Switchable Polymer Reactors：New-Concept Catalysts And Tunable Catalysts

Catalysis is the cornerstone of modern chemical industry and the realization of smart catalysts with switchable catalytic ability is increasingly becoming a common objective at this era. The recent advances in new-concept catalysts, particularly switchable polymer reactors represented by poly(N-isopropylacrylamide)(PNIPAm)-supported metal nanoparticles, have made possible this objective. Nonetheless, the development of polymer reactors with practical potentials for applications has been proven to be elusive, mainly because most of the reported polymers suitable for supporting metal nanoparticles are not PNIPAm, which clearly lack thermal phase transition and adjustable elements. As such, scientists have been under pressure to meet this challenge. This objective in this dissertation is to meet this challenge by introducing new concepts into the development of polymer reactors, including hierarchical molecular self-assembly, biomimetic self-adaption, hyperbranched networks and mobile molecular chains. The focal point of the dissertation has been put in the development of new designs, principles and switchable mechanisms involved in polymer reactors. The use of innovative designs and concepts endowed the prepared polymer reactors with new response features, which thereby made smart polymer reactors smarter.The first part is about the polymer reactor capable of self-sorting catalysis. Inspired by the protein can form ordered self-assembled architectures that automatically adapt to the change of environments,we aimed at the present challenge in self-controlled catalysis by developing a novel polymer reactor, which was furnished with self-assembled hierarchical access capable of sortable catalytic ability. The polymer reactor was constructed from Ag nanoparticles and a unique copolymer carrier containing poly(4-penten-1-ol)(PPol), poly(1-vinylimidazole)(PVI) and poly(2-trifluoromethylacrylicacid)(PTFMA). The hierarchical access of the smart carrier, by closing, relaxing and opening, acted as a molecular switch for providing sequenced entrance to the encapsulated metal nanoparticles, achieving the sortable catalytic ability. Actually, the basic reason is two different strength of interactions among PTFMA, PPol and PVI, weak hydrogen bonds(between PPol and PTFMA) and relatively stronger polymer complexes(between PVI and PTFMA). This polymer reactor showed poor catalytic reactivity at relatively low temperatures(<37 oC) due to the closed access, which blocked substrate from the encapsulated metal nanoparticles. This polymer reactor showed, however, significant reactivity for small molecules of substrate at modest temperatures(37~55 oC), arising from relaxing of the access, which allowed small molecules to gain entrance to the catalytic metal nanoparticles. This polymer reactor further showed significant reactivity for large molecules of substrate at relatively high temperatures(>55 oC), in response to the opening at the access. In this way, this polymer reactor demonstrated the sortable catalytic ability.In order to overcome the leaks and falling of the nanoparticles of the novel polymer reactor in the repeated switchable interaction process, which leads to the serious deficiencies of the practical use, in the second part, inspired by the compatible characters between marine organisms and aqueous environment, the paper introduces the mussels adaptive mechanism in the aqueous phase into the polymer reactor design and synthesis. The polymer reactor was consisted by metal nanoparticles and a mussel-inspired polymer carrier containing self-assembled adaptive domains. The self-assembled adaptive domains, by closing and opening, acted as a molecular switch for providing controlled entrance to the encapsulated metal nanoparticles. By the self-assembly behavior of the intelligent carrier, making the polymer reactor capable of the switchable “on/off” in aqueous phase. Unlike reported smart reactor, this smart polymer reactor was self-adaptive without having any leaching of the encapsulated metal nanoparticles, due to the strong anchoring between dopamine moieties and metal nanoparticles. Thesis clarifies the formation mechanism of the polymer reactor and molecular interaction on the basis of the study of self-assembly properties of the bionic functional monomer, the adaptive behavior of smart materials, the on/off character of the substrate access and catalysis and modulation from the polymer reactor to the substrate, laying the foundation for control and tunable in the aqueous phase catalytic process.In the third part, to overcome the restriction of PNIPAm in materials and types, the experiment uses the common and convenient monomer to synthesize hyperbranched polymer reactor. Firstly, ethylenediamine and methyl acrylate are used as the basic material to synthesize hyperbranched polyethylenimine. Then after the hydroxyethyl acrylate surface modification the intelligent responsive polymer reactor filled with rich hydrophilic hydroxyl groups and hydrophobic saturated aliphatic hydrocarbon is synthesized. In the study, below the transition temperature, the interactions between hydrophilic hydroxyl and aqueous medium facilitate the solution of the hyperbranched reactor in water, which provides the access to the active precursor to the substrate. At that time, the reactors is open. On the contrary, above the transition temperature, the relative balance between hydrophilic hydroxyl and hydrophobic aliphatic hydrocarbons is broken so the hydrophobic interaction plays a decisive role, which means the reactor insoluble in water. At this time, water has become a poor solvent of the polymer, quickly discharged from the inside, causing the “jam” of the substrate access and the catalysis is closed. In this unique way, hyperbranched polymer reactor obtains the immediate transition or “freeze” through the hydrophilic/hydrophobic thermal phase transition in the transition temperature conditions, skipping or stopping at preset position to achieve control and tunable of the aqueous phase catalytic process.In the fourth part, in order to meet the requirements of the fixed point temperature catalytic control, we have also developed a fixed point temperature controlled polymer reactor. Too high or too low temperatures will inhibit the catalytic effect. Only in the specific temperature range, it can show a significant catalytic role. Inspired by the mechanism of the living tissue automatically restoring the original shape after the external force, we creatively introduce the mobile phase of the shape memory polymer to the smart polymer reactor, which finally comes to the design and synthesis of the conceptual catalysts. The polymer reactor carrier is composed of the cross-linked polyacrylamide and the mobile phase is the dodecyl side chains capable of the heat movement. The polymer reactor showed weak reactivity at relatively low temperatures(<40 oC) due to the low mobility of molecular chains in the switchable domains, which inhibited the access of substrate to the encapsulated nanoparticles(i.e., catalytic ‘off’ status). The reactor also showed weak reactivity at relatively high temperatures(40 ~45 oC) in response to the significantly increased hydrophobicity(viz., catalytic ‘off’ status). The reactor only demonstrated significant catalysis at modest temperatures(>45 oC), arising from the relative balance between the mobility of molecular chains and the hydrophobicity in the switchable domains(i.e., catalytic ‘on’ status). In this unique way, the synthesis reactor shows a fixed point temperature catalytic ability. This novel design opens up the opportunity to develop localized smart polymer reactors for controlled catalytic processes.Thesis clarifies the regular of self-controlled catalysis of the polymer reactors and the influence of the factors on the adaptability and responsiveness of synthetic reactor. The research could provide experimental basis and theoretical guidance for develop the self-switchable polymer reactor. The new design provide the reactor new properties and create conditions for the more intelligent catalytic materials.