Synthesis and Characterization of Chitosan‐graft‐Poly(3‐(trimethoxysilyl)propyl methacrylate) Initiated by Ceric (IV) Ion

The grafting of 3‐(trimethoxysilyl)propyl methacrylate (TMSPM) onto chitosan by ceric ion initiation was studied under homogeneous conditions in 2% acetic acid solution. The grafted polymer was characterized by FT‐IR, ¹H‐NMR, TGA and XRD and swelling studies. TGA results showed that the incorporation of TMSPM to the chitosan chains decreased the thermal stability of the grafted chitosan. Due to the grafting of TMSPM, the crystallinity of chitosan derivatives was found to be destroyed. The solubility of the grafted chitosan in water was improved. The effects of reaction conditions such as initiator concentration, monomer concentration, reaction temperature and reaction time were studied by determining the grafting parameters such as grafting and grafting efficiency. Under optimum conditions, the grafting parameters were achieved as 1440 and 97%, respectively.     

On the Modification of Chitosan Through Grafting

Abstract

The feasibility of grafting poly(methyl acrylate) and poly[1-(methoxycarbonyl) ethylene] onto chitosan, poly-β(1←-4)-2-amino-2-deoxy-d-glucose, was investigated. The grafting reaction was carried out in aqueous solution by using ferrous ammonium sulfate (FAS) in combination with H₂O₂ as redox initiator. The effects of such reaction variables as chitosan, monomer and initiator concentrations, reaction time, and reaction temperature were determined. Through this study the grafting reaction could be optimized. The grafting yield reached its maximum value of 332% when 0.3 g chitosan was copolymerized with 3 mL monomer at 70°C for 120 minutes with [FAS] = 6 × 10^?5 M, [H₂O₂] = 6 × 10^?3 M, and 8 mL water. The grafted chitosan was found to be insoluble in solvents for chitosan and solvents for poly(methyl acrylate), but did show swelling in dilute acetic acid, methanol, acetone, and in an ethanol/2% acetic acid 1:1 mixture. The thermal stability of chitosan and grafted chitosan were studied by dynamic thermogravimetric analysis. The results show that the graft copolymer is thermally more stable than pure chitosan. The overall activation energy for graft copolymerization was estimated to be 32.8 kcal/mol.     

Synthesis of PVC‐g‐PS through stereoselective nucleophilic substitution on PVC

The substitution reaction of poly(vinyl chloride) (PVC) with sodium azide was performed in cyclohexanone. The evolution of unreacted iso‐, hetero‐ and syndiotactic triad contents with the degree of substitution has been followed by ¹³C NMR spectroscopy. By quantitatively comparing the microstructure changes with degree of substitution, taking into account that the reaction is of S_N2 type, only the mechanisms of substitution through the mm triad of mmr tetrad and the rm of rrmr pentads are shown to react. This conclusion was confirmed by FT‐IR. From this stereospecific chemical modification of PVC, the thermal decomposition of azide‐modified PVC and the consequent reaction with styrene offer a method for the preparation of stereoselective graft copolymers. After grafting, no variation of the microstructure of the chain has been demonstrated. These results have been used to study the effect of the aforementioned structures on the evolution of density as a function of free‐volume of the graft copolymers, and thus provide new approaches to a better understanding of the structure‐properties relationships at the molecular level. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2476–2486, 2006     

New associative EHEC‐g‐PAam copolymers: Their syntheses,characterization, and rheological behavior

