Reaction mechanisms of polyacrylonitrile on thermal treatment

A high-temperature radical scavenger, 2,2-diphenyl-l-picryl hydrazyl (DPPH), has been used to study the reaction mechanisms of polyacrylonitrile (PAN) on thermal treatment. The effect of DPPH on the cyclization reaction of PAN in both air and nitrogen, investigated by differential scanning calorimetry (DSC), helped to verify the proposed reaction mechanisms, i.e., the free radical and the ionic ones. For PAN homopolymer, the peak temperature of the reaction exotherm shifted to higher temperatures and the heat of reaction was decreased with increasing DPPH concentration. For PAN copolymer with methylacrylate and itaconic acid, however, the effects of DPPH on DSC thermograms were insignificant. The effects of IPPH suggest that the reaction of the nitrile groups proceeds by free radicals for the homopolymer while by ions for the copolymer. The activation energies for the thermal reactions of PAN in both air and nitrogen were also estimated by the dynamic DSC method, and they proved to be highly dependent on reaction mechanism, environment of thermal treatment, and DPPH concentration.     

ZnS deposition on oxadiazole–terpyridine copolymer

The combination of inorganic salts and macromolecules leads to supramolecular structures with new interesting physical and chemical properties. The deposition of ZnS (Wurtzite) on oxadiazole–terpyridine copolymer P‐90/10 synthesized by free radical copolymerization were investigated. The apparent order of the crystallization process was found to be 2 that indicated a surface diffusion‐controlled mechanism. Critical nucleus formation proceeds via complexation of the ZnS molecules to the ? N? atoms as concluded from computational chemistry calculations. The number of ions forming the critical nucleus was found experimentally to be (n*exp = 1.71 ± 0.24) in accordance with the computational chemistry calculations by the PM3 method of the MOPAC program package. The surface energy of the growing ZnS phase was found to be 121 mJ/m² typical for sparingly soluble salts. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1913–1918, 2006     

外源抗氧化剂7-(4-氨基-1,2,4-三唑-5-)硫乙氧基黄酮及其意外乙酰化产物的合成

7-溴乙氧基黄酮与3-取代-4-氨基-1,2,4-三唑-5-硫醇类化合物缩合反应得到7-(4-氨基-1,2,4-三唑-5-)硫乙氧基黄酮,为了增加其脂溶性,将该类化合物进一步与乙酸酐回流反应12 h,得到的化合物不是预期的7-(3-取代-4-乙酰氨基-1,2,4-三唑-5-)硫乙氧基黄酮衍生物,而是7-[3-取代-4-(2-乙酰氧基)-乙亚氨基-1,2,4-三唑-5-]硫乙氧基黄酮,分别用红外、核磁共振氢谱及碳谱、质谱和元素分析对这4个乙酰化产物的结构进行了确证。以清除超氧自由基、羟自由基、亚硝基自由基和2,2-二苯基-1-苦味酰基自由基的活性及总还原能力为指标,测定比较了4个7-(3-取代-4-氨基-1,2,4-三唑-5-)硫乙氧基黄酮化合物及其意外乙酰化产物的体外抗氧化活性。结果表明,在测定浓度下,乙酰化衍生物7-[3-对甲氧苯基-4-(2-乙酰氧基)-乙亚氨基-1,2,4-三唑-5-]硫乙氧基黄酮较其前体抗氧化活性强。     

Some well characterized chemical reactivities of buckminsterfullerene (C60)

The metalation, halogenation and free radical addition chemistry of C₆₀ is described. Vibrational spectroscopy is a useful tool in assigning the structures of the products. Several underlying principles emerge for C₆₀ chemistry, some of which are supported by molecular orbital calculations.     

The Peroxysilicate Question. 29Si-NMR Evidence for the Role of Silicates in Alkaline Peroxide Brightening of Mechanical Pulp

The influence of hydrogen peroxide on the chemistry of aqueous silicates was investigated by high-resolution ²⁹Si-NMR and electrochemical methods. The observations indicate that dissolved silicates form labile complexes with radical H₂O₂-decomposition products, possibly O₂·^?. An important role of soluble silicates in peroxide bleaching liquors thus might be to affect the activity of free radical species which mediate H₂O₂ bleaching and decomposition reactions. Attempts to prepare the widely reported peroxysilicates from silicate/H₂O₂/NaOH mixtures resulted in the isolation of Na₂O₂·8H₂O.     

