pxylylene

pXylylene, commonly referred to as para-xylylene, is a reactive hydrocarbon fragment used as the monomer in the chemical vapor deposition (CVD) process that creates poly-p-xylylene coatings, known commercially as parylene. The term describes the para isomer of xylylene, a divalent fragment derived from the benzene ring with methylene linkages at para positions. In practice, p-xylylene is generated in situ from a stable dimer precursor and then polymerizes upon contact with a surface to form a conformal, cross-linked polymer film.

Production and deposition methods

In typical parylene production, a dimer precursor is heated under vacuum to induce pyrolysis, producing the reactive p-xylylene monomer. This monomer then condenses on all surfaces inside the deposition chamber and polymerizes rapidly, forming a uniform, pinhole-free parylene coating at room temperature. The process is advantageous for coating complex geometries and high-aspect-ratio structures due to its conformal coverage and uniform thickness.

Properties and applications

Parylene coatings derived from p-xylylene offer high moisture and chemical barriers, excellent dielectric properties, and good mechanical strength. They are chemically inert, biocompatible, and optically transparent, making them suitable for protective coatings on medical implants, biomedical devices, electronics, sensors, and MEMS components. The coatings can be tuned for thickness from a few nanometers to several micrometers, with minimal processing temperatures.

Safety and handling

The process involves high-temperature and vacuum conditions with reactive intermediates. Proper engineering controls, ventilation, and enclosure are essential to manage hazards associated with the pyrolysis and deposition steps.

See also

Parylene, para-xylene, xylylene.