The main difference is on the stereochemistry.... you can have more control using Ziegler-Natta catalysts.

Where did you get free radical polymerized PP from??? I found only a fairly old reference to such polymer:

http://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/46922/1/rpcjpnv38p096.pdf

Most sources say that propylene cannot be polymerized by free radical mechanism or it yields branched and atactic polymer. The ZN catalysts yield highyl isotactic PP, while metallocene catalysts allow the synthesis of syndiotactic PP.

The properties of the two are really different, because you obtain branced atactic polypropylene by free-radical polymerization. aPP do not form crystall and can be used as hot melt such as amorphous EVA. It has the modulus of a rubber but not the elasticity because the interchain forces are very low.

propylene cannot be polymerized by radical polymerization because of allylic carbon. it can be produced only by coordination polymerization like ziegler natta or mettalocene catalyst.

but polyethylene can be produced by both methods. by radical polymerization it will bring out LDPE with long chain branch AND by coordination polymerization it will bring out HDPE or LLDPE. due to the different side chain the density and crystalinity of them are different. 

propylene cannot be polymerized by radical polymerization because of allylic carbon. it can be produced only by coordination polymerization like ziegler natta or mettalocene catalyst.

but polyethylene can be produced by both methods. by radical polymerization it will bring out LDPE with long chain branch AND by coordination polymerization it will bring out HDPE or LLDPE. due to the different side chain the density and crystalinity of them are different. 

propylene cannot be polymerized by radical polymerization because of allylic carbon. it can be produced only by coordination polymerization like ziegler natta or mettalocene catalyst.

but polyethylene can be produced by both methods. by radical polymerization it will bring out LDPE with long chain branch AND by coordination polymerization it will bring out HDPE or LLDPE. due to the different side chain the density and crystalinity of them are different. 

Пропилен не полимеризуется по свободно-радикальному механизму !!!