Oxygen and Carbon Dioxide Dual Responsive Nanoaggregates of Fluoro- and Amino-Containing Copolymer

We report herein a novel approach for preparing CO₂- and O₂-responsive polymer nanoaggregates. The polymer, synthesized via atom transfer radical polymerization (ATRP), has one hydrophilic poly­(ethylene glycol) (PEG) block, and the other hydrophobic block composed of 88 randomly distributed units of CO₂-responsive <i>N</i>,<i>N</i>-diethylaminoethyl methacrylate (DEA) and 43 units of O₂-responsive 2,2,2-trifluoroethyl methacrylate (FMA). The amphiphilic copolymer self-assembled into vesicular nanoaggregates in water. With O₂ bubbling, the vesicles expanded eight times in volume. With CO₂ bubbling, the vesicular morphology collapsed and transformed into a small spherical micelle. The dual gas-responsivity significantly expanded the scope in designing stimuli-responsive materials and processes

Ionic Liquids: Versatile Media for Preparation of Vesicles from Polymerization-Induced Self-Assembly

This work reports the development of a new polymerization-induced self-assembly (PISA) system through reversible addition–fragmentation chain transfer (RAFT)-mediated dispersion polymerization in ionic liquids. Three representative monomers (styrene, <i>n</i>-butyl methacrylate, and 2-hydroxyethyl methacrylate) were polymerized through chain extension from a trithiocarbonate-terminated poly­(ethylene glycol) (PEG) macro-RAFT agent, in a model ionic liquid [bmim]­[PF₆]. The block copolymers thus prepared could spontaneously form aggregates with vesicular morphologies. Moreover, by regulating the formulation, nanoaggregates with multiple morphologies were generated in ionic liquid via PISA

A Molecular Weight Distribution Polydispersity Equation for the ATRP System: Quantifying the Effect of Radical Termination

Polydispersity quantifies the breadth of polymer molecular weight distribution, making it an important and frequently quoted chain microstructural property for characterization. An explicit expression of such an important variable is desirable for ease of calculation, correlation with experiment data, and/or parameter estimation. A review of published literatures shows that great efforts have been put forth by many researchers to derive these equations for various polymerization mechanisms. In atom transfer radical polymerization (ATRP), polydispersity depends on three factors: monomer conversion, number of monomer addition per activation/deactivation cycle, and amount of dead chains. The existing expressions available in the literature only account for, at most, two of these three factors, with the contribution from dead chains commonly neglected. This assumption results in polydispersity monotonically decreasing with conversion, which is often not observed in experiments. In this work, a new equation for polydispersity, which accounts for contributions of all the three aforementioned factors, is proposed. The validity of assumptions involved in the derivation is evaluated by comparing the polydispersity profiles to those simulated by the method of moments. In addition, this new equation is used to correlate several experiment data sets for verification, namely from ATRP of 2-hydroxyethyl methacrylate, methyl methacrylate, and <i>N</i>-isopropylacrylamide, showing better agreement than the existing equation. Although the equation derived here is strictly applicable to homogeneous (bulk and solution) normal ATRP, with further effort it may be extended to other types of ATRP as well as NMP and RAFT systems

One-Pack Epoxy Foaming with CO₂ as Latent Blowing Agent

In this work, we have successfully developed a novel approach to epoxy foaming using CO₂ as the latent blowing agent. The active amine groups of a commercially available curing agent for epoxy resin are blocked by CO₂ to obtain ammonium carbamate. The prepared ammonium carbamate can be decomposed by heating. Above 100 °C, CO₂ is released from the amine groups and acts as the blowing agent, while the amine compound is used as the curing agent and cures the epoxy resin. The ammonium carbamate combines the functionalities of latent blowing agent and curing agent. The one-pack epoxy foaming formulation has good storage stability under ambient conditions. The thermoset epoxy foams prepared from the one-pack formulation have low density, good mechanical properties, and thermal stability, competitive with the epoxy foams prepared by other methods. This novel approach is simple, environmentally benign, and cost-effective, which represents a promising direction in the development of epoxy foaming technologies

Alginate Hydrogel: A Shapeable and Versatile Platform for <i>in Situ</i> Preparation of Metal–Organic Framework–Polymer Composites

This work reports a novel <i>in situ</i> growth approach for incorporating metal–organic framework (MOF) materials into an alginate substrate, which overcomes the challenges of processing MOF particles into specially shaped structures for real industrial applications. The MOF–alginate composites are prepared through the post-treatment of a metal ion cross-linked alginate hydrogel with a MOF ligand solution. MOF particles are well distributed and embedded in and on the surface of the composites. The macroscopic shape of the composite can be designed by controlling the shape of the corresponding hydrogel; thus MOF–alginate beads, fibers, and membranes are obtained. In addition, four different MOF–alginate composites, including HKUST-1–, ZIF-8–, MIL-100­(Fe)–, and ZIF-67–alginate, were successfully prepared using different metal ion cross-linked alginate hydrogels. The mechanism of formation is revealed, and the composite is demonstrated to be an effective absorbent for water purification

Sunscreen Performance of Lignin from Different Technical Resources and Their General Synergistic Effect with Synthetic Sunscreens

