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

Facile topological transformation of ABA triblock copolymers into multisite, single-chain-folding and branched multiblock copolymers via sequential click coupling and anthracene chemistry

Telechelic PtBA-b-PSt-b-PtBA copolymers were designed to achieve on-demand topological transformation into multisite, single-chain-folding and branched multiblock copolymers via click/click-like reactions.

Library of Derivatizable Multiblock Copolymers by Nucleophilic Substitution Polymerization and Targeting Specific Properties

Multiblock copolymers (MBCs) are fascinating in the field of biology-polymer chemistry interfaces. Synthesizing libraries of MBCs with tailor-made functionality is challenging as it involves multiple steps. Herein, a simple synthesis, analogous to polyurethane/Michael addition reactions, has been introduced to obtain a library of derivatizable MBCs. Nucleophilic substitution polymerization (S_NP) of poly(ε-caprolactone) and poly(ethylene glycol) blocks containing activated halide termini by primary mono/di/coamines or clickable amines provides functional MBCs. The structure of amines directs the properties of the MBCs. The self-assembly of small molecular weight primary diamine-based MBCs shows controlled release of hydrophobic model guest molecules and therapeutics. The primary diamine (no dangling chain) helps to form MBC micelles having a relatively tight core with a low diffusion property. Antimicrobial property in the MBCs has been introduced by separating the cationic centers from the lipophilic groups using a coamine as a nucleophilic agent and a small molecular weight dihalide as a chain extender. Clickable MBCs were synthesized by changing the structure of the nucleophile to obtain degradable amphiphilic conetworks and hydrogels. Varieties of macromolecular entities could be obtained by switching the nucleophilic agent and introducing a small molecular weight chain extender. This synthesis approach provides an opportunity to tune the chemical functionality, topological structure, and biological properties of macromolecular entities.

Synthetic approaches for multiblock copolymers

Multiblock copolymers (MBCs) are an emerging class of synthetic polymers that exhibit different macromolecular architectures and behaviours to those of homopolymers or di/triblock copolymers.

Synthesis of multisegmented block copolymer by Friedel–Crafts hydroxyalkylation polymerization

Friedel–Crafts (FC) polycondensation of 1,4-dimethoxybenzene with 4-substituted benzaldehyde species was used to prepare telechelic oligomers and high-molar-mass multisegmented block copolymers.

Effect of block copolymer architecture and composition on gold nanoparticle fabrication

Gold nanoparticles (AuNPs) fabricated via the self-assembly of block copolymers of various architectures.

Scalable syntheses of well-defined pentadecablock bipolymer and quintopolymer

The one-pot syntheses of two pentadeca-(15)-block methacrylate-based amphiphilic copolymers, specifically a bipolymer (AB)₇A and a quintopolymer (ABCDE)₃, are being reported using a fast and easy to scale up procedure that does not require any intermediate purification steps.

Phase Behavior and Self-Assembly of Perfectly Sequence-Defined and Monodisperse Multiblock Copolypeptides

This paper investigates how the properties of multiblock copolypeptides can be tuned by their block architecture, defined by the size and distribution of blocks along the polymer chain. These parameters were explored by the precise, genetically encoded synthesis of recombinant elastin-like polypeptides (ELPs). A family of ELPs was synthesized in which the composition and length were conserved while the block length and distribution were varied, thus creating 11 ELPs with unique block architectures. To our knowledge, these polymers are unprecedented in their intricately and precisely varied architectures. ELPs exhibit lower critical solution temperature (LCST) behavior and micellar self-assembly, both of which impart easily measured physicochemical properties to the copolymers, providing insight into polymer hydrophobicity and self-assembly into higher order structures, as a function of solution temperature. Even subtle variation in block architecture changed the LCST phase behavior and morphology of these ELPs, measured by their temperature-triggered phase transition and nanoscale self-assembly. Size and morphology of polypeptide micelles could be tuned solely by controlling the block architecture, thus demonstrating that when sequence can be precisely controlled, nanoscale self-assembly of polypeptides can be modulated by block architecture.

Surface and Aggregation Behavior of Pentablock Copolymer PNIPAM7-F127-PNIPAM7 in Aqueous Solutions

The triblock Pluronic F127 was modified by introducing poly(N-isopropylacrylamide) (PNIPAM) at both the poly(ethylene oxide) ends, and the pentablock copolymer so-prepared was characterized by gel permeation chromatography and (1)H NMR. The degree of polymerization of NIPAM blocks at the two ends was 7. The solution behavior and microstructure of copolymer aggregates in water and aqueous salt solution were examined and compared with F127 by UV-visible absorption spectroscopy, microdifferential scanning calorimetry, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The behavior of the pentablock copolymer at the air/water interface was determined by Langmuir film balance. Two lower critical solution temperatures were observed for pentablock copolymer, corresponding to poly(propylene oxide) and PNIPAM blocks, respectively. DLS studies show that micelle size increased with increase in temperature and in the presence of salt. SANS measurements provided temperature-dependent structural evolution of copolymer micelles in water and salt solution. The copolymer displays an isotherm with four classical regions (pancake, mushroom, brush, and condensed state). The study has potential applications in controlled drug delivery due to the tunable phase behavior and biocompatibility of the copolymer.

Ultrasound-responsive ultrathin multiblock copolyamide vesicles

This study reports the self-assembly of novel polymer vesicles from an amphiphilic multiblock copolyamide, and the vesicles show a special structure with an ultrathin wall thickness of about 4.5 nm and a combined bilayer and monolayer packing model. Most interestingly, the vesicles are ultrasound-responsive and can release the encapsulated model drugs in response to ultrasonic irradiation.

