Surface-initiated Reversible Addition-fragmentation Chain Transfer Research Articles

Cellulose nanocrystal thermal smart molecular brushes with upper critical aggregation temperature

Grafting thermo-responsive polymers onto cellulose nanocrystals (CNCs) and achieving critical temperature regulation has drawn significant research interest. The thermal transition behavior of CNCs can be controlled by adjusting the polymer molecular brushes on the CNCs surface. We synthesized poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA) grafted CNCs via surface-initiated reversible addition–fragmentation chain transfer, followed by modifying PDMAEMA brushes into poly-3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (PDMAPS) brushes via quaternization. The critical temperature was regulated by modifying and grafting of poly (ethylene glycol) methacrylate. Found the thermal stimulus-responsive type and transition point of CNCs can be controlled by adjusting the surface molecular brushes. Ultraviolet-visible spectroscopy and dynamic light scattering analyses indicated that CNC–PDMAEMA aggregated above 70 °C, whereas CNC–PDMAPS aggregated below 31 °C. The thermo-responsive materials based on CNCs exhibited a conversion from a lower critical aggregation temperature to an upper critical aggregation temperature (UCAT) type. CNC–PDMAPS–mPEG was obtained by modifying and grafting for UCAT to be regulated to approximately 37 °C, which is close to the human body temperature. CNC–PDMAPS and CNC–PDMAPS–mPEG exhibited only microscopic alterations and could encapsulate and release substances. Therefore, they demonstrate considerable potential for biomedical applications.

Chiral polymer brush growth on magnetic nanoparticles under ambient conditions

Magnetic nanoparticles (MNPs) grafted with functional polymers were prepared via surface-initiated reversible addition-fragmentation chain transfer polymerization using oxygen (O2-SI-RAFT polymerization) under ambient conditions. Two types of monomers, a charged monomer and a chiral monomer, were used in this study. The successfully prepared polymer-coated MNPs could be easily separated using a bar magnet. The modified MNPs were characterized by various analytical methods, including zeta potential determination, spectroscopic analyses, magnetic hysteresis, transmission electron microscopy, and elemental composition analysis by energy-dispersive X-ray spectroscopy. Circular dichroism spectroscopy analysis showed that chiral polymers grown from the MNPs have mirror images, confirming that chiral properties can be conferred on MNPs via O2-SI-RAFT polymerization.

Two birds with one stone: A magneto-optical dual-stimuli-responsive intelligent Pickering emulsion for efficient conversion of glucose to 5-hydroxymethylfurfural

The efficient conversion of glucose to 5-hydroxymethylfurfural (HMF) is a critical process for maximizing the value of lignocellulosic biomass. However, the existing systems of binary solvent and ionic liquids (ILs) commonly employed for this conversion often encounter significant interphase mass transfer resistance and exhibit lower utilization efficiency of ILs. Herein, the study presents the precise fabrication of a novel Pickering interfacial catalyst, P(0.8[CL8]-[ILs]2-[SP])@SiO2@Fe3O4 with immobilized magneto-optical bi-sensitizer and Brønsted&di-superimposed-Lewis acid functionalized ILs (B-L-ILs), realized through surface-initiated reversible addition-fragmentation chain transfer polymerization. The construction of an intelligent Pickering emulsion with dual-stimuli-responsive properties was effectively accomplished by accurate manipulation under Vis-light radiation, utilizing P(0.8[CL8]-[ILs]2-[SP])@SiO2@Fe3O4. The presence of this emulsion significantly enhances interphase mass transfer in a binary solvent system, while the incorporation of B-L-ILs at interphase interfaces in Pickering emulsion greatly facilitates the efficient conversion of glucose to HMF. The Pickering interfacial catalyst demonstrates exceptional and unprecedented performance, as evidenced by its ability to achieve a glucose conversion rate of 96.3% and HMF yield of 86.7%. Various characterizations, experimental analyses, and kinetic studies synergistically confirm the efficient conversion of glucose to HMF in the Pickering emulsion. The effective control of Pickering demulsification can be intelligently achieved by simultaneously applying magnetic stimulation and UV-light irradiation, while its catalytic activity remains unaltered even after undergoing five consecutive cycles. This study presents a novel approach to enhance the efficiency of HMF production by combining a cutting-edge Pickering emulsion with B-L-ILs, thereby accomplishing two objectives simultaneously.

