Effect of short-chain polymer on scission of long-chain polymer in solution by high-speed stirring

The effect of short-chain poly(methyl methacrylate) (PMMA) (P?_v = 950) on scission of longchain PMMA (P?_v = 6150) in solution by high-speed stirring was investigated by measuring changes in [η] and GPC, stirring at 30,000 ± 500 rpm at 30° ± 5°C benzene solutions containing the above two polymers at several concentrations and at various mixing ratios. It was found that the scission of long-chain PMMA was small or a little suppressed by addition of short-chain PMMA. The scission-suppressing effect of the coexisting polymers depended on the chain length. The longer the chain, the larger the effect. It was also found that the rate constant of scission, k, in Ovenall's equation had a certain significance in polymer systems with the same MWD but no significance in those with different MWDs.     

Comparison of Overall Gas‐Phase Mass Transfer Coefficient for CO2 Absorption between Tertiary Amines in a Randomly Packed Column

The mass transfer performance of CO₂ absorption into an innovative tertiary amine solvent, 1‐dimethylamino‐2‐propanol (1DMA2P), was investigated and compared with that of methyldiethanolamine (MDEA) in a packed column with random Dixon‐ring packing. All experiments were conducted under atmospheric pressure. The effects of inert gas flow rate, amine concentration, liquid flow rate, CO₂ loading, and liquid temperature on mass transfer performance were analyzed and the results presented in terms of the volumetric overall mass transfer coefficient (K_Ga_v). The experimental findings clearly indicate that 1DMA2P provided better mass transfer performance than MDEA. For both 1DMA2P and MDEA solutions, the K_Ga_v increased with rising amine concentration and liquid flow rate, but decreased with higher CO₂ loading. The inert gas flow rate only slightly affected the K_Ga_v. A satisfactory correlation of K_Ga_v was developed for the 1DMA2P‐CO₂ system.     

Mixed modifier effect in lithium‐calcium borosilicate glasses

The mixed modifier effect (MME) in the lithium‐calcium borosilicate glasses, which have a composition of 0.4[(1?x)Li₂O–xCaO]–0.6[(1?y)B₂O₃–ySiO₂] with x in the range of 0~1 and y in the range of 0.33~0.83, is investigated. The MME manifests itself as a positive deviation from linearity in the activation energy of electrical conductivity (Ea^σ) and as a negative deviation from linearity in the fraction of four‐coordinated boron (N₄), glass transition temperature (T_g), dilatometric softening temperature (T_d), Vickers microhardness (H_v), dielectric constant (ε), and dielectric loss (tanδ). Moreover, the deviation, which exhibits a maximum at [CaO]/([CaO]+[Li₂O])=0.5, is enhanced with increasing [SiO₂]/[B₂O₃] ratio in the glass network. The observed MME in T_g, T_d, and H_v are attributed to the bond weakening in the network; however, the MME in ε, tanδ, and Ea^σ are caused by the obstruction of modifier transport in the glass network.     

Synthesis and characteristics of a novel aliphatic polycarbonate,poly[(propylene oxide)‐co‐(carbon dioxide)‐co‐(γ‐butyrolactone)]

A novel aliphatic polycarbonate, poly[(propylene oxide)‐co‐(carbon dioxide)‐co‐(γ‐butyrolactone)] [P(PO? CO₂? GBL)], was synthesized by the copolymerization of carbon dioxide, propylene oxide (PO) and γ‐butyrolactone (GBL). The resulting copolymers were determined by FTIR and NMR spectral analysis with viscosity‐average molecular weights (M_v) from 50 000 to 120 000 g mol^?1. According to elemental analysis, the calculated data of elemental contents in P(PO? CO₂? GBL)44 were close to the found data. The result showed that GBL was inserted into the backbone of poly[(propylene oxide)‐co‐(carbon dioxide)] successfully. GBL offered an ester structural unit that gave the copolymer better degradability. The correlations between reaction conditions and properties were studied. When GBL content increased, the M_v and the glass transition temperature (T_g) of the copolymers improved relative to an identical copolymer without GBL. Prolonging the reaction time of the copolymerization resulted in increases in M_v and T_g. P(PO? CO₂? GBL) exhibited a high T_g above 40 °C. The rate of backbone degradation increased with increasing GBL content. Copyright © 2005 Society of Chemical Industry     

Photodegradation of chloroacetic acids over bare and silver-deposited TiO2: Identification of species attacking model compounds, a mechanistic approach

