Synthesis and characterization of high-temperature self-crosslinking polymer latexes and their application in water-based drilling fluid

Self-crosslinking soap-free latexes (PMS) were synthesized by semi-continuous polymerization from methyl methacrylate and styrene with N-(hydroxymethyl)acrylamide (NAM) as high-temperature self-crosslinker and 2-acrylamido-2-methyl-1-propanesulfonic acid as reactive emulsifier. All PMS latexes with varying NAM contents (0–7 wt%) processed high solid contents (~30%) and monodispersed nano-micro particle sizes (180–600 nm). With augment of NAM content, monomer conversion slightly decreased while particle size decreased and then gradually increased, accompanied with increase of coagulum content. The self-crosslinking behavior showed highly dependence on NAM content and temperature, and the self-crosslinked structures were confirmed by FT-IR, XPS, DSC and SEM. The self-crosslinking latexes effectively improved rheological and microporous filtration properties of bentonite-based drilling fluid. Owing to stronger interparticle interactions, the latexes exhibited better viscosity-increasing effect after thermal treatment and stronger fluid-loss-reducing ability at high temperature. The microporous plugging mechanism was revealed to be the combination of heat deforming and self-crosslinking film forming besides physical bridging and filling.