Harnessing entropy to direct the bonding/debonding of polymer systems based on reversible chemistry

Abstract

The widely accepted approach for controlling polymer debonding/rebonding properties in responsive materials has been to purposefully engineer the functional end-groups responsible for monomer dynamic bonding. Here, however, we evidence that the debonding temperature of a polymer can also be tuned by changing the chain length of the polymer building blocks, thus altering the entropy released on debonding. Entropy driven debonding, as governed by building block chain length, is suggested theoretically and realized experimentally for two Diels-Alder polymer systems, each based on a different difunctional diene and a common difunctional dienophile. In each case a significant decrease (as much as 60 C) in the retro Diels-Alder temperature was observed when the chain length of the difunctional dienophile building block was increased. These results have the potential to fundamentally change the approach utilized to design materials capable of bonding reversibly on demand. Scheme 1 (a) The experimental reversible crosslinking reaction of Inglis et al. 1 and (b) the corresponding small molecule model. (c) The experimental reversible crosslinking reaction of Zhang et al. 2 and (d) the corresponding small molecule model. Scheme 3 DA-based polymerization of Cp 2 -P(iBoA-nBA) with P-di-linker/PiBoA to generate P(Cp-PL)1-7.

Adaptable Hetero Diels–Alder Networks for Fast Self‐Healing under Mild Conditions

“…Alternative DA pairings which are suitable for self‐healing applications were reported by Murphy et al and the group of Lehn . Our group has recently designed a new low temperature reversible system based on covalent chemistry, utilizing acid activated dithioesters as dienophiles in hetero Diels–Alder (HDA) reactions with cyclopentadiene (Cp) . However, a disadvantage of these materials is their slow self‐healing kinetics in the absence of a catalyst.…”

State‐of‐the‐Art Analytical Methods for Assessing Dynamic Bonding Soft Matter Materials

“…If further information is available, the masses can be employed to extract more quantitative data. For instance, in the case of step growth reactions, Carother's equation can be used for relating the average molar mass to the conversion of the reaction: Calculating the degree of polymerization before and after the bonding (or debonding) reaction allows for the determination of a value representing the decrease in bonding, as shown in Equation where DP n,0 and DP n,t are the degree of polymerization before and after a time t of the debonding reaction, respectively. Converting the molar masses in percentage bonding decrease values is useful for comparing different reactions to each other with respect to their extent under certain conditions.…”

“…Subsequently, the mixture is snap frozen in liquid nitrogen to suppress further reactions. The solvent is removed at low temperatures in vacuo, the sample is redissolved in the SEC eluent and finally the analysis is performed . During all these steps one has to ensure that the molar mass distribution remains unchanged, which is not trivial for all types of reactions, especially for reversible ones.…”

Thermal Field‐Flow Fractionation for the Investigation of the Thermoresponsive Nature of Star and Linear Polystyrene

“…Temperature‐responsive (or thermoresponsive) polymers are polymers that exhibit discontinuous changes of their physical properties, for example, solubility or hydrodynamic size in a given solvent, with temperature . Promising areas of application of thermoresponsive polymers are tissue engineering, liquid chromatography, self‐healing materials, drug delivery, and bioseparation . Typically, the solution properties of thermoresponsive polymers (such as the phase transition temperature) are influenced by a number of molecular parameters such as molar mass and molecular topology .…”