Controlled Radical Polymerization for Novel Soft Materials

点击翻译按钮获取中文摘要

Reversible de-activation radical polymerization (RDRP) has emerged over the past two decades as a viable alternative to living polymerization (LP) methods to produce polymers with controlled microstructure. Virtually all modern technologies depend on materials with defined molecular properties; polymers are critical for microelectronics (directed self-assembly, lithography), biomaterials (eg. controlled release, membranes) and structural materials (coatings, sealants, thermoplastic elastomers). RDRP's key advantage over LP is it mimics superficially hallmarks of LP (linear progression of degree of polymerization vs. conversion, narrow molecular weight distribution, active chain ends) without applying the stringent purification and conditions required of the latter. Further, RDRP can be done in water and combine monomers that otherwise could not be done by LP. The research program applies RDRP to develop new materials, using mostly a variant termed nitroxide mediated polymerization (NMP), which avoids resin discolouration from metallic ligand catalyst residues or sulfur-based chain transfer agents that are present in other common RDRP processes. The program planned for the next 5 years will focus on using NMP for: 1) directed self-assembly of tapered/gradient copolymers towards patterning surfaces for microelectronics; 2) new functional materials via click chemistry for hydrogels and self-healing polymers; 3) synthesizing amphiphilic block copolymers for application in kinetic hydrate inhibitors/promoters. Directed self-assembly is already exploited in dielectric materials (IBM's AirGap technology) and is considered the successor microelectronics technology to photolithography, where it becomes more difficult to obtain smaller feature sizes by shrinking the wavelength. We will use gradient copolymers instead of block copolymers as an intermediate purification step is avoided when crossing from one block to the other. However, the more diffuse interface interesting self-assembly challenges. We will explore how to obtain smaller feature sizes while programming the interfacial width in a controlled manner. NMP has lagged behind other RDRP methods in adopting orthogonal functionalization methods like click chemistry and hydrogels. We will also examine initiator modification based on new designs which can homopolymerize methacrylates and cross-over cleanly to other monomer families, yielding new materials. Concurrently, we will also adopt orthogonal functionalization strategies like click chemistry to access a wider range of material properties than that was possible earlier by NMP. Finally, amphiphilic water-soluble block copolymers as kinetic hydrate inhibitors (KHIs) were recently reported by us to be quite effective. Formation of hydrates is one of the most critical problems facing flow assurance in gas pipelines. Our initial forays will be used to develop structure-property relationships and eventually design biodegradable non-toxic KHIs.