Vitrimers are a new type of material, in which chemical bonds are constantly exchanged. It has been — Organic Chemistry Chemistry Question
Vitrimers
Vitrimers are a new type of material, in which chemical bonds are constantly exchanged. It has been developed in France by L. Leibler et al. in the early 2010s [1]. These polymers can be easily processed at high temperature, which is used in self-healing materials [1]. Here, we will examine an early example of vitrimer. The polymer network [VISUAL] is formed by monomers A and B [1]. When a fraction ζ of the reactive groups (epoxy and Q groups) reacts (conversion = ζ × 100), all epoxy groups in A and all Q groups in B have reacted at 100% conversion (ζ = 1.0) [2].
Identify the nature of group Q [3].
Model Answer
Q is an acid (Other acceptable answers possible, e.g. Q can be an ester) [3].
Express the average number of ester bonds formed per molecule of A, nEA, as a function of ζ [2].
Model Answer
Each epoxy group in A reacts with two reactive groups from B, thus forming two esters. Since there are 2 epoxy groups, there can be at most 4 esters formed by a molecule of A, meaning nEA = 4 ζ [3].
Express the average number of ester bonds formed by a molecule B, nEB, as a function of ζ [2].
Identify the protonated intermediates U, W, and compounds V, X in the proposed transesterification mechanism [VISUAL] [4].
Model Answer
U, W are protonated intermediates, given in above figure; V = methanol (HOCH3), X = H+ see also the above figure [4].
Determine the activation energy EA from the linear regression of the kinetics plot [VISUAL] [4].
Model Answer
A linear regression of the plot gives y = 9.65 x – 1.54 with r2 = 0.994. From which we estimate EA = R × 1000 × 9.65 = 80.2 kJ mol–1 [4].