Photopolymerization, kinetic analysis

Johnson PM, Stansbury JW, Bowman CN (2008) High-throughput kinetic analysis of acrylate and thiol-ene photopolymerization using temperature and exposure time gradients. J Polym Sci Part A Polym Chem 46 1502-1509... 

Table 1 Performance of real-time techniques for kinetic analysis of high-speed photopolymerization reactions.

Preliminary results of the analysis of the photopolymerization kinetics according to the autocatalytic model of a series of alkylenediol dimethactylates (structure V) with an increasing number of CH2 groups in the spacer have been pre.sented recently [101]. The parameters k, m and n were calculated from a best fit between model prediction and the data points of the experimental polymerization rate vj. conversion degree curves (see Rgure 3.9). 

In one study [102], the expression for the autocatalytic reaction was modified to model diffusion effects (autoacceleration and vitrification) as well as the light intensity effect on the photopolymerization kinetics of a commercial acrylic resin. The parameters of the model were calculated using non-linear regression analysis. Expression of the rate constant k as k4.T)Io, where b is a fitting parameter and koiT) is temperature-dependent kinetic constant, enabled the authors to determine to the light intensity exponent. A value of about 0.7 was found, showing that the termination occurred following both monomolecular and bimolecular pathways. 

Photopolymerization processes used to be difficult to measure quantitatively by conventional techniques such as dilatometry, UV spectrometry, IR spectrometry and gravimetry. Using a special TA apparatus one can determine the fractional conversion according to the measurement of the polymerization heat. The advantages of measuring the photochemical reaction heat are as follows (1) photopolymerization analysis can be carried out on the system with the photosensitive resin produced from multi-component compounds (2) film-shaped samples can be measured using a high-sensitivity apparatus and (3) kinetic analysis of the polymerization heat can be performed directly. 

Above equation is based on an analysis that indieates eharge transfer and exciplex formation of acrylonitrile with earbazole forms as the intermediate. Gao et al., carried out kinetie studies of photopolymerization of methyl methacrylate by using piperazine sulfur dioxide eharge-transfer eomplex as a photoinitiator. The polymerization rate (Rp) is dependent on the molar ratio of piperazine to sulfur dioxide, and the eomplex with a eomposition of piperazine to sulfur dioxide in a molar ration of 1 2 is the most effeetive. By using the complex as die photoinitiator, flie polymerization kinetics was expressed as,... 

An analogous analysis of the kinetics of the photopolymerization of (ethoxylated Bisphenol A)dimethacrylate [78,98] gave constant (independent on temperature) values for the m and n exponents equal to 0.8 and 2, respectively. The rate constant k increased with the reaction temperature from 30 to 80 C, with a low activation energy of 2.2 kcaPmof. ... 

The analysis of equation (5.86) on maximum normalized rate of photopolymerization which in terms of the accepted value dP/ l-P)dt =-d/n(l-F)/d/ establishes the relationship between the ordinate F and rate W =(dF/d/), which corresponds to the point of inflection of the kinetic curve of the shape ln(l-P)=f /) and the maximum polymerization rate (-d(ln(l-F))/df)ma,... 

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