Synthesis of membrane adsorbers via surface initiated ATRP of 2-dimethylaminoethyl methacrylate from microporous PVDF membranes

Surface-initiated atom transfer radical polymerization(SI-ATRP) was used to tether poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) onto microporous PVDF membranes in order to synthesize membrane adsorbers for protein adsorption. The alkaline treatment and bromine addition reaction were used to anchor ATRP initiators on membrane surface. Then PDMAEMA was grafted from the membrane surface via SI-ATRP. Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM) revealed the chemical composition and surface topography of the PVDF-g-PDMAEMA membrane surfaces. These results showed that PDMAEMA was grafted from the membrane surface successfully and a grafting yield as high as 1500 μg/cm2 was achieved. The effects of the grafting time and the density of initiators on the static and dynamic binding capacity of bovine serum albumin(BSA) were systematically investigated. Both the static and dynamic binding capacities increase with the bromination and polymerization time. However, the benefits of the initiator density on binding capacities are limited by the graft density of PDMAEMA chains.     

聚合温度对负载型Ziegler-Natta催化剂催化丁二烯-异戊二烯共聚合的影响

非均相TiCl₄/MgCl₂-AlR₃型Ziegler-Natta(非均相Z-N)催化剂是聚烯烃工业最重要的催化剂,经烷基铝活化的非均相Z-N催化剂具有复杂的活性中心结构,改变聚合温度、聚合时间、烷基铝种类及浓度等均会影响活性中心结构与催化性能.本文研究了不同聚合温度下TiCl₄/MgCl₂-AlEt₃(三乙基铝)催化丁二烯(Bd)和异戊二烯(Ip)的共聚合动力学,研究发现,随着聚合时间的延长,聚合活性先升高然后降低,在50℃聚合活性最高.采用核磁共振波谱(¹H NMR)、紫外荧光定硫仪和凝胶渗透色谱(GPC)研究了共聚物的微观结构、活性中心数和分子量及其分布,发现随着聚合时间的延长及聚合温度的升高,活性中心数、共聚物中反式-1,4-结构、分子量及分子量分布均发生不同规律的变化.本文研究结果可为进一步理解非均相Z-N催化剂在不同聚合温度下催化共轭二烯烃聚合的动力学及其关键影响因素提供参考.     

External Electron Donor Technology in the Preparation of Polypropylene

从外给电子体在聚丙烯制备中的作用出发,从外给电子体种类、外给电子体对活性中心的影响和外给电子体的作用机理等方面,综述了丙烯聚合催化体系中外给电子体技术的研究进展,重点介绍了外给电子体的位阻效应和电子效应对丙烯聚合催化体系的影响,指出了性能优异的外给电子体应具备的结构特征,即带有大位阻烃类取代基和小位阻烷氧基取代基的硅烷类化合物,介绍了复合外给电子体技术和丙烯共聚中外给电子体的作用,并对聚丙烯制备中外给电子体技术的发展趋势进行了展望。     

Novel synthesis of rod‐coil block copolymers by combination of coordination polymerization and ATRP

Combination of coordination polymerization and atom transfer radical polymerization (ATRP) was applied to a novel synthesis of rod‐coil block copolymers. The procedure included the following steps: (1) monoesterification reaction of ethylene glycol with 2‐bromoisobutyryl bromide yielded a α‐bromo, ω‐hydroxy bifunctional initiator, (2) CpTiCl₃ (bifunctional initiator) catalyst was prepared from a mixture of trichlorocyclopentadienyl titanium (CpTiCl₃) and bifunctional initiator. Coordination polymerization of n‐butyl isocyanate initiated by such catalyst provided a well‐defined macroinitiator, poly(n‐butyl isocyanate)‐Br (PBIC‐Br), and (3) ATRP method of vinyl monomers using PBIC‐Br provided rod (PBIC)‐coil block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4037–4042, 2007     

Synthesis of the block copolymer of styrene and 1-butene with a novel supported Ti-catalyst

The present investigation deals with sequential block copolymerization of styrene and 1-butene with a novel MgCl₂-supported TiCl₄ catalyst modified with a rare earth compound NdCl_x(OR)_y (SN-1 catalyst), which was developed in our laboratory. The catalytic activities are 1300–2500 g/g·Ti·h. Analyses of copolymers with solvent extraction, ¹³C-NMR, WAXD, GPC, and DSC was performed. The results indicate that the SN-1 catalyst selectively gave crystalline diblock copolymers of isotactic polystyrene and isotactic poly(1-butene), with the styrene unit content of 30–60 mol %. © 1996 John Wiley & Sons, Inc.     

