Confinement driven crystallization of ABA crystalline soft crystalline block copolymers synthesized via RAFT mediated miniemulsion polymerization
Abstract Waterborne ABA block copolymers of stearyl acrylate (SA) and 2 ethylhexyl acrylate (2EHA) containing crystalline A block and soft middle B block, were synthesized via two step reversible addition fragmentation chain transfer (RAFT) polymerization, using S,S dibenzyl trithiocarbonate (DBTTC) bifunctional RAFT agent. First, miniemulsion polymerization was used for the synthesis of the crystalline domains. Then in the second step 2EHA was fed to the system as a pre emulsion and soft domains were formed. For the sake of simplicity sequential monomer addition was performed without any removal of the unreacted monomer in the first step. Thermal properties of the obtained block copolymers were investigated by means of DSC, which revealed reduced crystallinity by the formation of the block copolymers compared to the crystallinity of the polySA initial block. Morphological properties were studied by means of microscopic techniques after film formation at different conditions. Lamellar phase separation induced by confined crystallization in the particles was shown in the films dried at room temperature. Particle coalescence and higher ordering of the lamellar structure was obtained upon film annealing above the melting temperature of the crystalline domains and the structure obtained was comparable with the one of films casted from THF solution, indicating that equilibrium morphology was already obtained by annealing. Mechanical properties studied using DMTA revealed two transition temperatures and reduced storage modulus as the length of the middle block and casting temperature of the film was increased.