Kinetics of radiation polymerization of vinyl benzoate

Abstract

Vinyl benzoate was polymerized by γ-radiation from a cobalt-60 source and the kinetics of polymerization were studied at several temperatures. The results showed that the rate of polymerization was proportional to I^0.66 , where I is the radiation dose rate. The net activation energy for the polymerization reaction, (E_p -1/2 E_t ), was found to be 3.62 kcal, where E_p and E_t are the activation energies for the propagation and termination stages of the reaction. The radical yield measured by the loss of DPPH in the solution after irradiation was G=5.0, while the G (Radical) effective in initiating polymerization was 0.94. The ratio of the rate constants, k² _p/k_t = 5.8 × 10^?4 at 60° and 1.59 × 10^?4 at 25° The rate of polymerization was higher than that of styrene but lower than that of vinyl acetate under comparable conditions.     

Osmium tetroxide fixation of vinyl chloride emulsions

It is of interest to measure the monomer droplet size in emulsion polymerization. Unlike some monomers such as styrene and alkyl acrylates, vinyl chloride is in the gaseous state at the standard condition. Thus it is hard to measure the droplet size using any of the conventional methods. It is especially difficult when the droplet is smaller than 1 μm.

Using a high-pressure-proof syringe, vinyl chloride emulsion droplets can be fixed and stained through rapid reactions with osmium tetroxide dilute solution. The resulting stained particles are ready for transmission electron microscope (TEM) measurement. Emulsion droplets as small as 0.1 μm can be identified.

This technique can be utilized to study nucleation, particle growth mechanism, and the kinetics of emulsion polymerization.     

Characterization of poly(vinyl chloride): Abstract

Since the first International Symposium in 1970, studies on the characterization of PVC have mainly dealt with three topics: existence of supermolecular aggregates which a r e considered responsible for numerous thermornechanical and rheological properties of PVC; tacticity and chain defects which could alter the thermal sensitivity of PVC to processing conditions; morphology of the powder which is of paramount importance for the processability of the polymer.     

Ultrasonic separation of a suspension for in situ spectroscopic imaging

Optical Review - Application of spectroscopic techniques to suspensions is difficult because optical scattering caused by solid particles reduces the accuracy. At the extreme, dense suspensions...     

Ultrasonic investigation of magnetic nanoparticles suspension with PEG biocompatible coating

Water suspension of nanoparticles was studied by ultrasound spectroscopy. Nanoparticles have a core-shell structure with magnetic core Fe₃O₄ and surfactant shells. The surface of magnetic particles was coated with oleate sodium as the primary layer and polyethylene glycol as the secondary layer. The acoustic properties of suspensions, such as velocity and attenuation of ultrasonic waves, have been measured. From experimental data mechanical properties have been determined. Adiabatic compressibility of nanoparticles suspension decreased with increase of temperature. The changes of ultrasonic wave attenuation under the influence of the external magnetic field, show that magnetic liquids with high concentration of magnetic material (despite two surfactant shells) show tendency to aggregate.     

Infrared studies of crystallinity in poly(vinyl chloride)

The infrared spectrum of a solvent-cast film of commercial poly(vinyl chloride) (PVC) can be very sensitively compared to a rapidly quenched film of the same material by using a compensation technique. When this is done, crystalline bands, as seen in urea canal complex PVC, can be detected and measured in the solvent-cast film. The melting and recrystallization behavior as well as the broad melting range from 120° to 210°C indicate the presence of crystallites of widely different degrees of perfection. Crystallization kinetics from the quenched glassy state indicate that time-temperature superposition applies with an activation energy of 90 kcal/mole. Molecular mobility is indicated as the rate-controlling mechanism.     

Enthalpy determination of order in poly(vinyl chloride)

Enthalpy measurements by means of solution microcalorimetry were obtained on a PVC resin in the temperature range 37-110°C. Enthalpy measurements above T_g detect a heat of fusion of about 1.5 cal/g of polymer and thereby demonstrate the presence of a soluble ordered structure in PVC. Enthalpy measurements on samples quenched and slow-cooled from within the temperature interval 37-220°C confirm the value of 1.5 cal/g for the heat of fusion as well as demonstrate a broad melting range of 130-200°C.     

