Effects of Diisocyanate Structure and Disulfide Chain Extender on Hard Segmental Packing and Self-Healing Property of Polyurea Elastomers

Abstract

Four linear polyurea elastomers synthesized from two different diisocyanates, two different chain extenders and a common aliphatic amine-terminated polyether were used as models to investigate the effects of both diisocyanate structure and aromatic disulfide chain extender on hard segmental packing and self-healing ability. Both direct investigation on hard segments and indirect investigation on chain mobility and soft segmental dynamics were carried out to compare the levels of hard segmental packing, leading to agreed conclusions that correlated well with the self-healing abilities of the polyureas. Both diisocyanate structure and disulfide bonds had significant effects on hard segmental packing and self-healing property. Diisocyanate structure had more pronounced effect than disulfide bonds. Bulky alicyclic isophorone diisocyanate (IPDI) resulted in looser hard segmental packing than linear aliphatic hexamethylene diisocyanate (HDI), whereas a disulfide chain extender also promoted self-healing ability through loosening of hard segmental packing compared to its C-C counterpart. The polyurea synthesized from IPDI and the disulfide chain extender exhibited the best self-healing ability among the four polyureas because it had the highest chain mobility ascribed to the loosest hard segmental packing. Therefore, a combination of bulky alicyclic diisocyanate and disulfide chain extender is recommended for the design of self-healing polyurea elastomers.

A Robust and High Self‐Healing Efficiency Poly(Urea‐Urethane) Based on Disulfide Bonds with Cost‐Effective Strategy

“…However, SPU sample possessed more than 1 MPa modulus value and showed very low relaxation at temperatures below 60 °C. The relaxation times can be used to evaluate the self‐healing properties qualitatively, as they respond to the chain mobility . From these results, it is concluded that SPU sample can relax easily above 60 °C, suggesting high chain mobility and fast disulfide exchanges, being in agreement with the scratch healing tests mentioned before.…”

“…The critical temperature of SPU for hydrogen bonds breaking and regeneration is about 120 °C. When the temperature is higher than 120 °C, the quadruple hydrogen bondings can be disrupted . Conversely, when the temperature drops below 120 °C, the quadruple hydrogen bondings can be reformed again.…”

“…Yang et al reported a disulfide‐containing poly(urea‐urethane) network with 97.4% high self‐healing efficiency based on aromatic disulfide exchanges and formation of quadruple hydrogen bonding. Li et al developed a self‐healing cross‐linked poly(urea‐urethane) elastomer based on disulfide bonds and hydrogen bonding. It was concluded that both the exchanges of disulfide bonds and the dissociation/regeneration of hydrogen bonding brought about the reshuffling of the dynamic systems.…”

Influence of Polyol/Crosslinker Blend Composition on Phase Separation and Thermo-Mechanical Properties of Polyurethane Thin Films

“…However, PUs with PEG/PCL = 1 showed a sharp peak at the top of the broad halo. According to Ti et al [20], this reveals the existence of ordered microstructures that could be related to the tightly-packed HS. Additionally, there is an extra peak centering around 2θ = 27 • that can be attributed to a SS crystalline region [17].…”

“…The spacing values are small compared with those reported in the literature. Kim, H-N., et al [1] reported values of 12 nm and 20 nm for PUs synthetized from poly (tetramethylene ether glycol) as the polyol, BD, ISB and IMN as the chain extenders while Ti et al [20] reported spaces between 4.57 nm and 7.95 nm in polyureas obtained from diaminopolypropylene glycol as the polyols, IPDI, and hexamethylene diisocyanate, and bis(4-aminophenyl)disulfide and 4,4 -diaminodibenzyl as the chain extenders. Despite these findings, the distances observed in this study are similar to those described by Cao and Liu [21].…”