Styrenated urethane oil synthesis via CuAAC “click” chemistry approach

In this study, a novel route for the modification of sunflower oil-based partial triglycerides with styrene (St) was described. For this purpose, in the first step, copolymers of St and 4-chloromethyl styrene (P(St-co-CMS)) were synthesized by free radical polymerization (FRP) and controlled/living radical polymerization (nitroxide mediated radical polymerization (NMRP)) methods. In the second step, chloro groups of these samples were transformed into azido groups by using NaN₃/DMF and then azido groups were coupled with propargyl alcohol to achieve hydroxyl functional polystyrene chain (PSt-OH) via Cu(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition (CuAAC) “click” chemistry approach. Finally, alcohol groups of PSt-OH and the partial glyceride (PG) were combined by the reaction with toluene 2,4-diisocyanate (TDI). As a result, styrenated urethane oil (PG-TDI-PSt) was obtained as an oil-based binder. The structures were determined by FT-IR, ¹H NMR and GPC analyses, and film properties of the products were examined according to the related standards. (PG-TDI-PSt) gave good film properties, and therefore could be considered as an applicable oil-based binder.     

Use of in-situ electron paramagnetic resonance to assess formation of free radicals and their role in the hydroliquefaction of coal

The depolymerization of coal is generally presumed to proceed via a free radical mechanism. A unique electron spin resonance cavity that allows the observation of free radical formation and behaviour under hydroliquefaction conditions (500 °C and 12.4 MPa) was designed to facilitate the study of the effect of process variables on the formation of free radicals. Parallel experiments were carried out in autoclaves, and the degree of conversion and quality of coal-derived liquids produced was assessed. Correlative statistical models were established that allow the quantitative determination of the effect of process variables, and their interactions, on the production and behaviour of free radicals and of coal-derived liquids produced. Strong evidence was obtained that free radical chemistry plays a key role in determining the degree of coal conversion and quality of products. The kinetics and mechanism of hydroliquefaction are addressed with the explicit inclusion of experimental free radical concentration in the kinetic expressions. Progressive and regressive reactions are discussed. Optimum combinations (‘processing windows’) of process variables can be identified.     

Preliminary analysis of the 1H-NMR and 13C-NMR spectra of poly(2-vinylpyrazine)

Summary The title polymer was synthesized by free radical initiation. The ¹H-NMR and ¹³C-NMR spectra revealed several resonances that were sensitive to polymer stereosequence distribution. Analysis of these resonances showed that free radical initiated poly (2-vinyl pyrazine) is an atactic polymer, a result consistent with data accumulated for other poly vinylheterocycle initiated free radically.     

Synthesis and characterization of POSS hybrid organogels using Menschutkin quaternization chemistry

The present research describes a series of organic–inorganic hybrid gels based on polystyrene and polyhedral oligomeric silsesquioxanes (POSSs) prepared using free radical copolymerization and Menschutkin chemistry techniques. In the first step, poly(styrene‐co‐chloromethylstyrene) is readily achieved by thermally initiated radical copolymerization and the subsequently obtained copolymer reacts with diethanolamine functional POSS nanoparticles which are employed as the crosslinker. The resulting hybrid network possesses ionic moieties and inorganic POSS nanoparticles. The POSS‐containing hybrid gels exhibit excellent organic solvent absorption and show good mechanical behaviour. Gel containing 0.8 × 10^?3 mmol of POSS(DEA)₈ (DEA, diethanolamine) reached the highest swelling ratio; hence, the corresponding gel can absorb organic solvent up to 20× its weight. The rate constant, coefficients and diffusional behaviour of hybrid organogels in organic solvent were examined as well. The organic solvent intake of the hybrid gel follows a non‐Fickian type diffusion. © 2018 Society of Chemical Industry     

Kinetic and structural studies of the polymerization of N,N′‐bismaleimide‐4,4′‐diphenylmethane with barbituric acid

Both the isothermal and non‐isothermal polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) with barbituric acid (BTA) were investigated by the differential scanning calorimeter. The experimental results showed that the polymerizations of BMI with BTA were governed by the competitive Michael addition reaction and free radical polymerization mechanisms. Furthermore, the contribution of free radical polymerization becomes more important when the mole fraction of BTA decreases. ¹H NMR and ¹³C NMR measurements further support the coexistence of the Michael addition reaction and free radical polymerization mechanisms. A preliminary kinetic model that took into account the competitive Michael addition reaction and free radical polymerization mechanisms was developed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Free radical polymerization and lipid binding of lysozyme reacted with peroxidizing linoleic acid