Ultrasonic properties of a suspension of microspheres supporting negative group velocities

The ultrasonic attenuation coefficient, phase velocity, and group velocity spectra are reported for a suspension that supports negative group velocities. The suspension consists of plastic microspheres with an average radius of 80 microm in an aqueous medium at a volume fraction of 3%. The spectra are measured using a broadband method covering a range from 2 to 20 MHz. The suspension exhibits negative group delays over a band near 4.5 MHz, with the group velocity magnitude exceeding 4.3 x 10(8) m/s at one point. The causal consistency of these results is confirmed using Kramers-Kronig relations.     

Ultrasonic degradation of poly(vinyl alcohol) in aqueous solution

Solution of poly(vinyl alcohol) in water with different concentrations (by weight 1%, 1.5%, 2%) and different volumes (50, 75 and 100 ml) were subjected to ultrasonic degradation. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The degradation rate constant was correlated with the power input due to ultrasonic irradiation and reaction volume. It was found that rate constant decreases as the reaction volume and concentration increases. The proportionality index of the relation between rate constant, power input and reaction volume was found to be nearly equal for all concentrations studied. The proportionality constant was found to be approximately equal for 1% and 1.5% solution and for 2% solution it was approximately half the value for that of 1% and 1.5% solutions. The decrease in rate constant and proportionality constant is attributed to the fact that at higher concentration and at higher volume, the intensity of cavitation phenomenon is depressed and therefore the extent of polymer chain breaking decreases. The difference in the values of limiting viscosities (constant solution viscosity which does not decrease by further ultrasonic irradiation) for 50, 75 and 100 ml solutions for each of 1% and 1.5% concentration was negligible. But 2% solution at 100 ml volume showed slightly higher value of limiting viscosity than that for 50 and 75 ml.     

脉冲射频等离子体聚合沉积乙烯基乙酸

通过脉冲射频等离子体聚合方法获得乙烯基乙酸沉积薄膜，并用红外光谱、x射线光电子能 谱、表面张力、微分扫描量热分析及扫描电子显微镜等测试方法研究聚合沉积薄膜的化学结 构、表面物理形貌与脉冲放电条件的关系. 实验结果表明，采用脉冲放电，在脉冲占空比较 低时，能够保留较多的完整的单体分子官能团. 如果脉冲占空比较高或是采用连续波放电时 ，聚合沉积薄膜的化学结构与单体相比有较大改变. 聚合沉积薄膜在放置一段时间后表面为 规整的高度交联的网络状结构. 放电形式不同，结构有所区别. 因此可以根据实际需要，选 择不同的 关键词： 等离子体聚合 脉冲射频放电 乙烯基乙酸     

Self-assembled hemocompatible coating on poly (vinyl chloride) surface

A stable hemocompatible coating was fabricated by consecutive alternating adsorption of iron (III) and two kinds of polysaccharides, heparin (Hep) and dextran sulfate (DS), onto poly (vinyl chloride) (PVC) surfaces via electrostatic interaction. The fluctuation of contact angles with the alternative deposition of iron (III) and polysaccharides verified the progressive buildup of the mulitilayer coating onto the PVC surface. Atomic force microscopy (AFM) analysis revealed that the PVC surfaces were completely masked by iron-polysaccharides multilayer coatings. The activated partial thromboplastin time (APTT) assay showed that both Hep/Fe³⁺/Hep and DS/Fe³⁺/Hep coated PVC were less thrombogenic than the uncoated one. Chromogenic assay for heparin activity proved definitively that the inhibition of locally produced thrombin was ascribed to the thromboresistance of the surface-bound heparin. Compared with the unmodified PVC surfaces, iron-polysaccharide multilayer coating presented a drastically reduced adhesion in vitro of platelets, polymorphonuclear neutrophil leukocytes (PMN) and peripheral blood mononuclear cells (PBMC). Interestingly, the DS/Fe³⁺/Hep coating was found to exhibit higher hydrophilicity and stability, hence lower non-specific protein adsorption in comparison with Hep/Fe³⁺/Hep coating due to the incorporation of dextran sulfate into the multilayer coating.     

