N,O Donor zinc complexes in the ring opening polymerisation of cyclic esters

Plastics made from renewable raw materials are a very attractive alternative to petroleum- based materials and are playing an increasingly important role in the production of plastics. Polyesters like polylactide (PLA) and polycaprolactone (PCL) are bio-based and biodegradable bioplastics, which can be produced from starchy plants. Due to its favourable mechanical properties, PLA in particular is a good substitute for existing plastics. It is used as packaging material, in medical applications and in the electronics industry. The ring-opening polymerisation (ROP) of lactide (LA) on an industrial scale is usually carried out using the catalyst tin(II)octanoate (Sn(Oct)2). This catalyst polymerises lactide to the polymer via a coordination-insertion mechanism. Besides having good polymerisation properties, the catalyst is toxic and it remains in the polymer matrix after polymerisation and accumulates in the soil after composting. Therefore, the catalyst must be replaced by non-toxic systems in order to avoid risks to organisms and nature. Neutral N,O-guanidine ligands and zinc as a biocompatible metal represent a good alternative to the tin-containing catalyst. In this dissertation numerous non-toxic N,O-guanidine zinc complexes are presented. The guanidines have either an aromatic or an aliphatic backbone. The aromatic backbone of the guanidine was functionalised with substituents having electron-donating and electron- withdrawing properties at different positions of the aromatic backbone to investigate their electronic influence on the catalytic properties of the complexes. The structure of the synthesised zinc complexes was solved by X-ray crystallography and analysed by NMR and IR spectroscopy as well as mass spectrometry. The activity of the systems was investigated by polymerisation studies with technical non-purified lactide or distilled e-caprolactone. Polymerisation was monitored by 1H-NMR measurements or in situ Raman spectroscopy. The rate constants kapp and kp were determined to classify the catalytic activity of the systems. Some complexes reached the activity range of the industrially used catalyst Sn(Oct)2. In addition, the influence of the different aromatic substituents on the activity in the ROP of LA was highlighted out by determining the two rate constants. End group analyses were carried out by adding a co-initiator to clarify the mechanism. The analysis was performed by MALDI- ToF measurements and 1H and 19F NMR spectroscopy. In three cooperation projects N,O- donor zinc complexes with anionic ligand systems were tested for their catalytic activity in the ROP of lactide in bulk and in solution. The focus was laid on the industrial applicability of the systems and the activity in solution at room temperature.