Inhibited transesterification of PET/PBT blends filled with silica nanoparticles during melt processing

The blends of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) undergo transesterification reactions between PET and PBT during melt processing. In this research, PET/PBT transesterification has been investigated in the presence of nano-fillers, including pure SiO₂ and silane-coupling-agent-modified SiO₂. The results show that the incorporation of SiO₂ nanoparticles inhibits PET/PBT transesterification, and the influence of pure SiO₂ is higher than modified SiO₂. The inhibition of SiO₂ on transesterification is explained by the fact that the hydroxyl end groups of PET and PBT react with the surface hydroxyl groups of SiO₂ before transesterification due to the high activity of surface hydroxyl groups of SiO₂, and the reduction of hydroxyl end groups of PET and PBT leads to the inhibition of transesterification between PET and PBT. This has been demonstrated by the experimental data of TGA, FTIR, and XPS. And the reactivity of hydroxyl end groups of PBT is higher than that of PET.     

Synthesis and Fe(III)‐complexation ability of polyurethane bearing kojic acid skeleton in the main chain prepared by polyaddition of aliphatic hydroxyl groups without protection of phenolic hydroxyl groups

Polyaddition of a kojic acid dimer and diisocyanates yielded polyurethane with metal‐coordination ability owing to the phenolic hydroxyl groups of kojic acid. Although the kojic acid dimer contains two phenolic and two aliphatic hydroxyl groups, 1,5‐diazabicyclo[4.3.0]non‐5‐ene catalyzed polymerization proceeded through highly selective reactions of the aliphatic hydroxyl groups without any protection of the phenolic hydroxyl groups. The resulting polymers complexed with FeCl₃, and specific colorizations were observed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Selective reactivities and accessibilities of the hydroxyl groups in cotton cellulose based on equilibrium data from a reversible chemical reaction

In order to determine the relative equilibrium constants for reactions of the hydroxyl groups at C₂, C₃, and C₆ of the D-glucopyranosyl units, methyl vinyl sulfone was reacted with cellulose dissolved in benzyltrimethylammonium hydroxide. The reaction was carried to constancy in distribution of substituents between the 2–0– and 6–0–positions. The distributions of substituents in the D-glucopyranosyl units were measured by gas-liquid chromatographic analysis of the products from hydrolysis of the modified cellulose. Relative equilibrium constants were then evaluated, assuming complete accessibility of all three types of hydroxyl groups of the cellulose in solution. For determination of the relative accessibilities of the individual types of hydroxyl groups in heterogeneous reactions of cotton cellulose with methyl vinyl sulfone, the reactions were carried to equilibrium distributions in media of various normalities of sodium hydroxide (i.e., media of various swelling strength). The distributions of substituents in the D-glucopyranosyl units were measured. From these values and the ratio of equilibrium constants, the relative accessibilities of the hydroxyl groups at C₂ versus those at C₆ were calculated. Apparent accessibilities of the hydroxyl groups at C₂ are approximately double those at C₆ when the reaction is carried out in 1N sodium hydroxide and about triple those at C₆ when the reaction is carried out in 0.5N sodium hydroxide.     

IR spectroscopic investigation of structural hydroxyl groups in W−Si heteropolycompound supported on Al2O3

Structural hydroxyl and deuteroxyl groups within the K₄[SiW₁₂O₄₀]/Al₂O₃ and K₆[SiW₁₁PdO₃₉]/Al₂O₃ systems were studied by diffuse-reflectance FTIR spectroscopy in a spectral range of fundamental stretching vibrations, first overtones, and combination bands of stretching and bending vibrations. For hydroxyl groups, the region of combination vibrations is the most informative. The calculated frequencies of bending vibrations of hydroxyl groups (865 and 730 cm⁻¹) are characteristic of acidic OH groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2017–2020, October, 1999.     

Predicting H2S Oxidative Dehydrogenation over Graphene Oxides from First Principles

Spin-polarized periodic density functional theory was performed to characterize H₂S adsorption and dissociation on graphene oxides (GO) surface. The comprehensive reaction network of H₂S oxidation with epoxy and hydroxyl groups of GO was discussed. It is shown that the reduction reaction is mainly governed by epoxide ring opening and hydroxyl hydrogenation which is initiated by H transfer from H₂S or its derivatives. Furthermore, the presence of another OH group at the opposite side relative to the adsorbed H₂S activates the oxygen group to facilitate epoxide ring opening and hydroxyl hydrogenation. For H₂S interaction with -O and -OH groups adsorption on each side of graphene, the pathway is a favorable reaction path by the introduction of intermediate states, the predicted energy barriers are 3.2 and 10.4 kcal/mol, respectively, the second H transfer is the rate-determining step in the whole reaction process. In addition, our calculations suggest that both epoxy and hydroxyl groups can enhance the binding of S to the C-C bonds and the effect of hydroxyl group is more local than that of the epoxy.     