Photocatalytic degradation of chloroacetic acids (ClAAs) over various bare and silver-deposited Degussa P25 TiO₂ particles was studied. Adsorption measurements carried out using TiO₂ photocatalysts of different origin demonstrated significant dependence of the adsorption efficiency on the nature of semiconductor particles and on the number of chlorine atoms of the substrate. Irradiation of the reaction mixtures containing monochloroacetic acid (MCA), dichloroacetic acid (DCA) and trichloroacetic acid (TCA), respectively, over P25 titania were performed under anaerobic and aerobic conditions. The progress of photocatalysis was followed by measuring the substrate concentration, the total organic carbon content (TOC) and the concentration of the chloride ion in the liquid phase of reaction mixtures. Opposite trends in the photodecomposition rate of the substrates were obtained for aerobic v_MCA≈v_DCA>v_TCA and for anaerobic experiments v_TCA>v_DCA>v_MCA, respectively. The evolved CO₂ was also measured under aerobic photodecomposition of DCA. Important role of hydroxyl radicals in the photomineralization of mono- and dichloroacetic acid was confirmed by using coumarin (COU) as a hydroxyl radical scavenger and oxalic acid as an efficient scavenger for holes. Silver deposition onto the TiO₂ surface enhanced the efficiency of the semiconductor by a factor of 4 for the photooxidation of TCA and by a factor of 1.4 for DCA and MCA.     

Mixed modifier effect in Na2O·K2O·CaO aluminosilicate glasses: Pairwise and ternary interactions

The mixed modifier effect (MME) is one of the most challenging puzzles in the field of oxide glasses, as there exists no universal quantitative theoretical model for accurately describing and predicting the nonlinear deviation of property values. In this paper, pairwise and ternary interactions are examined experimentally to understand the MME in a series of aluminosilicate glasses. By keeping the glass network former concentration constant and adjusting the molar ratios of three network modifiers (Na₂O, K₂O, and CaO), the MMEs in glass transition temperature (T_g), Vickers hardness (H_v), and activation energy (E_a) for aqueous dissolution for each modifier cation are investigated. We examine whether a pairwise interaction model is sufficient, or if ternary interactions also need to be included to predict the MME in these aluminosilicate glass systems. This work reveals that the pairwise model can be used to predict the MME for T_g in complex multiple-modifier glass systems using only two-body interaction factors. However, ternary mixed-modifier interactions are present in other properties such as H_v and E_a.     

Rubber elasticity of poly(n-butyl acrylate) networks formed with multifunctional crosslinkers

The rubber elasticity characteristics of poly(n-butyl acrylate) networks crosslinked with tetrafunctional (EGDM and TEGDM), hexafunctional (TMPTM), and octafunctional (PETMA) vinyl crosslinkers were investigated. Both gel—sol analyses and crosslinking efficiency theories were used to evaluate the chemical crosslink contribution v_c and the entanglement contribution v_p to the elastically effective network chains v_e, and the effect of the crosslink junction functionality f on the front factor g. The front factors obtained were in the range of 0.50–0.92, depending upon the network system and the counting method for v_c. The relationship of g = [(f ? 2)/f]/〈r²〉/〈r²〉_o seems reasonable in the case of the tetrafunctional and hexafunctional networks, but deviates in the case of the octafunctional network. It is also evident that the functionality scheme for the front factor could only be valid under the postulate of a high v_p, which increases with increasing v_c, especially in the high v_c region near the Gaussian limit. The average energetic contribution to the retractive force of the present systems, expressed as F_e/F, is ?0.30 ± 0.1.     

Synthesis of a difunctional organolithium compound as initiator for the polymerization of styrene‐butadiene/isoprene‐styrene triblock copolymer

A difunctional organolithium compound was prepared by the addition of butyllithium (BuLi) to 1,4‐bis(4‐methyl‐1‐phenylethenyl)benzene (MPEB). The effects of the solvent, polar modifier (THF), butyl lithium structure, and reaction time on the formation of the difunctional organolithium compound were studied. Results showed that toluene as solvent was in favor of the addition reaction over cycohexane, in the absence of the polar modifier. However, cycohexane was a better option as solvent for the addition reaction, when polar modifier was employed. A small amount of polar modifier could efficiently accelerate the reaction rate and have no significant effect on the structure of the polydiene, which was initiated by the polar modifier containing organolithium compound. Results also showed that isobutyl lithium was more active in the addition reaction than n‐butyl lithium, because of inductive effect. The optimum molar ratio of THF/Li+ was determined as 4. The THF containing difunctional organolithium cyclohexane solution was sequentially used in the step‐wise polymerization of triblock thermoplastic copolymer SIBS. The so‐prepared SIBS shared the similar phase separation structure with SBS and exhibited excellent mechanic properties. As the content of the central polyisoprene block increases, the tensile strength of the copolymer is decreased, and the elongation at break is increased. The glass transition temperature T_g of the central block was correlated with its content as T_g = 0.33 × ?62.81, where × is the wt % of the central block, based on the triblock copolymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1395–1402, 2006     

