Cylindrical Polymer Brushes with Elastin-Like Polypeptide Side Chains

Monodisperse high molar mass elastin-like polypeptide macromonomers comprising 20 pentasequences (M = 8332 g/mol) were radically polymerized to high degrees of polymerization P-w=590. Polymerization was conducted in water well above the lower phase transition temperature, i.e., in the phase separated regime. The resulting polymers adopt a cylindrical shape as demonstrated by AFM pictures of solutions spin-cast on mica. The directional persistence of the cylindrical brushes was determined by static light scattering to Kuhn statistical segments lengths l(k) = 120 nm at 5 mM aqueous NaCl solution which decreased to l(k) = 54 nm at 0.65 M NaCl. Upon polymerization the phase transition temperature drops significantly and the transition interval becomes sharper. The change of the hydrodynamic radius of the cylindrical brushes was monitored by dynamic light scattering as a function of temperature and revealed a continuous decrease from 20 to 36 degrees C, above of which aggregates of several hundred nm in size start to form prior to phase separation.