Synthesis of biodegradable styrene copolymers

Abstract

Polystyrene (PS), a versatile polymer with many applications (e.g. packaging) representing about 10% of the total annual polymer consumption, shows practically no biodegradability. In this study a styrene (ST) based copolymer is synthesized and examined regarding its ability to degrade in a composting test. As second monomer, to introduce biodegradable ester groups, 5,6-benzo-2-metylene-dioxepane (BMDO) has been used in radical copolymerization reactions performed in inert and stirred 10 ml Schlenck bottles. The composition of the copolymers was measured by NMR.Their molecular weight (Mw) was done by GPC. Biodegradation was validated with a 4 months test in an aerated bioreactor by monitoring the CO2 production. In a typical copolymerization reaction 25 mol % of BMDO and 0,05 mol% dicumylperoxide (DCP) was added to styrene. Reaction was done during 24 hours at 120°C. The resulting copolymers contained 12 mol% ester groups and had a Mw of 115 000 g/mol. Copolymer reaction parameters are estimated at rBMDO = 0,52 and rST= 7,55. Time and temperature are indicated as important reaction parameters. Other parameters to be investigated are monomer concentrations, initiator and solvent. To validate the potential for biodegradation, 2 low Mw (23340 and 31060 g/mol) BMDO-ST copolymer with respectively 5,7 and 14,2 mol% BMDO were subjected to a 4 month composting resulting in a loss in weight of 21 and 27% respectively. This study showed a potential way to make polystyrene susceptible to biodegradation. In the follow-up study a comprehensive parameter study will be needed to obtain high Mw copolymers with sufficient ester groups incorporated to achieve biodegradation. The higher Mw material will be used to validate the material properties.