Structural and emission properties of Eu3+‐doped alkaline earth zinc‐phosphate glasses for white LED applications

Quaternary alkaline earth zinc‐phosphate glasses in molar composition (40 ? x)ZnO – 35P₂O₅ – 20RO – 5TiO₂ – xEu₂O₃ (where x=1 and R=Mg, Ca, Sr, and Ba) were prepared by melt quenching technique. These glasses were studied with respect to their thermal, structural, and photoluminescent properties. The maximum value of the glass transition temperature (T_g) was observed for BaO network modifier mixed glass and minimum was observed for MgO network modifier glass. All the glasses were found to be amorphous in nature. The FT‐IR suggested the glasses to be in pyrophosphate structure, which matches with the theoretical estimation of O/P atomic ratio and the maximum depolymerization was observed for glass mixed with BaO network modifier. The intense emission peak was observed at 613 nm (⁵D₀→⁷F₂) under excitation of 392 nm, which matches well with excitation of commercial n‐UV LED chips. The highest emission intensity and quantum efficiency was observed for the glass mixed with BaO network modifier. Based on these results, another set of glass samples was prepared with molar composition (40 ? x)ZnO – 35P₂O₅ – 20BaO – 5TiO₂ – xEu₂O₃ (x=3, 5, 7, and 9) to investigate the optimized emission intensity in these glasses. The glasses exhibited crystalline features along with amorphous nature and a drastic variation in asymmetric ratio at higher concentration (7 and 9 mol%) of Eu₂O₃. The color of emission also shifted from red to reddish orange with increase in the concentration of Eu₂O₃. These glasses are potential candidates to use as a red photoluminsecent component in the field of solid‐state lighting devices.     

Free volume of liquids and polymers from internal pressure studies

The free volume, v_f, of liquids is defined in many ways. Comparison of solid and liquid behavior indicates that the definition for free volume in terms of the internal pressure of the liquid (?E/?V)_T, is physically reasonable. Application of the definition of free volume, v_f = RT/(?E/?V)_T, to polymethylenes, coupled with surface energy values, leads to an evaluation of both polymer segmental volume, ?_s, and free volume per segment, (v_f)_s, as a function of temperature. These equilibrium thermodynamic measurements of ?_s and (v_f)_s lead to an energy of activation for viscous flow in good agreement with viscosity studies. Information of this type could be of great use in considering many current problems in polymer flow such as the effect of pressure on viscosity.     

Effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile using dialkylmagnesium as catalyst

An attempt was made to clarify the effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile (AN) initiated by dialkylmagnesium (R₂Mg) above 100°C. The triad isotacticity (i.e. the content of mm (m: meso)) as well as the viscosity-average molecular weight (M?_v) of polyacrylonitrile (PAN) increased when trialkylaluminum (R₃Al) and trialkylboron (R₃B) were used as additives. Diisobutylaluminum hydride [(i-C₄H₉)₂AlH] was found to be the best additive. in the stereospecific polymerization of AN, giving PAN with higher (mm) content (0.63), higher M?_v value (5.2 × 10⁴), and a yield approximately double that obtained using (n-C₆H₁₃)₂Mg alone. When the (n-C₆H₁₃)₂Mg/(i-C₄H₉)₂AlH system was used, the yield, (mm), and M?_v of PAN increased with polymerization temperature (T_p); maximum values of yield, (mm), and M?_v were obtained at c. 130°C. The optimum amount of additives was approximately equimolar to R₂Mg as initiator. The ¹³C chemical shift of α-carbon in R₂Mg at 90°C shifted by mixing with R₃Al and R₃B, respectively, indicating the existence of interaction between R₂Mg and the additives. The main role of the additives is considered to be suppression of the self-association of R₂Mg by strong interaction with R₂Mg.     