Ultrasonic monitoring of zeolite synthesis in real time

Variations of the phase and amplitude of a transmitted ultrasonic wave package were monitored in real time during the synthesis of zeolite A and zeolite X. For both materials, characteristic changes of the measured attenuation and the sound velocity of ultrasonic waves traveling in the reaction fluid were observed, correlating with the processes of gel formation and zeolite crystallization, respectively. Aging effects of the reaction fluids are demonstrated. The observation of the onset of the zeolite crystallization was verified with ex-situ X-ray diffraction (XRD) measurements.     

Physical and conductivity properties of poly (vinyl chloride) ionomers

Poly (vinyl chloride)(PVC) is a cheapest plastic. Importance of PVC based ionomer has been gradually being popularizing due to compatibility of PVC with a number of salts to replace polyethylene oxide based ionomer. Under present investigation few of chloride group of PVC chain have been replaced by basic thiouronium group and these thiouronium groups are further oxidized to sulfonate group. Introduction of thiouronium group in PVC is confirmed through FTIR and further its oxidation to sulfonate group is also confirmed by FTIR. Conductivity in different stoichiometric ratio of PVCTU and PVCSO₃H was studied and found that PVCTU: PVCSO₃H in 1:1 ratio has conductivity near to pure PVC (10⁻⁹ Ohm-1 cm⁻¹) and increases with proportion of PVCSO₃Na in the mixture (10⁻⁶ Ohm⁻¹ cm⁻¹) for pure PVC, PVCTU has less conductivity not much significant.     

Ultrasonic inspection of batters for on-line process monitoring

A new method for on-line batter monitoring using ultrasound techniques is presented. Air or gas incorporation is done during the beating process which produces bubbles in the mixture. The density and the compressibility of the batter vary as a function of mixing time and are quality index of batter. Traditionally, a batter sample of a fixed volume is removed and weighted in order to determine its density. This is a time consuming process. Batters are air filled mixtures of high viscosity which do not support significant transmission of ultrasound. For this reason conventional ultrasonic density sensors for liquids are not suitable for this application. Therefore, a special transducer has been developed. The sensor was constructed using a piezoelectric ceramic at the fundamental frequency of 1 MHz. Instead of measuring density, in this work, changes in compressibility in batters are monitored by measuring the acoustic impedance of the batter. Main advantage of this novel approach is that changes in acoustic impedance are easier to detect than changes in density especially when air incorporation is in small quantities. Experimental results on different liquids and batters with different gas contents are presented and discussed.     

Ultrasonic monitoring of malolactic fermentation in red wines

The progress of malolactic fermentation in red wines has been monitored by using ultrasonic techniques. The evolution of ultrasonic velocity of a tone burst 1 MHz longitudinal wave was measured, analyzed and compared to those parameters of oenological interest obtained simultaneously by analytical methods. Semi-industrial tanks were used during measurements pretending to be in real industrial conditions. Results showed that the ultrasonic velocity mainly changes as a result of the conversion by lactic acid bacteria of malic acid into lactic acid and CO₂. Overall, the present study has demonstrated the potential of the ultrasonic technique in monitoring the malolactic fermentation process.     

Nano-sized polystyrene prepared using bifunctional vinyl urethane macromonomer in emulsion polymerization

The linear-type bifunctional vinyl urethane macromonomer (L-VUM: Mw; 40,453) was synthesized and applied to emulsion polymerization of styrene in DDI water. The structure of L-VUM was confirmed using ¹H NMR and FT-IR. The macromonomer served as a good nonionic surfactant resulted in stable polystyrene nanospheres. Polystyrene particles were prepared with various concentrations of macromonomoer (1–30 wt% refer to monomer), initiator (0.5–2 wt%) and different temperatures (60–80 °C). Monodisperse PS nanospheres with 30 wt% L-VUM have a number-average diameter (D_n) of 200 nm with good uniformity (1.011) and molecular weight (M_w) 231,180 g/mol. The particle morphology, molecular weight and distribution, uniformity and the stability of the nanospheres upon the reaction temperature and concentration of L-VUM will be thoroughly discussed.     

