Table 1: Overview of the activation energies from the model compound study and stress-relaxation experiments of the vitrimer elastomers. Ea Ea Catalyst model reactions Stress-relaxation (kJ mol-1) (kJ mol-1) Having established Uncatalyzed 73 12 81 3 the effects of various pTsOH 73 3 70 4 DBTL 45 7 31 10 additives on model TBD 102 3 122 19 reactions involving low-MW compounds, the influence of additives on the viscoelastic behaviour on vinylogous urethane based polymer networks was examined. Therefore, low Tg vinylogous urethane networks were prepared by mixing priamine 1074 1, tris(2-aminoethyl)amine 2, acetoacetylated pripol 3 and one of the selected additives from the initial screening study. The spontaneous condensation reaction between acetoacetates and amines (Figure 3) was performed using a small excess of amines versus acetoacetates (a ratio of 0.95) in order to ensure that free amines, required for the exchange reaction, would be available throughout the polymer network. After curing for 6h at 90°C, full conversion of the acetoacetates to the vinylogous urethanes was observed according to infrared spectroscopy (Figure S3). Moreover, these curing conditions appeared also sufficient to remove all the water released during the condensation reaction as no more mass loss was observed by thermogravimetric analysis (TGA) after 4h (Figure S4). Using a monomer ratio of 0.40:0.40:0.95 of 1:2:3, a network with a Tg of - a Young modulus of 2.0 MPa, an elongation at break of 140% and a yield stress of 1.2 MPa was obtained. The mechanical properties of the vitrimers prepared according to this procedure can be tuned by simply changing the monomer ratios (Table S2 and Figure S5).
Table 1: Overview of the activation energies from the model compound study and stress-relaxation experiments of the vitrimer elastomers. Catalyst Ea model reactions (kJ mol-1) Ea Stress-relaxation (kJ mol-1) Uncatalyzed 73 12 81 3 pTsOH 73 3 70 4 DBTL 45 7 31 10 TBD 102 3 122 19 Having established the effects of various additives on model reactions involving low-MW compounds, the influence of additives on the viscoelastic behaviour on vinylogous urethane based polymer networks was examined. Therefore, low Tg vinylogous urethane networks were prepared by mixing priamine 1074 1, tris(2-aminoethyl)amine 2, acetoacetylated pripol 3 and one of the selected additives from the initial screening study. The spontaneous condensation reaction between acetoacetates and amines (Figure 3) was performed using a small excess of amines versus acetoacetates (a ratio of 0.95) in order to ensure that free amines, required for the exchange reaction, would be available throughout the polymer network. After curing for 6h at 90°C, full conversion of the acetoacetates to the vinylogous urethanes was observed according to infrared spectroscopy (Figure S3). Moreover, these curing conditions appeared also sufficient to remove all the water released during the condensation reaction as no more mass loss was observed by thermogravimetric analysis (TGA) after 4h (Figure S4). Using a monomer ratio of 0.40:0.40:0.95 of 1:2:3, a network with a Tg of a Young modulus of 2.0 MPa, an elongation at break of 140% and a yield stress of 1.2 MPa was obtained. The mechanical properties of the vitrimers prepared according to this procedure can be tuned by simply changing the monomer ratios (Table S2 and Figure S5). -
Chemical%20control%20of%20the%20viscoelastic%20properties%20of%20vinylogous%20urethane%20vitrimers-revised.docx