UV-reversible chain extendable polymers from thymine functionalized telechelic polymer chains

Abstract

Recently, significant attention has been paid to the preparation of polymeric materials that enable the reversible tuning of molecular weights and crosslink densities of polymers. Reversible polymers are of interest for applications in selfhealing 1-4 and reorganizable materials. 5,6 Reversible polymeric systems rely either on covalent or noncovalent bonds. 7These polymeric systems can usually be subdivided into reversibly crosslinkable polymers and reversible linear polymers which include supramolecular polymers and reorganizable polymers. In the reversibly crosslinkable polymers, multiple dynamic bonding units are present either as pendant groups on polymer chains, [8][9][10] or as terminal units in multifunctional macromonomers. 11,12 An external stimulus such as heat, light, or chemical is used to trigger the polymerization and the depolymerization. Supramolecular reversible polymers have been synthesized using noncovalent interactions such as hydrogen bonding, p-p interactions, ionomers, and coordinative bonds. [13][14][15][16][17][18][19][20] There are fewer examples of reversible polymers using dynamic covalent bonding, most of which are based on thermally reversible covalent bonds. 6,[21][22][23] Dynamic polymeric systems using photoreversible covalent reactions, such as photodimerization, are of particular interest because such reactions can be conducted at ambient temperature usually without the need for a solvent. 24 Several researchers have made attempts to polymerize coumarin or cinnamate telechelic oligomers under UV irradiation. 25,26 However, only low molecular weight polymers were obtained for these systems because of the low yield of the photochemical reaction. Thymine makes an interesting choice for incorporation in polymeric materials due to its ability to form hydrogen bonds as well as its propensity to undergo reversible photodimerization upon UV exposure. [27][28][29][30][31][32][33] Furthermore, thymine has demonstrated a high sensitivity and efficiency of photoreversion in comparison with coumarin and cinnamylidene (a derivative of cinnamic acid). 25,34-36In a previous work, 37 a,x-thymine functionalized telechelic poly(n-butyl acrylate)s (Thy-PnBuA-Thy) were synthesized by trithiocarbonate-mediated RAFT polymerization and used to prepare supramolecular block copolymers. In this article, the photoreactivity of thymine moieties in Thy-PnBuA-Thy is exploited to develop UV-reversible chain-extendable polymer chains. During the photopolymerization, the terminal thymines are expected to undergo 2p12p photodimerization upon UV irradiation from 270 to 320 nm, resulting in the formation of chain-extended linear polymer chains (Fig. 1). The cyclobutane rings formed in the resulting polymers should be cleaved when irradiated with shorter wavelength of UV light (<250 nm).To photopolymerize terminally thymine functionalized PnBuA, thin films with a thickness of 6.0 (6 0.5) lm were first prepared on glass substrates from THF solutions. The dried films were then irradiated using a 302-nm UV lamp to ach...

Dual Stimuli-Responsive Nucleobase-Functionalized Polymeric Systems as Efficient Tools for Manipulating Micellar Self-Assembly Behavior

“…The well-characterized [2π + 2π]cycloaddition reactions can be controlled by UV−vis spectroscopy. 30,31 This method has been used to monitor the characteristics of the absorbance of the π−π* transitions of the CC double bond in uracil and the corresponding cyclobutane photoproduct upon exposure to irradiation with UV light. 30,32 As a result, we used UV−vis spectroscopy to monitor the photoreactivity of BU-PPG and uracil in aqueous solution.…”

“…Inspired by this result, we compared the photoreactivity of BU-PPG micelles and uracil. The well-characterized [2π + 2π]-cycloaddition reactions can be controlled by UV–vis spectroscopy. , This method has been used to monitor the characteristics of the absorbance of the π–π* transitions of the CC double bond in uracil and the corresponding cyclobutane photoproduct upon exposure to irradiation with UV light. , As a result, we used UV–vis spectroscopy to monitor the photoreactivity of BU-PPG and uracil in aqueous solution. After UV irradiation (254 nm, 50–70 mW/cm 2 ), the intensity of the characteristic absorption peaks of BU-PPG at 265 nm gradually decreased and then leveled off as the duration of UV irradiation increased, suggesting near completion of the [2π + 2π] cycloaddition photoreaction , within 45 min (Figure b).…”

pH-Responsive Capsules Fabricated by Interfacial Photo-Cross-Linking Utilizing the Photoreactivity and pH-Responsiveness of Thymine

“…Saito and co-workers developed UV-reversible chain-extendable thymine-functionalized telechelic photoreactive poly-mers. 41 They also used thymine-functionalized polymers as self-healing materials. 42 We have previously applied the [2π + 2π] photoreactivity of thymine groups to interfacial photocross-linking and successfully prepared hollow and capsule particles.…”

“…In living systems, dimerization reactions between thymine groups occur in double-stranded DNA, which triggers apoptosis and carcinogenesis. − Nucleobase dimerization reactions have been utilized in polymer chemistry. Saito and co-workers developed UV-reversible chain-extendable thymine-functionalized telechelic photoreactive polymers . They also used thymine-functionalized polymers as self-healing materials .…”