Tuning crystallinity in PDMAEMA-g-PEG Bottlebrush Copolymers

Polymer crystallization has been attracting great scientific interest as it determines to a large extend the final properties of the materials. Moreover, tuning polymer crystallinity has emerged as a major challenge and a subject of intense research. In this work, we have developed a series of well-defined poly(2-(dimethylamino)ethyl methacrylate)-g-poly(ethylene glycol), PDMAEMA-g-PEG, graft copolymers with different lengths of the PEG side chains aiming to tune the PEG crystallinity. The main PDMAEMA chain had M_n = 44,000 g/mol and the graft copolymers were prepared by chemically attaching methyl terminated PEG chains of different molecular weights (M_n = 500 to 5000 g/mol) by a quaternization reaction on the tertiary amine groups of PDMAEMA. Graft copolymers comprising single- and mixed-length PEG chains of different mole ratios were synthesized. The crystallization behavior of all polymers was studied using non-isothermal and isothermal Differential Scanning Calorimetry (DSC) and Small- and Wide-Angle X-ray Scattering (SAXS-WAXS) measurements. Grafting of single PEG chains on the PDMAEMA backbone resulted in a reduced crystallinity compared to the bulk PEG, which was reduced even further in the case of mixed-length grafted chains. In this case, the overall crystallinity and the activation energy of the crystallization process decreased with increasing the fraction of lower length PEG chains.