Radical polymerization of styrene in the presence of C60

Radical polymerizations of styrene in the presence of C₆₀ have been conducted at 90°C in benzene using benzoyl peroxide (BPO) as initiator. The behaviors of C₆₀ are investigated by monitoring BPO concentration, C₆₀ content, and polymerization time. It is found that C₆₀ acts like a radical absorber which multiply absorbs primary radicals from BPO and propagating radicals. Therefore, in the presence of C the yield and molecular weight decrease significantly. However, the molecular weight distribution is narrowed down by its coupling characteristics. At the beginning of the reaction, owing to the radical-absorbing effect of C₆₀, it makes the chain-propagation restricted. However, the number of polystyrene chains added to C₆₀ increases with polymerization time. Direct dilatometric experiment proves that C₆₀ is mainly as inhibitor for radical polymerization of styrene by benzoyl peroxide. Besides, the glass transition temperature (T_g) of the copolymers increases with increasing content of C₆₀. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2969–2975, 1999     

Influence of Moisture on the Structure and Properties of the Interphase Layer of a Composite Based on an Epoxy Binder with a Disperse Filler

Properties of a model composite based on an ED-22 epoxy binder, cured with polyprophylene polyamine, and disperse LiF crystals as a filler were investigated by the methods of dilatometry and X-ray diffractometry. It was established that the density of cross-links of the epoxy binder in the interphase layer was lower than in a block specimen. Therefore, the thermal expansion of the composite on heating to 120°C, in terms of that of the binder, grew significantly with the degree of filling ϕ, and the water uptake also increased at the initial stage. The presence of absorbed water led to considerable changes in the structure and properties of the composite interphase: the binder became more cross-linked, its structural ordering decreased, the thermal expansion at heating diminished by a factor of 3. 7 (at ϕ = 50%), and the glass-transition temperature increased. As a result of long-term action of moisture, changes in the internal stresses had an extreme character.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 535–544, July–August, 2005.     

Volume recovery of polystyrene/silica nanocomposites

Macroscopic volume as well as capacitive dilatometry (CD) measurements have been performed on polystyrene/silica nanocomposites during the course of physical aging below the glass transition temperature (T_g). Our results show that the macroscopic volume recovery during physical aging is not affected by the presence of nanofillers, whereas the CD measurements, delivering also information on the polymer matrix density, show acceleration of the recovery with increasing the silica content. Hence, the main outcome of the present work is that the evolution of macroscopic and matrix densities are markedly different in polymer nanocomposites. We interpret these results invoking an equilibration mechanism based on volume holes diffusion. According to this model, excess free volume migration at the polymer/filler interface only modifies the matrix density, thereby explaining the faster recovery detected by CD measurements in comparison to the macroscopic volume one. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013     

Bulk and shear rheology of a symmetric three‐arm star polystyrene

The bulk and shear rheological properties of a symmetric three‐arm star polystyrene were measured using a self‐built pressurizable dilatometer and a commercial rheometer, respectively. The bulk properties investigated include the pressure–volume–temperature behavior, the pressure‐dependent glass transition temperature (T_g), and the viscoelastic bulk modulus and Poisson's ratio. Comparison with data for a linear polystyrene indicates that the star behaves similarly but with slightly higher T_gs at elevated pressures and slightly higher limiting bulk moduli in glass and rubbery states. The Poisson's ratio shows a minimum at short times similar to what is observed for the linear chain. The horizontal shift factors above T_g obtained from reducing the bulk and shear viscoelastic responses are found to have similar temperature dependence when plotted using T ? T_g scaling; in addition, the shift factors also exhibit a similar temperature dependence to linear polystyrene. The retardation spectra for the bulk and shear responses are compared and show that the long time molecular mechanisms available to the shear response are unavailable to the bulk. At short times, the two spectra have similar slopes, but the short‐time retardation spectrum for the shear response is significantly higher than that for the bulk, a finding that is, as yet, unexplained. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Phase transitions from density and order parameter from polarisabilities in symmetric dimeric liquid crystals

As a part of our systematic studies on liquid crystal dimers, we present in this article the nature of phase transitions across isotropic–nematic and nematic–smectic-A exhibited by DLCs, α,ω-bis-(4-n-alkylaniline benzylidene-4?-oxy) alkanes. Further, the orientational order parameter in the nematic phase of these DLCs are estimated from the molecular polarisabilities calculated using the experimental refractive indices and density results. The molecular polarisabilities α_e and α_o are obtained for the compounds using the above results for both Vuks and Neugebauer local field models applicable to nematic liquid crystal. α_e and α_o calculated in this way are used to obtain Δα. The polarisability anisotropy in the perfect order (absolute K) is calculated semi-empirically using the δ-function model developed by Lippincott et al. and molecular vibration method. The values of polarisability anisotropy for both local electric field models differ significantly. No criterion is known to decide which value is correct. To avoid the determination of uncertain α and Δα values considering different local field models, a simple procedure developed by Kuczynski et al. was used for evaluation of S, based solely on birefringence δn = (n_e-n_o) and this value of S is compared with those obtained from field models.     

