Herein, we report the development of a scalable and synthetically robust building block based on norbornadiene (NBD) that can be broadly incorporated into a variety of macromolecular architectures using traditional living polymerization techniques. By taking advantage of a selective and rapid deprotection with tetrazine, highly reactive "masked" cyclopentadiene (Cp) functionalities can be introduced into synthetic polymers as chain-end groups in a quantitative and efficient manner. The orthogonality of this platform further enables a cascade "click" process where the "unmasked" Cp can rapidly react with dienophiles, such as maleimides, through a conventional Diels−Alder reaction. Coupling proceeds with quantitative conversions allowing high molecular weight star and dendritic block copolymers to be prepared in a single step under ambient conditions.
A new
Diels–Alder (DA)-based photopatterning platform is presented, which exploits
the irreversible, light-induced decarbonylation and subsequent cleavage
of cyclopentadienone–norbornadiene (CPD–NBD) adducts.
A series of CPD–NBD adducts have been prepared and systematically
studied toward the use in a polymeric material photopatterning platform.
By incorporating an optimized CPD–NBD adduct into polymer networks,
it is demonstrated that cyclopentadiene may be unveiled upon 365 nm
irradiation and subsequently clicked to a variety of maleimides with
spatial control under mild reaction conditions and with fast kinetics.
Unlike currently available photoinduced Diels–Alder reactions
that rely on trapping transient, photocaged dienes, this platform
introduces a persistent, yet highly reactive diene after irradiation,
enabling the use of photosensitive species such as cyanine dyes to
be patterned. To highlight the potential use of this platform in a
variety of material applications, we demonstrate two proof-of-concepts:
patterned conjugation of multiple dyes into a polyacrylate network
and preprogrammed ligation of streptavidin into poly(ethylene glycol)
hydrogels.
Photosurfactants have shown considerable promise for enabling stimuli-responsive control of the properties and motion of fluid interfaces. Recently, a number of photoswitch chemistries have emerged to tailor the photoresponsive properties of photosurfactants. However, systematic studies investigating how photoresponsive surfactant behavior depends on the photochemical and photophysical properties of the switch remain scarce. In this work, we develop synthetic schemes and surfactant designs to produce a well-controlled library of photosurfactants to comparatively assess the behavior of photoswitch chemistry on interfacial behavior. We employ photoinduced spreading of droplets at fluid interfaces as a model for such studies. We show that although photosurfactant response is largely guided by expected trends with changes in polarity of the photoswitch, interfacial behavior also depends nontrivially and sometimes counter-intuitively on the kinetics and mechanisms of photoswitching, particularly at the interface of two solvents, as well as on complex interactions with other surfactants. Understanding these complexities enables the design of new photosurfactant systems and their optimization toward responsive functions including triggered spreading, dewetting, and destabilization of droplets on solid and fluid surfaces.
A novel method for facile postpolymerization
functionalization
of synthetic polymers using terminal norbornadiene (NBD) building
blocks is presented. Incorporation of the NBD functionality streamlines
the synthesis of a wide array of block polymers utilizing multistep
click chemistry strategies. Previously, the use of NBD-functionalized
initiators produced polymers that underwent a cascade of Diels–Alder
(DA) reactions to unveil a reactive cyclopentadiene (Cp) chain end.
When coupled with a maleimide-bearing counterpart, a highly efficient
DA cycloaddition with the terminal Cp can occur. To extend this concept
to a range of polyacrylates and commercially available poly(ethylene
glycol) systems, we developed a novel NBD acid building block for
postpolymerization functionalization. Employing this process, we have
demonstrated straightforward access to a library of block polymers
that leverage this NBD click platform.
An important but often overlooked feature of Diels–Alder (DA) cycloadditions is the ability for DA adducts to undergo mechanically induced cycloreversion when placed under force. Herein, we demonstrate that the...
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