Hybrid thiol-acrylate-epoxy polymer networks: Comparison of one-pot synthesis with sequential reactions and shape memory properties

• Published in: Polymer (Guilford) 2016-07, Vol.96, p.198-204
• Main Authors: Dhulst, Elizabeth A., Heath, William H., Torkelson, John M.
• Format: Article
• Language: English
• Subjects: Acrylates; Mechanical properties; Molecular weight; Networks; Shape memory; Shape memory polymer; Synthesis (chemistry); Thermal properties; Thiol-acrylate; Thiol-epoxide; Thiols
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2016.04.032

Hybrid polymer networks are synthesized using thiol-, acrylate- and epoxide-functionalized reactants. The thiols react with both acrylate and epoxide groups, but acrylate and epoxide groups are unreactive with each other. Past research efforts on this system have employed a combination of sequential photo-initiated and thermally initiated reactions of thiols with (meth)acrylate and epoxide functional groups and have led to single-phase materials. Analysis of reaction kinetics shows that thiol-acrylate reactions are much faster than thiol-epoxy reactions; consequently, we have also developed a one-pot synthesis of thiol-acrylate-epoxy hybrid networks using room temperature reactions and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalyst. For the DBU-catalyzed reaction conditions tested, such one-pot reactions yield materials with properties identical within error to those of materials made by sequential reactions involving thiol-acrylate first and thiol-epoxide second. With low molecular weight reactants, homogeneous, single-phase materials are produced which exhibit the same thermal and mechanical properties regardless of whether reactions are sequential or simultaneous. With some higher molecular weight reactants, e.g., 2000 g/mol diacrylate, novel phase-separated thiol-acrylate-epoxide polymer networks are produced with properties that are highly tunable by sequential reaction order. Beyond good mechanical properties, some of the resulting phase-separated networks are very good shape memory polymers, with shape-fixity values above 95% and shape-recovery values above 99% after multiple cycles. [Display omitted] •Thiol-click chemistry applied to multi-component polymer synthesis.•Thiol-acrylate-epoxy networks synthesized in one-step simultaneous synthesis.•Simultaneous synthesis allows for complete thiol conversion.•Thermal and mechanical properties enhanced over thiol-acrylate networks.•Phase-separated materials produce polymers with shape-memory characteristics.