Surface-Initiated PET-RAFT via the Z-Group Approach.

Surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) is a user-friendly and versatile approach for polymer brush engineering. For SI-RAFT, synthetic strategies follow either surface-anchoring of radical initiators (e.g., azo compounds) or anchoring RAFT chain transfer agents (CTAs) onto a substrate. The latter can be performed via the R-group or Z-group of the CTA, with the previous scientific focus in literature skewed heavily toward work on the R-group approach. This contribution investigates the alternative: a Z-group approach toward light-mediated SI photoinduced electron transfer RAFT (SI-PET-RAFT) polymerization. An appropriate RAFT CTA is synthesized, immobilized onto SiO2, and its ability to control the growth (and chain extension) of polymer brushes in both organic and aqueous environments is investigated with different acrylamide and methacrylate monomers. O2 tolerance allows Z-group SI-PET-RAFT to be performed under ambient conditions, and patterning surfaces through photolithography is illustrated. Polymer brushes are characterized via X-ray photoelectron spectroscopy (XPS), ellipsometry, and water contact angle measurements. An examination of polymer brush grafting density showed variation from 0.01 to 0.16 chains nm-2. Notably, in contrast to the R-group SI-RAFT approach, this chemical approach allows the growth of intermittent layers of polymer brushes underneath the top layer without changing the properties of the outermost surface.

NIR-triggered thermosensitive polymer brush coating modified intraocular lens for smart prevention of posterior capsular opacification

Posterior capsule opacification (PCO) is the most common complication after cataract surgery. Drug-eluting intraocular lens (IOLs) is a promising concept of PCO treatment in modern cataract surgery. However, the large dose of drugs in IOL leads to uncontrollable and unpredictable drug release, which inevitably brings risks of overtreatment and ocular toxicity. Herein, a low-power NIR-triggered thermosensitive IOL named IDG@P(NIPAM-co-AA)-IOL is proposed to improve security and prevent PCO by synergetic controlled drug therapy and simultaneous photo-therapy. Thermosensitive polymer brushes Poly(N-isopropylacrylamide-co-Acrylic acid) (P(NIPAM-co-AA)) is prepared on IOL via surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization. Then, Doxorubicin (DOX) and Indocyanine green (ICG) co-loaded Gelatin NPs (IDG NPs) are loaded in P(NIPAM-co-AA) by temperature control. The IDG NPs perform in suit photodynamic & photothermal therapy (PTT&PDT), and the produced heat also provides a trigger for controllable drug therapy with a cascade effect. Such functional IOL shows excellent synergistic drug-phototherapy effect and NIR-triggered drug release behavior. And there is no obvious PCO occurrence in IDG@P(NIPAM-co-AA) IOL under NIR irradiation compared with control group. This proposed IDG@P(NIPAM-co-AA)-IOL serves as a promising platform that combines phototherapy and drug-therapy to enhance the therapeutic potential and medication safety for future clinical application of PCO treatment.

A smart material: Multi-stimulus-responsive composite microspheres prepared via RAFT polymerization as recyclable pickering emulsifiers and their application in stabilizing real oil phases