Ultrasonic polymerization of CuO@PNIPAM and its temperature tuning glucose sensing behavior

The extraordinary high pressure and temperature produced during cavitation is crucial for ultrasonic sonochemistry. However, the cavitation effect is usually confined to a small zone nearby the ultrasonic horn, outside of which ultrasound produces much less effects on chemical reaction. In present work, in order to expand the range of effective zone and intensify the cavitation effect, N₂ aeration was introduced to an ultrasonic polymerization process of CuO@PNIPAM in aqueous solution. By increasing the number of bubble nucleus gathered on the CuO surface and lowering the surface tension of the aqueous solution, the cavitation effect is intensified on the CuO surface within the whole reaction vessel, which benefits the covalently bonding between PNIPAM and CuO to a large degree and results in the formation of CuO@PNIPAM hybrid composite with excellent interfacial bonding. It is promising that the hybrid composite can be applied as temperature responsive glucose sensing platform with ON and OFF states due to the wettability change of PNIPAM versus temperature.     

Ionic desorption in valence- and core-excited poly(vinyl chloride)

Photon stimulated ion desorption (PSID) studies have been performed in poly(vinyl chloride) (PVC) using synchrotron radiation, encompassing the valence and core electron (Cl 2p and C 1s) energy ranges. Data acquisition was performed at the Brazilian synchrotron light source (LNLS), operating in a multi-bunch mode and using a time-of-flight mass spectrometer (TOF-MS). A pulsed high voltage applied to the sample was used as a trigger for the TOF-MS experiments. Ionic desorption from PVC shows strong selectivity in the formation of chlorine ions around the Cl 2p-edge while very similar fragmentation patterns are observed for the other energies studied.     

Blending Optimization of Non-Dioctyl Phthalate Plasticized Poly (vinyl chloride) Formulations

The use of non-ortho-phthalate plasticizers in poly (vinyl chloride) (PVC) packaging materials and medical devices has been in increasing demand due to worldwide regulatory trends to minimize or eliminate phthalate plasticizers (particularly di(2-ethylhexyl)phthalate (DEHP) or dioctyl phthalate (DOP)) in the PVC industry. This study evaluates the dry-blending cycle time of a suspension grade PVC formulated with various non-DOP plasticizers, di-(2-ethylhexyl) terephthalate (DEHT or DOTP), tris (2-ethylhexyl) trimellitate (TEHTM or TOTM) and alkyl sulphonic phenyl ester (ASE), and compares them with the DOP standard. A design of experiments was also conducted to study the critical dry-blending parameters for optimization of PVC formulated with only DEHT. Effects of PVC temperature (measured during plasticizer addition to the blender), plasticizer pre-heat temperature, plasticizer and lubricant concentrations and the method of plasticizer addition on the dry-blending cycle time and peak amperage of the blender were studied. The blending cycle time is shown to be related to the resultant plasticizer efficiency and the peak amperage is related to the power consumption (the energy required to mix the PVC).     

Structure and Properties of Poly(vinyl chloride)/Halloysite Nanotubes Nanocomposites

Poly(vinyl chloride)(PVC)/halloysite nanotubes (HNTs) nanocomposites were prepared by melt blending. The effects of HNT content on the mechanical properties, morphology, and rheological properties of the nanocomposites were investigated. The results showed that HNTs were effective in toughening and reinforcing PVC nanocomposites. The notched impact, tensile and flexural strength, and flexural modulus of the nanocomposites were remarkably increased compared with those for the pure PVC. Scanning electron microscopy (SEM) results illustrated the ductile behavior of the nanocomposites, with a possible cavitation mechanism. Transmission electron microscopy (TEM) results showed that HNTs were uniformly dispersed in the PVC matrix. Interfacial interaction of hydrogen bonding between the HNTs and PVC matrix was substantiated. The plasticization times of PVC/HNTs nanocomposites were found to be shorter and the equilibrium torque was higher than that for the pure PVC.