The second model we use is a periodic supercell of the polymer that is periodic along the polymer chain, using a supercell with two explicit eight monomer chains of each polymer. This allows us to explore the impact of TMA content in the polymer, in particular the swelling of the two polymers, facilitating for the first time a direct comparison with the experimental results and also allows us to assess limitations associated with a non-periodic oligomer model of the polymer. Two further periodic models are used: the large model is used for infiltration and swelling described above and a smaller model of one chain that is six monomers long for the calculation of the IR vibrational modes upon TMA infiltration and adduct formation (due to the high cost of these calculations). The periodic DFT calculations were carried out using the Vienna Ab initio Simulation Package (VASP) 5.4. The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation of the exchangecorrelation functional was used. An 800 eV plane-wave cutoff energy was used which minimizes the Pulay stresses during ion and lattice relaxations. Projector augmented wave (PAW) potentials were used, with 1 valence electron for hydrogen, 4 for carbon, 6 for oxygen and 3 for aluminium. Gaussian smearing with a width of 0.1 eV was used for all calculations. Grimme's version 3 dispersion correction was included to improve the description of non-covalent interactions between the polymer chains. Structural relaxions used an electronic convergence criteria of 10 -4 eV for each ionic step and a force convergence of 0.02 eV/Å. Phonon vibration modes were calculated using finite central difference with a displacement of 0.015 Å, using an electronic convergence criteria of 10 -6 eV.