Organoboron polymers are important precursors to materials with potential utility in catalysis, separations, and sensing applications. Recent reports detail boron-containing polymers serving as electrolyte materials for batteries, blue emissive polymers, self-healing materials, and precursors for functional polyolefins. 1 These polymers have demonstrated promise in biological applications as well, which is especially evidenced by water-soluble boronic acid-containing polymers having garnered a great deal of attention for glucose or RNA sensing, diabetes treatment therapies, and as supramolecular materials. 2 To more fully realize the potential of boronic acid containing macromolecules in sensing and delivery applications, it is vital to expand the capability to prepare such polymers with precise control over topology, molecular weight, and composition. Herein, we report the first, to our knowledge, successful synthesis of well-defined water-soluble boronic acid copolymers from stable and easily manipulated boron-containing monomers.A variety of polymerization techniques have been considered for the synthesis of polymers with pendant boron functionality, with conventional radical polymerizations arguably being most successful due to facile experimental setup and lack of significant side reactions. 3 Controlled radical polymerization techniques facilitate the preparation of (co)polymers with predetermined molecular weights, narrow molecular weight distributions, and high degrees of chain-end functionalization, the latter of which facilitate the preparation of complex macromolecular architectures that lead to self-assembly and other advanced materials applications. 4 Jäkle et al. pioneered the efficient synthesis of organoboron vinyl (co)-polymers via atom transfer radical polymerization (ATRP), 5 either from silylated precursors that were subsequently borylated 6 or from the polymerization of organoboron monomers. 7 We are primarily interested in the synthesis and aqueous solution behavior of amphiphilic organoboron block copolymers, especially those with acrylamido hydrophilic blocks. While the success of ATRP for the polymerization of most acrylamido monomers has drastically improved over the past few years, reversible addition-fragmentation chain transfer (RAFT) polymerization 8 has proven excellent for the synthesis of a range of polyacrylamides. 9 RAFT can be conducted under relatively mild conditions, is applicable to nearly any monomer susceptible to radical polymerization, and has been employed to prepare a range of well-defined complex macromolecular topologies. The plethora of stimuli-responsive and watersoluble acrylamido polymers, coupled with the potential biological applications of controlled architecture boron-containing polymers, suggests significant value in developing synthetic capabilities to prepare such block copolymers.We prepared homopolymers of selected molecular weights and block copolymers with poly(N,N-dimethylacrylamide) (PDMA). While there have been reports of uncontrolled random copoly...