(93b) Polymerizations In The Service Of Nanotechnology And Intelligent Biomaterials Science

The polymerization of methacrylate and acrylate monomers occurs through the classic free radical mechanisms. A multifunctional monomer having two or more double bonds creates a tie-point or crosslink, resulting in the formation of a crosslinked polymeric network. Classically, the reaction scheme is described by a system of coupled differential equations that incorporate the mass balances, the energy balances, and the rate equations. The classical approach does not completely capture several important and fundamental processes occurring during polymerization. These non-idealities lead to decreased mechanical strength of the material, regions of phase separation, and to limited conversions. Such phenomane are particularly important in polymerizations and copolymerizations leading used in microelectronic applications, replication of sound, formation of recognitive, intelligent gels and variou sbiomedical polymers.

We have developed models that combine the reaction kinetics of free radical polymerizations and the statistical basis for network formation. These models involve the simultaneous solution of coupled differential equations that describe the reaction kinetics, mass, and energy balances. However, these models rely on a mean-field approach. While this approach yields good results for reaction conditions involving low crosslinking density, it shows deviation from experimental results for medium to densely crosslinked systems. Numerous non-idealities seen in densely crosslinked materials are not described by this model or by the mean-field approximation. Attempts have been made to account for several of the non-idealities in this model. Statistical methods have been developed and applied to the polymerization of crosslinked systems. This methods give good results for the calculation of molecular weight versus conversion and could handle phenomena such as cyclization and effects of gelation. Good agreement with experimental results is shown for polymerizations at low crosslinking density. The models accurately describe the effect of cyclization on the onset of gelation and on the final network structure.