Polymerization profiles

A new type of support has also been developed by reaction of predried silica with MAO and simultaneous cross-linking with aromatic diols." The carrier material is a supported MAO network, which can be used as a cocatalyst for activating ansa-metallocene dichlorides. Additional aluminum alkyls are necessary to activate the supported catalyst and to control the polymerization profile as well as other polymer properties. 

Figure 10. Propene polymerization profiles of a silica-supported metallocene/MAO catalyst prepared by suspension impregnation (a) depending on polymerization time and polymerization temperature and (b) depending on particle size and polymerization time, (c) Comparison of the activity profiles between an 1-octene prepolymerized catalyst and an untreated system, (d) Comparison of the activity profiles between a catalyst system employing 2 vol % hydrogen and the not activated system.

The kinetics of ultrafast polymerization of acrylic monomers exposed to UV radiation or laser beams has been investigated by IR spectroscopy. An 8 fold increase of the cure speed was observed by using diphenoxybenzophenone as photoinitiator instead of benzophenone. llie reactivity of polyurethane-acrylate or epoxyacrylate systems was markedly improved by adding acrylic monomers that contain carbamate or oxazolidone groups and which impart both hardness and flexibility to the cured polymer. Time-resolved infirared spectroscopy was used to directly record the actual polymerization profile for reactions taking place within a fraction of a second upon UV or laser exposure. Comparison with other techniques of real-time analysis show the distinct advantages of this method for an accurate evaluation of the important kinetic parameters and of the dark polymerization which develops just after the irradiation. 

Infrared spectroscopy (5.131. By following the disapearance of the IR absoipdon of the acrylic double tend one can quantitatively evaluate both the maximum rate of polymerization and the amount of residual unsaturation in the laser-cured polymer. Polymerization profiles are shown on Figure 8 for the curing of a polyester-aciylate photoresist under pulsed laser irradiation at 337.1 nm in the presence of air or pure nitrogen. The main disadvantage of IR spectroscopy is that, like gel fraction determination, it requires discrete measurements at various exposures and thus becomes a tedious, time consuming technique. 

Figure 9. Polymerization profiles recorded by laser-interferometry forapolyester-acrylate photoresist exposed to an Ar laser beam (X = 363.8 nm) at various light intensities in the presence of air.

Figure 11. Post-polymerization profiles recorded by RTIR spectroscopy for a polyurethane-acrylate + CL 960 photoresist irradiated for 50 ms with an Ai laser beam (1 = 363.8 nm) in the presence of air or pure nitrogen. Power output = 100 mW.

Xia Y, Boydston AJ, Yao Y, et al. Ring-expansion metathesis polymerization catalyst-dependent polymerization profiles. J Am Chem Soc. 2009 131 2670-2677. 

Figure 2 Polymerization profile recorded by RTIR spectroscopy upon UV exposure of an acrylate-based resin. Monitoring of the IR band at 1410 cm" ...

Fig.3 Polymerization profiles recorded by RTIR spectroscopy upon continuous (a) or a 0.2 s (b) UV exposure of an acrylate resin...

Figure 8 Influence of the chemical structure of the diacrylate oligomer on the polymerization profile recorded by RTIR spectroscopy...

The light intensity (I) is a key factor in photoinitiated polymerization as it controls directly the rate of initiation which can thus be modulated in a large range, making the reaction time vary between a fraction of a second up to a few minutes. Figure 14 shows some typical polymerization profiles recorded by RTIR spectroscopy with a polyurethane-acrylate sample exposed to UV-radiation of different intensities. In the relationship observed between the... 

Figure 1.3. Examples of push-pull dyes used in PISs a) UV-vis absorption spectra and b) typical polymerization profiles for emission wavelength 473 nm...

If the polymerization of f-caprolactone were to proceed in this manner (Mw/Mn=l) it would be followed by ester Interchange reactions until the establishment of the most probable distribution. This would result in a continuing increase in and hence of the melt viscosity (Figure 3). The polymerization of -cap-rolactone does in fact fulfill the second requirement above. However, fulfillment of conditions one and three are questionable making two alternative polymerization profiles possible. 

Fig. 1 Polymerization profiles of (A) trimethylolpropane triacrylate (TMPTA) using different photoinitiating systems (1) Irgacure 819 (0.5% w/w) or (2) Irgacure 819/(TMS)3SiH (0.5%/3% w/w) upon a LED(3385 nm exposure. (B) (3,4-Epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate (EPOX) using different photoinitiating systems (1) a Michler ketone derivative/iodonium salt or (2) a Michler ketone derivative/iodonium salt/(TMS)3SiH upon excitation by a laser diode at 532 nm. ...

IR spectroscopy is highly appropriate for the direct recording of curing rates -that is, the degree of conversion as a function of time [97,98]. Typical polymerization profiles obtained upon UV exposure of an urethane-acrylate resin and an acrylate/epoxide blend (diacryl derivative of bis-phenol A/bicycloaliphatic diepoxide) are shown in Figure 2.30. While the radical polymerization of the acrylate monomer occurred faster than the cationic polymerization of the epoxide... 

Figure 10.1 Polymerization profiles recorded by RTIR spectroscopy upon UV exposure of an aliphatic polyurethane-acrylate (PUA) or an aromatic polyether-acrylate (PEA) in the presence of a monoacrylate or a diacrylate reactive diluent (25 wt%), respectively. Light intensity 40 mW cm . Laminated film.

As iDentioned in the section 2, the refractive index modulation is caused by the composition modulation occurred during UY exposure. In order to find the mechanism of composition modulation, we used the two-component model chosen to have very different rates of polymerization and refractive indices. The two-component model system used urethanediacrylate as the high-reactivity monomer and diallyIphthalate as the low-reactivity monomer as shown in table 3. Fig.12 shows the photo-polymerization profile obtained the two component system and Fig. 13 shows time dependence of the haze profil during exposure. 

Real-time infirared spectroscopy proved particularly well suited to check whether the silicate platelets have any effect on the UV-curing process. The polymerization profiles recorded for a 25 /um thick polyurethane-acrylate film (Fig. 7.5) clearly show that the organoclay (5 wt.%) has no slowing down effect on the polymerization reaction which proceeds as extensively in the nanocomposite as in the unfilled resin. It means that the mineral filler is not acting as a radical scavenger and that the penetration of UV radiation into the sample is not reduced significantly by the nanoparticles. This is also true for up to 2 mm thick samples, where similar polymerization profiles were recorded... 

---