Simultaneous Bulk-and Surface-initiated Living Polymerization Studied with a Heterogeneous Stochastic Reaction Model

To better characterize the properties of surface-initiated polymers, simultaneous bulk-and surface-initiated polymerizations are usually carried out by assuming that the properties of the surface-initiated polymers resemble those of the bulk-initiated polymers. Through a Monte Carlo simulation using a heterogeneous stochastic reaction model, it was discovered that the bulk-initiated polymers exhibit a higher molecular weight and a lower dispersity than the corresponding surface-initiated polymers, which indicates that the equivalent assumption is invalid. Furthermore, the molecular weight distributions of the two types of polymers are also different, suggesting different polymerization mechanisms. The results can be simply explained by the heterogeneous distributions of reactants in the system. This study is helpful to better understand surface-initiated polymerization.

Oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient friction and wear reduction

Nanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure,suitable mechanical property,and tunable surface functionalities.However,the poor compatibility between nanomaterials and base oil limits their further applications.In this work,we demonstrated oil-soluble poly(lauryl methacrylate)(PLMA)brushes-grafted metal-organic frameworks nanoparticles(nanoMOFs)as lubricating oil additives that can achieve efficient friction reduction and anti-wear performance.Macroinitiators were synthesized by free-radical polymerization,which was coordinatively grafted onto the surface of the UiO-67 nanoparticles.Then,PLMA brushes were grown on the macroinitiator-modified UiO-67 by surface-initiated atom transfer radical polymerization,which greatly improved the lipophilic property of the UiO-67 nanoparticles and significantly enhanced the colloidal stability and long-term dispersity in both non-polar solvent and base oil.By adding UiO-67@PLMA nanoparticles into the 500 SN base oil,coefficient of friction and wear volume reductions of 45.3%and 75.5%were achieved due to their excellent mechanical properties and oil dispersibility.Moreover,the load-carrying capacity of 500 SN was greatly increased from 100 to 500 N by the UiO-67@PLMA additives,and their excellent tribological performance was demonstrated even at a high friction frequency of 65 Hz and high temperature of 120℃.Our work highlights oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient lubricating additives.

Friction between Strongly Compressed Polymer Brushes

We present the results of molecular dynamics simulations of steady shear between a pair of neutral polymer brushes,as well as a pair of charged polymer brushes in the strongly compressed regime.The results of the molecular dynamic simulations of neutral and polyelectrolyte brushes in implicit solvent including normal forces,shear forces,viscosities and friction coefficients as a function of separation between brushes,are presented in the study.The comparison of the simulation results of neutral and charged brushes shows that the charged brushes is in the quasi-neutral regime,and the dependence of viscosity on the separation distance show the similar power law of neutral brushes.Our simulation results confirm that the implicit solvent simulations of polyelectrolyte brushes that ignore hydrodynamics interaction are in agreement with the scaling predictions qualitatively because of screening of hydrodynamic interaction and long-range electrostatic interactions on the correlation length scale.Both of neutral and charged brushes show the lubrication properties that the friction coefficient decreases with the separation decreases at enough large loads.However,a maximum of friction coefficients is observed for polyelectrolyte brushes,which is in contrast to the neutral brushes with monotonical dependence.

Impact of Molecular Shape on Supramolecular Copolymer Synthesis in Seeded Living Polymerization of Perylene Bisimides

Supramolecular polymerization properties have been studied for a series of perylene bisimide(PBI)dyes containing identical hydrogen-bonding amide groups in imide positions but variable number or size of alkoxy substituents in bay-positions.

