There are certainly lower grade resin systems in the market.  One of the main ones used to produce lower cost wheels and tires is based on a polypropylene glycol (PPG) system.  This system is based on purchasing lower grade polyols to cut cost.  While the product is initially cheaper, the wheels and tires cannot withstand the load and heat buildup found in most applications on high performance narrow aisle trucks.  The initial savings is lost as back end labor and overhead costs rise from more frequent replacements.