Synthesis and pH/Temperature-Responsive Behavior of PLLA-b -PDMAEMA Block Polyelectrolytes Prepared via ROP and ATRP

Linear Block Copolymer Synthesis

Block copolymers form the basis of the most ubiquitous materials such as thermoplastic elastomers, bridge interphases in polymer blends, and are fundamental for the development of high-performance materials. The driving force to further advance these materials is the accessibility of block copolymers, which have a wide variety in composition, functional group content, and precision of their structure. To advance and broaden the application of block copolymers will depend on the nature of combined segmented blocks, guided through the combination of polymerization techniques to reach a high versatility in block copolymer architecture and function. This review provides the most comprehensive overview of techniques to prepare linear block copolymers and is intended to serve as a guideline on how polymerization techniques can work together to result in desired block combinations. As the review will give an account of the relevant procedures and access areas, the sections will include orthogonal approaches or sequentially combined polymerization techniques, which increases the synthetic options for these materials.

Synthesis of Block Copolymers by Mechanistic Transformation from Reversible Complexation Mediated Living Radical Polymerization to the Photoinduced Radical Oxidation/Addition/Deactivation Process

A versatile strategy for the fabrication of block copolymers by the combination of two discrete living polymerization techniques─reversible complexation mediated living radical polymerization (RCMP) and photoinduced radical oxidation addition deactivation (PROAD) processes─is reported. First, RCMP is conducted to yield poly(methyl methacrylate) with iodide end groups (PMMA-I). In the following step, PMMA-I is used as macroinitiator for living PROAD cationic polymerization of isobutyl vinyl ether. Successful formation of the block copolymers is confirmed by ¹H NMR, FT-IR, GPC, and DSC investigations.

Triblock Copolymer Micelles with Tunable Surface Charge as Drug Nanocarriers: Synthesis and Physico-Chemical Characterization

Polymeric micelles have gained increasing interest as efficient drug delivery systems for cancer treatment and diagnosis. The aim of the present study was to construct and to evaluate novel polymeric nanosized drug carriers with tunable surface charges. Initially, amphiphilic triblock copolymers with predetermined molar mass characteristics were synthesized by applying controlled polymerization techniques. The copolymers self-assembled in aqueous media into core–shell spherical micelles, comprising a biodegradable hydrophobic poly(D,L-lactide) core, positively charged middle layer of poly((2-dimethylamino)ethyl methacrylate), and an outer shell of neutral hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate), with various densities of the short polyether side chains. The block copolymer micelles with average diameters of about 70 nm and surface charges varying from strongly positive to neutral were characterized and loaded with the model, natural, hydrophobic drug curcumin. Characteristics such as drug loading efficiency, in-vitro drug release profiles, and stability under physiological conditions were evaluated and discussed in terms of nanocarriers’ composition. As a result, the most promising candidates for potential application in nanomedicine were identified.

Precision polymer nanofibers with a responsive polyelectrolyte corona designed as a modular, functionalizable nanomedicine platform

We describe the development of a modular, functionalizable platform for biocompatible core-shell block copolymer nanofibers of controlled length (22 nm – 1.3 μm) and low dispersity produced via living crystallization-driven...

Sequentially bridging anionic addition and ring-opening polymerization by cooperative organocatalysis: Well-defined block copolymers from methacrylates and cyclic esters

Organocatalytic sequential block copolymerization of dissimilar monomers with distinct chemical characteristics is great challenging, usually involving the integration of different polymerization mechanism. In this contribution, we reported the synthesis of...