Estimation of the Polymerization Rate of Liquid Propylene Using Adiabatic Reaction Calorimetry and Reaction Dilatometry

The use of pressure‐drop and constant‐pressure dilatometry for obtaining rate data for liquid propylene polymerization in filled batch reactors was examined. The first method uses reaction temperature and pressure as well as the compressibility of the reactor contents to calculate the polymerization rate; in the second, the polymerization rate is calculated from the monomer feed rate to the reactor. Estimated polymerization rates compare well to those obtained using the well‐developed isoperibolic calorimetry technique, besides pressure‐drop dilatometry provides more kinetic information during the initial stages of the polymerization than the other methods.

     

Dilatometry as a tool to study a new synthesis for calcium hexaluminate

By using a wet chemical route, pure calcium hexaluminate (CA₆) was yielded, significantly lowering the reaction temperature and shortening the synthesis time if compared to usual industrial procedures. owever, dilatometric studies performed on compacts made of the as-prepared powder, just after pre-heating at 450°C, has shown a superposition between sintering shrinkage and expansion related to CA₂ formation, an intermediate phase formed during calcination and phase evolution to CA₆. oupling of such opposite phenomena led to microcracking of the material, mainly if the heating rates (10°C min^-1) were high. However, lower heating rates (1-5°C min^-1) could quite avoid microcracking but also limit densification. This revised version was published online in July 2006 with corrections to the Cover Date.     

Formations of polyvinyltoluene microlatexes in quaternary oil in water cetyltrimethylammonium bromide microemulsions

Polymerization of vinyltoluene (VT) in quaternary microemulsions containing cetyltrimethylammonium bromide (CTAB) as the cationic surfactant is studied using laser Raman spectroscopy (LRS) and dilatometry. The influences of water soluble (potassium peroxodisulphate, ammonium peroxodisulphate) and oil soluble (azobisisobutyronitrile, benzoyl peroxide) initiators, monomer, surfactant, cosurfactants (n-alcohol and bifunctional alcohols) and temperature on the rates of polymerization (R _p), energy of activation (Ea), particle diameter (D), number of polymer particles (N _p), molecular weight of polyvinyltoluene (M _v) and number of polymer chains per latex particle (N _pc) are investigated. The dependencies of the kinetic and latex size parameters on the initiators and cosurfactants are discussed in terms of the efficiency of the initiators in initiating the polymerization and on the interfacial partitioning behavior of various cosurfactants. The polymerization mechanism seems to follow Smith Ewart Case II hypothesis with two distinct rate regions. Final polymer microlatexes are found to lie within 10–50 nm as observed by transmission electron microscopy (TEM). Molecular weights are in the range of (1 to 5)×10⁶. Each latex particle contains one to three polymer chains.     

A possibility of application of MTDIL to the Residual stresses analysis

The work demonstrates a proof of application of the modulated-temperature dilatometry (MTDIL) to the stresses investigations of the well known and commonly used hard coatings e.g. TiN, TiCN, TiAlN thin films deposited mainly on different type of tools for its higher performances. In the PVD (physical vapour deposition) processes such kind of coatings are formed in meta stable state caused, between other, by strong stresses between coating and substrate. These stresses have an important influence on the fundamental properties of the coatings, for example, adherence to the substrate, so they are the subject of many investigations by use of different methods, mainly XRD (X-ray diffraction). For the purpose of presentation of application of MTDIL for such kind of investigation two reference substrate materials were chosen: ARMCO steel and cemented carbide in the form suitable for dilatometric analysis covered, by actually the most conventional, TiN hard coating. In the article the experimental results are presented, discussed and compared with simple model formed by means of finite elements method (FEM). This revised version was published online in July 2006 with corrections to the Cover Date.     

Relaxation behavior of selenium based glasses

Summary Relaxation behavior of Ge_ySe_100-y (y=8 and 10) glasses related to the viscosity behavior was studied by dilatometry. The method of two consecutive temperature jumps was applied to study the volume relaxation. The relaxation response can be described by Tool-Narayanaswamy-Moynihan model and the parameters of this model h*, , x, A were determined using curve fitting method and characteristic times method. Viscosities of studied materials in the range of 10⁸-10¹³ Pas were measured by penetration method. The calculated values of activation energies of viscous flow E are close to the values of effective activation energies of relaxation h* for studied chalcogenide materials.