The syntheses and rheological behavior of ethyl hydroxyethyl cellulose (EHEC)‐based graft‐copolymers were studied. Copolymers were prepared by grafting EHEC with acrylamide (Aam) via reversible addition fragmentation chain transfer (RAFT) polymerization. Hydroxyl groups of EHEC were esterified with a carboxylic acid functional chain transfer agent (CTA) to prepare EHEC‐macroCTAs with different degrees of substitution. EHEC‐macroCTAs were characterized by ATR‐FTIR, ¹³C NMR, and SEC, and elemental analysis was used to quantify the degree of CTA substitution. EHEC‐macroCTAs with different degrees of substitution were copolymerized with acrylamide by “grafting from” technique. Formation of new cellulose‐based copolymers was comprehensively confirmed by ¹H NMR, ATR‐FTIR, and SEC measurements. Further, the associations of EHEC‐g‐PAam copolymers in water were studied at various concentrations and temperatures by means of UV–vis spectroscopy, fluorescence spectroscopy, and rheological measurements. The results indicate that copolymers have both intra and intermolecular association in water depending on the amount of grafts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1869–1879, 2009     

Graft copolymerization of methyl methacrylate onto curdlan

Graft copolymerization of methyl methacrylate onto curdlan was first investigated. In the graft copolymerization initiated by ammonium persulfate (APS) in DMSO under a homogeneous condition, the resulting graft copolymers had low molecular weights and low grafting percentages. However, the initiation by APS in water gave graft copolymers having relatively higher molecular weight ( ) and higher grafting percentage (548%) than those copolymers obtained by the homogeneous condition. When the graft copolymerization was carried out by cerium (IV) ammonium nitrate-HNO₃ initiation, the graft copolymer had the highest grafting percentage of 1620% without degradation of the curdlan backbone. The resulting graft copolymers were soluble in DMSO. The graft copolymers obtained by the cerium salt had narrow molecular weight distributions () compared with those by the APS catalyst in DMSO or water. The graft copolymers decomposed with sulfuric acid to isolate PMMAs, which molecular weights were larger than that of the corresponding homo-PMMAs. The structure of the grafted copolymers was characterized by IR, ¹³C NMR, DSC, and SEM. It was found that the graft copolymers exhibited the glass transition temperature (T_g), though curdlan had no T_g. As the grafting percentage increased, the T_g increased to reach 270°C, which was higher than the decomposition temperature of curdlan. The surface image of the grafted copolymers observed by SEM, showed smoothless compared with that of curdlan. It was also revealed that the graft copolymers having the grafting percentage of 1620% swelled in common organic solvents up to 4.5 times of the weight of the dry graft copolymer to form gels. © 1996 John Wiley & Sons, Inc.     

Thermo-responsive microfibrillar graft copolymer based on carboxymethylagarose and N-isopropylacrylamide

Carboxymethylation of agarose with ClCH₂COOH in 2-propanol, formamide or dimethyl sulfoxide were evaluated in order to obtain water soluble derivatives. Higher yield (86%) and degree of substitution of carboxymethylation in primary alcoholic groups (0.70) were obtained using dimethyl sulfoxide. Carboxymethylagarose-g-PNIPAAm copolymers were synthesized by free radical graft copolymerization using Ce⁴⁺ and S₂O₈²⁻/TEMED as initiators via conventional or microwave-assisted methods. Carboxymethyl derivatives and graft copolymers were characterized by FT-IR and NMR spectroscopies, elemental analysis, TGA and DSC and morphology analysis by SEM and AFM. High nitrogen content (9.7%) was found with Ce⁴⁺ by conventional method and the obtained analysis allowed to confirm the NIPAAm grafting on the carboxymethylagarose chain. Thermoresponsive materials have a low critical solution temperature between 32 and 34 °C. Thermal stability increased ca. 60% with PNIPAAm grafting. Surface analysis of copolymers reveals a microfibrillar type morphology with diameter of 4–6 μm. Synthesized glycoconjugates could find applications in bioactive compounds transport in biological systems.     

