The effect of aging on the thermal behavior of sulfonated polystyrene

The thermal properties of an ionomer glass, lightly sulfonated polystyrene, was studied as a function of aging at room temperature after being cooled from the melt. An anomalous endothermic event below T_g was observed by differential scanning calorimetry; the intensity of this excess enthalpy was a function of time and sulfonate concentration. It is suggested that the origin of this relaxation may be due in part to morphological changes that occur as a consequence of electrostatic interactions of the sulfonate groups.     

Intramolecular O-alkylation of gem-dinitro compounds

Summary In an alkaline medium-bromo gem-dinitro compounds undergo intramolecular O-alkylation with formation of cyclic esters of the aci forms of gem-dinitro compounds, namely 3-nitro-2-isoxazoline 2-oxides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1644–1648, September, 1965     

Synthesis and thermal properties of hybrid copolymers of syndiotactic polystyrene and polyhedral oligomeric silsesquioxane

Copolymerizations of styrene and the polyhedral oligomeric silsesquioxane (POSS)–styryl macromonomer 1‐(4‐vinylphenyl)‐3,5,7,9,11,13,15‐heptacyclopentylpentacyclo [9.5.1.1^3,9.1^5,15.1^7,13] octasiloxane have been performed with CpTiCl₃ in conjunction with methylaluminoxane. Random copolymers of syndiotactic polystyrene (sPS) and POSS have been formed and fully characterized with ¹H and ¹³C NMR, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. NMR data reveal a moderately high syndiotacticity of the polystyrene backbone consistent with this use of CpTiCl₃ as a catalyst and POSS loadings as high as 24 wt % and 3.2 mol %. Thermogravimetric analysis of the sPS–POSS copolymers under both nitrogen and air shows improved thermal stability with higher degradation temperatures and char yields, demonstrating that the inclusion of the inorganic POSS nanoparticles makes the organic polymer matrix more thermally robust. The polymerization activity and thermal stability are also compared with those of reported atactic polystyrene–POSS copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 885–891, 2002; DOI 10.1002/pola.10175     

Synthesis and thermal behavior of new N-heterotolan liquid crystals

[reaction: see text] The synthesis of liquid crystal series 9a-d was achieved using the Buchwald protocol and Sonogashira reaction.     

Boronated (co)polystyrene: monomer reactivity ratios,thermal behavior and flammability

Chemical modification based on incorporation of flame retardants (FR) into the polymer backbone was used in order to reduce polystyrene flammability. Boronated styrenes such as 4‐vinylphenylboronic acid (StB(OH)₂) and 6‐methyl‐2‐(4‐vinylphenyl)‐1,3,6,2‐dioxazaborocane‐4,8‐dione (StBcyclo) were applied as reactive FR. Homo‐ and copolymers of boronated styrenes and styrene (St) were synthesized with different feed ratios using free radical polymerization. It yielded in series of (co)polymers with various amounts of StB(OH)₂ and StBcyclo (5–20% mol/mol of St). Copolymer compositions were determined by ¹H NMR. The relative reactivity ratios of system St‐StBcyclo were determined by applying the Jaacks method. Glass transition temperature and thermal stability of obtained (co)polymers were determined from DSC and TGA analysis, respectively. The pyrolysis combustion flow calorimeter was applied as a tool for assessing the flammability of the synthesized (co)polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and thermal behavior of Janus dendrimers,part 1

Eight Janus-type dendrimers up to the second generation were synthesized, and their thermal properties were evaluated. Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-dihexyloxybenzoic acid or 3,4-dihexadecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The structures of the molecules were verified with ¹H NMR, ¹³C NMR, ESI TOF mass spectrometry and elemental analysis. The thermal stability was evaluated by thermogravimetric analysis, displaying onset decomposition temperatures (T_d) ranging from 241 to 308 °C. Phase transitions were studied by differential scanning calorimetry. Based on the performed studies it was confirmed that OH terminated dendrimers 2, 4, 6 and 8 exhibited liquid crystalline phases. Also, the X-ray powder diffraction measurements were accomplished for the dendrimers having terminal hydroxyl groups.     

Synthesis and thermal behavior of some diisocyanate–silane compounds

Some silica-organic compounds were prepared by an addition reaction between γ-amino-propyl-triethoxy silane and 4,4′-diphenylmethane diisocyanate. The obtained products were characterized by FTIR spectrometry. The essential synthesis parameter was the molar ratio between the two reactants. The thermal behavior of the products was rather good, until 150 °C no mass loss or thermal effects being observed. The thermal behavior was determined under non-isothermal conditions, using TG/DTG/HF diagrams. Due to the hydroxyl end-groups, these compounds are recommended for adhesives between organic and inorganic surfaces.     