Supercritical CO2 Extraction of Chlorophyll a from Spirulina platensis with a Static Modifier

Supercritical CO₂ extraction with a static modifier was applied to extract chlorophyll a from Spirulina platensis. The effects of the process were investigated by single‐factor and response surface analysis experiments. The optimal process parameters for supercritical CO₂ extraction were determined to be: ethanol/water as the modifier, 40 vol.‐% water content in the modifier, 21.2 mL modifier volume, 1 h static soaking time, 2 h dynamic extraction time, 48.7 MPa extraction pressure, 326.4 K extraction temperature, and 10 g min^–1 CO₂ flow rate. The optimized chlorophyll a extraction yield was 6.84 mg g^–1. A comparison of the experimental results suggested that the yield of chlorophyll a by supercritical CO₂ extraction with modifier was higher than that obtained by conventional solvent extraction.     

Initiation of combustion processes in a hydrogen-oxygen mixture under the action of a low-energy strong-current electron beam

The process of combustion initiation in a hydrogen-oxygen mixture by a beam of electrons with an energy of ≈10 keV and a mean cross-sectional size of ≈10 cm is considered theoretically and experimentally. The initial pressure in the mixture is 500 Pa. The reaction was visualized by recording the time evolution of fluorescence intensity in the lines of molecular (λ = 310 nm) and atomic hydrogen and sodium doublet (λ = 589 nm). The calculations are performed on the basis of a semi-empirical model developed in a three-temperature (T ₀, T _e , and T _v) approximation. The induction and burning times determined in experiments and calculations are in good agreement. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 10–17, March–April, 2007.     

Prediction of the gas permeability of heterogeneous polymer blends

A recently introduced predictive scheme is used to calculate the permeability of various types of heterogeneous polymer blends, which are characterized by the ratio of the permeability of constituents in the range 10–10,000. The scheme combines a two‐parameter equivalent box model and the data on the continuity of constituting phases acquired by modifying equations proposed by the percolation theory; it takes into account the permeability of components and the interval of phase duality (co‐continuity) delimited by the critical volume fractions of components v_1cr and v_2cr. The scheme can be used in two ways: (i) permeability of blends predicted by using the “theoretical” value of parameters v_1cr = v_2cr = 0.16 should be regarded as a first approximation which may not well approximate experimental data due to the fact that real v_1cr and v_2cr are affected by relative viscosities of the components, interfacial energy, conditions of blend mixing, phase structure coarsening, etc.; (ii) conversely, by fitting experimental data, it is possible to determine v_1cr and v_2cr for the studied system; thus the scheme can be alternatively viewed as an efficient tool for phase structure analysis of polymer blends.     

Effect of oxalic acid on the rheological properties of dope solution of poly[acrylonitrile‐co‐(methyl acrylate)‐co‐(itaconic acid)]

The very high dope viscosity of concentrated dope of poly[acrylonitrile‐co‐(methyl acrylate)‐co‐(itaconic acid)] (with M?_v = 10.67 × 10⁵g mol^?1) in DMF could be diminished significantly by the addition of oxalic acid (OXA). The change in steady shear rheological behaviour caused by OXA has been analysed for the dope using a rheometer working in the viscosity mode. The temperature dependence of η₀ conformed to the Arrhenius‐Frenkel‐Eyring equation. ΔG_v decreased marginally with OXA concentration, and the least value was observed at an OXA concentration of 0.63 % by weight. Shear thinning behaviour was observed under higher shear rates for the terpolymer solutions in the presence and absence of OXA. The pseudoplasticity index (n) showed an abrupt initial increase on addition of OXA. The OXA concentration of 0.63 % by weight was advantageous for decreasing the viscosity of the polymer dope. The reduction in viscosity is attributed to the disturbed polymer‐polymer interactions by way of H‐bonding of OXA with the polymer. OXA‐containing dope at higher shear rate could achieve very low viscosities. Copyright © 2004 Society of Chemical Industry     

Impact Fracture and Failure Behavior of in‐situ Polymerized,Ethylene/Butyl Acrylate Rubber Toughened Polyamide‐12

The fracture and failure behavior of in‐situ polymerized polyamide‐12 (PA‐12) blends prepared by reactive extrusion were studied in instrumented high‐speed (v = 1.2 m/s) impact bending tests using the linear elastic fracture mechanics approach. PA‐12 was polymerized in presence (up to 9 wt.‐%) of ethylene/butyl acrylate copolymers (E/BA) of varying BA content and melt viscosity. From the tests performed on injection molded specimens at ambient temperature and –40°C, respectively, the fracture toughness (K_d) and initiation fracture energy (G_d,i) were derived. K_d was less sensitive to either testing temperature or E/BA type and content. G_d,i, on the other hand, went through a maximum at room temperature and monotonously increased at T = –40°C as a function of modifier content. E/BA with higher melt viscosity and lower polarity (lower BA content) performed better than the lower melt viscosity, higher polarity E/BA counterpart. The dominant failure modes and their change both with temperature and modifier content were studied by fractography and discussed.     

