Polymer Blending through Host-Guest Interactions Marco Dionisio, † Lucia Ricci, ‡ Giulia Pecchini, † Daniele Masseroni, † Giacomo Ruggeri, ‡ Luigi Cristofolini, § Enrico Rampazzo, ⊥ and Enrico Dalcanale* ,† † Dipartimento di Chimica and INSTM, UdR Parma, Universita ̀ di Parma,Viale delle Scienze 17/A, 43124 Parma, Italy ‡ Dipartimento di Chimica e Chimica Industriale and INSTM, UdR Pisa, Universita ̀ di Pisa, Via Risorgimento 35, 56126 Pisa Italy § Dipartimento di Fisica, Universita ̀ di Parma, Viale delle Scienze 7/A, 43124 Parma, Italy ⊥ Dipartimento di Chimica “G. Ciamician” and INSTM, UdR Bologna, Universita ̀ di Bologna, Via Selmi 2, 40126 Bologna, Italy * S Supporting Information ABSTRACT: In this work, a supramolecular approach, based on molecular recognition, was used to direct the blending of immiscible polymers toward compatibility and even molecular miscibility. A slight modification of the two immiscible polymers polystyrene (PS) and poly(butyl methacrylate) (PBMA), with the introduction of the two recognition groups tetraphosphonate cavitand (HOST) and methylpyridinium (GUEST), respectively, led to the formation of compatible mixtures between them, characterized by a single T g and by an homogeneous texture at the surface level, as evidenced by AFM measurements. The energetically favorable host-guest interactions among polymeric chains overcome their repulsive interfacial energy, leading to the suppression of phase segregation at the level of material. The complexation between PS-HOST and PBMA-GUEST copolymers has been demonstrated to be reversible by the action of a specific external stimulus in the form of guest exchange with the competitive N-methylbutyl ammonium chloride. T he merging of polymer science with supramolecular chemistry has generated a new, thriving research field, broadly defined as supramolecular polymer chemistry. 1 The positive results of this merging is demonstrated by the appearance of supramolecular polymers presenting unique mechanical, 2 electronic, 3 biological 4 and self-healing proper- ties. 5 The supramolecular approach 6 is very attractive for the design of adaptive materials 7 featuring reversibility and responsiveness to external stimuli. Molecular recognition is the most sophisticated form of weak interaction in terms of precise responsiveness, since it requires a well-defined arrange- ment of complementary noncovalent interactions to operate at its best. For polymer science, the macroscopic expression of molecular recognition is the next step necessary to harness its full potential. 8 In this regard, the recent work of Harada and co- workers 9 on the selective gel formation through molecular recognition is groundbreaking. They nicely showed that molecular recognition events at the molecular level produce specific and controlled macroscopic responses. Polymer blending is a long-standing issue in polymer science, 10 with relevant practical implications. The blending of polymers is an economically attractive route to develop new materials that combine the desirable properties of more than one polymer. The microscopic segregation observed in most polymer blends, even for structurally related polymers, jeopardizes their use. The covalent introduction of compatibil- izers or reactive functional groups in the side chain of the polymers are usually employed to minimize the interfacial energy and, in turn, the phase segregation. Recently, Zimmer- man proposed the use of hydrogen bonding to overcome the miscibility problems in polymer chemistry. 11 Introduction of guanosine urea (UG) and 2,7-diamido-1,8-naphthyridine (DAN) in the side chain of poly(butyl methacrylate) and polystyrene, respectively, led to the formation of a polymer blend. This is due to the formation of an heterocomplex between the two recognition units even at low molar content. Interestingly, this approach was further improved by introduc- ing redox sensible molecular recognition units for the control of supramolecular polymer network. 12 More recently Hawker and Kramer introduced 2-ureido-4[1H]-pyrimidinone (UPy) and 2,7-diamido-1,8-naphthyridine (Napy) as chain end groups in Received: July 17, 2013 Revised: November 25, 2013 Published: January 8, 2014 Article pubs.acs.org/Macromolecules © 2014 American Chemical Society 632 dx.doi.org/10.1021/ma401506t | Macromolecules 2014, 47, 632-638