Grafting polymers from cellulose nanocrystals via surface-initiated atom transfer radical polymerization

Cellulose nanocrystals (CNC) are rod-like nanoparticles extracted from cellulose. Due to their fascinating properties—renewable, biocompatible, non-toxic, biodegradable, excellent mechanical performances, high specific surface area, water dispersible, can be assemble in chiral nematic phases—CNC have shown promise in various fields, including oil recovery, polymer composites reinforcing, hydrogels, aerogels, supercapacitors, energy saving buildings, cosmetics, papermaking, coatings, liquid crystals, and waste water treatment. However, the hydrophilic surface of CNC hinders their broader applications. In this context, surface modification of CNC via polymer grafting can be used to finely tune their surficial properties and endow CNC with a variety of functionalities, such as conductivity, pH or temperature responsiveness, reactivity…In particular, surface-initiated atom transfer radical polymerization (SI-ATRP) is a powerful tool to graft various polymers with a high grafting density and controlled chain length. In this review, the precise control of grafted polymers from CNC via SI-ATRP is first discussed, including issues related to the polymer grafting density, chain length and possibility to perform an asymmetric grafting. Then, the properties and applications of CNC grafted with a variety of polymers are presented. Finally, some challenges and outlook related to the SI-ATRP method applied to the field of CNC is discussed.     

Synthesis and antimicrobial activities of acrylamide polymers containing quaternary ammonium salts on bacteria and phytopathogenic fungi

Three series of acrylamide monomers/polymers containing quaternary ammonium salts (QASs), i.e., acrylamide QAS monomers (QDs), homopolymers of QDs (PQDs) and copolymers of QDs with acrylate monomer (PQDCs), were synthesized and employed in antimicrobial tests against both bacteria (Escherichia coli (E. coli) and Staphylococcus albus (S. albus)) and phytopathogenic fungi (Rhizoctonia solani (R. solani) and Fusarium oxysporum f. sp. cubense race 4 (Foc4)). The antibacterial activity of the QASs was evaluated by determining the minimum inhibitory concentration (MIC) against E. coli and S. albus by the TTC coloration method, and the antifungal activity was measured by mycelia growth inhibition as well as MIC and the minimum fungicidal concentration (MFC) values. The results indicated that PQD homopolymers and PQDC copolymers showed far better antimicrobial activities than QD monomers. PQDC copolymers by incorporating hydrophobic acrylate units into the main chain of polyacrylamide backbone displayed even better antimicrobial activities, depending on QAS structure and hydrophobic content. Moreover, polymers with benzyl group attached to nitrogen atom showed better inhibitory effect on bacteria and phytopathogenic fungi. The results could assist understanding and development of future design of antimicrobial polymers as potential fungicide agents to control plant disease.     

Photosensitive polymers containing pendent chalcone moieties via oxyethylene group

Vinylchalcone derivatives were prepared by the reaction of the sodium salt of 4-hydroxychalcone with 2-chloroethanol, followed by esterfication of the hydroxy groups with methacryloyl chloride in the presence of triethylamine as a base. The photosensitive monomers, 4-(methacryloyloxyethoxy)chalcone and its 4′-methyl and 4′-chloro-derivatives, have been homo- and copolymerized with p-nitrophenylmethacrylate under free radical conditions to give the copolymers containing different ratios of photosensitizer group. The photosensitivities of the polymeric chalcone derivatives were investigated through their photochemical reactions on exposure to UV light and measuring the changes in UV spectra before and after irradiation. The results of these measurements indicate that the insolubilization percentage, i.e. the rate of the double bond disappearance depends on the effects of (i) the time of exposure to UV light, (ii) the position of the substituent in the phenyl ring of the chalcone, (iii) the spacer between the active moiety and the polymer backbone, and (iv) the ratio of the photosensitizer group.     

Relationship between surface concentration of amphiphilic quaternary ammonium biocides in electrospun polymer fibers and biocidal activity

Electrospinning was utilized to generate antimicrobial Nylon and polycarbonate fibers for potential applications including self-decontaminating fabrics, wound dressings, and filtration media. The effects of quaternary ammonium salt concentration on fiber morphology, diameter, and antimicrobial activity of the resulting fiber mats were investigated. Fibers were characterized utilizing scanning electron microscopy and X-ray photoelectron spectroscopy, while antimicrobial activity was evaluated against Staphylococcus aureus. The co-electrospinning of soluble quaternary ammonium biocides within polymeric solutions generated uniform fibers with diameters ranging from 91 to 278 nm for Nylon and 0.55–2.34 μm for polycarbonate. Fiber morphology and diameter of the resulting fibers were shown to be dependent on polymer type and biocide concentration. A positive correlation between surface concentration of quaternary ammonium salts and antimicrobial activity was observed as fibers loaded with biocides exhibited up to a 7 log reduction of viable bacteria.     

