RAFT Dispersion Polymerization in Nonpolar Media: Polymerization of 3-Phenylpropyl Methacrylate in n-Tetradecane with Poly(stearyl methacrylate) Homopolymers as Macro Chain Transfer Agents

Abstract

Poly(stearyl methacrylate) (PSMA) homopolymers, prepared by RAFT radical polymerization, have been employed in the RAFT dispersion polymerization (RAFTDP) of 3-phenylpropyl methacrylate (PPMA) in n-tetradecane. RAFTDPs yielded block copolymers with narrow molecular weight distributions and tunable compositions and allowed for ready access to different polymorphic nanoparticle phases. Polymerization of PPMA at 20 wt %, for a fixed PSMA average degree of polymerization (X̅ n ) of 19, allowed for the in situ preparation of soft matter nano-objects with spherical, worm, and vesicular morphologies. For a fixed block copolymer composition increasing total solids (from 10 to 40 wt %) favored the formation of nanoparticles with higher ordered morphologies. For block copolymer samples that formed soft physical gels at ambient temperature, a macroscopic thermoreversible degelation−gelation phenomenon was observed. The fundamental reason for this was a worm-to-sphere morphology transition that was facilitated, in part, by the low glass transition temperature of the core-forming PPPMA block and an associated increase in the solvation of the core with increasing temperature. Finally, we note that degelation can also be effected by simple dilution with this macroscopic change now due to simple worm disentanglement and not a fundamental morphology transition. ■ INTRODUCTIONThe ability of block copolymers to undergo self-directed assembly in a selective solvent is well documented. 1 Assembly occurs to give soft matter nanoparticles with, most commonly, a spherical morphology although higher ordered; more complex structures are also accessible. 2−14 Traditionally, such selfassembled species are prepared by first synthesizing a welldefined block copolymer (most commonly, but not limited to, an AB diblock species) which, after characterization, is subjected to a processing step to give the nanoparticles. This may involve direct dissolution in a selective solvent or may require additional steps such as gradual stepwise dialysis against a selective solvent from a molecularly dissolved state. While these are well established and perfectly valid approaches to accessing polymeric nanoparticles, this is typically accomplished in dilute solution (≤1 wt % is common), and nano-objects other than spheres can be difficult to obtain.Reversible addition−fragmentation chain transfer dispersion polymerization (RAFTDP) 15−18 has recently been the topic of significant academic interest since it allows for the direct in situ preparation of self-assembled polymeric species of various morphologies (spheres, worms, and vesicles as the most common species) at high concentration (formulations at ≥ 50 wt % are readily achievable) in a one-pot process. The ease of execution and potential versatility of this technique have enabled the syntheses of a wide range of interesting nanoparticles in polar 19−32 (typically aqueous or alcoholic solvents), nonpolar, 33−36 and other, less common, media such as supercritical CO 2 . 37,38 Indeed, RAFTDP is now sufficient...

Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization

“…Compared to RAFT alcoholic dispersion polymerization, there are relatively few reports of RAFT dispersion polymerization being conducted in non-polar solvents [92][93][94][95][96][97][98][99]. Charleux and co-workers [92][93][94] reported an all-acrylic RAFT non-polar dispersion polymerization formulation that produced poly(2-ethylhexyl acrylate)-poly(methyl acrylate) (PEHA-PMA) diblock copolymer nanoparticles in iso-dodecane.…”

“…However, it is not yet clear whether such PISA formulations are as wellbehaved as those based on BzMA. Lowe and co-workers recently reported using SMA instead of LMA to prepare PSMA stabilizer macro-CTAs (Figure 2b) for the synthesis of PSMA-PPPMA diblock copolymer nanoparticles in n-tetradecane [97] and n-octane [98].…”

Poly( N -2-(methacryloyloxy)ethyl pyrrolidone)-poly(benzyl methacrylate) diblock copolymer nano-objects via RAFT alcoholic dispersion polymerisation in ethanol

“…When combined with the well-established principle of polymerisation-induced self-assembly (PISA), [12][13][14][15] RAFT polymerisation has enabled the rational synthesis of diblock copolymer nanoobjects in various media, including water, [13,[16][17][18][19][20] n-alkanes, [21][22][23][24][25][26][27] ionic liquids [28] and lower alcohols. [29][30][31][32][33][34][35][36] Pan and co-workers have made a number of notable contributions to the field of RAFT alcoholic dispersion polymerisation [37][38][39][40].…”

Characterization of Diblock Copolymer Order-Order Transitions in Semidilute Aqueous Solution Using Fluorescence Correlation Spectroscopy

“…[14][15][16] This versatile approach has enabled spherical, worm-like or vesicular copolymer morphologies to be generated in concentrated solution. [ 11,[17][18][19][20][21][22][23][24][25][26] Such a nonionic PGMA-PHPMA diblock copolymer exhibits a thermoreversibleThe temperature and pH-dependent diffusion of poly(glycerol monomethacrylate)-blockpoly(2-hydroxypropyl methacrylate) nanoparticles prepared via polymerization-induced self-assembly in water is characterized using fl uorescence correlation spectroscopy (FCS). Lowering the solution temperature or raising the solution pH induces a worm-to-sphere transition and hence an increase in diffusion coeffi cient by a factor of between four and eight.…”

“…[14][15][16] This versatile approach has enabled spherical, worm-like or vesicular copolymer morphologies to be generated in concentrated solution. [ 11,[17][18][19][20][21][22][23][24][25][26] Such a nonionic PGMA-PHPMA diblock copolymer exhibits a thermoreversible…”