Mechanical and Morphological Properties of Waterborne ABA Hard-Soft-Hard Block Copolymers Synthesized by Means of RAFT Miniemulsion Polymerization.

Gordana Siljanovska Petreska,Arantxa Arbe,Maria Paulis,Clemens Auschra

doi:10.3390/polym11081259

Gordana Siljanovska Petreska, Arantxa Arbe + Show 2 more

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https://doi.org/10.3390/polym11081259

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Abstract

High molecular weight waterborne ABA block copolymers of styrene (St) and 2-ethylhexyl acrylate (2EHA) containing hard and soft domains were synthesized by means of RAFT (mini)emulsion polymerization using a bifunctional symmetric S,S-dibenzyl trithiocarbonate (DBTTC) RAFT agent. Miniemulsion polymerization was initially used for the synthesis of the A-block, which forms hard domains, followed by 2EHA pre-emulsion feeding to build the B-block soft domains. Polymerization kinetics and the evolution of the Molecular Weight Distribution (MWD) were followed during the synthesis of different ABA block copolymers. The thermal properties of the final symmetric block copolymers were studied on dried films by means of DSC. It was found that the block copolymers have two glass transitions, which indicates the presence of a two-phase system. Phase separation was investigated by means of microscopic techniques (AFM and TEM) and SAXS, both of the particles in the latex form, as well as after film formation at room temperature and after different post-treatments. Films were annealed at temperatures well above the glass transition temperature (Tg) of the hard phase to study the bulk morphology of the films after complete particle coalescence. Moreover, for comparison purposes, the films were re-dissolved in THF, and films were again cast directly from the homogeneous THF solutions. As THF is a good solvent for both blocks, such films serve as a reference for the equilibrium morphology. Finally, DMTA studies of the films annealed at different temperatures were performed to correlate the morphology changes with the mechanical properties of the block copolymers.

Highlights

Well-defined block copolymers preparation is a synthetic challenge, but it is of high interest for the design of novel polymeric materials that provide superior combinations of properties
Waterborne ABA block copolymers of hard A block and soft B block were synthesized via two-step reversible addition fragmentation chain transfer polymerization, using S,S-dibenzyl trithiocarbonate bifunctional (DBTTC) RAFT agent
Min-iemulsion polymerization was used for the synthesis of the hard-polystyrene domains where the reaction proceeded up to 80% conversion in a controlled manner

Summary

Introduction

Well-defined block copolymers preparation is a synthetic challenge, but it is of high interest for the design of novel polymeric materials that provide superior combinations of properties. Reversible addition fragmentation chain-transfer polymerization (RAFT) [3]), has in the past years emerged as a technique of choice to prepare block, graft or comb copolymers of precise molecular and chemical structure. These types of polymers are increasingly involved in traditional structural. If the product of χ and N exceeds 10.5, the block copolymers phase separate into domains whose morphology depends on the relative volume fractions of the blocks [9]

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