases according to the following sequence:toluene or heptane＜THF＜chloroform.To obtain inorganic/organic hybrid mesoporous materials,the surface of two kinds of organized mesoporous silica,SBA15 and MSUF,was functionalized with a linear short-branched polyethylene（LBPE） via surface-initiated "living" coordination polymerization technique.First the surface of SBA15/MSUF silica was treated with 3-acryloxypropyltrichlorosilane,as a coupling agent,to introduce acryloyl group,and then the acetonitrile Pd-Diimine catalyst was covalently immobilized onto pore surface of SBA15/MSUF silica by reacting with the surface-bonded acryloyl group.The obtained SBA15/MSUF silica-supported Pd-Diimine catalyst（Pd-SBA15/Pd-MSUF） was subsequently used to catalyze ethylene polymerization at a temperature of 5℃and an ethylene pressure of 400 psi to covalently graft LBPE chains from the pore surface of SBA15/MSUF silica.The structure of SBA15/MSUF silica,before and after modification,was characterized using TGA,FTIR,ICP-MS,nitrogen adsorption-desorption testing,and DSC,respectively.The controllability of above polymerization was also evaluated.It was found that the acetonitrile Pd-Diimine catalyst could be homogeneously and covalently immobilized on the pore surface of SBA15/MSUF silica by using the coupling agent,and the resulting catalyst-functionalized SBA15/MSUF silica（Pd-SBA15/Pd-MSUF）still retained organized porous structure,in which the thickness of catalyst layer was 0.66 nm and 0.95 nm for Pd-SBA15 and Pd-MSUF silica,respectively.The LBPE chains can be covalently bonded to the pore surface of SBA15/MSUF silica through the ethylene polymerization catalyzed by Pd-SBA15/ Pd-MSUF.The thickness of homogeneous LBPE layer could be adjusted by controlling polymerization time to give the LBPE-functionalized SBA15/MSUF silica（PE-SBA15/PE-MSUF）with accessible porosity.It was found that PE20 min-MSUF silica,a sample taken at 20 min during ethylene polymerization catalyzed by the Pd-MSUF silica,exhibited typical mesoporous structure with a pore volume of 0.57 cm³/g and a BET of 141.54 m²/g.To improve the dispersibility of nm TiO₂ in polypropylene（PP）,polystyrene was grafted to the surface of nm TiO₂ and the in situ compatibilization between the resulting polystyrene-grafted nm TiO₂（PS-g-TiO₂）and polypropylene（PP）was carried out by means of Friedel-Crafts（FC）alkylation reaction.A dispersion polymerization of styrene （St）was first conducted in the presence of nm TiO₂ particles modified with a silane coupling agent,3-acryloxypropyltrichlorosilane（MPS）,to prepare the PS-encapsulated nm TiO₂ microspheres（PS@TiO₂）,and then the PS-grafted nm TiO₂ was obtained by purifying the resulting PS@TiO₂ microspheres with toluene to remover free PS.The prepared PS@TiO₂ microspheres and PS-g-TiO₂ particles were subsequently added into PP,respectively,along with FC catalyst（AlCl₃/St）of different concentration by melting blending process to give a series of PP nanocomposites.The structure of modified nm TiO₂ was characterized through TGA、FTIR、XPS、TEM、EA,and its dispersibility in PP matrix,and the resistance to UV aging of corresponding PP nanocomposites were compared using TEM,SEM,TGA,DSC,and UV artificially accelerating aging testing, etc.It was revealed that a few PS chains were covalently linked to the surface of nm TiO₂ particles.For the PP/PS@TiO₂ system,nm TiO₂ particles were found to exist selectively within PS phase of 100-120 nm due to the poor compatibilization between PP matrix and grafted PS.The dispersibility of PS-g-TiO₂ particles in PP could be further improved by using FC catalyst.For the PP/PS-g-TiO₂/AlCl₃/St system,when AlCl₃ concentration reached 1.0 wt%,the PS-g-TiO₂ particles were dispersed homogeneously within the whole PP matrix in nanoscale,with a considerably enhanced interfacial adhesion.Surface modification of nm TiO₂ by grafting with PS,as well as in situ compatibilization using FC catalyst,can impart the corresponding PP nanocomposite with highly enhanced resistance to UV aging and better thermal stability.更多还原