Branched polymeric architectures have attracted considerable research interest due to their distinct physical properties and ability to facilitate unique stimuli-responsive behavior. A subset of this class of architectures, star polymers consist of a densely connected center with linear “arms” radiating from it, providing a large molecular structure that can serve many purposes. Core-crosslinked star polymers with degradable cores have the potential to act as small molecule delivery agents by dissociating into linear arm polymers with an accompanying release of internalized cargo, however means to control this process still remains elusive. In this work, we utilize photoiniferter-mediated polymerization to prepare star polymers crosslinked with degradable imine linkages. Importantly, this approach allows the rate of core degradation to be controlled through modification of the imine N-substituent. Star polymers were prepared through an “arm-first” synthetic approach, in which a linear macroinitiator was chain extended with divinyl imine-containing crosslinkers to form the target star architecture. First, macroinitiator arms were prepared by photoiniferter-mediated polymerization of N,N-dimethylacrylamide, which preserves reactive trithiocarbonate end-groups for subsequent chain extension with multivinyl crosslinkers. Next, these macroinitiators were converted into star polymers via a similar photoiniferter polymerization in the presence of divinyl crosslinkers. We synthesized and evaluated crosslinkers containing oxime, semicarbazone, and hydrazone functional groups to serve as degradable crosslinks which create the core of the star polymer. Various factors such as the time spent irradiating, the addition of a diacetone acrylamide comonomer and crosslinker identities were precisely tuned to optimize crosslinker synthesis. After the synthetic procedure was optimized, the rate at which star polymers degraded under acidic conditions into lower molecular weight structures was analyzed by dynamic light scattering, and the extent to which the measured degradation rates correlated to a release of encapsulated dye cargo was also evaluated.

Degradable imine-containing core-crosslinked star polymers

2019 Spring National Meeting

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