The kinetics of photoinitiated dead-end polymerization

The kinetic expressions for a dead-end polymerization initiated by the photolysis of a sensitizer are derived. The phenomenon of dead ending amplifies the inherent differences between the kinetics of photoinitiated and thermally initiated polymerizations. The analysis clearly shows that photoinitiation has distinct advantages over thermal initiation for improving yields in a polymerization which exhibits dead ending.     

Primary radical termination rate constant at high conversion in radical polymerization

A primary radical termination rate constant given by: k_ti = A_1iD_i, where A_1i is a constant and D_i is the diffusion constant of the primary radical, was examined on the basis of the variation of conversion. It was proved that this rate constant is correct at high conversion. A relationship between primary radical termination rate constant and conversion was derived. The effect of variation of conversion on the gel effect is discussed.     

Matrix polymerization on polycationic backbones: A continuous method for following the polymerization kinetics

A novel method of following polymerization kinetics in dilute solutions of ionic monomers is described. The method, based on conductimetry, is very well adapted to follow polymerization of ionic species in very dilute solutions, in micellar solutions, or at interfaces, i.e., in all systems in which the polymerization process involves a shift in ionic equilibria. The method is applied to matrix polymerization of p-styrene sulfonate–(2,2,2)4-ionene complex and yields results in full agreement with the standard spectroscopic method frequently used in such systems. The conversion curves obtained by conductimetry are satisfactorily explained by Manning's ion condensation model and are in agreement with a previously proposed mechanism, based on ion condensation theory, for matrix polymerization of ionized monomers on polyelectrolytes.     

Initiation and termination kinetics in fluid-phase free-radical polymerization up to high pressure

Rate coefficients of peroxyester decomposition in solution of n-heptane have been measured as a function of temperature and pressure. The data is used to determine initiator efficiencies for the ethene high-pressure polymerization. The efficiency strongly depends on the structure of the peroxyester. Free-radical termination rate coefficients of (meth)acrylate systems have been studied up to about 50% monomer conversion. The reaction is controlled by segmental diffusion in the early period and by reaction diffusion at later stages of the polymerization.     

Consecutive reactions in chemical kinetics: A method for the treatment of experimental data

A method is proposed for the treatment of data from a kinetic system of first order consecutive reactions by using an optimization procedure which converges to the correct solution of the two mathematically possible solutions and which does not need initial estimates of the parameters close to those to be determined.

---

, , , .

     

An accurate simplified data treatment for the initial adsorption kinetics in conditions of laminar convection in a slit: application to protein adsorption

We present the derivation of a simple approximation for the original expression of the adsorption rate [Langmuir 10 (1994) 3898] in conditions of laminar flow in a slit, to relate the measured initial kinetic constant k with the interfacial kinetic constant k_a and the transport-limited Lévêque constant k_Lev. The same method of derivation is applied here to get a simple approximation of the average kinetic constant 〈k〉 [Biomaterials 20 (1999) 1621]. For the local value, at distance x from the entrance of the slit, we propose k(x)/k_a=(u−1)(au−1)/(bu+1), where u=k(x)/k_Lev, a=0.452, b=−0.625, with a maximal error of 1% in comparison with the exact solution. For the average value over the length of the slit, we propose 〈k〉/k_a=(U−1)(AU−1)/(BU+1), where U=〈k〉/〈k_Lev〉, A=0.203, B=−0.273, with a maximal error of 0.03%. These approximations lead to an easy determination of the adsorption constant and diffusion coefficient D of the solute, as appropriate plots of experimental data provide k_a and D^2/3 as the intercepts of the curve with the ordinate and abscissa axes, respectively. It is pointed out that the linear approximation k⁻¹=k_a⁻¹+k_Lev⁻¹ would lead to the overestimation of both the diffusion coefficient and adsorption kinetic constant. As an example, the application to the analysis of experimental data for adsorption of α-chymotrypsin onto mica plates is provided.     

Applications of generating functions to polymerization kinetics. 3. General procedure illustrated for propagation with monomer conversion

The derivation of the product distribution function for the catalytic polymerization mechanism involving propagation with monomer conversion is used to illustrate the general procedure for obtaining the exact discrete distribution arising from a polymerization mechanism. The coupled differential equations arising from the polymerization mechanism are integrated using a generating function substitution. Due to the stepwise growth of polymer chains, this approach is generally applicable to problems in polymerization kinetics. The integrated rate law for the mechanism under consideration is similar to the Poisson distribution, except for a time dependent parameter which suppresses chain growth as time passes. This distribution function has a limiting value as time approaches infinity determined by the ratio of initial monomer and catalyst. The number-average and weight-average degrees of polymerization are also derived using an elementary technique involving generating functions. Catalytic polymerizations frequently give rise to chemical kinetics problems which are difficult to solve due to difficulty in integrating the coupled rate equations. The procedures outlined in this paper permit these problems to be overcome in many cases.     

