Pulsed laser polymerization

From this we can see that knowledge of k f and Rf in a conventional polymerization process readily yields a value of the ratio kp fkt. In order to obtain a value for kf wc require further information on kv. Analysis of / , data obtained under non-steady state conditions (when there is no continuous source of initiator radicals) yields the ratio kvlkx. Various non-stcady state methods have been developed including the rotating sector method, spatially intermittent polymerization and pulsed laser polymerization (PLP). The classical approach for deriving the individual values of kp and kt by combining values for kp kx. with kp/k, obtained in separate experiments can, however, be problematical because the values of kx are strongly dependent on the polymerization conditions (Section... 

Measurements of kp were performed by the rotating sector method and its variations until the late 1980s [Flory, 1953 Odian, 1991 Walling, 1957]. In the late 1980s advances in pulsed laser technology and size exclusion chromatography resulted in the development of a technique called pulsed laser polymerization-size exclusion chromatography (PLP-SEC) [Beuermann and Buback, 2002 Beuermann et al., 1997, 2000 Buback et al., 1986, 1992,... 

Solvent effects including 2-methyl-l,3-dioxepane (MDOP), as a solvent, on the propagation kinetics of methyl acrylate (MMA) have been investigated using the PLP-SEC technique (PLP = pulse laser polymerization) <2005MI267>, and the composition of dioxolane-dioxepane copolymers has been studied by IR and differential scanning calorimetry (DSC) <2004PB349>. 

M. Ohoka, S. Misnmi, and M. Yamamoto. Determination of propagation rate coefficient of free-radical polymerization of A-vinylcarbazole by pulsed-laser polymerization. Po/ym. /., 31(10) 878-882, 1999. 

Mass spectrometry is useful also in thos cases in which the scope of the analysis is not simply to measure Mn and Mw of the sample, but the determination of the entire MMD. For instance, in the case of polymers obtained by Pulsed Laser Polymerization, the determination of Mn and Mw of the sample is not the primary goal. In fact, one has to determine the point of inflection Mj (see chapter on MALDI) and MS can be used for this purpose. One plots tire oligomer s abundance against mass, then takes the second derivative. The point at which the second derivative changes from negative to positive is tire point of inflection. 

Coote, M.L., Zammit, U.D., and Davies, T.P., Determination of Free-Radical Rate Coefficients using Pulsed-Laser Polymerization, Trends in Polym Sci., 6,189 (19%). 

Schweer, J., Samecki, J., Mayer Posner, F., Mullen, K., Rader, H.J., and Spickermann, J., Pulsed-Laser Polymerization/Matrix-Assisted Laser Desorption/ionization Mass Spectrometry. An approach toward Free-Radical Propagation Rate Coefficients of Ultimate Accuracy, Macromolecules 29, 4536 (1996). 

Danis, P.O., Karr, D.E., Westmoreland, D.G., Piton, M.C., Christie, D.I., Clay, P.A., Kable, S.H., and Gilbert, R.G., Measurement of Propagation Rate Coefficients Using Pulsed-Laser Polymerization and Matrix-Assisted Laser Desorption/ Ionization Mass Spectrometry, Macromolecules, 26, 6684 (1993). 

Figure 10.9 reports the MALDI-TOF mass spectrum of a polymer obtained by pulsed-laser polymerization that displays a series of peaks ranging from 3000 Da to 12000 Da. The MMD resulting from the MS was plotted, and the point of inflection of the MMD (Eq. 10.3) was determined. The data allow one to determine the rate constant of termination and the rate constant of chain transfer.The method based on MS has now become a standard. 

MALDI-TOF mass spectrum of a PMMA obtained by pulsed laser polymerization. The arrow indicates the position of the inflection point Mi f. (Reprinted with permission from Ref. 11, Copyright 1993 American Chemical Society)... 

Yin M, Bamer-Kowollik C, Heuts JPA, Davis TP. Complications in the 355 nm pulsed-laser polymerization of A-vinylcarbazole. Macromol Rapid Commun 2001 22( 13) 1035 0. 

Figure 2 shows the propagation rate constant of the copolymerization of methyl methacrylate (MMA) and STY as a function of the fraction of MMA in the reaction mixture. The experimental data have been determined via pulsed laser polymerization (PLP), which is known to be the most reliable method to measure propagation rate constants. The two curves are based on the implicit PUM and the TM. It is clear that the TM fails completely to describe kp versus feed composition. Contrarily, the implicit PUM provides a very satisfactory description of the experimental data. 

Here cm is monomer concentration, t time, kp propagation rate coefficient, f inu rate of initiation, and ki termination rate coefficient. Measurement of initiator decomposition rates, and thus specification of has never been a problem. However for much of the history of RP, the disentangling of kp and ki was a problem. This was solved in 1987 when it was shown that by relatively simple analysis of the molecular weight distribution from a pulsed-laser polymerization (PLP), the value of kp could be obtained without requirement for any knowledge of ki (or So enthusias-... 

In this equation, kp is the long-chain propagation rate coefficient, Ci = (kp-kp)l kp and iia is the chain length at which k -kp halves in value (i.e., a sort of half-life ). Available data thus far suggest Ci 10-50 and ii/2 0.5-1.5 t for MMA polymerization we found values of Ci = 15.8 and i/2 = 1.12. These latter values were obtained by fitting pulsed laser polymerization data obtained by Van Herk and co-workers and were found to describe well our (independently obtained) experimental steady state data (both rates and molecular weight distributions)... 

The investigation of BB carried out with commercially available polystyrene standards as well as polystyrene samples prepared by pulsed laser polymerization in microecmulsion revealed that the extent of BB is not constant over the entire... 

With respect to molecular weight distributions obtained when polymers are prepared with pulsed laser polymerization the situation is somewhat more comphcated. From... 

Number chain length distribution, n(L), calculated for homogeneous pulsed laser polymerization and Lo = 100. An ideal Poisson distribution centred at the same Lmax value Is included and the positions of the points of inflection are presented by circles and triangles. 

From several number chain length distributions simulated for pulsed laser polymerization for a great variety of experimental parametersl l which were converted to chromatographic dimensions and subsequently submitted to the infiuence of BB by applying the Tung equationl l correction functions were deduced. The comparison of the input values for the point of infiection and the maximum lead to the following correction functions ... 

Homogeneous and heterogeneous pulsed laser polymerization of styrene was carried out at 25 °C. For the extraction of the kp values as a function of the chain length from measured SEC curves it was necessary to determine the extent of BB. The analyses of narrow Poisson-like polystyrene standards revealed a non constant extent of BB over the complete separation range which could be described by a somewhat more elaborate van Deemter equation. The shift of the points of inflection and as a consequence the introduced error correlates directly to the extent of BB. ... 

Within the PLP-SEC experiments on non-ionized MAA in the presence of poly(MAA), the determination of points of inflection, via the maxima in the associated first-derivative curves of the MWD, is complicated by the pre-mixed polymer which obviously can not be removed prior to SEC analysis. Figures 2 and 3 depict MWDs (A) and the associated first-derivative curves (B) of polymer samples obtained by PLP-induced polymerizations of 15 wt.-% MAA dissolved in water containing 5 wt.% of pre-mixed polymer and of 10 wt.-% MAA dissolved in water containing 10 wt.-% of pre-mixed polymer, respectively. The full lines (a) represent the polymer sample after pulsed laser polymerization, whereas the dashed... 

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