Abstract
Self-immolative polymers are an emerging class of macromolecules with distinct disassembly profiles that set them apart from other general degradable materials. These polymers are programmed to disassemble spontaneously from head to tail, through a domino-like fragmentation, upon response to extremal stimuli. In the time since we first reported this unique type of molecule, several groups around the world have developed new, creative molecular structures that perform analogously to our pioneering polymers. Self-immolative polymers are now widely recognized as an important class of stimuli-responsive materials for a wide range of applications such as signal amplification, biosensing, drug delivery, and materials science. The quinone-methide elimination was shown to be an effective tool to achieve rapid domino-like fragmentation of polymeric molecules. Thus, numerous applications of self-immolative polymers are based on this disassembly chemistry. Although several other fragmentation reactions achieved the function requested for sequential disassembly, we predominantly focused in this Perspective on examples of self-immolative polymers that disassemble through the quinone-methide elimination. Selected examples of self-immolative polymers that disassembled through other chemistries are briefly described. The growing demand for stimuli-responsive degradable materials with novel molecular backbones and enhanced properties guarantees the future interest of the scientific community in this unique class of polymers.
Highlights
INTRODUCTION AND HISTORICAL OVERVIEWStimuli-responsive materials are a promising type of smart molecular compounds, with properties that can be significantly changed in a controlled fashion upon response to applied stimuli
Depolymerization reactions of polymers with low ceiling temperatures, such as poly(olefin sulfone) and poly(phthalaldehyde), were described by Ito and others, long before we reported the concept of self-immolative polymers.[4−6] there is a fundamental difference between such depolymerization processes and the disassembly pathway of self-immolative polymers
Generation, Lienkamp and co-workers used a self-immolative polymer with a poly(benzylcarbamate) backbone to prepare a functional surface in a multilayer device (Figure 3E).[37]
Summary
Stimuli-responsive materials are a promising type of smart molecular compounds, with properties that can be significantly changed in a controlled fashion upon response to applied stimuli. The disassembly of the self-immolative polymer with a poly(benzylcarbamate) backbone occurs upon removal of the head trigger by an external stimulus, which releases an aniline functional group that undergoes sequential fragmentation through azaquinone-methide elimination and decarboxylation reactions (Figure 1C). Generation, Lienkamp and co-workers used a self-immolative polymer with a poly(benzylcarbamate) backbone to prepare a functional surface in a multilayer device (Figure 3E).[37] The polymer head was capped with 4-hydroxy-2-butanone as a responsive group that can be removed under basic conditions through a β-elimination reaction. In 2010, the Phillips group developed self-immolative polymers that disassemble from head to tail by a chemistry different from the quinone-methide elimination.[42] They synthesized poly phthalaldehyde polymers, from phthalaldehyde monomeric units, using anionic polymerization conditions (Figure 5A). When the polymer was formulated into a thin film, the quinone-methidebased disassembly occurred in the solid phase
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