A novel method to synthesize click-ready latex based on reversible addition–fragmentation chain transfer (RAFT) miniemulsion polymerization is proposed. It involves the use of poly(acrylic acid)30-b-poly((butyl acrylate)2-co-(cyclohex-3-enylmethyl acrylate)3) amphiphilic macro-RAFT agent as both the surfactant and polymerization mediator. It is demonstrated that the cyclohexenyl groups incorporated onto polymer chains are located on the surface of polymeric particles and remained unreacted during miniemulsion polymerization. These surface-rich cyclohexenyl groups allow highly efficient radical-mediated thiol–ene click (TEC) reactions with the water-soluble thiol compound dithiothreitol. The TEC reaction with thiol-terminated poly(N,N-dimethylacrylamide) (SH-PDMAAm) yielded particles with over one PDMAAm brushes per square nanometer. Such densely grafted brushes increased the particles’ critical coagulation concentration of sodium chloride by 1 order of magnitude, compared with particles without covalent-bonded PDMAAm.

Flexible conductive polymer composite foams (CPCFs) are considered as promising materials for piezoresistive sensors. However, most of them have low strain sensitivity with gauge factor (GF) of around 1.0. Herein, for the first time, W/O emulsion-templated polymerization is developed to fabricate graphene-based flexible CPCFs with high strain sensitivity. Compared to the literature-reported CPCFs, our materials have conductive network with higher specific surface area, improving conductive pathways formation between fillers under compression. In the vicinity of conductive percolation threshold, the CPCF has highest GF of 6.0 within 0–5% strain range and piezoresistive stability, demonstrating its high strain sensitivity and promising applicability in strain sensors.Download high-res image (177KB)Download full-size image

Thermoplastic elastomers (TPEs) are of growing commercial importance in the worldwide non-tire rubber market. It is because of their unique thermomechanical properties that associate with the phase morphologies. Controlled/living radical (mini)emulsion polymerization holds good promise for synthesis of ABA-type triblock copolymer TPEs. Both the mechanical and morphological investigations have been conducted on the solvent films of this copolymer latex. However, neither the copolymer latex particle nor the latex film has been investigated in terms of morphologies or mechanical properties. This work reports the development of triblock copolymer latex particle morphologies through reversible addition-fragmentation chain transfer (RAFT)-mediated miniemulsion polymerization. ABA-type triblock copolymers consisting of outer polystyrene blocks and inner polyacrylate blocks are synthesized in two steps through chain extension from symmetric RAFT agents. A variety of novel particle microstructures are realized by regulating either block ratios or particle surface attraction for each blocks. The nanostructured latex are also used for casting latex films. It is observed that the film morphologies do not attain thermodynamic equilibrium even after thermal annealing. In comparison to the solvent films with similar hard block contents, the latex films have higher elastic modulus, but exhibit inferior mechanical responses in terms of elongation at break and ultimate strength. The possible reason is attributed to the suppressed interparticle self-assembly of copolymers during latex film formation and scarce of bridging configuration of central block connecting different glassy domains within the final films.

The objective of this research was the fabrication of visible wavelength-independent anti-reflection coatings by deposition and aggregation of silica nanoparticles. This approach to anti-reflection coatings is important for technologies which avoid sophisticated process and calcination at high temperature. The goal of this research was achieved by modification of a commercially available SiO2 dispersion with tetraethoxysilane (TEOS) and spin coating of the TEOS–SiO2 (T–SiO2) dispersion. The modification resulted in aggregation of T–SiO2 particles upon evaporation of ethanol aqueous solution and thus assembled into many enlarged bulges at the coating surface. The resulted coating surface morphology resembled moth-eye-like nanostructure that exhibited visible wavelength-independent transmittance enhancement for substrate. More promisingly, owing to this unique behavior, the coated colored substrates display deepened colors without sacrificing any color hues. Such coating is very attractive in many fields such as color displaying and color imaging.

We designed and used a cyclohexenyl-functionalized amphiphilic macromolecular reversible addition–fragmentation chain transfer (macro-RAFT) agent as surfactant and polymerization mediator for (mini)emulsion polymerization of styrene (St), aiming at synthesizing nanoparticles with vinyl-enriched surface and well-defined polymer chains. Unexpectedly, the pendent cyclohexenyl units in the macro-RAFT agent were found to undergo significant copolymerization with St exclusively during the nucleation period in the ab initio emulsion polymerization, leading to the consumption of cyclohexenyl groups, positive deviation of molecular weights, and broad molecular weight distributions. By contrast, in miniemulsion polymerization, the radical polymerization exhibited superb selectivity toward St monomers relative to the pendent cyclohexene vinyl units just as in the solution polymerization. The obtained polymer chains retained designed molecular weights, low polydispersity indexes, and quantitative cyclohexenyl functionalities confined to the particle surface. Thus, PSt particles with vinyl-enriched surface were obtained via miniemulsion polymerization.

•We prepare block copolymer shell–core particles having epoxy-enriched surface.•Controlled curing reactions proceed efficiently during latex film formation.•Cured films have stable morphologies correlating to those of source particles.•Cured films show improved mechanical properties and behave like ductile materials.RAFT (reversible addition–fragmentation chain transfer) miniemulsion polymerization was engaged to engineer latex particle morphology. With this approach, a macromolecular amphiphilic RAFT agent with epoxy groups was synthesized that assembled onto the surface of monomer mini-droplets. It caused the polymer chains to grow inwards gradually in particles as polymerization proceeded. The batch polymerization of n-butyl acrylate (BA) followed by addition of styrene (St) led to the formation of PBA-b-PSt diblock copolymer shell–core latex, where epoxy groups were enriched on the particle surface. The shell–core ratio was varied feasibly by changing the mass of St. When the structured latexes were dried, epoxy groups underwent efficient curing reactions triggered by a thermal-latent curing agent (dicyandiamide) in a controlled manner, leading to the formation of bonded PBA blocks connecting the PSt blocks in adjacent particles. Mechanical tests show that the films behaved like ductile materials, whose modulus and elongation at break were functions of copolymer compositions. Furthermore, curing reaction was a very robust method of preserving film morphology which correlated well with that observed for the latex particles. The results demonstrated a feasible method of preparation of latex films with stable microphase separation structures and thus improved mechanical properties.

RAFT-mediated silk graft copolymerizations with DMAAm (N,N-Dimethylacrylamide) were studied. Three types of macromolecular RAFT agents which released different R group radicals, namely, polyacrylic acid-b-polystyrene radical (PAA-b-PSt•), polyacrylic acid-b-polybutyl acrylate radical (PAA-b-PBA•) and polystyrene-b-polyacrylic acid radical (PSt-b-PAA•), were chosen as the transfer agents. During the graft copolymerizations, the newly born PAA-b-PSt• in the aqueous phase enhanced the formation of silk macroradicals, consequently accelerated the copolymerization rate and improved monomer grafting efficiency (Ge) greatly. The Ge was less improved when the RAFT agent capable of producing PAA-b-PBA• were substituted for the one producing PAA-b-PSt•. In addition, Ge also benefited from an increase in the chain length of PSt block in PAA-b-PSt•, as well as PBA block in PAA-b-PBA•. However, the addition of RAFT agent giving rise to PSt-b-PAA• had negligible effects on Ge. The reasons were ascribed to both the radical reactivity and capacity of radical adsorption onto silk fibers.