Combined Effect of Chain Extension and Supramolecular Interactions on Rheological and Adhesive Properties of Acrylic Pressure-Sensitive Adhesives

A new approach for the elaboration of low molecular weight pressure-sensitive adhesives based on supramolecular chemistry is explored. The synthesis of model systems coupled with probe-tack tests and rheological experiments highlights the influence of the transient network formed by supramolecular bonds on the adhesion energy. The first step of our approach consists of synthesizing poly­(butyl acrylate-<i>co</i>-glycidyl methacrylate) copolymers from a difunctional initiator able to self-associate by four hydrogen bonds between urea groups. Linear copolymers with a low dispersity (<i>M</i>_n = 10 kg/mol, Ip < 1.4) have been synthesized via atom transfer radical polymerization. Films of the copolymers were then partially cross-linked through reaction of the epoxy functions with a diamine. The systematic variation of the average ratio of glycidyl methacrylate and diamine per copolymer shed light on the respective role played by the supramolecular interactions (between bis-urea groups and with the side chains) and by the chain extension and branching induced by the diamine/epoxy reaction. In this strategy, the adhesive performance can be optimized by modifying the strength of “stickers” (via the structure of the supramolecular initiator, for instance) and the polymer network (e.g., via the length and level of branching of the copolymer chains) in order to approach commercial PSA-like properties (high debonding energy and clean removal)

Microstructure and Self-Assembly of Supramolecular Polymers Center-Functionalized with Strong Stickers

This manuscript describes the microstructure of a series of nearly monodisperse poly­(<i>n</i>-butyl) acrylate (PnBA) chains center-functionalized with a triurea interacting moiety, able to self-associate by six hydrogen bonds. Different molecular weights have been investigated, from 5000 g·mol^–1 up to 80 000 g·mol^–1. For molecular weights (<i>M</i>_n) below 40 000 g·mol^–1, X-ray scattering experiments and atomic force microscopy at ambient temperature clearly show that the systems organize as nanofibers hexagonally packed in oriented domains. This supramolecular structure explains the solid-like gel behavior of these polymers, which is suppressed at high temperature (at an order–disorder transition temperature). For higher molecular weights, nanofibers still form at ambient temperature but their concentration is too low to self-assemble in oriented domains. This is consistent with the reported viscoelastic behavior of these systems described in the companion paper