Utilizing self-immolative atom transfer radical polymerization initiators to prepare stimuli-responsive polymeric films from nonresponsive polymers

Stimuli-responsive polymers (SRPs) are designed to change their structure and properties in response to external stimuli by the introduction of responsive moieties that can undergo reversible or irreversible changes. Some moieties undergo reversible changes such as protonation and isomerization, while other groups can undergo irreversible transformations by cleavage of chemical bonds.^1-3

In this work we present a simple and modular approach for the introduction of self-immolative (SI) responsive junctions into non-responsive polymers to design splittable polymers.⁴ These polymers were synthesized by atom transfer radical polymerization using photo-responsive SI bifunctional initiator. The self-immolative mechanism was based on a double quinone methide elimination¹ that is designed to allow the splitting of the polymers at their middle. We demonstrate this modular approach by a series of photo-responsive poly(benzyl methacrylate) and polystyrene polymers of various molecular weights.

Taking advantage of the well-defined architecture of the polymers and location of the splitable SI group, we studied their photo-response in solution and in solid phase by casting thin films, in contrast to most of the reported SRPs, which have been studied in solution or in gel phase.^1,2 We examined the effects of irradiation time and solvent addition on the degree of response and splitting and showed that the SI elimination can occur in the solid phase. We also obtained insights into the role of the mobility of the polymer chains on the degree of splitting, in the presence and absence of solvent. Our modular approach⁴ opens the way to create wide range of SRPs from nonresponsive monomers.

Schematic presentation of splitable polymers containing photoresponsive self-immolative junctions.⁴

References:

1 Chem. Rev. 2016, 116, 1309−1352

2 Macromolecules 2007, 40, 3589−3598

3 Angew. Chem., Int. Ed. 2015, 54, 6200−6205

4 Macromolecules 2019, 52, 3268-3277