Structural and thermal characterization of sugarcane bagasse cellulose succinates prepared in ionic liquid

The chemical modification of SCB cellulose with succinic anhydride using 1-butyl-3-methylimidazolium chloride ionic liquid/DMSO system as reaction medium was studied. The parameters including the molar ratio of succinic anhydride/anhydroglucose units in cellulose from 1:1 to 12:1, reaction time 5-120 min, and reaction temperature 85-105 °C were investigated. The results showed that the degree substitution of succinylated cellulosic preparations ranged from 0.037 to 0.53. It was found that the treatment of the native cellulose in the ionic liquid/DMSO system under the conditions given significantly degraded the cellulose and completely destroyed the cellulose crystals. FT-IR and solid-state CP/MAS ¹³C NMR spectra produced evidence for succinoylation reaction and the results showed that succinoylation occurred at positions C-6, C-2 and C-3. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Anhydride-functionalized fullerene: a versatile precursor for fullerene-based materials

Soluble phthalic anhydride-functionalized fullerene was generated via simple pyrolysis of the corresponding di-t-butyl phthalate precursor at 200 °C for 120 min. This non-chemical method for generating electrophilic fullerene may be advantageous for the preparation of various fullerene-containing materials. The utility of the resulting fullerene anhydride was demonstrated by solution coupling reaction with PEG-amine, surface reaction with amine-functionalized glass, and hydrolysis reaction to form amphiphilic fullerene.     

Modification of the halogen end groups of polystyrene prepared by ATRP

The stabilization modification of the halogen end groups of polystyrene prepared by atom transfer radical polymerization (ATRP) has been attempted. The reaction mechanism adopted is radical chain transfer reaction, and iso-propylbenzene is employed as not only the chain transfer agent but also the solvent. Moreover, Cu⁰ is used as the acceptor of the transformed halogen atom in some experiments. As evidenced by ¹H NMR analysis of the modified products, the halogen end group can really be converted into the much more stable carbon-hydrogen structure. When Cu⁰ is not used, the conversion of the halogen end groups rises rapidly during the early stage and the increase rate slows down after about 8 h reaction. In view of the influence of reaction temperature on the modification, the conversion increases almost exponentially with temperature in the range of 80-100 °C, and the increase rate slows down at higher temperature. ¹H NMR and SEC analyses prove that the modification reaction does not destroy the polymer backbone and the molecular weights remain almost the same as those of the unmodified samples. When Cu⁰ is introduced, the modification reaction proceeds much rapidly, the conversion of the halogen end groups rises almost linearly at the early stage and the nearly complete (>95%) dehalogenation of the polymeric chains is observed after only 12 h reaction. However, the molecular weights rise and the polydispersities become wider after the modification, which implies that the modification is accompanied with the couple termination of the polystyrene radicals besides chain transfer reaction. Furthermore, the couple termination can be restrained at some lower catalyst concentration. Indeed, the modified polymers show improved thermal stability, the initial weight loss temperatures is increased from 196 °C to 378 °C for the linear polystyrene and from 203 °C to 261 °C for the hyperbranched polystyrene.     

Grafting of caprolacton to cellulose acetate by reactive processing

Cellulose acetate was successfully modified with caprolacton in an internal mixer at temperatures between 120 and 220 °C, and reaction times between 5 and 45 min in the presence of tin-octoate catalyst. The efficiency of modification and the structure of the product were analyzed by SEC, ¹H NMR, and FTIR spectroscopy. Significant modification of cellulose acetate did not occur at low temperatures, below 180 °C. Grafting efficiency increased with increasing temperature and time. The extent of grafting could be estimated from the amount of material extracted from the samples by toluene and by FTIR analysis, from the relative intensity of -CH₂- and -CH₃ vibrations. The amount of polycaprolacton homopolymer is relatively low at the end of the reaction; the efficiency of grafting is good. Although high temperature and long reaction time favor grafting, considerable degradation of the product occurs under these conditions. Quantitative analysis showed that the average length of grafted oligomeric caprolacton chains is around 3 monomer units. The chains attached to the CA backbone internally plasticize the polymer leading to a considerable decrease of its glass transition temperature.     

