Synthesis and Characterization of Novel Double-Functionalized Surface Modified Thermoplastic Elastomers

总结。这项聚合物科学项目由材料研究部的聚合物计划和国际科学与工程办公室的中欧和欧亚计划共同资助。本论文的目的是合成和表征新型非极性自组装纳米弹性体嵌段共聚物，其表面修饰有极性羟基官能团。具体地说，将合成包括树枝状(树枝状)聚异丁烯(ArbPIB)核的无定形嵌段共聚物(ArbPIB)，该核在每个支化点携带伯羟基，侧翼是构成聚合物约30wt%的聚(苯乙烯-co-对-胸基甲基苯乙烯)玻璃嵌段(arbPIB(OH)-b-P(St-co-TMeST))。异丁烯(IB)以4-(1，2-氧杂环烷-异丙基)-苯乙烯为引发剂-单体与TiCl4进行活性碳阳离子聚合，将在核的每个支化点引入一个极性伯羟基(arbPIB(OH))。初步证据表明，极性基团迁移到非极性聚合物的表面，可以进行进一步的修饰。用核磁共振、扫描电子显微镜、傅立叶变换红外光谱、X射线光电子能谱等手段对arbPIB(OH)核进行了表征。在确定最佳合成条件后，将通过活性碳阳离子聚合，采用顺序单体加成，然后对末端嵌段进行适当的官能化处理，合成嵌段共聚物。橡胶和塑料相的相分离控制了块的自组装，从而导致了材料的增强。静态和动态性能，后者在生物医学应用中至关重要，将通过在苯乙烯相中引入可逆氢键来优化。这将通过St和pClMeST的活性碳阳离子共聚来实现，然后将arbPIB-b-P(St-co-ClMeST)的侧链上的苄基氯基团转化为TME基团，得到一种新型的双官能化嵌段共聚物(arbPIB(OH)-b-P(St-co-TMeST))。这种嵌段共聚物将是一种热塑性弹性体(TPEs)，在室温下表现出类似橡胶的行为，而在玻璃块的玻璃化转变温度(Tg)以上作为塑料加工。我们将研究这种新型嵌段共聚物的本体和表面性质。具体地说，将研究其动态疲劳和蠕变性能，并将其与目前使用的生物材料(硅橡胶、聚酯和聚氨酯)进行比较。预计支化的PIB核和胸腺嘧啶功能基团之间的氢键结合将极大地改善这种新型生物材料的动态疲劳和蠕变性能。表面羟基有望改善生物相容性。疲劳测试将在德国拜罗伊特大学与Volker Altsdt教授合作进行，生物兼容性测试将在波兰什切钦的博美拉尼亚医学院与Miroslawa El Frait教授合作进行。线形和星形支化的PST-b-PIB-b-PST TPE(由PI共同发明)最近已获得FDA批准用作药物洗脱冠状动脉支架涂层。ArbPIB-b-PSt嵌段共聚物是以PIB为基础的热塑性弹性体家族的最新成员。目前的建议描绘了新的合成路线，在arbPIB基嵌段共聚物的表面引入羟基，并对玻璃端基进行官能化。这项研究将产生两个新的材料家族：arbPIB(OH)-b-P(St-co-ClMeSt)和arbPIB(OH)-b-P(St-TMeST)。由于氢键作用，P(St-co-TMeST)端块的玻璃化转变温度(Tg)有望高于PST(Tg~100℃)。此外，还将检验通过氢键改善非晶态嵌段热塑性弹性体的动态疲劳和蠕变性能的假设的正确性(氢键被认为是聚氨酯具有优异疲劳性能的原因)。这将是一个具有普遍适用性的新的、根本性的发展。这种新材料可能会成为医用级硅橡胶的替代品。更广泛的影响。这种新材料，就像其他TPE一样，是环保橡胶，因为它们可以再加工。生产和测试这些新生物材料的项目具有很强的国际性，在德国(机械测试)和波兰(生物兼容性测试)有直接相关的合作。它是对提交给德国和波兰研究基金会(DFG)的建议的补充，该建议旨在研究新型纳米结构弹性体材料的动态蠕变和疲劳性能，这些材料有可能在特定的生物医学应用中取代硅橡胶。去年，25万名美国女性接受了硅胶乳房植入物手术，其中25万人选择了硅胶乳房植入物。这方面在年轻人中很受欢迎，特别是女性，所以这个项目将吸引潜在的美国女性研究生，她们在化学和材料科学领域仍然没有得到充分的代表。这些项目的跨学科性质将使学生接触到各种各样的科学学科(聚合物化学、有机化学、材料科学、生物化学、表面科学、聚合物工程、生物医学工程)。他们还将有机会在德国和波兰进行部分研究。接触不同的文化、组织和职业道德将为学生在全球经济中更好地工作做好准备，使他们对潜在雇主更具吸引力。

Summary. This project in polymer science is co-funded by the Polymers Program of the Division of Materials Research and the Central Europe and Eurasia Program of the Office of International Science and Engineering. It is aimed at the synthesis and characterization of novel non-polar self-assembling nanostructured elastomeric block copolymers, whose surface is decorated with polar hydroxyl functional groups. Specifically, amorphous block copolymers comprising a core of dendritic (arborescent) polyisobutylene (arbPIB) carrying a primary hydroxyl group at each branching point, flanked by poly(styrene-co-p-thymylmethylstyrene) glassy blocks constituting about 30wt% of the polymer, will be synthesized (arbPIB(OH)-b-P(St-co-TMeSt). Living carbocationic polymerization of isobutylene (IB) by using 4-(1,2-oxirane-isopropyl)-styrene as inimer (initiator-monomer) in conjunction with TiCl4 will introduce one polar primary OH group at each branching points of the core (arbPIB(OH)). Preliminary evidence suggests that polar groups migrate to the surface of non-polar polymers, available for further modification. The arbPIB(OH) core will be characterized by NMR, SEC, FTIR, XPS and other appropriate techniques. After establishing optimum synthesis conditions, block copolymers will be synthesized by living carbocationic polymerizations using sequential monomer addition, followed by appropriate functionalization of the end blocks. Self-assembly of the blocks is governed by the phase separation of the rubber and plastic phases, leading to reinforcement of the material. Both the static and dynamic properties, these latter critical in biomedical applications, will be optimized by introducing reversible hydrogen bonding into the styrenic phases. This will be accomplished by the living carbocationic copolymerization of St with pClMeSt, followed by converting the pendant benzylic Cl groups of