Synthesis and Characterization of Amphiphilic Multiblock Copolymers: Effect of the Number of Blocks on Micellization

Abstract

Five linear amphiphilic multiblock copolymers based on 2-(dimethylamino)ethyl methacrylate (“D”) and methyl methacrylate (“M”), bearing from two to six blocks, were synthesized using sequential group transfer polymerization. All copolymers were obtained from the same polymerization flask (by the withdrawal of a sufficient amount of sample and appropriate adjustment of subsequent monomer loadings) to ensure better comparison between the various multiblocks. A theoretical degree of polymerization (DPth) of 20 was targeted for all D blocks, whereas a DPth of 10 was aimed for the M blocks. Upon characterization using gel permeation chromatography and 1H NMR spectroscopy, the copolymers were confirmed to have the expected values of molecular weights and compositions. Subsequently, the aqueous micellization behavior of these copolymers was probed using dye solubilization, dynamic light scattering, and small-angle neutron scattering. Dye solubilization experiments indicated that micelles readily formed at low copolymer concentrations equal to or less than 0.03% w/w. The scattering measurements revealed that despite the differences in their overall DPth values, the triblock, the tetrablock, and the pentablock copolymers self-assembled in water to form micelles with radii of gyration and hydrodynamic radii very similar to each other, suggesting chain looping and the formation of flowerlike micelles, which is in agreement with recent Monte Carlo simulations.

Size-Controlled Nanomicelles of Poly(lactic acid)–Poly(ethylene glycol) Copolymers with a Multiblock Configuration

“…Variations in the number of blocks led to differences in micelle size, micelle structure and aggregation number [29]. We also tried to evaluate the micelle structures.…”

Hierarchically organized micellization of thermoresponsive rod‐coil copolymers based on poly[oligo(ethylene glycol) methacrylate] and poly(ε‐caprolactone)

“…The reaction mixture immediately turned dark brown in color in addition of the ligand. Samples for analysis were taken periodically throughout the reaction to follow the polymerization by 1 H NMR in CDCl 3 and GPC. Termination reaction occurred rapidly on exposure to air, as indicated by the color change from brown to green [oxidation of Cu (I) to Cu (II)].…”

“…Several authors have pointed out the importance of the architecture of copolymers in the self-organization behavior [3][4] although the studies were restrained due to the lack of controlled synthetic routes for the preparation of well-defined block copolymers with low polydispersities. The development of new polymerization techniques, such as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and grafting-through, has allowed the synthesis of well-defined block copolymers with novel architectures giving rise to a growing number of papers devoted to their aggregation both in selective solvents and solid state.…”

Alternating Amphiphilic Multiblock Copolymers: Controlled Synthesis via RAFT Polymerization and Aqueous Solution Characterization

“…It was based on linear multiblock copolymers where the block number increased with the overall molecular weight and at constant block sizes. 14 Scattering experiments on aqueous solutions of the multiblock copolymers indicated that the triblock, the tetrablock, and the pentablock copolymers formed micelles but with very small aggregation numbers, typically 3. We attributed the low aggregation numbers to the short lengths of the hydrophilic blocks with degrees of polymerization (DPs) of 20, which conferred stiffness to these blocks and imposed an increased energetic cost for loop formation.…”