The PP alloy was synthesized directly in the reactor with a 4th generation Ziegler-Natta catalyst.It is very different from mechanically blended PP alloys

its properties

especially its impact strength

are superior to those of the latter.However

so far the studies on the stucture of this kind of PP alloys have not been reported.The microstructure of a PP alloy was characterized by IR

DSC

and 13C-NMR.The sample was first fractionated and 8 fractions were obtained.The IR analysis showed that the ethylene content of each fraction is different.Except for the first fraction

which is an elastomer

the others are all hard powders at room temperature.Therefore

the fractions above 50℃ perhaps are all composed of ethylene-propylene block copolymers.DSC analysis showed that the melting curve of the PP alloy became broadened compared with that of i-PP

and a small peak appeared at 120℃.The extracts of PP alloy in boiling heptane and every fractions of PP alloy are composed of ethylene-propylene blocks

whose sequence length are very different.The 13C-NMR spectrum of fraction at 90℃

similar to other fractions at 50～100℃

also indicated that there are long ethylene sequences in macromolecualr chains of PP alloy.According to the above analysis

a conclusion was reached that the E-P copolymer in PP alloy is composed of EPR and E-P blocks

with different ethylene sequence length.This polydispersity structure in PP alloy made it possess very high impact property.