Bioinspired multi-block molecules

Elaborately designed synthetic multiblock molecules and copolymers are able to undergo folding like biological macromolecules and form controlled and compartmentalized self-assemblies that exert characteristic functions in solution, the crystalline state, and membranous media.

Formation and structural characteristics of thermosensitive multiblock copolymer vesicles

The spontaneous vesicle formation of ABABA-type amphiphilic multiblock copolymers bearing thermosensitive hydrophilic A-block in a selective solvent is studied using dissipative particle dynamics (DPD) approach. The formation process of vesicle through nucleation and growth pathway is observed by varying the temperature. The simulation results show that spherical micelle takes shape at high temperature. As temperature decreases, vesicles with small aqueous cavity appear and the cavity expands as well as the membrane thickness decreases with the temperature further decreasing. This finding is in agreement with the experimental observation. Furthermore, by continuously varying the temperature and the length of the hydrophobic block, a phase diagram is constructed, which can indicate the thermodynamically stable region for vesicles. The morphological phase diagram shows that vesicles can form in a larger parameter scope. The relationship between the hydrophilic and hydrophobic block length versus the aqueous cavity size and vesicle size are revealed. Simulation results demonstrate that the copolymers with shorter hydrophobic blocks length or the higher hydrophilicity are more likely to form vesicles with larger aqueous cavity size and vesicle size as well as thinner wall thickness. However, the increase in A-block length results to form vesicles with smaller aqueous cavity size and larger vesicle size.

Investigations in the Stranski-Laboratorium of the TU Berlin – Physical Chemistry of Colloidal Systems – Going Towards Complexity and Functionality

The research topics of our group are in general from the field of physical chemistry of colloidal systems. Within this rather wide layout a large variety of quite different questions and systems are tackled, where the common bridging factor is the aim of understanding the properties of colloidal systems based on their mesoscopic structure and dynamics, which in turn are controlled by their molecular composition. With such an enhanced understanding of the correlation between mesoscopic structure and the macroscopic properties the goal then is to employ this knowledge in order to formulate increasingly complex colloidal system with correspondingly more variable and interesting functionalities. From this general context of investigations, some representative systems and questions that have been studied in recent time by us are covered in this text.

They comprise the phase behaviour and the structures formed in solutions of surfactants and amphiphilic copolymers. Once these static properties are known, we also have a high interest in the dynamic properties and the kinetics of morphological transitions as they are observed under non-equilibrium conditions, since they are frequently encountered in applications. A key property of amphiphilic molecules is their ability to solubilise sparingly soluble compounds thereby forming microemulsions or nanoemulsions, where the ability to form such systems depends strongly on the molecular architecture of the amphiphiles. By turning to polymeric amphiphiles the concept of surfactants and their architecture can be extended largely towards more versatile structures, more complex self-assembly and much larger length and time scales. Another direction is the surfactant assisted formation of nanoparticles or mesoporous inorganic materials. By combining copolymers with other polymers, copolymers, colloids, or surfactants – for instance via electrostatically driven co-assembly – one may then form increasingly complex colloidal aggregates. By doing so one is able to control rheological properties or develop complex delivery systems, whose properties can be tailor-made by appropriate choice of the molecular build-up. This striving towards well controlled complexity achieved by means of self- and co-assembly then leads to increasingly more functional systems and is the key direction for future research activities in our group.

Nanoparticle Formation from Hybrid, Multiblock Copolymers of Poly(Acrylic Acid) and VPGVG Peptide

Elastin-mimetic hybrid copolymers with an alternating molecular architecture were synthesized via the step growth polymerization of azide-functionalized, telechelic poly(tert-butyl acrylate) (PtBA) and an alkyne-terminated, valine and glycine-rich peptide with a sequence of (VPGVG)2 (VG2). The resultant hybrid copolymer, [PtBA-VG2]n, contains up to six constituent building blocks and has a polydispersity index (PDI) of ~1.9. Trifluoroacetic acid (TFA) treatment of [PtBA-VG2]n gave rise to an alternating copolymer of poly(acrylic acid) (PAA) and VG2 ([PAA-VG2]n). The modular design permits facile adjustment of the copolymer composition by varying the molecular weight of PAA (22 and 63 repeat units). Characterization by dynamic light scattering indicated that the multiblock copolymers formed discrete nanoparticles at room temperature in aqueous solution at pH 3.8, with an average diameter of 250-270 nm and a particle size distribution of 0.34 for multiblock copolymers containing PAA22 and 0.17 for those containing PAA63. Upon increasing the pH to 7.4, both types of particles were able to swell without being disintegrated, reaching an average diameter of 285-300 nm for [PAA22-VG2]n and 330-350 nm for [PAA63-VG2]n, respectively. The nanoparticles were not dissociated upon the addition of urea, further confirming their unusual stability. The nanoparticles were capable of sequestering a hydrophobic fluorescent dye (pyrene), and the critical aggregation concentration (CAC) was determined to be 1.09 × 10-2 or 1.05 × 10-2 mg/mL for [PAA22-VG2]n and [PAA63-VG2]n, respectively. We suggest that the multiblock copolymers form through collective H-bonding and hydrophobic interactions between the PAA and VG2 peptide units, and that the unusual stability of the multiblock nanoparticles is conferred by the multiblock architecture. These hybrid multiblock copolymers are potentially useful as pH-responsive drug delivery vehicles, with the possibility of drug loading through concerted H-bonds and hydrophobic interactions.