Structural Design of CANs with Fine-Tunable Relaxation Properties: A Theoretical Framework Based on Network Structure and Kinetics Modeling

Abstract

In this work, we present a model capable of reproducing the stress relaxation dynamics of a wide range of relaxation processes in covalent adaptable networks (CANs) produced by stepwise polymerization. The proposed model captures the effective elastic response of the material subject to an initial stress by analogy with a network decrosslinking process. The combination of a recursive structural model and a kinetic model for the bond exchange reaction makes it possible to predict the expected stress relaxation profile in simple and complex systems depending on the structure of the network, the rate of bond exchange of the different components, and the presence of permanent bonds. After the basic features of the model are analyzed, its prediction capabilities are validated by simulating a number of scenarios taken from the literature. The results show that tailoring of the network architecture enables unprecedented flexibility in the design of CAN-based materials.

Covalent Adaptable Networks Made by Reactive Processing of Highly Entangled Polymer: Synthesis-Structure-Thermomechanical Property-Reprocessing Relationship in Covalent Adaptable Networks

“…The average relaxation time, ⟨τ⟩, may be obtained from the fitted KWW parameters of β and the characteristic relaxation time, τ*, using the following: in which Γ represents the gamma function. While this method of analysis accounts for relaxation distribution breadth in a single mode or multiple, largely overlapping modes of stress relaxation, it does not account for multiple modes of stress relaxation that differ widely in time (and likely exhibit their own unique breadths) such as those we observed for our PHMA CANs . In fitting most of the stress relaxation data of the 5–2 and 15–1.5 PHMA CANs to a single KWW function, we obtained the parameters in Table S5 and the fits in Figures S20–S22, with a singular fit highlighted in Figure a.…”

Facile Preparation of Tunable Polyborosiloxane Networks via Hydrosilylation

“…To test this hypothesis, fish-shaped samples were prepared with different ratios of static and dynamic cross-links (Figure S13), followed by soaking in methanol for 4 days (Figure ). Significantly, the introduction of static cross-links to both the end-group and pendant-group networks provides structural integrity that prevents complete dissolution after methanolysis of the borate ester bonds …”

“…Significantly, the introduction of static cross-links to both the end-group and pendant-group networks provides structural integrity that prevents complete dissolution after methanolysis of the borate ester bonds. 46 ■ CONCLUSIONS A novel method for preparing polyborosiloxane networks was developed to take advantage of commercially available starting materials and robust hydrosilylation chemistry. Key to this approach is the use of tris(dimethylvinylsilyl)borate as an efficient cross-linker for PDMS precursors that contain Si−H bonds.…”