Heavy Metal Ions Removal by Nano-sized Spherical Polymer Brushes

Nano-sized spherical polymer brushes （SPBs） consisting of both a polystyrene （PS） core and a brush shell of poly（acrylic acid） （PAA）, poly（N-acrylcysteamine） （PSH）, or poly（N-acrylcysteamine-co-acrylic acid） （P（SH-co-AA））, were prepared by photo-emulsion polymerization. The core-shell structure was observed by dynamic light scattering and transmission electron microscopy. Due to the strengthened Donnan effect, the PAA brush can adsorb heavy metal ions. Effects of the contact time, thickness of PAA brush and pH value on the adsorption results were investigated. Due to the coordination between the mercapto groups and heavy metal ions as well as the electrostatic interactions, SPBs with mercapto groups are capable to remove heavy metal ions selectively from aqueous solutions. The order of adsorption capacity of the heavy metal ions by SPBs with mercapto groups is： Hg2＋ ≈ Au3＋ 〉 Pb2＋ 〉 CH2＋ 〉 Ni2＋. The adsorbed heavy metal ions can be eluted from SPB by aqueous HCI solution, and the SPBs can be recovered. After three regenerations the recovered SPBs still maintain their adsorption capacity.

Cylindrical polymer brushes-anisotropic unimolecular micelle drug delivery system for enhancing the effectiveness of chemotherapy

Polymer systems can be designed into different structures and morphologies according to their physical and chemical performance requirements,and are considered as one of the most promising controlled delivery systems that can effectively improve the cancer therapeutic index.However,the majority of the polymer delivery systems are designed to be simple spherical nanostructures.To explore morphology/size-oriented delivery performance optimization,here,we synthesized three novel cylindrical polymer brushes(CPBs)by atom transfer radical polymerization(ATRP),which were cellulose-g-(CPT-b-OEGMA)(CCO)with different lengths(~86,~40,and~21 nm).The CPBs are composed of bio-degradable cellulose as the carrier,poly(ethylene glycol)methyl ether methacrylate(OEGMA)as hydrophily block,and glutathione(GSH)-responsive hydrophobic camptothecin(CPT)monomer as loaded anticancer drug.By controlling the chain length of the initiator,three kinds of polymeric prodrugs with different lengths(CCO-1,CCO-2,and CCO-3)could be self-organized into unimolecular micelles in water.We carried out comparative studies of three polymers,whose results verified that the shorter CPBs exhibited higher drug release efficiency,more cellular uptake,and enhanced tumor permeability,accompanied by shortened blood circulation time and lower tumor accumulation.As evidenced by in vivo experiments,the shorter CPBs exhibited higher anti-tumor efficiency,revealing that the size advantage has a higher priority than the anisotropic structure advantage.This provided vital information as to design an anisotropic polymer-based drug delivery system for cancer therapy.

Biocompatible hierarchical zwitterionic polymer brushes with bacterial phosphatase activated antibacterial activity

Hierarchical polymer brushes have been considered as an effective and promising method for preventing implant-associated infections via multiple antibacterial mechanisms.Herein,a bacterial phosphatase re-sponsive surface with hierarchical zwitterionic structures was developed for timely dealing with the poly-meric implant-associated bacterial infection.The hierarchical polymeric architecture was subtly realized on model polypropylene(PP)substrate by sequential photo living grafting of poly(2-(dimethylamino)ethyl methacrylate(PDMAEMA)bottom layer and zwitterionic poly(sulfobetaine methacrylate)(PSBMA)upper layer,followed by the conversion of the PDMAEMA into the zwitterionic structure via succes-sive quaternization and phosphorylation reactions.Owing to shielding the bottom polycations,the hi-erarchical zwitterionic polymer brushes guaranteed the surface with the optimal biocompatibility under the normal physiological environment.Once bacteria are invaded,the surface bactericidal activity of the bottom layer can be rapidly and automatically activated owing to the transition triggered by bacterial phosphatase from zwitterion to polycation.Additionally,ameliorated by the upper layer,the hierarchical surface showed obvious adhesion resistance to dead bacterial cells and notably migrated the cytotoxic-ity of exposed polycation after completion of the bactericidal task.As a proof-of-principle demonstration,this self-adaptive hierarchical surface with sensitive bacterial responsiveness and biocompatibility showed great potential in combating hernia mesh-related infection.This work provides a promising and universal strategy for the on-demand prevention of medical device-associated infections.

