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How do hard and soft regions give copolyester elastomers both strength and elasticity?

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Copolyester elastomers derive their unique properties from a twin-phase composition consisting of hard polyester crystallites dispersed within a soft, flexible matrix.1

These materials are block copolymers containing long sequences of two distinct chemical units. The hard sequences, typically polybutylene terephthalate, spontaneously cluster into crystalline domains upon cooling. These domains act as physical cross-links that connect the softer, elastomeric sequences.1

This structure provides strength and elasticity through the following mechanisms:
* Strength: The hard crystalline regions provide structural integrity and mechanical reinforcement, held together by strong intermolecular attractions and mechanical interlocking.1
* Elasticity: The soft, flexible matrix allows the material to deform and recover its shape, mimicking the behavior of rubber.1

Unlike traditional vulcanized rubbers, these regions are not chemically interlinked into a permanent network. This allows the material to be heated above the melting point of the crystalline domains and reprocessed, making it a versatile thermoplastic elastomer.1