Simple technique for the simultaneous determination of solvent diffusion coefficient in polymer by Quantum Resistive Sensors and FT‐IR spectroscopy

A simple, quick and novel method for the determination of diffusion properties through polymer films, based on Quantum Resistive Sensors made of Conductive Polymer nanoComposites is presented. The integral time lag method is employed for the calculation of diffusion coefficient, and the results are compared simultaneously with that of Fourier transform infrared spectroscopy and sorption method. Two model polymers, a semi‐crystalline poly(lactic acid) and an amorphous poly(isobutylene‐co‐isoprene), are used to validate the study. A good correlation is established between the diffusion coefficient values derived from all techniques demonstrating the interest of such reliable, simple and cheap nanosensors for the quick determination (several minutes) of diffusion properties in polymer films. Our first results suggest that this technique is meaningful for the determination of barrier properties in nanocomposite membranes filled with platelets of graphene or clay. Copyright © 2013 John Wiley & Sons, Ltd.     

Poly(acrylate‐b‐styrene‐b‐isobutylene‐b‐styrene‐b‐acrylate) Block Copolymers via Carbocationic and Atom Transfer Radical Polymerizations

A series of polyacrylate‐polystyrene‐polyisobutylene‐polystyrene‐polyacrylate (X‐PS‐PIB‐PS‐X) pentablock terpolymers (X=poly(methyl acrylate) (PMA), poly(butyl acrylate) (PBA), or poly(methyl methacrylate) (PMMA)) was prepared from poly (styrene‐b‐isobutylene‐b‐styrene) (PS‐PIB‐PS) block copolymers (BCPs) using either a Cu(I)Cl/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. The PS‐PIB‐PS BCPs were prepared by quasiliving carbocationic polymerization of isobutylene using a difunctional initiator, followed by the sequential addition of styrene, and were used as macroinitiators for the atom transfer radical polymerization (ATRP) of methyl acrylate (MA), n‐butyl acrylate (BA), or methyl methacrylate (MMA). The ATRP of MA and BA proceeded in a controlled fashion using either a Cu(I)Cl/PMDETA or Cu(I)Cl/Me₆TREN catalyst system, as evidenced by a linear increase in molecular weight with conversion and low PDIs. The polymerization of MMA was less controlled. ¹H‐NMR spectroscopy was used to elucidate pentablock copolymer structure and composition. The thermal stabilities of the pentablock copolymers were slightly less than the PS‐PIB‐PS macroinitiators due to the presence of polyacrylate or polymethacrylate outer block segments. DSC analysis of the pentablock copolymers showed a plurality of glass transition temperatures, indicating a phase separated material.     

The effect of the counterion composition on the chain restriction in the cationic polymerization of isobutylene

The effects of the nature of halogens in the initiatingtert-butyl halide-aluminum-containing Lewis acid system on the number average molecular weightM _n and the structure of end groups of polyisobutylene macromolecules obtained in the cationic polymerization of isobutylene in hexane at -78 °C were studied. An increase inM _n is observed in the transition from chlorine to bromine and iodine, accompanied by a decrease in the fraction of end C=C groups and an increase in the relative content of C-Hal groups (Hal = Cl, Br, and I). When atoms of different halogens are present in the counterion, more bulky atoms preferentially participate in the formation of the end groups. The results are interpreted within the framework of the principle of hard and soft acids and bases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1184–1187, May, 1996.     

手性铜催化剂的制备及在环丙烷羧酯酯不对称合成中的应用

３类手性配体ｄ－１０－樟脑磺酸及其衍生物，α－（－）－羟蒎酮及其衍生物，又恶唑啉６衍生物分别与铜（Ⅱ）形成手性铜配合物，催化重氮乙酸酯与１，１－二苯乙烯或异丁烯的环丙烷化加成反应，得到光学活性环丙羧酸酯，不对称诱导最高可达９５％ｅ．ｅ．。     

Preparation and properties of isobutylene–isoprene rubber–clay nanocomposites

Isobutylene isoprene rubber (IIR)‐clay nanocomposites have been prepared successfully by melt intercalation with maleic anhydride‐grafted IIR (Ma‐g‐IIR) and organophilic clay. In IIR‐clay nanocomposites, the silicate layers of the clay were exfoliated and dispersed into the monolayer. The nanocomposites exhibited greater gas barrier properties compared with those of Ma‐g‐IIR. When 15 phr clay was added, gas barrier properties were 2.5 times greater than those of Ma‐g‐IIR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1182–1188, 2006     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids

The ionic complex of mesitoyl bromide with aluminum bromide in a 1∶1 composition (Mst-1) does not initiate the isobutylene polymerization inn-hexane or methylene dichloride at −78 °C. The corresponding ionic complex of the 1∶2 composition (Mst-2) acts as a cationogenic initiator of the polymerization. The addition of excess Lewis acid or introduction of organic electron acceptors increases the initiating activity of the Mst-1 complex and activates acyl complexes of the 1∶2 composition including Mst-2. The results are discussed in terms of the effect of specific solvation on the nucleophilicity of counteranions, which makes the addition of the monomer to the carbocation possible. For Part 9, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 52–56, January, 1998.     

Kinetics and mechanisms in carbocationic polymerization: The quest for true rate constants

This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (k_p) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, k_p = 1.35 × 10⁴ L mol^?1 s^?1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded k_p = 1.01 × 10⁷ L mol^?1 s^?1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl₄ from various laboratories yielded of ΔH ～?25 and ?34.5 kJ/mol for high and low TMPCl/TiCl₄ ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ～ ?40 kJ/mol, whereas H₂O/TiCl₄ in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = ?12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005     

Investigation of the effect of epoxide structure on the initiation efficiency in isobutylene polymerizations initiated by epoxide/TiCl4 systems

The effect of the chemical structure of styrene-based epoxides, namely, styrene epoxide (SE), α-methylstyrene epoxide (MSE), p-methylstyrene epoxide (pM-SE) and α-methyl-p-methylstyrene epoxide (pM-MSE), in conjunction with TiCl₄, on the initiation efficiency (I_eff) in the carbocationic polymerization of isobutylene (IB) was investigated. SE yielded living polymerization, but the initiation efficiency was low when compared to MSE (I_eff=8% and 35%, respectively). pM-SE led to non-living IB polymerization, while pM-MSE revealed linear M_n-conversion plot and narrow MWD with a non-linear first order rate plot. Among the epoxides investigated, MSE was the best initiator to scale up the one-step synthesis of polyisobutylenes (PIBs) carrying one primary hydroxyl head group and one tertiary chloride end group. The hydroxyl functionality of these PIBs determined by ¹H-NMR was F_n=1.09±0.16 from 24 experiments.