Improvement of the mechanical properties of chitosan films by the addition of poly(ethylene oxide)

The mechanical properties of films prepared from mixed acetic acid aqueous solutions of chitosan (M_w = 400,000; M_w/M_n = 3.8) and poly(ethylene oxide) (PEO) (viscosity average molecular weight of 200,000 or 600,000) were determined. A chitosan:PEO weight ratio of 10:2 improved the mechanical properties compared with pure chitosan films. The improvement of the mechanical properties correlated with a small reduction of the correlation length measured by small‐angle neutron scattering (SANS).     

Free radical scavenging activity of cellulase‐treated chitosan

Partially N‐acetylated chitosan was hydrolyzed by the cheap, commercially available, and efficient cellulase. The products, with different molecular weight, were comparatively investigated by GPC, FT‐IR, XRD, and NMR. The results show that the decrease of molecular weight led to transformation of crystal structure and increase of water‐solubility, but the chemical structures of residues were not modified. Superoxide anion radical and hydroxyl radical quenching assay were used for the evaluation of free radical scavenging activity of cellulase‐treated chitosan in vitro. Low molecular weight chitosan (LMWC3, M_w 1.7 × 10³) exhibited high scavenging activity against free radical. It scavenged 79.3% superoxide radical at 0.1 mg mL^?1. At 2.0 mg mL^?1, scavenging percentage of initial chitiosan, LMWC1 (M_w 27.3 × 10³), LMWC2 (M_w 5.9 × 10³), and LMWC3 (M_w 1.7 × 10³) against hydroxyl radical was 14.3%, 33.1%, 47.4%, and 65.9%, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of ternary‐copolymer of soluble fluorinated polyimides based on 1,4‐bis (4‐amino‐2‐trifluoromethylphenoxy) benzene

A series of novel ternary‐copolymer of fluorinated polyimides (PIs) were prepared from 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene (pBATB), commercially available aromatic dianhydrides, and aromatic diamines via a conventional two‐step thermal or chemical imidization method. The structures of all the obtained PIs were characterized with FTIR, ¹H‐NMR, and element analysis. Besides, the solubility, thermal stability, mechanical properties, and moisture uptakes of the PIs were investigated. The weight‐average molecular weight (M_w) and the number‐average molecular weight (M_n) of the PIs were determined using gel‐permeation chromatography (GPC). The PIs were readily dissolved not only in polar solvents such as DMF, DMAc, and NMP, but also in some common organic solvents, such as acetic ester, chloroform, and acetone. The glass transition temperatures of these PIs ranged from 201 to 234°C and the 10% weight loss temperatures ranged from 507 to 541°C in nitrogen. Meanwhile, all the PIs left around 50% residual even at 800°C in nitrogen. The GPC results indicated that the PIs possessed moderate‐to‐high number‐average molecular weight (M_n), ranging from 9609 to 17,628. Moreover, the polymer films exhibited good mechanical properties, with elongations at break of 8–21%, tensile strength of 66.5–89.8 MPa, and Young's modulus of 1.04–1.27 GPa, and low moisture uptakes of 0.54–1.13%. These excellent combination properties ensure that the polymer could be considered as potential candidates for photoelectric and microelectronic applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of water‐soluble chitosan

An improved method of preparing water soluble chitosan was studied by N‐acetylation with acetic anhydride. Its merits were a simple processing technique, very short reaction time, little agent, high molecular weight of the product, and good water solubility. This article not only discusses the effect of several factors, such as the amount of reactants, concentration of hydrogen ions in the solution, and solvent system, on N‐acetylation but also some influential factors on the water solubility of N‐acetylated chitosan. Experiments showed that the amount of acetic anhydride was the most important factor affecting the N‐acetylation degree of the chitosan. The effect of the means of adding materials and the amount of solvent on the reaction could not be ignored. The solubility of half N‐acetylated chitosan was not changed with an increase in the molecular weight in water, and the water solubility decreased with increasing molecular weight in the alkaline region. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3497–3503, 2004     

Synthesis,Characterization, and Performance of a Novel Polymeric Cationic Surfactant Based on Low Molecular Weight Chitosan and 3‐Chloro‐2‐Hydroxypropyl Dimethyl Dehydroabietyl Ammonium Chloride (CHPDMDHA)