Oxidative desulfurization of diesel fuel using amphiphilic quaternary ammonium phosphomolybdate catalysts

Phosphomolybdic acid (HPMo) modified respectively with tetramethyl ammonium chloride (TMAC), dodecyl trimethyl ammonium chloride (DTAC) and hexadecyl trimethyl ammonium chloride (HTAC) as the catalysts were prepared and characterized by FT-IR, XRD and SEM. The catalysts were evaluated for the oxidative desulfurization of benzothiophene (BT), dibenzothiophene (DBT) and straight-run diesel using hydrogen peroxide as an oxidant. Results show that all of the catalysts keep the Keggin structures and are finely dispersed with mixing of quaternary ammonium salts. Hexadecyl chains are more favorable to wrap up DBT to the catalytic center and form stable emulsion system with higher conversion rates of DBT. The shorter dodecyl chains can wrap up BT more suitably and bring smaller steric hindrance, which display higher conversion rates of BT. The oxidative reactions fit apparent first-order kinetics, and the apparent activation energies of DBT are much lower than those of BT. The desulfurization rate of straight-run diesel can be up to 84.4% with the recovery rate of 98.1% catalyzed by [HPMo][HTAC]₂ in 2 h. When increasing the extraction times, the desulfurization rates increase, but the recovery rates of diesel decrease significantly.     

羟基和酯基型Gemini双季铵盐表面活性剂在煤沥青表面的润湿特性

以自制的羟基和酯基型Gemini双季铵盐表面活性剂为研究对象,在考察其表面活性的基础上,进一步研究了表面活性剂在煤沥青表面的润湿性。研究表明,羟基型Gemini表面活性剂在煤沥青表面的接触角随疏水链长度的增长呈先减小后增大趋势,其中C₁₂-OH在煤沥青表面的润湿效果最好;对于m-n-m酯基型Gemini表面活性剂而言,接触角随疏水链长度的增长而降低。当疏水链长度一定时,m-6-m在煤沥青表面的润湿效果比m-2-m好。在一定浓度范围内,C₁₀-OH、C₁₂-OH和12-2-123种Gemini表面活性剂的表面张力与其在煤沥青表面黏附张力呈线性关系。煤沥青表面的Zeta电位随Gemini表面活性剂浓度的增大呈先增大后趋于平稳的趋势。     

Synthesis of amphiphilic copolymers by ATRP initiated with a bifunctional initiator containing trichloromethyl groups

Bifunctional polystyrene macroinitiators, having various molecular weights, were prepared by atom transfer radical polymerization (ATRP), initiated with bifunctional initiator 1,3-bis{1-methyl-1[(2,2,2-trichloroethoxy) carbonylamino]ethyl}benzene in conjunction with CuCl catalyst and polyamine ligands. These macroinitiators were subsequently used for ATRP of tert-butyl acrylate (t-BuA), giving BAB triblocks poly[(t-BuA)-b-(Sty)-b-(t-BuA)] as precursors of amphiphilic copolymers. Both the polymerization steps proceeded as controlled processes with linear semi-logarithmic conversion plots and lengths of the blocks following theoretical predictions. Hydrolysis of outer poly(t-BuA) blocks led to triblock copolymers with the central polystyrene block and outer blocks of poly(acrylic acid), the molecular weights of which ranged from ca. 5 × 10³ to almost 1 × 10⁵ Da.     

Synthesis of amphiphilic block copolymers via ARGET ATRP using an inexpensive ligand of PMDETA

Amphiphilic block copolymers, methoxy polyethylene glycol-b-poly(butyl methacrylate), were synthesized via activators regenerated by electron transfer for atom transfer radical polymerization(ARGET ATRP) of butyl methacrylate (BMA), where pentamethyldiethylene triamine (PMDETA) was utilized as the ligand. The results show that the minimum amount of the catalyst required in the ARGET ATRP of BMA with a high degree of control depends upon the molar ratio of [catalyst]₀/[initiator]₀. With PMDETA as the ligand and methoxy polyethylene glycol 2-bromo-iso-butyrate (MPEG-Br) as the macro-initiator, the ratio of [CuBr₂]₀/[MPEG-Br]₀ should be higher than 0.025:1. At this value, the copper catalyst level can be lowered to 50 ppm when the degree of polymerization of the BMA segment is set at 500. Reaction conditions that impact the controllability of the polymerization and the corresponding properties of the block copolymers were investigated.     

