Photo-controlled reversible-deactivation radical polymerization (photo-RDRP) has been investigated as a “green” and spatiotemporally controlling pathway for polymer synthesis. While the combination of photo-RDRP and flow chemistry has offered opportunities to increase light intensity and enable uniform light irradiation, problems associated with flow approaches still remain for photoflow-RDRP, which has hindered merging flow polymerization with other cutting-edge techniques. Herein, we summarize challenges and recent achievements in photoflow-RDRP including the development of (a) droplet/slug-flow to regulate residence time distribution, (b) mixing techniques to tailor polymer, (c) polymerization induced self-assembly, and (d) computer-aided synthesis. We hope this work will provide informative knowledge to people in related fields and stimulate novel ideas to promote polymer synthesis in both academia and industry.

Molecular oxygen is a radical scavenger in both conventional and controlled radical polymerization (CRP), resulting in many time-consuming methods for physically removing oxygen before the polymerization. Different approaches have been developed to have oxygen tolerance by chemically consuming or converting molecular oxygen into non-initiating species to address this issue. Recently, we propose another approach called oxygen initiation that directly transforms molecular oxygen into the initiating carbon radical in CRP. This feature article summarizes our recent developments in this direction. Oxygen-initiated reversible addition-fragmentation transfer (RAFT) polymerization has been successfully conducted using oxygen and trialkylborane as co-initiators under the ambient conditions and atmosphere without any prior degassed procedures. This gas-triggered initiation provides the opportunity for spatiotemporal control of the polymerization by molecular oxygen or air. Rationally synthesized alkylborane compounds could derive the predesigned structure of the initiating alkyl radical to minimize the side reactions and free polymer chains, achieving the synthesis of ultra-high molecular weight polymers. The challenges and perspectives are also discussed in the end.

Hybrids, produced by hybridization of proteins, peptides, DNA, and other new biomolecules with polymers, often have unique functional properties. These properties, such as biocompatibility, stability and specificity, lead to various smart biomaterials. This review mainly introduces biomolecule-polymer hybrid materials by reversible deactivation radical polymerization (RDRP), emphasizing reverse addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide mediated polymerization (NMP). It includes the methods of RDRP to improve the biocompatibility of biomedical materials and organisms by surface modification. The key to the current synthesis of biomolecule-polymer hybrids is to control polymerization. Besides, this review describes several different kinds of biomolecule-polymer hybrid materials and their applications in the biomedical field. These progresses provide ideas for the investigation of biodegradable and highly bioactive biomedical soft tissue materials. The research hotspots of nanotechnology in biomedical fields are controlled drug release materials and gene therapy carrier materials. Research showed that RDRP method could improve the therapeutic effect and reduce the dosage and side effects of the drug. Specifically, by means of RDRP, the original materials can be modified to develop intelligent polymer materials as membrane materials with selective permeability and surface modification.

Fluorinated polymers are important materials that are widely used in many areas as taking the advantage of inertness to chemical corrosion, prominent weather resistance, low flammability, and good thermal stability. Poly(vinylidene fluoride) (PVDF) based fluoropolymers is the most common type of commercial fluoropolymer especially used as dielectric materials. However, there are always some shortcomings in practical applications, so it is necessary to modify PVDF-based fluoropolymers for better application. Controlled/living radical polymerization (CRP) and related techniques have become a powerful approach to tailoring the chemical and physical properties of materials and have given rise to great advances in modification of PVDF-based fluoropolymers.

Polymerization-induced self-assembly (PISA) is an emerging method for the preparation of block copolymer nano-objects at high concentrations. However, most PISA formulations have oxygen inhibition problems and inert atmospheres (e.g. argon, nitrogen) are usually required. Moreover, the large-scale preparation of block copolymer nano-objects at room temperature is challenging. Herein, we report an enzyme-assisted photoinitiated polymerization-induced self-assembly (photo-PISA) in continuous flow reactors with oxygen tolerance. The addition of glucose oxidase (GOx) and glucose into the reaction mixture can consume oxygen efficiently and constantly, allow the flow photo-PISA to be performed under open-air conditions. Polymerization kinetics indicated that only a small amount of GOx (0.5 μmol/L) was needed to achieve the oxygen tolerance. Block copolymer nano-objects with different morphologies can be prepared by varying reaction conditions including the degree of polymerization (DP) of core-forming block, monomer concentration, reaction temperature, and solvent composition. We expect this study will provide a facile platform for the large-scale production of block copolymer nano-objects with different morphologies at room temperature.

