High performance polymeric flocculants based on modified polysaccharides—Microwave assisted synthesis

New generation of polymeric flocculants has been developed by optimally grafting polyacrylamide branches on purified polysaccharide backbone in authors’ laboratory. These flocculants are synergistically efficient at low doses, controlled biodegradable, shear resistant, and ecofriendly. Recently it has been observed in the authors’ laboratory that graft copolymers synthesized by microwave initiated and microwave assisted methods provide a better quality of graft copolymer with higher percentage of grafting in comparison with conventional redox grafting method. The synthesized graft copolymers were characterized by variety of material characterization techniques. The microwave assisted synthesized graft copolymers show superior flocculation characteristics when compared with graft copolymers synthesized by conventional and microwave initiated method as well as with commercially available flocculant. The details of material synthesis, mechanism, characterization and applications of these novel materials in the field of flocculation have been reported.     

Polyacrylamide grafted Agar: Synthesis and applications of conventional and microwave assisted technique

Polyacrylamide grafted Agar (Ag-g-PAM) has been successfully synthesized by conventional method and microwave assisted method. The former method employs ceric ammonium nitrate (CAN) as the free radical initiator while the latter uses the combination of ceric ammonium nitrate (CAN) and microwave irradiation. The synthesized graft copolymers have been characterized by elemental analysis (C, H, N, O and S), FTIR spectroscopy, intrinsic viscosity measurement and scanning electron micrograph (SEM); taking agar as a reference. Flocculation efficacy of synthesized graft copolymers was studied in kaolin suspension and in waste water through 'Jar test' procedure. In the present investigation, we have observed that polyacrylamide grafted agar synthesized by microwave assisted technique shows superior properties than conventional technique. These properties are reported in terms of intrinsic viscosity, flocculation efficacy and pollutant load reduction of waste water.     

Microwave assisted synthesis of polyacrylamide grafted agar (Ag-g-PAM) and its application as flocculant for wastewater treatment

Grafting of polyacrylamide (PAM) chains was performed onto the backbone of Agar by microwave assisted method, using microwave radiation in synergism with ceric ammonium nitrate (CAN) as the chemical free radical initiator. The intended grafting of the PAM chains were confirmed through intrinsic viscosity study, FTIR spectroscopy and elemental analysis (C, H, N, O & S). Further characterization of the grafted product was done in form of SEM morphology and TGA study. Flocculation efficacy of the synthesized graft copolymers was studied in kaolin suspension, through ‘Jar test’ procedure. Further, flocculation efficacy of the ‘best grade’ (as determined by ‘jar test’ in kaolin suspension) in wastewater was studied for possible application in reduction of pollutant load of wastewater.     

Synthesis and characterization of hydroxypropyl methylcellulose and ethyl acrylate graft copolymers

The synthesis of hydroxypropyl methylcellulose-g-poly (ethyl acrylate) was carried out by potassium persulfate induced graft copolymerization in homogeneous aqueous medium. By varying the reaction conditions, graft copolymers with different percentage of grafting were prepared. These graft copolymers were characterized by fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analyses (TGA), X-ray diffraction analysis (XRD), and dynamic light scattering (DLS) methods. The molecular weight of grafted and ungrafted polymer chains determined by gel permeation chromatography (GPC) increased with increasing monomer and matrix concentration but decreased with increasing initiator concentration and reaction temperature. The mechanical properties of graft copolymers were measured as function of the percentage of grafting. In addition, the equilibrium humidity adsorption behavior and the disintegration time of the grafted copolymer films were also studied.     

Synthesis, characterization and thermal sensitivity of chitosan-based graft copolymers

Novel chitosan-based graft copolymers (CECTS-g-PDMA) were synthesized through homogeneous graft copolymerization of (N,N-dimethylamino)ethyl methacrylate (DMA) onto N-carboxyethylchitosan (CECTS) in aqueous solution by using ammonium persulfate (APS) as the initiator. The effect of polymerization variables, including initiator concentration, monomer concentration, reaction time and temperature, on grafting percentage was studied. XRD, FTIR, DSC and TGA were used to characterize the graft copolymers. Surface-tension measurements, turbidity measurements and temperature-variable (1)H NMR analysis were combined to investigate the thermal sensitivity of CECTS-g-PDMAs in aqueous solution.     

