Two-Stage Reactive Polymer Network Forming Systems

There are distinct advantages to designing polymer systems that afford two distinct sets of material properties an intermediate polymer that would enable optimum handling and processing of the material, while maintaining the ability to tune in different, final polymer properties that enable the optimal functioning of the material. In this study, by designing a series of non-stoichiometric thiol-acrylate systems, a polymer network is initially formed via a base catalyzed Michael addition reaction that proceeds stoichiometrically via the thiol-acrylate click reaction. This self-limiting reaction results in a polymer with excess acrylic functional groups within the network. At a later point in time, the photoinitiated, free radical polymerization of the excess acrylic functional groups results in a highly crosslinked, robust material system. These two stage reactive thiol-acrylate networks that have intermediate stage rubbery moduli and glass transition temperatures that range from 0.5 MPa and -10 degrees C to 22 MPa and 22 degrees C, respectively, are formulated and characterized. The same polymer networks can then attain glass transition temperatures that range from 5 degrees C to 195 degrees C and rubbery moduli of up to 200 MPa after the subsequent photocuring stage. The two stage reactive networks formed by varying the stoichiometric ratios of the thiol and acrylate monomers were shown to perform as substrates for three specific applications: shape memory polymers, impression materials, and as optical materials for writing refractive index patterns.