Copolymerization behavior of direct polycondensation of AB2 and AB monomers that forms hyperbranched aromatic polyamide copolymers

The copolymerization behavior of the one‐step direct polycondensation of 3,5‐bis‐(4‐aminophenoxy)benzoic acid (AB₂ monomer) and 3‐(4‐aminophenoxy)benzoic acid (AB monomer) was investigated by IR and ¹³C NMR measurements. IR measurements revealed that the content of the AB₂ units in the polymer was higher in the early stages of polymerization. ¹³C NMR spectra of the polymers indicated that the number of dendritic units increased slowly with increasing reaction time. The stepwise copolymerization of the AB₂ and AB monomers was also carried out, and the structure was analyzed by ¹³C NMR measurements. Copolymer synthesized stepwise by adding AB₂ monomer first (polymer II ) had more dendritic units and less terminal units as compared with the one‐step copolymer (polymer I ). Copolymer synthesized stepwise by adding AB monomer first gave a resulting copolymer (polymer III ) composed of long AB chains. The solubility of the stepwise copolymers was low, and the inherent viscosity was high in comparison with the one‐step copolymer as a result of the difference in architecture of the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3304–3310, 2001     

Preparation and characterization of chitosan‐graft‐poly (ϵ‐caprolactone) with an organic catalyst

Chitosan‐graft‐poly(ϵ‐caprolactone) was prepared via the ring‐opening graft polymerization of ϵ‐caprolactone (CL) through chitosan with 4‐dimethylaminopyridine as a catalyst and water as a swelling agent. The graft content of PCL within the graft copolymer was adjusted by the feed ratio of CL to chitosan, and the highest grafting concentration of PCL was up to about 400%. Fourier transform infrared, ¹H NMR, and two‐dimensional heteronuclear single quantum coherence analyses indicated that the amino group (NH₂ CH‐2) of chitosan initiated the graft polymerization of CL through the backbone of chitosan, and the hydroxyl group (HO CH_2–6) of chitosan did not participate in initiating the graft polymerization. The percentage of amino groups initiating the graft polymerization decreased with an increasing molar ratio of CL to chitosan in the feed, and this was attributed to the fact that the graft polymerization system increasingly became heterogeneous with an increasing feed ratio of CL to chitosan. The physical properties of the graft copolymers were characterized by thermogravimetric analysis and wide‐angle X‐ray diffraction, respectively. These suggested that the introduction of PCL grafts through the chitosan backbone would to some extent destroy the crystalline structure of chitosan, and the PCL grafts existed in an amorphous structure. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5353–5361, 2006     

壳聚糖与N-异丙基丙烯酰胺接枝共聚凝胶的辐射合成及性能研究

采用γ辐射技术引发壳聚糖与N异丙基丙烯酰胺进行接枝共聚,制备了温度及pH敏感水凝胶.研究了单体浓度、辐射剂量等对接枝率和接枝效率的影响,并用13CCPMASNMR和TG表征了接枝物的结构.研究结果表明,用γ射线引发壳聚糖接枝异丙基丙烯酰胺具有较高的接枝率和接枝效率,接枝的聚合物具有明显的温度及pH敏感的特点.     

Grafting of living poly(ethylene oxide) onto polystyrene via aromatic nucleophilic displacement of activated nitro groups

Polystyrene of M?_ω = 2.2 × 10⁴ was alkylated with 4-nitrophthalimidomethyl groups as grafting sites. Several backbone polymers with various degrees of grafting sites (G = 2–100%) were prepared and characterized by elemental analysis, IR, ¹H- and ¹³C-NMR, and viscosity measurements. “Living” poly(ethylene oxide) with narrow molecular-weight distribution was prepared in the presence of 15-crown-5, and grafted onto the 4-nitrophthalimidomethylated polystyrene. The nitro displacement reaction was fast and the grafting yield was quantitative (100%). The graft copolymers are highly soluble in water and in organic solvents. The intrinsic viscosities of the graft copolymers are higher than those of the backbone polymers. The intrinsic viscosities show an initial increase followed by a decrease as the degree of grafting increase.     

