A Thermodynamic Analysis of Specific Interactions in Blends of Poly(styrene-co-N,N-dimethylacrylamide) and Poly(styrene-co-acrylic acid). Screening and Self-Association Effects ASSIA SIHAM HADJ HAMOU, 1 KHALED ELMILOUDI, 1,2 SAID DJADOUN 1 1 Laboratoire des Mate ´riaux Polyme `res, Faculte ´ de Chimie, Universite ´ des Sciences et de la Technologie Houari Boumediene, B.P. 32, El Alia, Algiers 16111, Algeria 2 Faculte ´ des Sciences et Sciences de l’Inge ´nieur, Universite ´ Hassiba Benbouali, B.P. 151, Chlef, Algeria Received 7 May 2009; revised 6 July 2009; accepted 10 July 2009 DOI: 10.1002/polb.21803 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: In a first step of this contribution, the observed glass transition tempera- ture-composition behavior of miscible blends of poly(styrene-co-N,N-dimethylacryla- mide) (SAD17) containing 17 mol % of N,N-dimethylacrylamide and poly(styrene-co- acrylic acid) (SAA18, SAA27, and SAA32) containing increasing acrylic acid content, are analyzed according to theoretical approaches. Both Kwei and Brostow equations describe well the experimental data though better fits were obtained with the Bros- tow’s approach. The specific interactions involved in these systems are a combination of intra and interassociation hydrogen bonding. The positive deviation from the lin- ear mixing rule of T g -composition observed within the SAA18þSAD17 blend system, indicates that interassociation interactions are prevailing. More pronounced intra- association interactions within the SAA32þSAD17 blend system led to a large nega- tive deviation while a fine balance is established between these two types of interac- tions within the SAA27þSAD17 blend. A thermodynamic analysis was carried out according to the Painter-Coleman association model. The miscibility and phase behavior of SAD17þSAA18 and SAD17þSAA27 blends are well predicted. However, this model predicts a partial miscibility of SAD17þSAA32 system. Finally, the fitting parameter free method developed by Coleman to predict the T g -composition behavior is applied. This method predicts fairly well the evolution trend of experimental T g s of the SAA18þSAD17 and SAA27þSAD17 blend systems. However, the compositional dependence of SAA32þSAD17 blend T g was not predictable by this method. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2074–2082, 2009 Keywords: blends; hydrogen bonding; miscibility; phase behavior; poly(styrene-co- 4-vinylpyridine); poly(styrene-co-acrylic acid); thermodynamics INTRODUCTION Blending two or more polymers still remains a convenient approach to the development of new materials. 1–3 The properties of these multicompo- nent systems could be tuned by simply adjusting the mixture composition. However, because of thermodynamic reasons, most polymer pairs do not mix. The energy of interaction between unlike macromolecular segments should be negative to ensure one phase system. So, very few miscible blends of nonpolar polymers are known. Journal of Polymer Science: Part B: Polymer Physics, Vol. 47, 2074–2082 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: S. Djadoun (E-mail: matpolylab@ yahoo.fr) 2074