Insolubilization and polymerization of proteins exposed to peroxidizing lipids may be due either to cross-linking with incorporation of fragments of the lipid oxidation products, or to free radical transfer from lipid to protein and subsequent free radical polymerization of protein. The second mechanism which has been proposed was inferred from measurements of electron spin resonance signals in proteins. In this study, uniformly labeled linoleic acid, [¹⁴C(U)] LA, was reacted with lysozyme. Volatile oxidation products of LA were also used in some experiments. Incubation was done in the absence of water. Oligomers of lysozyme, as well as the monomer, were isolated after incubation, and the [¹⁴C] label incorporated into each fraction was determined. The results show that the dominant mechanism of protein polymerization after exposure to peroxidizing linoleic acid is the transfer of free radical from lipid to protein, and subsequent free radical polymerization.     

An analysis of the 1H- and 13C-NMR spectra of poly(6-vinyl-1,4-benzodioxane)

Summary The title monomer was synthesized from the corresponding aldehyde via a Wittig reaction. The monomer was polymerized using free radical initiation and its high field ¹H- and ¹³C-NMR spectra were recorded. When analyzed in terms of stereochemistry the spectra showed poly(6-vinyl-1,4-benzodioxane) is an atactic polymer when synthesized via free radical initiation.     

Analysis of the 1H-NMR and 13C-NMR spectra of poly(5-ethyl-2-vinyl thiophene)

Summary The title polymer was synthesized by free radical initiation. The ¹H-NMR and ¹³C-NMR spectra were recorded and analyzed in terms of polymer stereochemistry. By comparison of the results to those previously obtained, free radical initiated poly(5-ethyl-2-vinyl thiophene) was shown to be an atactic polymer.     

Free Radical and Direct Ozone Reaction Competition to Remove Priority and Pharmaceutical Water Contaminants with Single and Hydrogen Peroxide Ozonation Systems

From the application of concepts derived from the gas-liquid absorption film model, the competition between ozone reactions with 72 water emerging or priority contaminants (pharmaceuticals, pesticides, polynuclear aromatic hydrocarbons, etc.) and the initiation steps of the hydroxyl radical decomposition of ozone in ozone alone and combined with hydrogen peroxide oxidation systems has been studied. With this information, the ozone preferential reaction, that is, the ozone direct reaction or the formation of free radicals and the kinetic absorption regime are known. In a second step, the ratio of removal rates of the contaminants studied by reacting with hydroxyl radical and ozone has also been estimated. With this, the way contaminants are preferentially removed (from their reaction with ozone or from the reaction with free radicals) can also be known and, hence, whether or not an ozone advanced oxidation system is convenient to be applied. For instance, most of the contaminants studied in this work at concentrations lower than 50 μgL^?1 and hydrogen peroxide at concentrations lower than 50 mgL^?1 react with ozone under chemical control regime so that both direct and free radical reactions theoretically compete. However, under chemical control, typical concentration of scavengers present in wastewater or surface water would inhibit the free radical reactions and, at least theoretically, for many contaminants studied here, the direct ozone reaction is the principal removal way. When mass transfer controls the process rate only contaminants with a hydroxyl and ozone rate constant ratio ≥ 1.6x10⁶ M^-1s^-1 would be preferentially removed through free radical way.     

An analysis of the 1H- and 13C-NMR spectra of poly(3-bromostyrene)

Summary The 300 MHz ¹H-NMR spectrum of free radical initiated poly(3-bromostyrene) is similar to the ¹H-NMR spectra of certain poly(vinyl heterocycles) and can be interpreted in a like manner. The ¹³C-NMR is typical of spectra for meta-substituted polystyrenes, with some of the carbon resonances showing a sensitivity to polymer stereochemistry. The spectra indicate that poly(3-bromostyrene) synthesized by free radical initiation is an atactic polymer.     

Increase of adhesive bond strength through the mechanochemical creation of free radicals: I

A new technique for improving the strength of bonded joints between various materials and different adhesives is described. Increased strength was obtained by mechanical Surface Activation Beneath Reactive Adhesives (SABRA). This technique results in higher bond energies due to the creation of free radicals. The surfaces were activated by abrasion with emery paper in the presence of the adhesive itself (epoxy), or of some suitable primer such as methyl methacrylate, acrylonitrile (AN) or hydrogen sulfide gas. The effects of this technique were demonstrated by four different methods: 1) Improved wetting of standard epoxy or water drops on the treated surface. 2) Achievement of bond energies between primers and polymeric surfaces exceeding the energy of solution in solvents, which were revealed by attenuated total reflectance infrared. 3) The detection of free radicals created by bond scission during abrasion by means of diphenylpicryl hydrazyl, (DPPH), a free radical scavenger, monitored by spec-trocolorimetry, 4) Destructive testing of single lap joint test Pieces, scarfed tube joints and pee) test samples. These experiments will be described in a second paper. The theoretical base of the new approach is supported by a tentative estimate of energies set free by mechanochemical creation of free radicals and the excess heat released during abrasion.     

An analysis of the 300 MHz spectrum of poly(3-vinyl pyridine)

Summary 3-Vinyl pyridine was synthesized and the monomer was then polymerized employing free radical initiation. The 300 MHz ¹H-NMR spectrum was recorded and analyzed in terms of polymer stereochemistry. The results of the analysis strongly indicate that poly(3-vinyl pyridine) synthesized using free radical initiation is an atactic polymer.     

An investigation into the degree and rate of polymerization of poly(methyl methacrylate) in the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate

Room‐temperature ionic liquids (ILs), including 1‐butyl‐3‐methylimidazolium hexafluorophosphate, [bmim⁺][PF₆^?], were investigated as replacements for volatile organic compounds in the free‐radical solution polymerization of poly(methyl methacrylate) (PMMA). The latter was synthesized in benzene and [bmim⁺][PF₆^?] at 70 °C via a free‐radical process and the degree and rate of polymerization were compared based on the solvent used. The degree of polymerization was found to be five times higher in [bmim⁺][PF₆^?] than in benzene, while the rate of reaction was approximately four times faster in [bmim⁺][PF₆^?]. The results indicate the potential for using ILs to produce high‐molecular‐weight polymers and block structures based on the increased free‐radical stability in ILs. Copyright © 2004 Society of Chemical Industry     

Poly(methyl methacrylate)/clay nanocomposites by photoinitiated free radical polymerization using intercalated monomer

A series of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposite were prepared by successfully dispersing the inorganic nanolayers of MMT clay in an organic PMMA matrix via in situ photoinitiated free radical polymerization. Methyl methacrylate monomer was first intercalated into the interlayer regions of organophilic clay hosts by “click” chemistry followed by a typical photoinitiated free radical polymerization. The intercalated monomer was characterized by FT-IR spectroscopy, elemental analysis and thermogravimetric analysis methods. The intercalation ability of the modified monomer and exfoliated nanocomposite structure were confirmed by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Thermal stability of PMMA/MMT nanocomposites was also studied by both differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

UV‐ and thermally triggered ring‐opening metathesis polymerization for the spatially resolved functionalization of polymeric monolithic devices

Porous polymeric monolithic supports were prepared via electron beam‐triggered free radical polymerization using a mixture of ethyl methacrylate and trimethylolpropane triacrylate in 2‐propanol, 1‐dodecanol and toluene. Bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl acrylate (1) was grafted onto these monolithic supports in a spatially resolved way with the aid of masks using both electron beam‐ (EB) and UV‐triggered free radical polymerization. The thus immobilized norborn‐2‐ene‐containing graft polymers were further treated with the 2^nd‐generation Grubbs initiator, i.e., RuCl₂(PCy₃)(IMesH₂)(CHPh) (4) (IMesH₂ = 1,3‐dimesitylimidazolin‐2‐ylidene), and then reacted with bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl pyrene‐1‐carboxylate (2). Alternatively, monoliths completely grafted with poly‐ 1 were surface grafted with 2 in a spatially resolved way in the presence of a latent, UV‐triggerable precatalyst, i.e., [Ru(IMesH₂)(CF₃COO)(t‐BuCN)₄⁺ CF₃COO^?] (5). Finally, to demonstrate the utility of this chemistry, a 2^nd‐generation Grubbs initiator‐based approach was used to prepare a trypsin‐functionalized monolith‐containing chip device that allowed for the online digestion of N‐α‐benzoyl‐L ‐argininethylester hydrochloride. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011