Homogeneous graft copolymerization and characterization of novel artificial glycoprotein: Chitosan‐poly(L‐tryptophan) copolymers with secondary structural side chains

A novel series of artificial glycoprotein, peptide‐chitosan copolymers with secondary structural side chain have been synthesized by ring‐opening polymerization of L ‐tryptophan N‐carboxyanhydride under homogeneous conditions. Their chemical structures and polymerization degree (DP) were characterized by IR, ¹³C NMR, and XRD spectra. Distinctly secondary protein structure has been found in the poly‐L ‐tryptophan side chains of copolymers and with the lengthening of side chain (i.e., the increase of DP at the same time), its conformations could transfer from β‐sheet to α‐helix. The content of α‐helix reaches about 41% when DP of polytryptophan is 22. The solubility of graft copolymers in polar solvent strongly depends on the length of poly‐L ‐tryptophan side chains. Unique fluorescence emission at 360 nm has been observed in the glycopolymers and the intensity shows the positive‐correlation with the increasing of DP of polytryptophan. Importantly, the fluorescence effect can be quenched easily by the coordination with copper ions which provides the possibility on the biosensor design. In comparison with chitosan, glycopolymers also present impressively enhanced compressive strength and elastic modules when it is blended with epoxy E 44 to form epoxy‐copolymer hybrid resin. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 925–934, 2009     

Dihydrophilic block copolymers with ionic and nonionic blocks. I. Poly(ethylene oxide)‐b‐polyglycidol with OP(O)(OH)2, COOH,or SO3H functions: Synthesis and influence for CaCO3 crystallization

Dihydrophilic block copolymers of poly(ethylene oxide)‐b‐polyglycidol were prepared and polyglycidol blocks converted into ionic blocks containing  OP(O)(OH)₂,  COOH, or  SO₃H groups. Although phosphorylation of polyhydroxy compounds with POCl₃ usually leads to insoluble products, phosphorylation of poly(ethylene oxide)‐b‐polyglycidol using a POCl₃/ OH ratio equal to 1/1 gave soluble products, predominantly monoester of phosphoric acid (after hydrolysis) (provided that the reaction was conducted in triethyl phosphate as solvent). All copolymers were characterized by ¹H NMR, ¹³C NMR, and/or ³¹P NMR spectra for confirming their structure. The degree of substitution was determined from quantitative ¹³C NMR spectroscopy (inverted‐gate decoupling‐acquisition mode). Preliminary results indicate that from these three groups of block copolymers the phosphoric acid esters are the most effective ones at least in controlling the growth of CaCO₃ crystals in aqueous solution. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 955–963, 2001     

Chitosan-graft-poly(ϵ-caprolactone)s: An optimized chemical approach leading to a controllable structure and enhanced properties

A novel synthetic approach was developed for the controllable modification of chitosan (CS) with poly(ϵ-caprolactone) (PCL). 6-O-Triphenylmethyl-chitosan (TMCS) was synthesized as a highly soluble intermediate in organic solvents to facilitate an efficient grafting reaction of PCL onto CS in a homogeneous reaction medium. Subsequently, the syntheses of CS-g-PCL copolymers with different degrees of substitution (ds) and various chain lengths of PCL (number-average molecular weight = 1200–11,000) were carried out by a coupling reaction between the carboxylic terminal groups of PCL chains and the amino groups of TMCS. The successful grafting reaction was confirmed by GPC measurements, which indicated that the products were graft copolymers rather than physical blends. The ds, defined as the number of PCL chains per saccharide unit, of the graft copolymers could be adjusted simply by changes in the molar feed ratios of PCL to CS, and graft copolymers with different ds values ranging from 0.28 to 0.49 were synthesized, as calculated by ¹H NMR and elemental analysis. DSC and X-ray measurements showed that the melting temperature and enthalpy of the PCL grafts of these graft copolymers could be adjusted by the ds and the chains length of PCL, respectively. Meanwhile, the CS-g-PCL copolymers exhibited better solubility in various solvents, such as in chloroform for some of the resultant graft copolymers, than the original CS. Finally, nanoparticles of 100–200 nm, having hydrophobic PCL domains and cationic hydrophilic surfaces, were obtained through the self-assembly of the copolymers in selective solvents. These types of graft copolymers have great potential in various applications, such as targeted drug and gene delivery as well as tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2556–2568, 2007     

