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Propagation rate coefficients, k p , for free-radical polymerization of butyl acrylate (BA) previously reported by several groups are critically evaluated. All data were determined by the combination of pulsed-laser polymerization (PLP) and subsequent polymer analysis by size exclusion (SEC) chromatography. The PLP-SEC technique has been recommended as the method of choice for the determination of k p by the IUPAC Working Party on Modeling of Polymerization Kinetics and Processes. Application of the technique to acrylates has proven to be very difficult and, along with other experimental evidence, has led to the conclusion that acrylate chain-growth kinetics are complicated by intramolecular transfer (backbiting) events to form a mid-chain radical structure of lower reactivity. These mechanisms have a significant effect on acrylate polymerization rate even at low temperatures, and have limited the PLP-SEC determination of k p of chain-end radicals to low temperatures (<20 8C) using high pulse repetition rates. Nonetheless, the values for BA from six different laboratories, determined at ambient pressure in the temperature range of À65 to 20 8C mostly for bulk monomer with few data in solution, fulfill consistency criteria and show excellent agreement, and are therefore combined together into a benchmark data set. The data are fitted well by an Arrhenius relation resulting in a preexponential factor of 2.21 Â 10 7 L Á mol À1 Á s À1 and an activation energy of 17.9 kJ Á mol À1 . It must be emphasized that these PLP-determined k p values are for monomer addition to a chain-end radical and that, even at low temperatures, it is necessary to consider the presence of two radical structures that have very different reactivity. Studies for other alkyl acrylates do not provide sufficient results to construct benchmark data sets, but indicate that the family behavior previously documented for alkyl methacrylates also holds true within the alkyl acrylate family of monomers.Arrhenius plot of propagation rate coefficients, k p , for BA as measured by PLP-SEC.

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The seeded semibatch emulsion polymerization of n-butyl acrylate was investigated using potassium persulfate as initiator at 75 °C. The effect of initiator concentration and monomer feeding time (feed flow rate) on the kinetics, fraction of gel, molecular weight distributions, and level of branches were studied. It was found that the amount of gel formed was independent of initiator concentration and monomer feed flow rate if the process proceeded under starved conditions. On the other hand, the higher the initiator concentration and the feeding times, the higher the level of branches but the lower the molecular weights. A high level of branches was found, which was attributed to intramolecular transfer to polymer or backbiting.

A mathematical model for the computation of kinetics, branching frequency, sol molecular weight distribution, and gel fraction for the seeded semicontinuous emulsion polymerization of n-BA is presented. The model incorporates mechanistic features that have been found to play an important role in the polymerization of n-BA, such as the intramolecular transfer to polymer, so-called backbiting, and the low reactivity of the tertiary radicals resulting from such a reaction. Model parameters for which values are not available in the literature were obtained by fitting the model predictions to the kinetic data and structural properties of the polymer (fraction of gel, sol molecular weight distribution, and level of branches) gathered in seeded semicontinuous emulsion polymerizations of n-BA carried out at 75 °C with potassium persulfate as the initiator. The model fits all of these experimental data quite well.

Objective: To examine the factors that could influence the decision of healthcare professionals to use a telemonitoring system. Materials and Methods: A questionnaire, based on the Technology Acceptance Model (TAM), was developed. A panel of experts in technology assessment evaluated the face and content validity of the instrument. Two hundred and thirty-four questionnaires were distributed among nurses and doctors of the cardiology, pulmonology, and internal medicine departments of a tertiary hospital. Cronbach alpha was calculated to measure the internal consistency of the questionnaire items. Construct validity was evaluated using interitem correlation analysis. Logistic regression analysis was performed to test the theoretical model. Adjusted odds ratios (ORs) and their 95% confidence intervals (CIs) were computed. Results: A response rate of 39.7% was achieved. With the exception of one theoretical construct (Habit) that corresponds to behaviors that become automatized, Cronbach alpha values were acceptably high for the remaining constructs. Theoretical variables were well correlated with each other and with the dependent variable. The original TAM was good at predicting telemonitoring usage intention, Perceived Usefulness being the only significant predictor (OR: 5.28, 95% CI: 2.12-13.11). The model was still significant and more powerful when the other theoretical variables were added. However, the only significant predictor in the modified model was Facilitators (OR: 4.96, 95% CI: 1.59-15.55). Conclusion: The TAM is a good predictive model of healthcare professionals' intention to use telemonitoring. However, the perception of facilitators is the most important variable to consider for increasing doctors' and nurses' intention to use the new technology.

Self-healing materials are a very promising kind of materials due to their capacity to repair themselves. Among others, diphenyl disulfide-based compounds (Ph2S2) appear to be among the best candidates to develop materials with optimum self-healing properties. However, few is known regarding both the reaction mechanism and the electronic structure that make possible such properties. In this vein, theoretical approaches are of great interest. In this work, we have carried out theoretical calculations on a wide set of different disulfide compounds, both aromatic and aliphatic, in order to elucidate the prevalent reaction mechanism and the necessary electronic conditions needed for improved self-healing properties. Two competitive mechanisms were considered, namely, the metathesis and the radical-mediated mechanism. According to our calculations, the radical-mediated mechanism is the responsible for this process. The formation of sulfenyl radicals strongly depends on the S-S bond strength, which can be modulated chemically by the use of proper derivatives. At this point, amino derivatives appear to be the most promising ones. In addition to the S-S bond strength, hydrogen bonding between disulfide chains seems to be relevant to favour the contact among disulfide units. This is crucial for the reaction to take place. The calculated hydrogen bonding energies are of the same order of magnitude as the S-S bond energies. Finally, reaction barriers have been analysed for some promising candidates. Two reaction mechanisms were compared, namely, the [2+2] metathesis reaction mechanism and the [2+1] radical-mediated mechanism. No computational evidence for the existence of any transition state for the metathesis mechanism was found, which indicates that the radical-mediated mechanism is the one responsible in the self-healing process of these materials. Interestingly, the calculated reaction barriers are around 10 kcal mol(-1) regardless the substituent employed. All these results suggest that the radical formation and the structural role of the hydrogen bonding prevale over kinetics. Having this in mind, as a conclusion, some new compounds are proposed for the design of future self-healing materials with improved features.

The seeded semibatch emulsion polymerization of n-butyl acrylate, n-BA, with varying amounts of styrene as comonomer was investigated using potassium persulfate as initiator at 75 °C. The kinetics, the gel fraction, the molecular weight distribution, MWD, and the level of branches were determined. It was observed that the instantaneous conversion, the fraction of gel, the average molecular weights, and the level of branches were affected by the amount of styrene in the recipe. In particular, the fraction of gel decreased from 55% to almosnt nil and the level of branches decreased from 14 to 5 branches per 1000 carbons of the backbone when the amount of styrene increased from 0 to 10%. These results have technological implications because the amount of gel and the level of branches can be controlled; this is something that was not possible when initiator concentration or monomer feed rates were used as control variables. A mathematical model for predicting the kinetics, the fraction of gel, the level of branches and the MWD was used to analyze the effect of styrene on the seeded semibatch emulsion polymerization of n-BA. In addition, it is shown that the adhesive properties of these latexes can be modified by adding small amounts of styrene.