A series of novel polymeric cationic surfactants based on low molecular weight chitosan (LWCS) and 3‐chloro‐2‐hydroxypropyl dimethyl dehydroabietyl ammonium chloride (CHPDMDHA), LWCS‐g‐CHPDMDHA, were obtained by the grafting modification of LWCS with CHPDMDHA as grafting agent. The structure of LWCS‐g‐CHPDMDHA was confirmed by FT‐IR and ¹H NMR, and the degree of quaternizing substitution (DS) of LWCS‐g‐CHPDMDHA was determined according to the results of elemental analysis. The aggregation behavior and surface activities of LWCS‐g‐CHPDMDHA in aqueous solution were investigated by transmission electron microscopy (TEM) and determination of surface tension, respectively. The experimental results showed that the DS and molecular weight (M_w) of LWCS have significant influence on the critical micelle concentrations (CMC) and the surface tensions at the CMC (γ_cmc). The shape of aggregates changed with the variation of concentration of LWCS‐g‐CHPDMDHA in aqueous solution. When the LWCS‐g‐CHPDMDHA was utilized as an emulsifier, the increase of DS of LWCS‐g‐CHPDMDHA and M_w of LWCS were favorable for improving the stability of emulsions composed of water and benzene.     

Effect of sonolysis on kinetics and physicochemical properties of treated chitosan

Low molecular weight chitosan with weight‐average molecular weight from 161 to 22,000Da were obtained by sonolysis. Optimal conditions for sonolysis were described. The influence of sonolysis condition and the molecular parameters of initial chitosan on the degradation rate and degradation rate constant were investigated in detail. Weight‐average molecular weight (M_w) and molecular weight dispersion (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of degraded chitosan were characterized by Fourier transform infrared, X‐ray diffraction, and electrospray ionization mass spectrometry. For a given sonolysis time, the decrease in molecular weight has been found to be greatest at lowest reaction temperature and lowest chitosan concentration. Molecular weight of samples decreased exponentially with increasing sonication time at early stages. The action mode of ultrasound on the splitting of molecular chain of chitosan has been discussed. The degree of deacetylation of the main hydrolysis products almost unchanged compared with the initial chitosan. The decrease of molecular weight led to transformation of crystal structure but the chemical structures of residues were not modified. Ultrasonic treatment on chitosan is an alternative, safe method to prepare chitosan having different molecular weights, which are more suitable for biomedical and food applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Moisture retention and antibacterial activity of modified chitosan by hydrogen peroxide

A series of chitosans with various molecular weights from 1.2 × 10³ to 30.0 × 10⁴ were prepared by oxidative degradation with H₂O₂ and characterized by IR, ¹³C‐NMR, and gel permeation chromatography. Their carboxylic contents increased with a decrease in molecular weight (M_w). The moisture‐absorption and moisture‐retention capacities of resulting chitosans were dependent on both the molecular weight and the degree of deacetylation (DD). Microcalorimetry was first used to study the kinetics of action of the chitosans on a strain of Staphylococcus aureus at pH 7. The antibacterial activity of the water‐soluble chitosan against S. aureus, Escherichia coli, and Salmonella typhi was evaluated by the conventional agar plate method at pH 7. The water‐soluble product with M_w of 0.45 × 10⁴ from initial chitosan of DD of 90% showed high moisture‐absorption and moisture‐retention capacities, and <2% concentration can completely inhibit the growth of these bacteria. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1724–1730, 2002     

Factors influencing molecular weights of methylcelluloses prepared from annual plants and juvenile eucalyptus

We studied the factors that influenced the molecular weights (M_w) of water‐soluble methylcelluloses prepared from annual plants and juvenile eucalyptus. Miscanthus and cardoon stalks, and bleached pulps of abaca, jute, sisal, hemp, and flax were the annual plant materials studied. A higher concentration of NaOH solution during the impregnation led to a spring cardoon methylcellulose having a lower molecular weight. As the impregnation times increased, so did the molecular weights of the water‐soluble methylcelluloses of spring cardoon. The impregnation conditions had less influence on the methylcelluloses of summer cardoon than on the methylcelluloses of spring cardoon. As the cooking times increased, so did the molecular weights of miscanthus methylcelluloses. A lower pulping severity increased the molecular weight of eucalyptus methylcellulose. The preliminary treatments (water soaking, premercerization, mercerization under pressure, and steam explosion) improved the molecular weights of water‐soluble abaca methylcelluloses. The steam explosion method was the best of the preliminary treatments for the abaca pulp. Different species led to different molecular weights for methylcelluloses synthesized from ECF bleached pulps, and these were further improved by preliminary mercerization. The molecular weight of α‐cellulose methylcellulose changed as the ratio of the methylation reagent was varied. To synthesize an optimum M_w of methylcellulose, the different raw materials can be chosen, the pulping parameters adjusted (including impregnation and cooking), the cellulose pretreated, and the methylcellulose conditions changed. The plant species is the decisive factor for the M_w of methylcellulose. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1785–1793, 2006     

