Longhai Guo

Synthesis of Polystyrene/Polysilsesquioxane Core/Shell Composite Particles via Emulsion Polymerization in the Existence of Poly(γ-Methacryloxypropyl trimethoxysilane) Sol

Here, we synthesized the polystyrene/polysilsesquioxane (PS/PSQ) core/shell latex particles via emulsion polymerization, which behave as an amusing morphology. First, the nanosized PSQ particles were prepared by the hydrolysis-condensation reaction of γ-methacryloxypropyl trimethoxysilane (MPTS) in ethanol medium. Subsequently, the as-obtained methacryloxypropylene functionalized PSQ (PMPTS) sol was directly added into the emulsion system of styrene (St) monomer, and PS/PSQ composite particles with core/shell structure were obtained through emulsion polymerization. We found that the structure of the composite particles can be affected by the synthesis parameters such as reaction time, content of PMPTS added in the reaction, amount of coemulsifier, and the pH value of emulsion system, which were systemically explored by transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), and thermogravimetric analysis (TGA) in this work. These results indicate that the PMPTS particles in the size of about 5 nm could first absorb onto the surface of PS latex particles so as to assemble in a strawberry-like morphology. The further coalescence among the PMPTS particles would result in a continuous PMPTS shell around the PS core. Moreover, the hollow PSQ capsules were prepared after extraction of the PS core by organic solvent, further confirming the core/shell structure of the as-synthesized PS/PMPTS particles. Meanwhile, we also explored the application of the PS/PSQ core/shell particles as a new kind of Pickering emulsifier in the emulsion polymerization of St, and composite particles with complex patchy morphologies have been obtained finally under different ratios of styrene monomer to PS/PMPTS colloidal emulsifier.

A novel fluoro-terminated hyperbranched poly(phenylene oxide) (FHPPO): synthesis, characterization, and application in low-k epoxy materials

A new AB2 monomer 4-hydroxyl-4′,4′′-difluorotriphenylmethane was successfully synthesized via a Friedel–Crafts alkylation of phenol from 4,4′-difluorodiphenylmethanol. Based on the AB2 monomer, novel fluoro-terminated hyperbranched poly(phenylene oxide)s (FHPPOs) were synthesized via the SNAr reaction by self-condensation in one step. The FHPPOs were characterized by various techniques, including NMR, FT-IR, GPC, TGA and DSC. It was found that the molecular weight and polydispersity index of the FHPPOs increased with monomer concentration and reaction time. The degree of branching of the FHPPOs, determined by 13C NMR and 19F NMR with the aid of model compounds, decreased from 0.63 to 0.53 as the molecular weight increased. The glass transition temperature (Tg) of the FHPPOs increased with increasing molecular weight, up to 164 °C when the Mn was over 6, 800. The FHPPOs showed excellent thermal stability up to a Td5 temperature of 559 °C. Because of the low polarity of the poly(phenyl oxide) (PPO) backbones, abundant fluoro-terminated groups, which have large molar free volume, low polarizability of C–F bonds, and inherent free volume or molecule-scale cavities in hyperbranched structures, the addition of FHPPO into diglycidyl ether of bisphenol A (DGEBA) could effectively lower the relative dielectric constant, the dissipation factor, and moisture absorption of the cured DGEBA/FHPPO composites. The free volume of the composites, which was quantified by positron annihilation lifetime spectroscopy (PALS), increased with increased FHPPO loading. The excellent dielectric and thermal properties make FHPPO a promising low-k modifier for epoxy resins.

