The influence of silicone shell on double-layered microcapsules in intumescent flame-retardant natural rubber composites

The mechanisms of the thermal degradation of polyhedral oligomeric octaphenylsilsesquioxane (OPS), octa(nitrophenyl)silsesquioxane (ONPS), and octa(aminophenyl)silsesquioxane (OAPS) were investigated. The –NO₂ or –NH₂ substituents on the phenyl group affected the mechanism of the POSS thermal degradation. The thermal stabilities of OPS, ONPS, and OAPS were characterized by TG and FTIR. Thermal degradation of OPS included mainly the degradation of caged polyhedral oligomeric silsesquioxane structures and phenyl groups. Nitro or amino substituents decreased its thermal stability. The thermal degradation processes of OPS, ONPS, and OAPS differed. Phenyl groups and cyclobutadiene were observed in the OPS degradation products. Oxygen radicals that caused intensive CO₂ release between 350 and 450 °C were generated by the degradation of ONPS –NO₂. OAPS released mainly aminophenyl groups at 370 °C, whereas a small number of phenyl groups decomposed at 500 °C. The OAPS reactivity could enhance the thermal stability of POSS structure in the polyimide OAPS composites.     

Controlled radical polymerization of styrene in the presence of cyclic 1,2‐disulfides

The thermal polymerization of styrene (St) in the presence of cyclic 1,2‐disulfides at 120 °C was investigated. In the polymerization of St in the presence of 1,2‐dithiane (DT), that is, six‐member cyclic 1,2‐disulfide, the polymer yields and molecular weights increased with the reaction time. The linear relation between the polymer yields and molecular weights was observed, and the line passed through an original point. The molecular weight distributions of the polymers remained almost constant but were not narrow. For this polymerization with a living nature, we proposed the following mechanism: the propagating St radical reacted with thiyl radicals derived from DT, leading to the formation of dormant species, and the formed C S bond of the dormant was dissociated again to give the propagating polystyryl radical and thiyl radical. Similar results were obtained in the thermal polymerization of St at 120 °C in the presence of 1,2‐dithiacycloheptane, that is, seven‐member cyclic 1,2‐disulfide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 145–151, 2001     

Study of molecular deformation mechanisms in the glassy state. I. Temperature effect on stress-birefringence and strain-birefringence responses of poly(methyl methacrylate)

In order to gain better understanding of the molecular deformation processes occurring in poly-(methyl methacrylate), a series of studies was carried out in uniaxial tension on the simultaneous stress and birefringence response in both constant-strain-rate and stress relaxation experiments. The former covered the temperature range ?120 to 75°C and the latter 0 to 90°C. Three deformation mechanisms, i.e., (i) change in intermolecular distance, (ii) distortion of the conformation of the COOCH₃ group from its thermal equilibrium state, and (iii) orientation of main-chain segments, are invoked to interpret the experimental results. It is concluded that, in the temperature range from ?120 to 75°C and possibly at higher temperatures as well, the polymer chains deform in the small-strain region by an orientation of those chain segments having lower potential-energy barriers to conformational changes and straining those chain segments having higher potential-energy barriers. Subsequent chain orientation of the already strained segments occur in the higher strain regions. Changes in intermolecular distances occur over the entire temperature range from ?120 to 90°C, but their magnitude decreases gradually as the temperature increases from ?40 to 40°C and then decreases sharply for temperatures above 40°C. Strain-induced distortion of the conformation of the COOCH₃ group may involve only rotation of the OCH₃ group around the C? O bond rather than rotation of the entire ester group itself.     

Macrothiuram disulfide for the free radical synthesis of PDMS-vinyl triblock copolymers. II. Studies of chain transfer

Chain transfer constants (C_tr) for thiuram disulfide (TD) groups, included in the backbone of polydimethylsiloxane (PDMS) of different chain lengths, in methyl methacrylate (MMA) and styrene (St) were determined from measurements of the degree of polymerization. Two methods were used. The first consisted of using the initiation and transfer properties of the thiuram disulfides groups, and the second, of using a more efficient free radical initiator than TD groups, in which case the former behaves only as a transfer agent. In both the methods, the C_tr of TD was evaluated in bulk polymerization of MMA at 60, 70, 80, and 90°C. Using the first method, the C_tr of TD was measured also in solution polymerization of MMA in toluene at 100°C and, with the second one, in bulk polymerization of styrene at 60, 80, and 90°C. PDMS-based macrothiuram disulfide (macroiniferter) behaves as an “azeotropic” transfer agent for MMA and styrene at 125°C and 110°C, respectively. © 1994 John Wiley & Sons, Inc.     

