Investigation of Hybrid Materials Based on Polyurethane Modified with Aliphatic Side Chains Combined with Nano-TiO2

In this study, methylene diphenyl diisocyanate (MDI) and polytetrahydrofuran ether diol (PTMG) were used as the raw materials for the synthesis of polyurethane (PU). 1,4-Butanediol, glyceryl monostearate, d-sorbitol tetrastearate, or d-trehalose hexastearate, all containing different amounts of aliphatic side chains, were used as the chain extenders and to introduce C18 side chains into the hard segments of PU, and hybrid materials were then fabricated by mixing PUs with nano-titanium dioxide (nano-TiO2). The effects of the different chain extenders on the surface properties of PU coatings and the hybrid materials were investigated. All the materials were characterised by NMR and FT-IR spectroscopy, differential scanning calorimetry, polarising microscopy, atomic force microscopy, scanning electron microscopy, nanoindentation, and contact angle measurements. The results indicate that incremental changes in the number of side chains decrease the degree of microscale separation from the PU coating and increase the crystallinity of the aliphatic side chains. By introducing the aliphatic side chains, the surface coating presents many tiny protrusions, which enhance the surface roughness and the contact angle. Moreover, both the nano-TiO2 and aliphatic side chain content affect the contact angle of the hybrid materials. The as-obtained superhydrophobic materials exhibit contact angles above 150° with a sliding angle below 3° and present excellent mechanical properties such as hardness and Young’s modulus. The nano-TiO2 was chemically bonded to the molecular chains of PU, resulting in superhydrophobic materials with good acidic and alkaline resistance and anti-stripping properties.

On the crystallization behavior of a poly(stearyl methacrylate) comb-like polymer inside a nanoscale environment

A “soft” or “hard” nanoscale template illustrates the confined processes of a poly(stearyl methylacrylate) comb-like polymer, indicating that reduced chain relaxation and mobility influence the crystallization behavior.

UV-responsive amphiphilic graft copolymers based on coumarin and polyoxazoline

A series of amphiphilic photo-responsive heterografted copolymers have been successfully synthesized. The random copolymers were composed of a methacrylate backbone, with various compositions of hydrophilic oligomeric 2-methyl-2-oxazoline side chains (OMOx) and hydrophobic long alkyl chains terminated by a coumarin moiety (Cm). Using dynamic (DLS) and static light scattering (SLS), and transmission electron microscopy (TEM), their self-assembling behavior was studied in water using the nanoprecipitation method. Depending on the system, one, two or three particle size distributions co-exist in solution. However, DLS measurements showed that monomodal and slightly polydisperse self-assemblies were obtained with the more hydrophobic copolymers (i.e., 85% of hydrophobic monomers with a long alkyl chain terminated by a coumarin moiety (MCm) per molecule) with hydrodynamic diameters ranging from ca. 130 to 300 nm. Morphological information on these self-assembly structures was obtained using SLS: a Gaussian behavior has thus been evidenced. Finally, these heterografted copolymers were illuminated using UV light at λ = 350 nm inducing photo-crosslinking of the coumarin units. The influence of UV illumination on the thus-formed nanoparticles was investigated by carrying out complementarily DLS-measurements and UV spectroscopy.

Interrelations Between Side Chain and Main Chain Packing in Different Crystal Modifications of Alkoxylated Polyesters

Interrelations between main chain and side chain packing are studied in a series of comb-like poly(1,4-phenylene-2,5-n-dialkyloxy terephthalate)s (PPAOTs) with C = 6-12 alkyl carbons per side chain by X-ray diffractometry. Two different polymorphic states, called modification A and modification B, are observed depending on thermal treatment and side chain length. For PPAOTs with short side chains (C ≤ 8), modification A is commonly observed. "As synthesized" (solution crystallized) PPAOTs with longer side chains (C ≥ 10) contain mostly modification B while modification A is growing during melt cooling. A solid-solid transition from modification B to modification A is observed above ≈70 °C for the decyl member (C = 10, PPDOT) while modification A converts under ambient conditions slowly to modification B. This indicates that modification B is thermodynamically stable at low temperature while modification A is stable at higher temperature. Crystallographic analysis shows that both modifications are characterized by an orthorhombic unit cell and a long-range ordered layered structure with alternating main chain and alkyl nanodomains. This is confirmed by 2D diffration data for shear oriented PPDOT fibers. The main difference between both modifications is the packing of the side chains which are in a crystalline state for modification B but disordered for modification A. This is concluded from values for the volume per CH₂ unit V_CH2 in alkyl nanodomains calculated without further assumptions from the obtained lattice parameters. Interestingly, the crystalline packing of the side chains in modification B leads to a significant increase (≈ 20%) in the application relevant π-π spacings within the main chain domains as compared to those for modification A. It is argued that the structure formation process and thermodynamic equilibrium in comb-like polymers might be strongly influenced by a competition of the individual packing tendencies of main and side chains.

