Kinetics of reaction of methyl α-eleostearate with phenol

The kinetics of addition reactions between methyl α-eleostearate which forms the main chain of tung oil and phenol when catalyzed by an acid, p-toluene sulfonic acid, have been studied. The addition reactions, carried out with phenol was shown to be second order with regard to methyl α-eleostearate concentration and first order with regard to phenol concentration. The reactions were additions of two phenol molecules to one methyl α-eleostearate molecule, and it was presumed that they proceed in the two steps given below in which the first step is rate determining: ((1)) ((2)) The apparent reaction rate constant (l/mol min) was found to be 0.036 and its value was nearly equal to that in the case of m-cresol. The apparent activation energie (kcal/mol) was found to be 4.76 and its value was larger than that in the case of m-cresol.     

Kinetics of reactions of methyl α-eleostearate with cresols

The kinetics of addition reactions between methyl α-eleostearate which forms the main chain of tung oil and cresols when catalyzed by an acid, p-toluene sulfonic acid, have been studied. The addition reactions, carried out with any one of the o-, m-, and p-cresols were shown to be first order with regard to both methyl α-eleostearate and cresol concentrations. The reactions were additions of two cresol molecules to one methyl α-eleostearate molecule, and it was presumed that they proceed in the two steps given below in which the first step in rate-determining. (1) (2) (E: methyl/α-eleostearate, C: cresols) The apparent reaction rate constants (L/mol min) were found to be 0.046 for o-cresol, 0.038 for m-cresol, and 0.033 for p-cresol. The apparent activation energies (kcal/mol) were found to be 0.95, 3.66, and 4.05, in the cases of o-, m-, and p-cresols, respectively.     

Evidence for several species of active sites in Ziegler-Natta catalysts

The kinetics of isoprene polymerization catalyzed by VCl₃ and Et₃Al were studied by measuring fractional conversions, polymer composition, and molecular weight distributions at a series of reaction times and temperatures. The rate of polymerization plotted against temperature shows an inflection point with a minimum and maximum in the 60–90°C range. The isomeric composition of the polymer changes with temperature but not with reaction time, while the molecular weight distribution undergoes substantial change with both of these variables. The rate of polymerization at sites producing low molecular weight polymers was measured, and the activation energy calculated to be about 10 kcal/mole. The active sites were found to deactivate at different rates. The results support the hypothesis that several species of active sites are present in the system and that these exhibit characteristic polymerization behavior.     

KINETIC ANALYSIS OF CO-CONDENSATION POLYMERIZATION OF AB2 AND AB MONOMERS

This work deals with the kinetics of co-condensation polymerization of AB2 and AB monomers, giving expressions of the two-dimensional molecular weight distribution function and the number/weight average molecular weights of the resulting copolymers. The two-dimensional molecular weight distribution depends on two indices, n and l, which are the respective numbers of AB2 and AB units in a copolymer species. The evolution of the two-dimensional weight and z distributions during the co-condensation polymerization has been evaluated systematically. Finally, the two-dimensional distribution was transformed into a one-dimensional molecular weight distribution with only one variable (the molecular weight of the products instead of the degree of polymerization). The calculated results show that the highly branched copolymer has a very broad molecular weight distribution when the co-condensation polymerization approaches completion.     

Analysis of resoles by gel-permeation chromatography

Resoles, the complex, heat-sensitive product mixture from the alkali-catalyzed reactions of phenol with formaldehyde were investigated by gel-permeation chromatography (GPC). The low molecular weight species of these resins which consisted of mono-and dinuclear methylol phenols were resolved into multiple peaks. Model compounds were used to identify the peaks of the specific methylol phenols or methylene etherbridged diphenols. Differences in the refractive index of individual species restricted the quantitative analysis of low molecular weight components in the resole. The effects of sodium and barium hydroxides and hexamethylene-tetramine as catalysts, reaction temperature, and time on the total composition of a resole are demonstrated with the gel-permeation chromatographic spectrum and with the aid of NMR. Formation of a “secondary” resole by methylolation of the bisphenol of formaldehyde was also monitored by GPC.     

Cationic polymerization of p-substituted α-methylstyrenes. III. Effect of polymerization conditions on tacticity and molecular weight for p-chloro-α-methylstyrene

The cationic polymerization of p-chloro-α-methylstyrene was investigated for the effect of initiator and solvent on polymer tacticity, molecular weight, and molecular weight distribution. The products were generally crystalline polymers of 80–90% syndiotactic content with fairly high molecular weights and broad molecular weight distributions. Tacticities and molecular weight distributions followed similar patterns suggesting that the effect of reaction conditions on ionpair end-group structures was the dominant factor.     