Multiresponsive Transitions of PDMAEMA Brushes for Tunable Surface Patterning

Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) is an attractive polymer for switchable surface coatings based on its multiresponsiveness toward environmental triggers (temperature, pH-value, ionic strength). In this in situ study, we present the complex and tunable thermoresponsiveness of PDMAEMA Guiselin brushes (9 nm, dry thickness), which were prepared via an efficient grafting-to approach. Combining in situ atomic force microscopy (AFM) visualizing the surface topography (x-y plane) and spectroscopic ellipsometry monitoring the swelling behavior of the polymer film (layer thickness, z-direction) offers for the first time a three-dimensional insight into thermoresponsive transitions on the nanoscale. While PDMAEMA films exhibit LCST behavior in the presence of monovalent counterions, it can easily be switched toward an UCST thermoresponsiveness via the addition of small quantities of multivalent ions. In both cases, the transition temperature as well as the sharpness and reversibility of the transition can be tuned via a second external trigger, the ionic strength. Whereas homogeneous surfaces were observed both below and above the LCST in monovalent salt solutions, the UCST transition was characterized by the in situ formation of a nanostructured surface of pinned PDMAEMA micelles with entrapped multivalent counterions. Moreover, it was demonstrated for the first time that the characteristic dimensions of the nanopattern (the diameter and height of the pinned micelles) could be tuned in situ by the pH- and induced UCST thermoresponsiveness of PDMAEMA. This approach therefore provides a novel bottom-up strategy to create and control polymeric nanostructures in an aqueous environment.

Cu (II) removal using electrospun dual-responsive polyethersulfone-poly (dimethyl amino) ethyl methacrylate (PES-PDMAEMA) blend nanofibers

A novel electrospun dual-responsive polyethersulfone-poly(dimethyl amino) ethyl methacrylate nanofibrous adsorbent was fabricated via electrospinning for the removal of Cu (II) from aqueous solution. Morphological, chemical, and dual-responsiveness of the composite nanofibrous adsorbent were characterized using scanning electron microscope equipped with energy dispersive x-ray, Fourier transform infrared, and UV-VIS spectrophotometer, respectively. The obtained uniform and bead-free nanofibers were then used for the removal of Cu (II) from aqueous solution. Results showed that the temperature-responsiveness of the nanofibers is dependent on the pH of the solution, as indicated by the decreasing lower critical solution temperature with increasing pH level. Temperature and pH offer a synergistic effect on the adsorption of Cu (II), with maximum adsorption observed at pH 6.5 at 55 °C. Kinetic, thermodynamic, and isotherm studies indicate that the adsorption of copper ions follows chemisorption and is thermodynamically favored at increasing temperature. From the Langmuir isotherm model, the obtained maximum adsorption capacity, q_m, was 161.30 mg g^-1 at 55 °C. From the desorption studies, results showed that the maximum desorption was observed at pH 3 at 25 °C. In conclusion, PES-PDMAEMA has the capability to adsorb and desorb Cu (II) by adjusting both pH and temperature, hence it can be considered as an efficient and economical adsorbent for heavy metals such Cu (II).

Stimuli-Responsive Lyotropic Liquid Crystalline Nanosystems with Incorporated Poly(2-Dimethylamino Ethyl Methacrylate)-b-Poly(Lauryl Methacrylate) Amphiphilic Block Copolymer

There is an emerging need to evolve the conventional lyotropic liquid crystalline nanoparticles to advanced stimuli-responsive, therapeutic nanosystems with upgraded functionality. Towards this effort, typically used stabilizers, such as Pluronics^®, can be combined or replaced by smart, stimuli-responsive block copolymers. The aim of this study is to incorporate the stimuli-responsive amphiphilic block copolymer poly(2-(dimethylamino)ethyl methacrylate)-b-poly(lauryl methacrylate) (PDMAEMA-b-PLMA) as a stabilizer in lipidic liquid crystalline nanoparticles, in order to provide steric stabilization and simultaneous stimuli-responsiveness. The physicochemical and morphological characteristics of the prepared nanosystems were investigated by light scattering techniques, cryogenic-transmission electron microscopy (cryo-TEM), X-ray diffraction (XRD) and fluorescence spectroscopy. The PDMAEMA-b-PLMA, either individually or combined with Poloxamer 407, exhibited different modes of stabilization depending on the lipid used. Due to the protonation ability of PDMAEMA blocks in acidic pH, the nanoparticles exhibited high positive charge, as well as pH-responsive charge conversion, which can be exploited towards pharmaceutical applications. The ionic strength, temperature and serum proteins influenced the physicochemical behavior of the nanoparticles, while the polymer concentration differentiated their morphology; their micropolarity and microfluidity were also evaluated. The proposed liquid crystalline nanosystems can be considered as novel and attractive pH-responsive drug and gene delivery nanocarriers due to their polycationic content.

