A Sweet Solution to Reducing Plastic Pollution?

The parallel issues of pollution, plastic waste, and the limited availability of natural resources drive efforts to find sustainable materials that are not based on petrochemicals and do not generate non-degradable waste. Tae-Lim Choi, Seoul National University, Republic of Korea, and colleagues have developed useful and fully biodegradable polymers from two readily available and potentially entirely sustainable sugars: D-glucose and D-galactose.

Cascade Polymerization

The team created monomers derived from glucose and galactose that contain an endocyclic alkene in the sugar ring and a terminal alkyne. These monomers can undergo a cascade polymerization to generate new polymers. The ring-opened sugar moiety is incorporated into the polymer backbone.

Tests on the resulting polymeric materials show that the polymerization reactions are well-controlled, show a linear increase in molecular weight, and have “generally narrow molecular weight dispersity values”. The team was also able to use the two different sugar derivatives to prepare a block copolymer. The polymers quickly fall apart under acidic conditions, showing their potential for degradation at end-of-life for any product made from them.

Sugar Diversity

While vegetable oils, terpenes, amino acids, lignin, and carbohydrates have all been used in polymerization schemes, the team points out that simple sugars have many advantages. First, mono- or di-saccharides are widely available from many different sources. These substances are generally environmentally benign and non-toxic. Critically, they are structurally diverse and relatively easy to functionalize, which means they could be used as the building blocks for degradable polymers with a wide range of properties and characteristics, given the right chemical tuning.

Of course, there are polymers with pendant sugar molecules on the polymer backbone and a few examples of polymers made from sugar monomers. The traditional approach to the latter has been the step-wise construction of a polymer from the sugar monomers. Bhaumik and colleagues hoped that a cascade polymerization approach would be much more efficient and allow for ease of manufacture in a way that is not possible via a step-wise polymerization. The team obtained high molecular weights up to 135 kilodaltons.

Next Steps

The next stages in this research will be optimizing the sustainability of the monomer synthesis and exploring post-polymerization functionalization to endow the materials with useful properties, such as making them water-soluble. The team also hopes to find ways to tune the degradability of the polymers so that they can be made for particular applications with specific lifetimes.