Luis C. Cesteros

Miscibility in blends of poly(vinyl acetate-co-vinyl alcohol) with poly(N,N-dimethylacrylamide)

Abstract Miscibility of poly(N,N-dimethylacrylamide) (PDMA) with poly(vinyl acetate) (PVAC), poly(vinyl alcohol) (PVAL) and poly(vinyl acetate co-vinyl alcohol) (ACAL copolymers) has been investigated over a wide composition range. Differential scanning calorimetry (DSC) results indicate that PDMA is immiscible with PVAC, but is miscible with PVAL and ACAL copolymers in certain range of compositions. The ACAL/PDMA phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with blend composition for miscible systems was found to follow the Kwei equation. Infrared spectroscopy studies of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups in vinyl alcohol units and the carbonyl group in the tertiary amide, which appear to be decisive for miscibility.

Polymer—polymer complexation between poly(monomethyl itaconate) and poly(vinylpyridine)s

Abstract Polymer-polymer hydrogen-bonded complexes of poly(monomethyl itaconate) with poly(2-vinylpyridine) and poly(4-vinylpyridine) were studied. Several solvents have been assayed for these systems: methanol, methylformamide and binary mixtures ( 50 50 ) of methanol with water, tetrahydrofuran, dimethylformamide and dimethylacetamide. In all cases, instantaneous precipitate formation was observed after mixing the solutions of poly(monomethyl itaconate) and poly(vinylpyridine)s. Polymer complexes prepared from methanol solutions show different stoichiometries depending on the feed composition, but that found in most cases was 3 : 2 of monomethyl itaconate:vinylpyridine repeat units. Complexes are insoluble in all the tested solvents; only fresh precipitate may be solubilized by increasing the pH of the solution. Complex formation is observed even when the density of pyridine groups is reduced to 25% by copolymerization with styrene. Differential scanning calorimetry analyses do not show a glass transition temperature for poly(monomethyl itaconate) polymer complexes; only a wide degradation peak was observed. Thermogravimetric experiments corroborate that the thermal degradation behaviour does not differ substantially from that of the pure components. In these conditions, Fourier-transform infra-red spectroscopy was used to study their hydrogen-bonding interactions. The infra-red spectra corresponding to polycomplexes clearly show evidence of hydrogen bonding between the components and there seems to be some evidence of partial pyridine protonation.

Highly interacting polymer blends: poly(monoethyl itaconate)/ poly(vinylpyridine)s

Abstract In this paper the interactions of poly(monoethyl itaconate) with poly(2-vinylpyridine) and poly(4-vinylpyridine) have been studied. Polymer blends or polycomplexes can be obtained, depending on the solvent employed. The stoichiometry found for the polycomplexes obtained was 2:1 of monoethyl itaconate: pyridine repeat units. Polymer complexes do not show a standard glass transition temperature. On the contrary, blends involving poly(monoethyl itaconate) and poly(2-vinylpyridine) show a broad glass transition. The thermal degradation behaviours of complexes and blends do not differ substantially from those of the pure components. Fourier-transform infra-red spectroscopy was used to study the hydrogen-bonding interactions in complexes and blends.

Study of the solvent role on complexation in systems poly(mono n-alkyl itaconate)/tertiary polyamide

Abstract This paper reports a study of the solvent role on complexation in systems composed by a polyacid and a polybase. Complexation has been found in water, n-alcohols, ethers and acetone, depending on the chosen polymer pair and temperature. The temperature at which the transition from a biphasic system to homogeneous solution occurs, has been employed as a measure of the relative stability of the complex. In general, complexes with bulky side groups are less stable than those with small ones. The influence of solvophobic and hydrophobic interactions has been discussed. The stability of complexes in ethers shows a marked dependence on the aliphatic character of the polymeric system, showing a complexing character similar to that of n-alcohols for the polymer systems with lower aliphatic character. Acetone is the most complexing solvent, probably due to its lower competing ability. Finally, it has been found that the relative stability of complexes with poly(ethyloxazoline) (compared with those with poly(N,N-dimethylacrylamide)) increases with the size of the side group of the poly(mono n-alkyl itaconate).

