Radical Polymerization Research Articles

Reproducible Superinsulation Materials: Organosilica-Based Hybrid Aerogels with Flexibility Control

In this study, we report highly crosslinked hybrid aerogels with an organic backbone based on vinylmethyldimethoxysilane (VMDMS) with tuneable properties. For an improved and highly reproducible synthesis, a prepolymer based on 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (D4V4) and VMDMS as monomers was prepared and purified. Di-tert-butylperoxide (DTBP) concentrations of 1 mol% initiate the radical polymerization of the mentioned monomers to achieve high yields of polymers. After purification, the obtained viscous polyorganosilane precursor could be reproducibly crosslinked with dimethyldimethoxysilane (DMDMS) or methyltrimethoxysilane (MTMS) to form gels in benzylic alcohol (BzOH), water (H2O) and tetramethylammonium hydroxide (TMAOH). Whereas freeze-drying these silica-based hybrid aerogels led to high thermal conductivity (>20 mW m−1K−1) and very fragile materials, useful aerogels were obtained via solvent exchange and supercritical drying with CO2. The DMDMS-based aerogels exhibit enhanced compressibility (31% at 7 kPa) and low thermal conductivity (16.5 mW m−1K−1) with densities around (0.111 g cm−3). The use of MTMS results in aerogels with lower compressibility (21% at 7 kPa) and higher density (0.124 g cm−3) but excellent insulating properties (14.8 mW m−1K−1).

Effect of Solvents on the Performance and Structure of Polymethylacrylimide Aerogels.

Solvent effects play a critical role in solution polymerization, especially in free radical polymerization, where they influence both monomer-solvent interactions and the resulting polymer structure. In this study, polymethacrylimide (PMI) aerogels were synthesized via freeze-drying using dimethylformamide (DMF), dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO) as solvents. The effects of monomer reactivity ratios, monomer distribution, and solvent-monomer interactions on the shrinkage, bulk density, pore size, and compressive properties of the aerogels were investigated. Results demonstrated that solvent choice significantly impacted the polymerization process, leading to variations in the structure and properties of the final aerogels. Notably, aerogels synthesized in DMSO, the most polar solvent, exhibited the lowest shrinkage (33.98%), highest density (0.1582 g·cm-3), and highest compressive stress (1695.48 kPa at 70% strain). These findings underscore the importance of solvent selection in controlling the microstructure and enhancing the mechanical performance of PMI aerogels.

Multifunctional Liquid Metal Active Material for Wound Repair and Motion Monitoring via Free Radical Polymerization Assembly

Multifunctional Liquid Metal Active Material for Wound Repair and Motion Monitoring via Free Radical Polymerization Assembly

Shape-Memory Property Acting as a Switch to Change the Surface Property of the Film

Shape-memory polyester films having functional groups were prepared and further grafted onto poly(N-isopropylacrylamide) (PNIPAAm) via atom-transfer radical polymerization. The grafting point of PNIPAAm was controlled by changing the composition of good and poor solvents. In the case of graft polymerization using only good solvents, the film swells, and polymerization proceeds not only from the surface but also from the internal polymerization initiation points. By increasing the proportion of poor solvents, PNIPAAm was grafted onto the surface of the film without swelling. The samples grafted to the interior regions of the film exhibited a decrease in the shape-memory recovery rate and recovery speed, whereas the samples grafted only to the surface of the film exhibited high shape-memory properties. Furthermore, contact-angle measurements revealed that the surface-grafted polymer exhibited changes in surface properties in response to film deformation. Because the deformation of the film is a large change, on the order of several millimeters, the deformation of the manually stretched film was shown to control molecular-level changes on the surface.

