Preparation and Polymerization Behavior of 2,4-Dicyanostyrene and 2,4,6-Tricyanostyrene

distribution will be considered. In conclusion, we have demonstrated the pronounced effect of laser repetition rate on the molecular weight distribution of photopolymerized methyl methacrylate. The narrow peaks found in the GPC chromatogram of poly(methy1 methacrylate) generated by firing the laser at a repetition rate of 40 Hz (25 ms between successive pulses) have been initially described by a simple kinetic model based upon a series of Poisson distribution functions. Complete details of the computer simulation of the molecular weight distributions as a function of pulsing frequency as well as several refinements to our current approach, will be published in a full paper. This paper serves to provide a basis for describing the crucial effect of laser parameters on the polymerization of monofunctional monomers. Extension of this work to encompass multifunctional monomers is in progress. Acknowledgment. This research is supported by National Science Foundation Grant DMR 85-14424 (Polymers Program). Acknowledgement is also made to NSF for assistance in purchasing the laser system utilized in the course of this investigation (Grant CHE-8411829-Chemical Instrumentation Program). References and Notes Registry No. PMMA, 9011-14-7. (1) Decker, C. ABSTRACT: 2,4-Dicyanostyrene (DCS) was successfully prepared in 18% yield via a series of six reactions and 2,4,6-tricyanostyrene (TCS) was barely in 0.15% yield via five reaction steps. It was found that DCS and TCS are polymerizable with radical and anionic initiators. DCS and TCS are copolymerizable in a random and an alternating fashion, respectively, with styrene (St) in the presence of 2,2'-azobis(isobutyronitrile) (AIBN) in acetonitrile to afford the monomer reactivity ratios rl(DCS) = 1.85 f 0.03 and rz(St) = 0.08 f 0.03 for the DCS-St system at 60 O C and r,(TCS) = 0.02 i 0.02 and rz(St) = 0.04 i 0.01 for the TCS-St system a t 60 "C. By using these values, the Alfrey-Price's Q and e values were determined to be Q = 4.10 and e = +0.58 for DCS and Q = 2.83 and e = +1.86 for TCS. When DCS or TCS was mixed with p-(dimethy1amino)styrene (DMASt), the former system was colored pale yellow and did not undergo further reaction, while the latter one was colored red and underwent spontaneous reaction to give polymeric product containing homopolymers of TCS and DMASt, suggesting that anionic polymerization of TCS and cationic one of DMASt occur at the same time. Introduction Only a few compounds have been reported of the electron-accepting group substituted styrenes carrying more than two strongly electron-withdrawing groups on the benzene nucleus, such as 2,4,6-trinitrostyrene (TNS),1-3 2,4,6-tris(trifluoromethyl)styrene (TFS),4 and 2,5-, 3,5-, and 3,4-bis(trifluoromethyl)styrenes.6 Although the cyano (up = 0.674)6 group is strongly electron withdrawing and its character is just intermediate between that of nitro (up = 0.778)6 and trifluoromethyl (ap = O l~3 2 )~ groups, polycyano-substituted styrenes have not yet been found in any literature, but 0-, m-, and p-monocyanostyrenes7-9 wer

Scanning Electrochemical Microscopy 50. Kinetic Study of Electrode Reactions by the Tip Generation-Substrate Collection Mode

A scanning electrochemical microscopy (SECM) methodology for localized quantitative kinetic studies of electrode reactions based on the tip generation-substrate collection (TG-SC) operation mode is presented. This approach does not use the mediator feedback required in typical kinetic SECM experiments. The reactant is galvanostatically electrogenerated on a tip placed in proximity to the substrate. It diffuses through the tip-substrate gap and undergoes the reaction of interest on the substrate surface. The substrate current is monitored with time until it reaches an apparent steady-state value. The process was digitally simulated using an explicit finite difference method, for an irreversible first-order electrode reaction at the substrate. Transient responses, steady-state polarization curves, and TG-SC approach curves can be used to obtain substrate kinetics. The effects of the experimental parameters were analyzed. The possibility of easily changing the experimental conditions with the SECM is an attractive approach to obtain independent evidence that can be used for a strict test of reaction mechanisms. The technique was applied for a preliminary simplified kinetic examination of the oxygen reduction reaction in phosphoric acid. Scanning electrochemical microscopy (SECM) is a powerful technique for studying kinetics of heterogeneous electron-transfer reactions. 1 Several reactions have been analyzed mainly using the amperometric feedback mode. [2][3][4][5][6][7][8][9][10] In this operation mode, kinetic information is extracted from the tip current as the mediator couple in solution reacts at tip and substrate. The mediator generates the reactant of the reaction of interest on the substrate through a diffusion-controlled reaction at an ultramicroelectrode (UME) tip. The electrogenerated reactant diffuses in the tipsubstrate gap and regenerates the mediator at the substrate surface. The change in the mediator concentration caused by this process is detected by the UME tip because of the proportionality between the diffusion tip current and the mediator concentration. 11 One condition for this approach to be used is that the initial mediator concentration must be sufficiently small that the tip reaction operates under diffusion control. Thus, the conditions where it is possible to perform kinetic measurements by SECM are limited in the range of mediator concentrations where positive feedback can be detected. Other SECM operation modes, like those based on generation-collection configurations, have been used less often for studying electrode reactions. 12-14 The substrate generation-tip collection (SG-TC) mode is very convenient for obtaining information about localized electrode processes on heterogeneous surfaces. 12,13 On the other hand, the tip generation-substrate collection (TG-SC) mode has been useful in studying coupled homogeneous chemical reactions in electrode reactions. [15][16][17] Recently, we suggested a modification of the TG-SC mode and demonstrated its application for imaging electrocatalytic activity. 18 This configuration does not require tip feedback and is thus appropriate for studying electrode reactions under conditions that are inaccessible to the conventional feedback mode, such as oxygen reduction and hydrogen oxidation in acidic and alkaline media, respectively. The ability of this mode for imaging activity has already been verified, 18 although a detailed theoretical analysis of the process is needed to make use of this configuration for obtaining quantitative kinetic information. Although most of the SECM configurations have been theoretically treated, 2,15,17,[19][20][21][22][23][24][25][26][27] * Corresponding author. E-mail: [email protected]