Photoenzymatic reversible addition-fragmenatation chain transfer (RAFT) emulsion polymerization, surfactant-free or ab initio, of various monomers is reported with oxygen tolerance. In surfactant-free emulsion polymerizatoin, poly(N,N-dimethylacrylamide)s were used as stabilizer blocks for emulsion polymerization of methyl acrylate, n-butyl acrylate and styrene, producing well-defined amphiphilic block copolymers, including those with an ultrahigh molecular weight, at quantitative conversions. The controlled character of surfactant-free emulsion polymerization was confirmed by kinetic studies, chain extension studies and GPC analyses. Temporal control was demonstrated by light ON/OFF experiments. In ab initio emulsion polymerization of methyl acrylate and methyl methacrylate, low-dispersity hydrophobic polymers were synthesized with predictable molecular weights. This study extends the monomer scope suitable for photoenzymatic RAFT polymerization from hydrophilic to hydrophobic monomers and demonstrates that oxygen-tolerance can be equally achieved for emulsion polymerization with excellent RAFT control.

We report a dynamic polymerization system based on the reversible nucleophilic Michael polyaddition of activated alkynes and dithiols. Four poly(dithioacetal)s (P1−P4) were prepared via the base-catalyzed thiol-yne “click” polyaddition of two dithiols (1,4-butanedithiol (4S) and 1,5-pentanedithiol (5S)) and two alkynones (3-butyn-2-one (Y1) and 1-phenyl-2-propyn-1-one (Y2)) at high concentrations. We systematically investigated the base-catalyzed polymerization of 4S and Y1 (for polymer P1) under different conditions, and found that this polymerization was a highly concentration-dependent dynamic system: polymer P1 was formed at high concentration, while seven-membered dithioacetal, 1-(1,3-dithiepan-2-yl) propan-2-one (C1), was obtained at low concentration. The polymerization of 4S and Y2 (for polymer P4) displayed similar polymerization behavior, generating 2-(1,3-dithiepan-2-yl)-1-phenylethanone (C4) at low concentration. On the contrary, polymer P2 (from Y1 and 5S) was exclusively obtained with no formation of eight-membered dithioacetal. The polymerizations of Y1 with 1,2-ethanedithiol (2S) and 1,3-dimercaptopropane (3S) only afforded corresponding five- and six-membered dithioacetals, 1-(1,3-dithiolan-2-yl) propan-2-one (C2) and 1-(1,3-dithian-2-yl) propan-2-one (C3). This dynamic behavior of P1 and P4 was attributed to the concentration-dependent retro-Michael addition reaction between a thiol and a β-sulfido-α,β-unsaturated carbonyl compound catalyzed by bases. Furthermore, polymers P1 and P4 could be depolymerized into C1 and C4 in yields of 58% and 95%, respectively. The ring-opening polymerization of C1 at high concentration could successfully regenerate polymer P1. Thus, a new type of closed-loop recyclable poly(dithioacetal)s was developed.

Dispersity (Đ) of polymers has a great effect on the properties of polymeric materials, and therefore how to control Đ is very important but still a huge challenge in polymer synthesis, especially for reversible-deactivation radical polymerization (RDRP) strategy. Herein, we successfully developed a novel strategy to adjust Đ of polymers by visible light-controlled reversible complexation mediated living radical polymerization (RCMP) and combination of single-electron transfer-degenerative chain transfer living radical polymerization (SET-DTLRP) at room temperature. In RCMP system, 2-iodo-2-methylpropionitrile (CP-I) and ethyl 2-iodo-2-phenylacetate (EIPA) were used as alkyl iodide initiators, by using methyl methacrylate (MMA) as the model monomer and n-butylacrylate (BA) as the end-capping reagent to regulate Đ of polymers. Subsequently, we successfully prepared the block copolymer PMMA-b-PBA with adjustable Đ by reactivating the polymer end-chains via SET-DTLRP in the presence of copper wire, fully demonstrating that it is a promising strategy that can keep the "living" feature of polymers while regulating their molar mass dispersities easily.

Reversible chain transfer catalyzed polymerization (RTCP) is a practical and efficient process for the precise synthesis of polymers with special architecture by using simple phenols (2,4,6-trimethylphenol, TMP) or hydrocarbons (xanthene, XT) as efficient organocatalysts. Herein, alkyl iodide (R-I), which was generated from in situ bromine-iodine transformation of alkyl bromide (R-Br) with sodium iodide (NaI), was served as initiator to mediate RTCP with TMP or XT. MMA and other functional methacrylates, including GMA, DEAM, DMAEMA and BzMA, were successfully initiated by combining organocatalysts and azo initiators to yield polymers with low-polydispersity (M_w/M_n=1.1−1.5) and ideal monomer conversions (50%−90%) at moderate temperature. Moreover, 3-armstar polymers were also obtained by this method. The high chain-end fidelity of the obtained poly(methyl methacrylate) with iodine as chain-end group (PMMA-I) was confirmed by chain-extension reaction. The environmentally friendly initiators and organocatalysts exhibit powerful polymerization properties toward RTCP, providing a significant method to synthesize functional polymers.

