The effect of surfactant (sodium dodecyl sulfate) concentration on particle size, molar masses, glass transition, and tacticity of poly(methyl methacrylate) (PMMA) nanoparticles synthesized by semicontinuous heterophase polymerization under monomer-starved condition at constant monomer feeding rate is reported. Starved conditions are confirmed by the low amount of residual monomer throughout the reaction and by the fact that the instantaneous polymerization rate is similar to the feeding rate of monomer. Under these conditions, polymer particles in the nanometer range (20-30 nm) were obtained with narrow size distribution (1.07 < D w /D n < 1.18), depending of surfactant concentration. Final particle size diminishes as the surfactant concentration is increased. Glass transition temperatures and syndiotactic content (54%-59%) of the produced polymers are substantially higher than those reported for commercial and bulkmade PMMA. Molar masses are much lower than those expected from termination by chain transfer to monomer, which is the typical termination mechanism in 0-1 emulsion and microemulsion polymerization of this monomer.

No abstract

The fundamental aspects of the manufacturing of gold nanoparticles (AuNPs) are discussed in this review. In particular, attention is devoted to the development of a simple and versatile method for the preparation of these nanoparticles. Eco-friendly synthetic routes, such as wet chemistry and biosynthesis with the aid of polymers, are of particular interest. Polymers can act as reducing and/or capping agents, or as soft templates leading to hybrid nanomaterials. This methodology allows control of the synthesis and stability of nanomaterials with novel properties. Thus, this review focus on a fundamental study of AuNPs properties and different techniques to characterize them, e.g., Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), UV-Visible spectroscopy, Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy, Small-angle X-Ray Scattering (SAXS), and rheology. Recently, AuNPs obtained by “green” synthesis have been applied in catalysis, in medicine, and as antibacterials, sensors, among others.

No abstract

In this study, the internal air temperature (IAT) profile was measured to analyze the thermal behavior of a polymer for a complete rotational molding cycle. Foamed and unfoamed linear low density polyethylene parts were produced by biaxial rotational molding using a chemical blowing agent based on azodicarbonamide at different concentrations (0, 0.15, 0.25, 0.50, 0.75, and 1.0% wt) with different oven temperatures (270, 280, and 285°C). The analysis proposed is based on the temperature profiles and their derivatives to better determine the different transitions occurring in a complete molding cycle. The analysis is completed with differential scanning calorimetry (DSC) to get more information related to the dynamics of the different processing stages like polymer melting, exothermic decomposition of the chemical blowing agent, and polymer crystallization. The results obtained show a good agreement between the melting and crystallization temperatures from IAT derivatives and DSC. POLYM. ENG. SCI., 58:E235–E241, 2018. © 2017 Society of Plastics Engineers

The synthesis of poly(N-isopropylacrylamide) nanogels by semi-continuous inverse heterophase polymerization (SIHP) under monomer starved conditions is reported here. This process consists in adding a N-isopropylacrylamide (NIPA) aqueous solution at a controlled rate over a monomer-free oleic solution containing surfactant and initiator. The nanogels became smaller with narrower size distributions as the addition rate was decreased. Moreover, nanogel sizes, the size distributions and more importantly, the polymer/surfactant ratios were smaller than those of PNIPA nanogels synthesized by batch inverse microemulsion polymerization (BIMP). The swelling behavior of these nanogels in water as a function of temperature is reported. As expected, all nanogels have a volume phase transition temperature at ca. 33-34 • C.

No abstract

The polymerization of aniline hydrochloride by inverse microemulsion in a batch process and the semicontinuous process was studied as a function of the surfactant ionic and nonionic. Polymerizations were carried out at 60°C for 4 h with a yield polymer of circa 67 and 27% wt. for ionic and nonionic surfactants. The conductivity of synthesized polyaniline by the semicontinuous process is higher up to three orders of magnitude than that of the batch process for both surfactants. The calculating degree of oxidation by UV-Vis showed the relative intensities of the quinoid to benzenoid unit around one. The morphology was determined by Scanning Electron Microscopy (SEM) and observed that the formation of the different morphologies is due to the self-assembly behavior of surfactant. The diameter z-average particle size (Dz) was studied by Transmission Electron Microscopy (TEM), which determined that the diameter particle in a semicontinuous state is larger than the one produced in a batch; this is due to the control of monomer addition in the system. These findings suggest that the polymerization process and the type of surfactant influence the properties of polyaniline.