Synthesis and electrospinning of poly(ε-caprolactone) from an aluminium-based catalyst

The intention of this doctoral work, first and foremost, has been the identification of a novel catalytic system for the production of Polycaprolactone (PCL) with added functionality through chemical tailoring of the synthetic process. Evaluation of the performance of these materials was conducted on three separate aspects; polymerisation kinetics, formulation into electrospun fibres and spin coated films and rheological responses.

PCL was successfully produced via the use of a Triisobutyl Aluminium (TiBAl) catalytic precursor initiated with each one of three different alcohols 1-Adamantanemethanol (A), Isopropanol (I) and 1H,1H,2H,2H-Perfluoro-1-octanol (F). The catalytic species were further modified via the use of 2,2’-Methylenebis(6-tert-butyl-4-ethylphenol) (MDBP).

Kinetic studies on these reactions concluded that each alcohol initiator affects the velocity of molecular weight increase differently, showing variant activity of three available catalytic sites with polymers of different molecular weights obtained. Introduction of MDBP to hinder two of the three sites caused linear incorporation of the monomer with time on the only available site while slowing down reaction velocity. Molecular weights obtained from these systems were comparable for all alcohol initiators.

A high degree of fibre porosity was achieved via electrospinning of these materials. Electrospun fibres showed no significant morphological differences between samples resulting from different initiators. F-initiated samples presented with improved water contact angles for both electrospun fibre mats and spin coated films. Moreover, F-initiated PCL fibre mats showed superior liquid loading capabilities across the board. These results confirmed the possibility of adding functionality via chemical tailoring of the synthesis.

Finally, rheological studies showcased different performance of in-house PCL compared to commercial counterparts, with higher crystallinities and increased time to achieve maximum storage modulus values under shear. Such observations, in similar fashion to ones for UHMWPE, hint at a disentangled character having been achieved due to processing conditions. It was theorised that synthetic and processing procedures lead to this result.