Effect Of Solvent On Polymerization-induced Block Copolymer Self-assembly

In the last few decades,block copolymer?BCP?nano-assemblies attracted close attention due to their applications in many fields.Generally,two strategies are proposed to prepare and/or synthesize these BCP nano-assemblies.The first strategy is via micellization of amphiphilic BCPs in block selective solvents..The second strategy is via polymerization-induced self-assembly?PISA?reported recently,Following this PISA,controlled/living radical polymerization most often the macro-RAFT agent mediated polymerization under heterogeneous condition is conducted,and in situ formation of BCP nano-assemblies with up to 50 wt%polymer concentration is fulfilled.However,these studies are focus on the effects of polymerization conditions such as pre-synthesized macro-RAFT agent,monomer concentration,and polymerization time on the morphology of particles.There are very few literatures reported the effect of solvent and different polymerization procedures on the nano-assemblies morphology.In view of this,the first part of this paper investigated the dispersion RAFT polymerization in the ionic liquids.And the second part explored dispersion RAFT polymerization in methanol/water mixture and effect of solvent properties on the morphology of PEO-b-PS block copolymer nanoparticles.The details are as follows:1.Dispersion RAFT polymerization in ionic liquid and Synthesis of PEO-b-PS nano-assembliesIonic liquids are room-temperature molten salts,and low vapor pressure,nonflammability,high thermal,and chemical stability make ILs attractive as an environmentally friendly alternative to organic solvents in many polymerization processes.In this section,the in situ synthesis of block copolymer nano-assemblies of poly?ethylene oxide?-block-polystyrene?PEO-b-PS?in the ionic liquid of1-butyl-3-methylimidazolium hexafluorophosphate?[BMIN][PF₆]?through the PEO₄₅-TTC macro-RAFT agent mediated dispersion polymerization is investigated.It is found that the kinetics of dispersion RAFT polymerization in the ionic liquid of[BMIN][PF₆]performs similarly faster than that in the alcoholic solvent,but the polymerization rate runs faster,and the dispersion RAFT polymerization in the ionic liquid affords good control over the molecular weight and the molecular weight distribution of the PEO-b-PS diblock copolymer.The morphology of the in situ synthesized PEO-b-PS diblock copolymer nano-assemblies,e.g.,nanospheres and vesicles,in the ionic liquid is dependent on the polymerization degree of the solvophobic block and the concentration of the fed monomer,which is somewhat similar to those in alcoholic solvent.It is believed that the dispersion RAFT polymerization in the ionic liquid broads a new way to prepare block copolymer nano-assemblies.2.Dispersion RAFT polymerization in methanol/water mixture and Effect of Solvent Properties on PEO-b-PS AssembliesFor in situ preparation of BCP nano-assemblies,the solvent and polymerization procedures have a great effect on the nano-assemblies morphology.In the mixed solvent of methanol/water,the styrene is soluble when water content is less than 30%,and becomes insoluble when the water content exceeds 30%.In order to investigate the dispersion RAFT polymerization in methanol/water mixture and effect of solvent properties on PEO-b-PS Assemblies,in this chapter,PEO₄₅-TTC macro-RAFT reagent and PEO₄₅-b-PS₁₅₁-TTC micelle were used to mediate dispersion RAFT polymerization and seeded dispersion RAFT polymerization of styrene in 80/20methanol/water mixture,and in 65/35 methanol/water mixture,we used PEO₄₅-b-PS₁₅₁-TTC micelle to mediate the seeded emulsion RAFT polymerization of styrene.Our results reveal that three RAFT polymerization afford good control over the molecular weight and the molecular weight distribution of the PEO-b-PS diblock copolymer,but dispersion RAFT polymerization undergoes much slower than other two PISA formulations of seeded dispersion RAFT polymerization and seeded emulsion RAFT polymerization.Besides,the results reveal that the BCP morphologies of poly?ethylene glycol?-block-polystyrene(PEO₄₅-b-PS)produced via three PISA cases are much different from each other.That is,dispersion RAFT polymerization affords vesicles,seeded dispersion RAFT polymerization affords the mixture of vesicles and porous nanospheres,and seeded emulsion RAFT polymerization affords porous nanospheres,respectively.The reason of formation of porous nanospheres by seeded RAFT polymerization is discussed,and the fed styrene monomer swelling the seeded vesicles is ascribed.