Ab initio studies of structural features not easily amenable to experiment. 22. Structural aspects of a long-chain hydrocarbon (n-nonane) and a study of the transferability of electronic effects through C?C single bonds

The molecular structure of the stretched form of n-nonane, as a typical long-chain hydrocarbon, was refined by geometrically unconstrained ab initio force relaxation on the 4-21G level. The C? C bonds and C? H bond distances in the interior of the hydrocarbon chain are found to be longer (by about 0.001 Å and 0.002 Å, respectively) than those near the end of the chain. Similarly, interior C? C? C bond angles are 0.4° larger than the terminal angles. The variation of structural parameters with distance from the molecular ends levels off after the second carbon atom, and the geometry of methylene is practically constant from C₃ on. However, if one end of the system is perturbed by moving the inplane methyl hydrogen away from equilibrium, the resulting destabilizing electronic effects are transmitted through the C? C bond distance chain in such a way that significant perturbations are still experienced at C₅. Molecular mechanics (MM 2) gives a structure in which the small changes in bond lengths and angles with chain location are well reproduced.     

Substituent effects on the chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane in the presence of disulfides and thiols

The chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane was investigated in the presence of four chain‐transfer agents: thiophenol (PhSH), thiobenzoic acid (BzSH), diphenyl disulfide (PhSSPh), and dibenzoyl disulfide (BzSSBz). The chain‐transfer constants for these compounds at 60 °C were 0.38 (PhSH), 0.76 (BzSH), 0.24 (PhSSPh), and 0.05 (BzSSBz). The variations in the thiol chain‐transfer constants could be explained in terms of the stability of the resulting radicals. The chain transfer to the disulfides, however, appeared to be determined by the electronic character of the disulfide bond, and this suggests that the transfer took place via an addition–fragmentation mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4421–4425, 2002     

Melt polycondensation approach for reduction degradable helical polyester based on l‐cystine

Melt polycondensation approach is developed for new classes of reduction responsive disulfide containing functional polyesters based on l ‐cystine amino acid resources under solvent free process. l ‐Cystine was converted into multi‐functional ester‐urethane monomer and subjected to thermoselective transesterification at 120 °C with commercial diols in the presence of Ti(OBu)₄ to produce polyesters with urethane side chains. The polymers were produced in moderate to high molecular weights and the polymers were found to be thermally stable up to 250 °C. The β‐sheet hydrogen bonding interaction among the side chain urethane unit facilitated the self‐assembly of the polyester into amyloid‐like fibrils. The deprotection of urethane unit into amine functionality modified the polymers into water soluble cationic polyester spherical nanoparticles. The reduction degradation of disulfide bond was studied using DTT as a reducing agent and the high molecular weight polymers chains were found be chopped into low molecular weight oligomers. The cytotoxicity of cationic disulfide nanoparticle was studied in MCF‐7 cells and they were found to be biocompatible and non‐toxic to cells upto 50 μg/mL. The custom designed reduction degradable and highly biocompatible disulfide polyesters from l ‐cystine are useful for futuristic biomedical applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2864–2875     

Hydrogenolysis of dimethyl disulfide in the presence of bimetallic sulfide catalysts

The hydrogenolysis of dimethyl disulfide in the presence of Ni,Mo and Co,Mo bimetallic sulfide catalysts was studied at atmospheric pressure and T = 160–400°C. At T ≤ 200°C, dimethyl disulfide undergoes hydrogenolysis at the S-S bond, yielding methanethiol in 95–100% yield. The selectivity of the reaction decreases with increasing residence time and temperature due to methanethiol undergoing condensation to dimethyl disulfide and hydrogenolysis at the C-S bond to yield methane and hydrogen sulfide. The specific activity of the Co,Mo/Al₂O₃ catalyst in hydrogenolysis at the S-S and C-S bonds is equal to or lower than the total activity of the monometallic catalysts. The Ni,Mo/Al₂O₃ catalyst is twice as active as the Ni/Al₂O₃ + Mo/Al₂O₃ or the cobalt-molybdenum bimetallic catalyst.     

