L-Lactide Polymerization by Calix[4]arene-Titanium (IV) Complex Using Conventional Heating and Microwave Irradiation

Since the first contributions by Gedye and Giguere in 1986, a growing attention has been registered on the use of microwave heating in organic synthesis. However still many aspects need to be clarified especially about the so called “microwave effect” and the possible degradation phenomena that may be recognized during polymer synthesis. In this work the complex cone-25,27-dipropyloxy-26,28-dioxo-calix[4]arene titanium (IV) dichloride (1) has been tested for the ring opening polymerisation of L-lactide, comparing the effect of conventional heating with a possible microwave assisted strategy. The polymers obtained were fully characterised (NMR, IR, HPLC-SEC, DSC, MALDI-TOF and WAXD analysis). As expected the use of microwaves irradiation induced an increase of the polymerisation rate. On the other side the use of microwaves resulted in a slightly loss on the control over molecular weight and molecular weight distribution if compared with a conventional thermal treatment.