Novel Hydrolytically Stable Silane Additives for Improving the Performance of Waterborne Acrylic Roof Coatings

By Jacob D. Shevrin

As global environmental regulations continue to tighten restrictions on coatings containing volatile organic compounds (VOCs), the need for hydrolytically stable additives in waterborne coatings has never been greater. Organofunctional alkoxysilanes are a class of widely used additives in the coatings industry. They act as a bridge between an organic coating and an inorganic substrate, providing adhesion promotion and other important performance improvements.

Given the high moisture sensitivity of organofunctional alkoxysilanes, most silane additives rapidly undergo condensation in waterborne coatings, leading to unworkable viscosities and gelling of the waterborne coatings within the first few weeks or months on the shelf. This has posed a significant barrier to using silane additives in waterborne coatings for all types of applications.

Two organofunctional silane additives that demonstrated positive hydrolytic stability over an extended period of time in waterborne acrylic roof coatings are investigated here. These organofunctional silane additives include an epoxy-functional silane oligomer, VPS 4721, and an aminefunctional silane monomer, Dynasylan® 1505 (Figure 1).

The oligomeric structure of the epoxy-functional silane oligomer allows for slower hydrolysis and condensation rates in a waterborne system compared to a monomeric epoxy-functional silane (such as glycidoxypropyltrimethoxysilane).