Fabrication of Spaced Concentric Vesicles and Polymerizations in RAFT Dispersion Polymerization

Abstract

Different from concentric vesicles without spacing between the walls, the concentric vesicles with uniform spacing between the walls were rarely fabricated. We successfully fabricate the spaced concentric vesicles (SCVs) via RAFT dispersion polymerization, and continuous propagation of the residual polymer chains inside the large vesicles induces self-assembling to form SCVs. Concentration of the residual polymer chains in the solution of the nascent-formed vesicles is the determining factor for formation of SCVs, and continuous propagation of less or too more residual polymer chains will not form SCVs but form other morphologies. Generally, the concentration of the residual polymer chains after formation of vesicles is too low to self-assemble, so formation of SCVs is impossible. By adjusting the ratio of St/methanol or macro-RAFT agent P4VP-b-PS/P4VP, the concentration of residual polymer chains can be controlled, and further control of the morphologies is achieved. Formation of the inner vesicles by self-assembling inside the large vesicles requires high molecular weight of the polymer chains due to their very low concentration. The polymers of inner vesicles possess very high molecular weight (×10 6 g/mol) in comparison with the polymer of outmost vesicles (×10 5 g/mol). Polymerization kinetic study reveals very high increasing rate of the molecular weight inside the vesicles probably owing to long duration of the chain radicals, and the polymerization rate (R p ) inside the vesicles is faster than the R p in the outmost vesicles, but both rates are in the same order. ■ INTRODUCTIONAs one of the efficient strategies for fabrication of nanostructural materials, the polymerization-induced self-assembly and reorganization (PISR) has been used to create a broad range of intricate polymeric nanomaterials. 1,2 The polymerizations used for this purpose include living anionic and living radical polymerizations, especially reversible addition−fragmentation transfer (RAFT) dispersion polymerization. 3 The factors influencing the polymer aggregates involve recipe, nature of starting materials, and reaction conditions. When the precipitator of one block chain is used as media of the RAFT dispersion polymerization, only spherical micelles are formed because a significant decrease of the polymerization rate in the spheres formed by microphase separation leads to transition of the spherical micelles to other morphologies impossible. 4,5 One feasible method for solving this problem is to minimize decrease of the polymerization rate after phase separation because one determining factor of morphologies formed via self-assembling strategy is chain length ratio of two blocks in the diblock copolymers, 6 which can be achieved by increasing concentration of the monomers in the cores of micelles. Consider monomer distribution between two phases formed by phase separation, two methods, enhancing initial monomer concentration and lowering solubility of the monomer in the reaction media, can be used for this purpose. Polymerization w...

Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization

“…The former component was subsequently stabilized by the P4VP-PS diblock copolymer chains, resulting in the formation of PS spherical nanoparticles within the vesicle lumen and hence the 'yolk/shell' morphology. More recently, Zhang et al [57] reported the formation of 'multi-shelled' vesicles when targeting highly asymmetric (e.g. P4VP 73 -PS 9400 ) diblock copolymers in methanol (Figure 4e).…”

“…Pan and co-workers [28,[52][53][54][55][56][57] have utilized a trithiocarbonate-based chain transfer agent (DDMAT, see Figure 2a) to prepare a range of poly(4-vinylpyridine) (P4VP) macro-CTAs for the subsequent dispersion polymerization of styrene in methanol. The resulting poly(4-vinylpyridine)-polystyrene (P4VP-PS) nanoparticles formed a wide range of copolymer morphologies ( Figure 3 andFigure 4) [28,[52][53][54][55][56][57].…”

“…Pan and co-workers [28,[52][53][54][55][56][57] have utilized a trithiocarbonate-based chain transfer agent (DDMAT, see Figure 2a) to prepare a range of poly(4-vinylpyridine) (P4VP) macro-CTAs for the subsequent dispersion polymerization of styrene in methanol. The resulting poly(4-vinylpyridine)-polystyrene (P4VP-PS) nanoparticles formed a wide range of copolymer morphologies ( Figure 3 andFigure 4) [28,[52][53][54][55][56][57]. Like the analogous RAFT aqueous dispersion formulations [17,25,58], purely spherical, worm-like or vesicular morphologies could be targeted by tuning the block composition, which is consistent with the geometric packing argument for surfactant selfassembly introduced by Israelachvili and co-workers [6], and subsequently extended to block copolymer self-assembly by Antonietti and Förster [7].…”

“…A trithiocarbonate-based DDMAT CTA (Figure 2a) was used to prepare poly(ethylene oxide)-polystyrene (PEO-PS) [60] and poly(acrylic acid)-polystyrene (PAA-PS) [26] block copolymer nano-objects in methanol, where access to the full range of morphologies (spheres, worms or vesicles) was observed in both cases. Similarly, a dithiobenzoate-based CTA (cyanoisopropyl dithiobenzoate or CPDB, Figure 2a) was utilized for the synthesis of poly(2-(dimethylamino)ethyl methacrylate)-polystyrene (PDMA-PS) diblock copolymer spheres, worms or vesicles [27], in addition to the P4VP-PS formulations previously discussed [57]. However, relatively low styrene conversions again remained a significant problem when targeting a pure PS core-forming block.…”

Template‐Directed Fabrication of Anatase TiO2 Hollow Nanoparticles and Their Application in Photocatalytic Degradation of Methyl Orange

“…[11][12][13][14] However, fabrication of polymeric nanoparticles is usually a tedious and time-consuming process, which is often uneconomic and difficult to scale up. [15][16][17][18] Direct fabrication of nano-objects via polymerizationinduced self-assembly (PISA), which have been developed in recent years, [19][20][21][22][23][24][25][26] may be one of the best methods to solve this problem. PISA strategy allows fabricating of polymeric nanoparticles at much high concentrations, and has become a powerful strategy for fabrication of polymeric nanoparticles.…”