新型聚季铵盐的合成、表征及其性能测试

以二氯乙醚和N,N,N’,N’-四甲基乙二胺为原料,通过共聚合反应制备出新型的水溶性聚季铵盐——聚[(氧亚乙基-二甲基亚氨基-亚乙基-二甲基亚氨基-亚乙基)二氯化物]。研究表明,最佳合成工艺条件为:四甲基乙二胺和二氯乙醚的摩尔配比为1.05∶1,反应温度控制在70℃,反应时间为6 h,滴加速度为30滴/min。采用红外、核磁共振对产物进行结构表征;测定了聚合物的热稳定性,特征粘数等;初步测试了该聚季铵盐的杀菌性能;杀菌时间9 h,药剂投加量为80 mg/L时杀菌效果最好,杀菌率达到98%;产物最大特征粘数为15.231 3 mL/g。     

Synthesis and characterization of AB2-type star polymers via combination of ATRP and click chemistry

Homo/miktoarm star polymers were successfully synthesized via combination of the “arm-first” and “coupling-onto” strategies. Firstly, the multifunctional coupling agent (core), 2, 4, 6-tris(3-ethynylphenyl)-1,3,5-triazine-2,4,6-triamine (TPTTA), was synthesized. Secondly, the linear polystyrene-Cl (PS-Cl) and poly(2-(dimethylamino)ethyl methacrylate)-Br (PDMAEMA-Br) were prepared by atom transfer radical polymerization (ATRP) method. Then, the linear PS-Cl and PDMAEMA-Br chains were modified by a nucleophilic substitution reaction with sodium azide. Finally, homo/miktoarm star polymers PS₃ and PS(PDMAEMA)₂ were designed by click reaction between the core (TPTTA) and the arm precursor (PS-N₃ or PDMAEMA-N₃). The structures of the PS₃, PS(PDMAEMA)₂ and the precursors were all characterized by NMR, FT-IR, UV and GPC analysis. Moreover, the self-assembly behaviors of the miktoarm amphiphilic copolymer PS(PDMAEMA)₂ was also investigated by transmission electron microscopy (TEM).     

季铵型阳离子聚丙烯酰胺水溶液的性质

季铵型阳离子聚丙烯酰胺作为阳离子助剂处理棉纤维,其水溶液性质影响助剂在纤维上的处理效果。考察水溶液黏度性质和电导性质,用助剂处理后纤维的无盐染色效果进行证明。结果表明：分子量低的季铵型阳离子聚丙烯酰胺在水溶液中比浓黏度较小,用其处理纤维有利于助剂在纤维上分布均匀,染色纤维匀染性好;阳离子化度高的助剂在水溶液中电离能力较强,处理后纤维所带正电荷数量增加,染色纤维色深K/S值增大。     

New amphiphilic fluorescent CBABC-type pentablock copolymers containing pyrene group by two-step atom transfer radical polymerization (ATRP) and its self-assembled aggregation

A series of novel amphiphilic fluorescent CBABC-type pentablock copolymers (Py-PMMA-PEG4600-PMMA-Py) were prepared from BAB-type amphiphilic triblock copolymer (PMMA-PEG4600-PMMA) as macroinitiator with various contents of 1-(methacryloyloxyethylamino-carboxylmethyl) pyrene (PyMOI) by atom transfer radical polymerization (ATRP) in toluene using CuBr/2,2-bipyridine as catalyst system. Triblock copolymer (PMMA-PEG4600-PMMA) was prepared by ATRP and obtained from Br-PEG4600-Br as macroinitiator with methyl methacrylate in tetrahydrofuran using the same catalyst. The molecular weights of pentablock copolymers which were reinitiated by PMMA-PEG4600-PMMA macroinitiator were calculated from ¹H NMR spectra up to 42,400 gmol⁻¹. The polydispersity of pentablock copolymers obtained from GPC analysis was narrow between 1.10 and 1.38. The crystallinity of triblock copolymer (PMMA-PEG4600-PMMA) was decreased slightly with incorporating PMMA segment. Introducing the bulky pyrene substituent into pentablock copolymer, the melting temperature was not observed and all pentablock copolymers showed amorphous patterns in wide-angle X-ray scattering (WAXS) due to decrease in the degree of crystallinity of polymer chain because of disturbing regular packing. The temperatures at 10% weight loss (Td₁₀), examined by TG analysis, showed values ranging from 265 to 323 °C in nitrogen and 264 to 313 °C in air. Fluorescence spectra of Py-PMMA-PEG4600-PMMA-Py exhibited stronger excimer emission at ca. 480 nm due to the aggregations of pyrene group formed via interaction of the hydrophobic chains. The more content of PyMOI segment in pentablock copolymers can obtain the higher emission intensity ca. 480 nm. When there were higher PyMOI contents (84.9 wt% PyMOI) in pentablock copolymers, they formed larger aggregates (210 nm) in SEM micrographs. On the other hand, while increasing the concentration of the polymer solution in THF, the morphology was changed from spherical (0.1 mg/mL) to chainlike (1.0 mg/mL) aggregates.     

