Living cationic polymerization of a vinyl ether with a triester pendant

Summary Cationic polymerization of CH₂=CH-O-CH₂CH₂C(COOC₂H₅)₃, a vinyl ether with three pendent esters, initiated by the HI/I₂ system in toluene at –40 °C afforded living polymers with a controlled molecular weight ( = 10³–10⁴) and a narrow molecular weight distribution ( = 1.1–1.2). The number-average molecular weight of the polymers was directly proportional to monomer conversion and the monomer-to-initiator (HI) feed ratio. The polymers obtained with BF₃O(C₂H₅)₂ had a fairly high molecular weight ( 10⁵, 5 × 10⁴) and a broad molecular weight distribution. The triester vinyl ether was similar in reactivity to alkyl counterparts and one order of magnitude more reactive than the corresponding mono- and diester vinyl ethers.     

Upper and lower critical solution temperatures in poly (ethylene glycol) solutions

Upper and lower critical solution temperatures have been determined for solutions of poly(ethylene glycol) in t-butyl acetate and water over the molecular weight range of M_η = 2.18 × 10³ to ～1020 × 10³. The phase diagram for solutions of poly(ethylene glycol) (M_η = 719 × 10³) in t-butyl acetate was expressed as the ‘hour glass’ type, while the phase diagram for solution of poly(ethylene glycol) (M_η = 2.18 × 10³ to ～2.29 × 10³) in water was expressed as the ‘closed loop’ type. The value of the pressure dependence of the lower critical solution temperature $\text{(}\text{d}\text{T}\text{d}\text{P}\text{)}{}_{\mathrm{c}}$ in the poly(ethylene glycol) (M_η = 1020 × 10³)/water system over the pressure range of 0 to ～50 atm was negligibly small and positive.     

Unique molecular aggregation of novel naphthalocyanine (near IR absorbing dye)

A series of organic-soluble naphthalocyanine derivatives (Y_mMNcX₄) have been synthesized. Their spectroscopic properties in organic solutions and in thin films were studied. MNcX₄ such as MNc(t-Bu)₄ (5a-5c) and MNc(On-Bu)₄ (5j) formed H-aggregates even in dilute solutions. MNc(CO₂R')₄ (5d-5i) had much stronger H-aggregation properties compared with those ofMNc(t-Bu)₄ and MNc(On-Bu)₄. Especially, MNc(CO₂R')₇ complexes (M=Cu, Pd and Ni) existed exclusively without monomers in the aggregated state even in highly dilute solutions. MNcX₄, which has strong H-aggregation properties, showed merely H- aggregate absorption maxima in thin films. In contrast, Y₂MNcX₄ (4), which has sterically hindered Y groups, showed monomerically pure characteristics in solution. However, thin films of Y₂MNcX₄ have a J-type molecular arrangement, exhibiting a red shift of Q-band absorption. The monomeric properties of Y₂MNcX₄ in solutions and J-type molecular arrangement in thin films arise from steric hindrance of two Y groups, such as R₃SiO-in Y₂MNcX₄, which prevents strong H-aggregation of naphthalocyanine.     

Living cationic polymerization of isobutyl vinyl ether by the diphenyl phosphate/zinc iodide initiating system

Summary The first example of the living cationic polymerization of isobutyl vinyl ether via the phosphate counteranion has been achieved in toluene below 0°C with a new initiating system that consists of diphenyl phosphate and zinc iodide, (C₆H₅0)₂P(0)0H/ZnI₂. The number-average molecular weight of the polymers increased in direct proportion to monomer conversion, and was in excellent agreement with the calculated value assuming that one polymer chain forms per unit diphenyl phosphate. On addition of a fresh feed of monomer at the end of the polymerization, the added feed was smoothly polymerized at nearly the same rate as in the first stage, and the polymer molecular weight further increased in direct proportion to monomer conversion. Throughout the reaction, the molecular weight distribution of the polymers stayed very narrow (¯M/¯M_n 1.1). At room temperature (+25 °C), however, the molecular weight distribution of the polymers slightly broadened (¯M_w/¯M_n 1.2) at high conversions where the polymer molecular weight became smaller than the calculated value. Evidently, the (C₆H₅0)₂-P(0)0H/ZnI₂ system indeed generates a propagating species of a long life-time at room temperature, but the perfectly living polymerization by this system operates below 0°C.Living cationic polymerization of vinyl ethers by electrophile     

Plasma developable photoresist containing electronic excitation energy quenching system

A dry developable negative working resist composition comprised of poly(methyl isopropenyl ketone) (PMIPK) and 4-methyl-2,6-di(4′-azido-benzylidene) cyclohexanone-1 was examined. The main photochemical product formed in the resist pattern was found to be a secondary amine which crosslinks PMIPK. Post-annealing forms a hydrogen-bonded product which shows a powerful electronic excitation energy quenching effect. The quencher is more powerful than the aromatic compound arising from the azide by post-annealing only. The residual resist thickness of the negative pattern is about 80 percent of the initial thickness of the coating in spite of all the azide compound remaining in the resist coating. The obtained dry developed resist pattern has a high dry etch resistance. Etchings of Si and SiO₂ were performed by plasma and reactive ion etching, respectively.     