The development of smart composites to sustainably separate and recover oil from oily water had attracted much attention. In this study, tri-block (P(LMA-b-NIPAM-b-AA)) polymer brushes were controllably “grown on” the Fe3O4 surface by three-step surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization to prepare Fe3O4-P(LMA-b-NIPAM-b-AA) (MNPLNA) magnetic nanospheres with interfacial activity. The MNPLNA nanospheres were characterized to demonstrate the triple response of pH, temperature and magnetism. Meanwhile, the comparison experiments showed that the MNPLNA nanospheres with tri-block structure had excellent interfacial activity. Then, the O/W type of Pickering emulsion was prepared by using MNPLNA nanospheres as the particle emulsifier. The size variation pattern of Pickering emulsion was comprehensively investigated by adjusting the concentration of nanospheres, oil-water ratio, electrolyte concentration and polarity of oil phase. Pickering emulsions were controllably separated by the action of an external magnetic field, and could be reversibly switched at least 10 cycles between emulsified and broken states under the trigger of pH and temperature. In addition, MNPLNA nanospheres exhibited excellent emulsification properties for stabilizing variety of real oil phases (e.g., canola oil, kerosene, diesel and crude oil). Based on this, MNPLNA nanospheres were applied as smart multifunctional materials in simulated kerosene-containing wastewater separation. MNPLNA nanospheres could be used to recover kerosene with high recovery rate after 10 separation cycles under the stepwise action of pH, temperature and magnetic field.

Chiral polymer coatings on substrates via surface-initiated RAFT polymerization under ambient conditions

Surface-initiated reversible addition-fragmentation chain transfer polymerization using oxygen (O2-SI-RAFT) was performed to endow the substrates with chiral properties. Chiral monomers were synthesized using methacrylic anhydride and l/d-amino acids (phenylalanine methyl ester, alanine methyl ester, valine methyl ester, and leucine methyl ester), and chiral polymers were grown on titanium and glass substrates. The polymer brushes grafted from the substrates were confirmed by ellipsometry analysis, water contact angles, X-ray photoelectron spectroscopy, and atomic force microscopy. Block copolymer brushes were also polymerized through chain extension. Using a glass substrate, chirality of the polymer brushes grown on the surface could be confirmed via circular dichroism spectroscopy.

Hemin-catalyzed SI-RAFT polymerization for thrombin detection

Ultrasensitive protein detection has considerable potential for early diagnosis and screening of diseases. Here, based on Hemin-catalyzed surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization, this work developed an assay for ultrasensitive fluorescent biosensing of proteins and established a thrombin fluorescent sensor. First, the amino-modified aptamer 1 was immobilized on Fe3O4 magnetic beads, and then thrombin was added to form the aptamer 1-thrombin bioaffinity complex. Another thiol-modified aptamer 2 binds to bound thrombin to form a sandwich structure. Fluorescein O-methacrylate was used as the monomer, acetylacetone (ACAC) as the initiator, and Hemin as the catalyst. Through Hemin-catalyzed SI-RAFT polymerization, a large number of thrombin molecules are labeled with fluorescein O-methacrylate, resulting in severalfold amplification of the fluorescent signal. By detecting the fluorescent signal in thrombin from 1.0 fM to 0.1 nM, the proposed super sandwich strategy can detect thrombin at 0.98 fM, which is lower than the detection limit of most other methods.

Synthesis and kinetic analysis of poly(N-acryloylmorpholine) brushes via surface initiated RAFT polymerization.

Polymer brushes are promising many applications as smart materials and biocompatible surfaces. Surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the most effective techniques for synthesis of well-defined polymer brushes. Herein, a biocompatible, uniform and stable poly(N-acryloylmorpholine)-silicon hybrid system was achieved using surface-initiated RAFT polymerization. Evidence of a well-controlled surface-initiated RAFT polymerization was confirmed by a linear increase of number average molecular weight (Mn) with overall monomer conversions. Water contact angle, ellipsometry, X-ray photoelectron spectroscopy and atomic force microscopy verified the presence of poly(N-acryloylmorpholine) (poly(NAM)) on silicon wafers. The grafting density (σ) and the average distance between grafting points (D) were estimated to be 0.58 chains/nm2 and 1.5 nm, respectively. The ratio of D value to radius of gyration (Rg) value is smaller than 1 (D/2Rg < 1), which corresponds to the brush regime of all grafted poly(NAM) films.