Analysis of temperature-dependent AC dielectric loss data

The analysis of dielectric loss data is frequently complicated by the presence of ohmic conductivity, especially at lower frequencies. Two simple methods are discussed for locating transition temperatures and for determining activation energies in such cases. In the first method the permittivity derivative [dε′(T)/dT] is used; in the second, permittivity difference spectra ε′(T, v₁) – ε′(T, v₂) (v₁ ? v₂ are used. The latter technique, however, cannot be used for activation energy determination. The theoretical basis of these methodologies and an analysis of representative experimental data are presented. The data set include measurements of pure and filled polyurethanes and of radiation-cured unsaturated polyester resins. Finally, the advantages of data presentation in the form of ε′ and ε″ instead of tan δ are discussed.     

Intrinsic viscosity–molecular weight relationship for low molecular weight nylon 6

Samples of nylon 6 have been prepared by the hexamethylene diamine-initiated polymerization of ?-caprolactam at 220°C. Fractionation of these with m-cresol–diethyl ether at 26°C yielded 15 amino-terminated fractions of M?_n of 337–10,940 determined conductometrically. Below M?_n = 4,306 the Mark-Houwink parameters in m-cresol at 30°C are K = 3.0 × 10^?3 dl/g and v = 0.53 ± 0.02. Thereafter v exhibits a pronounced increase. The value of K is similar to the values of Kθ derived from Stockmayer-Fixman plots of published data in good solvents. The findings thus corroborate a current hypothesis that fractionated, low molecular weight polymers in good solvents tend to behave viscometrically, as if they were under θ conditions (i.e., K = K_θ and v = 0.50).     

Column fractionation of polymers. VII. Computer program for determination of molecular weight distributions from gel permeation chromatography

Gel permeation chromatography produces a type of differential molecular weight distribution directly and rapidly. Conversion of these data to conventional molecular weight distributions and plots of distributions is time-consuming. A computer program is described to perform these operations readily. Input data from the automated chromatograph, elution volume, and recorder deflection are converted to unit sensitivity and base line corrections applied. The curve is then numerically integrated and a calibration curve used to convert elution volumes into molecular weights. Various calibration curves can readily be introduced into the program. The output, in addition to tabulation of cumulative and differential molecular weight distributions, contains values of M?_n, M?_v, M?_w, M?_z, and M?_z+1. Importantly, a reduced absolute area, i. e., area computed for unit sensitivity on a unit concentration basis, is tabulated. An additional time-saving eature is the printing out of differential and cumulative molecular weight distribution curves and of a differential histogram.     

Polymer/clay nanocomposite plasticization: Elucidating the influence of quaternary alkylammonium organic modifiers

The potential of nanoclay organic modifiers to induce plasticizing effects in resin and coatings systems was studied. In previous work, it was found that while low amounts of incorporation of organomodified clays significantly improved the physical and mechanical properties of a ultraviolet (UV)‐curable nanocomposite, further increasing the organomodified clay content could result in the reduction of properties. To investigate the potential impact of the organic modifier composition and concentration on polymer properties, a series of experiments were carried out using only the organic modifier. Methyl, tallow, bis‐2‐hydroxyethyl ammonium (MTEtOH), the organic modifier used in montmorillonite clay Cloisite® 30B, was dispersed with precursor polyester oligomers at 1–10 wt % through an in situ synthesis process and via sonication, and UV‐curable coatings were prepared from these MTEtOH‐containing resins. The organic modifier cetyltrimethylammonium bromide (CTAB) was also studied to examine the impact of the organic modifier structure. According to differential scanning calorimetry, small decreases in the glass transition temperatures (T_g) of the MTEtOH‐containing polyesters were observed, but CTAB‐containing polyesters had small T_g increases. Polyester molecular weight and viscosity were also affected by both the structure of the organic modifier as well as its concentration. The mechanical performance of the UV‐curable coatings diminished with increased MTEtOH concentration for the films containing the organic modifier compared to a control film. Furthermore, the crosslink density was found to reduce ～ 50% with increased MTEtOH loading into the UV‐curable films. The cure characteristics, thermal stability, and optical clarity were also studied. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013