Stimuli‐responsive polypeptoid block copolymers containing o‐nitrobenzyl groups with extremely sharp transition

Abstract

Bioinspired thermoresponsive polymers have received increasing attention for many applications. Here, we report a series of thermoresponsive polypeptoid block copolymers containing o-nitrobenzyl groups, that is, poly(ethylene glycol)-b-poly[N-[2-[N-(o-nitrobenzyloxycarbonyl)-amino]-ethyl]-glycine] (PEG-b-PN[oNB]G), prepared by ring-opening polymerization. The polypeptoid block copolymers show reversible lower critical solution temperature (LCST)-type behavior in water with tunable phase transition properties dependent on the pH values, chemical compositions, and concentrations of the copolymers. The dynamic light scattering results reveal the formation of spherical micelles and temperature-induced aggregation of PEG-b-PN(oNB)G. Notably, the phase transition of the block copolymer solution upon heating appears extremely sharp (ΔT < 1 C), superior to bench mark poly(N-isopropylacrylamide).In addition, we present the removal of photo-responsive o-nitrobenzyl groups can result in the increased clouding point and even the loss of phase transition properties, acting as an excellent regulator to tune the LCST behavior. We demonstrate that the hydrogen-bonding interaction may play a critical part on the LCST behavior. The prepared diblock copolymers show great potential for many applications and its structure-property may shed light on highly designable stimuli-responsive polymeric materials.

Dynamics in polymers with phase separated dynamic bonds: the case of a peculiar temperature dependence

“…This behaviour is known for some block copolymers, especially those with hydrogen bonds. 37,38,40 We speculate that glass transition prevents the dissolution of clusters in the polymer matrix at lower temperatures preventing in this way observation of the expected LCST. This leads to a regime of rheological behaviour in which terminal flow is defined largely by structural relaxation in the clusters at lower temperatures, whereas it is delayed substantially beyond this time at higher temperatures when the stickers become less miscible in the polymer matrix.…”