Synthesis and thermal behavior of Janus dendrimers,part 2

The thermal properties of twelve Janus-type dendrimers up to the second generation were evaluated by termogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-bis-dodecyloxybenzoic acid, 3,5-bis-dodecyloxybenzoic acid or 3,4,5-tris-dodecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The thermal stability of the compounds was evaluated by TGA, displaying onset decomposition temperatures (T_d) at around 250 °C. DSC measurements upon heating and cooling confirmed that OH terminated Janus dendrimers featuring large polarity difference in opposite sides display liquid crystalline phases with exception of 3,5-type G1 dendrimer; while acetonide terminated dendrimers displayed merely melting transitions. Dendrimers having terminal alkyl chains at positions 3,4 or 3,4,5 in aromatic moieties exhibited enantiotropic mesophases. However, the thermal behavior of the dendrimers with 3,5-substitution pattern was different: the 3,5-type G1 dendrimer exhibit a lack of mesomorphic transition, and in the case of the 3,5-type G2 dendrimer, the mesophase was absent in the first heating scan but was observed during the subsequent cooling and heating scans at the rate of 10 °C/min.     

Synthesis and thermal behavior of chiral oligomers derived from cholesterol

Synthesis and thermal properties of a series of Schiff base oligomers derived from naturally occurring cholesterol are described. In particular, four of them show smectic A and/or chiral nematic phase/s or an unknown mesophase, while the other is non-mesomorphic. Molecular packing in the SmA phase has been determined by the HRXRD experiment.     

Polyarylate–polystyrene block copolymer from macro-azoinitiator: Synthesis and its thermal properties

A macro-azoinitiator containing polyarylate segment and azo group was prepared by the solution polycondensation of azobiscyanopentanoyl chloride and hydroxy-terminated polyarylates having viscosity-average molecular weights of 6200, 8100, and 12 400. These macro-azoinitiators were used in the radical polymerization of styrene to synthesize polyarylate-polystyrene block copolymers. Thermal properties measured by the differential scanning calorimetry indicated the phase separated morphology of the block copolymers except at low molecular weight of the block constituents. © 1993 John Wiley & Sons, Inc.     

Photochemical behavior of p-dimethylaminobenzoylated polystyrene as polymerization photoinitiator: Synthesis of graft copolymers

The photochemical behavior of p-dimethylaminobenzoylated polystyrene (PS-MI) in benzene solution has been investigated, both in the presence and absence of methyl methacrylate (MMA). This behavior has been compared with that of the model compound, 4-isopropyl-4′-N,N-dimethylaminobenzophenone (CU-MI). PS-MI photoreduction takes place only through excimer formation due to the high local chromophore concentration, and therefore, PS-MI disappearance quantum yield is close to the previously calculated limiting value (0.02) and independent of chromophore concentration. Several parameters that characterize the polymerization process have been determined; it has been found that the obtained PMMA is photografted onto PS-MI backbone. This is in agreement with the proposed mechanism for radical generation. No homo-PMMA formation has been detected. © 1993 John Wiley & Sons, Inc.     

Melting behavior of isotactic polystyrene

The melting behavior of isotactic polystyrene, crystallized from the melt and from dilute solutions in trans-decalin, has been studied by differential scanning calorimetry and solubility measurements. The melting curves show 1, 2, or 3 melting endotherms. At large supercooling, crystallization from the melt produces a small melting endotherm just above the crystallization temperature T_c. This peak originates from secondary crystallization of melt trapped within the spherulites. The next melting endotherm is related to the normal primary crystallization process. Its peak temperature increases linearly with T_c, yielding an extrapolated value for the equilibrium melting temperature T_c° of 242 ± 1°C as found before. By self-seeding, crystallization from the melt could be performed at much higher temperature to obtain melting temperatures as high as 243°C, giving rise to doubt about the value of T_c° found by extrapolation. For normal values of T_c and heating rate, an extra endotherm appears on the melting curve. Its peak temperature is the same for both melt-crystallized and solution-crystallized samples, and independent of T_c, but rises with decreasing heating rate. From the effects of heating rate and partial scanning on the ratio of peak areas and of previous heat treatment on dissolution temperature, it is concluded that this peak arises from the second one by continuous melting and recrystallization during the scan.     

Precision branching in ethylene copolymers: Synthesis and thermal behavior

Acyclic diene metathesis polymerization allows the synthesis of sequenced polyethylene copolymers via step-growth propagation, thereby avoiding the inherent side reactions associated with chain polymerization. Here we review the synthesis and thermal behavior of ADMET polyethylene (PE) as well as ethylene/propylene (EP), ethylene/butene (EB), ethylene/octane (EO), and ethylene/vinyl ether (EVE) copolymers prepared by ADMET. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4981–4989, 2006     

Impact of chain architecture (branching) on the thermal and mechanical behavior of polystyrene thin films

The modulus and glass transition temperature (T_g) of ultrathin films of polystyrene (PS) with different branching architectures are examined via surface wrinkling and the discontinuity in the thermal expansion as determined from spectroscopic ellipsometry, respectively. Branching of the PS is systematically varied using multifunctional monomers to create comb, centipede, and star architectures with similar molecular masses. The bulk‐like (thick film) T_g for these polymers is 103 ± 2 °C and independent of branching and all films thinner than 40 nm exhibit reductions in T_g. There are subtle differences between the architectures with reductions in T_g for linear (25 °C), centipede (40 °C), comb (9 °C), and 4 armed star (9 °C) PS for ≈ 5 nm films. Interestingly, the room temperature modulus of the thick films is dependent upon the chain architecture with the star and comb polymers being the most compliant (≈2 GPa) whereas the centipede PS is most rigid (≈4 GPa). The comb PS exhibits no thickness dependence in moduli, whereas all other PS architectures examined show a decrease in modulus as the film thickness is decreased below ～40 nm. We hypothesize that the chain conformation leads to the apparent susceptibility of the polymer to reductions in moduli in thin films. These results provide insight into potential origins for thickness dependent properties of polymer thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Crystallization,thermal behavior,and compatibility in isotactic polystyrene/poly(o-chlorostyrene-co-p-chlorostyrene) blends

