Pulsed-laser-induced polymerization

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... 

Experimental details of pulsed-laser induced polymerizations of methacrylic acid (MAA) in aqueous solution with poly(MAA) being added. The overall concentration of MAA + poly(MAA) is 20 wt.-% in all experiments. Pulsed-laser polymerizations were performed at 25 °C and ambient pressure using a photolnitlator (DMPA) concentration of Cdmpa = 2 mmol L and a laser pulse repetition rate of 40 Hz. Listed are the virtual degree of monomer conversion, X in uai. the MAA concentration, c aa. the number of applied laser pulses, the molecular weight (MW) at the first point of inflection (POI), M and the ratio of MWs at the first and second POI. The final column contains the resulting propagation rate coefficients, kp. 

Under UV-laser irradiation, photosensitive multifunctional acrylate resins become rapidly cross-linked and completely insoluble. The extent of the reaction was followed continuously by both UV and IR spectroscopy in order to evaluate the rate and quantum yield of the laser-induced polymerization of these photoresist systems. Two basic types of lasers emitting in the UV range were employed, either a continuous wave (C.W.) argon-ion laser, or a pulsed nitrogen laser. 

Quantitative in-line spectroscopic analysis of polymerization processes depends on the aTOUahUity of autoclaves ecjuipped with windows that are transparent to the probing light and, for pulsed laser-induced studies, also to excimer laser light. A survey of such optical cells for vibrational spertroscopic online measurements up to kilobar pressures is given elsewhere. ... 

Figure 3.93. Scanning electron micrograph image of a photonic band-gap crystal obtained by TP induced crosslinking radical polymerization of acrylates in the presence of poly(styrene-co-acrylonitrile) as binder and an amino substituted distyrylbenzene as TP active initiator using a pulsed laser (730-nm excitation wavelength, 0.45-mW laser power, 50-mm/s scan speed, writing 9 layers of 1-mm spaced parallel rods with a layer spacing of 1 mm). (From Ref. [133] with permission of the Technical Association of Photopolymers, Japan.)...

A number of anomeric D-hex-2-ulopyranosyl azides have been synthesized and their photochemistry examined. For both a- and P-azides, the major photoproducts arise from cleavage of the C-2C-3 bond and migration of the C-3 carbon to the nitrene centre. Decomposition reactions of a glycidyl azide polymer have been induced by pulsed laser infrared pyrolysis and UV photolysis of thin films at 17-77 K and monitored by IR spectroscopy. The initial step is elimination of N2 and formation of imines, which decompose on warming, possibly with secondary polymerization. 

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... 

Single Pulse-Pulsed Laser Polymerization. Applying PLP in conjunction with infrared or near-infrared spectroscopic measurement of monomer conversion induced by a single laser pulse (SP-PLP) allows for the determination of the ratio of termination to propagation rate coefficients, kt/kp, in wide ranges of temperature, T, pressme, p, and monomer conversion. The SP-PLP technique was pioneered in the 1980s by Buback and co-workers (409). The monomer conversion induced by a single laser pulse, typically of 20 ns width, is measured by on-hne... 

The attractiveness and major advantage of using pulsed lasers in kinetic studies is a result of the short duration of the laser pulse (typically 10 to 20 ns). Opposed to more conventional methods such as rotating sector and spatially intermittent polymerization, the initiation period can now be considered to be instantaneous on the time scale of propagation. As a consequence, all radicals formed in one laser pulse are of approximately the same chain length at any moment in time, which greatly simplifies the kinetic scheme. It is this quality of laser-induced experiments that leads to the reliability of the PLP method to determine kp values (in conjunction with an accurate MWD determination). 

This chapter will focus on a particular LDW process that employs ultrashort pulsed lasers and photopolymerizable precursors two-photon polymerization (TPP). Also known as two-photon induced photopolymerization and two-photon... 

Monomer conversion in pulsed laser polymerization (PEP) induced by an SP is measured at a fixed wavenumber using an NIR light source, a monochromator, and a fast detection unit for recording NIR intensity as a function of time. °... 

Figure 15 Variation of termination rate coefficient with monomer conversion in laser-induced MMA bulk polymerizations at 30 °C and 1000 bar carried out at laser pulse repetition rates of 0.21 and 13.5 Hz the lines are fits to eqn [9]. From Beuermann, S. Ph.D. thesis, Cuvillier Verlag, Gottingen, 1994. ...

It is seen from Fig. 34 that the fluorescence wavelength of the dye was situated at the red end of the SPA absorbance curve, which may lead to fluorescence-induced polymerization. This problem can be solved by optimizing the fabrication-laser-pulse energy and the concentration of Rhodamine B so that local radical concentrations initiated by the TPA fluorescence are lower than the polymerization threshold, and then the radicals are quenched by dissolved oxygen. 

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