【作者】 于晓慧；

【导师】 陈春海；

【作者基本信息】 吉林大学 ， 精细化学品化学， 2011， 博士

【摘要】 聚酰亚胺薄膜由于其优异的耐高温、尺寸稳定性、耐辐照性、电气性能等被广泛用于微电子领域,如柔性印制电路板、自粘带、超大规模集成电路的绝缘隔层、电子包装等。近年来还被用于太空探测领域的研究,如用于柔性太阳能电池基板、人造卫星、太阳帆、太空望远镜等。随着航空、航天及微电子技术的飞速发展,飞行器的飞行速度在不断提高、有效荷载比逐渐增大、飞行距离不断增大、使用寿命也在延长,而电子产品体积也越来越小、质量越来越轻、集成电路向高密度化发展。因此对应用于该领域的聚酰亚胺薄膜也提出了更高的要求,如轻量化、高比强度、高比模量、高耐热性、尺寸稳定性、低线膨胀系数、光学透过性能、耐宇宙环境、可折叠等。这些性能除了由聚酰亚胺本身的化学结构决定外,还受聚集态结构的影响。由于拉伸可以诱导分子链沿着拉伸方向发生取向或促进聚合物结晶,因而该方法通常用于提高聚酰亚胺薄膜力学性能、光学透过性能、面内各向同性和尺寸稳定性能。目前商品化的高性能薄膜也是通过拉伸法制备得到,厚度基本在25μm以上,CTE大于12ppm·K-1,如Kapton、和Upilex。刚性非常大的分子结构使得分子链间相互作用很强,因此传统聚酰亚胺很难像PET、PP等热塑性聚合物可以在T_g附近实现大幅度拉伸,而是对含部分溶剂部分亚胺化的聚酰胺酸膜(PAA膜)进行拉伸,然后在拉伸过程中对其进行后续的酰亚胺化,从而制备得到高性能薄膜。由于PAA膜的亚胺化程度及后续的热处理过程比较难控制,因此该拉伸工艺不易操作。而拉伸完全亚胺化薄膜制备超薄、高性能薄膜则是一个操作简单,很有发展前途的方法,但是该拉伸方法要求用于拉伸的聚酰亚胺薄膜必须具有非常优异的热塑性能以及在高温时具有橡胶弹性体性能。论文从分子结构设计角度出发合成了含醚酮结构、多间位取代、长分子链的二胺单体BABB,并用BABB与商品化五种二酐(PMDA、BPDA、BTDA、ODPA、BPADA)通过两步法,采用热亚胺化制备了一系列新型聚酰亚胺。希望通过柔性结构和间位取代的引入,提高聚酰亚胺的热塑性能,另外醚键与羰基的同时引入,会使聚酰亚胺分子链由于CTC络合而相互缠绕,从而聚合物在高温时体现橡胶弹性体的性能,达到可以采用传统拉伸工艺对亚胺化薄膜进行拉伸制备高性能薄膜的目的。论文对聚酰亚胺的基本性能,如热性能、力学性能、线膨胀系数、聚集态结构、吸湿性能、光学透过性能等进行了研究,并讨论了结构与性能之间的关系。柔性结构的引入,分子链的增长使得所制备的聚酰亚胺具有较低的T_g(<225℃),五种聚酰亚胺的储能模量在T_g附近迅速降落(E’>103),这些表明这几种聚酰亚胺具有优异的热可塑性。五种聚酰亚胺均具有优异的热稳定性能(Td5 500～545℃)、力学性能(2.7～3.0 GPa)、光学透过性能(800nm UV%≈88%)、耐吸湿性能(<0.9%)和阻尼性能。优异的阻尼性能使得这五类聚酰亚胺很有潜力用作缓冲、减震、隔音等材料。高温力学性能研究发现这几种热塑性聚酰亚胺在高温下具有橡胶弹性体性能,尤其是由PMDA制备得到的PI-a在高温下具有最优异的弹性体性能及最突出的韧性(断裂伸长率达1600%),这使得它们可以像PET一样采用拉伸完全亚胺化薄膜的拉伸工艺制备超薄、高模量、高强度薄膜。论文首先通过单向热拉伸的方法将PI-a薄膜在T_g以上进行拉伸,希望制备得到超薄、高性能薄膜。拉伸后薄膜厚度降低70%,实验中获得的最薄的薄膜厚度为7μm。热拉薄膜的力学性能显著提高,模量由2.7 GPa提高到了4.9 GPa,强度由109 MPa提高到258 MPa。在不同牵伸比制备的热拉薄膜具有与铜、硅相近的线膨胀系数,18ppm·K-1和8 ppm·K-1,这使得热拉薄膜很有潜力用于柔性印制电路板。热拉薄膜具有非常优异的光学透过性能和光学双折射,紫外可见透过率高达89%。与商品化的高性能薄膜相比,本论文制备的热拉薄膜具有非常小的线膨胀系数。接着采用单向冷拉法,将PI-a在T_g以下进行拉伸,希望制备得到更高强度、高模量的聚酰亚胺薄膜。冷拉后薄膜具有突出的力学性能,模量为7.8 GPa,强度达386 MPa,与未拉伸薄膜相比,强度提高了2.5倍。冷拉后薄膜的线膨胀系数显著降低,由原来的52 ppm·K-1降低至-1～-3 ppm·K-1。与商品化的Kapton相比,本论文制备得到的薄膜具有更优异的力学性能和线膨胀系数。与Upilex相比,PI-a冷拉伸薄膜也具有非常突出的线膨胀系数。经过对拉伸后薄膜结构与性能的研究发现,单向拉伸使得分子链在拉伸方向发生取向,并伴随着结晶,且取向度及结晶度随着牵伸比的增加而增大,因此拉伸后薄膜在拉伸方向力学性能提高而线膨胀系数大幅度下降。同时拉伸提高了光学透过性能、增大了薄膜面积,降低了制造成本。柔性结构的引入不仅使新型热塑性聚酰亚胺具有较低温度的可熔融加工性能,还使采用拉伸亚胺薄膜的方式制备高性能的超薄薄膜成为可能。拉伸后制备得到的超薄高性能薄膜在航天和微电子领域具有重大的应用价值。更多还原