Synthesis and self-assembly of perylene-cored poly(amidoamine) dendrimers with poly[2-(dimethylamino)ethyl methacrylate]-modified arms as fluorescent bio-imaging probes and doxorubicin carriers

A poly(amidoamine) (PAMAM) dendrimer is prepared using a divergent method, with perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) as luminescent core. The peripheral amines are modified using α-bromoisobutyryl bromide, allowing the dendrimers to act as macroinitiators for the synthesis of poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) through atom transfer radical polymerization (ATRP) with three different degrees of polymerization. The successful synthesis is verified by conducting a range of analyses, including Fourier-transform infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, and X-ray diffraction (XRD). Additionally, the impact of changes in solution pH on the self-assembly of dendrimers is explored. Field emission scanning electron microscopy (FE-SEM) and dynamic light scattering (DLS) showed unique morphologies, including spherical micelles and cubic-hexagonal structures, at varying pH levels. The self-assembled dendrimers are utilized to load doxorubicin (DOX) and the drug release kinetics are studied under various conditions. The biocompatibility of the dendrimers is assessed using the MTT assay against SH-SY5Y cells. Additionally, higher dendrimer generations improved the solubility, compatibility, and fluorescent properties of the core. The dendrimers' capacity for cellular uptake and fluorescence imaging is also evaluated using SH-SY5Y cells, demonstrating their effectiveness in live-cell fluorescence imaging.

Versatile Light‐Mediated Synthesis of Degradable Bottlebrush Polymers Using α‐Lipoic Acid

AbstractBottlebrush polymers have a variety of useful properties including a high entanglement molecular weight, low Young's modulus, and rapid kinetics for self‐assembly. However, the translation of bottlebrushes to real‐world applications is limited by complex, multi‐step synthetic pathways and polymerization reactions that rely on air‐sensitive catalysts. Additionally, most bottlebrushes are non‐degradable. Herein, we report an inexpensive, versatile, and simple approach to synthesize degradable bottlebrush polymers under mild reaction conditions. Our approach relies on the “grafting‐through” polymerization of α‐lipoic acid (LA)‐functionalized macromonomers. These macromonomers can be polymerized under mild, catalyst‐free conditions, and due to reversibility of the disulfide bond in LA, the resulting bottlebrush polymers can be depolymerized by cleaving disulfide backbone bonds. Bottlebrushes with various side‐chain chemistries can be prepared through the atom transfer radical polymerization (ATRP) of LA‐functionalized macromonomers, and the backbone length is governed by the macromonomer molecular weight and solvent polarity. We also demonstrate that LA‐functionalized macromonomers can be copolymerized with acrylates to form degradable bottlebrush networks. This work demonstrates the preparation of degradable bottlebrush polymers with a variety of side‐chain chemistries and provides insight into the light‐mediated grafting‐through polymerization of dithiolane‐functionalized macromonomers.

Preparation of PAMgA/GL/GO antifreeze conductive hydrogel for wearable strain sensor based on physically cross-linked network

Conductive hydrogels have promising prospects in wearable strain sensor applications. However, the complex and diverse application scenarios put forward higher requirements on the conductivity, anti-freezing, tensile, self-healing, adhesion, and moisture retention properties of the conductive hydrogel. In this study, a polymagnesium acrylate/glycerol/graphene oxide (PAMgA/GL/GO) conductive hydrogel is prepared by free radical polymerization method, with magnesium acrylate (AMgA) as the polymer monomer, glycerol (GL) as the antifreeze filler, and graphene oxide (GO) as the conductive filler. Adding GL not only enhances the antifreeze properties of the composite hydrogels but also improves the moisture retention. The addition of GO increases the conductivity and the gauge factor (GF) of the composite hydrogels. When the GO content is 0.6 wt.%, the PAMgA/GL/GO conductive hydrogel demonstrates excellent properties of antifreeze, conductivity, self-healing, adhesion, and sensitivity. These excellent properties make it suitable as a wearable strain sensor for accurately monitoring human joint movements and subtle physiological signals.

