Structural/compositional nanoheterogeneity and glass‐transition plurality in amorphous polycyanurate–poly(tetramethylene glycol) hybrid networks

The nanostructure and dynamics over the temperature range of ?140 to 300 °C were studied in a series of polycyanurate (PCN)–poly(tetramethylene glycol) (PTMG) hybrid networks by wide‐angle X‐ray diffraction and small‐angle X‐ray scattering, with a synchrotron radiation setup, and by differential scanning calorimetry (DSC) and laser‐interferometric creep rate spectroscopy (CRS) techniques, respectively. The networks were synthesized from the dicyanate ester of bisphenol A and hydroxyl‐terminated PTMG with a number‐average molecular weight of 1.000 g/mol; the PTMG content varied from 0 to 40 wt %, and the degree of its chemical incorporation into the PCN network changed from 78.8 to 97%. The noncrystalline structure and considerable structural nanoheterogeneity of the hybrid networks were shown. CRS/DSC analysis revealed a complicated dynamic behavior, that is, a wide dispersion of glass transitions in the hybrid networks due to the presence of nanodomains with different degrees of rigid crosslinking (i.e., compositional nanoheterogeneity). Besides the physical significance, the plurality of glass transitions found in the PCN–PTMG hybrid networks was also of practical interest because it resulted in increasing mechanical strength of the brittle PCN network due to microplasticity arising at room temperature and moderate temperatures and the retention of some rigidity and creep resistance at temperatures much higher than the basic glass‐transition temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3261–3272, 2005     

Multiple melting behavior of poly(butylene succinate). I. Thermal analysis of melt‐crystallized samples

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were cooled from the melt (150 °C) at various cooling rates (CRs) ranging from 0.2 to 50 K min^?1. The peak crystallization temperature (T_c) of the DSC curve in the cooling process decreased almost linearly with the logarithm of the CR. DSC melting curves for the melt‐crystallized samples were obtained at 10 K min^?1. Double endothermic peaks, a high‐temperature peak H and a low‐temperature peak L, and an exothermic peak located between them appeared. Peak L decreased with increasing CR, whereas peak H increased. An endothermic shoulder peak appeared at the lower temperature of peak H. The CR dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of log(CR). T_m(L), T_re, and ΔH decreased almost linearly with log(CR), whereas T_m(H) was almost constant. Peak H decreased with the molecular weight, whereas peak L increased. It was suggested that the rate of the recrystallization decreased with the molecular weight. T_m(L), T_m(H), T_re, and T_c for the lowest molecular weight sample were lower than those for the others. In contrast, ΔH for the highest molecular weight sample was lower than that for the others. If the molecular weight dependence of the melting temperature for PBSu is similar to that for polyethylene, the results for the molecular weight dependence of PBSu can be explained. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2411–2420, 2002     

Smectic ordering in polymer liquid crystal-silica aerogel nanocomposites

Summary Two series of side chain liquid crystal (SCLC) polyacrylate-silica aerogel nanocomposites have been investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). The first series (ex-situ nanocomposite) was obtained by infiltration of a smectic SCLC polyacrylate prepared by polymerisation in solution into monolithic aerogel slabs. The second one (in-situ nanocomposite) was prepared by photopolymerisation of the monomer infiltrated in the aerogel. The results are compared with those obtained for bulk polyacrylates. It is shown that the smectic ordering is not destroyed by confinement in the aerogel. Spacing of the smectic layers and smectic correlation lengths were deduced from the fit of the SAXS profiles to a Lorentzian function with a quadratic correction. The principal results suggest that in-situ polymerisation enhances the degree of order and the stability of the smectic phase in the nanocomposite.     

Thermoanalytical,FTIR and X-ray studies of gemfibrozil-cyclodextrin complexes

Summary Inclusion complexation between dimethyl-β-cyclodextrin and a very poorly water-soluble serum lipid-regulating agent, gemfibrozil, was studied. Products were prepared by several methods (physical mixing, kneading, spray-drying and ultrasonic treatment) in four different molecular ratios (2:1, 1:1, 1:2 and 1:3). The possibility of complex formation between the drug and the host molecule was studied by thermal analysis. Supplementary techniques, such as Fourier transformation-infrared spectroscopy and X-ray diffractometry, were also applied to interpret the results of thermal study of the products.     