Reversible addition–fragmentation chain transfer polymerization of styrene with benzoimidazole dithiocarbamate as a reversible addition–fragmentation chain transfer agent

Two novel dithiocarbamates [2‐Y‐benzoimidazole‐1‐carbodithioic acid benzyl esters: Y = methyl (1b) or phenyl (1c)] were synthesized and successfully used in the reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene in bulk with thermal initiation. The effects of the temperatures and concentration ratios of the styrene and RAFT agents on the polymerization were investigated. The results showed that the polymerization of styrene could be well controlled in the presence of 1b or 1c. The linear relationships between ln([M]₀/[M]) and the polymerization time (where [M]₀ is the initial monomer concentration and [M] is the monomer concentration) indicated that the polymerizations were first‐order reactions with respect to the monomer concentration. The molecular weights increased linearly with the monomer conversion and were close to the theoretical values. The molecular weight distributions [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] were very narrow from 5.3% conversion up to 94% conversion (M_w/M_n < 1.3). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 560–564, 2006     

Synthesis of star‐shaped poly(ϵ‐caprolactone) by samarium‐based tetrafunctional initiator and its dilute‐solution properties

An in situ–generated tetrafunctional samarium enolate from the reduction of 1,1,1,1‐tetra(2‐bromoisobutyryloxymethyl)methane with divalent samarium complexes [Sm(PPh₂)₂ and SmI₂] in tetrahydrofuran has proven to initiate the ring‐opening polymerization of ?‐caprolactone (CL) giving star‐shaped aliphatic polyesters. The polymerization proceeded with quantitative conversions at room temperature in 2 h and exhibited good controllability of the molecular weight of polymer. The resulting four‐armed poly(?‐caprolactone) (PCL) was fractionated, and the dilute‐solution properties of the fractions were studied in tetrahydrofuran and toluene at 30°C. The Mark–Houwink relations for these solvents were [η] = 2.73 × 10^?2M_w^0.74 and [η] = 1.97 × 10^?2M_w^0.75, respectively. In addition, the unperturbed dimensions of the star‐shaped PCL systems were also evaluated, and a significant solvent effect was observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 175–182, 2006     

An amphoteric water‐soluble copolymer. II. Effect of its molecular weight on the dispersion of barium titanate in water

An amphoteric water‐soluble copolymer, that is, polyacrylamide/(α‐N,N‐dimethyl‐N‐acryloyloxyethyl)ammonium ethanate (PAAM/DAAE) was synthesized and it showed the ability to disperse BaTiO₃ (BT) particles in aqueous solutions. In this work, the effect of molecular weight of this polymer on the dispersing properties was further examined. The results indicate that the effectiveness of three polymer samples with different molecular weights in the dispersion of BT particles is P2 (M_w = 1.1 × 10⁵) > P1 (M_w = 1.2 × 10⁴) > P3 (M_w = 3.0 × 10⁵). Apparently, P2 is most effective in dispersing the particles, reducing the viscosity of the suspensions, and obtaining highest green and sintered densities. This is attributed to the highest adsorption of this polymer onto BT powder, and causes strongest electrostatic and steric repulsions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 886–891, 2006     

Evaluation of thermo‐viscosity parameters of dextran in polar and nonpolar solvent

Some thermo‐viscosity parameters like Viscosity‐molecular weight constant (K), the short‐range parameter, (A) and long‐range parameter (B) have been evaluated for the polymer “Dextran” of three different molecular weights (M?_w = 19,500, 75,000, and 250,000) in three different solvents like 6 (M) aqueous urea, 2 (M) aqueous glycine, and 50% aqueous glucose at temperatures ranging from 25 to 50°C. The study reveals that the viscosity‐molecular weight constant (K) decreases with increase in temperature for polar solvents like aqueous urea and aqueous glycine. The value of “K” increases with the rise in temperature within the range of 25 to 35°C in case of a nonpolar solvent aqueous glucose and then “K” decreases with the increase in temperature within the range of 40 to 50°C for the nonpolar solvent aqueous glucose. The short‐range parameter (A) shows the same trend as shown by “K” and the long‐range parameter “B” exhibits no definite trend with the variation of temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 440–452, 2001     

