Well-defined Block Copolymers Research Articles

Spontaneous Hydrogel Formation Through Hydrophobic Interactions in an ABA-type Block Copolymer Composed of Poly(2-methacryloyloxyethyl phosphorylcholine) and Poly(n-butyl methacrylate) Segments

ABSTRACTIn this study, the spontaneous formation of hydrogels from a water-soluble and amphiphilic ABA-type block copolymer in an aqueous system was examined. The block copolymers were composed of poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) as the B segment and poly(n-butyl methacrylate) (BMA) as the A segment. A two-step living radical polymerization of the corresponding monomers yielded a well-defined ABA-type block copolymer. By regulating the polymerization degree of each segment, the water solubility and amphiphilic natures of the resulting block copolymer could be controlled. The block copolymers spontaneously formed hydrogels when the composition of water in the medium increased to 80 vol% in the water/ethanol mixture. This was due to molecular aggregation of the block copolymers driven by the hydrophobic interactions between the poly(BMA) segments in the polymer. This hydrogel formation depended on the composition and polymerization degree of the MPC units. The poly(MPC) also showed good biocompatibility, thereby rendering the block copolymers applicable for the immobilization of biological components such as antibodies and enzymes and the encapsulation of cells under mild conditions.

Surface relief gratings formed by microphase-separated disperse red 1 acrylate-containing diblock copolymers

Sinusoidal surface-relief gratings (SRGs) formed by microphase separated photoresponsive poly(dimethylsiloxane)-block-poly(methyl acrylate-co-disperse red 1 acrylate) (PDMS-b-P(MA-co-DR1A)) chains are investigated. Different PDMS-b-P(MA-co-DR1A) were prepared by a multi-step synthetic approach which overcomes the challenges inherent to the synthesis of well-defined PDMS-based block copolymers (BCPs) having a DR1A dye content up to 50 wt%. A sinusoidal SRG (amplitude ≈ 5 nm, wavenumber ≈ 315 nm) interferometrically inscribed onto a thin PDMS-b-P(MA-co-DR1A) layer exhibiting an out-of-plane cylindrical structure with a period of ∼34 nm is demonstrated. Such kind of “two-colored” multiscale patterned surfaces could be envisioned as guiding patterns to efficiently direct the self-assembly of a BCP upper-layer via a hybrid chemo-/grapho-epitaxial alignment of BCP features.

Precise Synthesis of Bottlebrush Block Copolymers from ω-End-Norbornyl Polystyrene and Poly(4-tert-butoxystyrene) via Living Anionic Polymerization and Ring-Opening Metathesis Polymerization

A facile and efficient synthetic grafting-through strategy for preparing well-defined bottlebrush block copolymers (BBCPs) was developed through a combination of living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). ω-End-norbornyl polystyrene (NPSt) and poly(4-tert-butoxystyrene) (NPtBOS) were synthesized by LAP using terminator of chlorine moiety containing silane-protecting amine and coupled with a subsequent amidation using norbornyl activated ester. Bottlebrush homopolymers of NPSt were obtained by ROMP with ultrahigh molecular weights (MWs, Mw = 2928 kDa) and narrow molecular weight distributions (MWDs, Đ = 1.07) at high degree of polymerizations (DPw = 1084). Well-defined BBCPs with ultrahigh MWs (Mw ∼ 3055 kDa) and narrow MWDs (Đ ∼ 1.13) were synthesized through sequential ROMP of NPSt with NPtBOS. The effect of ultrahigh MWs was investigated by self-assembly of the BBCPs in which the phase-separated BBCPs presented periodic lamellar structures and exhibited structural colors from blue to pink.

Regioselective living polymerization of allylcyclohexane and precise synthesis of hydrocarbon block copolymers with cyclic units

Regioselective living polymerization of allylcyclohexane was catalyzed by a bulky α-diimine nickel catalyst. Well-defined hydrocarbon block copolymers with cyclic units were constructed by sequential monomer addition.

