Triggered Depolymerization of Poly(Phenylcarbamate)-based Materials in Response to Orthogonal Stimuli
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Triggered Depolymerization of Poly(Phenylcarbamate)-based Materials in Response to Orthogonal Stimuli Ahmed-Rufai Ibrahim1 and Valerie Sheares Ashby1, 2 1 University of North Carolina at Chapel Hill, Department of Chemistry, Chapel Hill, NC, 27599 2 Duke University, Department of Chemistry, Durham, NC, 27703 ABSTRACT The synthesis of a polyacetal-block-polyurethane copolymer was achieved which possesses the ability to depolymerize both selectively and in response to orthogonal stimuli, heat and pH. To utilize heat as a stimulus, poly(phthalaldehyde) (PPA) was used as a block of the copolymer, while poly(benzyl-4-hydroxymethylphenylcarbamate) (PPC) end-capped with a tertbutoxycarbonyl protecting group (Boc group) were explored for viability as a pH-responsive block. The stimulus-induced depolymerization was studied using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and attenuated total reflectance infrared spectroscopy (ATR-IR). These techniques confirmed that the depolymerization event did not affect the nature of the neighboring polymeric block. Depolymerization kinetics were measured for various chain lengths of each block. The results are presented and discussed to explore the ability of these materials to depolymerize in a controlled manner depending on the magnitude of the stimulus, as well as the ability for the blocks to remain unaffected by the orthogonal stimulus. This work shows promise for the development of advanced coatings systems and drug delivery applications. INTRODUCTION The design of precisely triggered degradation in materials is an underdeveloped area of macromolecular science. Degradable polymers carry a specific set of properties that are gradually lost after exposure to a particular stimulus, and can also inherit new properties upon degradation. The rate at which the degradation event occurs is dependent on several factors, which could include the pH of the solution, copolymer composition and structure, or percent crystallinity [1]. Current technologies for degradable polymers, however, have major limitations, namely the rate at which complete degradation can be achieved and the nature of formed byproducts. This can be detrimental especially in biomedical applications, where excretion of the degraded materials and toxicity of the newly-created degradation products are of paramount concern [2]. To address these concerns, researchers have sought to create mechanisms for materials to depolymerize completely. Depolymerization involves the reversion of the polymer back to its parent small molecules [3]. Studies in the field look at ways to create depolymerization events by forcing the polymer to respond to a specific stimulus using a responsive moiety as a trigger. Stimulus-induced depolymerization has tremendous implications for a number of fields, including coatings, medicine, and waste management [1]. The best-known class of materials capable of this controlled deconstruction of intricate macromolecules are self-immolative polymers (SIPs), which were developed in 2003
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