Molecular weight distribution and molecular structure of polyethylene produced by radiation-induced polymerization

The molecular weight distribution of polyethylene produced by radiation was calculated according to a kinetic scheme. The calculated molecular weight distribution was compared with the results deduced from gel-permeation chromatography. The observed distribution curve from GPC was broader and showed a lower degree of polymerization than the calculated one. Discrepancies between observed and calculated curves can be explained if the polymer contains nonsteady-state products and if the reaction mechanism includes chain transfer to dead polymer. By this reaction long-chain branching would occur. Several long-chain branches per polymer molecule were indeed found, as inferred from solution properties.     

Analysis of fractionation of ethylene–propylene copolymers

Analysis of the solution fractionation of ethylene–propylene copolymers was carried out by assuming a bivariate normal distribution function for the distribution of molecular weight and chemical composition. It was found that the variation of the molecular weight and composition distributions in fractions was complicated, because two distribution characteristics of the original copolymer affect fractionation to differing extents. The hypothetical cumulative weight distribution curves thus obtained agreed essentially with those obtained experimentally.     

Synthesis of star-branched oligomers by reaction of oligobutadienyllithium with diesters and epoxidized soyabean oil

Anionic polymerization can produce branches with low molecular weight and narrow molecular weight distributions. Post polymerization linking involving the still active chain ends can then be done to produce branched oligomers with a predetermined number of arms. These species are then excellent model compounds for testing high molecular weight branches. Here we chose the reaction of oligobutadienyllithium with ethyl acetate, dimethyl adipatc, diethyl adipatc, dimethyl phthalatcand epoxidized soyabean oil. For the last linking agent, we compared the result obtained with a high molecular weight poly(styryl-b-butadienyl)lithium.     

Ti-Hf双金属高效载体催化剂合成宽分子量分布聚乙烯的研究

乙烯聚合;乙烯-丁烯聚合;双金属催化剂;Ti-Hf双金属高效载体催化剂合成宽分子量分布聚乙烯的研究     

Production and Characterization of Biodiesel from Tung Oil

The feasibility of biodiesel production from tung oil was investigated. The esterification reaction of the free fatty acids of tung oil was performed using Amberlyst-15. Optimal molar ratio of methanol to oil was determined to be 7.5:1, and Amberlyst-15 was 20.8wt% of oil by response surface methodology. Under these reaction conditions, the acid value of tung oil was reduced to 0.72mg KOH/g. In the range of the molar equivalents of methanol to oil under 5, the esterification was strongly affected by the amount of methanol but not the catalyst. When the molar ratio of methanol to oil was 4.1:1 and Amberlyst-15 was 29.8wt% of the oil, the acid value decreased to 0.85mg KOH/g. After the transesterification reaction of pretreated tung oil, the purity of tung biodiesel was 90.2wt%. The high viscosity of crude tung oil decreased to 9.8mm²/s at 40 °C. Because of the presence of eleostearic acid, which is a main component of tung oil, the oxidation stability as determined by the Rancimat method was very low, 0.5h, but the cold filter plugging point, −11 °C, was good. The distillation process did not improve the fatty acid methyl ester content and the viscosity.     

Molecular weight distribution in polyacrylamide prepared by a photochemical method

The molecular weight distribution of polyacrylamide, prepared by uranyl ion-photosensitized polymerization of acrylamide in visible light of wavelength 436 mμ, was studied in detail. The polymer was fractionated and the experimental integral and differential distribution curves were drawn. The theoretical distribution function was derived from the kinetics of photopolymerization, assuming the rate constants calculated from previous studies. The theoretical and experimental molecular weight distributions were compared. The results support the mechanism proposed for the photopolymerization reaction.     

Depolymerization of xylan-derived products in an enzymatic membrane reactor

Rice husks were subjected to aqueous processing to obtain liquors containing xylan-derived products, which were assayed for composition. Liquors were diafiltered using 1 kDa ceramic membrane for purification purposes, and the retentate was concentrated using the same membrane. The molecular weight distribution of xylan-derived products in concentrated liquors was assayed by gel permeation chromatography. In order to achieve the one-step conversion of soluble, high molecular weight xylan-derived products into low molecular weight arabino-xylooligosaccharides (AXOS) and the recovery of low molecular weight AXOS, concentrated liquors were treated in a continuous enzymatic membrane reactor (EMR) with a commercial endoxylanase (Shearzyme 2X). Two operational modes were studied: in the first one, both enzymatic reaction and membrane operation began at the same time, whereas in the second case, permeation started when the reaction achieved a given conversion. Both operational modes are compared in terms of productivity.     

Degradation of lignin by ozone. II. Molecular weights and molecular weight distributions of the alkali-soluble degradation products

The molecular weights and molecular weight distributions of the alkali-soluble degradation products from the ozonolysis of spruce periodate and cuoxam lignins and spruce protolignin have been studied by gel permeation chromatography and ultracentrifugation. The bimodal distribution previously reported for soluble lignins was found to be an artifact; the correct distribution has one broad lowmolecular-weight maximum, with a long tail extending toward the high-molecular-weight end of the distribution. Weight-average molecuar weights of the alkali-soluble degradation products, obtained by sedimentation equilibrium measurements, increased with time of ozonization up to about 15 min. Beyond this time fragmentation of the partly degraded products results in a decrease in molecular weight. Lignin degradation followed the pattern expected of a three-dimensional, infinite-network polymer gel undergoing breakdown. Based on the molecular weights and the molecular weight distributions, a random stepwise mechanism is suggested as the mode of lignin degradation by ozone.     

