Polylactide (PLA) is a biodegradable and biocompatible polymer which is attracting much attention for environmental issues imposed by the petroleum-based polymers. PLA can be used as medical polymer in surgical sutures, implants tissue and many other areas. However, one of the main shortcomings of PLA is its brittleness in nature and relatively poor mechanical properties, which often limits its further application. It is generally accepted for polymeric materials that some mechanical properties of oriented structures can be improved as the molecular weight of PLA increases. The outcome of this thesis will provide the knowhow to achieve ultrahigh molecular weight of polylactides, and further to improve the mechanical properties and extend its range of applications. 

In this work, different catalytic systems for the synthesis of ultra-high molecular weight (UHMW) polylactide are considered. The ultra-high molecular weights are expected to exhibit superior mechanical properties of uniaxially oriented fibers and tapes, where the oriented chains are likely to provide enhanced mechanical and physical properties of this material in high performing applications. For the catalytic systems considered, the reaction conditions and initiators are investigated. The resulting molecular characteristics and mechanical properties of the synthesized polymers will be evaluated.

On the contrary to the brittle nature of PLA, Poly(ε-carprolactone) (PCL) is elastic and flexible with a relatively low melting point (60 oC) and low glass transition temperature (-60 oC). Hence, ultra-high molecular weight PCL will be also synthesized by using the same catalytic systems employed for achieving UHMWPLAs. PCL is also used in different biomedical applications, such as in scaffolds for tissue engineering of bone and cartilage owing to its excellent biocompatibility, flexibility, and thermoplasticity. 

It is well documented that the complementary physical properties of PLA and PCL have the potential to enhance toughness of PLA. Thus block copolymer synthesis in the literature is reported. To enhance the toughness and mechanical properties of the block copolymers attempt is made to synthesize ultra-high molar mass of the two polymers in the block copolymer. But their molar masses (and consequently their mechanical properties) are always on the low side. For this reason, the synthesis of high molecular mass PLA and PCL multiblocks (di- and tri-blocks) will be attempted. Furthermore, it is interesting to study the synthesis of high molar masses PLLA and PDLA stereoblocks especially their ability to crystallize during the polymerization and test the possibility to prepare stereocomplex only (no homopolymer) during synthesis. The resulting molecular characteristics (molar mass, microstructure) and mechanical properties (tensile strength and modulus) of the synthesized multiblock-polymers will be also evaluated.