Effect of the Structure of Small Anatase Nanoparticles on the Localization of Photogenerated Charge Carriers

The structure of nanoparticles and the spatial arrangement of photogenerated thermalized charge carriers are studied for a series of isomers of small anatase nanoparticles (TiO₂)₂₉(H₂O)₄, (TiO₂)₇₀(H₂O)₄, and (TiO₂)₇₀ with faces (001) and (101) on the surface. It is shown that the location of surface hydroxyl groups and their replacement by surface oxygen atoms affect the nature and degree of deformation of the nanoparticle structure. The location of the boundary orbitals depends both on the size of the nanoparticles and on the location of the hydroxyl groups, as well as on the degree of dehydroxylation, which leads to the replacement of the hydroxyl groups by the surface oxygen atoms. In the case of a certain arrangement of hydroxyl groups or surface oxygen atoms, uncharged small stoichiometric anatase nanoparticles begin to absorb light in the visible region of the spectrum (the band gap width E_g decreasing to 2.25 eV). This is associated with the energy levels at the edge of the band gap near the valence band and the conduction band.     

Radical cyclopolymerization of dimethacrylates bearing rigid adamantane-like core derived from naturally occurring myo-inositol

Dimethacrylates with rigid adamantane-like cores were synthesized from myo-inositol orthoester via a sequence of (a) acylation or silylation of the equatorially oriented hydroxyl group, followed by (b) attachment of methacrylate groups on the axially oriented hydroxyl groups. The radical homopolymerization of these compounds proceeded via cyclopolymerization without crosslinking, as the two axially oriented methacrylate groups were fixed in close proximity with each other. The dimethacrylates underwent radical copolymerization with methyl methacrylate (MMA) to afford the corresponding polymethacrylates, exhibiting high glass transition temperatures (T_g), due to the introduction of the rigid orthoester moieties originating from the monomers and the macrocyclic structures formed via intramolecular cyclization of the two methacrylate groups of the monomers. The polymers obtained by polymerization of the dimethacrylate bearing a silylated hydroxyl group served as precursors of hydroxyl-bearing polymers, which also exhibited high T_g due to the formation of a hydrogen bonding network between the hydroxyl groups.     

Improvement of Fluorescence Lifetime from Er-Doped Sol-Gel Silica Glass by Dehydration in CCl4

Monolithic Er-doped silica xerogels with erbium content of 5000 ppm were prepared by sol-gel technique. Samples were densified by thermal treatment in O₂/CCl₄ environment. The 1.55 m photoluminescence lifetimes after annealing at different temperatures were measured, together with the relative content of hydroxyl groups inside the samples. It was found that hydroxyl groups can be removed by CCl₄ effectively. Consequently the photoluminescence lifetime of the samples increased significantly after the removal of hydroxyl groups. For sample treated in O₂/CCl₄ at 900°C, fluorescence lifetime as long as 6ms was obtained and is pretty stable when the sample is kept in ambient air.     

Docking Site Modulation of Isostructural Covalent Organic Frameworks for CO2 Fixation

Three isostructural covalent organic frameworks (COFs) with either methoxyl, hydroxyl, or both groups on the channel wall, are synthesized and served as metal-free heterogeneous catalysts for chemical fixation of CO₂. Among them, the COF decorated with both hydroxyl and methoxyl groups named OMe-OH-TPBP-COF exhibits the highest catalytic activity and efficiency for CO₂ cycloaddition under mild conditions.     

