Synthesis and Spontaneous Polymerization of Oligo(ethylene glycol)-Conjugated Benzofulvene Macromonomers. A Polymer Brush Forming a Physical Hydrogel Andrea Cappelli,* ,† Simone Galeazzi, † Germano Giuliani, † Maurizio Anzini, † Mario Grassi, ‡ Romano Lapasin, ‡ Gabriele Grassi, § Rossella Farra, | Barbara Dapas, | Marianna Aggravi, ⊥ Alessandro Donati, ⊥ Lucia Zetta, # Antonella Caterina Boccia, # Fabio Bertini, # Filippo Samperi, ∇ and Salvatore Vomero † Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug DiscoVery and DeVelopment, UniVersita ` degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Department of Chemical Engineering DICAMP, UniVersity of Trieste, Piazzale Europa 1, I-34127, Trieste, Italy, Department of Life Sciences, UniVersity of Trieste, Via Giorgeri 7, I-34127, Trieste, Italy, Department of Clinical, Morphological and Technological Sciences, UniVersity Hospital of Cattinara, Strada di Fiume 447, I-34149, Trieste, Italy, Dipartimento di Scienze Chimiche e dei Biosistemi, UniVersita ` degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Istituto per lo Studio delle Macromolecole (CNR), Via E. Bassini 15, 20133 Milano, Italy, and Istituto di Chimica e Tecnologia dei Polimeri (CNR), Viale A. Doria 6, 95125 Catania, Italy ReceiVed October 30, 2008; ReVised Manuscript ReceiVed February 2, 2009 ABSTRACT: Two methyl end-capped oligo(ethylene glycol) esters (1a,b) of benzofulvene derivative BF1 were synthesized and induced to polymerize spontaneously by solvent removal to give poly-1a,b showing both NMR and absorption/emission spectra very similar to those of poly-BF1. Poly-1a,b showed relatively high molecular weight and the tendency to depolymerize to a different degree as a function of the temperature in the presence of solvents, while they exhibited appreciable stability in the absence of solvent. Poly-1b, bearing a longer oligo(ethylene glycol) side chain, featured an amphiphilic character and interacted with a number of organic solvents to produce transparent gel aggregates, and with water to give a quite compact physical gel. Rheological studies performed on the hydrogel suggested strong gel characteristics and the combination of rheology and NMR transverse relaxation measurements allowed the pore size distribution in the hydrogel to be defined. Finally, biological studies performed with poly-1b solutions showed neither cytotoxicity nor cell viability impairment suggesting potential biocompatibility features for this polymer. In conclusion, poly-1b can be considered a promising polymer for the preparation of hydrogels potentially useful in a range of biological and biotechnological applications such as drug delivery, molecular recognition, biosensing, protein and DNA separation, micro- and nanofluidics, as well as tissue engineering. 1. Introduction Poly(ethylene glycol) (PEG) is one of the most frequently studied and used polymers in the pharmaceutical field because of its various valuable features. Indeed, PEG is an inexpensive, water-soluble, biocompatible, and FDA-approved polymer. In fact, PEG can confer solubility in the physiological environment and prevent the interaction with plasma proteins and cells, and is therefore used as shielding agent for in vivo delivery of several bioactive compounds. 1,2 Moreover, PEG is used to shield drug carriers such as liposomes and nanoparticles. 3,4 A recent approach to the covalent conjugation of PEG (permanent PEGylation) with carrier polymeric matrices is represented by the polymerization of the preformed PEG macromonomers such as oligo(ethylene glycol) methacrylate (OEGMA). 5-11 In particular, Ishizone and co-workers used anionic polymerization of methacrylates showing short oligo- (ethylene glycol) alkyl ether side chains to obtain poly[oligo- (ethylene glycol) alkyl ether methacrylate]s characterized by different water solubility and lower critical solution temperature (LCST) depending on both the length and the terminal sub- stituent of the hydrophilic OEG side chains. 9 On the other hand, atom transfer radical polymerization (ATRP) of a commercially available OEGMA derivative was performed in aqueous media under remarkably mild conditions to obtain OEGMA polymers showing low polydispersities. 10,11 Moreover, ATRP of 2-(2- methoxyethoxy)ethyl methacrylate with OEGMA gave poly(MEO 2 MA-co-OEGMA) copolymers showing controlled chain length, narrow molecular weight distribution, interesting solution properties in water, and tunable thermosensivity. 6 Finally, homo- or copolymerization of macromonomers (the so- called “grafting through” method) has been used in the synthesis of cylindrical polymer brushes, which have received a great deal of attention in very recent times. 12 We recently reported that the spontaneous polymerization of benzofulvene derivative BF1 (Scheme 1) gave a new hydro- phobic polymer (poly-BF1) showing vinyl structure stabilized by aromatic stacking interactions. 13,14 Poly-BF1 obtained by spontaneous polymerization (poly-BF1-SP) shows very high molecular weight, high solubility in the most common organic solvents, a thermoreversible polymerization/depolymerization, and the tendency to give fractal-like macromolecular ag- gregates. 14 * Corresponding author. Telephone: +39 0577 234320. Fax: +39 0577 234333. E-mail: cappelli@unisi.it. † Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Universita ` degli Studi di Siena. ‡ Department of Chemical Engineering DICAMP, University of Trieste. § Department of Life Sciences, University of Trieste. | Department of Clinical, Morphological and Technological Sciences, University Hospital of Cattinara. ⊥ Dipartimento di Scienze Chimiche e dei Biosistemi, Universita ` degli Studi di Siena. # Istituto per lo Studio delle Macromolecole (CNR). ∇ Istituto di Chimica e Tecnologia dei Polimeri (CNR). 2368 Macromolecules 2009, 42, 2368-2378 10.1021/ma802429g CCC: $40.75  2009 American Chemical Society Published on Web 03/09/2009