一种用于肿瘤治疗的高光热转换效率和高稳定性的光热剂

基于香豆素荧光团设计合成了一种光热剂(ECEI),其光热转换效率可达 85.78%。此外,冷热循环的实验结果表明,ECEI 具有良好的光稳定性。即使在线粒体膜电位受损的情况下,ECEI 也能有效靶向线粒体,在激光照射下诱导癌细胞死亡。这使 ECEI能够最大程度地破坏线粒体,从而抑制肿瘤细胞的繁殖。对小鼠肿瘤照射 1次后,小鼠肿瘤在 10 d内逐渐消失,这表明ECEI具有良好的肿瘤抑制效果。     

一种用于肿瘤治疗的高光热转换效率和高稳定性的光热剂

基于香豆素荧光团设计合成了一种光热剂(ECEI),其光热转换效率可达 85.78%。此外,冷热循环的实验结果表明,ECEI 具有良好的光稳定性。即使在线粒体膜电位受损的情况下,ECEI 也能有效靶向线粒体,在激光照射下诱导癌细胞死亡。这使 ECEI能够最大程度地破坏线粒体,从而抑制肿瘤细胞的繁殖。对小鼠肿瘤照射 1次后,小鼠肿瘤在 10 d内逐渐消失,这表明ECEI具有良好的肿瘤抑制效果。     

马来酸酐聚合反应动力学的回归模拟

本文从函数变量相关内函规律出发，引用动力学物理概念，用数值逼近方法，对马来酸酐聚合反应的实验结果进行了模拟，得到了一符合实验规律的动力学方程。     

Relationship between the autoacceleration of polymerization rate and conversion in radical polymerization

By using a simple treatment for the kinetics of radical polymerization with primary radical termination, the ratio k_ty/k_tx of chain termination rate constant k_ty at conversion y to that k_tx at conversion x and the ratio k_tiy/k_tix of the primary radical termination rate constant k_tiy at conversion y to k_tix at conversion x were calculated for the polymerizations of methyl methacrylate and ethyl acrylate in the conversion range 0 to 0.4. k_ty/k_tx and k_tiy/k_tix were treated by using the following equations based on the variation of conversion: where g(T,y) is the average fractional free volume of radical chain end at conversion y and absolute temperature and β(T) is a function depending on T, and where g_i(T,y) is the average fractional free volume of primary radical at conversion y and T and β_i(T) is a function depending on T. The autoacceleration for the above monomers was successfully interpreted by the above treatment.     

Thermal polymerization of styrene: New data on the conversion dependence of the initiation rate

With the aid of new acceptors of free radicals usable at high temperatures (T > 100°C), the rate of initiation w _i has been measured experimentally for the thermal polymerization of styrene at 122.5°C in a wide range of conversions C = 0–80%. It has been shown that the value of w _i tends to increase in the course of polymerization transformation in agreement with the w _i = f(C) relationship calculated from the kinetic data on the thermal polymerization of styrene in the absence of counters of free radicals. Hypothetical reasons for this non-trivial tendency have been formulated. The experimental dependence w _i = f(C) has been measured for the first time and has been invoked to refine currently available mathematical models for the thermal polymerization of styrene that assume that w _i remains invariable in the course of polymerization transformation.     

Structure and polymerization kinetics of condensed phases

It is supposed that polymerization in the diffusion-controlled region occurs with chemically identical reaction centers in ordered and disordered parts kinetically nonequivalent, on account of differences in diffusion. Two types of medium are possible: in one the structure of the ordered regions favors the process, while defects act as kinetic traps in other defects more favorable to reaction than the ordered regions. The occurrence of several types of chemically identical but kinetically nonequivalent centers gives a qualitative explanation of various features of diffusion-controlled processes: stepwise loss of macroradicals, post-polymerization, anomalous temperature dependence of the molecular weight and polymerization rate near the phase transition point.     

Oxidative polymerization of aromatic hydrocarbons: A study of kinetics and mechanism

Aromatic hydrocarbons were homopolymerized by means of an oxidative polymerization reaction with the use of the catalyst system anhydrous aluminum chloride–cupric chloride. The kinetics of the benzene homopolymerization carried out under different experimental conditions was followed by the determination of the amounts of cuprous ion and polymeric product formed in the reaction. Cuprous ion was spectrophotometrically titrated in the form of its complex with 2,2′-biquinolyl (cuproine). The experimental results do not agree with cationic mechanism for this reaction previously proposed in the literature. Ethylbenzene was kinetically studied under the same experimental conditions. In view of the experimental evidences obtained in this work and on some literature data, a mechanism based on formation of cation-radicals is proposed for the oxidative polymerization reaction when carried out under the studied conditions.     

Inverse-microsuspension polymerization: Mechanism,kinetics and modelling

A mechanism has been developed for the inverse- microsuspension polymerization of acrylic water soluble monomers. This free-radical reaction scheme includes elementary reactions for polymerization in the aqueous and organic phases, nucleation in the monomer droplets and heterophase oligoradical precipitation. The latter being the dominant initiation process. A unimolecular termination reaction with interfacial species has also been elucidated and has been found to compete with and often dominate over the conventional biomolecular reaction. A kinetic model is developed which includes the influence of ionogenic monomers and polyelectrolytes and is able to predict the rate, molecular weight and composition data well for polymerizations of acrylamide and copolymerizations with quaternary ammonium cationic monomers. A categorization and systematic nomenclature for heterophase water-in-oil and oil-in-water polymerizations is also developed based on physical, chemical and colloidal criteria.     

A standard form for the presntation of field ionization kinetics data

It is suggested that division of the rates of molecular ion decomposition by the measured mass-resolved molecular ion current be adopted as the standard method of normalizing these data obtained through the field ionization kinetics technique.     

Modelling and simulation of styrene-acrylonitrile emulsion polymerization kinetics

The emulsion polymerization kinetics of the styrene-acrylonitrile system have been studied. A dynamic time-dependent model has been developed, which successfully describes the course of the conversion of styrene as compared with that of acrylonitrile. This model avoids the difficulties encountered by previous models when applied to high acrylonitrile-content polymers, and is able to predict the conversion process for both batch and continuous reactors. The model is aimed at the simulation and operation of composition-controlled semibatch and continuous processes.