Lianying Liu

Direct one-pot synthesis of chemically anisotropic particles with tunable morphology, dimensions, and surface roughness.

Previously, synthesis of anisotropic particles by seeded polymerizations has involved multiple process steps. In conventional one-pot dispersion polymerization (Dis.P) with a cross-linker added, only spherical particles are produced due to rapid and high cross-linking. In this Article, a straightforward one-pot preparation of monodisperse anisotropic particles with tunable morphology, dimensions, surface roughness, and asymmetrically distributed functional groups is described. With a cross-linker of divinylbenzene (DVB, 8%), ethylene glycol dimethacrylate (EGDMA, 6%), or dimethacryloyloxybenzophenone (DMABP, 5%) added at 40 min, shortly after the end of nucleation stage in Dis.P of styrene (St) in methanol and water (6/4, vol), the swollen growing particles are inhomogeneously cross-linked at first. Then, at low gel contents of 59%, 49%, and 69%, corresponding to the cases using DVB, EGDMA, and DMABP, respectively, the growing particle phase separates and snowman- or dumbbell-like particles are generated. Thermodynamic and kinetic analyses reveal that moderate cross-linking and sufficient swelling of growing particles determine the formation and growth of anisotropic particles during polymerization. Morphology, surface roughness, sizes, and cross-linking degrees of each domain of final particles are tuned continuously by varying start addition time and contents of cross-linkers. The snowman-like particles fabricated with DVB have a gradient cross-linking and asymmetrical distribution of pendant vinyl groups from their body to head. The dumbbell-like particles prepared using DMABP have only one domain cross-linked; i.e., only one domain contains photosensitive benzophenone (BP) groups. With addition of glycidyl methacrylate (GMA) or propargyl methacrylate (PMA) together with DVB or EGDMA, epoxy or alkynyl groups are asymmetrically incorporated. With the aid of these functional groups, carboxyl, amino, or thiol groups and PEG (200) are attached by thiol-ene (yne) click and photocoupling reactions.

Facile synthesis of core-shell/hollow anisotropic particles via control of cross-linking during one-pot dispersion polymerization.

Preparation of anisotropic particles based on seed phase separation involves multiple processes, and asymmetrical structures and surfaces cannot be produced when anisotropic shapes emerge. In conventional one-pot dispersion polymerization (Dis.P) using cross-linker, only spherical particles are prepared due to rapid and high cross-linking. Herein, monodisperse snowman-like particles with core-shell/hollow structures and partially rough surface were synthesized straightforward by a modified one-pot Dis.P, in which ethylene glycol and water (6/4, vol.) were used as medium, and ammonium persulfate (APS) aqueous solution, vinyl acetate (VA) and/or acrylic acid (AA), divinylbenzene (DVB) and styrene (St) were added at 6h. The cross-linking of growing particles was confined to exterior (forming cross-linked shell), and gel contents were low, leading to phase separation. Asymmetrical morphologies, structures, sizes and surface roughness were flexibly tuned by varying amounts of APS, VA and/or AA, water and DVB, and DVB adding speed. At low APS contents or high DVB amounts, the inhomogeneous cross-linking of head enabled its phase to separate, producing elongated head. With addition of VA and AA, phase separations inside head and body were induced, generating hollow structure. Adding DVB very slowly, nonlinear growth of third compartment occurred, forming bowed head.

Control of cross-linking and reactions in one-step dispersion polymerization toward particles with combined anisotropies

Previously, it was a challenge to develop a direct and convenient synthetic means for production of anisotropic particles, formation of structures (core–shell, cavity, hollow, etc.) and functionalization of domains all at once. Herein, we present a simple one-step dispersion polymerization (Dis.P) approach to synthesize particles with a combination of anisotropies in morphology, surface roughness, structure and composition. This approach needs no delayed addition of agents, and is of comparable simplicity to the preparation of conventional spherical particles. A cross-linker of dimethacryloyloxybenzophenone (DMABP) is added at the beginning of Dis.P of styrene (St). Evolution of monomer conversion, particle gel content and morphology during Dis.P indicates that DMABP is consumed early and rapidly, creating a high cross-linking of a growing particle at a low conversion, thus inducing phase separation and producing snowman- or dumbbell-like particles which contain a firstly cross-linked, coarse growing particle domain (G domain) and an uncross-linked or subsequently cross-linked, smooth, new domain (N domain). The size, surface roughness, structure and composition of the domains are tuned by initially adding various amounts of DMABP and a low amount of functional monomers. Due to the quick reaction of hydrophilic 4-vinylpyridine (4-VP), glycidyl methacrylate (GMA) or methacrylic acid (MAA), the G domain is enriched with pyridyl, epoxy or carboxyl groups, as detected by XPS and EDS. Through the delayed reaction of monomers containing alkynyl groups (–CC–), the N domain is enriched with –CC– groups, and the core–shell (cross-linked) structure is formed. With aids of thiols added during Dis.P, SH– or fluorine-containing groups are primarily incorporated on the N domain, and the porous, cavity or hollow structure of the N domain is generated due to phase separation between polystyrene (PSt) and the polymer produced by the click reaction. On adding two functional monomers (MAA and monomer containing –CC– groups), various functional groups enrich G and N domains, respectively, owing to the sequential reactions of monomers.