Non-ionic fluorinated amphiphilic block copolymer via RAFT polymerization and their application as surfactant in emulsion polymerization

This investigation reports the synthesis of block copolymer of poly(ethylene glycol) methyl ether methacrylate (PPEGMA) with poly(heptafluorobutyl acrylate) (PHFBA). The blockcopolymer was prepared via reversible addition-fragmentation chain transfer polymerization (RAFT). The RAFT end-capped poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) macro-chain transfer agent (CTA) was prepared using 2-cyano-2-propyl dithiobenzoate (CPBT) as RAFT agent. The synthesized PPEGMA was later used as macro-RAFT agent for the polymerization of 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) which yielded well-defined block copolymers of varied lengths. The PPEGMA-b-PHFBA block copolymer self-assembles in water produces spherical micelles with core-shell nano-structure where the core made of hydrophobic block (PHFBA) and shell is of hydrophilic block (PPEGMA). The synthesized block copolymers, PPEGMA−b−PHFBA, an amphiphilic block copolymers were used as surfactant in the surfactant free emulsion polymerization of styrene. Aqueous micellar solutions of the block copolymers were characterized by DLS and TEM analyses. The CMC value of polymeric surfactant was 0.046 mg. mL−1, determined by surface tension analysis. The block copolymers were characterized by GPC, 1H NMR, FT-IR, DSC analyses.

Light induced polyethylene ligation

We introduce a photoreactive polyethylene (PE) derivative, which upon light irradiation (λmax = 365 nm) can effectively react to form well-defined block copolymers with polystyrene and poly(methyl methacrylate).

Surfactant-Free RAFT Emulsion Polymerization of Styrene Using Thermoresponsive macroRAFT Agents: Towards Smart Well-Defined Block Copolymers with High Molecular Weights.

The combination of reversible addition–fragmentation chain transfer (RAFT) and emulsion polymerization has recently attracted much attention as a synthetic tool for high-molecular-weight block copolymers and their micellar nano-objects. Up to recently, though, the use of thermoresponsive polymers as both macroRAFT agents and latex stabilizers was impossible in aqueous media due to their hydrophobicity at the usually high polymerization temperatures. In this work, we present a straightforward surfactant-free RAFT emulsion polymerization to obtain thermoresponsive styrenic block copolymers with molecular weights of around 100 kDa and their well-defined latexes. The stability of the aqueous latexes is achieved by adding 20 vol % of the cosolvent 1,4-dioxane (DOX), increasing the phase transition temperature (PTT) of the used thermoresponsive poly(N-acryloylpyrrolidine) (PAPy) macroRAFT agents above the polymerization temperature. Furthermore, this cosolvent approach is combined with the use of poly(N,N-dimethylacrylamide)-block-poly(N-acryloylpiperidine-co-N-acryloylpyrrolidine) (PDMA-b-P(APi-co-APy)) as the macroRAFT agent owning a short stabilizing PDMA end block and a widely adjustable PTT of the P(APi-co-APy) block in between 4 and 47 °C. The temperature-induced collapse of the latter under emulsion polymerization conditions leads to the formation of RAFT nanoreactors, which allows for a very fast chain growth of the polystyrene (PS) block. In dynamic light scattering (DLS), as well as cryo-transmission electron microscopy (cryoTEM), moreover, all created latexes indeed reveal a high (temperature) stability and a reversible collapse of the thermoresponsive coronal block upon heating. Hence, this paper pioneers a versatile way towards amphiphilic thermoresponsive high-molecular-weight block copolymers and their nano-objects with tailored corona switchability.

Transiently Thermoresponsive Acetal Polymers for Safe and Effective Administration of Amphotericin B as a Vaccine Adjuvant.