Controlled Synthesis of Block Copolymers by Mechanistic Transformation from Atom Transfer Radical Polymerization to Iniferter Process

A straightforward transformation protocol combining two distinct living polymerization methods for the controlled synthesis of block copolymers is described. In the first step, bromo-terminated poly(methyl methacrylate) is prepared by atom transfer radical polymerization (ATRP). Then, a bromide end group is substituted with a triphenylmethyl (trityl) functionality under visible light irradiation using dimanganese decacarbonyl (Mn₂ (CO)₁₀ ) photochemistry. The resulting polymers with trityl end groups are used as macroiniferter for the polymerization of styrene and tert-butyl acrylate (tBA) to yield desired block copolymers with narrow molecular weight distribution. Moreover, the amphiphilic copolymers with acrylic acid functionalities are obtained by the hydrolyzation of poly(tert-butyl acrylate) containing block copolymers with trifluoroacetic acid.

HPW/PDMAEMA-b-PMAA/ZIF-8 Ternary Lamellar Composite and the Photocatalytic Degradation of Methylene Blue

PDMAEMA-b-PMAA block copolymers were prepared by the sequential RAFT polymerization of DMAEMA and tBMA, followed by hydrolysis. Phosphotungstic acid (HPW) was anchored to the PDMAEMA blocks through electrostatic interactions and the as-obtained HPW/PDMAEMA-b-PMAA was added to the synthesis of ZIF-8. During the formation of ZIF-8, the PMAA blocks coordinated to the Zn²⁺ ions through their carboxy groups, along with the HPW groups that were anchored to the PDMAEMA blocks. In this way, the block copolymer could consolidate the interactions between HPW and ZIF-8 and prevent the leakage of HPW. Finally, the HPW/PDMAEMA-b-PMAA/ZIF-8 ternary lamellar composite was obtained and the structure of the HPW/PDMAEMA-b-PMAA/ZIF-8 hybrid material was characterized by using powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). As a photocatalyst, the HPW/PDMAEMA-b-PMAA/ZIF-8 ternary lamellar composite showed excellent photoactivity for the degradation of methylene blue (MB). The rate of degradation of MB was 0.0240 min^-1 , which was 7.5-times higher than that of commercially available P25 (0.0032 min^-1 ). In the presence of H₂ O₂ , the kinetic degradation parameters of the composite reached 0.0634 min^-1 , which was about 19.8-times higher than that of P25.

Strategies to combine ROP with ATRP or RAFT polymerization for the synthesis of biodegradable polymeric nanoparticles for biomedical applications

The available strategies to combine CRPs and ROP in the synthesis of highly engineered polymer nanoparticles are here critically discussed.

Synthesis and self-assembly behavior of pH-responsive star-shaped POSS-(PCL-P(DMAEMA-co-PEGMA))16 inorganic/organic hybrid block copolymer for the controlled intracellular delivery of doxorubicin

Illustration of pH-responsive self-assembly of the star-shaped POSS-(PCL-P(DMAEMA-co-PEGMA))₁₆ copolymer for the efficient intracellular release of anti-cancer drugs triggered by the acidic microenvironment inside the tumor tissue.

Synthesis and thermo-responsive self-assembly behavior of amphiphilic copolymer β-CD–(PCL–P(MEO2MA-co-PEGMA))21 for the controlled intracellular delivery of doxorubicin

Well-defined amphiphilic β-cyclodextrin star-shaped copolymers with poly(ε-caprolactone)–poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-poly(ethylene glycol)methacrylate) (β-CD–(PCL–P(MEO₂MA-co-PEGMA))₂₁ were synthesized via (ROP) and (ATRP).

Synthesis of a dual pH and temperature responsive star triblock copolymer based on β-cyclodextrins for controlled intracellular doxorubicin delivery release

Well-defined dual pH and temperature responsive triblock star-shaped amphiphilic copolymers of β-CD-g-(PHEMA-b-PNIPAM-b-PDMAEMA)₃ were synthesized by the combination of RAFT polymerizations.