Novel conducting polymer poly[bis(phenylamino)disulfide]: Synthesis,characterization, and properties

A bis(phenylamino)disulfide was prepared through the reaction of S₂Cl₂ with aniline, and its configuration was confirmed with elemental analysis, Fourier transform infrared (FTIR), Fourier transform Raman (FT‐Raman), and ¹H NMR spectroscopy. A novel conducting polymer, poly[bis(phenylamino)disulfide] (PPAD), was synthesized from bis(phenylamino)disulfide by both chemical and electrochemical polymerization. The structure of this polymer, in which the side‐chain disulfide bonds were linked to the nitrogen atoms of the main‐chain polyaniline, was characterized with FTIR, FT‐Raman, gel permeation chromatography, electron spectroscopy, and X‐ray photoelectron spectroscopy. A four‐probe measurement revealed that the electrical conductivity of PPAD was 1.8 × 10^?2 to 2.1 × 10^?3 S cm^?1, depending on the doping agents and the pH of the medium for either chemical synthesis or electrochemical synthesis. The conductivity, molecular weight, and spectroscopic properties of the polymer, in comparison with those of polyaniline, showed decreases in the polaron delocalization, structural order, and doping level of the main chain because of the steric hindrance of side‐chain S? S bonds. The cyclic voltammograms of the polymer and the monomer showed that the redox reactions (doping/undoping processes) of the main chain (π‐conjugated system) occurred in almost the same potential range of ?0.3 to 0.3 V versus an Ag/AgCl (saturated KCl) electrode as that of thiol (thiolate anion)/disulfide of the side chain in PPAD; the bond cleavage (reduction) and formation (oxidation) reactions of the disulfide bond in the polymer became easier and more reversible than those of the monomer. These results suggested that this conducting organodisulfide polymer might be a candidate material for energy‐storage devices such as lithium secondary batteries, proton‐exchange batteries, and electrochemical capacitors. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2329–2339, 2004     

A thermogravimetric and infrared emission spectroscopic study of alunite

Thermogravimetric and differential thermogravimetric analysis has been used to characterize alunite of formula [K₂(Al³⁺)₆(SO₄)₄(OH)₁₂]. Thermal decomposition occurs in a series of steps (a) dehydration up to 225°C, (b) well defined dehydroxylation at 520°C and desulphation which takes place as a series of steps at 649, 685 and 744°C.The alunite minerals were further characterized by infrared emission spectroscopy (IES). Well defined hydroxyl stretching bands at around 3463 and 3449 cm^?1 are observed. At 550°C all intensity in these bands is lost in harmony with the thermal analysis results. OH stretching bands give calculated hydrogen bond distances of 2.90 and 2.84–7 Å. These hydrogen bond distances increase with increasing temperature. Characteristic (SO₄)^2? stretching modes are observed at 1029.5, 1086 and 1170 cm^?1. These bands shift to lower wavenumbers on thermal treatment. The intensity in these bands is lost by 550°C.     

C−X Bond Activation by Palladium: Steric Shielding versus Steric Attraction

The C−X bond activation (X = H, C) of a series of substituted C(n°)−H and C(n°)−C(m°) bonds with C(n°) and C(m°) = H₃C− (methyl, 0°), CH₃H₂C− (primary, 1°), (CH₃)₂HC− (secondary, 2°), (CH₃)₃C− (tertiary, 3°) by palladium were investigated using relativistic dispersion-corrected density functional theory at ZORA-BLYP-D3(BJ)/TZ2P. The effect of the stepwise introduction of substituents was pinpointed at the C−X bond on the bond activation process. The C(n°)−X bonds become substantially weaker going from C(0°)−X, to C(1°)−X, to C(2°)−X, to C(3°)−X because of the increasing steric repulsion between the C(n°)- and X-group. Interestingly, this often does not lead to a lower barrier for the C(n°)−X bond activation. The C−H activation barrier, for example, decreases from C(0°)−X, to C(1°)−X, to C(2°)−X and then increases again for the very crowded C(3°)−X bond. For the more congested C−C bond, in contrast, the activation barrier always increases as the degree of substitution is increased. Our activation strain and matching energy decomposition analyses reveal that these differences in C−H and C−C bond activation can be traced back to the opposing interplay between steric repulsion across the C−X bond versus that between the catalyst and substrate.     

