Maciej Dębowski

On the copolymerization of monomers from renewable resources: l-lactide and ethylene carbonate in the presence of metal alkoxides

Abstract The copolymerization of l-lactide with ethylene carbonate carried out at 120 °C in the presence of organic derivatives of aluminum, zinc and tin as catalysts leads to the formation of linear polymers of relative molecular masses in the 10 000–30 000 range containing up to 12 mol. % of carbonate monomeric units (m.u.). A decrease in Tg of copolymers down to 48 °C demonstrates the internal plasticization effect for polylactide matrix. In the first reaction step mainly lactide homopolymerization proceeds in the systems studied. Carbonate m.u. incorporate into the growing chain as a result of recurring transesterification processes. Back-biting type intramolecular transesterification reactions dominate in the system and macrocycle compounds containing 1 carbonate m.u. and 3–9 lactic acid m.u. are the main reaction products after prolonged time. On the basis of analysis of the low molecular weight products formed in the polymerization system and products of the model reaction of ethylene carbonate with metal alkoxides, the mechanism of elementary reactions leading to the incorporation of carbonate m.u. into the copolymer chains has been proposed.

Thermally induced structural transformations of linear coordination polymers based on aluminum tris(diorganophosphates)

The thermal transitions of inorganic-organic hybrid polymers composed of linear aluminum tris(diorganophosphate) chains with a general formula of catena-Al[O2P(OR)2]3 (where R = C1-C8 alkyl group or phenyl moiety) have been studied by means of DSC, powder XRD, TGA and TG-QMS, as well as optical spectroscopy. DSC and XRD reveal that most of them undergo reversible structural transformations in the solid state between -100 and 200 °C caused by the changes in conformation of their organic substituents; however, a translational displacement of the rigid polymeric chains occurs only in the case of the derivative bearing long 2-ethylhexyl groups, which becomes liquid at about 140 °C. The thermal decomposition of the studied polymers begins between 200 and 265 °C depending on the type of organic substituent R decorating their aluminophospate core. TGA combined with mass spectrometry of the evolved gaseous products shows that the pyrolytic decomposition of Al[O2P(OR)2]3 proceeds either through β-elimination of olefin (for compounds with C2-C8 aliphatic ligands), or a homolytic cleavage of the P-OR bond (for methyl and phenyl derivatives); both processes are accompanied by condensation of the newly formed POH groups and liberation of water. Powder XRD, FTIR and SEM analyses of the solid residues indicate that thermolysis of Al[O2P(OR)2]3 accompanied by olefin elimination leads to the formation of condensed aluminum phosphates, mainly aluminum cyclohexaphosphate, exhibiting porous morphology. On the other hand, thermal degradation of methyl or phenyl derivatives results in amorphous aluminophosphate residues, and the latter contains conducting carbonaceous phases.