Design of tough adhesive from commodity thermoplastics through dynamic crosslinking

Description


Fig. S1. 1 H NMR (400 MHz, CDCl3) of SEBS (black) and S-Bpin (red) triblock copolymer.
The degree of functionalization was calculated following a literature procedure (1) based on the relative intensity of the methyl group in 1,2-butylene unit of the polymer chain (peak c) with respect to the increased integral ratio of the overlapping SEBS-methylene and Bpin methyl resonance (peaks b and e at 0.9−1.5 ppm). It was observed that 95% of original styrene (30 mol %) was borylated. The concentration for both SEBS and S-Bpin (20 mg/0.6 mL) in CDCl3 was kept constant during the measurement.      TGA curve to check the water stability of this composite; TGA was measured before and after the sample was immersed under DI water for 7 days and compared, (C) FTIR spectra to investigate the chemical stability of composite sample before and after 7 days water exposure. Photo Credit: Md Anisur Rahman, ORNL.        To understand the impact on adhesive behavior of SiNP S-Bpin composite film with a smaller area, a 9 mm 2 , and 36 mm 2 composite adhesive film with 20 wt% SiNP S-Bpin was applied to Al and steel substrates and the lap shear strength was measured by the identical procedure (Fig. S14).
The measured adhesion is almost similar for both surface areas which is consistent with others.
The adhesion for dry adhesive is higher than the adhesion measured using a composite solution, which is consistent with the literature (37) and may be due to the uniform surface coverage by the adhesive composite film, compared to solution casting, where the drying process might create unavoidable voids.   S16. The latter structure has two OH groups in place of where the pinacol-type moiety was originally located when the polymer was synthesized. DFT calculations were conducted to assess the binding strengths of the boron ester moieties to a metal oxide surface: both for a mono-dentate product and for a bi-dentate product, where the molecule bonds to the surface via either one oxygen atom or via two oxygen atoms. The mono-dentate binding (State 2) was found to be more energetically favored than the bi-dentate binding (State 3). States 3 through 5 in Fig. S16 were included to explore the possibility of water or hydroxyl groups affecting the binding. It was found that reaction with water was unfavored, and even if such reaction occurred, the most stable result would remain a mono-dentate bound polymer, as explained further below. Surface hydroxyls and surface protons could facilitate such reactions with the same stoichiometry as water, without any explicit water molecules being present or created.
In all structures case, we included an iso-propyl group in para-position of the benzene ring to represent the scenario where the boron ester is part of a polymer chain (initially with a pinacoltype moiety). The binding energies were computed using density-functional theory (59, 60) as  (65) is used for the Brillouin zone integration due to the large size of the supercell. The optimization process allows the nuclear positions as well as the size/shape of the simulation box to change with force and energy convergence criteria of 0.05 eV/Å and 10 −5 eV, respectively. The aluminum surface is modeled as the hydroxylated -Al2O3 (001) surface as described in (31) Table S4, explained below.

DFT Calculated Energetics
We first optimized the pristine metal oxides, a silica (101) Table S4 and S6. Equations S1 and S3 are for mono-dentate adsorbates and Equations S2 and S4 are for bi-dentate adsorbates (note the subscripts in O2 and O1). The individual species energies, reaction energies, and state energies are shown in Tables S4 -S6, where for the reaction energies and the state energies a more negative is more energetically favored. The values in Table S5 are not adsorption energies nor binding energies, but energies for the full replacement reaction to assess the favorability of the reaction. The term − is the energy of the OH saturated metal oxide slab before reaction.  Table S4. The reaction energies for S1 through S4 are provided in Table S5. While it is useful to have these reaction energies, it is more useful to consider the state energetics for the mechanistic network shown in Fig. S16 on a common scale. This is done in Table S6. We cannot exclude the possibility that amorphous or otherwise curved oxide surfaces are capable of more strongly accommodating a bi-dentate configuration, but that was not seen in our calculations. In our calculations, we see that State 2, the mono-dentate state with pinacoxy moiety still bound is more stable than the bidentate state. We also see that humidity from the surroundings pushing the system to states 4 and 5 is not favored over any of the three oxide surfaces. Additionally, that even if humidity managed to push the system into states 4 and   Iron Oxide 5 M+C+B-2*A -3949.29 0.72 ‡States 4 and 5 have the energies subtracted of water molecules to account for the change in number of atoms in the electronic structure relative to State 1, as depicted in Fig. S16. Similarly, States 3 through 5 include the energy of a gas phase pinacoxyl molecule to ensure the absolute electronic structure energies are comparable.
The negative and positive ∆ρ correspond to the region where the electron density is lost and gain, respectively on forming combined system. This induced charge density analysis was only conducted for the most strongly bound state.