Tactic, Ionomer, and Long Branch Length Effects in Precision Polymer Chemistry

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NON-TECHNICAL SUMMARY:The largest-volume plastic in use in the world is polyethylene. It is made in various forms to meet the myriad of applications found today. Almost every person in developed countries around the world encounters polyethylene on a regular basis. The research in this project is designed to create new types of polymers similar to polyethylene, and to control and better understand their microstructure (i.e., the molecular structure of these different kinds of polyethylene). Over several years new chemistry, known as ADMET chemistry, has been developed in the PI's laboratory which permits synthesis of some polymer molecules and control of their microstructure in a clear, precise manner. Microstructure can be controlled more easily using ADMET chemistry than virtually any other approach. If this project is successful, not only better fundamental understanding but also potential improvements in properties and performance could be realized, a result which would touch a significant portion of the world's population.TECHNICAL SUMMARY:Three specific objectives comprise this proposal, all of which will benefit from collaboration with researchers providing complementary expertise.Objective 1. The most challenging objective will be to synthesize tactic versions of precision polymers with the substituent being a methyl group. Objective 1 is designed to build linear polyethylene with tactic methyl groups attached at precise spacer intervals. It will try to answer the question of how far apart must these stereogenic centers be before they no longer influence crystallization of the polymer (and ultimately its mechanical behavior). The synthetic strategy, which is quite challenging, has already been elucidated. The concept revolves around C2 symmetry within a monomer containing two stereogenic centers possessing methyl substituents.Objective 2. The synthesis and behavior of precision ionomers will be probed. Such ionomers can be created with the polymer backbone being either cationic or anionic. The primary question to be probed is whether combining the cationomer precision polymer with the anionomer precision polymer will lead to highly organized structures. Special molecular interactions and the resulting morphologies will be determined.Objective 3. Long-chain branching in polyethylene will be examined, a phenomenon which relates to structural questions for LLDPE as well as metallocene polyethylene. Precision polymers possessing branches 21 carbons long will be prepared. Spacing distances between branches can be as short as every 9th carbon or as long as every 75th carbon. The question here is related to how each "part" of the polymer (the polyethylene backbone and the long-chain branch) will interact, e.g. how will the individual long-chain branches crystallize and what potentially new phases might be formed.