Pulse laser polymerization method

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,... 

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. 

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. 

Electron Spin Resonance (ESR) spectroscopy can contribute to understanding both the kinetics and the mechanism of radical polymerizations.f Propagation rate constants (fep) of various kinds of monomers have been estimated using ESR spectroscopy. Indeed ESR is one of the most effective methods for estimating values for kp and it is a mutually complementary method to the Pulsed Laser Polymerization (PLP) method. Usually equation (1), and its integrated form (2), have been used to... 

W2N nanoparticles (below 10 nm) were prepared via a one-step pyloysis of polymeric mixture of WCI4 and urea glass like previous y-Mo2N synthesis (30). The surface area of W2N was 64 m /g after heat treatment with N2 gas at 1073 K. The W2N thin film with several micro-sized thicknesses on a Si wafer could be formed via the reactive pulsed laser deposition method (36). The thickness and phase was adjusted by N2 pressure and temperature of a vacuum chamber. 

In this chapter two novel methods are presented which enable the direct and model independent determination of chain-length dependent termination rate coefficients. Both methods are based on single-pulse pulsed-laser polymerization. After a theoretical derivation, both kinetic approaches are validated by means of computer simulations. As will be demonstrated, these simulations prove that the essential assumptions needed to gain access to the chain-length dependent coefficients are valid and do not significantly undermine the accurate and reliable determination of the termination rate coefficients. 

To increase the accuracy of the scaling of the number MWD, there seem to be two experimental techniques (or routes) that might prove to be useful. First of all, a combination of time-resolved single-pulse pulsed-laser polymerization with subsequent analysis of the MWD of the formed polymer product can be employed. From the time-resolved trace, accurate data on the radical concentration versus time can be deduced, which can then be used in the scaling of the number MWD. An alternative method to improve the scaling accuracy might arise form the use of mass-spectrometry techniques. Polymeric material with... 

After having validated both methods theoretically, the experimental application of one of these methods, the one based on time-resolved single-pulse pulsed-laser polymerization, turned out to fail due to the inherent noise sensitivity of this method. From the measured monomer trace versus time, only the time-resolved radical concentration could be determined accurately. Information about the chain-length dependence of termination rate coefficients, which is hidden in the latter time-resolved trace, could not be revealed with any reliability and/or accuracy. 

Pulse Laser Polymerization-Size Exclusion Chromatography Method of Determination 28... 

Scheme 29 shows the rate constants that are involved in CRP. The first reaction is the dissociation (activation) of the shortest chain (initiator of the same structure as RiX). The rate constants of propagation (kp) and of termination [kt] are the same as in the traditional radical polymerization (the new method of kp determination based on the pulse laser polymerization-size exclusion chromatography (PLP-SEC) is discussed in Section 3.02.14.4). Thus, k and feda are of major interest. These are discussed in detail in Chapter 3.05 by Fukuda et al. where it is separately described for the CRP with nitroxides (e.g., 2,2,6,6-Tetramethylpiperidinooxy (TEMPO) as the PR) and for the ATRP systems (Scheme 30). 

Pulsed-laser polymerization (PLP) [9-11] has emerged as a particularly reliable method for determining kp [3,12]. Some (but by no means all) chains photo-initiated by one laser pulse are terminated instantly by short radicals formed from the subsequent one, as illustrated in Fig. 2. 

The pulse laser polymerization (PLP) method has been developed as a new method of obtaining kp. In the PLP method, the value of kp can be estimated from the degree of polymerization of polymer formed, Vp, a knowledge of the monomer concentration, [M], and tf the time between pulses ... 

The conversion dependenee of termination was experimentally investigated in detail via the single-pulse pulsed-laser polymerization coupled with online time-resolved near infrared spectroscopy (SP-PLP-NIR) technique. " " This method provides access to chain-length-averaged termination rate coefficients, (kt). The variation of kt) towards increasing monomer-to-polymer conversion, X, is exemplified in Figure 1.5 for bulk polymerization of MMA. 

Pulsed laser photolysis (PLP) has emerged as the most reliable method for extracting absolute rate constants for the propagation step of radical polymerizations,343 The method can be traced to the work of Aleksandrov el al.370 PLP in its present form owes its existence to the extensive work of Olaj and eoworkers 71 and the efforts of an 1UPAC working party/45"351 The method has now been successfully applied to establish rate constants, /rp(overall), for many polymerizations and copolymerizations. 

Radiation grafting [83, 84, 85, 86, 87, 88, 89] is a very versatile and widely used technique by which surface properties of almost all polymers can be tailored through the choice of different functional monomers. It covers potential applications of industrial interest and particularly for achieving desired chemical and physical properties of polymeric materials. In this method, the most commonly used radiation sources are high-energy electrons, y-radiation, X-rays, U.V.-Vis radiation and, more recently, pulsed laser [90], infrared [91], microwave [92] and ultrasonic radiation [93]. Grafting is performed either by pre-irradiation or simultaneous irradiation techniques [94, 95]. In the former technique, free radicals are trapped in the inert atmosphere in the polymer matrix and later on the monomer is introduced into... 

A number of nonsteady polymerization rate techniques can be used to measure ftp [11]. The most widely used method involves pulsed-laser-induced polymerization in the low monomer conversion regime. Briefly, a mixture of monomer and photoinitiator (Section 6.5.3) is illuminated by short laser pulses of about 10 ns (10 sec) duration. The radicals that are created by this burst of ligh propagate for about 1 sec before a second laser pulse produces another crop of radicals. Many of the initially formed radicals will be terminated by the short, mobile radicals created in the second illumination. Analysis of the number molecular weight distribution of the polymer produced permits the estimation of ftp from the relation... 

Surface radicals produced in the exposed areas may also serve directly as polymerization initiators. However, their concentration will not be very high because they may be rapidly deactivated at the relatively high temperatures reached locally and because of possible reaction with volatile reaction products. Still, it was reported that poly(hydroxyethyl methacrylate) (PHEMA) could be grafted from PDMS surfaces treated with a C02-pulsed laser via the peroxide route [10]. However, the capability of the method to obtain surface structures was not explored in this case. 

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