Adsorption and desorption properties of cationic polyethylene film gels to organic anions and their regeneration

An investigation was undertaken on the adsorption and desorption properties of 2‐(dimethylamino)ethyl methacrylate grafted polyethylene (PE‐g‐PDMAEMA) films to anionic dye anions with one to three sulfonic groups in response to pH and temperature changes. The amounts of dye anions adsorbed on the PE‐g‐PDMAEMA films passed through the maximum values at about pH 3 because of an increase in the protonation of dimethylamino groups caused by a decrease in the pH value. The amounts of adsorbed dye anions decreased below pH 3 because the ionic strength increased with the addition of HCl to adjust the initial pH values of the aqueous dye solutions. The amounts of adsorbed dye anions decreased with an increase in the number of sulfonic groups in the dye molecules at the same pH value because electrostatic repulsion was generated between free sulfonic groups of the dye anions adsorbed onto the PE‐g‐PDMAEMA films and free dye anions in the medium. A large number of dye anions adsorbed were desorbed from the PE‐g‐PDMAEMA film with initial pH values above 11.0. The cyclic processes of adsorption at pH 3.0 and desorption at pH 11.0 were repeated without considerable fatigue. The PE‐g‐PDMAEMA films showed practically regenerative adsorption and desorption behavior in response to the pH changes. In addition, when the dye‐anion‐adsorbed PE‐g‐PDMAEMA films were alternately immersed in water at two different temperatures, dye anions were desorbed in water at higher temperatures without any chemical agents because of the deprotonation of dimethylamino groups and thermosensitive contraction of grafted PDMAEMA chains. These results indicate that PE‐g‐PDMAEMA films can be applied as regenerative ion‐exchange membranes for adsorption and desorption processes of anionic compounds in response to the pH and temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 381–391, 2006     

Note: Accuracy of velocity correction for impact of a laser-accelerated miniature flyer with lithium fluoride shock-compressed along the [100] axis

We performed miniature flyer impact experiments to investigate the relationship between the apparent (u(a)) and actual (u(A)) particle velocities measured by a velocity interferometer in single-crystal lithium fluoride (LiF) that was shock-compressed along the [100] axis. The miniature flyer was accelerated to velocities in the range 652.5-1937.6 m/s by a tabletop pulsed laser. An empirical relationship of u(a) = (1.2749 ± 0.0102)u(A) was obtained. The obtained relationship agreed well with the results of a previous study within the experimental errors and its uncertainty was less than ±1%. This result indicates that the present experimental technique is effective for measuring the relationship between u(a) and u(A) of shocked transparent materials with a comparable accuracy to conventional methods.     

Auto-tuning strategy for evolutionary algorithms: balancing between exploration and exploitation

Genetic Algorithms (GAs) and other Evolutionary Algorithms (EAs), as powerful and broadly applicable stochastic search and optimization techniques have been successfully applied in the area of management science, operations research and industrial engineering. In the past few years, researchers gave lots of great idea for improvement of evolutionary algorithms, which include population initialization, individual selection, evolution, parameter setting, hybrid approach with conventional heuristics etc. However, though lots of different versions of evolutionary computations have been created, all of them have turned most of its attention to the development of search abilities of approaches. In this paper, for improving the search ability, we focus on how to take a balance between exploration and exploitation of the search space. It is also very difficult to solve problem, because the balance between exploration and exploitation is depending on the characteristic of different problems. The balance also should be changed dynamically depend on the status of evolution process. Purpose of this paper is the design of an effective approach which it can correspond to most optimization problems. In this paper, we propose an auto-tuning strategy by using fuzzy logic control. The main idea is adaptively regulation for taking the balance among the stochastic search and local search probabilities based on the change of the average fitness of parents and offspring which is occurred at each generation. In addition, numerical analyses of different type optimization problems show that the proposed approach has higher search capability that improve quality of solution and enhanced rate of convergence.     

Randomized constraint solvers: a comparative study

The complexity of constraints is a major obstacle for constraint-based software verification. Automatic constraint solvers are fundamentally incomplete: input constraints often build on some undecidable theory or some theory the solver does not support. This paper proposes and evaluates several randomized solvers to address this issue. We compared the effectiveness of a symbolic solver (CVC3), a random solver, two heuristic search solvers, and seven hybrid solvers (i.e. mix of random, symbolic, and heuristic solvers). We evaluated the solvers on a benchmark generated with a concolic execution of 9 subjects. The performance of each solver was measured by its precision, which is the fraction of constraints that the solver can find solution out of the total number of constraints that some solver can find solution. As expected, symbolic solving subsumes the other approaches for the 4 subjects that only generate decidable constraints. For the remaining 5 subjects, which contain undecidable constraints, the hybrid solvers achieved the highest precision (fraction of constraints that a solver can find a solution out of the total number of satisfiable constraints). We also observed that the solvers were complementary, which suggests that one should alternate their use in iterations of a concolic execution driver.