Creating a unique environment for selecting reactive enzymes with DNA: 'Sticky' binding of oligocation-grafted polymers to DNA

To provide colloidally stable polyplexes formed between pDNA and cationic polymers, cationic polymers have been modified with hydrophilic polymers to form a hydrophilic shell. Block copolymers of cationic and hydrophilic polymers and cationic polymers grafted with hydrophilic polymers are representative designs of such polymers. Here, we report a new design of cationic polymers and oligocationic peptide-grafted polymers. We synthesized 15 kinds of graft copolymers by varying the number of cationic charges of the peptides and their grafting density. We found that graft copolymers with less cationic peptides and less grafting density formed colloidally stable polyplexes. Interestingly, the less cationic graft copolymers bind to excess amounts of pDNA. We also found that the graft copolymers showed selectivity toward reactive enzymes affording the reaction of pDNA with nucleases, while suppressing both the replication of DNA by DNA polymerase and gene expression. The suppression of the replication and expression is considered to result from the high capacity of the graft copolymers for binding with pDNA. The polynucleotides produced by DNA polymerase or RNA polymerase would be captured by the graft copolymers to impede these enzymatic reactions.     

Synthesis and characterization of the biodegradable polycaprolactone-graft-chitosan amphiphilic copolymers

A novel synthetic approach to biodegradable amphiphilic copolymers based on poly (epsilon-caprolactone) (PCL) and chitosan was presented, and the prepared copolymers were used to prepare nanoparticles successfully. The PCL-graft-chitosan copolymers were synthesized by coupling the hydroxyl end-groups on preformed PCL chains and the amino groups present on 6-O-triphenylmethyl chitosan and by removing the protective 6-O-triphenylmethyl groups in acidic aqueous solution. The PCL content in the copolymers can be controlled in the range of 10-90 wt %. The graft copolymers were thoroughly characterized by 1H NMR, 13C NMR, FT-IR and DSC. The nanoparticles made from the graft copolymers were investigated by 1H NMR, DLS, AFM and SEM measurements. It was found that the copolymers could form spherical or elliptic nanoparticles in water. The amount of available primary amines on the surface of the prepared nanoparticles was evaluated by ninhydrin assay, and it can be controlled by the grafting degree of PCL.     

Synthesis, characterization, and in vivo biodistribution of 125I-labeled Dex-g-PMAGGCONHTyr

Dextran graft poly (N-methacryloylglycylglycine) copolymer-tyrosine conjugates (dextran-g-PMAGGCONHTyr) were synthesized and characterized. Dynamic light scattering (DLS) results indicated that the graft copolymers are soluble in pH 7.4 PBS and 0.9% saline solutions. The graft copolymers were labeled with (125)I, and the labeling stability in 0.9% saline solution was investigated. Pharmacokinetics studies showed a rapid clearance of (125)I-labeled graft copolymers from the blood pool. Biodistribution images confirmed the preferable liver and spleen accumulation within 1 h after injection and rapid clearance from all the organs over time. The graft copolymer with molecular weight of 9.8 kDa was eliminated from the kidney significantly faster than those with higher molecular weight. The effect of the numbers of -COOH groups on the graft copolymers on the biodistribution was also investigated. It was found that the graft copolymers with the average number of -COOH groups per glucopyranose unit (DS(-COOH)) of 0.57 and 0.18 are mainly distributed in liver and spleen at 1 h after injection, whereas the graft copolymer with DS(-COOH) of 0.07 is mainly accumulated in kidney.     

