Thermoresponsive polymer nano-objects able to dynamically change their morphology in response to modifications in the local temperature are finding growing attention for biomedical, optical, and oil & gas applications. This smart behavior can be accessed by precisely controlling the microstructure of AB block copolymers, which can be obtained by leveraging the pseudoliving character of the reversible addition–fragmentation chain transfer (RAFT) polymerization. Most of the examples reporting the synthesis of highly controlled thermoresponsive nano-objects via RAFT dispersion polymerization currently refer to aqueous systems. However, the possibility of synthesizing thermoresponsive copolymers with a well-defined phase separation and bulk response in organic solvents is becoming more and more critical for applications in the oil & gas field and in lubricants for heat engines. In this study, we propose a convenient strategy for synthesizing modular thermoresponsive block copolymers dynamically self-assembling into nano-objects with different morphologies in the hydrocarbon blend dectol (50:50% v/v decane/toluene). Two macromolecular chain transfer agents (macroCTAs) with different degree of polymerization were synthesized from lauryl methacrylate. The chain extension of these macroCTAs with di(ethylene glycol) methyl ether methacrylate via RAFT dispersion polymerization led to copolymers forming, when the temperature is lowered below their cloud point, nano-objects whose morphology could be controlled by modulating the solid content of the formulation and the length of both blocks in the copolymer. We also revealed how the phase-separation temperature and bulk response is influenced by these same parameters, allowing us to tune the material response to the needs of the final application.

No abstract

After having demonstrated their potential in biomedical applications, thermo-responsive block copolymers that are able to self-assemble into nano-objects in response to temperature modifications are becoming more and more appealing in other sectors, such as the oil and gas and lubricant fields. Reversible addition−fragmentation chain transfer (RAFT) polymerization-induced self-assembly has been demonstrated as a valuable strategy for producing nano-objects from modular block copolymers in non-polar media, required for the mentioned applications. Although the influence of the nature and size of the thermo-responsive block of these copolymers on the properties of the nano-objects is extensively studied in the literature, the role of the solvophilic block is often neglected. In this work, we elucidate the role of the main microstructural parameters, including those of the solvophilic portion, of block copolymers produced by RAFT polymerization in the hydrocarbon blend decane/toluene 50:50 v/v on the thermo-responsive behavior and colloidal properties of the resulting nano-objects. Two long-aliphatic chain monomers were employed for the synthesis of four macromolecular chain transfer agents (macroCTAs), with increasing solvophilicity according to the number of units (n) or length of the alkyl side chain (q). Subsequently, the macroCTAs were chain-extended with different repeating units of di(ethylene glycol) methyl ether methacrylate (p), leading to copolymers that are able to self-assemble below a critical temperature. We show that this cloud point can be tuned by acting on n, p, and q. On the other hand, the colloidal stability, expressed in terms of area of the particle covered by each solvophilic segment, is only a function of n and q, which provides a way for controlling the size distribution of the nano-objects and to decouple it from the cloud point.