Riboflavin‐Catalyzed Photoinduced Atom Transfer Radical Polymerization

AbstractThe photoATRP of methyl acrylate (MA) is investigated using riboflavin (RF) and CuBr2/Me6TREN as a dual catalyst system under green LED irradiation (λ ≈ 525 nm). Both RF and CuBr2/Me6TREN enhanced oxygen tolerance, enabling effective ATRP in the presence of residual oxygen. High molar mass polymers (up to Mn ≈ 129 000 g·mol−1) with low dispersity (Đ ≤ 1.16) are prepared, and chain‐end fidelity is confirmed through successful chain extension. The molecular masses of the obtained polymer increased linearly with conversion and showed high initiation efficiency. Mechanistic studies by laser flash photolysis reveal that the predominant activator generation mechanism is reductive quenching of RF by Me6TREN (83%, under [CuBr2]/[Me6TREN] = 1/3 condition), supported by polymerization kinetics and thermodynamic calculations.

Supraparticles from Cubic Iron Oxide Nanoparticles: Synthesis, Polymer Encapsulation, Functionalization, and Magnetic Properties.

Supraparticles (SPs) consisting of superparamagnetic iron oxide nanoparticles (SPIONs) are of great interest for biomedical applications and magnetic separation. To enable their functionalization with biomolecules and to improve their stability in aqueous dispersion, polymer shells are grown on the SPs' surface. Robust polymer encapsulation and functionalization is achieved via atom transfer radical polymerization (ATRP), improving the reaction control compared to free radical polymerizations. This study presents the emulsion-based assembly of differently sized cubic SPIONs (12-30 nm) into SPs with diameters ranging from ∼200 to ∼400 nm using dodecyltrimethylammonium bromide (DTAB) as the surfactant. The successful formation of well-defined spherical SPs depends upon the method used for mixing the SPION dispersion with the surfactant solution and requires the precise adjustment of the surfactant concentration. After purification, the SPs are encapsulated by growing surface-grafted polystyrene shells via activators generated by electron transfer (AGET) ATRP. The polymer shell can be decorated with functional groups (azide and carboxylate) using monomer blends for the polymerization reaction. When the amount of the monomer is varied, the shell thickness as well as the interparticle distances between the encapsulated SPIONs can be tuned with nanometer-scale precision. Small-angle X-ray scattering (SAXS) reveals that cubic SPIONs form less ordered assemblies within the SPs than spherical SPIONs. As shown by vibrating sample magnetometer measurements, the encapsulated SPs feature the same superparamagnetic behavior as their SPION building blocks. The saturation magnetization ranges between 10 and 30 emu/g and depends upon the nanocubes' size and phase composition.

Artificial Zymogen Based on Protein-Polymer Hybrids.

This study explores the synthesis and application of artificial zymogens using protein-polymer hybrids to mimic the controlled enzyme activation observed in natural zymogens. Pro-trypsin (pro-TR) and pro-chymotrypsin (pro-CT) hybrids were engineered by modifying the surfaces of trypsin (TR) and chymotrypsin (CT) with cleavable peptide inhibitors utilizing surface-initiated atom transfer radical polymerization. These hybrids exhibited 70 and 90% reductions in catalytic efficiency for pro-TR and pro-CT, respectively, due to the inhibitory effect of the grafted peptide inhibitors. The activation of pro-TR by CT and pro-CT by TR resulted in 1.5- and 2.5-fold increases in enzymatic activity, respectively. Furthermore, the activated hybrids triggered an enzyme activation cascade, enabling amplification of activity through a dual pro-protease hybrid system. This study highlights the potential of artificial zymogens for therapeutic interventions and biodetection platforms by harnessing enzyme activation cascades for precise control of catalytic activity.