Synthesis and self-assembly of polystyrene-based diblock and triblock coil–brush copolymers

Anionic coil–brush, brush–coil–brush and coil–brush–coil type polystyrene-based di- and tri-block copolymers were synthesized and their micellization behavior was compared.

About different packing states of alkyl groups in comb-like polymers with rigid backbones

We report a comparative X-ray diffraction study on three series of comb-like polymers with rigid backbones and layered morphologies [regio-regular poly(3-alkyl thiophenes), alkoxylated polyesters, alkoxylated polyphenylenevinylenes] highlighting the importance of the volume per methylene unit V_CH2 in alkyl nanodomains for the overall packing state. We demonstrate that there is a large (≈30%) variation in the V_CH2 values for different polymer series and packing states but no significant change in V_CH2 depending on the length of the alkyl side groups. This calls into question commonly used structural models which are based only on tilting and interdigitation of ideally stretched alkyl side groups. We argue that a linear dependence of the layer spacings with side chain length can also be explained by a constant V_CH2 value and unchanged main chain packing. The potential importance of side chain packing for the occurrence of different (liquid-) crystalline modifications in various polymer series and possible interrelations between main and side chain packings are discussed.

Self-Assembly of Polyurethane Phosphate Ester with Phospholipid-Like Structures: Spherical, Worm-Like Micelles, Vesicles, and Large Compound Vesicles

Here, we report the preparation and self-assembly of amphiphilic polyurethane phosphate ester (PUP) polymers with phospholipid-like structures. The polymers, designed to have a hydrophilic phosphate head and two amphiphilic PPG-IPDI-MPEG (PU) tails were synthesized via coupling and phosphorylation reactions in sequence. These amphiphilic polymers could self-assemble into various interesting nanostructures in aqueous solution, such as spherical, worm-like micelles, vesicles, and large compound vesicles, depending on the hydrophobic chain length of PU tails and the initial polymer concentrations. It was found that the morphology transition is not only caused by the unique molecular structure of amphiphilic polyurethanes, but also influenced by the additional hydrophilic phosphate groups incorporated, which disturb the force balance governing the aggregation structures. This research supplies a new clue for the fabrication of well-defined nanostructures.

Synthesis and properties of stimuli-sensitive heterografted toothbrush-like terpolymers with a linear handle and two types of V-shaped grafts

Straightforward syntheses were performed to generate amphiphilic heterograftedPNIPAM(PAA)_2m(PCL)_2mcopolymers, which could self-assemble into versatile nanoobjects for thermo, pH and additive triggered controlled release of doxorubicin.

Fluorescent amphiphilic heterografted comb polymers comprising biocompatible PLA and PEtOx side chains

The comb polymers are synthesized in three independent steps by ROP, CROP, and RAFT.

Theranostic Gold Nanomicelles made from Biocompatible Comb-like Polymers for Thermochemotherapy and Multifunctional Imaging with Rapid Clearance

A new generation of photothermal theranostic agents based on assembling 6 nm gold nanoparticles (AuNPs) is developed by using a novel comb-like amphipathic polymer as the template. The small AuNPs are assembled into DOX@gold nanomicelles, which show strong absorbance in the near-infrared region, for multimodal bioimaging and highly effective in vivo chemotherapy and photothermal therapy.