Preparation and characterization of enzymes immobilized by graft copolymerization to different polysaccharides

A method of enzyme immobilization by graft copolymerization on polysaccharides is reported. Glycidylmethacrylate was used as a vinylating reagent and the reaction product with enzymes (HRP, GOD, Am, ChT) was copolymerized with different matrices (cellulose, Sepharose, Sephadex, Starch). Various factors affect the final activity of copolymers; these include the redox system, the type of support, and the quantity and type of vinyl monomer added. Using a fixed quantity of enzyme and support (3 mg enzyme, 100 mg support), the coupling efficiency varied from 2 to 50%. The most important characteristics in these immobilized systems were tested (stability in continuous washing, kinetic characteristics, storage, thermal, and lyophilization stability). Immobilized-enzyme graft copolymers have very similar kinetic behavior to that of the free enzyme. Diffusion is not seriously limited, as shown by kinetic parameters and energy activation values, and this indicates that the immobilization reaction does not alter the enzymatic activity.     

Synthesis, characterization, and degradation behavior of amphiphilic poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide]-g-poly(epsilon-caprolactone)

A series of biodegradable amphiphilic graft polymers were successfully synthesized by grafting poly(epsilon-caprolactone) (PCL) sequences onto a water-soluble poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide] (PHEA) backbone. The graft copolymers were prepared through the ring-opening polymerization of epsilon-caprolactone (CL) initiated by the macroinitiator PHEA with pendant hydroxyl groups without adding any catalyst. By controlling the feed ratio of the macroinitiator to the monomer, the copolymers with different branch lengths and properties can be obtained. The successful grafting of PCL sequences onto the PHEA backbone was verified by FTIR, 1H NMR, and combined size-exclusion chromatography and multiangle laser light scattering (SEC-MALLS) analysis. The hydrolytic degradation and enzymatic degradation of these graft copolymers were investigated. The results show the hydrolytic degradation rate increases with increasing content of hydrophilic PHEA backbone. While the enzymatic degradation rate is affected by two competitive factors, the catalytic effect of Pseudomonas cepacia lipase on the degradation of PCL branches and the hydrophilicity which depends on the copolymer composition. In situ observation of the degradation under polarizing light microscope (PLM) demonstrates the different degradation rates of different regions in the polymer samples.     

Functionalization of cellulosic fibers by graft copolymerization of acrylonitrile and ethyl acrylate from their binary mixtures

Functionalization of Agave fibers was carried out by graft copolymerization of acrylonitrile (AN) and ethyl acrylate (EA) from their binary solutions in presence of Ce (IV) ions at a temperature of 45 ± 0.1 °C. An increase in the graft copolymerization was obtained with the increase in the feed molarity of the comonomers up to certain extent. Contrary to lesser affinity of acrylonitrile to grafting on Agave fibers, a synergistic effect of ethyl acrylate on acrylonitrile was observed when graft copolymers were prepared using different feed compositions (f_AN). The graft copolymers were characterized by various techniques such as FT-IR, TGA/DTA, X-RD and SEM analysis. Further swelling behavior of grafted fibers in different solvents, moisture absorption behavior and resistance to chemicals was investigated as a function of percent grafting to define their end uses in different environments.     

A new method of controlled grafting modification of chitosan via nitroxide-mediated polymerization using chitosan-TEMPO macroinitiator

The controlled graft modification of chitosan has first been achieved by nitroxide-mediated polymerization using chitosan-TEMPO macroinitiator. Chitosan-TEMPO macroinitiator was obtained from the (60)Co gamma-ray irradiation of N-phthaloylchitosan and 4-hydroxy-TEMPO in DMF under argon atmosphere. The graft copolymers were characterized by (1)H nuclear magnetic resonance ((1)H NMR), Fourier transform infrared spectrometer (FT-IR), X-ray powder diffractometer (XRD) and high performance particle sizer (HPPS). The results indicate that the graft copolymers were successfully synthesized and that the graft polymerization was well controlled by the nitroxide-mediated process. The size distribution of chitosan-g-polystyrene in benzene is very narrow, which may be associated with the "well-defined" polystyrene (PSt) onto chitosan from nitroxide-mediated polymerization. This work provides a new method to prepare chitosan grafting copolymers with controlled molecular weights and "well-defined" structures.     

