Synthesis of a New Hyperbranched, Vinyl Macromonomer Through the use of Click Chemistry: Synthesis and Characterization of Copolymer Hydrogels with PEG Diacrylate David K. Wang, 1,2 David J. T. Hill, 3 Firas A. Rasoul, 1,2 Andrew K. Whittaker 1,2 1 The Australian Institute for Bioengineering and Nanotechnology (AIBN), Corner College and Cooper Roads (Bldg 75), The University of Queensland, Brisbane, QLD 4072, Australia 2 Centre for Advanced Imaging (CAI), The University of Queensland, Brisbane, QLD 4072, Australia 3 The School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia Correspondence to: F. A. Rasoul (E-mail: f.rasoul@uq.edu.au) Received 17 October 2011; accepted 24 November 2011; published online 21 December 2011 DOI: 10.1002/pola.25874 ABSTRACT: A new biodegradable, water-soluble macromono- mer based on the commercial hyperbranched polyester Boltorn V R H20 has been synthesized through the use of click chemistry. The macromonomer was developed with the aim of being injected with a comacromonomer, poly(ethylene glycol) (PEG) diacrylate, for in situ copolymerization to form biode- gradable polymer hydrogels. Copolymer hydrogels were pre- pared from the macromonomer and PEG diacrylate (FW 700) by free radical copolymerization. A degree of phase separation of the hydrogels was observed during polymerization and with increasing incorporation of the Boltorn macromonomer an increasing tendency for the formation of macropores was observed. The swelling ratios of the gels in water and phos- phate buffered saline solution, PBS, all increase with increas- ing Boltorn macromonomer concentration, as did the penetrant diffusion coefficients and the degradation rate in PBS. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 1143–1157, 2012 KEYWORDS: biodegradable; degradation; hydrogels; hyper- branched; morphology; phase separation; structure–property relations; swelling; synthesis INTRODUCTION Hydrogels have been long recognized as val- uable vehicles for delivery of bioactive molecules in medicine and dentistry due to their inherent physical and chemical properties. As drug delivery devices, the main role of the hydrogel is to provide a safe passage for the transfer of bio- active molecules through inhospitable physiological condi- tions to a particular treatment site. 1 In this respect, hydro- gels can be designed to provide their own therapeutic effect or they can be biologically inert and release an encapsulated drug by diffusion or they may be biodegradable in order to release any incorporated bioactive molecules through the breakdown of the hydrogel network. 2 For some treatment strategies, the hydrogel has to be formed at the treatment site, as is the case in the treatment of perio- dontitis, or inflammatory gum disease, for example, where the hydrogel must be formed within the defect in the alveo- lar bone around a tooth. 3 Here an aqueous solution of a drug and a polymerizable monomer, or macromonomer, is injected into the defect and polymerized in place to form a hydrogel that will completely fill the space within the defect. There are several requirements of the monomer or macro- monomer for such applications. Besides the requirement to be water soluble, it must be biocompatible so that it does not promote any inflammatory response from the surround- ing tissue. In addition, polymerization should be relatively fast but the accompanying exotherm should be small in order to avoid necrotic damage to the surrounding tissue. The latter requirement can be addressed through the use of macromonomers rather than monomers. It is also preferable for the hydrogel to be biodegradable over a defined period of time to preclude the need for later ex-plantation of the gel. The water uptake by the hydrogel should also be tunable for the particular application so that the rate of release of the drug can be controlled. It was with these requirements in mind that a new water-soluble macromonomer, based on the commercially available hyperbranched polyester Boltorn V R H20 (BH20), was synthesized and the properties of hydro- gels formed through its copolymerization with poly(ethylene glycol) diacrylate (PEGDA) were investigated. Poly(ethylene oxide), PEO, is well known to be biologically inert, 2 and it has been used for a wide variety of medical applications for more than 50 years. For example, radiation crosslinked PEO hydrogels have been thoroughly researched and used in many drug delivery devices. 2,4 However PEO is Additional Supporting Information may be found in the online version of this article. V C 2011 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1143–1157 1143 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE