Ultrasonic Solution Degradations of Poly(Alkyl Methacrylates)

Ultrasonic (70 W, 20 kHz) solution (2%) degradations of poly(alkyl methacrylates) have been carried out in toluene at 27°C and in tetrahydrofuran (THF) at -20°C. M_w and M_n of all polymers (before and after sonification) were computed from GPC. Irrespective of the alkyl substituent, M_w decreased rapidly at first and then slowly approached limiting values. All M_w/M_n ratios were in the vicinity of 1.5 at the limiting chain lengths. For identical M_n, the rate constants k were (4.2 ± 2.0) × 10^?6 min^?1 in toluene at 27°C and (5.4 ± 2.0) × 10^?6 min^?1 in THF at -20°C. For poly(isopropyl methacrylate) and poly(octadecyl methacrylate) with higher, but identical, M_n,0, k values were higher ((9.0 ± 1.0) × 10^?6 min^?1 at 27°C and (18.0 ± 1.5) × 10^?6 min^?1 at -20°C). This suggests that M_n,0 and not the bulk size of the alkyl substituents is the factor that determines the rate of degradation. Lowering of the temperature accelerates degradation due primarily to lower chain mobility of poly-(alkyl methacrylates) and enhanced cavitation. The average number of chain scissions ([(M_n)₀/(M_n)_t] - 1) calculated from component degradation data are much higher than those obtained with overall M_n,t values.     

Ultrasonic Modification of Polymers. I. Degradations of Polystyrene in the Presence of Various Poly(alkyl Methacrylates)

Ultrasonic (70 W, 20 kHz) degradations of polystyrene (PS) have been carried out with various poly(alkyl methacrylates) (PRMA) for periods of 3 h at 27°C in toluene (2.0 to 5.0% solutions). The isolation of sequence copolymers thus prepared from their associated homopolymers was achieved by employing selective solvents (solvent for one homopolymer but a precipitant for the second homopolymer in the mixture). The recovered products were analyzed by gel permeation chromatography (GPC), infrared spectroscopy (IR), and viscometry. These analyses showed that when the substituents in PRMA were methyl, ethyl, isopropyl, n-butyl, isobutyl, or phenyl, sequence copolymers with segments from PS as well as from poly(alkyl methacrylate) were obtained. However, when the substituents on PRMA were hexyl, isodecyl, lauryl, hexadecyl, octadecyl or isobornyl there were no sequence copolymers formed. The decrease in the intrinsic viscosity of the recovered homopolymers and shifts of their GPC chromatograms toward the low molecular weight end suggest that on sonification PRMA samples having bulkier substituents do degrade and yield radicals which, however, do not recombine with those from polystyrene. Furthermore, ultrasonic degradation of polystyrene is found to be dependent on the chain stiffness of the poly(alkyl methacrylates).     

A Reference Electrode for Electrochemical and Cryoelectrochemical Use in Tetrahydrofuran Solvent

We report a reference electrode for direct use in tetrahydrofuran (THF) at low temperatures. A reference solution containing equimolar amounts of ferrocene/ferrocenium hexafluorophosphate (Fc/Fc⁺) are prepared to give a 4 mM solution in THF that contains tetrabutylammonium hexafluorophosphate (TBAF) supporting electrolyte thus, minimizing liquid junction potentials. The reference solution is added to a sealed glass tube with a porous frit at one end, and a platinum wire is inserted into the tube. The reference electrode assembly is then inserted into a THF test solution. Potentiometric measurements show that the system responds in the expected Nernstian fashion over the concentration and temperature ranges, 4 mM to 40 μM and 20 °C to ?45 °C respectively. In addition, it is shown by steady–state cyclic voltammetry at a platinum microelectrode that the chemical reactivity of ferrocenium hexafluorophosphate (Fc⁺) otherwise seen in THF is suppressed by ion‐pairing with PF using tetrabutylammonium hexafluorophosphate (TBAF) as the supporting electrolyte.     

Ultrasonic Modification of Polymers. II. Degradation of Polystyrene,Substituted Polystyrene,and Poly(n-vinyl Carbazole) in the Presence of Flexible Chain Polymers

Abstract

Ultrasonic (20 kHz, 70 W) solution degradations of polystyrene, substituted polystyrenes, and poly(n-vinyl carbazole) have been carried in toluene and tetrahydrofuran at 27 and -20°C in the presence of flexible chain polymers. Polystyrene formed block copolymers at 27°C with stiff-chain polymer PVCz; however, in the presence of flexible chain polymers, e.g., poly(vinyl methyl ketone) or poly(vinyl methyl ether), there were no block copolymers formed. Poly(n-vinyl carbazole) does not seem to form any block copolymers at 27°C with flexible chain polymers, e.g., poly(octadecyl methacrylate) and poly(ethyl methacrylate). Poly(p-chlorostyrene) and poly(p-methoxystyrene) also do not form block copolymers at 27°C with poly(octadecyl methacrylate) but do so with poly(hexadecyl methacrylate). It is quite possible that these may only be blends of two homopolymers. Poly(octa-decyl methacrylate) does yield a block copolymer when sonicated at -15°C with poly(p-isopropyl α-methylstyrene).     

