Polymers from fatty acids: Poly(ω-hydroxyl tetradecanoic acid) synthesis and physico-mechanical studies

This Article describes the synthesis and physicomechanical properties of bioplastics prepared from methyl ω-hydroxytetradecanoic acid (Me-ω-OHC14), a new monomer available by a fermentation process using an engineered Candida tropicalis strain. Melt-condensation experiments were conducted using titanium tetraisopropoxide (Ti[OiPr] ₄) as a catalyst in a two-stage polymerization (2 h at 200 °C under N ₂, 4 h at 220 °C under 0.1 mmHg). Poly(ω-hydroxytetradecanoate), P(ω-OHC14), M _w, determined by SEC-MALLS, increased from 53K to 110K as the Ti(OiPr) ₄ concentration increased from 50 to 300 ppm. By varying the polymerization conditions (catalyst concentration, reaction time, second-stage reaction temperature) a series of P(ω-OHC14) samples were prepared with M _w values from 53K to 140K. The synthesized polyesters with M _w ranging from 53K to 140K were subjected to characterization by DSC, TGA, DMTA, and tensile testing. Influences of P(ω-OHC14) molecular weight, melting point, and enthalpies of melting/crystallization on material tensile properties were explored. Cold-drawing tensile tests at room temperature for P(ω-OHC14) with M _w 53K-78K showed a brittle-to-ductile transition. In contrast, P(ω-OHC14) with M _w 53K undergoes brittle fracture. Increasing P(ω-OHC14) M _w above 78K resulted in a strain-hardening phenomena and tough properties with elongation at break ∼700% and true tensile strength of ∼50 MPa. Comparisons between high density polyethylene and P(ω-OHC14) mechanical and thermal properties as a function of their respective molecular weights are discussed.