Simply constructing multiple responsive polymers with obvious shape and dimension variations on their assemblies upon different stimuli is still rarely reported. In this study, we report a hyperbranched polymer named HPAzoBAHB-star-PEG₉ with quadruple-response to light, temperature, pH and oxidation stimuli. The polymer contains azobenzene chromophore, sulfide, amide and amine groups in its hydrophobic hyperbranched core, and the core is capped with hydrophilic polyethylene glycol (PEG₉) arms. HPAzoBAHB-star-PEG₉ could assemble into unusual leaf-like lamellar micelles at 25 °C under the guidance of orderly arranged H-aggregate of azobenzene moieties. These leaf-like lamellar micelles can transform into vesicles upon UV irradiation and lower temperature, or convert to smaller spherical micelles in acidic or oxidative environments, respectively, with the destroy of ordered azobenzene arrangements. This quadruple-responsive hyperbranched polymer is suitable to construct multiple stimuli-responsive micro/nanostructures, or accurate delivery and release following subtle stimuli sequences.

Solid-stated smart polymers responsive to external stimuli have attracted much attention for potential application in the field of photoelectron devices, logic gates, sensor, data storage and security. However, it is a bigger challenge for polymers than that for small molecules in solid state to acquire stimuli-responsive properties, because polymers with high molecular weight are not as easy to change the packing structure as small molecules under external stimulation. Here, a D-A type alternating copolymer PTMF-o containing 3,4-bisthienylmaleimide (A unit) and fluorene (D unit) is designed and synthesized. Upon irradiation of sunlight, PTMF-o film exhibits a photo-response with the color altering from purple to colorless. It is attributed to the structure of copolymer transformed from ring-opening form (PTMF-o) to ring-closure form (PTMF-c), resulting from the oxidative photocyclization of 3,4-bisthienylmaleimide unit. Consequently, the ability of charge transfer (CT) from fluorene to 3,4-bisthienylmaleimide unit in PTMF-o can be easily weakened by light stimuli. PTMF-o film displays a WORM-type resistive storage performance for the strong CT. Interestingly, after exposure, the electrical memory behavior in situ transfers into FLASH type, due to weak CT in PTMF-c. PTMF-o film can also be employed as smart material to construct NAND and NOR logic gates by using light as input condition. The work provides a simple way to modify the electronic properties of polymers and realize stimuli-response in solid states.

The catalytic performance of rare-earth metal dialkyl complexes in combination with DMAO (dry methylaluminoxane) is explored. In the presence of 60 equivalents of DMAO, the half-sandwich complex (C₁₃H₈CH₂Ph)Sc(CH₂SiMe₃)₂(THF) (1) is inert for styrene polymerization, but (C₅Me₄Ph)Sc(CH₂C₆H₄NMe₂-o)₂ (2) converts 18% styrene into syndiotactic polystyrene. Under the same conditions, the constrained-geometry configuration sandium complex (C₁₃H₈CH₂Py)Sc(CH₂SiMe₃)₂ (3a) displays extremely high catalytic activity (>6420 kg·mol_Sc⁻¹·h⁻¹) and perfect syndiospecific (rrrr>99%) for styrene polymerization, while its lutetium (3b) and yttrium (3c) analogues are nearly inactive. Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization, it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene, 4-methylthiostyrene, 4-fluorostyrene, 4-dimethylhydrosilylstyrene, alkyne-susbstituted styrenes and 4-methylstyrene. In addition, the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass transition at 80 °C and 0.4 MPa ethylene pressures. By increasing styrene feed amount from 20 mmol to 60 mmol, the styrene content slight increases from 48.2 mol% to 53.8 mol%, but the polymerization activity is obviously promoted from 240 kg·mol_Sc^–1·h^–1 to 532 kg·mol_Sc^–1·h^–1.