Solution Properties of Star-Shaped Polystyrenes Having Peripheral Charged Ions

Functionalized polystyrene stars were prepared by copolymerization of polystyryl lithium with divinylbenzene in a mixture of benzene/tetrahydropyran, where the polystyrene arms were prepared by anionic polymerization using [2-[(N,N-dimethylamino)-methyl]phenyl]lithium as the initiator. These functional stars were converted by quaternization with methyl iodide into polystyrene stars having peripheral positive charges. We studied the charge effects on the solution properties of such stars. The hydrodynamic dimension of peripheral charged polystyrene (PS) stars depended strongly on the solubility parameter between PS segments and solvent. Copyright 2000 Academic Press.     

混合溶剂诱导PS膜的去润湿过程

采用光学显微镜及原子力显微镜等实验手段研究了聚苯乙烯(PS)膜在水和丙酮混合溶剂诱导下的去润湿过程.实验发现,在亲水基底上,随着丙酮含量的减少,在整个去润湿过程中孔半径与时间呈e指数关系[R～exp(t/τ)],然后呈线性关系(R～t),最后为R～t0.76,并且孔增长机理从成核增长机理转变为取代机理.在疏水基底上,随...     

Ultrasonic Degradation of Hydroxypropyl Cellulose Solutions in Water,Ethanol, and Tetrahydrofuran

Ultrasonic degradations of hydroxypropyl cellulose (HPC) have been carried out in water, ethanol, and tetrahydrofuran (THF) solutions. In the HPC-water system, cavitation intensity did not increase linearly with ultrasound intensity because of a lower threshold of ultrasonic intensity below which cavitation does not occur. At 27°C the rate of degradation in the three solvents followed the order water > ethanol > THF which is not in line with their characteristic impedance values. The rate of degradation for 20 kHz, 70 W ultrasound intensity was found to increase with a decrease in solution volumes, concentration of HPC, and temperature. Increased rate of degradation at lower temperatures supports the concept based on sonoluminescence experiments that it is the cavitation in a polymer solution that is responsible for ultrasonic degradations and the dissolved polymer molecules do not act as cavitation nuclei. Increased surface tension and density of the solvent are thought to be responsible for improved cavitation at low temperatures. Infrared spectroscopy and x-ray analysis of HPC subjected to ultrasonic treatments remained unchanged, suggesting that there were no chemical or structural (e.g., degree of order) changes on irradiation. The decreases in molecular weights on irradiation arise due to random chain scission whereas similar decreases in Huggins coefficients can be attributed to physical changes (decrease in molecular weight or branching) in the degraded HPC samples.     

Small Angle X-ray Scattering Study of PS Conformation in Tetrahydrofuran Solvent with Gas Anti-solvent

Compressed gases or supercritical fluids (SCFs) are highly soluble in some liquid solvents, and thus reduces the solvent strength of the liquids1. As a result, precipitation of the dissolved solutes occurs, which is called as gas anti-solvent (GAS) process. Recently, this new technique has been used to produce fine particles of different compounds, such as polymers2. Effect of the dissolved gases on the conformation of polymer molecules is a very interesting topic. In this work, we report t…     

磺化聚苯乙烯镧离子型聚合物的稀溶液性质

聚电解质行为;比浓粘度;电解质;磺化聚苯乙烯镧离子型聚合物的稀溶液性质     

False Results Caused by Solvent Impurity in Tetrahydrofuran for MALDI TOF MS Analysis of Amines

Tetrahydrofuran (THF) is one of the most frequently used solvents in the MALDI TOF MS analysis of synthetic compounds. However, it should be used with caution because a trace amount of 4-hydroxybutanal (HBA) might be generated and accumulated in THF during storage. Since only a tiny amount of analytes is required in MALDI MS measurements, a trace amount of HBA might have a significant effect on the MS results. It was found that HBA will quickly react with primary and secondary amino compounds, leading to false results about the sample composition with an extra series of ions with additional mass of 70 Da in between. The formation of HBA can be inhibited by butylated hydroxytoluene (BHT) antioxidant. Therefore, when THF is required as the solvent for sample preparation, it is strongly recommended to use a BHT-stabilized one, at least for the analysis of compounds with amino groups.

Solvent and Substituent Effects on the Spectra of Some Substituted Thioureas

A study on the effect of a number of solvents, covering a broad polarity range i.e. from dioxane (D=2.20) to acetonitrile (D=38.0), has been made on the electronic transitions of N-aryl, N′-2-(5-halo-pyridyl) thioureas (where aryl= -C₂H₅ or O-CH₃-C₆H₅-, and halo= -Cl, -Brand -I). Two intense absorption maxima in the regions 270-285 nm (assigned for thiocarbonyl π-π* transition) are exhibited by all the substituted thioureas studied. The excitation energies and oscillator strengths of these transitions have been calculated. A correlation between ‘E_T’ and ‘Z’ (an empirical measure of solvent polarity) has been attempted. Solvent sensitivities of these compounds have also been calculated. The effect of halo-substituents, in the pyridine ring, on the spectra of these substituted thioureas has also been studied. It has been proposed that there is a delocalization of electrons between the pyridine ring and the thiourea unit of these compounds. This delocalization of electronic charge is affected by the substitution of the halo-groups in the pyridine ring at para position to the thiourea unit which is reflected in the intensities and shifting of the absorption maxima.     

