Molecular Weight Development in Free‐Radical Polymerization with Polyfunctional Chain‐Transfer Agents, 1. Equal Reactivity Model

The analytic expression for the weight‐average molecular weight development in free‐radical polymerization that involves a polyfunctional chain‐transfer agent is proposed. Free‐radical polymerization is kinetically controlled; therefore, the probability of chain connection with a polyfunctional chain‐transfer agent as well as the primary chain‐length distribution changes during the course of polymerization. We consider the primary chains formed at different times as different types of chains, and the heterochain branching model is used to obtain the weight‐average chain length at a given conversion level in a matrix formula, described as P_w = W { D _w + ( I + T ) SP ( I – TSP )^–1 D_f }. Because the primary chains are formed consecutively, the number of chain types N is extrapolated to infinity, but such extrapolation can be conducted with the calculated values for only three different N values. The criterion for the onset of gelation is simply described as a point at which the largest eigenvalue of the product of matrixes, TSP reaches unity, i. e., det  ( I – TSP ) = 0. The present model can readily be extended for the star‐shaped polyfunctional initiators, and the relationships between the model parameters and kinetic rate expression for such reaction systems are also shown.     

Statistical branching of heterochains

A general theory for the statistical branching of heterochains is proposed on the basis of the random sampling technique. Consider a polymer mixture that consists of N types of chains whose weight fractions are w_i (i = 1, 2, …, N), and number- and weight-average chain lengths are P̄_np,i and P̄_wp,i, respectively. Suppose the transition probability that a branch point on a chain of type i is connected to a chain end of a type j chain is given by p_ij. When the branching density of chains of type i is ρ_i, the weight-average chain length is given by $\bar P_w = W\sum\nolimits_{m = 0}^\infty T ^m \sum\nolimits_{n = 0}^\infty {SU} ^n 1$, where S is the diagonal matrix whose elements are $S_{ii} = \bar P_{wp,i}$, 1 is the column vector whose elements are all unity, U is the transition matrix whose elements are given by $u_{ij} = \rho _i p_{ij} P_{np,j} ,T$ is another transition matrix whose elements are given by t_ij = (w_j/w_i)U_ji, and W is the row vector whose elements are w_i. Simpler expressions of P̄_w are presented for binary systems. In addition to the multicomponent systems, the present equation could also be used such as for free-radical polymerization with long-chain branching, by considering primary chains formed at different times as different types of polymer chains. For the prediction of the full molecular weight distribution, a Monte Carlo simulation method is used to illustrate the resulting distribution profiles.     

A simulation model for long-chain branching in vinyl acetate polymerization: 1. Batch polymerization

A new simulation model for the kinetics of long-chain branching formed via chain transfer to polymer and terminal double-bond polymerization is proposed. This model is based on the branching density distribution of the primary polymer molecules. The theory of branching density distribution is that each primary polymer molecule experiences a different history of branching and provides information on how each primary polymer molecule is connected with other chains that are formed at different conversions, therefore making possible a detailed analysis on the kinetics of the branched structure formation. This model is solved by applying the Monte Carlo method and a computer-generated simulated algorithm is proposed. The present model is applied to a batch polymerization of vinyl acetate, and various interesting structural changes occurring during polymerization (i.e., molecular weight distribution, distribution of branch points, and branching density of the largest polymer molecule) are calculated. The present method gives a direct solution for the Bethe lattice formed under nonequilibrium conditions; therefore, it can be used to examine earlier theories of the branched structure formation. It was found that the method of moments that has been applied successfully to predict various average properties would be considered a good approximation at least for the calculation of not greater than the second-order moment in a batch polymerization. © 1994 John Wiley & Sons, Inc.     

Simultaneous determination of YM-64227, a phosphodiesterase type 4 inhibitor, and its five metabolites in dog plasma by high-performance liquid chromatography with fluorescence detection

We developed and validated a reversed-phase high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of YM-64227 [4-cyclohexyl-1-ethyl-7-methylpyrido(2,3-d)pyrimidin-2-(1H)-one], a novel and selective phosphodiesterase type 4 inhibitor, and its fi ve hydroxylated metabolites in dog plasma. The plasma samples were extracted with tert-butyl methyl ether under alkali conditions. The analytes were well separated on a phenyl ethyl column (5 microm, 250 x 4.6 mm i.d.), opreating at 40 degrees C and using an acetonitrile-acetic acid gradient at a fl ow rate of 1.0 mL/min. The fluorescence signal was monitored at an excitation and emission wavelength of 330 and 400 nm, respectively. No interfering peak was observed at the retention time of YM-64227, its metabolites or the internal standard. The validated quantitation range of the method was 0.4-200 ng/mL for all analytes using 0.5 mL of the plasma sample. The recovery of analytes in the extraction process was more than 65.5%. The intra- and inter-assay precision was less than 5.1 and 12.6%, respectively, and the intra- and inter-assay accuracy ranged from -8.1 to 11.8% and -8.0 to 9.9%, respectively. Using this assay, the plasma concentration of YM-64227 and metabolites can be determined after the oral administration of YM-64227 to beagle dogs.     

