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A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0‐1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The synthesis, by two sequential inverse microemulsion polymerizations, of interpenetrating polymer networks (IPN) formed by polyacrylamide (PAM) and poly(acrylic acid) (PAA) and their response to changes in pH and temperature are reported here. The temperature and pH responses of the IPN nanoparticles are compared with those of polyacrylamide and random copolymers of polyacrylamide and poly(acrylic acid) P(AM-co-AA) nanoparticles also made by inverse microemulsion polymerization. We found that only the IPN nanogels exhibited a sharp swelling increase with temperature associated with its Upper Consolute Solution Temperature, driven by hydrogen bonding interactions, and with pH, driven by electrostatic repulsions of the PAA carboxylic groups, especially at pHs larger than the pKaof the PAA. The ς-potentials of the PAM, P(AM-co-AA) and IPN nanogels were measured as a function of pH and temperature, to determine the effects of these two variables, which in turn, affected the swelling of the nanogels. Field emission scanning electron microscopy revealed that the IPN nanogels were spheroidal with sizes similar to those determined by dynamic light scattering. [ABSTRACT FROM AUTHOR]

A generalized model is presented here for the semicontinuous heterophase polymerization of methyl and hexyl methacrylate, which have very different water solubility. In this polymerization technique, neat monomer is fed at a controlled rate over a monomer-free aqueous solution of surfactant and initiator, to produce nanometer size particles with controlled molar masses, and high polymer/surfactant ratios similar to those used in conventional emulsion polymerization. For the two monomers studied at three different addition rates, model predictions accurately reproduce conversion-versus-time curves, the evolution of particle size, and the number density of particles. The model reveals that the controlling nucleation mechanism shifts from micellar to homogeneous nucleation as the monomer solubility in water increases. [ABSTRACT FROM AUTHOR]

A simple four-state model containing five-parameters, in conjunction with experimental conversion, particle number density and average molar masses, is presented to reproduce the semicontinuous heterophase polymerization of butyl methacrylate. The model adequately describes the experimental evolutions of conversion, particle size, average number of particles, average number of radicals per particle, and molar mass. A coagulation mechanism was detected and its rate constant was evaluated. The entry coefficient and the critical radical concentration in the aqueous phase were approximately constant and the exit rate coefficient decreased with monomer feed rate. Homogeneous nucleation is the dominant mechanism of production of particles, micellar nucleation occurs at the slowest feeding rate examined. [ABSTRACT FROM AUTHOR]

New oil-in-alcohol highly concentrated emulsions wereformulatedand were used as a templates to obtain macroporous poly(furfuryl alcohol)monoliths by a one-step method. The oil-in-alcohol highly concentratedemulsions were prepared by stepwise addition of the oil phase to thesurfactant-alcohol solution and were characterized by optical microscopyand by laser diffraction. The typical structure of highly concentratedemulsions, with close-packed polyhedral droplets, has been observed.Poly(furfuryl alcohol) monoliths were obtained by polymerizing inthe external phase of these emulsions. These materials are mainlymacroporous and retain the size distribution and morphology from thehighly concentrated emulsions. The internal structure of the monolithswas observed by scanning electron microscopy. The images showed aninterconnected network with pore size similar to the droplet sizeof the highly concentrated emulsions used as templates. [ABSTRACT FROM AUTHOR]

The synthesis of stimulus-responsive poly(N-isopropylacrylamide-co-N-isopropylmethacrylamide)/chitosan core/shell nanohydrogels made by batch emulsion polymerization in the presence of chitosan (CS) micelles is reported. The ratio of monomers required to obtain copolymers with a volume phase transition temperature (TVPT) in the range of the temperatures observed in the human body in response to an infection (38 to 40 °C) was estimated with the Fox equation. The conversion was determined by gravimetry; mean particle size, size distribution, and thermal response were measured by quasi-elastic light scattering (QLS). The core/shell structure was confirmed by TEM, and FTIR showed the presence of N-isopropyl acrilamide (NIPA), N-isopropyl methacrylamide (NIPMA), and CS in the nanohydrogels. The nanohydrogels were loaded with the drug doxycycline hyclate, and their release kinetic profile was determined at pH = 2.0 and 7.4 at their volume phase transition temperatures (TVPT). A higher amount of drug was released at acidic pH. Some mathematical models described in the literature were used to fit the experimental drug release data. [ABSTRACT FROM AUTHOR]

Several studies have addressed the benefits of mentoring from the mentor's perspective, especially those related to soft skills. However, to the best of our knowledge, there are no studies that either relate the mentoring in STEM areas with female role models or that analyze them from a data-mining perspective. In this work, a questionnaire was elaborated to address the mentor's benefits related to soft skills and technical knowledge; afterward, a data-mining methodology was used to analyze the mentor's perceptions related to female role models and STEM reinforcement. In addition, sentiment analysis was performed in order to determine the emotional polarity in the text used by the mentors to describe their mentoring experience. The results show that soft and technical skills are acquired by the mentors, and participating in mentoring programs allows them to perceive themselves as female role models. Additionally, by using decision trees, it was possible to determine the mentors' characteristics that perceive a STEM reinforcement or that produce attraction. In addition, the results show that the general perception of the mentors' experience was positive. Finally, the use of machine learning techniques, specifically data mining and sentiment analysis, allowed us to both confirm the results obtained in a qualitative way and to obtain new interesting results. [ABSTRACT FROM AUTHOR]