Kinetics of the Photopolymerization of Vinyl Monomers by Bis(Isopropylxanthogen) Disulfide. Design of Block Copolymers

Bis(isopropylxanthogen) disulfide (BX) has been used as a photoinitiator with various vinyl monomers at 30°C. The kinetics of polymerization of styrene (St) and methyl methacrylate (MMA) at 30°C were studied for various concentrations of monomer and initiator. The observed deviations in polymerization rate from simple kinetic theory could be explained in terms of primary radical termination. The fraction of primary radical terminating chains was obtained as a function of various concentrations. The ratio of the rate constants for chain initiation and chain termination by a primary radical was determined to be 3.34 ± 10⁷ for St and 2.60 ± 10⁷ for MMA. The number-average degree of polymerization (DP _n) of polymers obtained by photopolym-erization with BX was found to increase linearly with conversion. However, the DP _n extrapolated to zero conversion was in good agreement with that calculated on the basis of the kinetic scheme. It was found that BX had interesting properties for the design of block copolymers, i.e., BX acts as a terminator and a chain transfer agent as well as an initiator in these polymerizations. The polymers obtained with BX contained two reactive isopropyl xanthate groups bonded at their chain ends, which could also act as macrophotoinitiators.     

Rendering polyureas melt processible

Because of the presence of extensive H‐bonding in the hard segments, polyureas are processed by solution techniques (e.g., dry spinning) by the use of relatively costly and environmentally unfriendly solvents. Thus, the objective of this research was to render polyureas melt processible, (i.e., to reduce their flow temperature, T_flow) without compromising their excellent mechanical properties. We hypothesized and herein demonstrate that by using conventional chain extenders (CEs) in combination with small amounts of H‐bond acceptor chain extenders (HACEs), the T_flow of polyureas can be significantly reduced from ～230 to ～180 °C, and thus melt processible products with excellent mechanical properties can be obtained. We document the synthesis of conventional polytetramethylene oxide‐based and novel polyisobutylene (PIB)‐based polyureas with T_flows ～ 180 °C and excellent mechanicals by the addition of few percents of commercially available HACEs. Products were characterized by various techniques, including Instron (tensile strengths, elongations), durometer (Shore A Hardness), dynamic mechanical thermal analysis (T_flow), and thermal gravimetric analysis (TGA) (thermal weight loss). According to TGA, a polyurea with T_flow of ～180 °C did not degrade up to ～234 °C in air. A micromorphology for melt processible polyureas is proposed that emphasizes flexibilized hard segments in the presence of HACEs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of intramolecularly cyclized poly(phenylene sulfide)s of the thianthrene-type

Oligomers containing thianthrene units in the chain are synthesized by AlCl₃-catalyzed reaction of diphenylsulfide, thianthrene, poly(p-phenylene sulfide), and poly(m-phenylene disulfide) with sulfur at 80°C. The products are compared with that obtained by the reaction of diphenylsulfide with AlCl₃ at 225°C. IR spectra and elemental analyses are consistent with cyclic chain structures and show a higher cyclization for CHCl₃-insoluble fractions. X-ray diffraction analysis indicates the same structure for the samples obtained with the different methods of synthesis. A possible structural model is tentatively proposed.     

Mass spectra of gliclazide drug at various ion sources temperature

Gliclazide (GL, C₁₅H₂₁N₃O₃S) drug is used as non-insulin-dependant diabetes mellitus. The drug was investigated using thermal analysis (TA) measurements (TG/DTG) and electron impact mass spectral (EI–MS) fragmentation at 70 eV techniques. The mass spectra of GL at different values of ion source temperatures (400, 416, 425, and 440 K) are recorded and investigated. Semiempirical MO calculation, using PM3 procedure, has been carried out on neutral molecule and positively charged species. These calculations included bond length, bond order, bond strain, partial charge distribution, ionization energy, and heats of formation (ΔH _f). PM3 procedure provides a basis for fine distinction among sites of initial bond cleavage, which is crucial to the rationalization of subsequent fragmentation of the molecule. The primary fragmentation pathway in both TA and MS (at different values of ion source temperature) is initiated by S–N bond rupture. TA and DTG show one main weight loss at 250.38 °C and four peaks at 271.6, 360.99, 427.93 and 479.17 °C in DTA, which may be attributed to various fragments. Also, the rate constant (K′) of thermal degradation has been tested isothermally at 210 and 600 °C. The calculated rate values are 9.6 × 10⁻³ and 0.33 × 10⁻³ s⁻¹, respectively, and discussed. In MS, the effect of ion source temperature on mass spectral fragmentation processes is discussed on the basis of energy considerations using quasi equilibrium theory.     