The quest for new potent and safe adjuvants with which to skew and boost the immune response of vaccines against intracellular pathogens and cancer has led to the discovery of a series of small molecules that can activate Toll-like receptors (TLRs). Whereas many small molecule TLR agonists cope with a problematic safety profile, amphotericin B (AmpB), a Food and Drug Administration approved antifungal drug, has recently been discovered to possess TLR-triggering activity. However, its poor aqueous solubility and cytotoxicity at elevated concentrations currently hampers its development as a vaccine adjuvant. We present a new class of transiently thermoresponsive polymers that, in their native state, have a phase-transition temperature below room temperature but gradually transform into fully soluble polymers through acetal hydrolysis at endosomal pH values. RAFT polymerization afforded well-defined block copolymers that self-assemble into micellar nanoparticles and efficiently encapsulate AmpB. Importantly, nanoencapsulation strongly reduced the cytotoxic effect of AmpB but maintained its TLR-triggering capacity. Studies in mice showed that AmpB-loaded nanoparticles can adjuvant an RSV vaccine candidate with almost equal potency as a highly immunogenic oil-in-water benchmark adjuvant.

‘Schizophrenic’ behavior of poly (N-isopropylacrylamide)-b-poly (2-vinylpyridine) in aqueous solutions

A series of well-defined double hydrophilic block copolymers Poly (N-isopropylacrylamide)-b-poly (2-vinylpyridine) (PNIPAM38-b-P2VP43) were synthesized. The ‘schizophrenic’ behavior and the aggregation process of PNIPAM-b-P2VP in response to temperature and pH in dilute aqueous solution were tested via transmittance measurements, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The results revealed that: i) both PNIPAM-core and P2VP-core micelles can be induced from an intermediate unimers state via the adjustment of temperature and pH; ii) The lower critical solution temperature (LCST) of PNIPAM homopolymers is narrowly in the range of 31–34 °C, while PNIPAM-b-P2VP diblock copolymers at pH = 7 and 2 have broad LCSTs of 25–40 °C and 41-50 °C, respectively; iii) SANS results show that only the PNIPAM-b-P2VP solution at pH = 7 and 50 °C (both blocks are hydrophobic) has a sphere form factor with diameter of about 110 nm.

Deep eutectic solvents (DES): Excellent green solvents for rapid SARA ATRP of biorelevant hydrophilic monomers at ambient temperature

An eco-friendly type III deep eutectic solvent (reline: choline chloride/urea) was used for the supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) of different biorelevant hydrophilic monomers (HEA: 2-hydroxyethyl acrylate, HEMA: 2-hydroxyethyl methacrylate and AMPTMA: (3-acrylamidopropyl)trimethylammonium chloride) near room temperature (30 °C). The polymerization of HEA mediated by a safe and inexpensive SARA agent (Na2S2O4) revealed controlled features, with polymers exhibiting low dispersity (Đ ≈ 1.3) throughout the course of the polymerization. Results also showed that typically, a slow and continuous feeding of the SARA agent to the reaction mixture afforded PHEA-Br with higher chain-end functionality and lower dispersity (Đ ≈ 1.1), in comparison to the one obtained without Na2S2O4 feeding. As proof-of-concept, purified PHEA-Br macroinitiators were used for the preparation of different well-defined block copolymers (PHEA-b-PAMPTMA and PHEA-b-PMA).

A Useful Method for Preparing Mixed Brush Polymer Grafted Nanoparticles by Polymerizing Block Copolymers from Surfaces with Reversed Monomer Addition Sequence

The preparation of well-defined block copolymers using controlled radical polymerization depends on the proper order of monomer addition. The reversed order of monomer addition results in a mixture of block copolymer and homopolymer and thus has typically been avoided. In this paper, the low blocking efficiency of reversed monomer addition order is utilized in combination with surface initiated reversible addition-fragmentation chain-transfer polymerization to establish a facile procedure toward mixed polymer brush grafted nanoparticles SiO2 -g-(PS (polystyrene), PS-b-PMAA (polymethacrylic acid)). The SiO2 -g-(PS, PS-b-PMAA) nanoparticles are analyzed by gel permeation chromatography deconvolution, and the fraction of each polymer component is calculated. Additionally, the SiO2 -g-(PS, PS-b-PMAA) are amphiphilic in nature and show unique self-assembly behavior in water.

