Guadalupe del C. Pizarro

Comparative study of the self-aggregation of rhodamine 6G in the presence of poly(sodium 4-styrenesulfonate), Poly(N -phenylmaleimide- co -acrylic acid), poly(styrene- alt -maleic acid), and poly(sodium acrylate)

The interaction between rhodamine 6G and different polyelectrolytes is analyzed. Structural aspects differentiate these polyelectrolytes, such as the presence of aromatic groups and the number and localization of their respective charges, which may be directly attached to the aromatic groups or to the polymeric main chain. In the case of poly(sodium acrylate), which does not bear aromatic groups, the polyelectrolyte induces cooperative self-stacking between the dyes which is highly sensitive to the ionic strength, due to the predominance of long-range electrostatic interactions between the polymer and the dye. In the case of poly(sodium 4-styrenesulfonate), whose charge is directly attached to the aromatic groups, a high dispersant ability of the dyes is found and the interaction is less dependent on the ionic strength, due to the predominance of short-range aromatic-aromatic interactions between the dye and the polymer. Among the two polyelectrolytes studied for which the polymeric charge is directly attached to the main chain, and separated from the aromatic group, poly(styrene-alt-maleic acid) shows a lower dependence of the interaction on the ionic strength than poly(N-phenylmaleimide-co-acrylic acid) at a comonomer composition of 1:2, due to a higher linear aromatic density and a lower linear charge density, indicating the importance of hydrophobic forces. Both copolymers exhibit a high ability to induce cooperative self-aggregation of the dye.

HYDROGELS FROM ACRYLIC ACID WITH N,N-DIMETHYLACRYLAMIDE: SYNTHESIS, CHARACTERIZATION, AND WATER ABSORPTION PROPERTIES

Copolymer hydrogels of acrylic acid (AA) with N,N-dimethylacrylamide (NNDMAAm) were synthesized by solution free radical polymerization at different feed mol monomer ratios. The monomer reactivity ratios were determined by Kelen-Tudos method. According to that, the monomer reactivity ratios for poly(AA-co-NNDMAAm) were r1 = 0.650 (M1=AA) and r2= 1.160 (M2=NNDMAAm), (r1 x r2= 0.753). The effect of reaction parameters including: the concentration of cross-linking reagent, monomer concentration, pH, temperature, salt solutions, and solvent polarity on the water absorption have been studied. The hydrogels achieved water-absorption values of 544 g water/ g xerogel for the copolymer poly(AA-co-NNDMAAm) 3:1 atpH 5. Low critieal solution temperature (LCST) values of hydrogels, showed an increase whenthe hydrophilic AA moiety eontent increased in the copolymers.

Polyaromatic-Anion Behavior of Different Polyelectrolytes Containing Benzenecarboxylate Units

The polyaromatic-ion behavior of poly(sodium N-maleoyl-2-aminobenzoate-co-sodium acrylate) in a comonomer composition 1:2, poly(sodium N-maleoyl-4-aminobenzoate-co-sodium acrylate) in a comonomer composition 1:2, and poly(sodium N-maleoyl-4-aminobenzoate-co-N,N-dimethylacrylamide) in a comonomer composition 1:1 is studied. The copolymers undergo short-range aromatic-aromatic interactions with methylene blue and rhodamine B, as a consequence of which their UV-vis monomer band is shifted to lower energies. As a result of their polyaromatic-anion behavior, methylene blue is easily dispersed on the polymeric domains. Moreover, the pK(a) of rhodamine B is shifted from 3.2 to 4.5-5 in the presence of these copolymers. This behavior is also observed in the presence poly(sodium 4-styrenesulfonate), but not in the presence of poly(sodium vinyl sulfonate), which are taken as reference polymers. Compared with poly(sodium 4-styrenesulfonate), a lower resistance to the cleaving effect of added NaCl on the interaction with methylene blue is found. A different influence on the reduction of 2,3,5-triphenyl-2H-tetrazolium chloride with ascorbic acid was found for the different polyelectrolytes.

Different Models on Binding of Aromatic Counterions to Polyelectrolytes

The standard theory regarding the interactions between polyelectrolytes and their counterions is based on long-range electrostatic interactions. However, aromatic counterions may undergo short-range aromatic-aromatic interactions with polyelectrolytes containing aromatic rings so that ion pairs may be formed. The charge of the polymeric aromatic groups and the linear aromatic density of the polyelectrolytes play an important role on the behavior of the systems. Self-aggregation of counterions on the polymer environment can be controlled.

HYDROGELS FROM N,N'-DIMETHYLACRYLAMIDE-co-2-ACRYLAMIDO-2-METHYL-1-PROPANESULFONIC ACID WITH SALT-, TEMPERATURE- AND pH-RESPONSIVENESS PROPERTIES

The synthesis of copolymer hydrogels of N, N′-dimethylacrylamide (NNDMAAm) with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were prepared by solution free radical polymerization at different feed mole ratios (mole ratios of n NNDMAAm /n AMPS = 0.5/0.5; 0.33/0.66; 0.66/0.33; 0.25/0.75; 0.75/0.25). In this reaction ammonium persulfate (APS) and N,N´-methylene-bis-acrylamide (MBA) were used as initiator and cross-linking reagents respectively. These copolymers were insoluble in water and it were characterized by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Aqueous solutions of the copolymers showed lower critical solution temperature behavior (LCST). The phase transition temperatures of aqueous solutions of these copolymers increased with increasing of hydrophilic AMPS comonomer content in the copolymers. The effects of reaction parameters, including the concentration of cross-linking reagent, the monomer concentration, pH, temperature, salt solutions, and solvent polarity on the water absorption have been also studied. Under the experimental conditions, the copolymer poly(NNDMAAm-co-AMPS) with a feed mol ratio 1:2 presents the best swelling properties. The monomer reactivity ratios for poly(NNDMAAm-co-AMPS) are the following: r 1 = 0.217 and r 2 = 2.20, (r 1 x r 2 = 0.48).

Monitoring morphological and optical properties on hybrid porous polymer films

ABSTRACT This work focuses on an optical and morphological comparative study of hybrid functional polymer porous films on glass substrates using the spin coating technique. The covering of these membranes, by a predeposited Zn2+ seed layer, was done applying the dip casting technique, which allows the synthesis of a large area and the control of the orientation of ZnO nanoparticles. It was possible to observe changes on the optical properties and surface morphology, which were attributed to both the spatial structure of the macromolecule and their interaction with the inorganic nanoparticles. It was also clear that hybrid porous matrices exhibit a blueshift with decreasing particle size.