Cosurfactant effects on the polymerization of vinyl acetate in anionic microemulsion media

The polymerization of vinyl acetate at 60 °C in microemulsions stabilized with the anionic surfactant, Aerosol OT, with or without cosurfactant (n-butanol) is examined. Partial phase diagrams at 60 °C show that the addition of n-butanol enhances the one-phase microemulsion region. Results indicate that the reaction rate is not affected by the presence of the alcohol. However, average molar masses are smaller although particles are bigger throughout the reaction compared to those values obtained in the absence of n-butanol. An explanation for these results is presented.

Infrared Study of the Interactions between Poly(vinyl pyridines) and Poly(mono- n -alkyl itaconates)

In this paper we have performed a spectroscopic study of the polymer–polymer complexes and polymer blends formed by mixing poly-acids [a series of poly(mono-n-alkyl itaconates)], and polybases [poly(2-vinyl pyridine) and poly(4-vinyl pyridine)]. The poly(mono-n-alkyl itaconates) are proton donors and the poly(vinyl pyridines) are good proton-acceptor polymers. Therefore, these pairs of polymers can interact via hydrogen bonding under given conditions. The obtained spectroscopic results point out the existence of hydrogen bonding in the studied systems. In addition to the qualitative hydrogen-bonding evidence observed in the hydroxyl and carbonyl stretching region, the curve-fitting analysis of the characteristic modes of the pyridine groups allows a quantitative study of the specific interactions to be performed.

Effect of the Acrylic acid Content on Miscibility and Mechanical Properties of Mixtures of Poly(ethylene-co- (acrylic acid)) and Poly(2-ethyl-2-oxazoline)

Full Paper: The miscibility behavior of blends of poly(2ethyl-2-oxazoline) (PEOX) and poly[ethylene-co-(acrylic acid)] was studied as a function of the acrylic acid content with the help of differential scanning calorimetry (DSC), modulated DSC and dynamic mechanical thermal analysis (DMTA). Miscibility, ascertained by the existence of a single glass transition in the mixtures, is achieved only between the PEOX and the copolymers with a high acrylic acid content (20%). The other two polymer pairs are immiscible at all compositions. FTIR spectroscopy demonstrates that miscibility is enhanced by hydrogen bonding interactions between the amide groups of the PEOX and the carboxylic groups of the acrylic acid units in the copolymer. Tensile stress and compressive creep tests reveal that the 20 and the 40 wt.-% PEOX blends exhibit synergistic mechanical properties, i. e., better ultimate properties, smaller Young’s moduli and higher creep compliances.

Study of the melting and crystallization behaviour of poly(ethylene oxide)-poly(vinyl alcohol) blends

Abstract The melting and crystallization behaviour of blends of poly(ethylene oxide) and poly(vinyl alcohol) has been analysed. Hoffman-Weeks plots of the observed melting points versus crystallization temperatures are constructed. From these plots, melting-point depressions have been found. However, measurements of glass transition temperatures by dynamic mechanical thermal analysis have shown no changes for poly(ethylene oxide). Crystallization kinetics became slower as the poly(vinyl alcohol) content was increased.

A study of the thermal degradation of several poly(monoalkylaryl itaconates)

Abstract Thermal degradation processes in poly(monobenzyl itaconate), poly(mono-2-phenylethyl itaconate) and poly(mono-3-phenyl-1-propyl itaconate), have been studied by DSC, TGA, EGA and FTIR. These analyses have indicated the absence of glass transitions in the three polymers and the occurrence of thermal degradative processes at temperatures of 120 δC. This thermal behaviour is confirmed by thermogravimetric analyses (TGA) which allows us to distinguish between at least three different degradative processes below 250 δC. Evolved gas analyses (EGA), employing an FTIR detector, and the infrared spectra of the residue allow us to speculate about the degradative reaction mechanisms. Three main degradation reactions have been proposed at temperatures below 250 °C, namely cyclic and linear anhydride formation, with loss of water and the corresponding alcohol, and decarboxylation reactions at higher temperatures.

Polymerization of vinyl acetate in microemulsions stabilized with dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide

The polymerization of vinyl acetate in microemulsions stabilized with dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) or mixture of these surfactants is examined. The polymerization rate diminishes as the surfactant mixture becomes richer in DTAB. Also, particles grow with conversion and become increasingly larger as the DTAB content in the mixture increases. Our results indicate that chain transfer reactions to monomer are more important than chain transfer reactions to polymer even at high conversions with CTAB. However, as the content of DTAB increases, bimolecular termination induced by coagulation, terminal double bond polymerization and chain transfer reactions to polymer become increasingly more important.