Mechanism of cellulose polymer reactions with some cation-exchanged montmorillonite catalysts

The degradation of cotton cellulose polymer by Li⁺-, K⁺- and NH₄ ⁺-exchanged montmorillonite has been studied. A general reaction scheme is proposed. The mechanism of this reaction would most probably involve chain breaking and increasing the reducing power of cellulose polymer by dissociation of water molecules coordinated to the central metal ion.     

Reactions of elemental phosphorus and phosphine with electrophiles in superbasic systems: XVIII. Phosphorylation of 1-(chloromethyl)naphthalene with the elemental phosphorus

1-Chloromethylnaphthalene reacts with white and red phosphorus, and also with the “activated red phosphorus,” the complex organophosphorus polymer of unknown structure obtained by irradiation of a solution of white phosphorus in benzene by the ⁶⁰Co source, in a system including KOH water solution, dioxane or benzene, and a phase transfer catalyst (22–98°C, argon), to form bis(1-naphthylmethyl)-and tris-(1-naphthylmethyl)phosphine oxides, and also (1-naphthylmethyl)phosphonous-and bis(1-naphthylmethyl)-phosphinic acids. The yield and the ratio of the reaction products depend on reaction conditions as well as on the nature of phosphorylating agent. It is shown that the reactivity of the “activated red phosphorus” is not worse than that of the white phosphorus and significantly exceeds the reactivity of the usual technical red phosphorus.     

Binding cellulose and chitosan via click chemistry: Synthesis,characterization, and formation of some hollow tubes

A novel cellulose‐click‐chitosan polymer was prepared successfully in three steps: (1) propargyl cellulose with degrees of substitution (DS) from 0.25 to 1.24 was synthesized by etherification of bamboo Phyllostachys bambusoide cellulose with propargyl chloride in DMA/LiCl in the presence of NaH. The regioselectivity of propargylation on anhydrous glucose unit determined by GC‐MS was in the order of 2 >> 6 > 3; (2) the functional azide groups were introduced onto the chitosan chains by reacting chitosan with 4‐azidobenzoic acid in [Amim]Cl/DMF and the DS ranged from 0.02 to 0.46; (3) thus, the cellulose‐click‐chitosan polymer was obtained via click reaction, that is, the Cu(I)‐catalyzed Huisgen 1,3‐dipolar cycloaddition reaction, between the terminal alkyne groups of cellulose and the azide groups on the chitosan backbone at room temperature. The successful binding of cellulose and chitosan was confirmed and characterized by FTIR and CP/MAS ¹³C NMR spectroscopy. TGA analyses indicated that the cellulose‐click‐chitosan polymer had a higher thermal stability than that of cellulose and chitosan as well as cellulose–chitosan complex. More interestingly, some hollow tubes with near millimeter length were also observed by SEM. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of urea additive on the thermal decomposition of greige cotton nonwoven fabric treated with diammonium phosphate

This study showed that greige cotton nonwoven fabric can effectively be flame retardant by applying the phosphorus of diammonium phosphate (DAP) as low as 0.8 wt% with the addition of urea. At such a low content of phosphorus, the char length and limiting oxygen index (LOI) were continuously decreased and increased, respectively, as the concentration of urea increased. The effect of urea additive on the thermal decomposition of flame retardant greige cotton nonwoven fabric was investigated by thermogravimetry, ATR-FTIR, XRD, ¹H → ¹³C CP/MAS NMR, and SEM. The results indicated that, upon heating, urea not only facilitated the phosphorylation reaction of DAP but also introduced carbamate groups into cellulose to decrease the degree of crystallinity prior to the decomposition of the crystalline cellulose. Compared with DAP treatment alone, the addition of urea accelerated the decomposition of glycosyl units, which resulted in a slight increase of weight loss and decrease of char yield. The char morphology observed after LOI tests indicates that urea released nonflammable gases, which blew the carboneous char layer to protect the underlying substrate.     

Cellulose membranes grafted with vinyl monomers in a homogeneous system

The homogeneous grafting of hydrophilic monomer onto cellulose derivatives was carried out in an aqueous system at 30, 50, 70 and 90 °C during reaction periods of 30 to 180 min. The graft polymer was isolated by ethanol from the reaction mixture, dried, and weigh. The grafted polymer was characterized by IR spectroscopy as well as microscopic sample morphology detected by electron scanning microscopy. The water absorption capacities and grafting values of grafted cellulose derivatives were also determined. The maximum grafting yield was obtained at 30 °C. Copyright © 2002 John Wiley & Sons, Ltd.     