Free radical copolymerization of methyl substituted stilbenes with maleic anhydride

Stilbene-maleic anhydride is a well-known donor-acceptor comonomer pair which undergoes free radical copolymerization to form an alternating copolymer. A series of methyl substituted stilbenes were synthesized and copolymerized with maleic anhydride. A conversion versus time study was undertaken to understand the methyl substituent effect on copolymerization rates. Methyl substituents on the phenyl ring of stilbene can change the reactivity of stilbene by changing the resonance stability of the propagating radical and steric hindrance in the propagation step and thereby change the copolymerization rate. Methyl substituted stilbene-maleic anhydride copolymers were determined by quantitative ¹³C 1D NMR to be alternating copolymers. Size exclusion chromatography (SEC) measurements showed that the weight-average molecular weights of these copolymers varied from 3000 to over 1,000,000 g/mol. Interchain aggregation was observed in poly((E)-4-methylstilbene-alt-maleic anhydride) by dynamic light scattering (DLS). The SEC trace for poly((E)-4-methylstilbene-alt-maleic anhydride) exhibited bimodal peaks. No glass transition temperature or crystalline melting temperature was observed between 0 °C and 250 °C by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) showed that these polymers have 5% weight loss around 290 °C.     

Synthesis and characterization of some novel aromatic polyimides

Three new diamines 1,2-di(p-aminophenyloxy)ethylene, 2-(4-aminophenoxy)methyl-5-aminobenzimidazole and 4,4-(aminopheyloxy) phenyl-4-aminobenzamide were synthesized and polymerized with 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BP), 4,4′-(hexafluoroisopropyledene)diphthalic anhydride (HF) and 3,4,9,10-perylene tetracarboxylic acid dianhydride (PD) either by one step solution polymerization reaction or by two step procedure. The later includes ring opening poly-addition to give poly(amic acid), followed by cyclodehydration to polyimides with the inherent viscosities 0.62-0.97 dl/g. Majority of polymers are found to be soluble in most of the organic solvents such as DMSO, DMF, DMAc, m-cresol even at room temperature and few becomes soluble on heating. The degradation temperature of the resultant polymers falls in the ranges from 240 °C to 550 °C in nitrogen (with only 10% weight loss). Specific heat capacity at 300 °C ranges from 1.1899 to 5.2541 J g⁻¹ k⁻¹. The maximum degradation temperature ranges from 250 to 620 °C. T_g values of the polyimides ranged from 168 to 254 °C.     

Synthesis of 1-vinylpyrrole-2-carbonitriles

A new highly synthetically potent series of bifunctional pyrroles, 1-vinylpyrrole-2-carbonitriles, were synthesized from readily available 1-vinylpyrrole-2-carbaldehyde oximes by two methods: (1) reaction with acetylene (KOH/DMSO, 70 °C, 10 min, yields 58-67%) and (2) reaction with acetic anhydride (90-100 °C, 5 h, yields 83-93%). Starting from 2-phenyl-1-vinylpyrrole, the one-pot synthesis of the corresponding 1-vinyl-2-carbonitrile was accomplished directly by successive treatment with a DMF/(COCl)₂ complex, NH₂OH·HCl/NaOAc, and acetic anhydride (yield 58%).     

Study on thermal cure and heat-resistant properties of N-(3-acetylenephenyl)maleimide monomer

N-(3-acetylenephenyl)maleimide (3-APMI), was synthesized by reacting 3-aminophenylacetylene (3-APA) with maleic anhydride by the usual two-step procedure that included ring-opening addition to give maleamic acid, followed by cyclodehydration to maleimide. Structure of the monomer was confirmed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), elemental analysis (EA) and mass spectrum (MS). Thermal cure of the monomer was investigated by differential scanning calorimetry (DSC) and FTIR, then processing parameters and cure kinetics parameters were determined. The results showed that the monomer possesses excellent reactivity, whose cure peak temperature was 197.9 °C and cure reaction was almost complete after 4 h cure at 200 °C. Thermal properties of the cured monomer were determined by dynamic mechanical analysis (DMA) and the results show that glass transition temperature (represented by onset temperature of storage modulus) is high up to 460 °C. The results of thermogravimetry analysis (TGA) reveal that the cured monomer possessed excellent thermal stability, whose 10% weight loss temperature (T_10%) is 515.6 °C and char yield at 800 °C is 59.1%. All these characteristics make the 3-APMI monomer be an ideal candidate for matrix of thermo-resistant composites.     