High immobilization of antibacterial moieties onto monodisperse microspheres by dispersion polymerization using bicationic viologen surfmer

In order to achieve monodisperse particles with high content of antibacterial groups covalently bonded on surface, a bicationic viologen, N-hexyl-N′-(4-vinylbenzyl)-4,4′-bipyridinium bromide chloride (HVV) was devised as a surfmer in dispersion polymerization of styrene (St) using a mixture of methanol (or ethylene glycol) and water as media. Effects of content of HVV, its addition profile and composition of reaction media on particles size and incorporation of HVV moieties were mainly investigated. The attachment of silver and gold nanoparticles on particle surface under UV irradiation ascertained the surface-bonded HVV segments. SEM, TEM observations and XPS, zata potential measurements indicated that increase of initial HVV contents and addition of HVV (when polymerization had been performed for 3 h) led to grown particles and enhanced immobilization of HVV moieties. Using a mixture of ethylene glycol and water as reaction media, small particles (5202-142 nm) with highly attached HVV moieties were prepared. Furthermore, antibacterial efficacy of the resultant particles against S. aureus was assayed, and particles with more HVV moieties anchored on surface demonstrated greater efficiency of antibacterial activity.

Combined chain- and step-growth dispersion polymerization toward PSt particles with soft, clickable patches

Simple and convenient synthetic methods are highly in demand for the preparation and application of patchy particles (PPs) with diverse morphologies, functionalities and behaviors. Very recently, step-growth heterogeneous click polymerizations have been developed to fabricate monodisperse, spherical, soft and clickable particles. However, so far, this technique has seldom involved forming structures (core–shell, or pores, etc.), anisotropic shapes and compositions of particles. Herein, we prepare PPs with a hard body and soft, clickable dimple- or bulge-patches by incorporating step-growth thiol–ene polymerizations into the chain-growth polymerization of styrene (St) in a dispersion system. The phase separation between thiol–ene polymers and PSt in growing particles occurs due to their differences in the glass transition temperature (Tg) and hydrophilicity, forming core–shell and dimple- or bulge-patched particles. SEM and TEM images of the degraded particles confirm that the patches are primarily composed of click polymers. Varying the addition time, amounts, feed ratio and type of thiol/ene monomer, degree of phase separation, shape, number and size of patches, and contents of thiol/ene segments in/on patches are tuned flexibly. FI-IR analyses reveal that off-stoichiometric thiol and ene segments are incorporated, owing to off-stoichiometric thiol–ene reactions concurrent with the polymerization of St, even when stoichiometric thiol and ene are added. Moreover, Fe3O4 or Ag nanoparticles are attached on the PSt body with –SO3− groups or on click polymer patches with –SH groups. Post-modifications of PPs are carried out through reactions of excess –SH or –CC– groups on patches with –CC– or –SH group-containing monomers. Superhydrophobic or hydrophilic particulate films, or fluorescent tagged PPs are prepared.

Copolymerization of α-Methylstyrene and Styrene

In this paper, the effects of temperature from 60 °C to 80 °C and the molar ratios in monomer feed on the copolymerization of α-methylstyrene (AMS) and styrene (St) were studied. The resulting copolymers, designated as PAS, were characterized by FTIR, GPC, NMR and TGA. When the reaction temperature was below 75 °C, the molecular weights increased almost linearly as the evolution of the copolymerization. The phenomenon revealed that AMS could mediate the conventional free radical polymerization having some features of a controlled system. As the AMS/St = 50/50 (molar) in feed, the overall fraction of the AMS unit incorporated into the copolymer was as high as 42 mol%, the monomer conversion could be more than 90 wt% and the molecular weights could reach as high as 4400. However, since the styrene is more reactive than AMS, the AMS fraction in copolymer increased with the overall monomer conversion. The 13C-NMR revealed the products were random copolymers which had triads, such as -AMS-AMS-AMS-, -St-AMS-AMS-(-AMS-AMS-St-) and -St-AMS-St-. TGA curves demonstrated that the degradation temperature of the resulting copolymers went down from about 356.9 °C (0 mol% AMS) to 250.2 °C (42 mol% AMS). This behavior demonstrated that there exist weak bonds in the AMScontaining sequences which could be used as potential free radical generators.

Structure-Colored Polymer Film Fabricated by Surface Immobilizing Amorphous Photonic Crystals

Amorphous photonic crystals display isotropic photonic band gaps and angle-independent non-iridescent, structural color, which leads to increasing interest and promising applications in image display, laser light, environment-friendly ink/coating, etc. However, previous amorphous photonic crystals usually exhibit low strength, and their structure is easily destroyed. Thus, their unique optical properties cannot be fully exhibited. Herein, amorphous photonic crystals of core (polystyrene-PSt) and shell (poly (4-methacryloyloxybenzophenone)-PMABP) structured microspheres are formed. Using polymer films (PET, PP, PMMA and PE) coated with poly (4-(methacryloxy) benzophenone-co-N-Isopropyl acrylamide) as substrates, the amorphous photonic crystals are immobilized under UV-irradiation. Adding cross-linker of ethoxylated trimethylolpropane triacrylate (ETPTA) in microsphere dispersion, transparent and flexible free-standing films of photonic crystals are fabricated. Angle-independent structural colors are observed and tuned by varying microsphere concentration in dispersions and content of cross-linker.