ATRP法合成甲基丙烯酸羟丙酯

以2-溴丙酰溴为溴化剂,在离子液体([Amim]Cl)中与纤维素反应制备大分子引发剂,以溴化亚铜/五甲基二乙烯三胺(CuBr/PMDETA)为引发体系,N,N-二甲基甲酰胺(DMF)及丁酮(Butanone)为溶剂,研究了甲基丙烯酸羟丙酯的原子转移自由基聚合(ATRP)。通过FT-IR,1HNMR和GPC对聚合物进行了分析,考察了聚合反应的活性特征,反应时间、催化体系、溶剂对聚合物分子量及分子量分布的影响。结果表明,反应转换率随时间呈线性增加,且合成反应是可控活性聚合。     

非依赖细胞表面疏水性的季铵盐抗菌特性

使用4-羟基吡啶、1,5-二氯戊烷和1-碘代烷,合成了系列新型双子季铵盐4,4'-(1,5-戊撑二羟基)双(1-碘化烷基吡啶)(PA-n,n=6、8、10、12、14、16和18).抗菌试验结果表明,PA-12具有该系列中最高的抗菌活性,对于E.coli IFO 3301和S.aureus IFO 12732的最小抑菌浓度(MIC)分别达到0.5 umol/L和0.4 umol/L.相对于单季铵盐苯扎氯铵(BAC),PA-12的抗菌活性不但对温度和pH环境因素的变化基本稳定,而且不依赖微生物细胞表面的疏水性,对革兰氏阴性菌和革兰氏阳性菌两类菌群都表现出了优异的抑制和杀灭能力.     

Graft copolymerization of water‐soluble monomers containing quaternary ammonium group on poly(vinyl alcohol) using ceric ions

Graft copolymerization of water‐soluble monomers containing quaternary ammonium onto PVA was studied in an aqueous medium using ceric ammonium nitrate‐nitric acid as the redox initiator. To optimize the reaction conditions for obtaining a maximum percent of grafting, the concentrations of methacryloxyethyl trimethylammonium chloride (DMC) monomer, ceric ammonium nitrate, and temperature were varied, and the effects on the grafting copolymerization were discussed. Under optimum conditions, a series of water‐soluble monomers containing quaternary ammonium, such as methacryloxyethyl trimethylammonium chloride (DMC), DMAEMA^˙C₂H₅Br, DMAEMA^˙C₄H₉Br, DMAEMA^˙C₁₆H₃₃Br, and DMAEMA^˙C₇H₇Cl, were successfully grafted onto PVA. The resulting grafted PVA were characterized with IR, NMR, and viscosity measurements. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2186–2191, 2005     

Surface properties of a segmented polyurethane containing amphiphilic polymers as additives

Two different types of amphiphilic polymers were used as surface-modifying additives to a polyetherurethane, Pellethane 2363–75D, which has T_g close to room temperature. The additives used were a segmented polyetherurethane designated Pol C, and Pluronics PE6800 and PE9400, i.e., triblock copolymers of propylene oxide and ethylene oxide. Pol C was prepared from poly(ethylene glycol), methylene diphenylene diisocyanate, and a fatty acid monoglyceride. The properties of the blends were investigated in their unhydrated state and after water immersion at 23°C and 80°C. Surface composition, water absorption, and leakage of additives to the aqueous phase have been studied. From ESCA and contact angle measurements it was concluded that Pol C was enriched in the surface layer of the matrix material after water immersion at 80°C. The Pluronics showed less effects on the surface properties of the matrix material, probably because of their high water solubility. © 1994 John Wiley & Sons, Inc.     

