ABC Triblock Copolymers Prepared Using Atom Transfer Radical Polymerization Techniques

Effect of Block Sequence on the Solution Self-Assembly of Symmetric ABCBA Pentablock Polymers in a Selective Solvent

Solution self-assembly of multiblock polymers offers a platform to create complex functional self-assembled nanostructures. However, a complete understanding of the effect of the different single-molecule-level parameters and solution conditions on the self-assembled morphology is still lacking. In this work, we have used dissipative particle dynamics to investigate the solution self-assembly of symmetric ABCBA linear pentablock polymers in a selective solvent and examined the effect of the block sequence, composition, and polymer concentration on the final morphology and polymer conformations. We confirmed that block sequence has an effect on the self-assembled morphologies, and it has a strong influence on polymer conformations that give place to physical gels for the sequence where the solvophilic block is located in the middle of the macromolecule. Our results are summarized in terms of morphology diagrams in the composition-concentration parameter space.

Effects of Chemical Modifications on the Thermoresponsive Behavior of a PDMAEA-b-PNIPAM-b-POEGA Triblock Terpolymer

In this work, the synthesis, selective chemical modifications, and self-assembly behavior in aqueous media of a novel poly(2-(dimethylamino)ethyl acrylate)₂₀-b-poly(N-isopropylacrylamide)₁₁-b-poly(oligo ethylene glycol methyl ether acrylate)₁₈ (PDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈) dual-responsive (pH and temperature) and triply hydrophilic amino-based triblock terpolymer are reported. The amine functional triblock terpolymer was synthesized by sequential reversible addition fragmentation chain transfer polymerization (RAFT) polymerization and molecularly characterized by size exclusion chromatography (SEC) and ¹H-NMR spectroscopy that evidenced the success of the three-step polymerization scheme. The tertiary amine pendant groups of the PDMAEA block were chemically modified in order to produce the Q₁PDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈ as well as the Q₆PDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈ quaternized triblock terpolymers (Q₁ and Q₆ prefixes show the number of carbon atoms (C1 and C6) attached on the PDMAEA groups) using methyl iodide (CH₃I) and 1-iodohexane (C₆H₁₃I) as the quaternizing agents and the SPDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈ sulfobetainized triblock terpolymer using 1,3 propanesultone (C₃H₆O₃S) as the sulfobetainization agent. The self-assembly properties of the triblock terpolymers in aqueous solutions upon varying temperature and solution pH were studied by light scattering and fluorescence spectroscopy experiments. The novel triblock terpolymers self-assemble into nanosized aggregates upon solution temperature rise above the nominal lower critical solution temperature (LCST) of the temperature-responsive PNIPAM block. The remarkable stimuli-responsive self-assembly behavior of the novel triblock terpolymers in aqueous media make them interesting candidates for biomedical applications in the fields of drug and gene delivery.

A Single Enzyme Mediates the "Quasi-Living" Formation of Multiblock Copolymers with a Broad Biomedical Potential

This study describes a unique "quasi-living" block copolymerization method based on an initiation by a single enzyme. We use this term to describe a process where a preformed polymer chain can be reactivated to continue propagating with a second or third comonomer without addition of new catalyst. The presented strategy involves a laccase (oxidoreductase) mediated initial polymerization of 4-hydroxyphenylacetic acid to a homopolymer containing phenolic terminal units, which in turn can be easily reactivated by the same enzyme in the same reaction vessel to continue propagation with a second monomer (tyramine). Increased copolymer yield (up to 26.0%) and polymer molecular mass (up to M_w = 116 000 Da) are achieved through the addition of previously developed micellar and hydrogel enzyme complexing agents. The produced poly(tyramine)-b-poly(4-hydroxyphenylacetic acid)-b-poly(tyramine) is water-soluble and able to self-assemble in aqueous solution. Both tyramine blocks were successfully modified with ibuprofen moieties (up to 24.6% w/w load) as an example for potential polymer drug conjugation. The copolymerization could be further extended with addition of a third (fluorescent) comonomer in the same reaction vessel to yield a fluorescent pentablock copolymer. The successful modifications and advantageous solution behavior of the produced copolymers demonstrate their viability as versatile drug delivery and/or bioimaging agents, as confirmed by cytotoxicity and cellular uptake studies.

