Polymerization - curves photoinitiation

Figure 6.2. Typical kinetic curves of glycidyl methacrylate polymerization at photoinitiator...

The polymerization reaction was found to develop both faster and more extensively as IQ was increased, up to a certain value above which identical RTIR curves were recorded. Consequently, the (Rp)max value reaches an upper limit, as shown in Figure 5 where (Rp)max was plotted versus Iq on a logarithmic scale. The slope of the straight line obtained at low light intensities, 0.55, is close to the 0.5 value expected for a photoinitiated radical polymerization involving bimolecular termination reactions. 

Gosh and Gosh [105] studied photoinitiated polymerization of methyl methacrylate initiated by the BP-TV,A-dimethylaniline couple, and Clarke and Shanks [106] tested the influence of a variety of amines on benzophenone-initiated polymerization. That amino radicals resulted during the initiation the polymerization by benzophenone-tertiary aromatic amines was shown by Li through the use of ESR and spin-trapping methods [107]. It was shown that the rate of photoinitiated polymerization depends on the structure of the amine. More recently [108] benzophenone-tertiary aromatic amines were studied as initiators of the free-radical polymerization of polyol acrylates. Illustrative kinetic curves recorded during photoinitiated polymerization of TMPTA are shown in Figure 23. 

Figure 4. Thermogravimetric analysis curves in N2 and air for monomer III polymerized by S seconds irradiation using 0.5 mole % (4-octyloxyphenyl)phenyliodonium hexafluoro-antimonate as photoinitiator.

A second point should be noted for the curves in Figure 4. For curves a-e, unlike the corresponding systems in Figure 3 where the maximum conversion is obtained at 1 Hz, die maximum percent conversion occurs at 5 Hz (curves a-c), 10 Hz (curve d), and 20 Hz (curve e). This is due to a lack of effective premature termination of growing polymer chains, as previously discussed, which occurs when using lower photoinitiator concentrations. Apparently, if premature termination reactions did not occur, we would expect to observe higher extents of polymerization with increasing repetition rate for even low total numbers of pulses. 

Figure 5 Influence of the radical-type photoinitiator on the light-induced polymerization of a polyurethane-acrylate resin. Decay curve of the phosphine oxide photoinitiator...

The above-mentioned phenomenological model is usually used to describe the kinetics of autocatalytic reactions that are characterized by a maximum reaction rate between 20 and 40% conversion. The shape of the photoinitiated polymerization rate curves... 

Figure 3.8. Typical photoinitiated polymerization rate versus time curve at 50 C. (—) Experimental curve and ( ) modelization according to equation (3.14) [78].

In the same way, Al-vinyl carbazole (NVK) appeared as a cheap and efficient alternative to (TMS)3SiH. Figure 2 shows that the polymerization in the presence of NVK is better than in the absence of this compound (final conversions = 25% and 13% for Irgacure 819/NVK/Ph2l and Irgacure 819/ Phal, respectively). With no added photoinitiator (Irgacure 819), no polymerization is observed (Fig. 2, curve l) this shows that NVK is an additive and not a photoinitiator. 

As one can see in Figure 2 4, kinetic curves of polymerization in the presence of SGS have typical S-like shape. However, the rate of photoinitiated polymerization of diaciylate composition with increase of SGS content decreases as compared with initial polymerizing composition. Maximal rate of polymerization w at SGS content of 70% V. diminishes approximately by 2 times in comparion with w for initial composition, whereas, time of achievement of maximal rate increases by 2 times. Possible explanation of this fact may be that an inorganic constituent forms steric limitations for the process of polymerization of diaciylate monomer. An additional spatial network of nanoparticles of silica phase which appears as a result of sol-gel process leads to macroradicals decay and accordingly, to deceleration ofpolymerization process. 

FIGURES Integral kinetic curves (a) and their differential anamorphoses (b) of photoinitiated polymerization of PC-SGS depending on its composition. 

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