Abstract
Free-radical emulsion polymerization (eFRP) is widely adopted in industries due to the great advantages that this technique offers in terms of a high polymerization rate, good heat management, and conduction in a non-toxic solvent like water. On the other hand, eFRP requires surfactants to stabilize the produced polymer nanoparticles (NPs). At the same time, the recovery of a bulk material from a NP suspension needs the addition of salts or alkali for the destabilization of the emulsion and the precipitation of the polymer. These can contaminate the final product and affect its properties. For this reason, alternative strategies able to coagulate the NP latex avoiding the addition of exogenous compounds are needed. In this work, we synthesized thermo-responsive polymeric surfactants that are able to promote the NP formation during the eFRP and to allow the recovery of the bulk polymer by simply increasing the environment temperature. Surfactants with a tunable hydrophilic–lipophilic balance were produced through reversible-addition fragmentation chain transfer (RAFT) emulsion polymerization by chain-extending a polyethylene glycol-based macromolecular chain transfer agent with butyl methacrylate, in order to obtain a series of block copolymers with high blocking efficiency, controlled molecular weight distribution, and well-defined thermo-responsive behavior. Then, the RAFT agent was removed to avoid the further extension of the block copolymers, and the surfactants were tested in the eFRP of different monomers (i.e., butyl methacrylate, methyl methacrylate, and styrene) to produce stable NP latexes. Finally, the possibility of triggering the NP aggregation and of guaranteeing the recovery of both surfactants and bulk material by simply changing the temperature of the system was assessed.
Highlights
With an annual production above 370 million tonnes,[1−3] polymer materials are currently playing a leading role in a variety of everyday commodities, including synthetic rubbers, plastics, adhesives, paints, and coatings
We synthesized via reversible-addition fragmentation chain transfer (RAFT) solution polymerization the thermo-responsive portions of the surfactants, namely 20EG4 and 40EG4, reported with an lower critical solution temperature (LCST) of approximately 64 °C.19,33
We developed a new class of thermo-responsive surfactants for the production of high molecular weight polymers via eFRP
Summary
With an annual production above 370 million tonnes,[1−3] polymer materials are currently playing a leading role in a variety of everyday commodities, including synthetic rubbers, plastics, adhesives, paints, and coatings. Most of these products are processed and used as bulk materials. A bulk material can only be obtained following the latex coagulation This can be achieved by water evaporation, which is often disregarded due to the high energy demand, or by precipitation following the addition of huge amounts of salt, acid, or alkali. This leads to the product contamination and to the production of high volumes of wastewater
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