Synthesis and pH-responsive self-assembly behavior of a fluorescent amphiphilic triblock copolymer mPEG-b-PCL-b-PDMAEMA-g-PC for the controlled intracellular delivery of doxorubicin

Schematic illustration of the pH-responsive self-assembly of a mPEG-b-PCL-b-PDMAEMA-g-PC copolymer with fluorescent coumarin units for controlling DOX release.

Synthesis and self-assembly behavior of thermo-responsive star-shaped POSS–(PCL–P(MEO2MA-co-PEGMA))16 inorganic/organic hybrid block copolymers with tunable lower critical solution temperature

Star-shaped copolymers have been synthesized and the LCSTs of thermo-responsive micelles were well controlled by adjusting the content of PEGMA.

Poly(ethylene glycol) conjugated poly(lactide)-based polyelectrolytes: synthesis and formation of stable self-assemblies induced by stereocomplexation

A series of pH-responsive amphiphilic poly(N,N-dimethylaminoethyl methacrylate)-block-poly(D-lactic acid)-block-poly(N,N-dimethylaminoethyl methacrylate) conjugated with poly(ethylene glycol) (D-PDLA-D@PEG) and D-PLLA-D@PEG copolymers were synthesized using a combination of ring-opening polymerization and atom-transfer radical polymerization followed by sequential quaternization of PDMAEMA chains and azide-alkyne click reaction with alkyne-end PEG. Gel permeation chromatography, nuclear magnetic resonance, and Fourier transform infrared spectroscopy results demonstrate the successful synthesis of the copolymers, and the conjugated PEG percentages in the copolymers can be tuned by the feeding ratios in the quaternization reaction. Conjugating PEG onto the PDMAEMA segments also successfully facilitated the D-PDLA-D@PEG, D-PLLA-D@PEG, and its corresponding 1:1 D/L mixtures to be dissolved directly in aqueous solution at the desired concentration range without using any organic solvents unlike the copolymers without PEG conjugation (D-PDLA-D and D-PLLA-D). We demonstrate control over micellar size, charge, and stability via three different preparation pathways, i.e., solution pH, percentages of PEG conjugation in the copolymers, and formation of PLA stereocomplex in micellar core. Static and dynamic light scattering studies demonstrate that the size of the core-shell micelles increases when the solution pH is reduced due to the protonation of the PDMAEMA segments that caused the osmotic pressure within the micelle to increase until the micelles reached a maximum size. It is interesting to note that the micelles formed by 1:1 D/L mixtures have larger swelling ratios as well as aggregation number and hydrodynamic radius that do not change significantly with pH and dilution, respectively, as compared to micelles formed from individual D or L forms of the copolymers. The enhanced stability of the pH-responsive micelles prepared by direct dissolution of the 1:1 D/L mixtures of the PEG conjugated PLA-based polyelectrolytes in aqueous medium is attributed to the stereocomplex formation between PLLA and PDLA in the micellar core as confirmed by wide-angle X-ray scattering measurements.

One-pot synthesis of poly(l-lactide)-b-poly(methyl methacrylate) block copolymers

The combination of ROP and ATRP in a one-pot process with DBU as ATRP ligand and ROP catalyst results in the synthesis of poly(l-lactide)-b-poly(methyl methacrylate) block copolymers.

Unusual thermogelling behaviour of poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA)-based polymers polymerized in bulk

The bulk synthesis of (PDMAEMA)-based polymers and their unusual thermoreversible gelation in aqueous solutions are described.

pH/Temperature-responsive behavior of amphiphilic block copolymer micelles prepared using two different methods

The pH- and temperature-responsive behavior of amphiphilic block copolymer poly(L-lactide)-b-poly(2-(dimethylamino)ethyl methacrylate) (PLLA-b-PDMAEMA) in aqueous solutions is investigated using static and dynamic light scattering. Electrostatic force, hydrophobic interaction, and hydrogen bonding coexist in the system. Micelles with different structures are prepared using water addition (WA) and direct dissolution (DD) methods. The aggregation from loose micelles into large micellar clusters is observed above the transition temperature under basic conditions. Only micellar clusters from the DD method could disaggregate when temperature was decreased to 24.3 °C after heating. The behavior of the micelles prepared with the DD method indicates that only the outer parts of the PLLA-b-PDMAEMA chains in the corona are solvated.