Design of Waterborne Asymmetric Block Copolymers as Thermoresponsive Materials

Gordana Siljanovska Petreska,Clemens Auschra,Christof Van Sluijs,Marı́a Paulis

doi:10.3390/polym12061253

Gordana Siljanovska Petreska, Clemens Auschra + Show 2 more

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https://doi.org/10.3390/polym12061253

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Abstract

AB diblock waterborne copolymers made of styrene (St) and 2-ethylhexyl acrylate (2EHA) were synthesized by means of two-step reversible addition fragmentation chain transfer (RAFT) (mini)emulsion polymerization. Monofunctional asymmetric RAFT agent was used to initiate the polymerization. The hard polystyrene “A” block was synthesized via miniemulsion polymerization followed by 2EHA pre-emulsion feeding to form the soft “B” block. Polymerization kinetics and the evolution of the molecular weight distribution were followed during synthesis of both initial and final block copolymers. DSC measurements of the block copolymers revealed the existence of two glass transition temperatures (Tgs) and thus the occurrence of two-phase systems. Microscopic techniques (atomic force microscopy (AFM) and transmission electron microscopy (TEM)) were used to study the phase separation within the particles in the latex form, after film formation at room temperature cast directly from the latex and after different post-treatments well above the Tg of the hard-polystyrene domains, when complete particle coalescence had occurred. The morphological differences observed after different annealing temperatures were correlated with the mechanical properties analyzed by DMTA measurements. Finally, the differences found in the mechanical properties of the block copolymers annealed at different temperatures were correlated to their heat seal application results.

Highlights

The synthesis of block copolymers bearing polymers with different properties (i.e., different glass transition temperatures (Tgs)), provides a great opportunity to obtain chemical linkages between polymer chains that could otherwise be completely phase separated
2-(((dodecylthio)carbonothioyl)thio)propanoic BM1430 reversible addition fragmentation transfer (RAFT) agent were used to synthesize a series of waterborne AB block copolymers containing hard and soft domains
The synthesis of the hard-polystyrene domains was done first using miniemulsion polymerization and 2-ethylhexyl acrylate (2EHA) soft blocks were incorporated by emulsion polymerization

Summary

Introduction

The synthesis of block copolymers bearing polymers with different properties (i.e., different glass transition temperatures (Tgs)), provides a great opportunity to obtain chemical linkages between polymer chains that could otherwise be completely phase separated. Three main types of reversible-deactivation radical polymerizations (RDRPs)—(i) nitroxide mediated polymerization (NMP) [1], (ii) atom transfer radical polymerization (ATRP) [2], and (iii) reversible addition fragmentation transfer (RAFT) polymerization [3,4]—were developed and received great attention for the synthesis of well-defined block copolymers. Among all the RDRPs, RAFT is the most versatile and robust technique which allows the polymerization of a broader range of functional monomers (both polar and nonpolar) [5]. It has a higher tolerance to diverse functional groups than do competing techniques (NMP and ATRP), in a wide range of reaction conditions, including bulk, solution, and aqueous dispersions [6,7] using different classes of chain transfer agents (CTAs). When the polymerization is complete (or stopped) most of the chains retain the thiocarbonylthio end group upon completion of the polymerization and can be isolated as stable materials, which can be Polymers 2020, 12, 1253; doi:10.3390/polym12061253 www.mdpi.com/journal/polymers

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