Specific Interactions in Poly(styrene-co-2-Hydroxyethyl acrylate)/Poly(styrene-co-N, N-dimethylacrylamide) Systems Fatiha Bouzouia, Said Djadoun Laboratoire des Mate ´riaux Polyme `res, Faculte ´ de Chimie, Universite ´ des Sciences et de la Technologie Houari Boumediene, BP 32, El Alia, Algiers, Algeria 1611 Received 26 January 2008; accepted 28 June 2008 DOI 10.1002/app.28905 Published online 15 September 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Amphiphilic copolymers of poly(styrene-co- 2-hydroxyethyl acrylate) (SHEA) and poly(styrene-co-N, N- dimethylacrylamide) (SAD) of different compositions were prepared by free radical copolymerization and character- ized by different techniques. Depending on the nature of the solvent and the densities of interacting species incorpo- rated within the polystyrene matrices, novel materials as blends or interpolymer complexes with properties different from those of their constituents were elaborated when these copolymers are mixed together. The specific interpolymer interactions of hydrogen bonding type and the phase behavior of the elaborated materials were investigated by differential scanning calorimetry (DSC) and Fourier trans- form infra red spectroscopy (FTIR). The specific interactions of hydrogen bonding type that occurred within the SHEA and within their blends with the SAD were evidenced by FTIR qualitatively by the appearance of a new band at 1626 cm 1 and quantitatively using appropriate spectral curve fitting in the carbonyl and amide regions. The variation of the glass transition temperature with the blend composition behaved differently with the densities of interacting species. The thermal degradation behavior of the materials was studied by thermogravimetry. V V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3574–3581, 2008 Key words: poly(styrene-co-2-hydroxyethyl acrylate); poly(styrene-co-N, N-dimethyl acrylamide); interpolymer complexes; specific interactions; FTIR; DSC INTRODUCTION Poly(2-hydroxyethyl acrylate) is an acrylic polymer that behaves as a rubber at room temperature. Because of its high capacity of water uptake, it may form hydrogels with good biological acceptance. Although the tendency of this polymer to replace poly(2-hydroxyethyl methacrylate) has been reported in many instances, particularly to simulate the me- chanical properties of soft tissues without loosing its water sorption capacity, 1 the mechanical properties of this polymer are rather poor and need however to be improved. Khutoryanski and coworkers. 2 have synthesized amphiphilic copolymers based on 2-hydroxyethyl ac- rylate and vinyl butyl ether and studied their inter- actions with poly(carboxylic acids). Hybrid networks have been previously prepared from hydrophobic polymers such as polystyrene. 3 Rodriguez Herman- dez et al. 4 have recently reported the preparation of poly(2-hydroxyethyl acrylate)-silica nanocomposites by sol-gel process that led to a hybrid material with improved mechanical properties. Although Hydrogels made of single polymers have been used in various applications particularly in drug delivery, it is rather rare for a single poly- mer to satisfy simultaneously the desired properties, cost, and performance. Because blending is a simple method expected to lead to combined properties of polymers of different nature, different kinds of het- erogeneous hydrogels have been investigated. 5 Among the various hydrogel networks that may be elaborated, physical hydrogels are networks formed by physical interactions involving low energy. Such materials can be prepared by complex- ation through specific interactions of hydrogen bonding type between polymeric chains without addition of any crosslinkers. It is well known that depending on the nature of solvent used, polymer complexes are formed only when polymer–polymer interactions that occurred between the components of the mixture are stronger than polymer-solvent interactions and exceed a cer- tain level. Such strong hydrogen bonding interac- tions between polymers are expected to increase the thermal stability of the resulting material. Poly(N, N-dimethylacrylamide) is a typical proton acceptor polymer that formed interpolymer com- plexes through hydrogen bonding with poly(2- hydroxypropyl methacrylate) 6 and other polymers Journal of Applied Polymer Science, Vol. 110, 3574–3581 (2008) V V C 2008 Wiley Periodicals, Inc. Correspondence to: S. Djadoun (matpolylab@yahoo.fr).