Polystyrene ionic interactions

Smith P. and Eisenberg A., lonomeric blends. I. Compatibilization of the polystyrene-poly(ethyl acrylate) system via ionic interactions, J. Polym. Sci., Polym Lett., 21, 223, 1983. 

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

The work described in the present paper concerns the Influence of water and organic solvents on the ionic interactions in lightly sulfonated polystyrene (SFS) ionomers. The focus will be specifically directed towards the Influence of the solvent environment on the cation-anion and cation-cation interactions. Fourier transform Infrared spectroscopy (FTIR) was used to probe the former while electron spin resonance spectroscopy (ESR) was used to study the latter. Experiments were carried out with dissolved, swollen, and bulk ionomers. 

To be informative, it is desirable that the comparisons of these two different technologies be based on identical polymer backbones, having identical molecular weights, and having comparable levels of ionic functionality present. In addition, it is the purpose of these studies to make such comparisons with the same metal cation and thereby quantify, insofar as possible, the nature of the ionic interactions that exist. To do this, ionomers were prepared based on a polystyrene (PS) hydrocarbon backbone into which the ionic functionality was incorporated. PS was selected as the backbone because of the relative ease of functionalization and the relative freedom of side reactions during the sulfonation or carboxylation reactions. The polymers prepared were designed to come as close as possible in terms of ionic functionality for both sulfonate and carboxylate ionomers over a range of ionic contents. 

The tetraanionic 47 (M = Cu, Zn, Ag, Cd R = -C6H4-SO3H) has been incorporated into different polymers including linear and cross-linked chloromethylated polystyrenes partially quartemized with pyridine (ionic interactions with the metal porphyrin), poly(4-vinylpyridine) (coordinative interactions with the metal porphyrin via the metal) and poly(ethylene glycol) (dipolar interactions with the metal porphyrin) [159,160]. Spectra of the samples were measured in solution or in the solid state. Red-shifts of both Q-and B-bands in the electronic spectra of the porphyrin occurred in the order poly(ethylene glycol) < poly(4-vinylpyridine) < quartemized poly(styrene). The greatest interaction occurred in ionic bonds between the carrier and the porphyrin [159]. 

Qutubuddin and coworkers [43,44] were the first to report on the preparation of solid porous materials by polymerization of styrene in Winsor I, II, and III microemulsions stabilized by an anionic surfactant (SDS) and 2-pentanol or by nonionic surfactants. The porosity of materials obtained in the middle phase was greater than that obtained with either oil-continuous or water-continuous microemulsions. This is related to the structure of middle-phase microemulsions, which consist of oily and aqueous bicontinuous interconnected domains. A major difficulty encountered during the thermal polymerization was phase separation. A solid, opaque polymer was obtained in the middle with excess phases at the top (essentially 2-pentanol) and bottom (94% water). The nature of the surfactant had a profound effect on the mechanical properties of polymers. The polymers formed from nonionic microemulsions were ductile and nonconductive and exhibited a glass transition temperature lower than that of normal polystyrene. The polymers formed from anionic microemulsions were brittle and conductive and exhibited a higher Tj,. This was attributed to strong ionic interactions between polystyrene and SDS. 

DSC data for SSEBS gave a large broad endotherm at about 0 °C which was unattributed. T for the SSEBS hard block (sulphonated polystyrene) was at about 64 °C and decreased to 54 °C on addition of 27 wt % PCL to the copolymer Tg of the ethylene-butylene block was about -40 °C. This change in Tg of the hard block was attributed to disruption of ionic interactions in the sulphonated polystyrene microphase. It was also suggested that swelling of the sulphonated polystyrene blocks by PCL also allowed more facile development of a well-ordered lamellar morphology. 

One promising approach to producing a true molecular composite is to make rod and coil components thermodynamically miscible by introducing attractive interactions, such as hydrogen bonds (16-18), between them. This method has proven useful for enhancing miscibility in flexible-flexible blends. Even more useful (stronger) interactions may be ionic interactions, such as ion-ion and ion-dipole interactions various studies on ionomer blends have demonstrated that ionic interactions can enhance the miscibility of otherwise immiscible polymer pairs (79). Polymers studied include polystyrene, poly(ethyl acrylate), poly(ethyleneimine), nylon, and poly (ethylene oxide) (20-22). 

In the case of the p-sulfonated polystyrene ionomer, the ion pairs are at the same distance from the backbone as in thep-carboxylated polystyrene ionomer. As was mentioned above, however, the ionic interaction in the sulfonated ionomer is stronger than that in the carboxylated ionomer. Thns, at the identical ion content, the modulus-temperature curves show longer ionic platean, and the volume fraction of reduced mobility regions for the p-sulfonated ionomer is smaller than for the p-carboxylated ionomer (103), leading to less clnstering for the p-snlfonated ionomers. 

For systems of rigid poly diacetylenes with functional or ionic side groups and car-boxylated or sulfonated polystyrene or sulfonated polyester-urea urethanes, molecular composites could be achieved by ionic interactions [51]. The blends exhibited no microphase separation and the miscibility on a molecular length scale was proven by infrared spectroscopic, dynamic mechanical and differential scanning calorimetry analysis. The molecular reinforcement amounted to up to 1 order of magnitude in compliance with a Halpin Tsai description and was achieved by only a few weight percent of the rigid compound. 

Higashihara, T., Takahashi, A., Tajima, S. et al. (2010) Synthesis of block copolymers consisting of poly(3-hexylthiophene) and polystyrene segments via ionic interaction and their self-assembly behavior. Polymer Journal, 42,43-50. 

Orler, E. B., Moore, R. B. Influence of ionic interactions on the crystallization of lightly sulfonated syndiotactic polystyrene ionomers. Macromolecules, 27, 4774-4780 (1994). 

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