The synthesis and thermotropic behaviour of an ethyl cellulose derivative containing azobenzene-based mesogenic moieties

An ethyl cellulose derivative containing azobenzene-based mesogenic moieties was prepared by the reaction of 4-methoxyazobenzene-4′-oxyacetic acid and ethyl cellulose by esterification in the presence of N,N′ -dicylcohexylcarbodiimide and 4-dimethylaminopyridine. Its chemical structure and liquid crystalline properties were characterized by FTIR, ¹H NMR, POM, DSC and WAXD. The degree of substitution of the cellulose backbone by the azobenzene-based mesogenic moieties is 0.9. The polymer is thermotropic and exhibits liquid crystalline behaviour over the temperature range 125–172°C.     

Synthesis of poly-yne polymer containing platinum and silicon atoms in the main chain by oxidative coupling and its reactions with transition-metal carbonyl complexes

The platinum poly-yne polymer, [? C?C? SiMe₂? C?C? Pt(PBu₃)₂? C?C? SiMe₂? C?C? ]_n (2), was synthesized by the oxidative coupling of a silicon–platinum monomer, trans-(PBu₃)₂Pt(C?C? SiMe₂–C?CH)₂ (1). The reaction of platinum poly-yne polymer 2 with dicobaltoctacarbonyl gave μ-coordinated complexes, {[? C?C? SiMe₂? C?C? Pt(PBu₃)₂? C?C? SiMe₂? C?C? ] [Co₂(Co)₆]₂}_n (4). the electric conductivity of iodine adducts of the polymer complexes 4 was 3.0×10^?5 S cm^?1. As an aid to spectroscopic characterization of the polymer complex 4, a model complex, {trans-[(PBu₃)₂Pt? (C?C? SiMe₂? C?CH)₂]} {[Co₂(CO)₆]₂} (3), was also prepared by the reaction of 1 with dicobaltocatacarbonyl. Selective coordination of Co₂(CO)₆ groups to ? SiMe₂? C?C C?C? Si(Me)₂? Moieties and coordinative inertness of the Pt? C?C? moieties were confirmed by comparison of the NMR spectra of 3 with those of 4. All new compounds have been characterized by analytical and spectral analysis (IR, ¹H NMR).     

Syntheses and characterizations of allyl cellulose and glycidyl cellulose

Allyl cellulose was synthesized by reacting cellulose with allyl bromide in homogeneous LiCl/DMAc solution containing NaOH powder. The degree of substitution (DS) per anhydroglucose (AHG) unit was determined by titrating the allyl cellulose with bromine in chloroform solution, and an allyl DS of 2.80 was found. Glycidyl cellulose was then prepared by reacting this allyl cellulose with peracetic acid in methylene chloride at ambient temperature for 6 days. The measured reaction rate constant was 1.33 × 10^?3 min^?1. The glycidyl cellulose thus obtained with a glycidyl DS of 2.58 was determined by titrating the product with perchloric acid in conjunction with tetrabutylammonium iodide. The 2.58 of glycidyl DS was also confirmed by ¹H-NMR integration. Both allyl cellulose and glycidyl cellulose were analyzed and characterized with FTIR, ¹H-NMR, ¹³C-NMR, TGA, and GPC. During epoxidation of allyl cellulose, possible side reaction leading to ester formation was evidenced from the continuous increase of v_{C? O} at 1735 cm^?1 in FTIR analyses. In addition, a bimodal distribution and a decreased molecular weight for glycidyl cellulose were found from GPC data, which might suggest a possible chain scission at the cellulosic ether linkage. © 1992 John Wiley & Sons, Inc.     

Raman spectral changes during the solid-state polymerization of diacetylenes

Raman spectral changes resulting from the solid-state 1,4-addition polymerization of conjugated diacetylenes are reported. The monomers show an intense C?C stretching frequency near 2260 cm^?1, where as the polymers showed two strong bands, a C?C vibration near 2100 cm^?1 and a C?C vibration near 1500 cm^?1. The presence of both double and triple bonds in the polymers suggests the backbone structure (?C? C?C? C?)_n. The alternate mesomeric structure (? C?C?C?C? )_n can be eliminated as a possibility by the presence of the strong C?C vibration in the polymer. Sequential Raman spectra obtained during radiation-induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate-state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.     

