Polymer Communication Novel moisture-sensitive shape memory polyurethanes containing pyridine moieties Shaojun Chen, Jinlian Hu * , Chun-wah Yuen, Laikuen Chan Institute of Textiles and Clothing, Hong Kong Polytechnic University, Hung Hom, Hong Kong, China article info Article history: Received 6 May 2009 Received in revised form 19 June 2009 Accepted 21 July 2009 Available online 24 July 2009 Keywords: Shape memory Polymer Supramolecular structure abstract In this communication, novel moisture-sensitive shape memory polyurethane (SMPU) was synthesized from 1,6-hexamethylene diisocyanate (HDI) and N,N-bis(2-hydroxylethyl) isonicotinamide (BINA) and 1,4-butanediol (BDO). Results show that the BINA based SMPUs have excellent moisture absorption properties which are not only influenced by the temperature, but also by the relative humidity (RH). As a result, high strain recovery with fast recovery speed is obtained after immersion in the moisture condition for a short time. FT-IR spectra provide a proof to the mechanism of moisture-sensitive SME which is based on the dissociation or disrupt of hydrogen bonding in the pyridine ring induced by moisture absorption. Thus, the strain recovery is achieved in the moisture-sensitive SMPUs by decreasing the glass transition temperature (T g ) below ambient temperature without external heating. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Shape memory polymers (SMPs), which are known to have the ability of memorizing temporary shapes and recovering their permanent shapes upon external stimulation [1], are elastic networks equipped with suitable stimuli-sensitive switches; and their shape memory effect (SME) may be induced by temperature, light, pH, etc. [2]. For example, in the thermal-induced SMPs, thermal reversible phase serving as a ‘‘switch’’ is either a glass transition or a melting transition [3]. In the light-induced SMPs, stimulation has been realized by incorporation of reversibly reacting molecular switches [4]. In addition, SMEs are also observed in the polymer blends consists of immiscible elastomer and switch polymer [5]. Therefore, various SMEs including moisture-sensitive SME are expected to be achieved in elastic networks by incorpo- rating suitable switches including molecular switches, switch segment and switch polymer. Now, the most attractive SMPs are still thermal-induced SMPs due to their wide availability and broad possible applications [5]. The shape memory behavior of thermal-induced SMPs is gener- ally triggered by heating the specimen above the melting point (T m ) of the crystalline soft segment or glass transition tempera- ture (T g ) of amorphous soft segment [6,7]. However, sometimes, the application temperature is limited to a low temperature range, e.g. in the biomedical applications. Thus, the prestored strains are expected to be recovered without external heating. Recently, water-driven SMPU programmable shape memory behavior was observed in the shape memory polyurethane (SMPUs) since the T g of SMPU was found to reduce dramatically after immersing in water. Further investigation shows that the hydrogen bonding is the key player behind the water-driven SME in SMPUs; and water or moisture absorbed in the polymer plays a main role in the shape recovery process [8–10]. However, their shape recovery is limited to water; and the strain recovery could not be triggered by moisture due to their very low moisture absorption. In an earlier communication [11], we reported that hydrogen- bonded supramolecular polyurethane networks containing pyri- dine moieties could be used as shape memory materials. It was confirmed that the movement of polymer chain of pyridine con- taining polyurethane (PUPy) was influenced greatly by the hydrogen bonding; and the dissociation of hydrogen bonding in the pyridine ring resulted in the strain recovery in the PUPys. In addition, the humidity absorption of poly(vinyl pyridine) was observed to be a few times high during the investigation of humidity and solvent effects of polythiophene and poly(vinyl pyridine) by Jaczewska et al. [12]. It was suggested that the pyridine unit was responsive to the moisture absorption. Thus, the moisture-sensitive SME should be expected in the SMPU con- taining pyridine moieties since the pyridine based molecular ‘‘switches’’ shows response to the moisture. In the present study, the novel moisture-sensitive SMPUs based on pyridine derivative: N,N-bis(2-hydroxylethyl) isonicotinamide (BINA) was synthesized for the first time. * Corresponding author. Tel.: þ86 852 2766 6437; fax: þ86 852 2775 1432. E-mail address: tchujl@inet.polyu.edu.hk (J. Hu). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2009.07.031 Polymer 50 (2009) 4424–4428