An Investigation of the Selective Chain Scission at Centered Diels–Alder Mechanophore under Ultrasonication

Abstract

It is a challenging topic to disconnect a linear polymer selectively at the mechanophore site by an external force in a "cold" fashion. In this work, the effect of the power output of ultrasonication on the selective cleavage at the centered urfuryl-maleimide Diels−Alder (DA) mechanophore of poly(methyl acrylate)s (DA-PMA-a and DA-PMA-b) were quantitatively investigated by comparative study on experimental and simulated chain scission kinetics as well as high-resolution 1 H NMR spectroscopy (600 MHz). At low power output of the ultrasonication (2.10 W), DA-PMA-a with M n of ca. 2M lim (M lim , below which no further chain scission was observed) presented a DI (degradation index)−t (sonication time) plot with a turnover point at ca. 1.0 and no clear variation of the molecular weight after the turnover, which met well with the calculated center cleavage mode. At 5.52 W, DA-PMA-a and a poly(methyl acrylate) that contained two centered ester bonds (ester-PMA) presented similar DI−t plots with turnover points less than 1.0 within same sonication times, while poly(methyl acrylate) with fully carbon−carbon chain (PMA) had a turnover at DI value of ca. 0.5. By way of contrast, high power output of the ultrasonication (5.52 W) caused a possible cleavage of ester bonds of DA-PMA-a, which would mask the selective cleavage at the DA site. High-resolution 1 H NMR result of DA-PMA-b (115.8 kDa, M n was slightly higher than 2M lim ) showed that DA conversions were up to 55% under 2.10 W and 38% under 5.52 W. The kinetics from GPC traces and 1 H NMR results of DA-PMA-b as well as 1 H NMR results of DA-PMA-c (68.4 kDa, M n was slightly higher than M lim ) under sonication confirmed the observation that low power output favored selective chain scission at DA site. The turnover point in the DI−t plot might be used as characteristic parameter to gauge the selective chain scission at mechanophore site for single mechanophore-centered polymers.

Recyclable Multilayer Packaging by Means of Thermoreversibly Crosslinking Adhesive in the Context of Food Law

“…The maleimide functional group, N -(2-hydroxyethyl)maleimide, was prepared via a Diels–Alder and retro-Diels–Alder reaction in a three-step process [ 22 , 23 ]. Methyl ethyl ketone (≥99.5%) was purchased from TH Geyer and, if necessary, dried with molecular sieve (4 Å) to an H 2 O content <50 mg/kg and stored under nitrogen (H 2 O ≤ 50 mg/kg).…”

Recent innovations of ultrasound green technology in herbal phytochemistry: A review

“…Hydrocarbon) enabled the efficient mechanochemical scission and the release of this monoterpene molecule [ 69 ]. A US mechanophore breakage (mechanochemically breakage of the polymer reactive units like cyclic rings) can occur in extracts solutions via the shear stress caused by the collapse of US-induced cavitation bubbles [ [73] , [74] ]. These modifications in the structure of extracted compounds caused US can facilitate better bioavailability of the herbal bioactive molecules [ 75 ].…”

The photoregulation of a mechanochemical polymer scission

“…DA adducts that emit fluorescence or release small molecules upon mechanical cleavage of the DA bond have already been developed, and these have provided deep insight into the fundamental aspects of polymer mechanochemistry. 11 , 37 , 42 , 43 We envisaged that control over the mechanical cleavage could possibly be established by photoisomerization of a photochromic diarylethene (DAE). 44 Recently, control over the thermally induced bond cleavage of DAE-conjugated DA adducts (DAE/DA) has been reported using a light stimulus, 45 – 50 and this approach also holds promise for mechanically induced retro-DA reactions.…”