Poly(N-vinyl triazole-b-N-vinyl imidazole) Grafted on MWCNTs as Nanofillers to Improve Proton Conducting Membranes

Carbon nanotubes (CNTs) are of particular interest because of their ability to enhance the mechanical strength in the material; however, processing difficulties of CNTs often restrict utilization up to its full potential. To resolve this, in the current study, we have developed a simple and efficient method to functionalize the surface of a multiwalled carbon nanotube (MWCNT) with precise functional polymer chains, which were covalently grafted on the surface of the MWCNT, and delved into an application to demonstrate this material as an efficient nanofiller in developing a proton conducting membrane (PEM) from polybenzimidazole (PBI). At first, the MWCNT surface was converted to a polymerizable surface by attaching a trithiocarbonate based chain transfer agent (CTA). Then, a N-heterocyclic block copolymer, namely poly-N-vinyl-1,2,4-triazole-b-poly-N-vinyl imidazole (pNVT-b-pNVI), was grown from the CTA anchored surface with a one-pot surface initiated reversible addition–fragmentation chain transfer (SI-RAFT) technique. Grafting of block copolymer chain was confirmed by GPC, NMR, TGA, TEM, FESEM, and EDX studies. To the best of our knowledge, this will be the first report of a growing block copolymer structure grafted covalently on the surface of the MWCNT. The novelty of the work was further enhanced by incorporating pNVT-b-pNVI-g-MWCNT as a nanofiller into the oxypolybenzimidazole (OPBI) membrane to obtain homogeneous nanocomposite membranes with excellent thermomechanical and tensile properties, thermal stability, superior proton conduction when doped with phosphoric acid (PA), and PA holding capacity. The nanocomposite membrane with 2.5 wt % nanofiller loading displayed a tensile stress of 1.8 MPa and a strain of 176% at break. The basic N-heterocyclic rings dangling from the block copolymer chains grafted on the MWCNT surface allowed formation of strong H-bonding, acid–base interaction with PA, which is responsible for high acid uptake and superior PA retention, and also exhibited proton conductivity as high as 0.164 S cm–1 at 180 °C, which is a 2.6-fold increment when compared with a pristine OPBI membrane. This significant increase in conductivity is attributed to the proton conducting nanochannel pathway generated along the polymer-g-MWCNT surface.

Quaternized salicylaldehyde Schiff base side-chain polymer-grafted magnetic Fe3O4 nanoparticles for the removal and detection of Cu2+ ions in water

In this study, quaternized salicylaldehyde Schiff base side-chain polymer grafted magnetic Fe3O4 nanoparticles (Fe3O4@SiO2-PAP) were formed via the surface-initiated reversible addition-fragmentation chain-transfer polymerization of 2-(dimethylamino)ethyl methacrylate, subsequent quaternization with 5-chloromethylsalicylaldehyde and Schiff condensation with 2-aminophenol. The prepared nanohybrid was characterized by scanning and transmission electron microscopes, Fourier transform infrared spectroscopy, X-ray diffractometer, vibrating sample magnetometer and X-ray photoelectron spectroscopy. Fe3O4@SiO2-PAP was found to disperse well in water due to the strong hydrophilicity of the immobilized polymer. Cu2+ ion adsorption by the nanohybrid followed both pseudo-second-order kinetic and Langmuir isotherm models, and a maximum adsorption capacity of 59.98 mg/g was attained, with good repeatability. In addition, the nanohybrid exhibited significant and sensitive fluorescence quenching characteristics after capturing Cu2+ ions in water with good selectivity among the other studied cations. The fluorescence detection linear range was 0.1–2 mg/L, with the lowest detection limit measured as 0.125 μmol/L. Moreover, the nanohybrid exhibited high reusability for Cu2+ ion adsorption and sensing applications. Finally, the interaction of grafted Schiff base ligand with Cu2+ ions was analyzed using theoretical calculations. Consequently, the developed nanohybrid offers a new pathway for the removal and detection of Cu2+ ions in water.

