Since acrylic polyols have higher molecular weights and solution viscosity than isocyanate crosslinkers, efforts to reduce the VOC content of urethane coatings have primarily focused on lowering the solvent demand of the acrylic polyols. Usually, lowering the molecular weight (Mn) or hardness (Tg) of the polyols reduces solvent demand but also has a negative impact on coating performance and ease of use. The main reason for this drop in performance is that the functionality of the polyol decreases linearly with molecular weight. Hence, as Mn goes down, the crosslinking ability of the polyol and the performance of the coating decrease.
Over the past several years, we have been working to overcome this inherent limitation by developing a new class of acrylic polyols based on allyl alcohols. Lyondell is a leading producer of allyl alcohol, which it produces by isomerization of propylene oxide. This has led to the development of liquid and solids polyols with improved functionality and lower solvent demand compared to conventional polyols made from HFAs.1