Primary Chain Length Research Articles

Comparative studies on the kinetic parameters and product analyses of chicken and rat liver and yeast fatty acid synthetase

1. 1. Comparative kinetics and product analyses of chicken and rat liver and yeast fatty acid synthetase. 2. 2. V max' s for the three enzymes studied decrease with increasing primer chain-length, while K m' s (except for yeast) increases. 3. 3. Palmitate is the main product (∼90%) of the rat synthetase whereas palmitate (60%) and stearate (40%) are the products of chicken and yeast enzymes. Increasing the primary chain length does not alter palmitate synthesis by rat and chicken enzymes but increases stearate synthesis by the yeast synthetase. 4. 4. The three synthetases could not synthesize fatty acids in the absence of primer acetyl-CoA suggesting that malonyl-CoA decarboxylase is not a component.

Studies of the polymerization of diallyl compounds. XXV. Gel point in the polymerization of diallyl esters of aromatic dicarboxylic acids

AbstractStudies on gelation in the radical polymerization of diallyl dicarboxylates have been conducted by Simpson,9,11 Gordon,10 and Oiwa.13 However, the results obtained have not always been consistent and are still far from full elucidations. In this paper, the gel point in the polymerization of diallyl aromatic dicarboxylates, including diallyl phthalate (DAP), diallyl isophthalate (DAI), and diallyl terephthalate (DAT) is experimentally reexamined in detail and discussed according to Gordon's theory; the discrepancy between actual and theoretical gel point conversion was quite large and was enhanced in the order DAT > DAI > DAP. Moreover, from detailed inquiry into the primary chain length of the prepolymer it is suggested that the intramolecular chain transfer reaction plays an important role in the polymerization of diallyl ester accompanying the intramolecular cyclization reaction. The polydispersity coefficient (Pw,0/Pn,0) of the initial prepolymer of DAP is also estimated to be 2.0 from the extrapolation of Pw/Pn to zero conversion.

Studies of the polymerization of diallyl compounds. XXIV. Effect of temperature on the polymerization of diallyl phthalate

AbstractThe effect of temperature on the polymerization of diallyl phthalate was investigated in the temperature range of 80–150°C. The degree of polymerization increased slightly with temperature up to 100°C and then decreased; together with the results of primary chain length and the dependence of Rp on initiator concentration, these findings were interpreted in terms of the enhancement of the reinitiation ability of the allylic radical produced by the intramolecular chain‐transfer reaction and of the reactivity of the cyclized radical at elevated temperature. The tendency for cyclization became more marked with increasing temperature. The gel point was almost unaffected.

The composition of beeswax alkyl esters

AbstractThe alkyl esters of beeswax, after isolation from the unhydrolyzed wax by preparative layer chromatography (PLC), have been analyzed directly by high temperature GLC using 1.5% OV1 as liquid phase. In two commercial wax samples examined the ester homologues are predominantly even carbon numbered ranging from C36 to C54. The principal alkyl esters are C40, C42, C44, C46 and C48. The GLC analysis of the ester hydrolysis products revealed that the variations in ester chain length are produced by variations in the esterified primary alcohol chain lengths. The esterified fatty acid is chiefly hexadecanoic acid. The esterified fatty acids differ in composition from the free fatty acids which are also present in the wax.

Theory of Branching Processes and Statistics of Rubber Elasticity

Abstract Recent efforts to reformulate statistical theories of polymeric systems in terms of the theory of branching (“cascade”) processes, are here extended to calculations of statistical parameters for the theory of rubber elasticity, viz., the number and mean length of various forms of active network chains. New simple results are given for random ƒ-functional polycondensation; it is shown that such systems are of interest in rubber elasticity studies in the region just after the gel point, where the concentration of active network chains varies rapidly with conversion, while the mean length of these chains diverges at the gel point. General exact formulas are derived for random crosslinking of arbitrary primary distributions, without assuming that the mean primary chain length is necessarily large; examples are worked out for uniform (homodisperse) chains, random, self-convoluted random, or Poisson primary distributions. Calculations are extended also to the cross-polymerization type of vulcanization reaction attributed to the cure of polybutadiene with peroxides. The results suggest reasons for differences in technical performance observed with such rubbers.

Theory of Branching Processes and Statistics of Rubber Elasticity

Recent efforts to reformulate statistical theories of polymeric systems in terms of the theory of branching (``cascade'') processes, are here extended to calculations of statistical parameters for the theory of rubber elasticity, viz., the number and mean length of various forms of active network chains. New simple results are given for random f-functional polycondensation; it is shown that such systems are of interest in rubber elasticity studies in the region just after the gel point, where the concentration of active network chains varies rapidly with conversion, while the mean length of these chains diverges at the gel point. General exact formulas are derived for the random cross linking of arbitrary primary distributions, without assuming that the mean primary chain length is necessarily large; examples are worked out for uniform (homodisperse) chains, random, self-convoluted random, or Poisson primary distributions. Calculations are extended also to the cross-polymerization type of vulcanization reaction attributed to the cure of polybutadiene with peroxides. The results suggest reasons for differences in technical performance observed with such rubbers.

