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碳纳米管对聚酯共混体系酯交换反应的影响
【作者】 孙玉蓉；
【导师】 吴德峰；
【作者基本信息】 扬州大学 ， 材料物理与化学， 2010， 硕士
【摘要】 针对聚酯共混体系中的酯交换反应的研究是近年来日益受到人们关注的一个重要课题。这类体系在熔融状态下可以通过酯交换反应原位形成嵌段或无规共聚物,这不仅为制备具有特定组成和序列的共聚物提供了新的途径,还为探究大分子之间的反应提供了良好的模板。因此,深入了解这类共混体系中影响酯交换反应的各种因素,对于控制和设计共混物的化学结构和物理形态,乃至材料的宏观性能,具有十分重要的理论和实践意义。在线型饱和聚酯家族中,聚对苯二甲酸丙二醇酯(PTT)是近年来出现的新成员。它兼具了家族中聚对苯二甲酸乙二醇酯(PET)的强度高、耐热性佳和聚对苯二甲酸丁二醇酯(PBT)的柔性好、易加工的优点,因此在热塑性工程塑料领域具有美妙的应用前景。此外,由于其聚合单体来源于玉米糖等可再生资源,因而被誉为新世纪的绿色材料之一,并越来越受到人们的关注。不过与传统的聚酯PET、PBT的改性工作相比,针对PTT的改性研究才刚刚起步。这其中,通过简单易行的共混改性制备高性能及功能化的PTT复合材料是研究工作的主要方向。然而围绕PTT与其他聚酯的共混体系在加工过程中可能发生的酯交换反应及其对宏观性能的影响其研究尚不充分。如果能够明确PTT共混体系的酯交换反应对加工工艺的依赖性,并在此基础上进一步确定这些反应引起的化学结构的变化与材料宏观性能之间的关系,就可以为制备高性能及功能化的PTT复合材料提供理论基础和加工依据,从而达到对PTT复合材料进行结构设计和性能控制的目的。这对PTT应用领域的拓展具有重要意义。因此本论文首先采用熔融共混制备了聚对苯二甲酸丙二醇酯／聚对苯二甲酸丁二醇酯(PTT/PBT)和聚对苯二甲酸丙二醇酯／聚碳酸酯(PTT/PC)两种共混体系。随后通过核磁共振波谱仪(NMR)、差示扫描量热仪(DSC)等方法研究了共混体系中的酯交换反应,重点考察了共混工艺、传统的酯交换催化剂(正钛酸四丁酯)以及表面改性的纳米粒子(碳纳米管)作为新型的酯交换催化剂对酯交换程度和共混物形态的影响,建立了不同体系中聚合物的数均序列长度和无规度与组分间酯交换反应之间的关系。得到的结果叙述如下：(1)PTT/PBT为典型的热力学相容体系。在不添加催化剂的情况下,延长共混时间对体系的酯交换程度几乎无影响；正钛酸四丁酯(Ti(OBu)4)对PTT与PBT的酯交换具有较佳的催化活性,酯交换度随Ti(OBu)4含量的增加单调增加；酯交换反应的产物为PTT-PBT共聚物,随着酯交换度增加,共聚物中PTT和PBT嵌段的数均序列长度趋于变短,共聚物也由嵌段型逐渐变为无规型,体系的无规度相应增加；此外,共混体系的熔点Tm和结晶温度Tc随酯交换的进行逐渐降低,结晶度和结晶的完善程度减弱；表面改性的碳纳米管对PTT/PBT体系的酯交换反应同样具有催化作用：少量碳纳米管(CNT)的加入能够促进酯交换反应的进行,不过随CNT浓度的增加,共混体系黏度的上升使酯交换度有所下降,但仍高于未加CNT的体系；此外,与羟基化的碳纳米管(OH-CNT)相比,羧基化的碳纳米管(COOH-CNT)能够更好的促进酯交换反应；不过COOH-CNT的存在会使得相容的PTT/PBT体系发生晶相分离；(2)PTT/PC为典型的热力学不相容共混体系。Ti(OBu)4对该体系同样具有较佳的催化活性,PTT与PC酯交换度随Ti(OBu)4含量的增加单调增加,反应产物为PTT-PC共聚物；酯交换反应显著改善了共混体系的不相容性,共混物的相形貌由宏观两相结构转变为宏观均相结构；与此同时,体系两组分的玻璃化转变温度合二为一,PTT的熔融峰也随着酯交换反应程度的增加而消失,晶区转变为无定形区；少量COOH-CNT的加入同样能够一定程度上促进PTT/PC体系的酯交换反应,而随COOH-CNT含量继续增加,酯交换程度略有下降；不过COOH-CNT的存在有利于共混体系玻璃化转变温度的提高。
【Abstract】 Transesterification in the polyester blends is an important subject which has gained increasing attention in recent years. The block or random copolyesters could be in-situ formed via transesterification between the components during melt mixing, which not only provides a new route to fabricating novel copolymers with designed composition and sequential order, but also provides a good template to explore the reaction between macromolecules.Therefore, understanding the factors on the transesterification is vital to design the chain structure and the physical morphology of the blends, and to control the final properties of produced materials.Poly(trimethylene terephthalate) (PTT) is a new member of linear saturated polyester family. It combines high mechanical strength and good heat resistance of poly(ethylene terephthalate) (PET) and nice flexibility and processing features of poly(butylene terephthalate) (PBT), and hence, is a promising candidate in the field of engineering thermoplastics.Moreover, the monomer of PTT, namely propanediol, can be derived from corn sugar, a renewable resource, and hence PTT has also drawn considerable attention for having a biobased origin yet having the properties of an engineering plastic. Comparing with those already on the traditional polyester PET and PBT, however, the modification work on the PTT is not sufficient and the transesterification in the blends based on PTT and other polyesters