The synthesis of bottlebrush cellulose-graft-diblock copolymer elastomers via atom transfer radical polymerization utilizing a halide exchange technique

A novel kind of bottlebrush cellulose-graft-diblock copolymer thermoplastic elastomer (Cell-g-PBA-b-PMMA) was synthesized by grafting from cellulose backbones via surface-initiated atom transfer radical polymerization (ATRP). The mechanical properties of the bottlebrush copolymer elastomers can be adjusted by controlling the block lengths and composition of the side chains.

Transition Metal Mediated Living Radical Polymerisation

Living radical polymerisation has witnessed an unprecedented interest from polymer and materials scientists. Traditionally, polymers tended to replace natural materials such as wood, cotton and glass, and were used primarily for their structural features and performance and cost advantages. New functional polymers are essential for the manufacture of cell phones, lap-top computers, new cosmetics, and many pharmaceuticals. It is important to be able to control how monomers are put together within the macromolecule for the design at the molecular level for specific applications. Living polymerisation allows for end group control, polymer chain length and relatively narrow polydispersity polymers. In nature, the ability to control monomer distribution and chain length is obvious with approximately 20 amino acids being the monomers for polymers as diverse as hair, insulin and haemoglobin. Living radical polymerisation solves many of the problems in the use of monomers that contain heteroatoms and functional groups. These tend to be reactive towards strong nucleophiles and electrophiles which are required in ionic polymerisation. Protecting group chemistry as used in small molecule organic synthesis is not practical in polymer synthesis. Thus radicals that are inert to most functional groups and in particular protic species seem to be the answer. The mechanism of the transition metal mediate systems is extremely complicated with a range of organometallic species present in the reaction mixture. Solvents and coordinating monomers drastically affect the ideal reaction conditions and it is impossible to predict the optimum conditions for each synthesis without certain experiments being carried out. Nevertheless, catalyst systems are available which are acceptable and work well enough to be able to make a plethora of different macromolecules for a diverse range of applications /properties.

Block copolymer self-assembly in ionic liquids

Recent developments in block copolymer self-assembly in ionic liquids are reviewed from both fundamental and applied aspects.

Heterofunctional Poly(ethylene glycol) (PEG) Macroinitiator Enabling Controlled Synthesis of ABC Triblock Copolymers

ABC triblock copolymers with a poly(ethylene glycol) (PEG) midblock have attractive properties for biomedical applications because of PEG's favorable properties regarding biocompatibility and hydrophilicity. However, easy strategies to synthesize polymers containing a PEG midblock are limited. In this study, the successful synthesis of a heterofunctional PEG macroinitiator containing both an azoinitiator and an atom transfer radical polymerization (ATRP) initiator is demonstrated. This novel PEG macroinitiator allows the development of elegant synthesis routes for PEG midblock-containing ABC copolymers that does not require protection of initiating sites or polymer end-group postmodification. Polymers with outer blocks composed of different monomers were synthesized to illustrate the versatility of this macroinitiator. N-Isopropylacrylamide (NIPAM) was included to obtain thermosensitive polymers, 2-(dimethylamino)ethyl methacrylate (DMAEMA) provided pH-sensitive properties, and 2-hydroxyethyl acrylate (HEA) functioned as a noncharged hydrophilic block that also allows for postmodifications reactions. This synthesis approach can further contribute to the design of high-precision polymers with tailorable block compositions and polymer topologies, which is highly attractive for applications in nanotechnology.

Preparation of micrometer-sized, onionlike multilayered block copolymer particles by two-step AGET ATRP in aqueous dispersed systems: effect of the second-step polymerization temperature

The polymerization rate, control/livingness, and particle morphology in seeded activators generated by electron transfer for the atom-transfer radical polymerization of styrene with PiBMA-Br macroinitiator particles were investigated at 70, 90, and 110 degrees C. At 110 degrees C, the polymerization proceeded quickly until 60% conversion was reached, but control/livingness was not observed. This seems to be the reason for the high activation rate and spontaneous initiation of styrene, which significantly increased the radical concentration, resulting in a number of radical terminations. As a result, the block copolymer was not sufficiently formed, leading to a sea-island structure. However, at 70 and 90 degrees C, the polymerizations were almost complete in 14 and 7 h, respectively. Control/livingness was maintained, resulting in PiBMA-b-PS. As a result, onionlike multilayered particles were successfully synthesized. These polymerization behaviors were discussed from the viewpoint of the radical concentration and propagation rate coefficient at various temperatures.