Synthesis and Characterization of Defined Branched Poly(propylene)s with Different Microstructures by Copolymerization of Propylene and Linear Ethylene Oligomers (Cn = 26–28) with Metallocenes/MAO Catalysts

Summary: Copolymers of propylene and hexacosene (C_n = 26–28) were synthesized in the presence of three different metallocene catalysts activated by methylaluminoxane. The poly(propylene) copolymers were prepared with iso‐, syndio‐, and atactic backbone microstructures by using different symmetric metallocenes such as rac‐{Me₂Si2‐Me‐4‐(1‐Naph)Ind]₂}ZrCl₂ ( 1 ), Ph₂C(Cp)(Flu)]ZrCl₂ ( 2 ), and (H₃C)₂Si(9‐Flu)₂]ZrCl₂ ( 3 ) and up to 46.6 mol‐% comonomer content in the feed. The influence of the incorporated linear, ethylene‐based side chains into the poly(propylene) backbone were investigated by DSC, GPC, and ¹³C NMR. Generally, a decreasing content of comonomer in the feed enhances the activity of metallocene based catalysts. The determination of the branched microstructure by ¹³C NMR of the copolymers allows a smart identification of the amount of inserted hexacosene because of the separated backbone and side chain signals. Moreover, the relationship between the population of the side chains and the melting behavior of resulting copolymers were discussed. The melting point of the syndiotactic and isotactic poly(propylene) backbone decreases with increasing hexacosene content. When the inserted comonomer content exceeds 2 mol‐%, a second melting point of the crystallized ethylene based side chains can be observed which increases with an increasing amount of hexacosene.

Thermal behavior of isospecific hexacosene/propylene copolymers in dependence on the incorporation of hexacosene.