Novel sulfonated poly(arylene biphenylsulfone ether) copolymers containing bisphenylsulfonyl biphenyl moiety: structural,thermal, electrochemical and morphological characteristics

A series of sulfonated poly(arylene biphenylsulfone ether) polymers containing up to two pendant sulfonic acid groups per repeat unit were successfully synthesized from 4,4′‐bis[(4‐chlorophenyl)sulfonyl]‐1,1′‐biphenyl (BCPSBP), disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone (SDCDPS) and bisphenol A via aromatic nucleophilic displacement polycondensation. The resulting polymers were characterized by means of Fourier transform infrared and ¹H NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis (TGA). The number‐average molecular weight (M_n) of the synthesized polymers was in the range 15 300–22 900 g mol^?1, and the polydispersity indices (M_w/M_n) varied from 2.5 to 4.4. Tough membranes with SDCDPS/BCPSBP mole ratio up to 50:50 were successfully cast using N‐methyl‐2‐pyrrolidone (NMP). An increase of sulfonic acid groups in the polymer backbone resulted in increased solubility in aprotic polar solvents and glass transition temperature. The TGA curves of all the copolymers in acid form exhibited two distinct weight‐loss profiles. The influential characteristics of the polymer electrolyte membranes, such as tensile strength, water uptake, ion‐exchange capacity and proton conductivity, were characterized with respect to the pendant sulfonic acid groups. Atomic force microscopy phase images of the acid‐form membranes clearly showed the hydrophilic domains, with sizes increasing as a function of the degree of sulfonation. Copyright © 2010 Society of Chemical Industry     

Relationship between the structure and mechanical properties of polypropylene: Effects of the molecular weight and shear‐induced structure

A series of homopolymer polypropylenes (PPs), within a weight‐average molecular weight (M_w) range of 100–1600 kg/mol, were manufactured as dumbbell microspecimens. The effects of the molecular weight and shear‐induced crystallization on the mechanical properties and morphology were studied to gain a better understanding of the structure–property relationship. The results showed that the crystallinity decreased from 50 to 41% and the lamellar thickness increased as M_w increased. Tensile tests demonstrated that the stiffness and especially the tensile strength rose to extremely high values (Young's modulus = 2400 N/mm², stress at 30% strain = 120 N/mm²). Furthermore, the strain hardening effect was strongly affected by the lamellar thickness and highly oriented superstructures. Dynamic mechanical analysis demonstrated that the mobility of the molecular chains depended on M_w and on the lamellar thickness. In addition, the viscoelastic properties of unannealed and annealed samples indicated further the existence of shish‐kebab structures caused by shear‐induced crystallization during injection molding. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 519–533, 2007     

Urea‐induced conformational changes of chitosan molecules and the shift of break point of Mark–Houwink equation by increasing urea concentration

Chitosan solutions of the same 83% degree of deacetylation (DD) but different weight average molecular weights (M_ws) (78–914 kDa) in 0.01M HCl containing different concentrations of urea (0–6M) were prepared. Intrinsic viscosity ([η]) and weight average molecular weight (M_w) of chitosan were measured with a capillary viscometer and light scattering, respectively. Mark–Houwink exponent a was used as the parameter of conformational index. The Mark–Houwink exponent a increased with increasing concentrations of urea. When solutions contained 0, 2, 3, 4, and 6M urea, the value of a increased from 0.715 to 0.839, 0.894, 1.000, and 1.060, respectively. This indicates the occurrence of urea‐induced conformational transitions of chitosans. The break point shifted from 223 kDa in solutions containing no urea to 280 kDa in 2M urea solutions, to 362 kDa in 4M urea solutions and further to 481 kDa in 6M urea solutions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 452–457, 2000     

Synthesis of 1,3‐benzodioxole end‐functionalized polymers via reversible addition–fragmentation chain transfer polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene was carried out in the presence of a novel RAFT reagent, bearing 1,3‐benzodioxole group, benzo [1,3]dioxole‐5‐carbodithioic acid benzo [1,3]dioxol‐5‐ylmethyl ester (BDCB), to prepare end‐functionalized polystyrene. The polymerization results showed that RAFT polymerization of styrene could be well controlled. Number–average molecular weight (M_n(GPC)) increased linearly with monomer conversion, and molecular weight distributions were narrow (M_w/M_n < 1.4). The successful reaction of chain extension and analysis of ¹H NMR spectra confirmed the existence of the functional 1,3‐benzodioxole group at the chain‐end of polystyrene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3535–3539, 2006     