On the friction and adhesion hysteresis between polymer brushes attached to curved surfaces: Rate and solvation effects

Computer simulations of friction between polymer brushes are usually simplified compared to real systems in terms of solvents and geometry.In most simulations,the solvent is only implicit with infinite compressibility and zero inertia.In addition,the model geometries are parallel walls rather than curved or rough as in reality.In this work,we study the effects of these approximations and more generally the relevance of solvation on dissipation in polymer-brush systems by comparing simulations based on different solvation schemes.We find that the rate dependence of the energy loss during the collision of brush-bearing asperities can be different for explicit and implicit solvent.Moreover,the non-Newtonian rate dependences differ noticeably between normal and transverse motion,i.e.,between head-on and off-center asperity collisions.Lastly,when the two opposing brushes are made immiscible,the friction is dramatically reduced compared to an undersaturated miscible polymer-brush system,irrespective of the sliding direction.

Enhancing the ionic conductivity in a composite polymer electrolyte with ceramic nanoparticles anchored to charged polymer brushes

Polymer electrolytes a re essential for next-gene ration lithium batteries because of their excellent safety record.However,low ionic conductivity is the main obstacle restricting their commercial application.Composites with nanoparticles are a promising route to overcome this obstacle.In this work,lithium polystyrene sulfonate brushes(LiPSS)is anchored to silicon dioxide nanoparticles with chemical bonding using atom transfer radial polymerization(SI-ATRP).The composite polymer electrolytes are made by mixing vinylene carbonate and nanoparticles via a facile in situ polymerization process.The ionic conductivity of composite polymer electrolytes is improved to 7.2×10^-4 S/cm at room temperature,which is attributed to the low degree of crystallinity of polymer electrolyte and the fast ion transport on the surfaces of polymer brush layers that act as a conductive network.The composite polymer electrolytes show a wide electrochemical window of approximately 4.5 V vs.Li^+/Li and excellent cycling performance retention of approximately 95%after 100 cycles at ambient temperature.The results also prove that surface groups of ceramic na noparticles are an important way to increase the electrochemical properties of composite polymer electrolytes.

"LIVING" FREE RADICAL SYNTHESIS OF NOVEL RODCOIL DIBLOCK COPOLYMERS WITH POLYSTYRENE AND MESOGEN-JACKETED LIQUID CRYSTAL POLYMER SEGMENTS

The synthesis of rod-coil diblock copolymers was achieved for the first time by TEMPO-mediated 'living' free radical polymerization of styrene and 2,5-bis [(4-methoxyphenyl)oxycarbonyl] styrene(MPCS). The block architecture of the two diblock copolymers thus prepared, MPCS-b-St(5400/2400) and MPCS-b-St(10800/8700), was confirmed by GPC, DSC studies and the formation of multimolecular micelles. (Author abstract) 10 Refs.

Structures and Surface States of Polymer Brushes in Good Solvents:Effects of Surface Interactions

The influence of the surface interaction on the mesoscopic structure of grafted polymers in good solvents has been examined. At high surface coverage, tethered polymers are in the brush state and the parabolic segment density profile is confirmed by self-consistent field theory （SCFT） calculations. It is found that this is a universal behavior for a whole range of surface interactions from complete repulsion to strong attraction. More interestingly, finite surface repulsion may lead to the maximum in the proximal layer of its segment density profile, which is significantly different from both the depletion layer of pure repulsion and the adsorbing layer of attraction. In addition to the brush state on both repulsive and attractive surfaces, three additional surface states were identified by analyzing the scaling behavior of the layer thickness of polymer brushes： the mushroom state on repulsive substrates, the dilute and the semidilute surface states on attractive substrates.