The Reaction of some Carbonyl and Thiocarbonyl Compounds with Prenyl- and Crotyllithium in Tetrahydrofuran Solution

Prenyllithium (3-methylbut-2-enyl-lithium) ( 1 ) and cis-crotyllithium (Z-but-2-enyl-lithium) ( 2 ) in tetrahydrofuran solution, prepared according to the method of Eisch & Jacobs, react with carbonyl compounds to give the branched alcoholates with moderate to high selectivity, unless access to the carbonyl group is strongly hindered (see the Table). Adamantanethione ( 12 ) reacts with 1 to give the unbranched thiolate.     

混合溶剂对磺化聚苯乙烯水基微乳液体系形态的影响

利用相反转技术制备磺化聚苯乙烯(SPS)水基微乳液,研究发现,通过选择溶剂和控制混合溶剂的组成,可制备不同颗粒形态结构的SPS水基微乳液,并研究了相反转过程、乳液稳定性与混合溶剂组成之间的关系。     

The Rate of Degradation by Ultrasonation of Polystyrene in Solution

Abstract

The rate of degradation by ultrasonation of polystyrene in tetrahydrofuran solutions has been measured at various concentrations, temperatures, and irradiation intensities. As reported earlier, the course of the changes in molecular weight distributions is independent of the molecular weight (MW) of the initial polymer and of the degradation conditions. Therefore, the time dependence of the extent of the degradation can be meaningfully compared for various reaction conditions and for polymers with different original MWs. The extent of the scission process was expressed in terms of the degradation index (DI), the ratio of the number of chain bonds broken to those initially present. The problem of the existence of a minimum MW required for sonic scission is considered and arguments are advanced in favor of the assumption of a minimum degradable chain length for the purpose of evaluation of degradation data. This minimum MW was found to be about 30,000. DI values were corrected for the “unbreakable” chain ends.

It was observed that curves representing the time dependence of DI were linear on double logarithmic plots for all experiments, DI being proportional to t^0.85. By shifting these lines along the time axis a master curve was obtained representing all data for all experimental conditions over almost three decades of DI. Thus the time-dependent rate of scission of any run relative to that under reference conditions can be expressed by a single value of the time transposition factor, a measure of the shift. This transposition factor provides a simple method for assessing the effects of experimental conditions. Some data are reported expressing the effect of MW of the initial polymer, concentration, temperature, and irradiation intensity on degradation rate.     

Selective Guest Uptake from Solvent Mixtures in the Clathrate Phase of Syndiotactic Polystyrene

Summary: Selective absorption uptake during the guest‐exchange processes in the δ form of syndiotactic polystyrene (sPS) was confirmed by IR spectroscopy. When films of the δ form were immersed in hexane/decane or chloroform/decane mixtures, decane molecules were incorporated preferentially in the δ form. Sorbate uptake by the δ form was greatly accelerated when the sorbate was mixed with a solvent penetrable to the amorphous region of sPS.

Concentration changes in a δ‐form film during sorption processes: sorption of a chloroform(D)/decane(H) mixture (1:1 molar ratio).     

Determination of Volatile Organic Compounds as Impurities in Polystyrene Food Containers and Polystyrene Cups

Abstract

Volatile organic compounds in polystyrene food containers and polystyrene cups were determined using direct headspace sampling with gas chromatographic and gas chromatographic/mass spectrometric analysis. Compounds which were detected in polystyrene food containers and cups included 2-methy 1-2-propen-1-ol, ethylbenzene, styrene, β-methylstyrene, and trimethy 1- and tetramethylbenzenes. Individual concentrations of these impurities in the polymeric materials were estimated as 5 to 270 μg/g. Several impurities including styrene were extracted into water at 88 to 93°C within 2 to 3 minutes upon contact. VAriations in aqueous concentrations of styrene as a function of time in contact with polystyrene cups are reported here. Maximum concentrations of styrene in hot water were 35 μg/L after 15 to 20 minutes of contact of water with cups.     

Preparation of Polystyrenes Containing Sulfonamide Moieties and Their Use as Phase Transfer Catalysts

Styrenes containing sulfonamide moieties such as N-methyl-N-(P-vinylbenzyl)methanesulfonamide and N,N-dimethyl-p-styrene-sulfonamide were prepared. The copolymerization parameters of these monomers were obtained from copolymerization with styrene under free radical conditions. Crosslinked polymers prepared by free radical terpolymerization of the sulfonamide monomer, styrene, and divinylbenzene served as phase transfer catalysts for the reaction of n-octyl bromide with sodium thiophenoxide in the toluene-water system. However, the corresponding monomeric sulfonamides were practically inactive. These polymer catalysts were stable even under strongly alkaline conditions, and the recovered catalysts were used without a significant loss in activity.