Traditional polyurethane reactive hot-melt (RHM) adhesives make use of blends of polyester, polyether and, in rare cases, conventional petroleum-based polycarbonate polyols. Although polyesters and polyethers contribute properties to RHM adhesives such as good workability and rapidly building strength, polyesters have poor hydrolytic stability and polyethers are prone to oxidation under UV light. Conventional petroleum-based polycarbonates have excellent performance properties in these areas but come at a much greater cost, making them suitable only for specialty applications.
Due to their high carbon dioxide (CO2) content, polypropylene carbonate polyols are a sustainable and cost-effective option with performance properties that exceed those of conventional polyols in polyurethane RHM systems. CO2-based polyols are formed by the copolymerization of epoxides and CO2. This results in aliphatic polycarbonate structures, the most common of which are polypropylene carbonate (PPC; from propylene oxide, PO), and polyethylene carbonate (PEC; from ethylene oxide, EO). The degree of CO2 incorporation is controlled primarily by the reaction catalyst, where perfectly alternating material has the highest CO2 content (43 wt% for PPC, 50 wt% for PEC).