have not yet been fully studied, which is very important to fabricate PTT based materials with high performance and to extend their applications.Thus, in this work, the poly(trimethylene terephthalate)/poly(butylenes terephthalate) blend (PTT/PBT) and poly(trimethylene terephthalate)/polycarbonate blend (PTT/PC) were prepared by melt mixing. Then, the transesterifications in these two blends were studied by nuclear magnetic resonance spectroscopy (NMR) and differential scanning calorimetry (DSC).The effects of blending time, addition of the traditional catalyst (tetrabutyl orthotitanate) and a new type catalyst (surface modified carbon nanotube) on the transesterification level and the morphologies of these two blends were deeply explored, aiming at relating number-average length, degree of randomness to the transesterification level among the component polymers. The preliminary results are as follows.(1)Miscible PTT/PBT BlendFor the PTT/PBT blend, the morphological characterization results show that the system is thermodynamically miscible. Prolonging the blending time has few effects on the transesterification level.But the tetrabutyl orthotitanate (Ti(OBu)4) shows high catalytic activity to the transesterification, which yields the PTT-PBT copolymers.The transesterification level increases monotonically with the increase of Ti(OBu)4 contents, and the number-average length of PTT and PBT in the copolymers tends to be reduced and the degree of randomness of blends increases as a result, accompanied by the decrease of melt temperature (Tm) and crystallization temperature (Tc) of blends.The presence of surface-modified carbon nanotube could also catalyze the transesterification between two component polymers.Small addition of carbon nanotubes (CNT) could promote transesterification remarkably while excessive addition of CNT depressed the transesterification slightly becauses of increasing viscosity of the blends.Compared with hydroxy carbon nanotubes (OH-CNT), carboxylic carbon nanotubes (COOH-CNT) can better promote the transesterification. But the presence of COOH-CNT leads to the crystalline separation between PTT and PBT.(2) Immiscible PTT/PC BlendFor the PTT/PC blend,two typical immiscible morphologies, i.e.,spherical droplet and co-continuous structures can be observed at various compositions. The Ti(OBu)4 also has high catalytic activity to the transesterification between PTT and PC,yielding the PTT-PC copolymers.The transesterification level increases monotonically with increasing Ti(OBu)4 contents, which improved the compatibility of the PTT/PC blend evidently. After transesterification, the original two glass transition temperatures (Tg) of the blends were found to shift to each other and finally merge into one single Tg, and the transesterificated system exhibits a homogeneous phase morphology. With increasing transesterification level, the melting behavior of semicrystalline PTT disappears and the PTT component becomes amorphous.Small addition of COOH-CNT also promotes the transesterification remarkably, while superfluous COOH-CNT reduces reaction levels slightly. However, the presence of COOH-CNT could increase Tg of PTT/PC blends.