Techniques to monitor the UV curing of potential solvent-free film-coating polymers

Abstract

A methodology has been established for systematically evaluating polymer films produced by UV curing. Cast films of 1,3-bis[(p-acryloxymethyl)phenethyl] tetramethyldisiloxane (I) and norborenylpolydimethylsiloxane (II) were cured by UV irradiation. The films were evaluated from real-time FTIR studies, a non-rheologically destructive method for determining microviscosity, dynamic mechanical thermal analysis (DMTA) and leaching and swelling studies. Real-time FTIR indicated that while conversion from prepolymer to network was complete for II, conversion was only 80% for I with 0.05% benzoin methyl ether (BME), an initiator, and only 60% with 0.5% BME. Results of DMTA show the glass transition temperatures (T g values) of the films to have an inverse rank order correlation with conversion. Along with microviscosity results, this is indicative of a diffusion rate-limited curing reaction. Results of leaching and swelling studies demonstrated greater rates and extents of leaching and swelling from films prepared with a lower concentration of initiator (0.05% BME). These observations were in good agreement with the results from the microviscosity and DMTA studies which showed larger free volumes and lower T g values as well as slightly lower crosslinking densities in films prepared with less initiator. The methods presented in this paper have been shown to be useful in quantifying the reaction of this new class of film formers and in identifying the mechanisms of film formation.