Effects of interaction between a polycation and a nonionic polymer on their cross-assembly into mixed micelles

In this paper, to investigate the effects of interactions between poly(quaternary ammonium) salts (PQAs) and poly(ethylene glycol) on their mixed micellar surface structures and properties under spontaneous conditions, a series of PQAs were first designed and synthesized by atom transfer radical polymerization (ATRP) using 2-(dimethylamino) ethyl methacrylate (DMAEMA) quaternized by bromobutane, bromooctane, and bromododecane, respectively. Poly(poly(ethylene glycol) methyl ether methacrylate) (PPEG) with a similar degree of polymerization was also prepared using poly(ethylene glycol) methyl ether methacrylate by ATRP. Next, these PQAs were mixed with an equal weight of PPEG in water to cross-assemble into mixed micelles. The structures and features of these mixed micelles were characterized by fluorescence measurements, transmission electron microscopy (TEM), dynamic light scattering (DLS), phase analysis light scattering (PALS), proton nuclear magnetic resonance ((1)H NMR), and hydrogen-hydrogen correlation spectroscopy nuclear magnetic resonance (H-H COSY NMR). These results suggest that PQAs and PPEG mixtures can cross-assemble into mixed micelles with low CMC. The surface structures, particle sizes, size distributions, and zeta potentials of PQAs and PPEG mixtures can be tailored by varying the alkyl chain length in quaternary ammonium salts, and the alkyl chain length also influences the distribution and the alkyl chain orientation of quaternary ammonium salts on mixed micelle surfaces. In addition, cytotoxicity of these mixed micelles can be markedly reduced by PPEG compared with their corresponding PQAs, but their good antibacterial activities are still maintained to a certain degree, as evaluated by methyl tetrazolium assay (MTT) and minimum inhibitory concentration (MIC). Our present work provides a new avenue for the preparation of biocompatible and antibacterial materials for biomedical applications.

Liquid crystalline macrocyclic azacalix[4]pyridine and its complexes with the zinc ion: conformational change from the saddle to flattened shape

Regulation of phase behaviors by macrocyclic conformational variation.

Multi-responsive graft copolymer micelles comprising acetal and disulfide linkages for stimuli-triggered drug delivery

Dual-cleavable polymeric aggregates were efficiently used for thermo-, pH and reduction triggered controlled release of doxorubicin due to the stimuli-dependent topological transformation and reaggregation of copolymer aggregates.

Synthesis of Anisotropic, Amphiphilic Grafted Multi-Star Polymers and Investigation of their Self-Assembling Characteristics

Herein, we report the synthesis of amphiphilic multi-star architectures consisting of discrete poly(methacrylic acid)-based core cross-linked star polymers joined together by polystyrene-grafted linear connectors by a combination of atom transfer radical polymerisation of protected macroinitiator precursors and a copper-catalysed azide-alkyne cycloaddition grafting-to approach. The anisotropic multi-star architectures, which were obtained as individual di- and tri-star polymers with segregated hydrophobic and hydrophilic domains, undergo aggregation in apolar solvents resulting in the formation of large nanometre-scale vesicles. The self-assembling behaviour of these large amphiphilic multi-star polymers (Mw = 869–1097 kDa) was studied using dynamic light scattering, transmission electron microscopy, and atomic force microscopy.

Synthesis and properties of heterografted toothbrush-like copolymers with alternating PEG and PCL grafts and tunable RAFT-generated segments

Novel (A-g-D)(B-alt-C)_mD-type heterografted toothbrush-like copolymers with great potential in smart drug delivery systems and thermo-responsive surface materials are investigated.

Sequence Effects on Properties of the Poly(p-phenylene terephthalamide)-based Macroinitiators and their Comb-like Copolymers Grafted by Polystyrene Side Chains