Grafted wood pulp containing quaternary ammonium group and its application in the removal of different anions from aqueous solution

Network wood pulp based on acrylonitrile (AN) has been chemically modified through different reactions to obtain group capable of anion exchange. Graft copolymerization of AN onto wood pulp was carried out by using γ‐radiation ⁶⁰Co. Factors affecting the grafting process, e.g., radiation dose and monomer concentration, was investigated. The chemical modification of cyano groups were carried out by reaction with ethanolamine producing oxazoline group followed by quaternization of tertiary amine by reaction with benzyl chloride producing quaternary ammonium salt. The grafted and modified wood pulp were characterized by FTIR, SEM, and TGA. Qualitative adsorption experiments were conducted to evaluate the ability of modified wood pulp to fix sulfate, phosphate, nitrate, and dichromate from aqueous solution using batch extractions. Based on the results obtained, it may be concluded that it is possible to modify chemically wood pulp containing cyano groups by different routes to use it as anion exchanger for different anions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3120–3128, 2007     

Synthesis and properties of triblock copolymers containing PDMS via AGET ATRP

The bromo-terminated macroinitiator was prepared by direct addition reaction of difunctional poly(dimethylsiloxane) (PDMS) containing methyl methacrylate end groups with hydrobromic acid in acetic acid under mild conditions, and well-defined triblock copolymers of poly(methyl methacrylate-b-dimethylsiloxane-b-methyl methacrylate) (MMA-b-DMS-b-MMA) were synthesized via activators generated by election transfer atom transfer radical polymerization (AGET ATRP). The gel permeation chromatography data obtained verified the polymerization and showed the well controlling of the reaction. FTIR and ¹H NMR measured the structure of the macroinitiator and copolymers. The contact angle measurement indicated that the water contact angles decreased gradually with the increasing of PMMA block content. The self-assembly behaviors of the triblock polymer were studied by transmission electron micrograph, scanning electron microscopy, and dynamic light scattering measurement. The results indicated that the polymers could self-assemble into various complex morphologies in different solvents and the morphologies depended on the properties of solvents. The possible molecular packing models for self-assembly behaviors of the ABA triblock polymers were proposed.     

Well-defined core-shell structures based on silsesquioxane microgels: Grafting of polystyrene via ATRP and product characterization

Silsesquioxane microgel nanoparticles characterized by low diameters (below 30 nm) and reduced polydispersity can be produced in an acid-catalyzed sol-gel process in an aqueous microemulsion. Suitable surface modification of such structures leads to macroinitiators for atom-transfer radical polymerization (ATRP). This polymerization method was applied in order to graft polystyrene chains onto the surface of the microgels. Well-defined structures exhibiting a core-shell architecture were produced with the M_w of grafted polymers ranging from 8.5 to about 30 kg/mol. The products were extensively characterized with light scattering, X-ray scattering, thermal analysis (TGA/DSC) and microscopy (TEM/SEM) to obtain information on parameters characterizing polystyrene brush. Polymer-grafted nanoparticles will be used for the modification of homopolymer and block copolymer matrices.     

Preparation and evaluation of an antibacterial dental cement containing quaternary ammonium salts

A novel PQAS‐containing antibacterial glass‐ionomer cement has been developed. The functional QAS and their constructed PQAS were synthesized, characterized, and formulated into the light‐cured cements. Compressive strength (CS) and bacterial (S. mutans and lactobacillus) viability were used to evaluate the mechanical strength and antibacterial activity of the cements. Flexural (FS) and diametral tensile strengths (DTS) were tested as well. Fuji II LC cement was used as control. The specimens were conditioned in distilled water at 37°C for 24 h prior to testing. All the PQAS‐containing cements showed a significant antibacterial activity, accompanying with an initial CS reduction. The effects of chain length, loading, and grafting ratio of the QAS were significant. Increasing chain length, loading, grafting ratio significantly enhanced antibacterial activity but reduced the initial CS of the formed cements. The antibacterial effect of the substitute chain lengths from free QAS seem more significant in water than those from their polymers (PQAS) after integrating to the cement. The experimental cement showed less CS reduction and higher antibacterial activity than Fuji II LC. The long‐term aging study indicates that the cement might have a long‐lasting antibacterial function with no PQAS leaching. Within the limitations of this study, it appears that the experimental cement is a clinically attractive dental restorative that can be potentially used for long‐lasting restorations due to its high mechanical strength and long‐lasting antibacterial function. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.