The thermal decomposition of methylene chloride

The thermal decomposition of methylene chloride has been studied in the temperature range 500 to 650 °C by both the static technique of pressure-time measurement and the use of a flow system in conjunction with gas chromatographic analysis. The reaction, which leads principally to carbon and hydrogen chloride is characterized by a slow acceleration, the rate of which decreases with the vessel diameter. In vessels of diameter less than 5 mm the reaction is almost completely inhibited. The reaction rate is increased by the addition of inert gas, nitric oxide and, particularly, by dichlorethylene. Using the flow system a number of chlorinated hydrocarbons were detected as minor products of the reaction and their rate of formation relative to the major products was followed in detail. By identifying some of these as radical recombination products and one, dichlorethylene, as a degenerate branching agent, a delayed branching mechanism has been deduced which explains most of the kinetic features of the reaction as well as the formation of the observed minor products. This involves the production of the intermediate, dichlor­ethylene, in a chain carried by chlorine atoms and dichlormethyl radicals, and the conversion of this to carbon and hydrogen chloride by a coupled chain also involving chlorine atoms. The average primary chain length has been estimated as fifteen by measurement of the rate of formation of the supposed recombination products, but this figure is uncertain since the termination products appear to be destroyed in turn by chlorine atoms generated in the main chain.

The curing of polyester resins, and the general mechanism of the later stages of polyfunctional polyadditions

AbstractThe study of each of three stages in the bulk polymerization of an unsaturated polyester resin requires different methods and theoretical models. A model system (polyethylene fumarate/methyl methacrylate) was earlier shown to behave as a classical copolymerization system in the first stage which extends to the gel point. To the kinetics of the second stage, that of diffusion control of the termination step after the gel point, the model proposed by GORDON and ROE is here applied successfully. In a later report, the kinetics of the third stage, where general diffusion control sharply arrests the polymerization, will be treated in terms of the appropriate relaxation theory. It is shown here that, contrary to the assumptions of the Gordon‐Roe model, diffusion control of the termination step does not set in at the viscosimetric gel point in systems of relatively short primary chain lengths, such as a styrene‐based polyester or triallyl cyanurate.The final conversions obtainable by polymerization at 62° C of the model polyester are measured as a function of the feed ratio R of fumarate to methacrylate unsaturation. As a first approximation, it is confirmed that the reaction becomes arrested when the second order transition reaches the polymerization temperature. This generally happens when about 80% of the methacrylate and 10% of the fumarate unsaturation have been polymerized. These proportions confirm the earlier conclusion, according to which the polymerization is largely carried by the methacrylate unsaturation, and show incidentally that a polyfumarate is not an efficient cross‐linker for methacrylate. As a second approximation, the final state of cure, as deduced from the second order transitions, is somewhat variable with R. To account for these variations, the theory of the state of cure is developed in terms of three parameters: the concentration of cross links, the concentration of residual methyl methacrylate, and the concentration of residual free polyethylene fumarate chains. A statistical theory leads to symmetrical formulae for the first and third of these parameters. The results suggest that in the present model system the variations in the final state of cure are dominated by the concentration of residual methyl methacrylate acting as plasticizer.

Crosslinking in isoprene polymerization

AbstractA study has been carried out on the emulsion polymerization of isoprene in an attempt to evaluate the relative rate of the crosslinking reaction and its variation with temperature. From the relation between primary chain length and gel formation during polymerization, the following values were obtained for the relative crosslinking rate constant, i.e., ratio of the velocity constants of the crosslinking and propagation reactions. Temperature, °C. K = kx/kp 60 3.4 × 10−5 70 4.3 × 10−5 80 5.2 × 10−5 The above data lead to a calculated value for the difference in the activation energy between the crosslinking and the propagation reaction (Ex − Ep) of 5.0 kcal. From these data and the known value of the propagation rate constant, it is possible to calculate the following absolute rate expression for the crosslinking reaction itself: It is noteworthy that the relative crosslinking rate in isoprene polymerization is only about one‐sixth that found for butadiene (K = 2 × 10−4 at 60°C.) apparently owing largely to a higher steric factor. Hence longer chains are possible for polyisoprene before network formation leads to gelation. In the Mutual Recipe, the rate per particle for isoprene polymerization is about three times as fast as for butadiene, although it is still short of the rate found in the ideal low temperature systems.