Thinset cement, to which polymers have been added, is commonly called latex-Portland cement mortar. In fact, this term is a bit of a misnomer.
The original polymers used to modify thinset were based on latex and the term originates from their use. Today, there are over 10,000 polymers considered by cement chemists when formulating their products. Polymers such as EVA, PVA, SBR, and others are all commonly used in the industry. Many of these polymers are acrylics and not latex chemicals.
The use of these polymers allows specific properties to be imparted to the cement; commonly, freeze/thaw resistance, improved flexibility, and improved adhesion. There are also polymers used to make the cement waterproof or sufficiently elastic so that it acts like an anti-fracture membrane.