Melt-Miscible Polyethylene Block Copolymers

技术摘要：将开发与聚乙烯(PE)具有低相互作用能量密度(X，与Flory-Huggins相互作用参数成正比)的碳氢化合物聚合物；将这些聚合物与PE以嵌段共聚物的形式结合，可以得到强度更高的半结晶塑料，或易于加工的熔融相容热塑性弹性体，具体取决于聚合物组成和嵌段结构。最近，研究表明，通过降冰片烯衍生物开环歧化聚合(ROMP)然后催化加氢制备的某些聚合物对PE表现出相对较低的X，尽管这些特定的ROMP聚合物的玻璃化转变温度(Tg)略低于室温，因此没有提供机械增强。这个项目将研究其他取代的降冰片烯，包括带有苯基、环己基和降冰片基的聚合物，所有这些聚合物的玻璃化转变温度都远高于室温。这些聚合物之间的相互作用强度，统称为“PX”，以及这些聚合物与线性PE(由ROMP聚环戊烯加氢制备的LPE)之间的相互作用强度，将通过合成目标分子量的定义明确的嵌段共聚物，以及通过小角X射线散射测量熔体相行为，包括热致有序-无序转变温度来测量。采用无规共聚物嵌段来调节降冰片烯基聚对苯二甲酸乙二酯嵌段的溶解度参数，以提高其与LPE的相容性。测量的相互作用能密度，如果被发现服从规则混合，则在溶解度参数框架内解释(产生一个溶解度参数“阶梯”，其中每个“梯级”是一种新型的ROMP聚合物)，或者如果被发现不规则混合，则在三元混合框架内解释。反过来，这些框架将允许设计含PE的材料--通过选择嵌段化学成分和长度--形成均匀的、易于加工的熔体。将探索两种特殊的体系结构，作为通过加入高玻璃化转变温度PX块来实现性能改进的“试验台”：PX-LPE-PX三块块，具有大部分可结晶的中间块，以及LPE-PX-橡胶-PX-LPE五块块，具有主要的橡胶中间块。非技术摘要：聚乙烯(PE)无疑是最普遍的合成聚合物--2012年在美国生产了390亿磅(随着页岩气中乙烯的可获得性，产量还在增加)--在日常生活中从奶瓶到耐候板到髋关节置换物的应用都很熟悉。PE还与其他聚合物以嵌段共聚物的形式结合在一起，在许多特殊应用中，包括热塑性弹性体(TPE)，这两种聚合物是共价结合的，热塑性弹性体(TPE)是可以熔融加工和回收的橡胶。在热塑性弹性体中，熔体之间的可混性促进了熔体加工，大大减少了所需的能量。本工作旨在开发一种既可与PE熔融相容，又具有室温以上玻璃化转变温度(软化点)的聚合物，以赋予最终嵌段共聚物玻璃态聚合物的强度特性。拟议的工作将为三至四名研究生和三至六名本科生提供综合研究和教育体验。学生将成为明确定义的聚合物的合成、大分子表征、小角x射线散射的结构表征、聚合物混合热力学以及聚合物的机械性能和结构-性能关系方面的专家。通过让学生在项目的所有阶段工作，从合成到测试应用，他们获得了一个“大图景”，这将为他们未来的基础提供很好的服务。PI和学生们将通过在普林斯顿大学校园和附近学校的科学推广活动来吸引普通公众，最直接的方式是开发一个大型礼堂“聚合物秀”，将于2014年首次亮相。一个明确的目标是促进中学生对聚合物材料科学和技术的兴趣和欣赏，包括特伦顿公立学校系统的学生。

TECHNICAL SUMMARY:Hydrocarbon polymers exhibiting a low interaction energy density (X, proportional to the Flory-Huggins interaction parameter) against polyethylene (PE) will be developed; combining these polymers with PE in the form of block copolymer can lead to either higher-strength semicrystalline plastics, or easily-processed melt-miscible thermoplastic elastomers, depending on polymer composition and block architecture. Recently, it has been shown that certain polymers prepared via ring-opening metathesis polymerization (ROMP) of norbornene derivatives followed by catalytic hydrogenation show a relatively low X against PE, though those particular ROMP polymers have glass transition temperatures (Tg) slightly below room temperature, hence providing no mechanical reinforcement. This project will investigate other substituted norbornenes, including polymers with phenyl, cyclohexyl, and norbornyl sidegroups, all of which show Tg well above room temperature. Interaction strengths between these polymers, collectively denoted as "PX", and between these polymers and linear PE (LPE, prepared by hydrogenation of ROMP polycyclopentene), will be measured via the synthesis of well-defined block copolymers, at targeted molecular weights, and measurements of the melt phase behavior, including the thermotropic order-disorder transition temperature, by small-angle x-ray scattering. Random copolymer blocks will be employed to tune the solubility parameter of the norbornene-based PX block, to promote miscibility with LPE. The measured interaction energy densities will be interpreted within a solubility parameter framework if found to obey regular mixing (generating a solubility parameter "ladder" where each "rung" is a novel ROMP polymer), or within a ternary mixing framework if found to mix irregularly. These frameworks will, in turn, permit the design of PE-containing materials -- through selection of block chemistries and lengths -- which will form homogeneous, easily-processed melts. Two particular architectures will be explored, as "test beds" for the property modifications which can be achieved through the incorporation of high-Tg PX blocks: PX-LPE-PX triblocks with a majority crystallizable midblock, and LPE-PX-rubber-PX-LPE pentablocks, with a majority rubbery midblock. NON-TECHNICAL SUMMARY:Polyethylene (PE) is far and away the most ubiquitous synthetic polymer -- 39 billion pounds produced in the US in 2012 (and increasing, with the availability of ethylene from shale gas) -- and is familiar in daily life in applications ranging from milk jugs to weatherproofing sheet to hip replacements. PE is also combined with other polymers, in the form of a block copolymer -- where the two polymers are covalently bound -- in numerous specialty applications, including thermoplastic elastomers (TPEs): rubbers which can be melt-processed and recycled. In TPEs, melt-miscibility between the blocks facilitates melt-processing, greatly diminishing the amount of energy required. The present work seeks to develop a polymer which is both melt-miscible with PE and which has a glass transition temperature (softening point) above room temperature, to impart the strength characteristic of glassy polymers to the final block copolymer. The proposed work will provide an integrated research and educational experience for three to four graduate students and three to six undergraduates. Students will become expert in the synthesis of well-defined polymers, macromolecular characterization, structural characterization by small-angle x-ray scattering, polymer mixing thermodynamics, and polymer mechanical properties and structure-property relationships. By having students work across all phases of the project, from synthesis to test application, they gain a "big picture" outlook which will serve them well as a future foundation. The PI and students will engage the general public through science outreach, on the Princeton University campus and nearby schools, most immediately through the development of a large-auditorium "Polymer Show" to debut in 2014. A specific aim is to promote interest in, and appreciation for, polymeric materials science and technology among middle school students, including those in the Trenton public school system.