The microcapsule-type formaldehyde scavenger: The preparation and the application in urea-formaldehyde adhesives

The limitation and regulation of formaldehyde emissions (FE) now shows great importance in wood-based materials such as plywood and particle board manufactured for building and furnishing materials. The widely used formaldehyde-based adhesives are one of the main sources of FE from the wood products. In this work, a new kind of long-term effective formaldehyde scavenger in the microcapsule form was prepared by using an intra-liquid desiccation method. The characterizations of the capsule (UC) were performed including the morphologies, the yields, the loading efficiency as well as its sustained-release of urea in aqueous conditions. The prepared UC could be integrated in urea-formaldehyde resins by simply physical blending, and the mixtures were available to be applied as the adhesives for the manufacture of plywood. The bonding strength (BS) and the FE of the bonded plywood in both short (3h) and long (12 week) period were evaluated in detail. It was found that the FE profile of the plywood behaved following a duple exponential law within 12 week. The addition of UC in the adhesive can effectively depress the FE of the plywood not only in a short period after preparation but also in a long-term period during its practical application. The slow released urea would continuously suppress the emission of toxic formaldehyde in a sustained manner without obviously deteriorating on the BS of the adhesives.

A “green” method for preparing ABCBA penta-block elastomers by using RAFT emulsion polymerization

A clean method for preparing ABCBA penta-block terpolymers was developed in a surfactant and organic solvent free emulsion system via one-pot RAFT polymerization. The prepared ABCBA penta-block terpolymers show large fracture tensile strain, low permanent set and potential application as elastomer materials. During the preparation process, polyacrylic acid (PAA) was firstly synthesized as the A block via RAFT polymerization in water in the presence of a dual-functional RAFT agent. Subsequently, we selected a partially water-soluble monomer 2,2,2-trifluoroethyl acrylate (TFEA) to synthesize the B block, and ABA tri-block copolymers could be obtained via organic solvent free RAFT emulsion polymerization. Using the ABA tri-block copolymers as a surfactant, the ABCBA penta-block terpolymers were further synthesized using 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) as the third monomer in an organic solvent free system. It has been found that the emulsification efficiency of the ABA tri-block copolymers is higher than that of the corresponding AB di-block copolymers. The assembly mechanism of penta-block terpolymers to form a tri-layer core–shell latex particle was proposed and confirmed by TEM images. Finally, we obtained a transparent and hydrophobic elastomeric film by directly casting the synthesized penta-block terpolymer latexes and subsequent heat treatment. The films have excellent mechanical properties and water resistance.

Novel tri-block copolymers of poly(acrylic acid)-b-poly(2,2,3,3,4,4,4-hexafluorobutyl acrylate)-b-poly(acrylic acid) prepared via two-step RAFT emulsion polymerization

A facile method for preparing ABA tri-block functional elastomers via two-step RAFT emulsion polymerization is introduced in this work. Poly(acrylic acid)-b-poly(2,2,3,3,4,4,4-hexafluorobutyl acrylate)-b-poly(acrylic acid) (PAA-b-PHFBA-b-PAA) tri-block copolymers were synthesised, and transparent films were obtained by directly casting the synthesized latexes. The water contact angle (WCA) of the as-prepared films was dramatically improved after heat treatment at 120 °C for 4 h, and the films were changed from hydrophilic to hydrophobic. By using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), the surface structure of the films was investigated in this work, to illustrate the mechanism of the variation in the surface properties of the films upon heat treatment. Moreover, the synthesized tri-block copolymers behave as elastomeric materials, with a high elongation at break of around 1200% and a permanent deformation of below 25%.

Synthesis of polypyrrole–polystyrene composite microspheres via pseudo-multicomponent heterophase polymerization and the potential application on Cr( vi ) removal

Polypyrrole–polystyrene (PPy–PS) composite hollow microspheres with a dry-plum-like morphology were prepared via pseudo-multicomponent heterophase polymerization in an aqueous dispersion system. The monomers of pyrrole (Py) and styrene (St) were simultaneously added into the reactor with the existence of azodiisobutyronitrile. The oxidization polymerization of Py was first initiated by the addition of ammonium persulfate, and the radical polymerization of St was subsequently initiated by the elevated temperature. Finally, composite micron-sized spheres were obtained with hierarchical structures. The microspheres are hollow inside, with PPy nano-particles bound by a PS matrix for the building of the wall-shell. The decoration of tiny PPy particles at the surface leads the microspheres to be an effective adsorbent to isolate Cr(VI) ions from water. The adsorption kinetics and isotherm result of the microspheres agree well with the pseudo-second-order rate model and Langmuir isotherm mode, respectively.