Part 3: TPO and PVC
TPO is a single-ply roofing material that can be manufactured in bright white; there is not an urgent need to coat a newly installed TPO roof system. However, there is a demand for coatings that will extend TPO roof systems' life cycles.
Unfortunately, TPO roof systems' smooth, inert surfaces present a significant adhesion challenge to coatings. For TPO roof systems, manufacturer-approved primers are available, allowing for an elastomeric white top coat, such as water-based acrylic. Suffice to say this is not a common application and is an area of ongoing research.
PVC also is smooth, chemically resistant, water-resistant and not easily coated—special primers are required to coat these roof systems. PVC's high levels of liquid plasticizer seem to present a bigger challenge than its slick surface. The polymer's chemical resistance also inhibits the development of suitable primers. PVC gets its white color from pigments added to the polymer during the manufacturing stage.
It's worth mentioning that TPO and PVC membranes easily can be misidentified in the field. Because they require different primers and coatings, examining a test patch is a prudent caution before coating an unidentified white membrane.
Source: Professional Roofing