High-Efficiency Cell-Penetrating Helical Poly(phenyl isocyanide) Chains Modified Cellular Tracer and Nanovectors with Thiol Ratiometric Fluorescence Imaging Performance

In order to precisely tail the endocytosis process and determine the internal location of drug carriers in cells, fluorescent tracers with high sensitivity and versatility are one of the most powerful tools. Nevertheless, conventional single fluorescent probes always suffered from the interference of background fluorescence or the lack of long-time monitoring capability, resulting in the low resolution and efficiency. To overcome this drawback, nanocarriers capable of multicolor fluorogenic and ratiometric properties became an urgently needed solution. In this contribution, starting from pentafluorophenyl ester (PFP)- and tetraphenylethene (TPE)-functionalized phenyl isocyanide (PI) monomers as well as l-hydrophilic (HP) PI monomers, a type of well-defined amphiphilic block copolymer, P(PFPPI-co-TPEPI-co-HPPI)-b-HPPPI, with controlled molecular weights and tunable compositions was prepared through sequential living copolymerization with phenylethynyl Pd(II) complex as a single catalyst in one pot. Disulfi...

Antimicrobial surfaces obtained from blends of block copolymers synthesized by simultaneous ATRP and click chemistry reactions

A series of amphiphilic block copolymers based on styrene (S) and a monomer bearing both thiazole and triazole groups (MTA) were synthesized by combination of ATRP and click chemistry. In particular, two approaches were followed; the direct ATRP from a PS macroinitiator of the pre-synthesized MTA antimicrobial monomer; and the simultaneous synthesis and polymerization of the MTA through a one-step ‘click chemistry’/ATRP process. Both strategies conduct to well-defined block copolymers with controlled molecular weight and low polydispersity. Subsequent quaternization of the thiazole and triazole groups of MTA units with butyl iodine renders systems with antimicrobial properties. Although these systems presented relatively low antimicrobial activity against bacteria and fungi in aqueous media, the preparation of surfaces functionalized with these copolymers leads to potent antimicrobial surfaces, especially against gram-positive bacteria.

Solubilisation of oils in aqueous solutions of a random cationic copolymer

HypothesisReports of random copolymers capable of solubilising hydrophobic oils are rare. This is primarily because random copolymers are unlikely to self-assemble into suitable aggregates (or micelles) in water. A random copolymer with a “blocky” (or lumpy) microstructure may have potential to solubilise hydrophobic oils in water. This type of polymer would have advantages over block copolymers which are more laborious and costly to synthesise. ExperimentsThe solubilising capacity of a blocky random copolymer, namely poly(methyl methacrylate-co-2-dimethylaminoethyl methacrylate) (PMMA-co-PDMAEMA) is assessed by UV–visible spectroscopy and compared with common reference surfactants. The relative solubilising performance of random copolymers (across a narrow range of DMAEMA mol % fraction) for aromatic and aliphatic oils was also studied. The morphology of the aggregates was monitored as a function of the solubilisation capacity by small-angle neutron scattering (SANS) and dynamic-light scattering (DLS). FindingsSimilarly to well-defined block copolymers, these random copolymers have a specific preference for solubilising aromatic over aliphatic oils. Increasing hydrophobicity of the copolymer enhances the solubilisation capacity. SANS has highlighted that aggregates become swollen and more uniform/spherical with increasing concentration of aromatic solubilisate, and that the aromatic solubilisate partitions throughout the random copolymer aggregates.