Collapse of Four-Arm Stars Polyelectrolyte Brushes Under An Electric Field in the Presence of Trivalent Salt Coions

Langevin dynamics simulations were conducted to study the collapse of grafted partially charged 4-arm star chains onto the oppositely charged grafting electrode in the presence of trivalent salt coions.Simulation results reveal that the average charge fraction of the grafted star chains and the salt concentration play critical roles in the competitive adsorption of charged monomers and trivalent salt coions onto the oppositely charged electrode.For grafted star chains with relatively high charge fraction,charged monomers are the dominant species collapsing on the oppositely charged electrode with the emergence of charge reversal on the grafting electrode.At a low charge fraction such that the total amount of charges on a grafted star molecule is comparable to that of a trivalent salt coion,trivalent salt coions absorb more strongly onto the electrode than grafted stars even at very low salt concentration.It is found that at relatively low charge fraction of star chains,the addition of trivalent salt coions does not lead to charge overcompensation of the surface charges on the grafting electrode.The stretching of star brushes under an electric field in the presence of trivalent salt coions was also briefly investigated.

Synthesis of PMMA-co-PMAA Copolymer Brush on Multi-Wall Carbon Nanotubes

Poly(methyl methacrylate)/poly(methacrylamide) copolymer (PMMA-co-PMAA) was synthesized by a free radical copolymerization of MMA and MAA monomers in methylethyl ketone using AIBN as radical initiator. Multi-wall carbon nanotubes (MWCNT) were oxidized in KMnO4 acidic suspension. Carboxyl groups on the surface oxidized MWCNT were reacted with primary amide group of PMMA-co-PMAA copolymer in MEK solution under ultrasound to form polymer brush on the surface of MWCNT. With the help of TG analyses the amount of covalently grafted PMMA-co-PMAA copolymer onto MWCNT surface was determined as ?47 wt%. TEM analyses identified thin co-polymer layer adhered onto MWCNT surface with average thickness ?5 nm.

NITROXIDE-MEDIATED FREE RADICAL SYNTHESIS OF MESOGEN-JACKETED LIQUID CRYSTAL POLYMERS

The first TEMPO-mediated 'living' free radical polymerization of liquid crystalline monomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene (MPCS), was carried out at 130 degrees C with BPO as an initiator. The molecular weight of the polymer can be varied from rather low values to high values while maintaining narrow polydispersity. It was observed that the polymerization of MPCS proceeded much faster than that of styrene. A tentative explanation for this fast polymerization was suggested.

Tuning Polymer-Grafted Particle Monolayer Structure at the Air-Water Interface by Introducing Anisotropic Features

Fabrication of anisotropic material is one of the important topics and we examined to introduce “anisotropic” nature by spreading polymer-grafted particle on the medium with polymer-reactive potential. Poly (tert-butyl methacrylate) (PtBMA) was polymerized from polystyrene latex (PSL) surface by ATRP to give PtBMA-grafted PSL (PSL-PtBMA). Particle monolayer was formed at air-water and air-acidic water interfaces and the monolayer characteristics were compared by π-A isotherm measurements, SEM observations, and contact angle measurements. π-A isotherms, in particular, indicates that the interaction between polymer chains become stronger by changing the subphase condition, which suggests that anisotropicparticle monolayer formation.

Research progress in the living/controlled polymerization of(meth)acrylate monomers by Lewis pair

Lewis pair polymerization(LPP)has demonstrated its unique advantages,such as high activity,high stability,and adjustable variability,towards the polymerization of(meth)acrylate monomers in comparison with the other polymerization techniques.The combination of Lewis acid(LA)and Lewis base(LB)to construct Lewis pairs(LPs)with appropriate Lewis basicity,Lewis acidity,and steric effects would significantly impact the polymerization process,including chain initiation,propagation,termination and chain transfer reaction,as well as polymerization manner of monomers.In this feature article,we briefly review recent progress made by our research group towards the living/controlled polymerization of(meth)acrylate monomers,which were accomplished by a series of newly designed LPs,including monofunctional LPs,dual-initiating LPs and intramolecular tethered trifunctional LP.This article is divided into three parts:(1)the development of monofunctional living/controlled LP polymerization system;(2)the design and preparation of dual-initiating LPs in synthesizing thermoplastic elastomers;(3)the application of intramolecular trifunctional LP to the synthesis of cyclic polymers.These developed LPPs have demonstrated their powerful capability in precise control over the molecular weight,molecular weight distribution,and monomer sequence as well as the topology of polymers.This review will serve as a good resource or guideline for researchers currently working in the area of LPP and for those who are interested in synthesizing new materials by LPP.

