Synthesis, Characterization and Thermolysis of Hyperbranched Homo- and Amphiphilic Co-Polymers Prepared Using an Inimer Bearing a Thermolyzable Acylal Group Maria Rikkou-Kalourkoti, † Krzysztof Matyjaszewski, ‡ and Costas S. Patrickios †, * † Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus ‡ Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States ABSTRACT: Degradable hyperbranched polymers were synthesized via self-condensing atom transfer radical copolymerization of methyl methacrylate (MMA) with a novel inimer bearing a thermolyzable acylal group. This inimer was 1-(2- bromoisobutyryloxyl)ethyl methacrylate (BIB1EMA) and was synthesized in a one-step reaction between 2-bromoisobutyric acid and vinyl methacrylate at 40% yield. The inimer was subsequently used for the preparation of three degradable hyperbranched homopolymers of MMA (monomer conversion ∼80%) with molecular weights in the range from 36 000 to 51 000 g mol -1 synthesized using initial MMA-to-inimer molar ratios between 25 and 100. The inimer was also used for the preparation of two degradable hyperbranched amphiphilic copolymers of MMA and 2-(dimethylamino)ethyl methacrylate (DMAEMA) with an MMA hydrophobic hyperbranched core and different compositions, 10 and 38 mol % DMAEMA, afforded by changing the relative loadings in the two comonomers. Both hyperbranched amphiphilic copolymers were soluble in THF: water mixtures with up to 50% w/w water content, whereas they precipitated at higher water contents. All hyperbranched (co)polymers were thermolyzed in a vacuum oven at 200 °C within 24-56 h. The molecular weights of the thermolysis products were consistent with the inimer content and the complete thermolysis of the hyperbranched (co)polymers. Hyperbranched polymers of MMA, also prepared in this investigation, but using a nondegradable inimer, isomeric to BIB1EMA, 2-(2-bromoisobutyryloxyl)ethyl methacrylate (BIB2EMA), did not present any reduction in their molecular weight when subjected to the same thermolysis conditions as those applied for the degradable hyperbranched polymers (200 °C, ∼24 h). ■ INTRODUCTION Hyperbranched polymers represent an interesting macro- molecular architecture, with features intermediate between those of linear polymers and polymer networks. Similar to polymer networks, hyperbranched polymers are highly branched, but yet soluble as linear polymers. As mentioned in the review by Hult et al., 1 hyperbranched polymers were first reported by DuPont in an effort to replace dendrimers, also highly branched polymers but of highly ordered structure which are difficult and time-consuming to prepare and, therefore, less appropriate for industrial use. The high degree of branching of hyperbranched polymers is responsible for their unique physical properties, such as their compact shape resulting in low viscosity in solution and in the molten state compared to their linear counterparts, 2,3 and their large number of functional groups on their periphery. Because of these properties, hyperbranched polymers 4-6 find numerous applications in surface modification, 7-12 in coatings, 13-16 in controlled drug and gene delivery, 17,18 in nonlinear optics, 19,20 and can form the cross-linking nodes in designer’s hydrogels. 21-25 As mentioned before, the main advantage of hyperbranched polymers compared to dendrimers is their facile synthesis. Hyperbranched vinyl polymers can be synthesized following three different techniques: (a) copolymerization of monovinyl with small amounts of di- or multivinyl monomers, (b) polymerization of di- or multivinyl monomers with a large excess of initiator, and (c) self-condensing vinyl polymerization of AB* initiator-monomers, known as inimers. Whereas the first two techniques can be applied using either controlled or conventional polymerization methods, the third technique requires the use of a controlled polymerization method. Of special interest are the different controlled radical polymer- ization methods which have been used for the preparation of hyperbranched polymers applying all three above-mentioned techniques, including atom transfer radical polymerization (ATRP), 26-32 reversible addition-fragmentation chain transfer polymerization (RAFT), 33-40 and nitroxide-mediated radical polymerization (NMP). 41-44 Furthermore, controlled/“living” ionic polymerization methods have also been used for the synthesis of hyperbranched polymers, including “living” cationic polymerization 45 and group transfer polymerization (GTP). 46-49 In the present study, self-condensing vinyl copolymerization of a degradable inimer bearing a thermally labile acylal group Received: September 5, 2011 Revised: December 27, 2011 Published: January 19, 2012 Article pubs.acs.org/Macromolecules © 2012 American Chemical Society 1313 dx.doi.org/10.1021/ma202021y | Macromolecules 2012, 45, 1313-1320