Synthesis and NMR Characterization of Multi‐hydroxyl End‐groups PEG and PLGA‐PEG Barbell‐like Copolymers

Multi‐hydroxyl end‐groups poly(ethylene glycol) (PEG) was prepared from PEG and epichlorohydrin. Then, PEG‐supported poly(lactic‐ran‐glycolic acid) (PLGA)_n‐PEG‐(PLGA)_n (n=1, 2, 4) linear‐dendritic barbell‐like copolymers were synthesized through direct polycondensation under bulk condition from the multi‐hydroxyl end‐groups PEG, lactic acid and glycolic acid. Arm numbers were varied, with 2, 4 and 8, by using bis‐, tetra‐, and octa‐hydroxyl end‐groups PEG, respectively. The chemical structures, absolute number‐average molecular weight, the monomer units per single arm and the molar ratio of hydroxyl acid monomer units of the (PLGA)_n‐PEG‐(PLGA)_n barbell‐like copolymers were analyzed by NMR spectroscopy. The result indicated that the structures of the multi‐hydroxyl end‐groups PEG and (PLGA)_n‐PEG‐(PLGA)_n barbell‐like copolymers were consistent with design. Compared with the theoretical values, molecular weights determined by ¹H‐NMR end‐group analysis gave reasonably consistent values, but the values determined by gel permeation chromatography (GPC) were considerably less than theoretical values. The results indicated that (PLGA)_n‐PEG‐(PLGA)_n copolymers have linear‐dendritic structures.     

IR spectra of long-chain α,ω-alkanediols: 1,22-docosanediol and 1,44-tetratetracontanediol

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH₂)₂₂OH and HO(CH₂)₄₄OH, in the spectral range of 400–5000 cm^?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm^?1 (rocking vibrations of CH₂ groups) and 1463–1473 cm^?1 (bending vibrations of CH₂ groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH₂ wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.     

Hydroxyl‐Mediated Non‐oxidative Propane Dehydrogenation over VOx/γ‐Al2O3 Catalysts with Improved Stability

Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt‐based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface‐bound hydroxyl groups on VO_x / γ‐Al₂O₃ catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VO_x /Al₂O₃ catalyst (V?OH) are produced under H₂ pre‐reduction, and the catalytic performance for PDH is closely connected to the concentration of V?OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.     

DFT Theoretical Calculation of the Site Selectivity of Dihydroxylated (5, 0) Zigzag Carbon Nanotube

Functionalization is an important method to change electrical and thermodynamic properties of carbon nanotubes. In this study, the effect of functionalization of a single-walled carbon nanotube (SWCNT) was investigated with the aid of density functional theory. For this case, a (5, 0) zigzag SWCNT model containing 60 C atoms with 10 hydrogen atoms added to the dangling bonds of the perimeter carbons was used. To model hydroxyl CNT two terminal H atoms were replaced by two –OH groups. All the functionalized CNTs are thermodynamically more stable and have higher dipole moment with respect to the pristine CNT. Depending on the positions of hydroxyl groups on CNT five isomers of C₆₀H₈(OH)₂ were obtained. The structure of these five isomers and molecular properties such as the HOMO–LUMO gaps, the dipole moments, and the density of state were calculated. Our results indicate that the HOMO–LUMO gap strongly depends on the placement of the hydroxyl groups on the nanotubes. The isomers were hydroxyl groups locate on the anti-position show the highest distortions in the structure of the CNT.

     

Studies of the polymerization of diallyl compounds. XXVI. Enhanced polymerizability by the hydroxyl group in the polymerization of diallyl hydroxydicarboxylates

In order to elucidate the effect of the hydroxyl group on the polymerization of diallyl hydroxydicarboxylates, we investigated in detail the radical polymerizations of diallyl succinate (DASu), diallyl malate (DAMa), and diallyl tartrate (DATa), each of which have similar structure differing only in the number of hydroxyl groups present. The rate of polymerization (R_p) was quite enhanced in the order DASu < DAMa < DATa, in accord with the increase in the number of hydroxyl groups within a monomer unit. The enhanced ability of the allylic monomer radical to reinitiate chain growth was also in the same order, as was clear from the dependence of R_p on the initiator concentration. The dependence of the residual unsaturation of the polymer on the monomer concentration in the polymerizations of DAMa and DATa was abnormal in terms of cyclopolymerization. These results are discussed in connection with the formation of the intermolecular hydrogen bond through the hydroxyl groups.     

Methyl 3‐O‐β‐l‐fucopyranosyl α‐d‐glucopyranoside trihydrate

The water content of the title compound, C₁₃H₂₄O₁₀·3H₂O, creates an extensive hydrogen‐bonding pattern, with all the hydroxyl groups of the disaccharide acting as hydrogen‐bond donors and acceptors. The water molecules are arranged in columns along the crystallographic b axis and form, together with one of the hydroxyl groups, infinite hydrogen‐bonded chains. The conformation of the disaccharide is described by glycosidic torsion angles of −38 and 18°.     

CO2 Capture by Hydroxylated Azine-Based Covalent Organic Frameworks

Covalent organic frameworks (COFs) RIO-13, RIO-12, RIO-11, and RIO-11m were investigated towards their CO₂ capture properties by thermogravimetric analysis at 1 atm and 40 °C. These microporous COFs bear in common the azine backbone composed of hydroxy-benzene moieties but differ in the relative number of hydroxyl groups present in each material. Thus, their sorption capacities were studied as a function of their textural and chemical properties. Their maximum CO₂ uptake values showed a strong correlation with an increasing specific surface area, but that property alone could not fully explain the CO₂ uptake data. Hence, the specific CO₂ uptake, combined with DFT calculations, indicated that the relative number of hydroxyl groups in the COF backbone acts as an adsorption threshold, as the hydroxyl groups were indeed identified as relevant adsorption sites in all the studied COFs. Additionally, the best performing COF was thoroughly investigated, experimentally and theoretically, for its CO₂ capture properties in a variety of CO₂ concentrations and temperatures, and showed excellent isothermal recyclability up to 3 cycles.     

Synthesis of hydroxyl‐bearing polyurethanes from naturally occurring myo‐inositol

A route from naturally occurring myo‐inositol to hydroxyl‐bearing polyurethanes has been developed. The diol prepared from the bis‐acetalization of myo‐inositol with 1,1‐dimethoxycyclohexane was reacted with a rigid diisocyanate, 1,3‐bis(isocyanatomethyl)cyclohexane to afford the corresponding polyurethane, of which glass transition temperature (T_g) was quite high as 192 °C. The polyurethane contains side chains inherited from the acetal moieties of the diol monomer and was treated with trifluoroacetic acid to hydrolyze the acetal moieties and afford the target polyurethane functionalized with hydroxyl groups. The presence of many hydroxyl groups in the side chains, which can form hydrogen bonds with each other, resulted in a high T_g, 186 °C. In addition, the hydroxyl groups were reacted with isocyanates to achieve further side‐chain modifications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1358–1364     

Preparation of Silica Supported Tin Chloride: As a Recyclable Catalyst for the Silylation of Hydroxyl Groups with HMDS

Silica‐supported tin chloride [SiO₂‐Sn(Cl)_4‐n] has been prepared by mixing tin chloride with activated silica gel in toluene under refluxing conditions for one day. A range of primary, secondary, and tertiary alcohols as well as phenolic hydroxyl groups were converted into their corresponding trimethylsilyl ethers with hexamethyldisilazane in the presence of catalytic amounts of silica‐supported tin chloride at room temperature. An excellent chemoselective silylation of hydroxyl groups in the presence of other functional groups was also observed. This catalyst could be recycled and reused fifteen times without loss of efficiency.     

A DFT study on structure, stability, and optical property of fullerenols

The impact of hydroxyl group adsorption on fullerene surface (namely fullerenol) has been systematically investigated in this study using the hybrid density-functional theory calculations. We find that the relative stability of fullerenol clearly depends on the distribution of hydroxyl group on the surface. The eight hydroxyl groups in C₂₀(OH)₈ structure show preference to accumulate on two adjoining five-numbered rings. Analysis of reaction energy indicates that the formation of fullerenol from the C₂₀ fullerene and hydroxyl group is energetically favorable. The highly hydroxylated fullerene is found to have high kinetic stability and low chemical reactivity, which is mostly associated with its electron distribution of HOMO and LUMO orbitals. In addition, the electronic structure of the most stable fullerenols has been analyzed by means of the total and partial density of states.     

Synthesis of Novel Glycidol Copolymers with Pendant Alkene and Hydroxyl Groups

A series of linear poly glycidol copolymers, tethering with both alkene and hydroxyl groups, were prepared by a combination of anionic ring-opening polymerization （ROP） using specific reactions of ethoxy ethyl glycidyl ether （EEGE） and allyl glycidyl ether （AGE） firstly, and subsequently removal of the protection group of glycidol in EEGE to achieve the linear copolymer pendant with both hydroxyl groups and double bonds. The EEGE/AGE monomer reactivity ratio is measured to be 3.30/1.13. The chemical compositions of the as-synthesized polymers were characterized by tH NMR and GPC, and the glass transition temperatures （Tg） of as-synthesized polymers were determined by DSC. The final copolymers have abundant double bonds and hydroxyl as side groups. Furthermore, the ratio of the double bonds to hydroxyl groups can be controlled by the ratio of the starting materials in a wide range.