the arbPIB-b-P(St-co-ClMeSt) into TMe groups, yielding a novel double-functionalized block copolymer (arbPIB(OH)-b-P(St-co-TMeSt). This block copolymer will be a thermoplastic elastomer (TPEs), displaying rubber-like behavior at room temperature while processing as plastics at above the glass transition temperature (Tg) of the glassy blocks. The bulk and surface properties of the novel block copolymer will be investigated. Specifically, the dynamic fatigue and creep properties will be investigated and compared to currently used biomaterials (silicone rubber, polyesters and polyurethanes). It is expected that the combination of the branched PIB core and the hydrogen bonding between the thymine functional groups in the styrenic hard phases will dramatically improve dynamic fatigue and creep properties of this novel biomaterial. The surface hydroxyl groups are expected to improve biocompatibility. Fatigue testing will be carried out at the University of Bayreuth, Germany, in collaboration with Professor Volker Altsdt, and biocompatibility testing will be carried out at the Pomeranian Medical Academy in Szczecin, Poland, in collaboration with Professor Miroslawa El Fray.Intellectual Merit. Linear and star-branched PSt-b-PIB-b-PSt TPEs (coinvented by the PI) have recently received FDA approval for use as drug-eluting coronary stent coating. arbPIB-b-PSt block copolymers are the newest members of the family of PIB-based TPEs. The current proposal charts new synthetic routes to introduce OH groups at the surface of arbPIB-based block copolymers, and to functionalize the glassy end blocks. This research would lead to two new families of materials: arbPIB(OH)-b-P(St-co-ClMeSt), and arbPIB(OH)-b-P(St-TMeSt). The P(St-co-TMeSt) end blocks are expected to have higher Tg than PSt (Tg ~100 C), due to hydrogen bonding. In addition, the validity of the hypothesis of improving the dynamic fatigue and creep properties of amorphous block TPEs by hydrogen bonding will be tested (hydrogen bonding is believed to be the reason for the excellent fatigue properties of polyurethanes). This would be a new, fundamental development with general applicability. The new materials may emerge as an alternative to medical grade silicone rubber. Broader Impacts. The new materials, just like other TPEs, are environmentally friendly rubbers since they can be reprocessed. The project to produce and test these new biomaterials has strong international aspects, with directly relevant collaborations in Germany (mechanical testing) and Poland (biocompatibility testing). It is complementary to proposals submitted to the German and Polish Research Foundations (DFG) to investigate the dynamic creep and fatigue properties of novel nanostructured elastomeric materials that have the potential to replace silicone rubber in specific biomedical applications. Silicone-based breast implants were the single "choice" for a quarter of a million American women who underwent the procedure last year. This aspect is very popular with young people, especially females, so this program will be appealing to potential female American graduate students, still under-represented in the field of chemistry and material science. The interdisciplinary nature of the projects will expose students to a great variety of scientific disciplines (polymer chemistry, organic chemistry, material science, biochemistry, surface science, polymer engineering, biomedical engineering). They will also have a chance to carry out part of their research in Germany and Poland. Exposure to different cultures, organizations and work ethics will prepare the students to work better in the global economy, making them more attractive to potential employers.