Ionic conductivity and tensile properties of hydroxyethyl and hydroxypropyl chitosan membranes

Hydroxyethyl chitosan and hydroxypropyl chitosan were prepared through the reaction of alkali‐chitosan with 2‐chloroethanol and propylene epoxide, respectively. Fourier transform infrared and ¹³C NMR measurements were made to examine the substitution on the chitosan unit. According to a comparison of the peak areas between the modified chitosan and unmodified chitosan and the integration of peak areas of ¹H NMR spectra, for both modified chitosans, the maximum degree of substitution was less than 25%. The ionic conductivity and mechanical properties of modified chitosan membranes were investigated. In comparison with the unmodified chitosan membrane, hydrated hydroxyethyl and hydroxypropyl chitosan membranes with a higher degree of substitution showed an increase in ionic conductivity of about one order of magnitude; moreover, the crystallinity of hydroxyethyl and hydroxypropyl chitosan membranes was remarkably reduced, and their swelling indices increased significantly. However, these modified membranes did not exhibit significant changes in their tensile strength and breaking elongation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1379–1397, 2004     

Graft copolymerization of methacrylic acid onto carboxymethyl chitosan

Carboxymethyl chitosan (CMCTS) was prepared and characterized by FTIR, ¹H NMR, and elemental analysis. The graft copolymerization of methacrylic acid (MAA) onto CMCTS using ammonium persulfate (APS) as an initiator was carried out in an aqueous solution. Evidence of grafting was obtained by comparison of FTIR spectra of CMCTS and the grafted copolymer as well as solubility characteristics of the products. The effects of APS, MAA, reaction temperature and time on graft copolymerization were studied by determining the grafting parameters such as grafting percentage and grafting efficiency. With keeping other conditions constant, the optimum conditions were shown as following: [APS]=8 mmol/l, [MAA]=2.4 mol/l, reaction temperature=60-70 °C, reaction time=120 min.     

Preparation of a sorbent for metal ions based on N-(5-methylimidazol-4-ylmethyl) chitosan with medium degree of substitution

A procedure was developed for preparing a heterocycle-containing chelating amino polymer, N-(5-methylimidazol-4-ylmethyl) chitosan, by polymer-analogous transformations of chitosan in reaction with 4-chloromethyl-5-methylimidazole. The procedure allows synthesis of the polymer with the degree of substitution of up to 0.8, with simultaneous formation of the cross-linked structure. The structure of the polymers prepared was proved by IR and ¹³C NMR spectroscopy. The ability of N-(5-methylimidazol-4-ylmethyl) chitosan with the degree of substitution of 0.54 to sorb Cu²⁺ and Ni²⁺ ions was evaluated. According to the sorption isotherms, the sorption capacity of this derivative exceeds that of the unmodifi ed polymer by a factor of 5.     

Grafting of 1-Cyanoethanoyl-4-acryloylthiosemicabazide onto Chitosan and Biocidal Activity of the Graft Copolymers

Chitosan was grafted with a novel monomer 1-Cyanoethanoyl-4-acryloylthiosemicabazide (CEATS). The graft copolymerization was conducted using potassium persulfate (K₂S₂O₈) and sodium bisulfite (NaHSO₃) as redox initiators. The grafted samples were characterized by FTIR spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. The data may indicate that grafting has occurred at the surface of chitosan. The grafted samples showed high water swelling. The antifungal behavior of chitosan and its graft copolymers was investigated in vitro and it has been found that grafting with CEATS noticeably enhances the antifungal activity.     

