Thermal stability and degradation of some polyacrylate salts

The work carried out in this study has involved the preparation, characterisation and subsequent thermal degradation of homopolymers and copolymers with structures based on metal salts of acrylic acid. Four transition metal salt homopolymers of poly(acrylic acid) were prepared and characterised. The polymers were prepared by polymerisation of metal acrylate monomer and neutralisation of poly(acrylic acid) by the appropriate metal salt. The metals used were cobalt, nickel, copper and zinc. Three copolymers of acrylic acid with styrene and their zinc salts were also prepared. These copolymers contained 1.7%, 5.8% and 11.8% acrylic acid units. The second section of the work involved the thermal degradation of these polymers and copolymers. The thermal degradation experiments were carried out either by ramped programmed or isothermal heating in oxygen free environments. The techniques used to study the thermal degradation of the polymers were thermogravimetry (TG), differential thermal analysis (DTA) direct scanning calorimetry (DSC) and thermal volatilistaion analysis (TVA), with fractionation of the products of degradation by sub-ambient TVA. Mechanisms of polymer degradation are discussed with respect to the degradation products obtained during TVA. The degradation products were identified by mass spectroscopy, gas chromatography-mass spectroscopy and fourier transform infra-red spectroscopy. The thermal degradation of transition metal salts of poly(acrylic acid) occurred by a free radical decomposition process. The thermal stability of the polyacrylates was affected by the particular metal involved. The metal polyacrylates followed the stability sequence Zn=Co>Ni>Cu. The polymers made by neutralisation of poly(acrylic acid) and those made by polymerisation of metal acrylate monomer exhibited similar thermal stability and degradation characteristics. The thermal degradation of the three copolymers of acrylic acid with styrene and the zinc salts of these copolymers occurred by a free radical mechanism. The thermal stability of the copolymers decreased with increasing acrylic acid content. The zinc salt copolymers showed a slight increase in thermal stability compared to the acid copolymer In isothermal heating experiments the rate of degradation of the acid copolymers was decreased by converting them to their zinc salts