Fracture, fatigue, and friction of polymers in which entanglements greatly outnumber cross-links

In gels and elastomers, how entanglements affect deformation has long been studied, but how entanglements affect fracture, fatigue, and friction has not. Here we synthesize gels and elastomers in which entanglements greatly outnumber crosslinks. We demonstrate that such polymers resolve a long-standing conflict: crosslinks stiffen polymers but embrittle them. When a polymer of dense entanglements and sparse crosslinks is stretched, before a polymer chain breaks, tension transmits in the chain along its length, and to many other chains through entanglements. This distribution of tension leads to high toughness, strength, and fatigue resistance. Upon swell in water to equilibrium, the hydrogels exhibit low hysteresis, low friction, and high wear resistance. Such an exceptional combination of properties opens doors to broad and immediate applications.