单电子转移活性自由基聚合法制备表面活性聚合物及性能

以丙烯酰胺(AM)和α-烯基磺酸钠(AOS)为功能单体,2-氯丙酰胺(CPA)为引发剂,采用单电子转移自由基聚合方法,制备无规二元共聚物PAM-co-PAOS。结果表明,最佳工艺条件为c(单体)=2.5 mol/L,n(单体)∶n(CPA)∶n(CuBr)∶n(Me_(6)TREN)=769∶1.2∶1∶3.8;m(AOS)∶m(AM+AOS)=3.5%。对表面活性聚合物PAM-co-PAOS进行性能研究,在大庆模拟盐水中具有较好的增黏性及表面活性。

超支化聚合物在生物医学材料中应用研究进展

超支化聚合物(HBPs)具有高活性功能端基,便于修饰改性,能够设计合成结构明确且具有特定功能的高分子材料,在生物医学领域具有潜在应用价值。可控/活性自由基聚合(CLRP)技术在聚合物合成领域受到广泛关注,并将其运用到医疗产品、纳米材料、航天器件等众多领域中。近年来,在合成具有生物可降解和生物相容性的HBPs的发展方面已取得了诸多进展,对HBPs在生物医学领域的最新研究进展进行了总结,重点介绍了HBPs在药物传递、基因转染、组织工程、抗菌/防污材料、生物医学成像等方面的应用,并对HBPs的发展前景进行了展望。

Synthesis of Glutathione Imprinted Polymer Particles via Controlled Living Radical Precipitation Polymerization

A general protocol was described for fabricating uniform molecularly imprinted polymer （MIP） particles via controlled living radical precipitation polymerization at ambient temperature. By adopting glutathione as model template, benzyl dithiocarbamate as iniferter agent, 4-vinylpyridine as monomer, and ethylene glycol dimethacrylate as cross-linker, it is demonstrated that the polymerization parameters including the iniferter concentration, monomer loading and molar ratio of cross-linker to functional monomer have profound effect on the final particle size and recognition property of the MIP particles. The batch static binding experiments were carried out to estimate the adsorption kinetics, adsorption isotherms and selective recognition of the MIP particles. The adsorption behavior followed the pseudo-second order kinetic model, revealing that the process was chemically carried out. Two adsorption isotherm models were applied to analyze equilibrium data, obtaining the best description by Langmuir isotherm model. In addition, the MIP particles also could selectively recognize glutathione over similar analogs, indicating the possibility for the separation and enrichment of the template from complicated matrices.

Amphiphilic Dendrimer-like Copolymers with High Chain Density by Living Anionic Polymerization

We report here a method for the preparation of amphiphilic dendrimer-like copolymers with dendritic polystyrene (PS) core and protonated poly(2-vinyl pyridine)(P2VP) or poly(methacrylic acid)(PMAA) shell. The method employed the efficient coupling reaction of anionic living polymer chains and chlorosilane. The synthesis started from a functionalized 3rd generation dendritic polystyrene, G3PS-g-SiCl, used as the precursor. The dendrimer-like copolymer of styrene and 2-vinyl pyridine, G3PS-g-P2VP, was synthesized by direct coupling of living P2VPLi to the precursor. The dendrimer-like copolymer of styrene and Zer/-butyl methacrylate, G3PS-g-PtBMA, was synthesized by an indirect procedure in which a living polymer containing mainly PtBMA segment was attached to the precursor. Both methods resulted in the formation of dendrimer-like copolymers with the high molecular weights (up to 8.5 × 10^6 Da), large molecular sizes (diameter up to 73 nm), and dense shells (number of arms up to 1300). These products, G3PS-g-P2VP and G3PS-g- PtBMA, were protonated with trifluoroacetic acid and acidic hydrolyzed, respectively. After transformation, amphiphilic dendrimer-like copolymers, G3PS-g-P2VPH^+ and G3PS-g-PMAA, were obtained. Preliminary results on the solution properties of the amphiphilic products were presented.