658 Macromolecular Research, Vol. 17, No. 9, pp 658-665 (2009) Dynamic Mechanical and Morphological Studies of Styrene-co-Methacrylate and Sulfonated Polystyrene Ionomers Containing Aliphatic Dicarboxylate Salts Mohammad Luqman and Joon-Seop Kim* Department of Polymer Science & Engineering, and BK21 Education Center of Mould Technology for Advanced Materials & Parts, Chosun University, Gwangju 501-759, Korea Kwanwoo Shin Department of Chemistry, Interdisciplinary Program of Integrated Biotechnology, Sogang University, Seoul 121-742, Korea Received November 17, 2008; Revised January 20, 2009; Accepted January 21, 2009 Abstract: This study examined the effects of the sodium salts of aliphatic dicarboxylic acids (DCAs) on the dynamic mechanical properties and morphology of two sets of poly(styrene-co-sodium methacrylate) (MNa) and poly(styrene-co-sodium styrenesulfonate) (SNa) ionomers. When the DCA content was relatively low, the ionic moduli of the MNa and SNa ionomers increased but the matrix and cluster glass transition temperature (T ) did not change significantly. The increasing ionic modulus was almost independent of the type of the ionic groups of the ionomer, and the chain length of DCAs. When a large amount of the sodium succinate (DCA4) was added to the MNa and SNa ionomers, the ionic moduli of the two ionomers increased strongly but the matrix and cluster T ’s increased slightly and significantly, respectively. In the case of sodium hexadecanedioate (DCA16), DCA16 increased the ionic moduli of the two ionomers. The addition of DCA16 changed the matrix and cluster T ’s of the MNa ionomer slightly, but decreased the cluster T of the SNa ionomer significantly with no change in the matrix T . In addition, the DCA-containing ionomers showed an X-ray diffraction peak indicating the presence of ordered domains of DCAs in the ionomers. Hence, DCA4 acts mainly as a reinforcing filler in MNa and SNa systems. In the case of DCA16, it initially behaved like a filler but also functioned as a preferential plasticizer for the clusters at high content. Keywords: ionomers, aliphatic dicarboxylic acids, phase-separation, fillers, plasticization. Introduction Ionomers are polymeric materials containing a small amount of ionic groups (< 15 mol%) embedded in a rela- tively non-polar polymer matrix. 1 The presence of the ionic groups in the polymer matrix generally causes ion aggrega- tion. The interpretation of the mechanical properties and morphology of random ionomers can possibly be done with the help of the multiplet-cluster or so-called Eisenberg-Hird- Moore (EHM) model. 2 The ionic aggregates, i.e. multiplets, cause the restriction of the mobility of the polymer chains emanating from the multiplets. As the ion content increases, the partially restricted mobility regions begin to overlap. Eventually, the restricted mobility regions form sufficiently large domains, the so-called “clusters”. At this point, the ionomer starts to show characteristics of phase-separated materials such as a second glass transition at much higher temperatures, compared to the glass transition temperature (T g ) of the matrix regions. As the ion content increases fur- ther, the ionomer undergoes a transition from a matrix-dom- inant material to a cluster-dominant material. Since 1970s, the mechanical properties and morphology of ionomers have been studied extensively by varying a number of factors, including the type, size, position of ionic units, the degree of neutralization, and the type of plasticizers, additives and neutralizing agents. 1 Plante et al. performed dynamic mechanical studies on matrix-dominant and cluster-dominant carboxylated poly- styrene (PS) ionomers blended with chemically identical mono- and bi-functional styrene oligomers. 3 The mono- functional oligomers were found to plasticize both the matrix and cluster regions of the ionomers. In the case of the bi- functional oligomers, however, the oligomers in the matrix- dominant ionomers showed anti-plasticization behavior at low oligomer contents. However, in the cluster-dominant system, the oligomers were phase-separated because of the insufficient amounts of non-ionic polymer matrix. In a sub- sequent study, Plante and Bazuin investigated the effects of *Corresponding Author. E-mail: joon@mail.chosun.ac.kr