Time‐delayed photo‐induced depolymerization of poly(phthalaldehyde) self‐immolative polymer via in situ formation of weak conjugate acid

Abstract

Poly(phthalaldehyde) (PPHA) can be used as a structural material in transient devices and photo‐catalytically depolymerized at the end of device life by the use of a photo‐acid generator (PAG). However, device degradation requires the presence of a radiation source at the end of device mission. It has been found that the onset of PPHA depolymerization after PAG photo‐exposure can be delayed by incorporation of a particular weak bases in the PPHA/PAG mixture. This method of delayed PPHA depolymerization allows for PAG activation prior to or during device deployment when the device is under full user control. The basicity of specific lactams and amides was found to slow the PPHA depolymerization, giving the transient device a longer but finite mission lifetime. The weak base reacts with the photo‐generated strong acid to form a weak conjugate acid, which reacts more slowly with PPHA to extend the onset of PPHA depolymerization. The addition of a molar excess of specific lactams or amides, with respect to PAG, maintains PPHA stability and mechanical properties for more than 80 minutes after photo‐exposure at room temperature. The amide or lactam mediated acid activation of PPHA follows first‐order kinetics. The time delay of PPHA depolymerization can allow for prelaunch photo‐exposure and eliminates the need for postmission photo‐exposure where reliable light‐sources may not be available.

Functional design of stimuli-responsive poly(phthalaldehyde)-based adhesives: depolymerization kinetics and mechanical strength management through plasticizer addition

“…10,25 While both linear and cyclic PPAs are intrinsically sensitive to acid, heat, and mechanical forces due to the vulnerable bonds in the hemiacetal units of the polymer backbone, [25][26][27] the reactivity of linear PPAs can be altered by installing an end group that can be selectively cleaved by a predetermined stimulus. [26][27][28] Plenty of studies that demonstrate site-specific depolymerization of linear end-capped PPA exist in the literature, with a library of investigated stimuli including palladium, 29 conjugate acids, 30 UV light, 27 fluorides, 31 and ultrasound. 32 Given the proven capability to functionally customize its end groups, in addition to its ability to depolymerize in the solid-state, 29,33 linear PPA stands out as a strong candidate for adhesive modulation by chemical triggers.…”

Kinetic Investigation on the Cationic Polymerization of o-Phthalaldehyde: Understanding Ring-Expansion Polymerization

“…o -Phthalaldehyde (oPHA), T C = −35 °C, , is a versatile monomer that can be ionically polymerized or copolymerized with aldehydes and alkenes to create a variety of functional, depolymerizable materials. − Polyphthalaldehyde (PPHA) and its derivatives have shown to be promising materials for probe-based lithography − and other stimuli-responsive applications − because of their ability to rapidly depolymerize from the solid-state polymer. − The cationic polymerization route to PPHA is often preferred over the anionic route because the polymer has a longer shelf-life and higher molecular weight that improves the mechanical properties of the resulting material. , The anionic route provides lower dispersity and greater synthetic control with the opportunity to utilize functional endcaps.…”