Poly(styrene-graft-hyperbranched polyglycidol): synthesis and solution behavior of a hyperbranched polyelectrolyte† Andrew Goodwin, * a Sachin Bobade, a Nam-Goo Kang, a Durairaj Baskaran, a Kunlun Hong b and Jimmy Mays * ac This work presents a three-step synthetic procedure to obtain a hypergrafted copolymer composed of a glassy backbone with flexible branched pendant segments. The desired hypergrafted structure was obtained by using a polyfunctional macroinitiator, linear poly(styrene- co-4-hydroxystyrene), to yield polystyrene-graft-hyperbranched polyglycidol with randomly placed branch junctions. Atomic force microscopy, dynamic light scattering, and viscometry probed the aggregation and viscometric behavior of the polymer in DMF and DMF–LiBr solutions. The polymer exhibited polyelectrolyte behavior demonstrated by a large increase in the reduced viscosity prior to neutralization with LiBr salt. Additionally, conformational changes were observed by dynamic light scattering in both the average aggregate size and aggregate population with the addition of LiBr salt. The synthesis of hyperbranched polyglycerols (hbPG) has been extensively investigated in order to discover a controlled poly- merization method yielding high molecular weights with uniformly branched dendritic structures. 1–4 The primary synthetic approach adopted to date has been “ring-opening multibranching polymerization” (ROMBP) of latent cyclic AB m monomers, which has thrived due to its advantage of elimi- nating multi-step reactions and multiple purication steps usually needed in the synthesis of polyether dendritic systems. 2,4 The use of ROMBP to synthesize hyperbranched polymers has resulted in products with considerably narrower polydispersity indices (PDI < 1.5), but has been limited to low molecular weight products (M w < 6000 g mol 1 ). 2 More recently, schemes have been developed to obtain hyperbranched polyglycerols with molecular weights greater than 600 000 g mol 1 , but they provide limited control over sample poly- dispersity (PDI > 2.0 and increasing with molecular weight). As a result of these limitations, reported size exclusion chromatog- raphy (SEC) traces exhibit low molecular weight shoulders or distinct bimodality. 1,4–6 Incorporation of hbPGs into various polymer architectures, such as block copolymers, stars, dendrimers, and necklace polymers, has been demonstrated and are attractive to a wide verity of applications originating from their ability to be tailored and lack of chain entanglement. 7–17 One example of such an approach has been the introduction of densely branched poly- glycerol side chains onto semi-exible backbones, via a “hypergraing” mechanism. 18–20 Work by Schluter et al. and Percec et al. has revealed two distinct chain conformations for such materials, spherical or cylindrical, and governed by the side chains' degree of polymerization (DP). 21–23 The sterically cumbersome dendritic side chains force the backbone into an extended conformation with side chain DPs greater than 15 resulting in a cylindrical structure, while a side chain DP below 15 resulting in the semi-exible backbone collapsing into spherical structures, with each conformation resulting in a polyglycerol sheath being created around the polymer back- bone. Another example of hard-sphere structures, termed molecular nanocapsules, have been demonstrated with hyper- branched polyglycerol-amphiphiles. 24 In solution the hyper- branched amphiphiles behaved differently than their linear counterparts by collapsing, leading to the core–shell architec- ture. 24 With small angle neutron scattering it was apparent that amphiphilic derivatives of hyperbranched polyglycerols formed large aggregates in apolar solution, increasing in size with increasing hydroxyl group functionality and polymer concentration. 12 In this work, we present a new synthetic strategy, incorpo- rating the mechanism of hypergraing, to obtain a gra copolymer architecture composed of randomly placed branched polyglycerols graed from a polystyrenic backbone via a three- step approach (Scheme 1). This novel scheme utilizes both a Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA. E-mail: Goodwin@ion.chem.utk.edu; Jimmymays@utk.edu b Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA c Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA † Electronic supplementary information (ESI) available: Additional 1 H-NMR, SEC, and DSC traces of precursor copolymers and nal hypergraed material. See DOI: 10.1039/c4ra11568f Cite this: RSC Adv. , 2015, 5, 5611 Received 30th September 2014 Accepted 5th December 2014 DOI: 10.1039/c4ra11568f www.rsc.org/advances This journal is © The Royal Society of Chemistry 2015 RSC Adv., 2015, 5, 5611–5616 | 5611 RSC Advances COMMUNICATION