Preparation of dual stimuli‐responsive PET track‐etched membrane by grafting copolymer using ATRP

A dual stimuli‐responsive (pH and thermo) polyethylene terephthalate (PET) track‐etched membrane has been prepared using atom transfer radical polymerization (ATRP). First, ATRP initiator 2‐bromoisobutyryl bromide was anchored onto the membrane surface. Then, 2‐hydroxyethyl‐methacrylate (HEMA) and N‐isopropylacrylamide (NIPAAm) were grafted onto the membrane surface using ATRP. X‐ray photoelectron spectroscopy, ATR‐Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis were used to characterize the membrane structure and thermal properties; water flux measurement was used to investigate the double stimuli‐responsive property of the obtained membrane. The results indicate that the PHEMA and PNIPAAm binary grafted PET track‐etched membrane has double environmental responsiveness. This method provides a potential modification method for preparing functional membranes. Copyright © 2012 John Wiley & Sons, Ltd.     

基于ATRP技术的多嵌段共聚物研究进展

原子转移自由基聚合(ATRP)技术是合成结构规整性聚合物的有效途径。综述了近十年来采用ATRP技术合成多嵌段共聚物的研究进展。从引发剂、共聚单体和反应条件等方面讨论了ABA型、ABC型和ABCBA型等类型多嵌段共聚物的合成、性质与潜在应用。对原子转移自由基聚合技术在合成功能性多嵌段共聚物中的应用前景进行了展望。     

Synthesis of poly(n‐butyl acrylate) homopolymer and poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) triblock copolymer via AGET emulsion ATRP using a cationic surfactant

Cationic emulsions of triblock copolymer particles comprising a poly(n‐butyl acrylate) (PⁿBA) central block and polystyrene (PS) outer blocks were synthesized by activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP). Difunctional ATRP initiator, ethylene bis(2‐bromoisobutyrate) (EBBiB), was used as initiator to synthesize the ABA type poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) (PS‐PⁿBA‐PS) triblock copolymer. The effects of ligand and cationic surfactant on polymerizations were also discussed. Gel permeation chromatography (GPC) was used to characterize the molecular weight (M_n) and molecular weight distribution (MWD) of the resultant triblock copolymers. Particle size and particle size distribution of resulted latexes were characterized by dynamic light scattering (DLS). The resultant latexes showed good colloidal stability with average particle size around 100–300 nm in diameter. Glass transition temperature (T_g) of copolymers was studied by differential scanning calorimetry (DSC). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 611–620     

Effect of spacer length on the liquid crystalline property of azobenzene-containing ABA-type triblock copolymers via ATRP

The effect of flexible spacer length on the liquid crystalline property of ABA-type triblock copolymers containing azobenzene groups was investigated.For the study,the monomers,n-[4-(4-ethoxyphenylazo)phenoxy]alkyl methacrylates with varying methylene groups(n=0,2,6)were used to synthesize a series of azobenzene-containing amphiphilic triblock copolymers PAnC-PEG-PAnC by atom transfer radical polymerization(ATRP).Differential scanning calorimetry(DSC),polarizing optical microscopy(POM),and one-dimensional X-ray diffraction(1D WAXD)have shown that the glass transition temperatures of these copolymers decreased with increasing n,PAOC-PEG-PAOC has no mesophase,while both PA2C-PEG-PA2C and PA6C-PEG- PA6C have a nematic mesophase.These differences derive from the length of spacer groups between the polymer backbone and side-chain LC monomers.     

A novel approach to modify poly(vinylidene fluoride) via iron‐mediated atom transfer radical polymerization using activators generated by electron transfer

Iron‐mediated atom transfer radical polymerization using activators generated by electron transfer directly from the secondary fluorine atoms on the poly(vinylidene fluoride) (PVDF) backbone, using methyl methacrylate (MMA) and poly (ethylene glycol) methyl ether methacrylate (PEGMA) as the monomers, FeCl₃·6H₂O as the catalyst, PPh₃ as the ligand, and vitamin C as the reducing agent, was demonstrated in the presence of limited amounts of air. The successful syntheses of the corresponding graft copolymers PVDF‐g‐PMMA and PVDF‐g‐PPEGMA were characterized by nuclear magnetic resonance, Fourier transform infrared and X‐ray photoelectron spectroscopy, respectively. The graft copolymers PVDF‐g‐PPEGMA can be readily cast into porous hydrophilic microfiltration membranes by phase inversion in an aqueous medium. The morphologies were characterized by scanning electron microscopy. The surface and bulk hydrophilicity were evaluated on the basis of static water contact angle and the steady adsorption of bovine serum albumin. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of ligand on the synthesis of star polymers by resorcinarene‐based ATRP initiators

The effect of the steric hindrance on the initiating properties of two multifunctional resorcinarene‐based initiators in atom transfer radical polymerization (ATRP) was studied by using Cu(I)‐complexes of three multidentate amine ligands in the polymerization of tert‐butyl acrylate and methyl methacrylate. These ligands are less sterically hindered and have higher activities in the catalysis of ATRP of (meth)acrylates than 2,2′‐bipyridine. The polymerizations were faster and more controlled than with the 2,2′‐bipyridyl catalyst, but the tendency for bimolecular coupling increased. Even though the initiator was octafunctional, the resulting star polymers had only four arms. This indicates that the steric hindrance arising from the conformations of the initiators determines the structure of the polymer, but the ligand noticeably affects the controllability of the polymerization © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3349–3358, 2005     

Straightforward synthesis of poly(lauryl acrylate)-b-poly(stearyl acrylate) diblock copolymers by ATRP

Lauryl (LA) and stearyl (SA) acrylates were successfully polymerized by atom transfer radical polymerization (ATRP), leading to well defined homopolymers and diblock copolymers (PDI < 1.2). Interestingly, the polymerization was very well controlled using N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), a ligand which had initially been reported to be unadvisable for the polymerization of such monomers. Both kinetic studies and chain extension reactions supported our conclusions. A PLA₆₅-b-PSA₄₇ diblock copolymer was characterized by differential scanning calorimetry and dynamic thermo-mechanical analysis, revealing that both blocks exhibit side-chain crystallinity and phase segregate in the crystalline state. The diblock behaves as a brittle rigid polymer when both blocks are crystalline, as a ductile material after the melting of the PLA phase and becomes a viscous liquid when both blocks are molten. This work could be extended to the preparation of PSA-b-PLA-b-PSA bio-issued thermoplastic elastomers.     

A facile strategy to modify TiO2 nanoparticles via surface‐initiated ATRP of styrene

A core‐shell hybrid nanocomposites, possessing a hard core of nano titanium dioxide (n‐TiO₂) and a soft shell of brushlike polystyrene (PS), were successfully prepared by surface‐initiated atom transfer radical polymerization (ATRP) at 90 °C in anisole solution using CuBr/PMDETA as the catalyst, in the presence of sacrificial initiator. FTIR, ¹H NMR, XPS, TEM, SEM, TGA, and DSC were used to determine the chemical structure, morphology, thermal properties, and the grafted PS quantities of the resulting products. TEM images of the samples provided direct evidence for the formation of a core‐shell structure. The thermal stabilities of the grafted polymers were dramatically elevated relative to that of pristine PS according to TGA results. DSC results demonstrated that the TiO₂‐PS nanocomposites exhibited higher glass transition temperature (T_g) compared with pristine PS. The molecular weights of the free polymers formed by sacrificial initiator, which were similar to that of surface‐attached polymers were measured by GPC instrument which showed that the molecular weights of PS were well controlled with a relatively narrow polydispersity index (PDI < 1.2). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1782–1790, 2010     

Novel superhydrophobic silica/poly(siloxane‐fluoroacrylate) hybrid nanoparticles prepared via surface‐initiated ATRP and their surface properties: The effects of polymerization conditions

A series of superhydrophobic poly(methacryloxypropyltrimethoxysilane, MPTS‐b‐2,‐2,3,3,4,4,4‐heptafluorobutyl methacrylate, HFBMA)‐grafted silica hybrid nanoparticles (SiO₂/PMPTS‐b‐PHFBMA) were prepared by two‐step surface‐initiated atom transfer radical polymerization (SI‐ATRP). Under the adopted polymerization conditions in our previous work, the superhydrophobic property was found to depend on the SI‐ATRP conditions of HFBMA. As a series of work, in this present study, the effects of polymerization conditions, such as the initiator concentration, the molar ratio of monomer and initiator, and the polymerization temperature on the SI‐ATRP kinetics and the interrelation between the kinetics and the surface properties of the nanoparticles were investigated. The results showed that the SI‐ATRP of HFBMA was well controlled. The results also showed that both the surface microphase separation and roughness of the hybrid nanoparticles could be strengthened with the increase of the molecular weight of polymer‐grafted silica hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of i‐PP‐based functional block copolymer by a facile combination of styryl‐capped i‐PP and ATRP

This article demonstrates a facile and efficient method to combine olefin coordination polymerization with atom transfer radical polymerization (ATRP) for the synthesis of isotactic polypropylene (i‐PP)‐based functional diblock copolymers. The chemistry involves a styryl‐capped i‐PP precursor prepared through the controlled consecutive chain transfer reaction, first to 1,2‐bis(4‐vinylphenyl)ethane and then to hydrogen in propylene polymerization mediated by an isospecific metallocene catalyst. The i‐PP precursor can be quantitatively transformed into i‐PP terminated with a 1‐chloroethylbezene group (i‐PP‐t‐Cl) by a straightforward hydrochlorination process using hydrogen chloride. With the resultant i‐PP‐t‐Cl as a macroinitiator of ATRP, methyl methacrylate (MMA) polymerization was exemplified in the presence of CuBr/pentamethyldiethylenetriamine, preparing i‐PP‐b‐PMMA copolymers of different PMMA contents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A Highly Active Iron‐Based Catalyst System for the AGET ATRP of Styrene

