Polymer Chemistry Blog

Stereogradient polymers are a new class of polymers in which the tacticity continuously changes from one chain end to the other. Such polymers may exhibit special properties or functions that originate from gradual changes in the physical or chemical properties along the polymer backbone. In this article, the synthesis of stereogradient polymers with tacticities that vary from predominantly syndiotactic to highly isotactic was investigated by reversible addition–fragmentation chain transfer (RAFT) copolymerization of bulky methacrylates, such as triphenylmethyl methacrylate (TrMA) and 1-phenyldibezosuberyl methacrylate (PDBSMA) and methacrylic acid (MAA) in both non-polar and polar solvents. With the differing reactivities and stereospecificities or TrMA and MAA, the isotacticity of the resulting copolymer gradually increased from 11% to nearly 100% along the polymer chain. Interestingly, the reported method can be applied to the synthesis of various stereogradient poly(MAA)s or polymethacrylates by postpolymerization modification.

From-syndiotactic-to-isotactic stereogradient methacrylic polymers by RAFT copolymerization of methacrylic acid and its bulky esters by Kenji Ishitake , Kotaro Satoh , Masami Kamigaito and Yoshio Okamoto, Polym. Chem., 2012, 3, 1750-1757.

The glucose blood level should be carefully monitored in people suffering from diabetes mellitus. In this view, a wide variety of glucose sensing molecules have been developed in the recent decades, based on boronic acid functionalized dyes that change colour or emission in the presence of glucose. The incorporation of boronic acid moieties as polymer side chains

indeed results in glucose responsive polymers that are insoluble in the absence of glucose and are solubilised in the presence of glucose due to the higher polarity of the stabilized tetragonal anionic boronic acid form. The present work of Hoogenboom and co-workers aims at developping a simple macromolecular synthesis procedure for the preparation of boronic acid containing polymers, making them accessible to a wide range of polymer scientists, beyond polymer chemists. They used a combination of commercial products; the unprotected 4-vinylphenylboronic acid (4-VBA) and the BlocBuilder alkoxyamine initiator for nitroxide mediated polymerization (NMP). The developed NMP method opens up new avenues towards 4-VBA containing polymers to evaluate glucose responsivity of various copolymers, including block copolymers for autonomous insulin delivery upon increasing glucose concentration.

Direct nitroxide mediated (co)polymerization of 4-vinylphenylboronic acid as route towards sugar sensors by Gertjan Vancoillie , Simon Pelz , Elisabeth Holder and Richard Hoogenboom, Polym. Chem., 2012, 3, 1726-1729.

The design of efficient drug delivery vehicles has been a long standing challenge in polymer and materials science. A variety of polymeric platforms have been developed in recent years based on an array of different structures including micelles, dendrimers, hydrogels and encapsulant nanoparticle. Exploiting the concept of dispersion self-assembly of soft materials in the drug delivery arena requires the incorporation of multiple functionalities into a judiciously designed BCP platform. In this paper, Hawker and co-workers reported the design of nanoparticles made of well-defined block copolymers (BCPs) containing an alkyne-functional, biodegradable polylactide (PLA) conjugated with azide-functional coumarin dyes, as a model drug, via copper catalyzed azide alkyne cycloaddition ‘click’ chemistry. Self-assembled nanoparticles with internal nanophase-separated morphologies were accessed by carefully controlling the composition of the BCPs and release of the covalently attached model payload was shown to occur under physiological conditions via the degradation of the PLA scaffold. These results demonstrated the potential of self-assembled nanoparticles as modular delivery vehicles with multiple functionalities, nanostructures, and compartmentalized internal morphology.

Functional block copolymer nanoparticles: toward the next generation of delivery vehicles by Maxwell J. Robb, Luke A. Connal, Bongjae F. Lee, Nathaniel A. Lynd and Craig J. Hawker, Polym. Chem., 2012, 3, 1618-1628.