Synthesis and characterization of polymeric soybean oil-g-methyl methacrylate (and n-butyl methacrylate) graft copolymers: biocompatibility and bacterial adhesion

Peroxidation, epoxidation, and/or perepoxidation reactions of soybean oil under air at room temperature resulted in cross-linked polymeric soybean oil peroxides on the surface along with the waxy soluble part, sPSB, with a molecular weight of 4690, containing up to 2.3 wt % peroxide. This soluble polymeric oil peroxide, sPSB, initiated the free radical polymerization of either methyl methacrylate (MMA) or n-butyl methacrylate (nBMA) to give PSB-g-PMMA and PSB-g-PnBMA graft copolymers. The polymers obtained were characterized by (1)H NMR, thermogravimetric analysis, differential scanning calorimetry, and gel permeation chromatography techniques. Polymeric oil as a plasticizer lowered the glass transition of the PSB-g-PMMA graft copolymers. PSB-g-PMMA and PSB-g-PnBMA graft copolymer film samples were also used in cell culture studies. Fibroblast and macrophage cells were strongly adhered and spread on the copolymer film surfaces, which is important in tissue engineering. Bacterial adhesion on PSB-g-PMMA graft copolymer was also studied. Both Staphylococcus epidermidis and Escherichia coli adhered on the graft copolymer better than on homo-PMMA. Furthermore, the latter adhered much better than the former.     

Supramolecular hydrogels formed from biodegradable ternary COS-g-PCL-b-MPEG copolymer with α-cyclodextrin and their drug release

On the basis of the synthesis of novel biodegradable amphiphilic MPEG-b-PCL-grafted chitooligosaccharide (COS-g-PCL-b-MPEG) copolymers, supramolecular hydrogels were fabricated rapidly via their inclusion complexation with α-cyclodextrin (α-CD) in aqueous solutions. The graft copolymers were characterized by ¹H NMR spectroscopy, gel permeation chromatography (GPC), and fluorescence measurement, and the supramolecular structure of the resultant hydrogels was confirmed by X-ray diffraction measurements. Rheological studies of as-obtained hydrogels indicate that the physical properties could be modulated by controlling the concentration and the graft content of the graft copolymers as well as the molar feed ratio of the graft to α-CD. The in vitro release kinetics studies of bovine serum albumin (BSA) entrapped in the hydrogels show that the drug release profiles are dependent on the supramolecular hydrogel compositions.     

Synthesis of graft copolymer (CgOH-g-AGA): Physicochemical properties, characterization and application

A graft copolymer of κ-carrageenan and 2-acrylamidoglycolic acid (CgOH-g-AGA) was synthesized via free radical polymerization initiated by potassium peroxymonosulphate/malonic acid redox pair. For affording maximum percentage of grafting, optimum conditions were determined by varying the concentrations of κ-carrageenan, 2-acrylamidoglycolic acid, potassium peroxymonosulphate, malonic acid, hydrogen ion, time and temperature. The swelling, metal ion uptake and flocculation studies were investigated with water, three metals (Ni(2+), Pb(2+) and Zn(2+)) solutions, coal (coking and non-coking) suspensions, respectively. Both, polymer backbone and its corresponding graft copolymer samples were characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis.     

Graft copolymerization of methyl methacrylate onto mercaptochitin and some properties of the resulting hybrid materials

The graft copolymerization of methyl methacrylate onto mercaptochitin and some properties of the resulting graft copolymers have been studied. Methyl methacrylate was efficiently graft copolymerized onto mercaptochitin in dimethyl sulfoxide, and the grafting percentage reached 1300% under appropriate conditions. Although the side-chain ester groups were resistant to aqueous alkali, hydrolysis could be achieved with a mixture of aqueous sodium hydroxide and dimethyl sulfoxide. Subsequent treatment with acetic anhydride in methanol transformed the sodium carboxylate groups into carboxyl groups. Although the graft copolymers exhibited an improved affinity for organic solvents, those having sodium carboxylate or carboxyl units were characterized by a much more enhanced solubility and were soluble in common solvents. The hygroscopic nature of chitin decreased with an increase in the grafting extent but increased significantly upon hydrolysis of the ester groups. The enzymatic degradability of the graft copolymers, as evaluated with lysozyme, was also dependent on the grafting extent and much higher than that of the original chitin. DSC measurements revealed the presence of a glass transition phenomenon, which could be ascribed to the poly(methyl methacrylate) side chain.     