Preparation of poly(acrylamide‐co‐acrylonitrile) grafted glass and thermal stimulated detachment of surface‐attached human immortalized mesenchymal stem cells

AbstractNovel cell culture substrates for non‐invasive‐targeted cell recovery were developed by grafting an upper‐critical‐solution‐temperature (UCST)‐type poly(acrylamide‐co‐acrylonitrile) (PAA) onto a glass substrate as a cell attachment scaffold by surface‐initiated reversible addition‐fragmentation chain‐transfer (Si‐RAFT) polymerization. To optimize the UCST of PAA, the cloud point of the free polymer was first determined. Varying the chain lengths of PAA with an optimized AN‐compositions of 31 mol% followed by Si‐RAFT produced immobilized glass substrate (PAA‐g). The PAA‐g surface became hydrophilic, and the polymer brushes swelled as the temperature increased from 30 to 38°C. In addition, the viscoelasticity of PAA‐g was increased by the polymer brushes swelled. Thermal detachment of PAA‐g attached human immortalized mesenchymal stem cells (hiMSC) was observed by raising the temperature from 30 to 38°C. The polymer brushes length of PAA‐g affects the degree of hiMSC detachment, likely due to the change in viscoelasticity with the polymer brushes length.

Light-regulated growth of polymer chains from the surface of RAFT agent primed mesoporous silica nanoparticles

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the extensively explored and studied controlled radical polymerization methods. Recently, in comparison to the conventional RAFT polymerization process, visible light-regulated photo-induced electron/energy transfer (PET)-RAFT polymerization has picked up interest. With an ever-increasing desire for greener and more sustainable methods for synthesis, techniques such as PET-RAFT polymerization can be well adapted as an alternative approach for performing a variety of syntheses. Keeping this in mind we step forward with the synthesis of mesoporous silica nanoparticles containing an in-built RAFT agent using a stepwise co-condensation method. Herein, we report a facile synthesis of an organic-inorganic hybrid system in which surface-initiated RAFT polymerization was performed using several monomers (hydrophobic and hydrophilic) from RAFT agent primed mesoporous silica nanoparticles (RAFT-MSNs). The surface-initiated RAFT polymerization was carried through thermally initiated polymerization using AIBN and visible light-regulated PET-RAFT polymerization using Eosin Y as a photocatalyst. The light-regulated PET-RAFT polymerization was carried out smoothly in a shorter time frame as compared to the thermally initiated RAFT polymerization. A variety of characterization methods were used to confirm the successful grafting of polymeric chains from the surface of RAFT-MSNs. Hence, by appropriate polymer functionalization of mesoporous silica nanoparticles with stimuli-responsive polymers or polymers bearing functional groups, these organic-inorganic hybrids can be studied in a wide variety of applications such as drug delivery, catalysis, nanoconfinement, etc.

Sensitive electrochemiluminescence analysis of lung cancer marker miRNA-21 based on RAFT signal amplification.

An electrochemiluminescence approach based on surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) was developed for miRNA-21 detection for the first time. The SI-RAFT polymerization generates polymer chains with functional groups that are used to recruit luminol, enabling strong ECL signal output with low concentrations of miRNA-21, and greatly improving the detection sensitivity.

Chemiresistor sensor based on ion-imprinted polymer (IIP)-functionalized rGO for Cd(II) ions in water

This study reports the design and development of a novel chemiresistor (CR) sensor using ion imprinted polymer (IIP)-functionalized reduced graphene oxide (rGO) [IIP/rGO-CR] for cadmium ions (Cd(II)) determination in water. The sensor consisted of a CR transducer made of rGO channel bridging source and drain electrodes prepared by self-assembly and thermal reduction of graphene oxide (GO) on Au interdigitated electrodes chip fabricated on Si/SiO2 substrate. The IIP was then grafted on rGO using surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization with polyethylenimine (PEI) and methylacrylic acid (MAA) as dual functional monomers and Cd(II) ions as template through UV light-initiated copolymerization. The IIP functionalized on rGO acted as an effective recognition element that modulated the resistance of rGO-CR upon binding of Cd(II), enabling Cd(II) detection at ppb level in aqueous solutions. The prepared IIP/rGO-CR sensor worked effectively in the linear range of 2～200 ppb and achieved a limit of detection (LOD) of 0.83 ppb, which is lower than the World Health Organization guidelines of 3 ppb for drinking water quality. The developed sensor of IIP/rGO-CR showed a high selectivity against a variety of trace and heavy metal ions found in water and good stability for up to 60 days when stored at room temperature for Cd(II) determination in water. Further, the sensor was successfully applied to analyzing Cd(II) spiked in tap, lake and river waters with a 94.5%–113.5% recovery, demonstrating a high degree of accuracy even in complex water samples. Our results illustrated that the CR sensor of IIP functionalized rGO provides a potential platform for sensitive, robust and low-cost environmental analysis of Cd(II) in water.

