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ABSTRACT In this work, four polymerization mechanisms with flow are proposed where sustained oscillation can be present: (1) Polyaddition initiated by radicals produced by initiator decomposition, which is catalyzed by the polymer, first-order termination, a polymer disappears by a reaction with a third substance and by leaving the system in the exit flow. (2) Polycondensation where the polymer has catalytic activity upon H to produce a monomer, first-order termination and a monomer disappears by a reaction with a third substance, and there is exit flow for all the species. (3) Polycondensation with catalytic activity of the polymer upon A to produce a monomer, first-order termination, conformational transitions of the polymers, one of the polymer conformations disappears by a reaction with a monomer and exit flow for all the species. (4) Polycondensation combined with polyaddition where the polycondensation polymer product has catalytic activity on the monomer, first-order termination and exit flow of all the species. [ABSTRACT FROM AUTHOR]

Copolymeric nanohydrogels based on N-isopropylacrylamide, N-(pyridin-4-ylmethyl)acrylamide and tert-butyl-2-acrylamidoethyl carbamate, synthesized by microemulsion polymerization, were characterized using Fourier transform infrared spectroscopy and their size (38-52 nm) determined using quasielastic light scattering. Folic acid was covalently attached to the nanohydrogels (1.40 ± 0.07 mmol g−1). Tamoxifen (6.7 ± 0.2-7.3 ± 1.2 µg TMX mg−1 nanohydrogel), a hydrophobic anticancer drug, and 5-fluorouracil (7.7 ± 0.7-10.14 ± 1.75 µg 5-FU mg−1 nanohydrogel), a hydrophilic anticancer drug, were loaded into the nanohydrogels. Maximum in vitro TMX release (77-84% of loaded drug) depended on interactions of the drug with hydrophobic clusters of the nanogels; however, no nanogel/5-FU interactions allowed total release of the loaded drug. The cytotoxicity of unloaded nanohydrogels in MCF7, T47D and HeLa cells was low. Cell uptake of nanogels without bound folic acid took place in the three cell types by unspecific internalization in a time-dependent process. Cell uptake increased for folic acid-targeted nanohydrogels in T47D and HeLa cells, which have folate receptors. The administration of 10 and 30 µmol L−1 TMX by TMX-loaded nanogels and 10 µmol L−1 5-FU by 5-FU-loaded nanogels was effective on the three cell types, and the best results were obtained for folic acid-targeted nanohydrogels. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: For two variable chemical oscillators, a simple strategy is to combine autocatalysis with a term including a binomial Michaelian denominator (constant+concentration). This strategy is applied in this paper to the context of polymerization reactions. In order to achieve autocatalysis a kinetic scheme of the form is applied, where the dimeric form D is included. The Michaelian term can be obtained in different ways, for example: (i) a third compound Z flows through the system and eliminates the monomer, (ii) compound Z can be radical initiators, and (iii) compound Z, which eliminates monomer, can be a special conformation (adsorbent) of the polymer. Three mechanisms are developed using these Michaelian terms. After decreasing the number of variables to two, by assuming a non-significant variation of the others, and normalizing the kinetic equations with respect to a certain steady state, phase plane techniques are applied to prove the existence of a limit cycle in the three models. Both monomer concentration and propagator concentration in the three models (cases 2.1 and 2.2) or the concentration of the adsorbent polymers are taken as oscillating variables. [Copyright &y& Elsevier]

Abstract: A simple polymerization scheme has been studied introducing small modifications leading to a stable focus type steady state (with damped oscillations) or unstable focus type (which combined with a no return enclosure for phase trajectories will show cycle limit sustained oscillations). Two variables have been employed in this analysis: X∝ monomer, . Limit cycle oscillations requires the addition of autocatalysis with respect to the monomer, J+X→2X, and so does an “enzymatic” block assuming that . The combination of both collateral additions makes the steady state an unstable focus and allows a simple Poincaré–Bendixson proof for the existence of the limit cycle. [ABSTRACT FROM AUTHOR]

The article discusses a study which examined the semicontinuous inverse microemulsion copolymerization of [2-(acryloyloxy)ethyl]trimethylammonium chloride/acrylamide in an isoparaffin solvent. Particular focus is given to the effect of the total comonomer concentration (TCC), emulsifier concentration and isopropyl alcohol concentration on the copolymers' molar mass and absolute viscosity. Results showed a rise in molecular weight and viscosity with TCC and hydrophilic-lipophilic balance (HLB).

The article focuses on a study which examined the influence of copolymerization variables on the flocculation performance (FP) of highly concentrated cationic flocculants based on 80/20 weight percent [2-(acryloyloxy)ethyl]trimethylammoniumchloride/acrylamide in an inverse microemulsion. Using the measurement of the capillarity suction time (CST), the FP of the cationic polymers was analyzed. The action mechanisms of the generally accepted flocculation theory were noted.