Adsorption of chromium and zinc ions from aqueous solutions by cellulosic graft copolymers

Cellulosic graft copolymers were prepared by the reaction of bast fibers of the kenaf plant (Hibiscus cannabinus) with acrylonitrile and methacrylonitrile monomers in aqueous media initiated by the ceric ion-toluene redox pair. The cellulose-polyacrylonitrile (Cell-PAN) and cellulose-polymethacrylonitrile (Cell-PMAN) graft copolymers were used for the removal of Zn(II) and Cr(III) ions from aqueous solutions at 30°C. Zn(II) ion was more sorbed than Cr(III) ion by both copolymers by an average factor of 1.80 ± 0.40. For each metal ion, the Cell-PAN graft copolymer was a more effective sorbent than the Cell-PMAN derivative. The amount of ion sorbed decreased with an increase in percentage graft and over the range 38–149% of the graft the amounts of Zn(II) and Cr(III) ions sorbed by Cell-PAN decreased by 44% and 56%, respectively.     

Kinetic and thermal characteristics of enzyme-graft copolymers

The characteristics of horseradish peroxidase (HRP) immobilized onto Sepharose by a photochemical-initiated graft copolymerization are presented. Active copolymers were synthesized using different amounts of glycidylmethacrylate (GMA), bisacryloylpiperazine (BAP), or 1,3,5-hexhydrotriacryloyl-(s)-triazine (HTsT) as functional monomer. The activities, the K'(m) values (pGMA) copolymers: 0.53-0.76 x 10(-4)M; pBAP copolymers: 0.90-1.4 x 10(-4); pHTsT copolymers: 1.8-2.6 x 10(-4)M and the thermal stabilities of the enzyme copolymers were strictly connected to the type of polymer. By varying the polymer amount present in a given copolymer, significant differences were found in the thermostability properties of pBAP and pHTsT copolymers both when checked in water or in phosphate buffer. No differences were found for pGMA copolymers. The samples in which there are the lowest pBAP or pHTsT content resulted the most stable. The activity retained after 240 min at 60 degrees C by free HRP and pGMA-HRP was 30% whereas by pBAP-HRP and pHTsT-HRP it was 50 and 75% of the original. Operational stability of the materials was in agreement with thermostability data. These results are discussed in terms of enzyme microenvironment which is strongly affected by the different network of the three polymers.     

Characterization and evaluation of methyl methacrylate-acetylated Saccharum spontaneum L. graft copolymers prepared under microwave

Hybridization of the natural polymers with synthetic polymers is of great interest because of its application to biomedical and biodegradable materials. Synthesis of graft copolymers of methyl methacrylate (MMA) onto acetylated Saccharum spontaneum L. fiber using ferrous ammonium sulphate–potassium per sulphate (FAS–KPS) redox initiator under the influence of microwave radiation (MWR) was carried-out. Different reaction parameters such as time, initiator molar ratio, monomer concentration, microwave power, pH and solvent were optimized to get maximum graft yield (72.2%). On grafting, percentage crystallinity decreases rapidly with reduction in its stiffness and hardness. The graft copolymers thus formed were characterized by FTIR, SEM, XRD, TGA, DTA and DTG techniques. Moreover, graft copolymers have been found to be more moisture resistant and also showed higher chemical and thermal resistance.     

Graft copolymerization of amino acids onto partially deacetylated chitin

Novel graft copolymers have been synthesized by the reaction of N-carboxyanhydrides of amino acids with partially deacetylated chitins. The graft copolymers had different swelling ability from the original chitin.