The dependence of the kinetics of crystallization and melting behavior in isotactic polystyrene/poly-o-chlorostyrene-co-p-chlorostyrene (iPS/Po-CIS-co-p-CIS) blends on temperature, thermal history, and blend composition has been investigated. The crystallization rate at a given temperature and copolymer composition decreases with increasing copolymer content in the blend when the samples are premelted. These effects can be ascribed to the reduction of mobility of the crystallizable chains due to the presence of the copolymer and to the decrease in the number of heterogenous iPS nuclei as a result of the premelting process. The Avrami exponent values and the analysis of the blend morphology indicate that the growth mechanism of the crystals is strongly influenced by thermal treatment. There is no measurable change in the melting temperature of iPS in the blends, with composition indicating that, on the basis of the Flory-Huggins approximation of the thermodynamics of polymer mixing, the net interaction parameter at the melting temperature is close to zero. From the comparison of the phase diagram for the isotactic polystyrene-containing blend with that of the atactic-containing blend, it can be concluded that in the amorphous state polystyrene with a regular configuration is slightly less compatible with the P(o-CIS-co-p-CIS) than is polystyrene with random configuration.     

Synthesis and thermal behavior of a new high-energy organic potassium salt

A new high-energy organic potassium salt, 1-amino-1-hydrazino-2,2-dinitroethylene potassium salt [K(AHDNE)], was synthesized by reacting of 1-amino-1-hydrazino-2,2-dinitroethylene (AHDNE) and potassium hydroxide in methanol aqueous solution. The thermal behavior of K(AHDNE) was studied using DSC and TG/DTG methods and can be divided into three obvious exothermic decomposition processes. The decomposition enthalpy, apparent activation energy and pre-exponential factor of the first decomposition process were ?2662.5?J?g^?1, 185.2?kJ?mol^?1 and 10^19.63 s^?1, respectively. The critical temperature of thermal explosion of K(AHDNE) is 171.38?°C. The specific heat capacity of K(AHDNE) was determined using a micro-DSC method, and the molar heat capacity is 208.57?J?mol^?1 K^?1 at 298.15?K. Adiabatic time-to-explosion of K(AHDNE) was also calculated. K(AHDNE) presents higher thermal stability than AHDNE.     

Synthesis, curing behavior and thermal properties of fluorene containing benzoxazines

A series of difunctional fluorene-based benzoxazine monomers were synthesized from the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with formaldehyde and primary amines including aniline, o-toluidine, n-butylamine, and n-octylamine. Their chemical structures were confirmed by FT-IR, ¹H and ¹³C NMR analyses. The curing behaviors of the precursors were monitored by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polymers were evaluated with DSC and thermogravimetric analysis (TGA). The fluorene-based polybenzoxazines show the typical curing characteristic of oxazine ring-opening for difunctional benzoxazines centred at 231-250 °C, and remarkably higher glass transition temperature and better thermal stability ascribed to the high rigidity, high aromatic content, and intermolecular and intramolecular hydrogen bonding. The thermal decomposition temperature and char yield of aromatic amine-fluorene-based polybenzoxazines are much higher than those of aliphatic amine-based polybenzoxazines.     

Synthesis and thermal behavior of RAFT-based copolymers of acrylonitrile and 1-vinylimidazole

The copolymers of acrylonitrile and 1-vinylimidazole with a narrow molecular weight distribution (MWD) were synthesized for the first time by the reversible addition–fragmentation chain transfer (RAFT) polymerization in a DMSO solution in the presence of acetic acid. Their thermal behavior difference upon heating in argon and in air along with ability to melt make them promising precursors for carbon fiber production.     

Synthesis and characterization of phosphorylated polystyrene derivatives for use in chromatography: DNA-like and phospholipid-like behavior

New functional crosslinked polystyrene derivatives have been synthesized. These polymers are substituted with chemical groups such as phosphate, purine, and pyrimidine bases, choline, serine, and nucleotides in order to mimic DNA and phospholipids. For this purpose, hydroxylated polystyrene beads were prepared, where monomer units were substituted via spacers. Then, phosphomonoester groups at various substitution ratios were grafted onto hydroxylated resins by using a phosphorus oxychloride method. Nucleosides and nucleic acid bases derivatives were coupled with dicyclohexylcarbodiimide on phosphorylated polymers whereas nucleotides, phosphorylcholine, and phosphorylserine were grafted on to hydroxylated polystyrene. The synthesis and characterization of these DNA-like and phospholipid-like polystyrene resins are described here extensively.