An Improved Synthetic Method for Preparing Polyoxyethylene Macromers and a Study of Their Copolymerization with Alkyl Acrylates

Polyoxyethylene macromers were synthesized by polymerization of ethylene oxide in dimethylsulfoxide by using potassium napthalide in tetrahydrofuran as initiator, followed by termination with methacroyl chloride. Potassium naphthalide is more active as an initiator than sodium naphthalide. The initiator in this case was confirmed to be of the monoanionic type. The molecular weight of the macromers can be varied from 2 × 10³ to 1.2 × 10⁴with M_w/M_n = 1.07-1.12. The macromers were characterized by UV, IR, and ¹H NMR, and copolymerized with butyl acrylate, methyl acrylate, or methyl methacrylate. The grafting efficiency can reach about 90%. The graft copolymers were purified by extractions and characterized by GPC, IR, and a Bruss membrane osmometer. The average grafting number of the copolymers varied from 10 to 15.     

On some regularities of grafting of vinylpyridine derivatives onto acetyle cellulose

The radical graft copolymerization of vinylpyridine derivatives onto acetyl cellulose was investigated using Fe²⁺/H₂O₂ redox system as an initiator. It was proved that the addition of hydrazine hydrate increased the degree of grafting many times. The reaction mechanism of hydrazine hydrate was also investigated. A. correlation between nitrogen content and the total anion exchange capacity was established. The vinylpyridine derivatives were ordered according to their reactivity. The effects of reaction conditions on the total anion-exchange capacity, the total conversion, the degree of grafting, and the grafting efficiency of the copolymers obtained were examined. The copolymers were characterized by IR and H-NMR spectra, thermogravimetric analysis, elemental analysis, and total anion-exchange capacity.     

Recent advances in molecuar and supermolecuar characterization of cellulose and cellulose derivatives

Recent advances between 1985 and early 1993 in the following topics of the characterization of molecular structure and molecular properties of cellulose and its derivates (CD) made in the authors' laboratories are briefly reviewed: (1) A theoretical basis of the assignment of carbonyl carbon peaks of ¹³C NMR spectra on cellulose acetate (CA) was given, especially when the total degree of substitution <<f>> is below 3. (2) Molar fractions of 8 kinds of unsubstituted and partially or fully substituted anhydroglucopyranose units were successfully determined for CA and sodium cellulose sulfate (NaCS). (3) The sequence distribution of substituted and unsubstituted anhydroglucopyranose units along a water–soluble CA chain was evaluated. (4) C₆-substituted (i.e., 6-O-acetyl) CA and C₂- and C₆-substituted CA were synthesized, and the full assignment of the ¹³C NMR spetrum of the former was given and a new method for evaluating the degree of substitution at C₆ position was proposed. (5) By destructing the intramolecular hydrogen bonding, cellulose becomes soluble in aq. sodium hydroxide. The specific supermolecular structure of aq. sodium hydroxide, dissolving mechanism, dissolved state and molecular parameters of cellulose in aq. sodium hydroxide were discussed. (6) The solubility behavior of CA with a wide range of total degree of substitution in solvents including water, acetone/water and acetone is controlled by the distribution of substitution and the supermolecular structure. (7) The existence of O₃-H … O'₅ intramolecular hydrogen bonds in a water-in soluble cellulose derivative with hydrophilic substituent (NaCEC) was confirmed by CP/MAS ¹³C NMR and deuteration IR method. At a relatively low degree of substitution the solubility of the derivative in water or aqueous alkali was mainly governed by considerable destruction of the intramolecular hydrogen bonds. (8) The persistence length q, evaluated directly by small-angle X-ray scattering (SAXS) on CA with different total degree of substitution <<f>> ranging from 0,8 to 2,9 confirmed definitely the conclusion drawn before by Kamide and Saito on the molecular rigidity of CD, especially the effect of <<f>> on q. (9) C₆-substituted CA shows different solubility towards dimethylacetamide and water at 20°C, as compared with C₂- and C₃-subsituted CA and C₂-, C₃- and C₆- substituted CA, whose <<f>> is ca. 0,6.