Bo-Geng Li

A General Approach Towards Thermoplastic Multishape‐Memory Polymers via Sequence Structure Design

The chain sequence of a poly(styrene-co-methyl acrylate) copolymer is designed to form a V-shaped gradient sequence via controlled/living radical emulsion copolymerization. This specially designed chain sequence gives this common copolymer the capacity of multishape memory. The copolymer can sequentially recover to its permanent shape from three or more previously programmed temporary shapes with the stimulus of temperature.

Preparation of CO2/N2‐Triggered Reversibly Coagulatable and Redispersible Polyacrylate Latexes by Emulsion Polymerization Using a Polymeric Surfactant

We report here a novel approach for making reversibly coagulatable and redispersible polyacrylate latexes by emulsion (co)polymerization of methyl methacrylate (MMA) using a polymeric surfactant, poly(2-(dimethylamino)ethyl methacrylate)(10) -block-poly(methyl methacrylate)(14) . The surfactant was protonated with HCl prior to use. The resulted PMMA latexes were readily coagulated with trace amount of caustic soda. The coagulated latex particles, after washing with deionized water, could be redispersed into fresh water to form stable latexes again by CO(2) bubbling with ultrasonication. The recovered latexes could then be coagulated by N(2) bubbling with gentle heating. These coagulation and redispersion processes were repeatable by the CO(2) /N(2) bubbling.

Preparation of N2/CO2 triggered reversibly coagulatable and redispersible latexes by emulsion polymerization of styrene with a reactive switchable surfactant.

This work reports the development of a reversibly coagulatable and redispersible polystyrene latex system that can be triggered by N(2)/CO(2). The coagulatability and redispersibility of the latexes were achieved by employing 0.9-5.6 wt % (N-amidino)dodecyl acrylamide (DAm), a reactive switchable surfactant, in an emulsion polymerization of styrene under CO(2) atmosphere. The resulted latex particles were readily coagulated by N(2) bubbling at 60 °C and redispersed by CO(2) bubbling and ultrasonication, which switched amidine moieties between neutral and ionic states. The coagulation/redispersion processes were repeatable. The prepared latexes showed good stabilities against electrolytes, especially with higher charges.

Ultrafast Digital Printing toward 4D Shape Changing Materials

Ultrafast 4D printing (<30 s) of responsive polymers is reported. Visible-light-triggered polymerization of commercial monomers defines digitally stress distribution in a 2D polymer film. Releasing the stress after the printing converts the structure into 3D. An additional dimension can be incorporated by choosing the printing precursors. The process overcomes the speed limiting steps of typical 3D (4D) printing.

pH Responsivity and micelle formation of gradient copolymers of methacrylic acid and methyl methacrylate in aqueous solution.

A series of gradient copolymers of methacrylic acid (MAA)/methyl methacrylate (MMA) with four end-to-end composition profiles (uniform, linear gradient, triblock with linear gradient midblock, and diblock) but all having an average chain composition of ̅F(MMA) ≈ 0.5 and an average chain length of 200 were synthesized via model-based, computer-programmed, semibatch atom-transfer radical copolymerization (ATRcoP). These samples allowed us to investigate systematically the effects of the gradient composition profile on the pH responsivity and micelle formation of the copolymers in an aqueous solution. Measurements included light transmittance, TEM, AFM, DLS, (1)H NMR, and pH titration. It was found that linear gradient, triblock, and diblock copolymers formed spherical micelles at high pH. The micelles of the linear gradient copolymer contained MMA units in their hydrophilic shells, and those of the triblock and diblock copolymers had all of their MMA units residing in their cores. The composition profile showed a strong effect on the degree of acid dissociation at a given pH. The conformational transition of the copolymer chains was determined by both the pH value and composition profile. Copolymers having sharper gradients required a lower pH to trigger the conformational transition and a narrower pH range to complete the transition.

A conveniently synthesized polyethylene gel encapsulating palladium nanoparticles as a reusable high-performance catalyst for Heck and Suzuki coupling reactions

The synthesis of a polyethylene (PE) gel containing self-incarcerated palladium(0) nanoparticles is described. The PE gel matrix without any special functionality was synthesized by one-pot chain walking copolymerization of ethylene and 1,6-hexanediol diacrylate facilitated by a Pd–diimine complex (1). The Pd(II) species from 1 were immobilized in situ onto the gel matrix and further reduced to Pd(0) nanoparticles as a result of catalyst 1 deactivation during polymerization and methanol (a reducer) washing in the polymer purification process. The resulting Pd-containing PE gel (2) is shown to be a high-performance and facilely reusable heterogeneous catalyst for the Heck and Suzuki coupling reactions of iodobenzene or aryl bromides. An average TOF of 460 h−1 was achieved with an average 0.57 ppm Pd leaching in each cycle of the Heck reaction of iodobenzene when the PE gel 2 was recycled 10 times. A maximum TOF of 3.33 × 104 h−1 was reached and less than 0.64 ppm of Pd was leached in the Suzuki reactions of aryl bromides with water as solvent.