Terminal cationization of poly(N-isopropylacrylamide) brush surfaces facilitates efficient thermoresponsive control of cell adhesion and detachment

ABSTRACT A variety of poly(N-isopropylacrylamide) (PIPAAm)-grafted surfaces have been reported for temperature-controlled cell adhesion/detachment. However, the surfaces reported to date need further improvement to achieve good outcomes for both cell adhesion and detachment, which are inherently contradictory behaviors. This study investigated the effects of terminal cationization and length of grafted PIPAAm chains on temperature-dependent cell behavior. PIPAAm brushes with three chain lengths were constructed on glass coverslips via surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization. Terminal substitution of the grafted PIPAAm chains with either monocationic trimethylammonium or nonionic isopropyl moieties was performed through the reduction of terminal RAFT-related groups and subsequent thiol-ene reaction with the corresponding acrylamide derivatives. Although the thermoresponsive properties of the PIPAAm brush surfaces were scarcely affected by the terminal functional moiety, the zeta potentials of the cationized PIPAAm surfaces were higher than those of the nonionized ones, both below and above the phase transition temperature of PIPAAm (30°C). When bovine endothelial cells were cultured on each surface at 37°C, the number of adherent cells decreased with longer PIPAAm. Notably, cell adhesion on the cationized PIPAAm surfaces was higher than that on the nonionized surfaces. This terminal effect on cell adhesion gradually weakened with increasing PIPAAm length. In particular, long-chain PIPAAm brushes virtually showed cell repellency even at 37°C, regardless of the termini. Interestingly, moderately long-chain PIPAAm brushes promoted cell detachment at 20°C, with negligible terminal electrostatic interruption. Consequently, both cell adhesion and detachment were successfully improved by choosing an appropriate PIPAAm length with terminal cationization.

Cross-Linked Polymer Brushes Containing N-Halamine Groups for Antibacterial Surface Applications.

Microbial contamination is a significant issue in various areas, especially in the food industry. In this study, to overcome microbial contamination, cross-linked polymer brushes containing N-halamine were synthesized, characterized, and investigated for antibacterial properties. The cross-linked polymer brushes with different N-halamine ratios were synthesized by in-situ cross-linking methods with reversible addition−fragmentation chain transfer (RAFT) polymerization using a bifunctional cross-linker. The RAFT agent was immobilized on an amine-terminated silicon wafer surface and utilized in the surface-initiated RAFT polymerization of [N-(2-methyl-1-(4-methyl-2,5-dioxoimidazolidin-4-yl)propane-2-yl)acrylamide] (hydantoin acrylamide, HA), and N-(2-hydroxypropyl)methacrylamide) (HPMA) monomers. Measurement of film thickness, contact angle, and surface morphology of the resulting surfaces were used to confirm the structural characteristics of cross-linked polymer brushes. The chlorine content of the three different surfaces was determined to be approximately 8–31 × 1013 atoms/cm2. At the same time, it was also observed that the activation–deactivation efficiency decreased during the recharge–discharge cycles. However, it was determined that the prepared N-halamine-containing cross-linked polymer brushes inactivated approximately 96% of Escherichia coli and 91% of Staphylococcus aureus. In conclusion, in the framework of this study, high-performance brush gels were produced that can be used on antibacterial surfaces.