Solid‐state polymerization of poly(ethylene terephthalate): Effect of organoclay concentration

Poly(ethylene terephthalate) (PET)/Cloisite 30B (C30B) nanocomposites of different organoclay concentrations were prepared using a water‐assisted extrusion process. The reduction of the molecular weight (M_w) of the PET matrix, caused by hydrolysis during water‐assisted extrusion, was compensated by subsequent solid‐state polymerization (SSP). Viscometry, titration, rheological, and dynamic scanning calorimetry measurements were used to analyze the samples from SSP. The weight‐average molecular weight (M_w) of PET increased significantly through SSP. PET nanocomposites exhibited solid‐like rheological behavior, and the complex viscosity at high frequencies was scaled with the M_w of PET. The Maron–Pierce model was used to evaluate the M_w of PET in the nanocomposites before and after SSP. It was found that the extent and the rate of the SSP reaction in nanocomposites were lower than those for the neat PETs, due to the barrier effect of clay platelets. Consequently, the SSP rate of PET increased with decreasing particle size for the neat PET and PET nanocomposites. The effect of the M_w of PET on the crystallization temperature, crystallinity, and the half‐time, t_½, of nonisothermal crystallization was also investigated. With increasing M_w of PET, t_½ increased, whereas T_c and X_c decreased. POLYM. ENG. SCI., 54:2925–2937, 2014. © 2014 Society of Plastics Engineers     

Facile synthesis of dendronized polyamides with chloromethyl groups in the periphery and some properties

A novel dendronized aromatic polyamide with a polyamide backbone and chloromethylene‐end‐functionalized polyamide dendrons is reported for the first time. An attempt at a one‐pot synthesis of end‐functionalized dendronized polymers with a macromonomer strategy without protection and deprotection procedures is also reported for the first time. The results from Fourier transform infrared and NMR spectral analysis indicated that perfect coverage of the chloromethyl groups in the periphery of the resulting polymers was obtained. Data from gel permeation chromatography analysis showed a typical weight‐average molecular weight (M_w) of 76,678 and a polydispersity of 2.44 for the first‐generation polymers and an M_w of 41,554 and a polydispersity of 2.74 for the second‐generation polymers. The solubility in solvents for the resulting polymers was improved remarkably because of the introduction of the dendritic fragments and the existence of the periphery functional groups. Both the glass‐transition temperature and onset decomposition temperature decreased versus those of the linear aromatic polyamides, but the 50% weight loss temperature was still up to 723°C. The X‐ray diffractograms indicated only an amorphous peak in the wide‐angle region of 24–25°. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Polymerization of diisopropyl fumarate under microwave irradiation

Diisopropyl fumarate (DiPF), a representative monomer of dialkyl fumarates, was polymerized by microwave irradiation at three different powers (140, 210, and 280 W), using a domestic microwave oven. The nature and concentration of initiators [2,2′‐azobisisobutyronitrile (AIBN) and benzoyl peroxide (BP)], power and energy of microwave irradiation on the conversion, weight average molecular weight (M_w), and polydispersity index (M_w/M_n) were analyzed. The results indicate that the microwave conditions have a significant nonthermal effect in enhancing the polymerization rate of DiPF. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3785–3791, 2007     

Characterization of branched polyethylene fractions from the elution column

Fractions from several elution column runs on samples of up to 6 g. of a well-characterized high-pressure polyethylene were analyzed by absolute molecular weight methods and several other techniques. The M_n and M_w integral distribution curves are free from any reversal, as was the viscosity distribution curve. Fractions with M_w as high as 8 × 10⁶ were recovered, more than 20 times higher than the original sample's M_w. The polydispersity of the fractions increases from M_w/M_n = 1.5 or less in the low molecular weight fractions to a nearly constant value of 4.5–5.0 in fractions above 60% cumulative sample weight. Nonetheless, refractionation on the elution column shows that the fractions are narrowly distributed in terms of solubility, while GPC analysis reveals that the fractions have an extremely narrow size distribution. It is concluded from the combined results that long-chain branching plays an important role in determining the equilibrium solubility and, further, that long-chain branching increases the polymer solubility. Sample calculations are provided, which illustrate the effect of fraction polydispersity on calculated original sample molecular weights and the fit of the fractionation results to several model distribution functions.