Mimicking the complex structure of natural bone remains a challenge for bone tissue scaffolds. In this study, a novel processing strategy was developed to prepare the bone-like scaffolds that are featured by highly oriented and fully interconnected pores. This type of biomimetic scaffolds was evolved from solid phase stretching of immiscible polycaprolactone (PCL)/poly(ethylene oxide) (PEO) blends with co-continuous structure and the pore morphology was inherited from selective extraction of water soluble PEO phase. The pore anisotropy was readily tuned by varying the stretching strain without loss of interconnectivity. Significant promotion in preosteoblast proliferation, alkaline phosphatase activity and osteogenic gene expression was observed in the oriented porous scaffolds compared to the isotropic porous counterpart. The oriented architecture provided a topographical cue for aligned growth of preosteoblasts, which activated the Wnt/β-catenin signaling pathway. The proposed strategy enriches the toolbox for the scaffold design and fabrication for bone tissue engineering.

Thermosetting resin matrix is the key component of advanced wave-transparent composites, where low dielectric constant, excellent processability, high thermal stability, as well as good bonding ability are required for resins. Herein, we prepared a series of phenylethynyl terminated polyimide (PI) resins by grafting amine-functionalized hyperbranched polysiloxane (HBPSi) to PI chains during the in situ polymerization. The effects of HBPSi on the processability of oligomers, molecular packing, thermal stability, dielectric property and bonding ability to reinforce Kevlar fibers of the cured PI/HBPSi composite resins have been examined in detail. The dielectric constants of the cured composite resins were greatly reduced from 3.29 to 2.19 without compromising its processability and thermal stability. Meanwhile, the 10 wt% HBPSi-containing PI resin demonstrated better bonding ability to reinforce fibers with the interfacial shear strength (IFSS) of 37.64 MPa, compared with that of neat PI-6 matrix (27.34 MPa), and better adhesion to metal with the lap shear strength of 10.48 MPa, 50% higher than that of neat resin PI-6 (6.98 MPa). These resultant PI/HBPSi composite resins exhibit excellent comprehensive properties, indicating their great potential as low-dielectric constant resin matrix in radar radome.

Crystallinity of bottlebrush polymers due to side chain crystallization has been considered to be related to the length of the side chains only under the assumption of complete participation of crystallization by all side chains. Recent experimental results revealed that in poly(n-alkyl methacrylate)s a fraction of side chains could not crystallize due to constraints imposed by the trapped main chain entanglements and required expansion of main chain-main chain distance. This result renders the original simplified consideration of the origin of crystallinity in bottlebrush polymers questionable. In this work, we introduce a new parameter f_c, the fraction of crystallizable side chains, to better describe the crystallinity of bottlebrush polymers. A linear relationship between the melting enthalpy and the number of alkyl groups in side chains for bottlebrush polymers reported repeatedly indicates that f_c remains essentially unchanged when bottlebrush polymers had the same main chain structure and grafting degree but different side chain lengths. The slope of the above-mentioned linear relationship is thus Δ$H_{{\rm{CH}}_2} $×f_c, where Δ$H_{{\rm{CH}}_2} $ stands for the melting enthalpy of one mole alkyl group packed into the crystal. With a known value of f_c, it is possible to estimate the value of Δ$H_{{\rm{CH}}_2} $. In case of poly(n-alkyl methacrylate)s, we estimated Δ$H_{{\rm{CH}}_2} $ of hexagonal crystal being at most 5.74 kJ/mol with the knowledge of possibly smallest f_c of 0.67 obtained from small angle X-ray scattering data. Therefore, the crystallinity of bottlebrush polymer would be calculated based on the equation ${X_{\rm{c}}} = {f_{\rm{c}}} \times \dfrac{{{N_{\rm{c}}}}}{N}$ with N and N_c being the number of alkyl groups in a side chain and those packed in the crystalline structure, respectively. Both chemical structure and grafting degree of bottlebrush polymers affect f_c.

The liquid-liquid phase separation (LLPS) widely exists in biology, synthetic chemistry, crystallization kinetics and other fields, and it is very important to realize the related functions. The research on the competition between LLPS and micellization/vesiculation has made considerable progress. However, the way to effectively control the formation paths from homogeneous state to aggregates has not been completely solved, which is vital to determine its structure and properties and even its future functions. Here we describe the phenomenon of LLPS and its effect on the dynamic process of self-assembly of amphiphilic diblock copolymers (BCPs). Starting from the establishment of phase diagram, we explore the existence conditions of LLPS state, the internal morphology and external size of large droplets, and its significant implications to the dynamic path of vesicle formation. Vesicles formed via LLPS have larger sized outer dimensions and inner cavities, and contain more solvents during certain stages. The detailed research of LLPS and its self-assembly simulation has contributed to completing its theoretical basis and practical applications in the future in various fields.