【Abstract】 Thermoplastic polyimide films (TPI) are widely used in the fields of microelectronic industry such as flexible printed circuit, tape automated bonding, interlayer dielectrics in multilevel large-scale integrated circuits and electronic skins for their considerable resistance to high temperatures, high dimensional accuracy and high tolerance against radiation. Recently, research on space exploration also takes advantages of TPI films for the fabrication of the base films for flexible solar cells, artificial satellites, solar films and space telescope.With the development of aerospace and electronic industry, higher speed, greater effective load, longer flying distance and lifetime are required for spacecraft, while the electronic products will be oriented to higher density integrated circuit with small volume and light weight. Thus the PI films should offer light weight, high strength, high modulus, thermal stability, dimensional stability, transparent, resistance to space environmental effects, low coefficient of thermal expansion (CTE), foldable, and so on. These properties are affected by the chemical structures and the aggregation structures of the PIs. The stretching method is commonly used to enhance the mechanical properties, optical properties, in-plane isotropy and reduce the CTE through inducing alignment of molecular chains in the direction of stretch and promote the crystallization of the polymers during the drawing processes. The commercial high performance PI films such as Kapton and Upilex, are prepared with uniaxial or biaxial streching to a thickness of at least 25μm and CTEs higher than 12 ppm·K-1. Traditional PIs are rigid for their strong interaction between polymer chains, stretching near T_g like other thermoplastic polymers, e.g. PET, PP, etc, are hardly achieved. To our knowledge, commercial high performance polyimide films are probably stretched with partially imidized poly (amic acid) precursor and imidized completely during the stretching process. However, the simultaneous solvent outgassing and the succeeding high-temperature imidization reaction during the stretching process are contaminative and also difficult to manage. The other potentially simpler and alternative approach is to stretch the thermoplastic and fully imidized polyimide films to prepare ultra-thin high performance films. However, for this stretching methodology, PIs should possess outstanding thermoplastic in nature and excellent rubbery properties at high temperature.A series of novel polyimides were prepared with designed diamine 1,3-bis(3-aminophenoxy-4’-benzoyl) benzene (BABB) containing ether and ketone moieties, meta-substituted linkages, and five kinds of commercial dianhydrides by two-step thermal imidization. By introducing flexible linkages and meta-substituted rings in the polymer chains, improved thermoplastic properties are anticipated. The ether and carbonyl groups may provide the polymer rubbery properties at high temperature owing to the CTC and cross links between the molecular chains, so that traditional stretching method could be applied to the fabrication of high performance polyimide films. Basic properties of these PI films, such as thermal properties, mechanical properties, CTE, aggregation, water absorption and optical properties are characterized and the relationship between the structures and properties are studied. All the PI films exhibited excellent thermoplastic properties owing to their very low glass transition temperature (<225℃) and drop of storage modulus at T_g (higher than 103). All the polyimides exhibited outstanding thermal stability (Td5 500～545℃), mechanical properties (2.7-3.0 GPa), optical properties (UV transmittance% about 88% at 800 nm), very low water absorption (<0.9%) and remarkable damping properties (tanδ2.0～3.0). The outstanding damping properties make these polyimides maybe useful as materials for shock absorption and sound insulation. All polyimides had excellent mechanical and rubbery properties at high temperature, especially, the PI-a exhibited the most remarkable rubbery properties and the largest strain (1600%), which indicated these polyimides can potentially be used to prepare ultra-thin film with ultra-high strength and ultra-high modulus by traditional stretching method as the PET polymer.Firstly, ultra thin and high performance PI films were obtained by hot stretching of the PI-a above T_g. The thickness of the films reduced at above 70%, and the thinnest locality is about 7μm. The mechanical properties of hot stretched films improved a lot, the tensile modulus increased from 2.7 GPa to 4.9 GPa, and the tensile strength enhanced from 109 MPa to 258 MPa. The hot stretched films are potentially used as flexible printed circuit due to appropriate CTEs with copper and silicon substrates. The stretched films showed excellent UV-visible transparence and optical birefringence, the transmittance enhanced from 84% to 89%.To prepare ultra high strength and ultra high modulus PI films, the PI-a film was uniaxially stretched at a temperature below its T_g. The stretched films exhibited outstanding mechanical properties, the tensile modulus was about 7.8 GPa and the tensile strength was about 386 MPa, which was about 3.5 times of that of undrawn film. The CTE of stretched films reduced from 52 ppm·K-1 to -1～-3 ppm·K-1. The stretched films exhibited higher mechanical properties and lower CTE as compared with that of Kapton. The stretched films also showed lower CTE than that of Upilex.The study of relationship between structures and properties of stretched films showed that the molecular chains developed a high degree of orientation along the stretching direction and promoted the crystallization during the stretch process, and the degree of orientation enhanced with the increase of stretch ratio. So the tensile properties improved and the CTE decreased along the stretch direction. The uniaxial stretch method also improved the optical properties and brought down the cost owing to the increased acreage.Not only does the introduction of the flexible linkages make the novel TPI has excellent thermoplastic properties but also make it possible to prepare high performance ultra thin films by stretching the imidized films, which is very valuable for the aerospace and micro-electronic industry.更多还原