Enhanced magnetocaloric effect in a Co-doped Heusler Mn50Ni37Co3In10 unidirectional crystal

A high-pressure optical zone-melting technique was employed to grow a Mn-rich Heusler Mn₅₀Ni₃₇Co₃In₁₀ unidirectional crystal in the present study. It was found that the Co-doped Mn₅₀Ni₃₇Co₃In₁₀ unidirectional crystal showed a low magnetic hysteretic loss and a widened working temperature interval in the vicinity of the martensitic transformation. The inverse magnetic entropy change (∆S_M) reached 7.84 Jkg⁻¹K⁻¹ around 237.5 K under a magnetic field change of 30 kOe, and the corresponding effective refrigeration capacity (RC_eff) was about 127.2 Jkg⁻¹. The experimental results demonstrated a high potential to develop high-performance Mn-rich Heusler Mn–Ni–In magnetocaloric materials by means of Co doping in combination with the high-pressure optical zone-melting fabrication technique.     

Synthesis and characterization of copolymerizable one‐component type II photoinitiator

A copolymerizable one‐component Type II photoinitiator (CMEBP), based on 4‐hydroxybenzophenone (HBP), epichlorohydrin, morpholine, and acryloyl chloride, was synthesized and its structure was confirmed by ¹H‐NMR. The properties of CMEBP were investigated with UV spectroscopy and photo‐differential scanning calorimetry (photo‐DSC). The maximum of UV absorption red‐shifted significantly compared to benzophenone (BP). Photopolymerization results of tripropylene glycol diacrylate (TPGDA) indicated that CMEBP had larger maximum rate of polymerization than that of BP/triethanolamine (TEOHA) and HBP/triethylamine (TEA), larger final double bond conversion than that of HBP/TEA, but lower than that of BP/TEOHA. The rate of polymerization, final conversion increased and the induction period shortened with increase in CMEBP concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectroscopic studies of zinc(II)tetraphenylporphyrin molecular complex with 1,4-dioxane

The molecular complex of zinc(II)tetraphenylporphyrin with 1,4-dioxane has been obtained. The IR spectra of the [Zn(TPhP)(1,4-dioxane)2] stabile molecular complex between 4000 and 50cm(-1) have been studied. An interpretation is given on the base the "chair" conformation of 1,4-dioxane molecule.     

Thermal stability evaluation of doping compounds before GC-MS analysis by DSC

The Medical Commission of the International Olympic Committee forbids the use of anabolic androgenic steroids, β-agonists, stimulant and narcotic compounds to improve athletic performance. In this work, we evaluated the thermal stability of 17 compounds by the use of the DSC for their potential GC-MS analysis either under free form or under TMS derivative form. In DSC, esterified and unesterified anabolic steroids were characterized by a true melting peak, followed by a large exothermic peak at about 251–316°C due to oxidative degradation. They could be analysed by GC-MS mainly under TMS derivatives. Hydroxylated and unhydroxylated stimulant compounds (xanthines) seemed to be more stable at high temperature. As unhydroxylated xanthines were not silylated with BSTFA - TMCS, their GC analysis would be done under their free forms. TMS derivatisation of albuterol hemisulfate and codeine phosphate is preferable. In our conditions, to analyse by GC-MS all 17 doping compounds in the same GC-MS run, the optimal silylation temperature and best column initial temperature were determined at both 60°C.     

Reactive incompatibility of DTBP mixed with two acid solutions

Organic peroxides are commonly employed as an initiator for polymerization, a source of free radicals, a hardener, and a linking agent. Due to its relatively weak oxygen-oxygen bond, di-tert butyl peroxide (DTBP) has been categorized as flammable type or Class III by the National Fire Protection Association (NFPA). The transport of dangerous goods (TDG) has published a warning against DTBP that it could potentially induce violent heat, explosion, fire and self-ignition under certain circumstances. DTBP has been recommended as an international standard sample for estimating the performance of several calorimeters, such as glass tube tests, differential scanning calorimetry (DSC), and vent sizing package 2 (VSP2). In this study, we measured the precise temperature changes and heat flow with the above-mentioned testing instruments. However, some runaway incidents caused by DTBP have demonstrated the reaction temperature could be as low as ambient temperature. The reactivity and the hazardous incompatibility with sulfuric acid (H₂SO₄) and hydrochloric acid (HCl) of DTBP have not been evident, and the runaway hazards involved in different processing conditions were clarified in this study by implementing the two calorimeters. Acid-catalyzed characteristics and reaction hazards of DTBP could be acquired, such as heat of decomposition (ΔH _d) and exothermic onset temperature (T ₀).