Pretreatment of water samples using UV irradiation-peroxodisulfate for the determination of total mercury

Potassium peroxodisulfate (14 g l⁻¹, 25 ml) has been observed to readily oxidize water under UV irradiation (30 W mercury arc tube), even at room temperature. The reaction is complete in 20 min, producing oxygen in stoichiometric amounts. The reaction was applied to pretreatment for the determination of total mercury by cold vapor atomic absorption spectrometry (AAS).The response of mercury(II) chloride by the UV irradiation method was higher than that by the standard permanganate method (95 °C, 2 h). The conversion efficiency of mercury by the UV irradiation method, the standard method and by non-treatment was found to be 100, 93.6 and 85.0%, respectively. The study is also applied to methylmercury, ethylmercury and phenylmercury chlorides.     

Microwave-assisted high-throughput derivatization techniques utilizing silicon carbide microtiter platforms

Parallel microwave-assisted gas chromatography (GC) derivatization protocols utilizing a silicon carbide (SiC)-based microtiter plate platform fitted with screw-capped GC vials were developed. For three selected standard derivatization protocols such as acetylation (exemplified for morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) complete derivatization was achieved within 5 min at 100 °C in a dedicated multimode microwave instrument using online temperature monitoring. Microwave irradiation leads to rapid and homogeneous heating of the strongly microwave-absorbing SiC plate, with minimal deviations in the temperature recorded at different positions of the plate. The current platform allows the simultaneous derivatization of 80 reaction mixtures under strictly controlled temperature conditions. Similar results can also be obtained using a standard hotplate as heating source, although heating to the target temperature of 100 °C is slightly slower. The results demonstrate that parallel microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

A comparison of solid-phase microextraction and stir bar sorptive extraction coupled to liquid chromatography for the rapid analysis of resveratrol isomers in wines, musts and fruit juices

A comparison of direct immersion solid-phase microextraction (DI-SPME) and stir bar sorptive extraction (SBSE) coupled to liquid chromatography (HPLC) with fluorimetric detection for the rapid analysis of resveratrol isomers is described. For DI-SPME, a polar Carbowax-template resin (CW/TPR) 50 μm fiber was the most efficient and optimum extraction conditions were 40 °C and an extraction time of 30 min, stirring in the presence of 5% (m/v) sodium chloride and 0.07 M acetate/acetic acid buffer (pH 6). Desorption was carried out using the static mode for 10 min. Linearity was obtained in the 5-150 and 2-150 ng mL⁻¹ ranges for trans- and cis-resveratrol, with detection limits of 2 and 0.5 ng mL⁻¹, respectively. When using SBSE, a polydimethylsiloxane (PDMS) twister provided best extraction by means of a derivatization reaction in the presence of acetic anhydride and potassium carbonate. The same time and temperature were used for the extraction step in the presence of 2.5% (m/v) sodium chloride, and liquid desorption was performed with 150 μL of a 50/50 (v/v) acetonitrile/1% (v/v) acetic acid solution in a desorption time of 15 min. Linearity was now between 0.5 and 50 ng mL⁻¹ for trans-resveratrol with a detection limit of 0.1 ng mL⁻¹, while cis-resveratrol could not be extracted. The proposed methods were successfully applied to determining the resveratrol isomer content of wine, must and fruit juices.     

Dynamic mechanical and thermal behavior of liquid-crystalline polybutadiene-diols with mesogenic groups in side chains

Liquid-crystalline polybutadiene-diols (LCPBDs) with the comb-like architecture were synthesized by reaction of a LC thiol with the double bonds of telechelic HO-terminated polybutadiene (PBD). LCPBDs with various initial molar ratios of thiol to double bonds of PBD, R₀, in the range from 0.15 to 1, were prepared by the radical reaction at temperature 60 °C for 48 h. The experimentally obtained degree of modification, R_e, after the reaction and purification, was determined from elemental analysis - from the amount of sulphur bounded in LCPBDs, GPC and from ¹H NMR spectra. The physical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. With increasing R_e ratio the glass transition temperature of LCPBDs, T_g, increases from ∼ − 45 °C (neat PBD) to ∼20 °C (R_e ∼ 0.5). LC transition starts at R_e ∼ 0.27 (the transition temperature T_m ∼ 27 °C). With increasing R_e temperature T_m increases and for R_e ∼ 0.5 reaches the value T_m ∼ 74 °C; at the same time also the change in enthalpy at LC transition increases. The LC transition could be detected also by the dynamic mechanical spectroscopy; especially shape and position of mechanical functions on frequency and free volume parameters strongly depend on degree of modification.     

