Model Transient Networks from Strongly Hydrogen-Bonded Polymers

Abstract

Random copolymers consisting of n-butyl acrylate backbones with quadruple hydrogenbonding side chains based on 2-ureido-4[1H]-pyrimidinone (UPy) have been synthesized via controlled radical polymerization and postpolymerization functionalization. Through this synthetic strategy high UPy monomer content (15 mol %) can be reached while maintaining low polydispersity and excellent control over molecular weight, providing model reversible networks with well-defined molecular architecture. Despite low T g s and a lack of entanglements or crystallinity, these materials behave as thermoplastic elastomers through the strong but reversible association of UPy groups. Bulk properties such as the plateau modulus, tensile modulus, and relaxation time scale are primarily determined by the average distance between UPy's along the chain. Starting from a difunctional initiator, triblock copolymers can also be synthesized containing a homopolymer midblock and random copolymer end blocks, effectively concentrating the hydrogen-bonding groups near the chain ends. By controlling both the average composition and distribution of UPy's along the polymer chain, macroscopic material properties such as stiffness and resistance to creep can be independently tuned.

Linear shear and nonlinear extensional rheology of unentangled supramolecular side-chain polymers

“…These results are consistent with results for several other reported supramolecular polymers [63][64][65][66]. As discussed in the introduction, we predict that all our polymer samples are unentangled.…”

“…Generally, it is thus important to understand the rheological response for a proper control of the material behaviour. The effect of UPy addition on the linear viscoelasticity of supramolecular polymers has previously been investigated [20,[63][64][65][66]. However, few studies exist where the rheological response is characterised for a systematic variation of supramolecular side-group density [41,66,67].…”

Dendronized Polymers with Ureidopyrimidinone Groups: An Efficient Strategy To Tailor Intermolecular Interactions, Rheology, and Fracture

“…As shown previously in the literature for other randomly UPyfunctionalized copolymers, the T g values of the PG1-40-UPy samples increase in a linear fashion with the number of hydrogen bonding side groups (from ~38 °C in PG1-40-UPy0 to ~127 °C in PG1-40-UPy50). [27][28][29] At virtually identical backbone chain lengths (P n ≈ 40), the enthalpy steps involved in the glass transition of these copolymers decrease with increasing UPy content, consistently, as inferred from the relative DSC heat flow traces normalized by the sample weight (cf. Figure S4(a) of the Supporting Information).…”

“…This group can form an array of four hydrogen bonds with an exceptionally strong dimerization constant in chloroform (K dim > 10 6 M -1 ) and is synthetically readily accessible. 23 Functionalization with UPy has already been proven to be a good strategy to form novel supramolecular polymers [24][25][26] and strong transient supramolecular networks [27][28][29][30] starting from rather simple unentangled molecules. Incorporation of UPy groups in structurally complex systems such as dendronized polymers is an unexplored field yet offering the attractive possibility to explore the impact of UPy on the dynamics of dendronized polymers.…”

Polystyrene supramolecular networks based on DA-AD hydrogen bonds

“…[34] Feldman prepared model networks from polymers bearing Upy moieties. [37] Butyl acrylate and 6-(tertbutoxycarbonylamino)hexyl acrylate were copolymerized by ATRP, with pendant butoxycarbonylamino groups to finally graft onto the Upy moieties. Subramani et al [38] prepared a triple hydrogen bonding moiety grafted onto a polystyrene backbone.…”