Five types of industrial lignin are blended with a pure cream and a commercial sunscreen lotion. Lignin is found to significantly boost their sunscreen performance. Photostability of the lignin-modified lotions is analyzed. The results show that hydrophobic lignin has better sunscreen performance than hydrophilic counterpart. Sun protection factor (SPF) of the pure cream containing 10% organosolv lignin (OL) reaches 8.66. Small amount of hydrophobic lignin dramatically increases SPF value of the sunscreen lotions. Adding 1% lignin almost doubles the sun lotion’s SPF. Addition of 10% OL to the lotion boosts its SPF from 15 to 91.61. However, it is also found that hydrophilic lignin tends to demulsify the lotions due to an electrostatic disequilibrium. After 2 h of UV radiation, UV absorbance of all the five lignin-modified sunscreen lotions increases up to the limit of measuring instrument. All the lignin types studied in this work are found to have a general synergistic effect with sunscreen actives in the commercial lotion. An effort is also made to elucidate radical mechanisms of the synergy

Polyolefin Thermoplastics for Multiple Shape and Reversible Shape Memory

This work reports the first pure hydrocarbon thermoplastic polyolefin material with reversible shape memory effect under stress-free or very small external loading condition. A thermoplastic ethylene/1-octene diblock copolymer with designed chain microstructure was synthesized. The polyolefin material performed not only the conventional one-way multishape memory effects, but also a two-way reversible shape memory effect (RSME). The elongation and contraction induced by oriented crystallization with heating was confirmed as the mechanism of RSME without chemical cross-linking. This work demonstrated that the thermoplastic reversible shape memory could be achieved through careful design of chain microstructure, based on sole hydrocarbon materials such as ethylene-1-octene copolymer

Highly Porous Poly(high internal phase emulsion) Membranes with “Open-Cell” Structure and CO₂‑Switchable Wettability Used for Controlled Oil/Water Separation

Polymer membranes with switchable wettability have promising applications in smart separation. Hereby, we report highly porous poly­(styrene-<i>co</i>-<i>N</i>,<i>N</i>-(diethylamino)­ethyl methacrylate) (i.e., poly­(St-<i>co</i>-DEA)) membranes with “open-cell” structure and CO₂-switchable wettability prepared from water-in-oil (W/O) high internal phase emulsion (HIPE) templates. The open-cell porous structure facilitates fluid penetration through the membranes. The combination of CO₂-switchable functionality and porous microstructure enable the membrane with CO₂-switchable wettability from hydrophobic or superoleophilic to hydrophilic or superoleophobic through CO₂ treatment in an aqueous system. This type of membrane can be used for gravity-driven CO₂-controlled oil/water separation, in which oil selectively penetrates through the membrane and separates from water. After being treated with CO₂ switching wettability of the membrane, a reversed separation of water and oil can be achieved. Such a wettability switch is fully reversible, and the membrane could be regenerated through simple removal of CO₂ and oil residual through drying. This facile and cost-effective approach represents the development of the first CO₂-switchable polyHIPE system, which is promising for smart separation in a large volume

Synthesis and Redispersibility of Poly(styrene-<i>block</i>-<i>n</i>‑butyl acrylate) Core–Shell Latexes by Emulsion Polymerization with RAFT Agent–Surfactant Design

A coagulatable and redispersible poly­(styrene-<i>block</i>-<i>n</i>-butyl acrylate) (PS-<i>b</i>-PnBA) copolymer latex system was developed. A series of PS-<i>b</i>-PnBA diblock copolymers with the PnBA content up to 70 wt % were prepared via a reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization. An amphipathic poly­(acrylic acid-<i>b</i>-styrene) trithiocarbonate was synthesized and employed as macro-RAFT agent and surfactant. The resulted latex particles contained a soft poly­(<i>n</i>-butyl acrylate) core and a hard polystyrene shell. The hard plastic shell could prevent the elastomer core from deformation and fusion at room temperature. It was found that the latex particles with the nBA content ⩽60 wt % could be easily coagulated by HCl and redispersed by NaOH with some ultrasound treatment. The coagulation and redispersion processes were repeatable. When the nBA content reached 70 wt %, the plastic shell became too thin, resulting in collapsed sticky particles. The critical shell thickness for redispersible latexes was about 8 nm

Mechanical Force Sensitive Acrylic Latex Coating

We prepared force sensitive acrylic latex coatings by covalently incorporating spiropyran mechanophore. The acrylic latexes were obtained through emulsion copolymerization of butyl acrylate (BA), methyl methacrylate (MMA) with vinyl­triethoxysilane (VTES) as interparticle cross-linker, and (1′-(2-(methacryl­oyloxy)­ethyl)-3′,3′-dimethyl­spiro­[chromene-2,2′-indolin]-6-yl)­methyl methacrylate) (SP) as intraparticle cross-linker. The latexes of P­(BA-<i>co</i>-MMA-<i>co</i>-SP-<i>co</i>-VTES) were subsequently cast onto Teflon-coated surface to form latex coatings. The condensation of hydrolyzed VTES provided interparticle cross-linking and improved mechanical properties of the formed thin films. Intraparticle cross-linker SP endowed the coatings with mechanoreponsiveness. The mechanoactivation of SP-containing latex films was demonstrated. Increasing the content of intra-cross-linker SP resulted in higher stress sensitivity and lower critical stress required for mechanoactivation. Increasing the content of interparticle cross-linker VTES resulted in higher critical stress for SP mechanoactivation but had little effect on the stress sensitivity. <i>T</i>_g and operation temperature also showed significant effect on mechanoactivation. Slower strain rate allowed for higher SP-to-MC conversion. This work represents the first example of mechanochromic acrylic latexes and provides insight into the design of force sensitive and self-reporting polymer coatings