Retention characteristics of aliphatic compounds on cellulose acetates as a stationary phase with an aqueous mobile phase

Summary Cellulose and cellulose mono-, di-, and triacetate were used as stationary phases for liquid chromatography with water as a mobile phase, and the retention behavior of alcohols, ethers, ketones, and chlorides was examined. For cellulose acetate columns, the logarithm of the specific retention volume, (logV _g ^* ), correlated linearly with the logarithm of partition coefficient between 1-octanol and water (log K_o/w), for each homologous group, but all solutes were unretained on cellulose columns. With the exception of chlorides, the intercept values of the log V _g ^* –log K_o/w regression lines increased significantly with increase of acetyl content of cellulose acetates, but the slopes of the regression lines changed little. This suggests that hydrophobic interaction between the acetyl groups of cellulose acetates and the alkyl chains of the solutes is the dominant factor in the retention.The capacity factors for 1-alcohols with cellulos diacetate column indicated a maximum at a column temperature of about 40°C. This unique retention behavior was assumed to be caused by small structural change of the cellulose acetate polymer, because this temperature effect on the retention corresponded with effects observed by differential scanning calorimetry (DSC).     

Coordination polymers of glutaraldehyde with glycine metal complexes: synthesis,spectral characterization,and their biological evaluation

Glycine metal complexes were prepared by the reaction of glycine with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) in 1?:?2 molar ratio. Thereafter their condensation polymerization was done with glutaraldehyde to obtain polymer metal complexes. All the synthesized polymer metal complexes were characterized by elemental analysis, FT-IR, ¹H-NMR, and UV-Vis spectrometry, magnetic susceptibility, and thermogravimetric studies. The analytical data of all the polymers agreed with 1?:?1 molar ratio of metal complex to glutaraldehyde and magnetic moment data suggest that PGG–Mn(II), PGG–Co(II), PGG–Ni(II), and PGG–Cu(II) have an octahedral geometry around the metal atom, whereas the tetrahedral geometry was proposed for PGG–Zn(II) polymer. The PGG–Mn(II) and PGG–Cu(II) showed octahedral geometry. Thermal behavior of the polymer metal complexes was obtained at a heating rate of 10°C?min^?1 under nitrogen atmosphere from 0°C to 800°C. The antimicrobial activities of synthesized polymers were investigated against Streptococcus aureus, Escherichia coli, Bacillus sphaericus, Salmonella sp. (Bacteria), Fusarium oryzae, Candida albicans, and Aspergillus niger (Yeast).     

Influence of cation on the cellulose dissolution investigated by MD simulation and experiments

Cellulose is the most abundant natural polymer on the earth, and effective solvents are essential for its wide application. Among various solvents such as alkali/urea or ionic liquids, cations all play a very important role on the cellulose dissolution. In this work, the influence of cation on the cellulose dissolution in alkali/urea via a cooling process was investigated with a combination of MD simulation and experiments, including differential scanning calorimetry (DSC) and NMR diffusometry (PFG-SE NMR). The results of DSC proved that the dissolution of cellulose in both solvents was a process within a temperature range, starting at above 0 °C and completing at low temperature (?5 °C for LiOH/urea and ?20 °C for NaOH/urea), indicating the necessity of low temperature for the cellulose dissolution. Molecular dynamic (MD) simulation suggested that the electrostatic force between OH^? and cellulose dominated the inter-molecular interactions. In our findings, Li⁺ could penetrate closer to cellulose, and displayed stronger electrostatic interaction with the biomacromolecule than Na⁺, thus possessed a greater “stabilizing” effect on the OH^?/cellulose interaction. PFG-SE NMR demonstrated a more significant binding fraction of Li⁺ than Na⁺ to cellulose, which was consistent with MD. These results indicated that the direct interactions existed between the cations and cellulose, and Li⁺ exhibited stronger interaction with cellulose, leading to stronger dissolving power.     

