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Since the invention of polymer networks such as cross-linked natural rubber in the 19th century, it has been a dogma that stiffer networks are less stretchable. We report a universal strategy for decoupling the stiffness and extensibility of single-network elastomers. Instead of using linear polymers as network strands, we use foldable bottlebrush polymers, which feature a collapsed backbone grafted with many linear side chains. Upon elongation, the collapsed backbone unfolds to release stored length, enabling remarkable extensibility. By contrast, the network elastic modulus is inversely proportional to network strand mass and is determined by the side chains. We validate this concept by creating single-network elastomers with nearly constant Young’s modulus (30 kilopascals) while increasing tensile breaking strain by 40-fold, from 20 to 800%. We show that this strategy applies to networks of different polymer species and topologies. Our discovery opens an avenue for developing polymeric materials with extraordinary mechanical properties.
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Gelation Dynamics in Polydimethylsiloxane Bottlebrush Elastomers
Abstract Network formation in elastomers with grafted side chains is investigated to understand the entanglement‐free nature of the bottlebrush architecture. Competition between elastically effective cross‐linkers and dangling side chains creates a unique environment where reaction kinetics and steric effects dictate network percolation. The evolving viscoelasticity of linear and bottlebrush networks with an equivalent number of cross‐linkers to backbones is measured during a catalytic curing reaction using time‐resolved rheology. The impact of reaction kinetics on network formation is addressed through the sol−gel transition by tuning catalyst concentration. Solidification falls into a rate‐limited regime where the modulus growth rate increases with increasing catalyst. The network formation process remains independent of the cure rate in the bottlebrush and linear systems. Side chains significantly decrease the fractal dimension of the critical gel cluster despite a comparable number of cross‐links. Time‐cure superposition is applied to quantify dynamics in the pre‐ and post‐gel states. The divergence of the shift factors around the gel point is independent of cure kinetics. The collapse of shift factors in the post‐gel region further suggests the universality of the network formation process. The approach to understanding internal structure development during processing will be critical as bottlebrush elastomers are utilized among a wide range of applications.
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- Award ID(s):
- 2326933
- PAR ID:
- 10600128
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Macromolecular Rapid Communications
- Volume:
- 46
- Issue:
- 14
- ISSN:
- 1022-1336
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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