Fast Gelation and Mechanical Reinforcement of Tetrahydroxydiboron-Induced Free Radical Polymerized Hydrogels under Harsh Conditions

Fast Gelation and Mechanical Reinforcement of Tetrahydroxydiboron-Induced Free Radical Polymerized Hydrogels under Harsh Conditions

Fabrication of PBAT/lignin composite foam materials with excellent foaming performance and mechanical properties via grafting esterification and twin-screw melting free radical polymerization

As one of the mainstream biodegradable materials, poly(butylene adipate-co-terephthalate) (PBAT) foams offer a sustainable alternative to traditional plastic foams, effectively reducing environmental pollution. However, the high cost and poor mechanical performance of PBAT foams impede their practical application. Herein, the glycidyl methacrylate-grafted biomass lignin (GML) was used to produce a PBAT/GML composite foam with good foaming performance and mechanical properties at high lignin-filling amounts by twin-screw melting free radical polymerization and supercritical CO2 foaming process. The compatibility of GML in the PBAT matrix was improved due to the formation of ester bonds in modified lignin, endowing the PBAT/GML (PGML) composite foam with exceptional foaming performance. Additionally, the mechanical properties of PGML composite foam were remarkably enhanced due to the introduction of the abundant aromatic structures of GML and the construction of a stable covalent crosslinking network. The compressive strengths and compression modulus of the PGML foam were improved by 2.53 times and 2.47 times, while its bending strength and bending modulus were improved by 1.27 times and 3.92 times compared to the neat PBAT. This research affords a new strategy for developing low-cost biodegradable biomass PBAT/lignin composite foam materials with good foaming performance and mechanical properties.Graphical abstract

Pesticide delivery microcapsule based on maleic anhydride‐functionalized cellulose nanocrystals‐stabilized pickering emulsion

AbstractThe efficient use of pesticides is conducive to the harmonious coexistence of humans and nature, and pesticide transport carriers can enhance the utilization value of pesticides. However, design flaws in many pesticide carriers have resulted in numerous environmental and toxicity problems. Therefore, this paper proposed a method for synthesizing pesticide microcapsules using Pickering emulsion templates stabilized by maleic anhydride‐functionalized cellulose nanocrystals‐g‐poly (methyl methacrylate) (MACNCs‐g‐MMA), viz., simple radical polymerization of maleic anhydride‐functionalized cellulose nanocrystals with methyl methacrylate in Pickering emulsion. The structure and morphology of microcapsules were characterized via the FT‐IR, XRD, TG‐DTG, and SEM techniques. The imidacloprid‐loaded MACNCs‐g‐MMA (IMI@MACNCs‐g‐MMA) presented a high encapsulation efficiency (~94.13%) and drug loading efficiency (~24.00%). The release behavior was affected by temperature, viz., higher temperature promoted the release of IMI. Regarding the spread and retention on the leaf surface, the IMI@MACNCs‐g‐MMA demonstrated significant advantages over commercial IMI water‐dispersible granules (CG) (36.9° vs. 104.9° for contact angle, 14.3 vs. 30.0 mg cm−2 for retention). This study provides a promising pesticide formula for sustainable agriculture.

Metal‐Free, Light‐Catalyzed ATRP For the Synthesis of Functional PVDF‐Based Block Copolymers and Their Characterization

AbstractThe synthesis and characterization of poly(vinylidene fluoride) (PVDF)‐based block copolymers using a metal‐free light‐catalyzed atom transfer radical polymerization (ATRP) approach are described. A PVDF macroinitiator with C─Br bonds at both ends of the chain is synthesized, and an organic photoredox catalyst (OPRC) is used to control the process. The metal‐free process expands the possibilities for the synthesis and application of PVDF‐based block copolymers, as it allows the use of monomers that is previously incompatible with classical ATRP due to their interaction with metal catalysts. The synthesized block copolymers are characterized structurally and thermally as powder materials and in thin films. Fourier‐transform infrared spectroscopy (FT‐IR) analysis revealed that the crystalline phase of PVDF changes when thin films are formed. Specifically, the disappearance of the FT‐IR peaks related to the gamma phase and the presence of characteristic peaks related to the alpha and beta phases indicate that film formation rearranged the PVDF chains, leading to changes in their crystalline phases. These PVDF‐based block copolymers have unique properties, including high thermal stability, chemical resistance, and piezoelectricity, making them potential candidates for use in various fields, such as biomedical engineering, energy storage, and electronic devices.