Preparation of Polar Ethylene–Norbornene Copolymers by Metallocene Terpolymerization with Triisobutylaluminium‐Protected But‐3‐en‐1‐ol

But-3-en-1-ol has been pre-protected by triisobutylaluminium and terpolymerized with ethylene and norbornene by rac-[Et(Ind)(2) ]ZrCl(2) /MAO catalysts. The strong polarity of diisobutyl(but-3-en-1-oxy)aluminum causes a slight reduction in the catalyst activity and yields a small fraction of crystallinity. The but-3-en-1-ol content in the terpolymer is as high as 3.2% and can be readily adjusted by varying the reaction conditions. When the norbornene/ethylene ratio is over 10, the norbornene incorporation efficiency is not affected by the polar monomer and is close to that of the copolymerization. Similar to the ethylene/norbornene copolymers, the thermal properties of the obtained terpolymers are mainly determined by their norbornene contents.

PREPARATION AND CHARACTERIZATION OF MMA-BA-DMAEMA TERPOLYMER LATEX

Abstract The terpolymer latex of methyl methacrylate (MMA)/butyl acrylate (BA)/dimethylaminoethyl methacrylate (DMAEMA) was prepared by batch and semi-continuous emulsion copolymerization. The effects of emulsifier type and concentration, polymerization temperature, and feed policy of emulsified monomers on process stability of the copolymerization and properties of the terpolymer latex were studied systematically. The results suggest that the selection of emulsifier should not be based on the HLB values for the DMAEMA-containing systems. The co-emulsifiers suitable for stabilizing the copolymerization process are in the order of SDS/OP>SDBS/OP>OT/OP. The results also indicate that an increase in amount of the co-emulsifiers, sodium dodecyl sulfate (SDS) and octyl phenol polyoxyethyl ether (OP), improves the process stability, decreases the surface tension and particle size of latices; however, it has little influence on the electrolyte stability when SDS/OP ratio is unchanged. A decrease in reaction temperature improves the process stability of polymerization but decreases the electrolyte stability of latices. The DMAEMA content does not affect the process stability significantly under investigated conditions but contributes to improve the electrolyte stability of latices. Compared to the batch polymerization process, the semi-continuous polymerization with a lower monomer feed rate provides better process stability for the polymerization and better electrolyte stability for the latices.

Progress in reactor engineering of controlled radical polymerization: a comprehensive review

Controlled radical polymerization (CRP) represents an important advancement in polymer chemistry. It allows synthesis of polymers with well-controlled chain microstructures. Reactor engineering is essential in bringing lab-scale chemistry to industrial realization. This paper reviews the research progress in reactor engineering of CRP, namely, atom transfer radical polymerization (ATRP), reversible addition–fragmentation chain transfer radical polymerization (RAFT), and nitroxide-mediated or stable free radical polymerization (NMP or SFRP). Research activities in semi-batch reactors, tubular reactors, and continuous stirred-tank reactors (CSTR) of both homogeneous (bulk and solution) and heterogeneous (emulsion, mini-emulsion, heterogeneous catalyst, etc.) CRP systems are summarized. Typical examples are selected and discussed in detail. Perspectives on the current status and future development are also provided.

Micron-size uniform poly(methyl methacrylate) particles by dispersion polymerization in polar media. IV. Monomer partition and locus of polymerization

Abstract A thermodynamic model has been proposed for the simulation of monomer partition between the particles phase and the continuous phase in the dispersion polymerization of methyl methacrylate in methanol/water medium. The monomer concentrations in the polymer particles and in the continuous phase decrease as the polymerization proceeds. It is strongly dependent not only on initial monomer concentration but also polymerization temperature. The partition coefficient of methyl methacrylate between the polymer particles phase and continuous phase is almost constant in limited range with increasing conversion. There are two polymerization loci in dispersion polymerization, namely the continuous and particle phases, based on the molecular weight and its distribution, and the monomer partition study.