A simple radical polymerization is proposed in this paper, with step-by-step chain growth (Ri + M → Ri+1), and termination by transfer to a third body (Ri + S → polymer) such as the solvent. It is assumed that, for a certain critical degree of polymerization n, the propagator Rn reacts with substrate H to produce a deactivator (V) of the first propagator (H + Rn → Rn + V; V + R1 → P1) R1. Assuming that monomer, M, and precursor concentrations are constant, and assuming that the deactivator reaches fast a steady state, the resulting kinetic equations are formally linear, but they admit, perturbations rj(t) of the steady-state concentrations of the propagators R1, R2, ..., Rn, which are periodic functions of time. Even more, they can be purely sinusoidal functions (which have been called “harmonic,” in analogy to the solutions of the well-known classical harmonic oscillator) with phase shift between perturbations rj(t) = Rj- (Rj)0 and rj+1(t) = Rj+1 - (Rj+1)0. Based on these periodic solutions and aiming to a model as simple as possible, a theoretical analysis is made, resulting in that the minimum value for n would be n = 3. Of course, these harmonic oscillations “driven by trimer” are equally found in the group of all the remaining propagators with polymerization degree higher than 3 (variable Y = ∑∞j=4 Rj). © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 507–511, 2009 [ABSTRACT FROM AUTHOR]

In this paper, the possibility for autocatalysis in polymerization reactions is explored by introducing part of a polymerization mechanism in a model known as Brusselator. It is assumed that monomer concentration is practically constant. Four possibilities are examined: (1) a first radical propagator X, which has an isomer of position of the free electron, Y, dimerizes reversibly and this dimer catalyzes the isomerization of Y to X; (2) the radical propagator X is a polymer with a critical degree of polymerization and has an isomer of position of the free electron Y. This critical radical propagator catalyzes the conversion of Y to X; (3) any radical propagator has an isomer of position of the free electron, Y, and any polymer obtained by recombination of the radicals can catalyze the conversion of Y into its corresponding isomer X; and (4) any radical propagator with a critical degree of polymerization can catalyze the conversion of Y into its corresponding isomer. Isomorphism equations are obtained in all mechanisms, which implies the possibility of limit cycle oscillations (Brusselator model). © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 617–623, 2008 [ABSTRACT FROM AUTHOR]

The influence of HLB (hydrophilic-lipophilic balance) and surfactant blend concentration (SBC) on flocculating performance of latex particles of acrylamide and [2-(acryloyloxy)ethyl]trimethylammonium chloride copolymers with a cationic charge density of 40%, obtained by inverse microemulsion copolymerization by using a surfactant blend of Arlacel 83 and Softanol 90 as emulsifier and Rolling M-245, a mixture of n-decane and n-tetradecane in about 40/60 weight ratio, as oil phase, has been studied for a total comonomer concentration of 32.5% (w/w). Comonomer inverse microemulsion copolymerizations were carried out in the semicontinuous mode by adding continuously an aqueous solution of sodium metabisulfite (SMB) as initiator into stirred inverse comonomer microemulsions. From 7.75 to 8.26, HLB has a strong influence on average molar mass (Mw) and flocculating performance (FP), the higher the HLB the higher the FP. A small decrease in SBC causes a dramatic increase in Mw and a decrease in FP although the influence on copolymer viscosity is small. Results are explained in terms of copolymer structuring degree and collapsed state of copolymer chains inside latex particles as well as in terms of the observed composition drift with conversion. [ABSTRACT FROM AUTHOR]

The influence of initiator concentration, specific flow rate of initiator addition (Qsp), initial copolymerization temperature (Ti), aqueous phase pH and total comonomer concentration (TCC) on flocculating performance of latex particles of acrylamide and [2- (acryloyloxy)ethyl]trimethylammonium chloride copolymers with a cationic charge density of 40%, obtained by inverse microemulsion copolymerization by using a surfactant blend of Arlacel 83 and Softanol 90 as emulsifier and Rolling M-245, a mixture of n-decane and n-tetradecane in about 40/60 weight ratio, as oil phase, has been studied for high TCC, ranging from 28 to 34.5% (w/w). Comonomer inverse microemulsion copolymerizations were carried out in the semicontinuous mode by adding continuously an aqueous solution of sodium metabisulfite as initiator into stirred inverse comonomer microemulsions. Initiator concentration has a strong influence on viscosity, viscometnc structunng degree (VSI) and average weight molar mass (Mw) of copolymers in the range from 5 to 25 g/L. Both viscosity and Mw decrease with increasing initiator concentration. Best flocculating performance is obtained from 10 to 20 g/L, values at which VSI shows a minimum. Under the experimental conditions used, Qsp (153 to 310 mL/h/kg of comonomer), T (25 to 35°C) and aqueous phase pH (2.5 to 4.5) have almost no influence on both viscosity and VSI and, hence, on flocculating performance. On the contrary, TCC has a slight influence on copolymer viscosity but a strong one on VSI which increases dramatically with TCC, being the worst flocculating performance obtained at the highest TCC studied (34.5% (w/w)). Flocculating performance results are explained in terms of copolymer structuring degree and collapsed state of copolymer chains inside latex particles as well as in terms of the composition drift with conversion. [ABSTRACT FROM AUTHOR]

Abstract: The polymerization of n-hexyl methacrylate (n-HMA) in three-component microemulsion stabilized with dodecyltrimethylammonium bromide (DTAB) is reported as a function of monomer and initiator concentrations and temperature. The obtained latices were bluish, transparent, and translucent. Particle sizes and molar masses were on the order of 20 nm and , respectively. In all cases, high reaction rates and final conversions of 98% were obtained. Polymerization temperature has a strong effect on reaction rate and conversion. [Copyright &y& Elsevier]