Threo-selective aldol condensations of lithium enolates in the presence of trialkylboranes

The reaction of preformed lithium enolates in the presence of trialkylboranes, such as Et₂B and n-Bu₃B, with aldehydes leads to product mixtures rich in the more stable threo aldol.     

Periodate oxidation analysis of carbohydrates : Part I. Spectrophotometr1c determination of glyoxal in dialdehyde fragments formed from glycosides with 2,4-dinitrophenylhydrazine

A simple procedure for the determination of glyoxal in dialdehyde fragments, formed from glycosides by periodate oxidation, is proposed. By heating sample solutions prepared by dilution of reaction mixtures for periodate oxidation, with an aqueous dimethylsulfoxide solution of 2,4-dinitrophenylhydrazine hydrochloride. followed by addition of an aqueous ethanolic solution of potassium hydroxide, intense color with an absorption maximum at 576 nm developed. The spectrophotoinetric method based on this color reaction makes it possible to determine selectively 1·10^?2–2·10^?1 μmole amounts of conjugated glyoxal without a prior liberation process. Data for glyoxal content obtained by this procedure are discussed in relation to overoxidation.     

Synthesis and crystal structure of an open capsule-type octanuclear heterometallic sulfide cluster with a linked incomplete double cubane framework without an intramolecular inversion center

An open capsule-type octanuclear heterometallic sulfide cluster without an intramolecular inversion center [Ru(eta(6)-C(6)Me(6)){P(OMe)(3)}{MoO(mu(3)-S)(3)}(CuI)(2)](2) (5) has been synthesized for the first time by stepwise connection of three mononuclear building blocks, i.e., (i) [RuCl(2)(eta(6)-C(6)Me(6)){P(OMe)(3)}] (1a) as an octahedral terminal building block to control the direction of cluster expansion, (ii) [MoOS(3)](2)(-) as a tetrahedral polydentate building block owing to the strong coordination ability of the S atoms, and (iii) a CuI building block to form a trigonal planar (mu-S)(2)CuI unit or to form a linkage unit of two incomplete cubane-type octanuclear frameworks. The stepwise connection was made in the following order: [RuCl(2)(eta(6)-C(6)Me(6)){P(OMe)(3)}] (1a, mononuclear) --> [Ru(eta(6)-C(6)Me(6)){P(OMe)(3)}{MoOS(mu(2)-S)(2)}] (2a, dinuclear) --> [Ru(eta(6)-C(6)Me(6)){P(OMe)(3)}{MoO(mu(2)-S)(2)(mu(3)-S)}CuI] (3a, butterfly-type trinuclear) --> [Ru(eta(6)-C(6)Me(6)){P(OMe)(3)}{MoO(mu(3)-S)(3)}(CuI)(2)](2) (5). When P(OMe)(3) was replaced by P(OEt)(3), which is more bulky than P(OMe)(3), in the starting ruthenium building block [RuCl(2)(eta(6)-C(6)Me(6)){P(OEt)(3)}] (1b, mononuclear), only the tetranuclear incomplete single cubane cluster [Ru(eta(6)-C(6)Me(6)){P(OEt)(3)}{MoO(mu(3)-S)(3)}(CuI)(2)] (6) was generated, owing to the steric effect of P(OEt)(3).     

pH-dependent H2-activation cycle coupled to reduction of nitrate ion by CpIr complexes.

This paper reports a pH-dependent H2-activation [H2 (pH 1-4) --> H+ + H- (pH -1) --> 2H+ + 2e-] promoted by CpIr complexes [Cp = eta5-C5(CH3)5]. In a pH range of about 1-4, an aqueous HNO3 solution of [CpIr(III)(H2O)3]2+ (1) reacts with 3 equiv of H2 to yield a solution of [(CpIr(III))2(mu-H)3]+ (2) as a result of heterolytic H2-activation [2[1] + 3H2 (pH 1-4) --> [2] + 3H+ + 6H2O]. The hydrido ligands of 2 display protonic behavior and undergo H/D exchange with D+: [M-(H)3-M]+ + 3D+ <==>[M-(D)3-M]+ + 3H+ (where M = CpIr). Complex 2 is insoluble in a pH range of about -0.2 (1.6 M HNO3/H2O) to -0.8 (6.3 M HNO3/H2O). At pH -1 (10 M HNO3/H2O), a powder of 2 drastically reacts with HNO3 to give a solution of [CpIr(III)(NO3)2] (3) with evolution of H2, NO, and NO2 gases. D-labeling experiments show that the evolved H2 is derived from the hydrido ligands of 2. These results suggest that oxidation of the hydrido ligands of 2 [[2] + 4NO3- (pH -1) --> 2[3] + H2 + H+ + 4e-] couples to reduction of NO3- (NO3- --> NO2- --> NO). To complete the reaction cycle, complex 3 is transformed into 1 by increasing the pH of the solution from -1 to 1. Therefore, we are able to repeat the reaction cycle using 1, H2, and a pH gradient between 1 and -1. A conceivable mechanism for the H2-activation cycle with reduction of NO3- is proposed.