Year: 2007
Type: dissertation
Abstract: Propylene was polymerised with individual and mixed metallocenes activated by methylaluminoxane. Homogeneous as well as heterogeneous systems were applied, and copolymerisations were conducted with ethylene, 1-hexene and 1,9-decadiene.\n\nThe copolymers showed lower heat of fusion values and melting temperatures as compared with the corresponding homopolymers. Copolymerisation with 1,9-decadiene resulted in the formation of long-chain branched structures, which was observed as an increase in molecular weight and broader molecular weight distribution. Homopolymers produced with combined heterogeneous catalyst systems had broader or bimodal molecular weight distribution and improved processability.\n\nIn the case of rac-Me2Si(2-Me-4-Ph-1-Ind)2ZrCl2, the presence of ethylene decreased the molecular weight due to β-H transfer to a coordinated ethylene monomer. For rac-Me2Si(2-i-Pr-4-[3,5-Me2-Ph]-Ind)2ZrCl2 this termination route was blocked due to the sterical hindrance created by the bulky substituents of the catalyst. Chemical treatment of methylaluminoxane solution with a sterically hindered phenol was an effective method to remove trimethylaluminium residuals and suppress chain transfer to aluminium.\n\nPropylene was polymerised with a homogeneous binary catalyst system consisting of catalyst precursors Ph2C(Cp)(Flu)ZrCl2 (syndiospecific catalyst) and rac-Me2Si(4-t-Bu-2-Me-Cp)2ZrCl2 (isospecific catalyst). The polymerisation behaviour of the catalysts in the binary catalyst system deviated from the behaviour observed for the catalysts individually, indicating an interaction between the catalysts. It was demonstrated that trimethylaluminium operated as a chain shuttling agent and transferred growing polymer chains between active catalyst sites; a stereoblock copolymer consisting of syndiotactic and isotactic blocks was formed. The binary catalyst system was also applied in 1,9-decadiene copolymerisations, and a novel copolymer structure was produced, in which diene linked together polypropylene chains of different tacticities. The copolymer was tested as compatibiliser in a blend of syndiotactic and isotactic polypropylenes. The compatibilised blend showed higher modulus and yield strength values than a 1:1 blend of syndiotactic and isotactic polypropylenes.
Source: Aaltodoc (Aalto University)
Author: Antti Tynys
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2566976192