(755a) Systematic Tuning of Cross-Linking in Vapor-Deposited Polymer Thin Films

Initiated Chemical Vapor Deposition (iCVD) is a low-energy process for synthesizing functional polymer thin films. In the iCVD process, vapor-phase monomer(s) and thermally-labile initiator pass through an array of heated filaments.  The initiator decomposes into radicals; these radicals and the monomer(s) adsorb onto a cooled substrate, and simultaneous free radical polymerization and thin film formation occur. Since surface tension and de-wetting effects are absent, iCVD thin films conform to the geometry of the underlying substrate. Additionally, the benign reaction conditions inherent to this process allow for complete retention of polymer functionality, as well as the ability to deposit on delicate substrates. Divinylbenzene (DVB) is an excellent cross-linking molecule for iCVD copolymers due to its high vapor pressure and vinyl bond reactivity.   The vinyl bonds and aromatic ring of DVB are also IR-active, facilitating quantitative study of DVB reactivity and incorporation into copolymers. 

Despite the utility of DVB, the properties of iCVD poly(divinylbenzene) (PDVB) and DVB-containing copolymers are not well-studied. The effect of initiator concentration on vinyl bond reactivity of DVB has been explored using FTIR spectroscopy. The incorporation of DVB into a poly(4-vinylpyridine) (P4VP) and PDVB copolymer has also been quantified, as well as the effect of DVB concentration on the number of hanging vinyl bonds.  Experimentally-determined sticking probabilities and monomer reactivity ratios and the effect of DVB incorporation on mechanical properties such as Young’s modulus are also explored.