Solid-state cis-trans isomerization reaction of (η-MeC5H4)W(CO)2P(OPr)3I

cis-(η⁵-MeC₅H₄)W(CO)₂P(OⁱPr)₃I (1) was converted to the trans isomer 2 in the solid state (90-110 °C). The reaction was monitored by heating 1 in NMR tubes for periods of time (2-60 min), cooling the tubes to room temperature and determining the conversion by solution ³¹P and ¹H NMR spectroscopy. The data were consistent with a first-order reaction and yielded an activation energy of 59 ± 3 kJ mol⁻¹. Comparative kinetic data were obtained from an in situ analysis of a powder-XRD study of 1. The powder-XRD study was conducted at 80-100 °C (10-60 min), yielding an activation energy of 52 ± 2 kJ mol⁻¹ (first-order reaction). The reaction could not be monitored by single crystal X-ray diffraction as the crystal disintegrated over time on heating. This disintegration process was monitored by optical microscopy and revealed that while the bulk crystal morphology was retained the crystal surface roughened with time. The compounds 1 and 2 were also structurally characterised by X-ray crystallographic techniques.     

An evaluation of microwave-assisted derivatization procedures using hyphenated mass spectrometric techniques

The potential of microwave-assisted derivatization techniques in systematic toxicological analysis using gas chromatography coupled with mass spectrometry (GC–MS) was evaluated. Special emphasis was placed on the use of dedicated microwave reactors incorporating online temperature and pressure control. The use of such equipment allowed a detailed analysis of several microwave-assisted derivatization protocols comparing the efficiency of microwave and conventional heating methods utilizing a combination of GC–MS and liquid chromatography coupled with mass detection (LC–MS and LC–MS/MS) techniques. These studies revealed that for standard derivatization protocols such as acetylation (exemplified for codeine and morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) a reaction time of 5 min at 100 °C in a microwave reactor was sufficient to allow for an effective derivatization. Control experiments using standard operating procedures (30 min at 60 °C conventional heating) indicated that the faster derivatization under microwave irradiation is a consequence of the higher reaction temperatures that can rapidly be attained in a sealed vessel and the more efficient heat transfer to the reaction mixture applying direct in core microwave dielectric heating. The results suggest that microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

Microwave fluorination: a novel, rapid approach to fluorination with Selectfluor

Fluorination of electron rich aromatic systems with electrophilic fluorination reagents such as Selectfluor^® and Accufluor^® is a well-established process. Herein we report results from investigations into the use of such procedures to perform rapid, small-scale fluorinations under microwave irradiation. We have investigated the transformation with a range of different substrates and discuss the effects of two key factors, namely reaction time and choice of fluorination reagent. The use of Selectfluor^® in acetonitrile at 150 °C with microwave heating for 10 min affords products in comparable yields to those obtained by prolonged heating in acetonitrile at its reflux temperature.     

Phenylethynylnaphthalic endcapped imide oligomers with reduced cure temperatures

A series of 4-(2-phenylethynyl)-1,8-naphthalic anhydride (PENA) endcapped imide oligomers with different chemical backbones and calculated number average molecular weights (Calc’d M_n) were successfully synthesized and characterized. The PENA-endcapped imide oligomers were mixtures of mono- and double-endcapped imide oligomers with polymerization degree (P_n) of 1-5 and number average molecular weights (M_n) of 2515-3851 g/mol. determined by GPC. Study on effect of chemical structures on the curing behaviors of two model compounds: PENA-m based on PENA and PEPA-m derived from 4-phenylethynylphthalic anhydride (PEPA) revealed that PENA-m showed the cure temperature of 50 °C lower than PEPA-m and the activity energy of thermal curing reaction for PENA-m was also lower than that of PEPA-m. The PENA-endcapped imide oligomers could be melt at temperatures of >250 °C with the minimum melt viscosity of 1.2-230 Pa s at 275-301 °C and the widen melt processing windows, along with 10-40 °C lower cure temperature than the PEPA-endcapped analogue.The PENA-endcapped imide oligomers could be thermally cured at 350 °C/1 h to afford the thermally cured polyimides with good combined thermal and mechanical properties including T_g of 344-397 °C (DMA), T_d of 443-513 °C, tensile strength of as high as 54.7 MPa, flexural strength of as high as 126.1 MPa and modulus of as high as 2.3 GPa, respectively.     