Synergistic Radical Taming by Concurrent Degenerative Transfer and Atom Transfer Radical Polymerization in Emulsion

Synergistic Radical Taming by Concurrent Degenerative Transfer and Atom Transfer Radical Polymerization in Emulsion

Poly(lactide) Upcycling Approach through Transesterification for Stereolithography 3D Printing.

The legislature determines the recycled and waste contents in fabrication processes to ensure more sustainable production. PLA's mechanical recycling and reuse are limited due to the performance decrease caused by thermal or hydrolytic instability. Our concept introduces an upcycling route involving PLA depolymerization using propylene glycol as a reactant, followed by the methacrylation, assuring the liquid systems' curability provided by radical polymerization. PLA-containing curable systems were studied from a rheological and thermomechanical viewpoint. The viscosity levels varied from 33 to 3911 mPa·s at 30 °C, giving a wide capability potential. The best system reached 2240 MPa storage modulus, 164.1 °C glass-transition temperature, and 145.6 °C heat-resistant index, competitive values to commercial systems. The printability was verified for all of the systems. Eventually, our concept led to SLA resin production containing PLA waste content up to 51 wt %.

Low-Dispersity Polymers via Free Radical Alternating Copolymerization: Effects of Charge-Transfer-Complexes.

Alternating copolymers are crucial for diverse applications. While dispersity (Ð, also known as molecular weight distribution, MWD) influences the properties of polymers, achieving low dispersities in alternating copolymers poses a notable challenge via free radical polymerizations (FRPs). In this work, we demonstrated an unexpected discovery that dispersities are affected by the participation of charge transfer complexes (CTCs) formed between monomer pairs during free radical alternating copolymerization, which have inspired the successful synthesis of various alternating copolymers with low dispersities (>30 examples, Ð=1.13-1.39) under visible-light irradiation. The synthetic method is compatible with binary, ternary and quaternary alternating copolymerizations and is expandable for both fluorinated and non-fluorinated monomer pairs. DFT calculations combined with model experiments indicated that CTC-absent reaction exhibits higher propagation rates and affords fewer radical terminations, which could contribute to low dispersities. Based on the integration of Monte Carlo simulation and Bayesian optimization, we established the relationship map between FRP parameter space and dispersity, further suggested the correlation between low dispersities and higher propagation rates. Our research sheds light on dispersity control via FRPs and creates a novel platform to investigate polymer dispersity through machine learning.

Heterogenization of Palladium Trimer and Nanoparticles Through Polymerization Boosted Catalytic Efficiencies in Recyclable Coupling and Reduction Reactions.

The development of heterogeneous palladium catalysts has shown continuous vitality in the field of catalysis and materials. In this work, we report one concise free radical polymerization approach to accomplish the aromatic palladium trimer functionalized polymers PSSy-[Pd3]+ (2) and its derived palladium nanoparticles (3). Full characterizations could confirm the successful combination of cationic [Pd3]+ or nanoparticles with poly(p-sulfonated styrene) skeleton. Compared to their monomeric tri-palladium precursor (1) and common Pd(dba)2, Pd(PPh3)4, Pd(OAc)2, heterogeneous PSSy-[Pd3]+ (2) shows much superior catalytic activities (0.15 mol %, TOF=1333.3 h-1) in the SMCC reaction. The identically ligated PdNPs (3) are formed in-suit in the presence of NaBH4 and accomplish quantitative reduction of 4-nitrophenol in just 320 s (0.50 mol %, TOF=2250 h-1). Moreover, these heterogeneous catalysts are reused for 5-6 times without significant loss of catalytic activity. Their superior catalytic ability is probably attributed to the synergistic effect of polymer entanglement and the tri-palladium fragment. This work enlightens that the immobilization of palladium clusters or nanoparticles by polymerization could offer multiple advantages in stability, efficiency and recyclability for their involved catalyses and show far-reaching future implications.

