No, polyurethane upholstery on kitchen chairs or anywhere else is not prone to splitting open with regular use. It's a very durable material.

You're probably thinking of PVC. PVC oils from plasticizers migrate to the upholstery leaving it brittle and causing it to crack and peel. Polyurethane doesn't have these oils, and hence doesn't have the issue with splitting.

This is called "Key Selling Points," but I think you'll find it helpful

http://asint2.ki.com/prod/pkb/pkb.nsf/113c13b71d41aebf86256e68005c904a/7a9da4e774e74be7862576f9005abe04/$FILE/P201006_Polyurethane_Upholstery.pdf

A negative might be cost relative to PVC. PVC is generally considered to be less beneficial for the environment/health, although the extent to which that is true is debatable.

See this:

"Urethane upholstery is made in a process similar to expanded PVC. However the softness of the urethane is controlled by the amount of cross-linking sites built into the polymer and the degree of cross-linking achieved by catalyst level added to the compound. The solvents used in manufacture still have to be incinerated but there is no plasticizer used so it causes no migration and hardening and cracking problems. However, this material can be relatively much more expensive; usually the price point for this type of material is $20-$30 per yard, depending on weight and backing type."

http://www.faqs.org/patents/app/20090068412

Patricia