Poly(vinyl chloride), PVC, is a particularly important commodity polymer that accounts for an annual world-wide production of 26 million tons. It is used frequently in the medical field as blood storage bags, endotracheal and dialysis tubing and intravenous catheters. Common plasticizers, namely di(2-ethylhexyl) phthalate (DEHP), are added to PVC to improve the processability and flexibility by lowering the glass transition temperature. However, most phthalate plasticizers are potential carcinogens. There has been extensive research on PVC with surface coatings to improve biocompatibility, surface crosslinking to create a barrier to the plasticizer leaching and surface grafting of hydrophilic polymers for both biocompatibility and reduced plasticizer migration.
A novel surface grafting technique is the grafting of hydrophilic monomers by physisorbed free radical initiators. This modification method can be applied to PVC to attach vinyl hydrophilic monomers by the “grafting from” method. This approach, extending on earlier work involving polymer brush formation on poly(dimethylsiloxane), involves a two-step process: physisorption of a hydrophobic free radical initiator onto a polymer surface followed by radical polymerization of hydrophilic monomers in water. The key step is creating a hydrophobic/hydrophilic diffusional barrier that promotes radical reactions at the polymer surface.
Polymers that have been successfully grafted from PVC films and tubing include:
poly(hydroxyethyl methacrylate) (PHEMA), poly(dimethylacrylamide) (PDMA), poly(hydroxyethyl acrylate) (PHEA), poly(dimethylaminoethyl methacrylate) (PDMAEMA), poly(acrylic acid) (PAA), and poly(4-vinylpyridine) (P4VP). Characterization methods performed include bulk chemical composition by transmission infrared spectroscopy, surface composition using X-ray photoelectron spectroscopy, surface wettability by tensiometry and capillary rise, film thickness determination by infrared, gravimetric analysis and UV-Vis spectroscopy and Mn by gel permeation chromatography. The hydrophilic modification was demonstrated to decrease plasticizer migration via UV-Vis spectroscopy.
A particular system of interest is PVC with grafted poly(4-vinylpyridine) that has been quaternized due to its potential in killing bacteria such as escherichia coli, staphylococcus aureus, staphylococcus epidermis, and pseudomonas aeruginosa. Quaternization has been measured with IR spectroscopy.