Ring-opening polymerization of ethylene organophosphorothioates: Stereoregular polymerization involving asymmetry at phosphorus

Stereoregular polymerization involving asymmetry at phosphorus has been obtained from ethylene methyl or phenyl phosphorothioate with R₂Mg? NH₃ catalysts, or, in some cases, with R₂Mg alone. The methyl ester gave two types of polymer: an amorphous rubber and a low-melting (75°C) crystalline polymer. The phenyl ester gave mainly a low-melting (68°C) crystalline polymer of 2.2 inherent viscosity. Proton and ³¹P NMR and infrared spectra of these polymers are in accord with the expected chain unit, ? CH₂CH₂? O? P(S)(OR)? O? . The polymerization mechanism probably involves an anionic ring-opening step with P? O cleavage. Ring opening with C? O cleavage appears to be largely excluded. This conclusion is based on the expectation that anionic ring opening with C? O cleavage should lead to a rearranged chain unit, ? CH₂CH₂? O? P(O)? (OR)? S? , because of the high nucleophilicity of sulfur as compared with oxygen. Proton and ³¹P NMR spectra give no evidence for the rearranged unit within the limit of detection (ca. 3%). However, on aging, the methyl ester polymer changes drastically to form up to 40% CH₂SP groups. Presumably, the polymer undergoes the well-known thiono-thiolo rearrangement characteristic of simple phosphorothioate esters to form ? CH₂CH₂? O? P(O)(SCH₃)? O? chain units. The phenyl ester polymer is stable under the same aging conditions.     

Untreated and alkali treated fibers from Alfa stem: effect of alkali treatment on structural,morphological and thermal features

Alfa stems are rich in cellulose and they are an inexpensive, easily renewable source of natural fibers with the potential for polymer reinforcement. However, large amounts of non-cellulosic materials, surface impurities and low degradation temperature make natural fibers less attractive for reinforcement of polymeric materials, unless they can be modified in a proper way. In this paper, Alfa stems were treated with NaOH solution with two different concentrations (1 and 5 wt%). Raw and treated stems were crushed to obtain fibers. Stems and fibers were characterized by scanning electron microscopy (SEM) and optical microscopy, respectively. Their crystallinity index was determined by X-ray diffraction, thermal stability by thermogravimetry and structural change by FT-IR and ¹³C NMR spectroscopy. Comparison and analysis of results confirmed some thermal, structural and morphological changes of the fibers after treatment due to removal of some non-crystalline constituents from the plant. SEM showed rougher surfaces after alkalization. FT-IR and ¹³C NMR showed a gradual improvement in cellulose level by alkali treatment with increasing NaOH concentration. The crystallinity index and thermal stability of treated Alfa fibers were also found to be improved.     

Attenuated total reflectance Fourier-transform Infrared spectroscopy analysis of crystallinity changes in lyocell following continuous treatment with sodium hydroxide

Cellulose is a linear 1,4-β-glucan polymer where the units are able to form highly ordered structures, as a result of extensive interaction through intra- and intermolecular hydrogen bonding of the three hydroxyl groups in each cellulose unit. Alkali has a substantial influence on morphological, molecular and supramolecular properties of cellulose II polymer fibres causing changes in crystallinity. These physical changes were observed herein using ATR-FTIR spectroscopy, following continuous treatment of the cellulose II fabrics with aqueous sodium hydroxide solution under varying condition parameters. Post-treatment, maxima for total crystallinity index and lateral order index, and minima for hydrogen bond intensity, were observed at concentrations of 3.3 and 4.5 mol dm⁻³ NaOH, when treated at 25 °C and 40 °C, respectively. Under these treatment conditions, it is proposed that maximum molecular reorganisation occurs in the amorphous and quasi-crystalline phases of the cellulose II polymer.     

Solid products from thermal decomposition of polyethylene terephthalate: Investigation by CP/MAS 13C-NMR and fourier transform-IR spectroscopy

The solid reaction products from pyrolysis of polyethylene terephthalate in the presence and absence of red phosphorus were characterized by CP/MAS ¹³C-NMR, FR-IR, and MAS ³¹P-NMR spectroscopy. Over the temperature range of 300–400°C, polyethylene terephthalate was converted in a sealed vial to a highly crosslinked polymer of terephthalic acid. Pyrolysis in the presence of red phosphorus, which functions as a flame retardant by increasing the amount of char, yielded an intractible polyaromatic phosphate ester. After thermal cleavage of polyethylene terephthalate with formation of free carboxyl and vinyl ester groups, there are two competing reaction pathways. The smaller molecular weight fragments may enter the vapor phase where they undergo further degradation primarily to CO₂, CO, and acetaldehyde, as described by others. However, if volatilization of the oligomeric fragments is inhibited, an alternate reaction pathway gives rise to the formation of highly crosslinked char. Red phosphorus decreases the volatility of the oligomeric fragments by converting them to phosphates and thereby enhances char formation.     

