Ramiro Guerrero-Santos

Alkoxyamine-functionalized latex nanoparticles through RAFT polymerization-induced self-assembly in water

The use of a new symmetrical trithiocarbonate holding two alkoxyamine moieties (I), was explored in surfactant-free emulsion polymerization of styrene or n-butyl acrylate through reversible addition–fragmentation chain transfer (RAFT). I was revealed as an effective chain transfer agent in the synthesis of well-defined end-functionalized poly(acrylic acid)s (PAA). These macroRAFT agents were further used in water for the preparation of amphiphilic triblock copolymers by polymerization induced self-assembly (PISA). The corresponding final latex particles decorated with alkoxyamine moieties were used to trigger NMP polymerization of sodium 4-styrene sulfonate (SSNa) in water. The thermal activation of the surface alkoxyamine groups which had hitherto been dormant induced the formation of a double hydrophilic corona PAA-b-PSSNa and a sharp reorganization of latex particles.

New dialkoxyamine-trithiocarbonate for the synthesis of multiblock copolymers through in tandem RAFT/NMP

A new strategy for synthesizing multiblock copolymers comprising polystyrene, polyacrylates, poly(N-isopropylacrylamide), etc. is described. The methodology involves the use of a dialkoxyamine-trithiocarbonate (I) to prepare highly end-functionalized polymers through reversible addition–fragmentation chain transfer (RAFT) polymerization at T = 60–70 °C. Under RAFT conditions, the integrity of the alkoxyamine end-group is preserved and the central trithiocarbonate group remains active for the preparation of triblock copolymers. Either the α,ω-dialkoxyamine homopolymer or triblock copolymers were subsequently chain-extended with styrene using nitroxide-mediated radical polymerization (NMP) at T = 120 °C. At this temperature, a tandem polymerization reaction occurs since the trithiocarbonate unit is activated simultaneously. This approach afforded highly pure multiblock copolymers with a narrow molar mass distribution (Đ = 1.3–1.7), which was assessed by size-exclusion chromatography. The diffusion ordered spectroscopy (DOSY) analysis of multiblock copolymers suggests that samples fit well to a single-population model with no evidence of uncoupled blocks detectable. The effectiveness of I for the preparation of a number of multiblock copolymers was demonstrated.

Trithiocarbonates prepared from iodo-functionalized RITP-polymers

Iodo-terminated polymers (polystyrene, polybutyl acrylate and polyvinyl acetate) were synthesized by reverse iodine transfer polymerization (RITP) and then used to form homopolymeric trithiocarbonates through a coupling reaction induced by Cs2CO3/CS2. The resulting polymeric trithiocarbonates were subsequently used in RAFT polymerization to form ABA block copolymers. This coupling reaction was extended to some iodo-terminated AB diblock copolymers prepared entirely by RITP to form ABA triblock copolymers.

Thermosensitive spontaneous gradient copolymers with block- and gradient-like features

Reversible addition–fragmentation chain transfer (RAFT) copolymerization was used to prepare copolymers of N-isopropyl acrylamide (NIPAM) and vinyl acetate (VAc) with mole fractions of NIPAM ranging from 0.1 to 0.6 and targeted degrees of polymerization of 100 and 250. The measured kinetic parameters and obtained experimental results revealed that this copolymerization system leads to a “one pot” synthesis of amphiphilic gradient copolymers, which have thermoresponsive and self-assembly characteristics resembling those of the analogous block copolymers but with some intriguing differences. Their self-assembly behavior in water suggests the formation of dynamic aggregates which respond rapidly to changes in solubility as revealed by 1H NMR spectroscopy, in contrast to the kinetically frozen aggregates formed by block copolymers. Furthermore, despite their block-like composition profiles, these copolymers display a single and broad glass transition, as is typically found in linear gradient copolymers. The synthetic approach presented in this contribution could readily be adapted to other comonomer systems to provide an accessible and economic alternative to the conventional multi-step preparation of block copolymers.

Opportunities for dual RDRP agents in synthesizing novel polymeric materials

Combining reversible-deactivation radical polymerization (RDRP) techniques in a single system provides access to exciting new polymeric materials which would be difficult to obtain by other means. Dual RDRP agents are species which can undergo two (or more) distinct RDRP processes sequentially without any chemical transformations between the polymerization steps. By incorporating multiple controlling functions in the same species, dual agents offer elegant pathways to functional polymers without resorting to end-group conversions or coupling of pre-formed polymers. Dual agents have been used to synthesize a range of innovative structures such as well-defined block copolymers from monomers with disparate reactivities, degradable drug delivery vehicles and surface-tethered brushes which both exploit mid-chain functionality, complex architectures such as bottlebrush, star, and multiblock copolymers, and novel nanoparticles in which the controlling functions are physically isolated through self-assembly. The present review highlights the state of the art of dual systems, with a particular emphasis on orthogonality considerations and the potential of dual agents for accessing new polymeric materials.