The temperature-dependent structure of glass-forming poly and oligo(methyl acrylate)

Glassy polymers are important in applications ranging from structural (medical implants, additive manufacturing), to optical components, coatings, or membranes for controlled ion or gas transport. However, the fundamental mechanisms behind glass formation are not well understood, and chain connectivity and flexibility makes glass-formation in polymers particularly complex. The chain-length plays an important role in polymer structure and dynamics and the glass-transition behaviour can be divided into three main regimes: (I) a short-chain regime, (II) an intermediate (~2-10 Kuhn steps), and (III) a long-chain regime where the dynamics are chain-length independent. These regimes show clear structural and dynamic signatures, but the detailed behaviour within these three regimes are not well understood. To address this, we here propose to use neutron diffraction at NIMROD to determine the temperature-dependent structural evolution, in terms of the position and width of the structure factor contributions for a model polymer: poly(methyl acrylate) (PMA). PMA is identified as an ideal model polymer for this investigation due to its: (i) clear regime behaviour, (ii) well-controlled synthesis, (iii) suitability for complementary experimental and computational studies. The analysis of the diffraction data will be supported by MD simulations, and the diffraction data will form an essential basis for future QENS investigations of the dynamics in PMA.