Structure-activity correlations of calcined Mg-Al hydrocalcites for aliphatic polycarbonate synthesis <Emphasis Type="Italic">via</Emphasis> transesterification process

Mg-Al mixed oxides with different Mg/Al molar ratio were prepared by thermal decomposition of hydrotalcitelike precursors at 500 °C for 5.0 h and used as catalysts for the transesterification of diphenyl carbonate with 1,4-butanediol to synthesize high-molecular-weight poly(butylene carbonate) (PBC). The structure-activity correlations of these catalysts in this transesterification process were discussed by means of various characterization techniques. It was found that the chain growth for the formation of PBC can only be obtained through connecting ―OH and ―OC(C)OC₆H₅ end-group upon removing the generated phenol, and the sample with Mg/Al molar ratio of 4.0 exhibited the best catalytic performance, giving PBC with M _w of 1.64 × 10⁵ g/mol at 210 °C for 3.0 h. This excellent activity depended mainly on the specific surface area and basicity rather than pore structure or crystallite size of MgO.     

The design,synthesis, and nonlinear optical properties of novel X‐type polyurethane containing dicyanovinylnitroresorcinoxy group with enhanced SHG thermal stability

Novel X‐type polyurethane 5 containing 4‐(2′,2′‐dicyanovinyl)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature (T_g) obtained from differential scanning calorimetry thermogram of around 120 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064‐nm fundamental wavelength is around 6.12 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 5 °C higher than T_g, and there was no SHG decay below 125 °C due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Pyrolysis study of fluorinated sol-gel silica

Fluorinated silica gels at various fluorine content were prepared via sol-gel by hydrolysis of 3,3,3-trifluoropropyltrimethoxysilane and tetraethoxysilane mixtures. The gels, of nominal stoichiometry Si(CH₂CH₂CF₃)_XO_(2-X/2)(X=0.1-1), were characterized by FT-IR, X-ray photoelectron spectroscopy (XPS) and N₂ adsorption analysis. The thermal stability of the fluorinated samples was investigated by coupling thermogravimetric measurements with mass spectrometric and gas chromatographic analyses of the evolved gaseous species. The chemical reactions occurring in the gel matrices during heating were siloxane chain rearrangements involving condensation between residual hydroxyl and ethoxyl groups in the 100-350°C temperature range, whereas the thermal decomposition of the fluoroalkyl groups were observed at higher temperatures (450-600°C). The release of the fluoroalkyl moieties also involved C-F/Si-O bond exchanges inside the siloxane chains, with gas-phase evolution of different fluorinated silicon units. This revised version was published online in July 2006 with corrections to the Cover Date.     

Methyl 3‐(4‐methoxyphenyl)prop‐2‐enoate

The title mol­ecule, C₁₁H₁₂O₃, is almost planar, with an average deviation of the C and O atoms from the least‐squares plane of 0.146 (4) Å. The geometry about the C=C bond is trans. The phenyl ring and –COOCH₃ group are twisted with respect to the double bond by 9.3 (3) and 5.6 (5)°, respectively. The endocyclic angle at the junction of the propenoate group and the phenyl ring is decreased from 120° by 2.6 (2)°, whereas two neighbouring angles around the ring are increased by 2.3 (2) and 0.9 (2)°. This is probably associated with the charge‐transfer interaction of the phenyl ring and –COOCH₃ group through the C=C double bond. The mol­ecules are joined together through C—H?O hydrogen bonds between the methoxy and ester groups to form characteristic zigzag chains extended along the c axis.     

Negative thermal expansibility change for dissociation of lysozyme variant amyloid protofibril

A disulfide‐deficient variant of hen lysozyme, 0SS, is known to form an amyloid protofibril spontaneously, and to dissociate into monomers at high hydrostatic pressure. We carried out native PAGE at various temperatures (20–35°C) and pressures (0.1–200 MPa), to characterize the dissociation equilibrium of disulfide‐deficient variant of hen lysozyme amyloid protofibril. Based on the density profiles, the partial molar volume and thermal expansibility changes for dissociation, Δv_D and Δe_D, were obtained to be ?74 cm³/mol at 25°C and ?2.3 cm³ mol^?1 K^?1, respectively. The dissociation of amyloid fibril destroys the cross β‐structure, and such conformational destruction in native protein fold rarely accompanies negative thermal expansibility change. We discussed the negative thermal expansibility change in terms of hydration and structural packing of the amyloid protofibril.