Tailoring the polarity of polymer shell on BaTiO3 nanoparticle surface for improved energy storage performance of dielectric polymer nanocomposites

Nanocomposites comprising flexible polymers and high dielectric constant inorganic nanoparticles are considered to be one of the promising candidates for electrostatic capacitor dielectrics. However, the effect of interfacial property on electrical energy storage of dielectric polymer nanocomposites is still not clear. Herein, the role of the polarity of the interfacial region is investigated. For this purpose, three polymers with different polarity, polymethyl methacrylate (PMMA), polyglycidyl methacrylate, and polymethylsulfonyl ethyl methacrylate (PMSEMA) are attached onto BaTiO3 (BT) nanoparticle surface via surface-initiated reversible addition-fragmentation chain transfer polymerization. It is found that the polarity of shell polymers shows an apparent effect on the dielectric and energy storage of dielectric polymer nanocomposites. For example, PMSEMA@BT (shell polymer possesses the highest polarity) increases dielectric loss and decreases the breakdown strength of the nanocomposites, leading to lower energy storage capability. However, PMMA@BT (shell polymer possesses the lowest polarity) can induce higher breakdown strength of the nanocomposites. As a result, the PMMA@BT nanocomposite exhibits the highest electrical energy storage capability among the three nanocomposites. This research provides new insight into the design of core-shell nanofillers for dielectric energy storage applications.

Effect of alkyl chain length and fluorine content on the surface characteristics and antibacterial activity of surfaces grafted with brushes containing quaternized ammonium and fluoro-containing monomers

Although considerable efforts have been made to vary the alkyl chain length in the quaternary ammonium compounds (QACs) for optimizing the antibacterial activity, only few researchers have systematically investigated the combinatory effects of alkyl chain length and another acryl monomers with the different chemical configuration on the antibacterial activity of the modified substrate. In this study, by surface grafting of various copolymeric brushes, different modified cotton substrates were prepared by surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization reaction for exploring the effects of alkyl chain length of QACs and the fluorine content on antibacterial and anti-microbial adhesion characteristics. The quaternized monomers used were prepared by quaternization of 2-(dimethylamino) ethyl methacrylate (DMAEMA) with 1-bromooctane (DMAEMA + 8), and 1-bromopropane (DMAEMA + 3). The fluoro-containing monomer was 2,2,2-Trifluoroethyl methacrylate (TFEMA). Ethyl methacrylate (EMA) was also used for comparison. Results have shown that the optimal antibacterial and anti-microbial adhesion characteristics were noted on the substrates grafted with DMAEMA + 8 and TFEMA. This can be attributed to the enhanced degree of surface quaternization due to the hydrophobic interactions between the grafted TFEMA and DMAEMA + 8 chains, leading to an increase in antibacterial efficacy of modified cotton substrates.

Nanocomposites of polyhydroxyurethane with nanocrystalline cellulose: Synthesis, thermomechanical and reprocessing properties

A commercial novolac epoxide was used to react with carbon dioxide (CO2), to obtain a novel five-membered cyclic carbonate. This novel novolac epoxide-based five-membered cyclic carbonate (NE5CC) was successfully utilized to prepare polyhydroxyurethane (PHU) thermoset. To improve the thermomechanical properties of the PHU thermoset, nanocrystalline cellulose (NCC) was used as the modifier. To facilitate dispersion of the modifier, the surface of NCC was functionalized with poly(N-vinylpyrrolidone) (PVPy). The functionalized NCC (NCC-PVPy) was prepared via the surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP). It was found that NCC-PVPy was readily dispersed in PHU matrix in the form of single nanocrystals. The nanocomposites of PHU with NCC displayed the enhanced glass transition temperatures and improved mechanical properties. In the meantime, the nanocomposites had good shape recovery properties; the nanocomposites can be reprocessed at elevated temperature. The reprocessing properties can be utilized to reprogram the original shapes of the shape memory nanocomposites.