Pyrolytic characteristics and kinetics of pistachio shell by thermogravimetric analysis

Pyrolytic characteristics and kinetics of pistachio shell were studied using a thermogravimetric analyzer in 50?C800?°C temperature range under nitrogen atmosphere at 2, 10, and 15?°C?min^?1 heating rates. Pyrolysis process was accomplished at four distinct stages which can mainly be attributed to removal of water, decomposition of hemicellulose, decomposition of cellulose, and decomposition of lignin, respectively. The activation energies, pre-exponential factors, and reaction orders of active pyrolysis stages were calculated by Arrhenius, Coats?CRedfern, and Horowitz?CMetzger model-fitting methods, while activation energies were additionaly determined by Flynn?CWall?COzawa model-free method. Average activation energies of the second and third stages calculated from model-fitting methods were in the range of 121?C187 and 320?C353?kJ?mol^?1, respectively. The FWO method yielded a compatible result (153?kJ?mol^?1) for the second stage but a lower result (187?kJ?mol^?1) for the third stage. The existence of kinetic compensation effect was evident.     

Reaction of cellulose phosphonate with N-vinyl-2-pyrrolidone and flame-retardant properties of the product

The reaction of cellulose phosphonate and N-vinyl-2-pyrrolidone in ethanol in the presence of sodium ethoxide was investigated and thermal stabilities and flame-retardant properties for cellulose phosphonate modified with N-vinyl-2-pyrrolidone were discussed. The results in this study point out the following important aspects of flame retardation of cellulose fabrics: (1) The reaction of cellulose phosphonate and N-vinyl-2-pyrrolidone in the presence of sodium ethoxide results in graft polymerization of N-vinyl-2-pyrrolidone at P? H sites in cellulose phosphonate; an average chain length of the graft polymer is about five units of vinylpyrrolidone. (2) The graft polymerization of N-vinyl-2-pyrrolidone can improve both stabilities, especially the flame-retardant properties of cellulose fabrics. (3) Amides, whether noncyclic or cyclic, are suitable for nitrogen compounds that can effectively operate as synergists.     

Chemoselective Phototransformation of CH Bonds on a Polymer Surface through a Photoinduced Cerium Recycling Redox Reaction

It is generally accepted that Ce⁴⁺ is unable to directly oxidize unreactive alkyl C?H bonds without the assistance of adjacent polar groups. Herein, we demonstrate in our newly developed confined photochemical reaction system that this recognized issue may be challenged. As we found, when a thin layer of a CeCl₃/HCl aqueous solution was applied to a polymeric substrate and the substrate subjected to UV irradiation, Ce³⁺ was first photooxidized to form Ce⁴⁺ in the presence of H⁺, and the in situ formed Ce⁴⁺ then performs an oxidation reaction on the C?H bonds of the polymer surface to form surface‐carbon radicals for radical graft polymerization reactions and functional‐group transformations, while reducing to Ce³⁺ and releasing H⁺ in the process. This photoinduced cerium recycling redox (PCRR) reaction behaved as a biomimetic system in an artificial recycling reaction, leading to a sustainable chemical modification strategy for directly transforming alkyl C?H bonds on polymer surfaces into small‐molecule groups and polymer brushes. This method is expected to provide a green and economical tool for industrial applications of polymer‐surface modification.     

Structural Changes and Activation of Cellulose by Caustic Soda Solution with Urea

Investigations on the activation of cellulose by mixed solutions of caustic soda and urea are reported. The structural effects of those solutions on various dissolving pulps are studied by ¹³C-CP/MAS-NMR spectroscopy. In a series of steeping lyes, the concentration of NaOH was varied in a range from 0% to 8% and the urea-concentration in a range from 15% to 40% at ambient temperature and −25 °C. Using solely the single NaOH or urea solutions in the concentration ranges given above, no or only minor structural changes were found. In contrast to that, the cellulose I structure was partially or completely destroyed by using the bicomponent solution with urea added to caustic soda. The structural effect of the bicomponent solutions is comparable with the effect of solely caustic soda solutions of approx. 10% to 18% NaOH. However, the ¹³C-CP/MAS-NMR-spectra from the bicomponent pretreated samples indicate a structure different from the usual ordered structures of sodium cellulose I or II, namely a special urea-NaOH-cellulose complex. The results show that for cellulose activation the NaOH concentration of the caustic soda can be remarkably reduced by adding urea. The improved activating effect of an optimized caustic soda solution with added urea was proved to be useful for the synthesis of cellulose carbamate.