- 1:30 PM

Initiated Chemical Vapor Deposition of Polymer Thin Film Hydrogels

Ranjita K. Bose and Kenneth K.S. Lau. Department of Chemical and Biological Engineering, Drexel University, 3141 Chestnut St., Philadelphia, PA 19104

Initiated Chemical vapor deposition (iCVD) is a one step surface polymerization technique without the use of solvents. The elimination of solvents is especially beneficial in biomedical applications because residual organic solvents in solvent-processed matrices decrease the activity of incorporated factors and promote inflammatory responses in vivo. In iCVD selective thermal decomposition of species is achieved using resistively heated filament wires. Furthermore, iCVD combines the dry environment of chemical vapor deposition (CVD) with a radical polymerization solution chemistry without the liquid phase by thermally creating an initiator radical and combining it with monomer units repeatedly. Additionally, to promote surface adsorption of reactive species, iCVD relies on a cooled particle bed that is at a temperature (usually room temperature) much lower than the initiator activation temperature. This conveniently enables particle materials, for example, pharmaceutical drugs, proteins and polymer systems that may degrade at elevated temperatures to be treated via iCVD without compromising their material integrity. Also, by using controlled polymerization chemistries, iCVD produces exceptionally clean polymers with stoichiometric compositions, high molecular weights, and with no residual solvents, excipients, glidants, or plasticizers.

In this work, we produce thin films of hydrogel-like polymers for potential bio-applications. Poly(ethylene glycol) (PEG) is a technologically important polymer with many biomedical applications including tissue engineering, drug delivery, non-biofouling membranes and spatial patterning of cells. In this work, we created PEG thin films by iCVD without the use of solvents. We also created thin films of poly(2-hydroxyethyl methacrylate) (PHEMA), which is a hydrogel and does not dissolve in water. In addition to synthesis of homopolymers of PEG and PHEMA we also synthesized copolymers of PEG-PHEMA. Depending on the composition, PEG–PHEMA block copolymers may be water soluble or water insoluble. The presence of a second monomer gives us the freedom to change many variables including the percentage of each monomer.

Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies showed that the chemistry of PEG obtained by iCVD synthesis matched closely to PEG obtained from solution synthesis. The effect of substrate temperature, system pressure and reactant flowrates were studied to develop a kinetic model for the iCVD of PHEMA and PEG. This work showed that iCVD can be used to create copolymers of PEG-PHEMA. Cationic polymerization of PEG as well as copolymerization in vapor phase was shown to correspond well to those in the liquid phase. This work demonstrates that iCVD can directly apply liquid polymerization chemistries with great versatility.