Characterization and thermal stability of nano eight arm copolymers synthesized by atom transfer radical polymerization

The synthesis of nano eight-armed poly{POSS lactide-b-N, N-(dimethylamino)ethyl methacrylate} copolymers is reported in this paper. Thio-click chemistry combined with living/controlled polymerization methods that allow the preparation of well-defined polymeric building block copolymers. This was carried out using Thio-Click reaction of octavinyl POSS with 2-mercapto ethanol to prepare Thiolate-POSS. Thiolate POSS-lactide polymers containing different l-Lactide repeated units (10, 25, 50 and 100) were synthesized by ring-opening polymerization of (l-lactide) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst. The resulting polymers were copolymerized with N-hydroxyethyl-2-(dimethylamino) ethyl methacrylate (DMAEMA) via atom transfer radical polymerization. All the prepared polymers and copolymers are characterized by different spectroscopic and analytical techniques, such as infrared spectroscopy, nuclear magnetic resonance (1H NMR and 13C NMR) and by gel permeation chromatography (GPC), where all these analyses have verified the expected structure and compositions. On the other hand, images obtained from Scanning Electronic Microscopy (SEM) revealed the existence of nanostructures in the prepared copolymers due to the presence of the lactide array to give nanofiber within final compositions prepared, and with the presence of POSS in their structures, they enhance the copolymers thermal stability, and they are expected to be suitable for different applications as nano-carriers in the biomedical field.

Polymerization-Induced Cooperative Assembly of Block Copolymer and Homopolymer via RAFT Dispersion Polymerization.

Polymerization-induced cooperative assembly (PICA) is developed to promote morphological transitions at high solids via RAFT dispersion polymerization, using both a macromolecular chain transfer agent (macro-CTA) and a small molecule chain transfer agent (CTA) to generate nano-objects consisting of well-defined block copolymer and homopolymer. PICA is demonstrated to promote morphological transitions under various conditions. Elemental mapping provides unambiguous evidence for the uniform distribution of the homopolymer within the core of the nano-objects. It is proposed that the growing homopolymer first reaches its solubility limit and forms aggregates, which induce the adsorption of the growing block copolymer. This effective and robust PICA approach significantly expands the capability to promote morphological transitions in RAFT dispersion polymerization and will facilitate the efficient synthesis of various higher-order morphologies at high solids.

Controlled Synthesis and Degradation of Poly(N-(isobutoxymethyl) acrylamide) Homopolymers and Block Copolymers

The homopolymerization of the water-insoluble N-(isobutoxymethyl)acrylamide (IBMA) is investigated for the first time by nitroxide-mediated polymerization. The homopolymerization is characterized by a linear increase in number average molecular weight (Mn) versus conversion (X) to X > 0.80 while maintaining dispersities of Mw/Mn < 1.30. A strong Arrhenius relationship correlates the apparent rate constants and the homopolymerization temperatures between 105 and 120 °C. All poly(IBMA) homopolymers are then successfully chain-extended with styrene (S) to form well-defined block copolymers of poly(IBMA)-b-poly(S) suggesting a high degree of livingness of the poly(IBMA) macroinitiators. Thermogravimetric analysis and differential scanning calorimetry are both used to characterize the thermal properties of the homopolymers and block copolymers and identify possible unique degradation of the poly(IBMA) block through imide formation at elevated temperatures.

Reduction of Line Edge Roughness of Polystyrene-block-Poly(methyl methacrylate) Copolymer Nanopatterns By Introducing Hydrogen Bonding at the Junction Point of Two Block Chains.