Two poly(p-phenylene terephthalamide) (PPTA)-based macroinitiators with random and alternate sequences, i.e. poly(p-phenylene terephthalamide)-ran-poly[p-phenylene (2,2,6,6-tetramethylpiperidinyl-1-oxy)terephthalamide)] (CPPTA-ran) and poly(p-phenylene terephthalamide)-alt-poly[p-phenylene (2,2,6,6-tetramethylpiperidinyl-1-oxy)terephthalamide)] (CPPTA-alt), were prepared via copolycondensation of terephthaloyl chloride, 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)-functionalized terephthaloyl chloride, and p-phenylenediamine. The graft copolymers consisting of rigid PPTA backbones and polystyrene side chains were obtained by nitroxide-mediated radical polymerization. Both macroinitiators and graft copolymers were characterized by thermal gravimetric analysis, differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. The regular incorporation of the TEMPO-containing co-unit gives rise to remarkable effects on the thermal stability, lyotropic liquid crystallinity, and macromolecular packing in bulk. CPPTA-alt shows better thermal stability and more ordered intermolecular structure than CPPTA-ran. The former generates a nematic phase at a concentration of 18 wt-% in concentrated sulfuric acid, whereas the latter does so at a concentration of 12 wt-%. For the graft copolymers, the alternative main chains exhibit sharper diffraction than the random ones. However, the sequence change exerts no discernible effect on other properties.

25th anniversary article: what can be done with the Langmuir-Blodgett method? Recent developments and its critical role in materials science

The Langmuir-Blodgett (LB) technique is known as an elegant method for fabrication of well-defined layered structures with molecular level precision. Since its discovery the LB method has made an indispensable contribution to surface science, physical chemistry, materials chemistry and nanotechnology. However, recent trends in research might suggest the decline of the LB method as alternate methods for film fabrication such as layer-by-layer (LbL) assembly have emerged. Is LB film technology obsolete? This review is presented in order to challenge this preposterous question. In this review, we summarize recent research on LB and related methods including (i) advanced design for LB films, (ii) LB film as a medium for supramolecular chemistry, (iii) LB technique for nanofabrication and (iv) LB involving advanced nanomaterials. Finally, a comparison between LB and LbL techniques is made. The latter reveals the crucial role played by LB techniques in basic surface science, current advanced material sciences and nanotechnologies.

Comb-like amphiphilic copolymers bearing acetal-functionalized backbones with the ability of acid-triggered hydrophobic-to-hydrophilic transition as effective nanocarriers for intracellular release of curcumin

The pH-responsive micelles have enormous potential as nanosized drug carriers for cancer therapy due to their physicochemical changes in response to the tumor intracellular acidic microenvironment. Herein, a series of comb-like amphiphilic copolymers bearing acetal-functionalized backbone were developed based on poly[(2,4,6-trimethoxybenzylidene-1,1,1-tris(hydroxymethyl) ethane methacrylate-co-poly(ethylene glycol) methyl ether methacrylate] [P(TTMA-co-mPEGMA)] as effective nanocarriers for intracellular curcumin (CUR) release. P(TTMA-co-mPEGMA) copolymers with different hydrophobic-hydrophilic ratios were prepared by one-step reversible addition fragmentation chain transfer (RAFT) copolymerization of TTMA and mPEGMA. Their molecular structures and chemical compositions were confirmed by (1)H NMR, Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). P(TTMA-co-mPEGMA) copolymers could self-assemble into nanosized micelles in aqueous solution and displayed low critical micelle concentration (CMC). All P(TTMA-co-mPEGMA) micelles displayed excellent drug loading capacity, due to the strong π-π conjugate action and hydrophobic interaction between the PTTMA and CUR. Moreover, the hydrophobic PTTMA chain could be selectively hydrolyzed into a hydrophilic backbone in the mildly acidic environment, leading to significant swelling and final disassembly of the micelles. These morphological changes of P(TTMA-co-mPEGMA) micelles with time at pH 5.0 were determined by DLS and TEM. The in vitro CUR release from the micelles exhibited a pH-dependent behavior. The release rate of CUR was significantly accelerated at mildly acidic pH of 4.0 and 5.0 compared to that at pH 7.4. Toxicity test revealed that the P(TTMA-co-mPEGMA) copolymers exhibited low cytotoxicity, whereas the CUR-loaded micelles maintained high cytotoxicity for HepG-2 and EC-109 cells. The results indicated that the novel P(TTMA-co-mPEGMA) micelles with low CMC, small and tunable sizes, high drug loading, pH-responsive drug release behavior, and good biocompatibility may have potential as hydrophobic drug delivery nanocarriers for cancer therapy with intelligent delivery.