New Reactive Surfactants For Emulsion Polymerization

The advantages of emulsion polymerization including the synthesis of polymer with high molecular weight at rapid polymerization rate, the good temperature control, and the low processing viscosity have long been recognized. In emulsion polymerization, large amounts of surfactant are needed to maintain the stability of the emulsion. However, it is found that in many cases the surfactant only play a role in a certain stage, in the later stage they are nolonger needed and even bring some negative impacts. What’s more, the thorough removal of surfactant is very difficult, which not only enhances the synthetic cost, but also causes the environmental pollution. In recent years, functional surfactant has attracted great research interest. On the one hand, functional surfactant makes the synthetic polymer latex particles with more diverse performance; on the other hand, functional surfactant especially those with reactive groups can covalently bond onto the latex particle, which avoids the removal of surfactant and such synthetic strategy is therefore considered convenient and energy conservation. The purposes of this dissertation are to research and develop new kinds of reactive surfactants and investigate their application in emulsion polymerization. Generally speaking, the content of this dissertation involves three aspects:1. One-stage synthesis of cagelike porous polymeric microspheres and application as catalyst acaffold of Pd nanoparticlesPorous microspheres are one of the most interesting candidates for the immobilization of noble metal nanoparticles since the porous character provides good accessibility for reactants just as the micro-and mesoporous inorganic support. However, the synthesis of porous polymeric microspheres generally involves multiple and complex procedures. In this section, one-stage synthesis of cagelike porous polymeric microspheres and their application as catalyst scaffold of Pd nanoparticles are discussed. The synthesis of cagelike porous polymeric microspheres is achieved by W/O/W emulsion polymerization of a surfactant monomer of N-(4-vinylbenzyl)-N,N-dibutylamine hydrochloride and a hydrophobic monomer of styrene in water. Ascribed to the surfactant monomer, convenient one-stage synthesis of cagelike porous polymeric microspheres is afforded, and cagelike porous polymeric microspheres with size ranging from300to600nm and pore volume as large as0.31cm3/g are fabricated. The porous character and the inherent quaternary ammonium moieties make the cagelike porous polymeric microspheres to be the promising catalyst scaffold of Pd nanoparticles, and up to10wt%Pd catalyst with the metal particle size ranging from2.1to5.7nm is loaded. The catalytic hydrogenation of nitrobenzene by H2demonstrates that the heterogeneous Pd catalyst is efficient and reusable.2. RAFT-mediated batch emulsion polymerization of styrene using poly[N-(4-vinylbenzyl)-N,N-dibutylamine hydrochloride] trithiocarbonate as both surfactant and macro-RAFT agentAs is known, emulsion polymerization has been recognized as a convenient and green industrial process in the large-scale synthesis of polymer due to the facile control in the polymerization kinetics and the convenience in the product isolation. However, the precise control over the polymer molecular weight in emulsion system is usually difficult. In this section, the reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization in the precence of poly[N-(4-vinylbenzyl)-N,N-dibutylamine hydrochloride] trithiocarbonate (PVBAH-TTC) is proposed to prepare polymer colloid with controlled molecular weight. PVBAH-TTC is synthesized by the RAFT polymerization of N-(4-vinylbenzyl)-N,N-dibutylamine monomer and followed hydrochloride acidification. PVBAH-TTC contains the reactive trithiocarbonate group and the appending surface-active group, is used as both surfactant and macromolecular reversible additionfragmentation chain transfer (macro-RAFT) agent in batch emulsion polymerization of styrene. Under the conditions at high monomer content of～20wt%and with the molecular weight of the macro-RAFT agent ranging from4.0to15.0kg/mol, well-controlled batch emulsion RAFT polymerization initiated by the hydrophilic2-2’-azobis(2-methylpropionamidine) dihydrochloride is achieved. The polymerization leads to formation of nano-sized colloids of the poly[N-(4-vinylbenzyl)-N,N-dibutylarnine hydrochloride]-b-polystyrene-b-poly[N-(4-vinylbenzyl)-N,N-dibutylamine hydrochloride] triblock copolymer. The colloids generally have core-shell structure, in which the hydrophilic block forms the shell and the hydrophobic block forms the core. The molecular weight of the triblock copolymer linearly increases with increase in the monomer conversion, and the values are well-consistent with the theoretical ones. The molecular weight polydispersity index of the triblock copolymer is below1.2at most cases of polymerization.3. RAFT-mediated emulsion polymerization of styrene using brush copolymer containing PEG side chains as surfactant macro-RAFT agentBlock copolymer assemblies with well-defined morphologies have gained a great deal of interest because of their potential applications in many areas. Traditionally, the preparation of block copolymer assemblies is through the self-assembly of amphiphilic block copolymers in the block-selective solvent. It is found that the self-assembly is usually achieved at low polymer concentration (<1%), and not only the thermodynamic parameters but also the dynamic ones can affect the morphology of the assemblies. This makes the scaled-up production of block copolymer assemblies rather problematic. Herein, the RAFT emulsion polymerization in the precence of brush copolymer macro-RAFT agent is employed to synthesize block copolymer colloids with different morphologies. In this section, the nonionic amphiphilic brush polymers such as poly[poly(ethylene oxide) methyl ether vinylphenyl-co-styrene] trithiocarbonate [P(mPEGV-co-St)-TTC] and poly[poly(ethylene oxide) methyl ether vinylphenyl-b-styrene-b-poly(ethylene oxide) methyl ether vinylphenyl] trithiocarbonate [P(mPEGV-b-St-b-mPEGV)-TTC] with different monomer sequence and chemical composition are synthesized and their application as macro-RAFT agent in the emulsion RAFT polymerization of styrene is explored. It is found that the monomer sequence in the brush polymers exerts great influence on the emulsion RAFT polymerization kinetics, and the fast polymerization with short induction period in the presence of P(mPEGV-co-St)-TTC is demonstrated. Besides, the chemical composition in the brush polymermacro-RAFT agent effect on the emulsion RAFT polymerization is investigated, and the macro-RAFT agent with high percent of the hydrophobic PS segment leads to fast and well controlled polymerization. The growth of triblock copolymer colloids in the emulsion polymerization is checked, and it reveals that the colloidal morphology is ascribed to the hydrophobic PS block extension, and the P(mPEGV-co-St) block almost have no influence on the colloidal morphology but just on the size of the colloids. This may be the first example to study the monomer sequence and the chemical composition in the macro-RAFT agent on emulsion RAFT polymerization, and will be useful to reveal the block copolymer particle growth.As a whole, kinds of new reactive surfactants such as the N-(4-vinylbenzyl)-N,N-dibutylamine hydrochloride summer, the poly[N-(4-vinylbenzyl)-N,N-dibutylamine hydrochloride] trithiocarbonate macro-RAFT agent and the nonionic amphiphilic brush polymers poly[poly(ethylene oxide) methyl ether vinylphenyl-co-styrene] trithiocarbonate have been synthesized and their application in emulsion poltmerization have been explored. Strategies for one-stage synthesis of cagelike porous polymeric microspheres and batch synthesis of block copolymer colloids with controlled molecular weight and tailored morphology also have been proposed.