A novel sequential dual-curable thermosetting system with a custom-tailorable structure based on a click thiol–epoxy reaction and excess epoxy is presented.

An extensive characterization of a sequential dual-curing system based on off-stoichiometric "thiol-epoxy" mixtures was carried out using thiol compounds of different functionality. The intermediate and final materials obtained after each curing stages at different thiol-epoxy ratios were studied by means of thermomechanical and rheological experiments. The storage and loss modulus and the loss factor tan δ were monitored during the curing process to analyse gelation and network structure build-up. The critical ratio for gelation was determined making use of the ideal Flory-Stockmayer theory and compared with experimental results. Intermediate materials obtained in the vicinity of the theoretical critical ratio did not have the mechanical consistency expected for partially crosslinked materials, did not retain their shape and even experienced undesired flow upon heating to activate the second curing reaction. The rheological results showed that the critical ratio is higher than the predicted value and that a softening during the second curing stage affects the shape-retention at this ratio. From the thermomechanical results, a wide range of intermediate and final materials with different properties and applicability can be obtained by properly choosing the thiol-epoxy ratio: from liquid-like to highly deformable intermediate materials and from moderately crosslinked (deformable) to highly crosslinked (brittle) final materials.

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This paper presents a new methodology to develop "thiol-epoxy" shape-memory polymers (SMPs) with enhanced mechanical properties in a simple and efficient manner via "click" chemistry by using thermal latent initiators. The shape-memory response (SMR), defined by the mechanical capabilities of the SMP (high ultimate strength and strain), the shape-fixation and the recovery of the original shape (shape-recovery), was analyzed on thiol-epoxy systems by varying the network structure and programming temperature. The glass transition temperature (T g ) and crosslinking density were modified using 3-or 4-functional thiol curing agents and different amounts of a rigid triglycidyl isocyanurate compound. The relationship between the thermo-mechanical properties, network structure and the SMR was evidenced by means of qualitative and quantitative analysis. The influence of the programming temperature (T prog ) on the SMR was also analyzed in detail. The results demonstrate the possibility of tailoring SMPs with enhanced mechanical capabilities and excellent SMR, and intend to provide a better insight into the relationship between the network structure properties, programming temperature and the SMR of unconstrained (stress-free) systems; thus, making it easier to decide between different SMP and to define the operative parameters in the useful life.

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© 2017 Elsevier B.V. A new triglycidyl eugenol derivative (3EPO-EU) was synthesized and characterized by spectroscopic techniques, and used as starting monomer in the preparation of novel bio-based thiol-epoxy thermosets. As thiols, commercially available tetrathiol derived from pentaerythritol (PETMP), a trithiol derived from eugenol (3SH-EU) and the hexathiol derived from squalene (6SH-SQ) were used in the presence of 4-(N,N-dimethylamino)pyridine as the basic catalyst. A flexible diglycidyl ether derived from hexanediol (2EPO-HEX) was also introduced in order to enhance conversion in formulations containing 6SH-SQ. The evolution of the curing was monitored by differential scanning calorimetry. The materials obtained are rigid at room temperature and showed Tgs up to 103 °C. The thermal stability, thermomechanical and mechanical properties were evaluated and discussed in terms of the structural characteristics of the resulting materials.Postprint (author's final draft

A series of shape-memory epoxy thermosets were synthesized by crosslinking diglycidyl ether of bisphenol A with mixtures of commercially available hyperbranched poly(ethyleneimine) and polyetheramine. Thermal, mechanical and shape-memory properties were studied and the effect on them of the content and structure of the hyperbranched polymer was discussed. Measurements showed that the glass transition temperature can be tailored from 60 C to 117 C depending on the hyperbranched polymer content, and all formulations showed an appropriate glassy/rubbery storage modulus ratio. Shape-memory programming was carried out at TgE 0 given the excellent mechanical properties of the materials, with maximum stress and failure strain up to 15 MPa and 60%, respectively. The resulting shape-memory behavior was excellent, with maximum shape recovery and shape fixity of 98% as well as a fast shape-recovery rate of 22%/min. The results show that hyperbranched poly(ethyleneimine) as a crosslinking agent can be used to enhance mechanical and shape-memory properties with different effects depending on the crosslinking density. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 00, 000-000

Novel bio-based and dual-curable thermosets were prepared from eugenol derivatives. The curing sequence combined two click reactions, a photoinduced radical thiol-ene reaction followed by a thermally activated thiol-epoxy reaction.\ud Eugenol was transformed into a triallyl (3A-EU) and a diallyl glycidyl derivative (2AG-EU) with high yields, and they were used as starting monomers in order to study the thiol-ene reaction and the dual-curing process, respectively. Three different thiol crosslinkers were tested, one commercially available tetrathiol derived from pentaerythritol (PETMP) and two other that were also synthesized: a trithiol derived from eugenol (3SH-EU) and a hexathiol derived from squalene (6SH-SQ).\ud \ud FTIR and DSC were used to monitor both curing stages and analyze the obtained materials. The results evidenced the occurrence of side reactions that led to incomplete thiol-ene reaction. The dual-curable materials showed higher Tgs than the materials obtained by a simple thiol-ene process and presented higher mechanical and thermomechanical performance.Postprint (author's final draft