Intermacromolecular complexation because of specific interactions 11. Ionic interaction complexation and its comparison with hydrogen-bonding complexation

Abstract

The ionic interaction complexation between metal carboxylated polystyrene ionomers and poly(butyl methacrylate-co-vinyl pyridine) (BVP) in both solution and bulk was studied by viscometry, laser light scattering (LLS) and differential scanning calorimetry (DSC) and compared with that between BVP and carboxylated polystyrene (CPS), in which the interacting groups are in acid form. The results show that both kinds of complexation strongly depend on the level of the specific interaction and give rise to an increased hydrodynamic radius over the component polymer coils. However, the ionic interaction complexation generally results in an increased viscosity in the solution and almost always exhibits two glass transition temperatures (T_gs), in contrast, the hydrogen bonding complexation leads to a decreased viscosity and only one T_g. The different behavior is attributed to the difference in spatial distributions of the interacting sites in the complexes.

Introduction

Intermacromolecular complexation between unlike chains through secondary bonding or specific interactions has aroused considerable interests experimentally and theoretically for years [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], because of its significant importance in understanding some biological processes and self-assembly of molecules, as well as in developing new functional assembled materials. The development made on H-bonding complexation in the last decade has been reviewed quite recently by Jiang et al. [1]. It has been demonstrated that H-bonding complexation in solution generally shows a decreased viscosity compared to the expected value by additivity law and only one T_g in bulk. By laser light scattering (LLS), we found that H-bonding complexation usually leads to an increase in hydrodynamic radius and narrowing in hydrodynamic radius distribution compared to the component polymer coils in solution [1], [2], [3], [4]. On the other hand, in the literature, attention has also been paid to the intermacromolecular complexation caused by the ionic interaction [4]. The complexation of sulfonated random ionomers such as those based on poly(ethylene-co-propylene-co-ethylidiene nobornene) (SEPDM) [6], [7], [8] and poly(phenylene oxide) (SPPO) [9], [10] and polystyrene (SPS) [9], [10], [11] with pyridine-containing random copolymer, i.e. poly(styrene-co-4-vinylpyridine) (SVP) in nonpolar and polar solvents were investigated by viscometry in several laboratories [6], [7], [8], [9], [10], [11]. MacKnight et al. [12] assessed the complexation between SPS and poly(ethyl acrylate-co-4-vinylpyridine) (EVP) in solution by means of the fluorescent probe technique. These studies reported that the ionic intercomponent complexation in bulk often show two glass transition temperatures (T_gs) in bulk, and an increase in viscosity in solution. Similar behavior has been observed for the blends containing ionic interaction groups located at the chain ends exclusively leading to non-covalent block or graft architectures [13], [14], [15], [16], [17], [18], [19]. Our investigations on the blends of triblock ionomers based on poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) and pyridine-unit-containing copolymers indicate the complexation between the block ionomer and the copolymer leading to complex aggregates [20], [21].

The difference between the two kinds of complexation has puzzled us for a long time. As both the ionic-interaction complexation and H-bonding complexation are dependent on many factors such as the molecular weight and its distribution of the component polymers, the level of the interaction, the solvent used, making a comparison by using two polymer blends differing only in the type of the specific interactions is not easy. Fortunately, we accumulated some data on complexation between the carboxylated polystyrene (CPS) and pyridine-containing copolymers because of H-bonding [2], [3]. Parallel to the previous work, in this article, we report the complexation between CPS ionomers and BVP, due to ionic interactions. The blend systems used in the two studies are similar in chemistry. The main difference is that the interacting sites in CPS are carboxylic acid and in the ionomers the corresponding metal ions. Based on the results of the two systems, we attempt to explore the origin of the difference and correlate it with the complex structure.