Molecular Weight Characterization and Structural Properties of Controlled Molecular Weight Dextrans Synthesized by Acceptor Reaction using Highly Purified Dextransucrase

ABSTRACT

Controlled molecular weight dextrans were synthesized using a highly purified dextransucrase from Leuconostoc mesenteroides NRRL B-512F in a multi-step process. Maltose was used as acceptor for the first reaction step. The purified product obtained at a given reaction step was used as acceptor for the next reaction step. Dextrans of molecular weights ranging from 1,000 to 100,000 were thus obtained with a good yield (80 %). After purification, the molecular weight distribution of the products was characterized using size exclusion chromatography coupled with low angle laser light scattering (LALLS). Polydispersity of the products was shown to be similar to that of commerical dextrans.

¹³C NMR spectra and enzymatic hydrolysis data are consistent with the fact that the enzymatically synthesized dextrans are essentially composed of α(1->6) linkages. It was observed that controlled molecular weight dextrans were less branched than commercial products obtained by acidic hydrolysis of high molecular weight dextrans.     

Copolymerization of ethylene and 1-hexene with supported metallocene catalysts: Effect of support treatment

The effect of different catalyst support treatments in the 1-hexene/ethylene copolymerization with supported metallocene catalysts was investigated through the analysis of molecular weight and chemical composition distributions by means of high temperature gel permeation chromatography (GPC) and crystallization analysis fractionation (CRYSTAF). The molecular weight distributions of all copolymers are narrow, indicating a uniform catalyst site. However, with respect to chemical composition distribution, some supported catalysts show broad and sometimes bimodal distributions, which indicates the presence of two or more active site types.     

Polyaryläther-Kondensationsprodukte des 4,4′-bis(chloromethylphenyl) äthers mit manchen diphenolen

Poly(aryl ethers) as products of the polycondensation of 4,4′-bis(chloromethylphenyl) ether with sodium salts of various phenols have been prepared in the Williamson reaction. The reaction was carried out at three different temperatures (78, 140, and 185°C.) in ethanol, xylene, and tetralin, respectively. The effect of the polycondensation and the nature and composition of initial components on the properties of the products has been studied. The molecular weights and the melting temperature of the synthesized resins increased with increasing reaction temperature. The structure and molecular weight have a pronounced effect on the properties of the resins. Resins prepared from 4,4′-dihydroxydinaphthyl had the highest melting temperature and were practically insoluble, while the resins prepared from 2,2′-dihydroxydinaphthlmethane had the lowest melting temperature and were soluble in practically all organic solvents. On the basis of the experimental data a reaction scheme appropriate for the synthesis of poly(aryl ethers) from the phenolates as well as from the free phenols in the presence of NaOH has been proposed. Some thermal and mechanical properties of poly(aryl ethers) have been determined. Thermal treatment of the resins above theri softening temperature resulted in an elevated softening point too. This is explained by the supplementary condensation of both chlorine or hydroxyl endgroups in the molten resins.     

Electrochemical polymerization to a controlled molecular weight distribution

Living polyanions were generated by the passage of electrolytic current through solutions in tetrahydrofuran (THF). The concentration of living polyanions was controlled by the current and could be increased by further electrolysis or decreased by electrolysis with reversal of polarity. Inasmuch as the living end (LE) concentration determines the molecular weight at a given monomer concentration it was possible to program a molecular weight distribution. Model distributions were attempted by (1) indirect methods in which an electrolytic formation of initiating dianions was followed by monomer addition, polymerization, current reversal and further polymerization and (2) direct methods in which monomer was present throughout the electrolysis. The molecular weight distributions were obtained by gel-permeation chromatography and corresponded closely to the values calculated from the simple kinetic model of anionic polymerization. For styrene a sharp low molecular weight fraction and a clear binodal high molecular weight fraction were obtained. The binodal character was attributed to the growth of active single-ended and double-ended polyanions. The yields of high and low molecular weight material, the ratios of molecular weights obtained, and the values of the molecular weights were in agreement with expectation. The direct electrochemical polymerization methods were employed for α-methylstyrene, but the high k_p for styrene thwarted efforts to apply the direct technique with this monomer.     

酚类聚合物在水相胶束中的酶促合成

本文报道辣根过氧化物酶在水相胶束中催化聚合取代酚类的研究。水相胶束中酶催化活力高，产物分子量均一；通过调节表面活笥剂和单体的浓度，可以有效地控制产物的分子量，从而建立了不同聚合度有机纳米材料酶促合成的新方法。产物具有较强的蓝紫色荧光及较好的耐热性能，是一种很有应用前景的蓝光材料。