The atom transfer radical polymerization of styrene using activators generated by electron transfer (AGET ATRP) has been carried out in bulk in a limited amount of air at 110 °C, using 1,3,5‐(2′‐bromo‐2′‐methylpropionato)benzene (BMPB) as an initiator and FeCl₃ · 6H₂O/tris(3,6‐dioxaheptyl) amine (TDA‐1)/ascorbic acid (VC) as a novel Fe^III‐mediated catalyst system. The results of the polymerizations demonstrate the features of ‘living’/controlled free‐radical polymerization, such as the number‐average molecular weights being close to their corresponding theoretical values and increasing linearly with monomer conversion, and narrow molecular weight distributions ( = 1.18–1.26). The end functionality of the obtained polymers was confirmed by ¹H and ¹³C NMR spectra as well as a chain‐extension reaction.

     

Multiblock copolymer synthesis via controlled radical polymerization in aqueous dispersions. Part 1: Synthesis of S-tert-alkyl-N,N-alkoxycarbonylalkyldithiocarbamates

In a novel two- or three-step synthetic route, S-(1,4-phenylenebis(propane-2,2-diyl)) bis(N-methyldithiocarbamate) is reacted at low temperature with various alkyl chloroformates to form various S-tert-alkyl-N,N-alkoxycarbonylmethyl-dithiocarbamate RAFT agents. Also an alternative and novel synthetic route towards S-(1,4-phenylenebis(propane-2,2-diyl)) bis(N-methyldithiocarbamate), is proposed.     

A novel route to the marasmane skeleton via a tandem rearrangement-cyclopropanation reaction. total synthesis of (+)-isovelleral

A general and efficient route to the marasmane skeleton is described. Total syntheses of two simple marasmanes (35 and 37) in racemic form were achieved using a MgI2-catalyzed rearrangement-cyclopropanation reaction of trimethylsilyl enol ether 31 derived from naphthalenone 30. The reaction proceeds in high yield with complete diastereoselectivity and does not require the use of special cyclopropanation reagents. Application of this novel route to the marasmane framework was extended to the synthesis of naturally occurring (+)-isovelleral (41).     

石墨烯/二氯化镁负载钛系齐格勒-纳塔催化剂制备及其乙烯聚合性能

石墨烯自2004年发现以来,由于其独一无二的优异性迅速成为科学家们的研究热点.由于石墨烯具有极其优异的电学、力学和热学等性能,因此被广泛应用于高性能聚合物基复合材料的制备.众所周知,纳米填料在聚合物中的分散状态以及与基体间的界面作用是构筑高性能聚合物纳米复合材料的关键因素.由于石墨烯极易团聚,难以通过传统的熔融共混法制备均匀分散的石墨烯增强-聚烯烃纳米复合材料.另一方面,聚烯烃通常需要在较高温度下才能溶于部分有毒溶剂(如:三氯苯和二甲苯等),因此溶液共混法也不适用于聚烯烃-石墨烯纳米复合材料的制备.有鉴于此,本文开发了一种共沉积法制备石墨烯/二氯化镁负载钛系齐格勒-纳塔催化剂的路线.通过原位聚合直接制备出石墨烯均匀分散的聚烯烃/石墨烯纳米复合材料.考察了石墨烯的加入量对催化剂形态及其催化乙烯聚合行为的影响.当石墨烯加入量较低时,多个石墨烯片被包裹于较大的催化剂粒子中.随着石墨烯加入量的增加,催化剂趋向于在石墨烯表面聚集.继续增加石墨烯量将导致石墨烯包裹催化剂粒子,降低过渡金属钛的负载效率.通过三乙基铝活化后,所制备的催化剂具有非常高的乙烯催化活性,所生成的聚乙烯/石墨烯纳米复合材料复制了催化剂的片状结构.同时,通过对所制备的聚乙烯/石墨烯纳米复合材料进行电子显微镜和X射线衍射分析可知,石墨烯均匀分散于聚乙烯基体中,并且没有任何团聚现象发生.该复合材料的热重分析表明,仅加入非常少量的石墨烯就可以使其具有比纯聚乙烯更高的热稳定性,当石墨烯加入量为0.66 wt%时,其5 wt%热分解温度较纯聚乙烯升高了54°C.同时,所制备聚乙烯/石墨烯纳米复合材料具有更优异的机械性能.因此,本研究提供了一个简单高效的高性能聚烯烃/石墨烯纳米复合材料的制备方法.