Surface characterization and platelet adhesion studies of plasma polymerized phosphite and its copolymers with dimethylsulfate.
Due to its capability for using a wide variety of organic and inorganic compounds as the monomer source, including those which are not polymerizable by conventional methods, plasma polymerization has been used to incorporate various functional groups onto the substrates of interest. Plasma polymerization of trimethylphosphite and triisopropylphosphite was attempted with an aim to deposit a thin film with phosphorous-containing functional groups such as phosphate or phosphite onto the glass substrate. Sulfur-containing functional groups, such as sulfonate, were incorporated as well with the addition of dimethylsulfate to the phosphite monomer inlet. These plasma polymers and plasma copolymers were very hydrophilic. Incomplete surface coverage was noticed under the processing conditions of low phosphite flow rate, low RF input power and shorter deposition time. Extended deposition duration and higher power input resulted in the formation of voids and pits on the plasma polymer surface. In addition, the surface coverage of the plasma copolymers becomes discontinuous if the flow rate ratio of dimethylsulfate to triisopropylphosphite is too high. In vitro platelet adhesion studies indicated the plasma polymers and plasma copolymers with continuous surface coverage are less platelet activating than the glass control. Moreover, the addition of dimethylsulfate into the phosphite monomer flow led to a further reduction in platelet adhesion and activation than the comparable one. This may be attributed to the effect of the sulfur-containing functionalities, such as sulfonate or sulfate, found on the plasma copolymers.