To apply well-defined block copolymer nanopatterns to next-generation lithography or high-density storage devices, small line edge roughness (LER) of nanopatterns should be realized. Although polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) has been widely used to fabricate nanopatterns because of easy perpendicular orientation of the block copolymer nanodomains and effective removal of PMMA block by dry etching, the fabricated nanopatterns show poorer line edge roughness (LER) due to relatively small Flory-Huggins interaction parameter (χ) between PS and PMMA chains. Here, we synthesized PS-b-PMMA with urea (U) and N-(4-aminomethyl-benzyl)-4-hydroxymethyl-benzamide (BA) moieties at junction of PS and PMMA chains (PS-U-BA-PMMA) to improve the LER. The U-BA moieties serves as favorable interaction (hydrogen bonding) sites. The LER of PS line patterns obtained from PS-U-BA-PMMA was reduced ∼25% compared with that obtained from neat PS-b-PMMA without BA and U moieties. This is attributed to narrower interfacial width induced by hydrogen bonding between two blocks, which is confirmed by small-angle X-ray scattering. This result implies that the introduction of hydrogen bonding into block copolymer interfaces offers an opportunity to fabricate well-defined nanopatterns with improved LER by block copolymer self-assembly, which could be a promising alternative to next-generation extreme ultraviolet lithography.

Sustainable poly(ε-decalactone)−poly(l-lactide) multiarm star copolymer architectures for thermoplastic elastomers with fixed molar mass and block ratio

To improve the thermal and mechanical properties of thermoplastic elastomers derived from plant-based monomers, a series of well-defined multiarm star block copolymers was investigated. Controlled bulk ring-opening polymerization of ε-decalactone (DL) with multiarm initiators yielded hydroxyl-terminated (PDL−OH)n, which were subsequently converted to (PDL−PLLA)n using l-lactide (LLA) through a one-pot, two-step process. The multiarm copolymers were designed for targeting on Mn,NMR and fPLLA of 180 kg mol−1 and 0.27, respectively. Structural analysis proved that PLLA hard domains were thinner, and thus, more compact microphase-separated structures with hexagonally packed cylinders were induced by increasing n. Thermal and tensile property measurement demonstrated that, although the copolymers had a lower crystallinity in PLLA due to the shorter chain length, the thermal degradation stability and mechanical strength were enhanced, which was caused by to an amplified pinning effect caused by the more closed packed PLLA domains, in addition to chemical crosslinking of the PDL strands.

Redox-Responsive Self-Assembly Micelles from Poly(N-acryloylmorpholine-block-2-acryloyloxyethyl ferrocenecarboxylate) Amphiphilic Block Copolymers as Drug Release Carriers.

Novel well-defined redox-responsive ferrocene-containing amphiphilic block copolymers (PACMO-b-PAEFC) were synthesized by ATRP, with poly(N-acryloylmorpholine) (PACMO) as hydrophilic blocks and poly(2-acryloyloxyethyl ferrocenecarboxylate) (PAEFC) as hydrophobic blocks. The copolymers were characterized by FT-IR and 1H NMR spectroscopies and gel permeation chromatography, and the crystalline behavior was determined by X-ray diffraction and small-angle X-ray scattering. The results showed that the size of the lamellar crystals and crystallinity vary with the systematic compositions while the periodic structure of the lamellar stacks has no obvious change. These block copolymers could self-assemble and form globular nanoscaled core-shell micellar aggregates in aqueous solution. The reductive ferrocene groups could be changed into hydrophilic ferrocenium via mild oxidation, whereas the polymer micelles at the oxidation state could reversibly recover from their original states upon reduction by vitamin C. The tunable redox response was investigated and verified by transmission electron microscopy, ultraviolet-visible spectroscopy, cyclic voltammetry, and dynamic light scattering measurements. The copolymer micelles were used to entrap anticancer drug paclitaxel (PTX), with high drug encapsulation efficiency of 61.4%, while the PTX-loaded drug formulation exhibited oxidation-controlled drug release, and the release rate could be mediated by the kinds and concentrations of oxidants. MTT assay was performed to disclose the biocompatibility and security of the copolymer micelles and to assess anticancer efficiency of the PTX-loaded nanomicelles. The developed copolymer nanomicelles with reversible redox response are anticipated to have potential in targeted drug delivery systems for cancer therapy.