A rapid, one-pot, four-component route to 2H-indazolo[2,1-b]phthalazine-triones

A new, efficient, and environmentally benign protocol for the one-pot, four-component synthesis of 2,2-dimethyl-13-phenyl-2,3-dihydro-1H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione by condensation of phthalic anhydride, hydrazinium hydroxide, aromatic aldehydes, and dimedone catalyzed by Ce(SO₄)₂·4H₂O as an ecofriendly catalyst with high catalytic activity and reusability at 125 °C under solvent-free conditions is reported. The reaction proceeds to completion within 5-10 min in 71-95% yield. To the best of our knowledge, this new procedure provides the first example of an efficient synthetic method for 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione via a four-component reaction.     

Stereoselective Heck arylation of a functionalized cyclopentenyl ether using (S)-N-methyl-pyrrolidine as the stereochemical controller

The study of a series of palladium(0)-catalyzed C2-arylations of a 1-cyclopentenyl ether equipped with a chiral (S)-N-methyl-pyrrolidine auxiliary is reported. Stereoselective Heck monoarylations were performed using aryl iodides under classical heating conditions for 1.7-3.0 h at 80 °C and in one case using 30 min of microwave irradiation at 110 °C. To further explore the scope and nature of this stereoselective methodology, aryl bromides were also utilized as arylating agents, using 20 min of microwave processing at 120-130 °C. High to excellent diastereopurities (90-98% de) were obtained according to ¹H NMR and GC-MS analyses. The prolinol fragment apparently controlled the diastereoselectivity of the Heck reaction by presenting the arylpalladium species from the preferred side of the double bond. By X-ray structure diffraction analysis of an N-quaternized Heck product, the absolute configuration of the new stereocenter was established as (R), supporting a Si-face migratory insertion.     

A kinetic study of the decross-linking of cross-linked polyethylene in supercritical methanol

The recycling of cross-linked polyethylene (XLPE) by a decross-linking reaction in supercritical methanol was studied using a batch reactor. XLPEs with initial gel contents of 45, 55 and 65% were employed and subjected to reaction temperatures between 320 and 360 °C. Complete decross-linking of XLPE was achieved in 10 min in supercritical methanol at 360 °C and 15 MPa. For the first time, chemical kinetics for the decross-linking reaction is proposed based on the gel concentration, and applicable to the reactor design. With respect to the gel concentration, the first-order reaction model agreed well with the experimental results. The evaluated kinetic constant was 0.0867 ± 0.0082 cm³/mg min at 350 °C, and the activation energy was 578 ± 25 kJ/mol.     

Lipase-catalyzed synthesis of biodegradable copolymer containing malic acid units in solvent-free system

This work is to explore a new route to synthesize functional polyesters bearing pendant hydroxyl groups. The approach is via biocatalyzed direct polycondensation. l-Malic acid, adipic acid and 1,8-octanediol were used as comonomers and lipase Novozym 435 as a biocatalyst. ¹H NMR studies on the structure of the products indicated that Novozym 435 was strictly selective for esterification of l-malic acid carboxyl groups while leaving the hydroxyl groups unchanged. The influences of the monomer feeding ratio, reaction temperature, and reaction time on the molecular weight of the products were investigated. By varying l-malic acid feed ratio in the total monomers from 0 to 20 mol%, the molecular weight (M_W) of the product changed from 9.5 kilo Dalton (kD) to 4.7 kD while reaction was held at 70 °C for 48 h. The maximum M_W could reach 7.4 kD at 80 °C when varying temperature between 70 and 90 °C if l-malic acid is 20 mol% and reaction time is 48 h. At 75 °C the M_W increased from 5.2 kD to 6.6 kD when reaction time was elongated from 48 h to 72 h. However, little change in M_W was observed at 80 and 85 °C when the reaction time was above 48 h. Thermal property of the copolyesters was studied by differential scanning calorimetry (DSC). Increasing the l-malic acid content in copolyesters resulted in melting temperature depression.