Preparation and performance evaluation of a low‐damage fracturing fluid for unconventional reservoirs

AbstractThe characteristics of tight matrix, underdeveloped natural fractures, small pore throat radius, poor pore connectivity, and abundant clay minerals result in a high potential for damage to the tight sandstone reservoirs of the Shaximiao Formation in the Qiulin Block in the Sichuan Basin. In order to reduce the retention damage caused by fracturing fluid to the tight sandstone reservoir, a low damage fracturing fluid system applicable to the target reservoir is developed in this work, and the indoor performance meets the requirements of on‐site fracturing operation. A low‐damage, heat‐resistant, shear‐stable amphiphilic polyacrylamide (PAAD) was prepared by free radical polymerization in aqueous solution using acrylamide, acrylic acid, and methacryloyloyloxyethyl dimethyloctadecyl ammonium bromide (DM18) as the monomers. The amphoteric polyacrylamide was characterized by Fourier infrared spectroscopy, nuclear magnetic resonance spectroscopy (1H NMR), light scattering molecular weight determination, and thermogravimetric analysis. Fracturing fluids were formulated with the amphiphilic hydrophobic associative polymer PAAD as a drag‐reducing agent, the fluorine‐containing and nonionic complex surfactant FD1 as a clean‐up additive, CT10‐4B as a bactericide and CT1‐12 as an emulsion breaker. The fracturing fluid formulation was preferred, and the performance of the fracturing fluid was evaluated in terms of temperature resistance and shear resistance, drag reduction, anti‐expansion, and core damage. The fracturing fluid showed good temperature and shear resistance, with a viscosity retention of 58.4% at 120°C and 170 s−1 shear for 1 h. At a loading of 0.1%, the drag reduction rate reaches 72.3%, the anti‐expansion rate of the gel‐breaking fluid is 86.04%, and the damage rate to the tight sandstone core is 16.25%. The results show that the fracturing fluid has good heat resistance and shear stability, as well as low damage and good resistance reduction and anti‐expansion properties. This work can provide new strategies for designing polymeric fracturing fluids with low damage, good heat resistance and shear stability.

Rational design of pH-responsive nano-delivery system with improved biocompatibility and targeting ability from cellulose nanocrystals via surface polymerization for intracellular drug delivery

Cellulose nanocrystals (CNCs), derived from diverse sources and distinguished by their inherent biodegradability, excellent biocompatibility, and facile cellular engulfment due to their rod-like structure, hold great promise as carriers for the development of nano-delivery systems. In this work, highly efficient rod-like CNCs were employed as substrates for grafting glycidyl onto their surfaces through ring-opening polymerization, forming hyperbranched polymers with superior cell uptake properties. Subsequently, 4-vinylbenzeneboronic acid (VB) and poly (ethylene glycol) methyl ether methacrylate (PEGMA) were employed as monomers in the polymerization process to fabricate a pH-responsive targeted nano-delivery system, denoted as CNCs-VB-PEGMA, via single electron transfer reactive radical polymerization (SET-LRP) reaction. The CNCs-VB-PEGMA was successfully prepared and used for the loading of curcumin (Cur) to form a pH-responsive nano-delivery system (CNCs-VB-PEGMA-Cur), and the loading rate of Cur was as high as 70.0 %. Studies showed that this drug delivery system could actively targeting liver cancer cells with the 2D cells model and 3D tumor microsphere model, showing efficient liver cancer cell-killing ability. Collectively, the CNCs-VB-PEGMA drug delivery system has potential applications in liver cancer therapy as an actively targeting and pH-responsive drug delivery system.