Melt-Miscible Polyethylene Block Copolymers

技术概述：将开发对聚乙烯（PE）表现出低相互作用能量密度（X，与Flory-Huggins相互作用参数成比例）的烃类聚合物;将这些聚合物与PE以嵌段共聚物的形式组合可以产生更高强度的半结晶塑料，或容易加工的熔融混溶热塑性弹性体，这取决于聚合物组成和嵌段结构。 最近，已经表明，通过异丙基烯衍生物的开环易位聚合（ROMP）随后催化氢化制备的某些聚合物显示出相对于PE的相对低的X，尽管那些特定的ROMP聚合物具有略低于室温的玻璃化转变温度（Tg），因此不提供机械增强。 本项目将研究其他取代的异戊二烯，包括具有苯基、环己基和异戊烯基侧基的聚合物，所有这些聚合物的Tg都远高于室温。 这些聚合物（统称为“PX”）之间以及这些聚合物与线性PE（LPE，通过ROMP聚环戊烯的氢化制备）之间的相互作用强度将通过在目标分子量下合成明确定义的嵌段共聚物以及通过小角X射线散射测量熔融相行为（包括热致有序-无序转变温度）来测量。 将采用无规共聚物嵌段来调节基于异丙基苯的PX嵌段的溶解度参数，以促进与LPE的相容性。 如果发现遵守规则混合（产生溶解度参数“阶梯”，其中每个“梯级”是新的ROMP聚合物），则将在溶解度参数框架内解释测量的相互作用能量密度，或者如果发现不规则混合，则在三元混合框架内解释测量的相互作用能量密度。 这些框架反过来将允许设计含PE的材料-通过选择嵌段化学和长度-这将形成均匀，易于加工的熔体。 两个特定的架构将被探索，作为“测试床”的性质修改，可以通过合并高Tg PX嵌段实现：PX-LPE-PX三嵌段与大多数可结晶的中间嵌段，和LPE-PX-橡胶-PX-LPE五嵌段，与大多数橡胶中间嵌段。 聚乙烯（PE）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用性而增加）-并且在日常生活中很常见，从牛奶罐到防风雨板到髋关节置换。 PE还与其他聚合物结合，以嵌段共聚物的形式-其中两种聚合物共价结合-在许多特殊应用中，包括热塑性弹性体（TPE）：可以熔融加工和回收的橡胶。 在TPE中，嵌段之间的可熔融性有利于熔融加工，大大减少了所需的能量。 本工作旨在开发一种聚合物，它既与PE熔融混溶，又具有高于室温的玻璃化转变温度（软化点），以赋予最终嵌段共聚物玻璃状聚合物的强度特性。 拟议的工作将为三到四名研究生和三到六名本科生提供综合研究和教育经验。 学生将成为定义明确的聚合物的合成，大分子表征，通过小角度X射线散射，聚合物混合热力学，聚合物机械性能和结构-性能关系的结构表征的专家。 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“大局”的前景，这将为他们提供良好的未来基础。 PI和学生将通过科学推广活动吸引公众，在普林斯顿大学校园和附近的学校，最直接的是通过一个大礼堂的“聚合物展”的发展，在2014年首次亮相。 一个具体的目标是促进兴趣，并赞赏，聚合物材料科学和技术的中学生，包括那些在特伦顿公立学校系统。

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.