Diphilic Macromolecular Brushes with a Polyimide Backbone and Poly(methacrylic acid) Blocks in Side Chains

Novel macromolecular brushes with a polyimide backbone and diphilic diblock copolymer side chains consisting of a hydrophilic block of poly(methacrylic acid) adjacent to the backbone and the outer hydrophobic block of poly(methyl methacrylate) are synthesized. The synthesis includes the grafting of poly(tert-butyl methacrylate) to the polyimide chain followed by the polymerization of methyl methacrylate on the graft copolyimide as a branched multicenter macroinitiator. Brushes with diphilic side chains are obtained via the acidic hydrolysis of ester groups in the first block of side chains. The grafting polymerization of methacrylates is performed according to the “grafting from” approach by the method of pseudoliving atom transfer radical polymerization using two methodologies of polymerization activated by either copper- or iron-containing complexes. Conditions providing the controlled regime of the polymerization processes under study are found, and pathways for the targeted regulation of the degree of polymerization of methacrylate blocks and their grafting density are determined. As is shown by dynamic light scattering and transmission electron microscopy, the macromolecules of brushes with diphilic side chains form in ethanol homotypic, obviously spherical, supramolecular micellar structures with hydrodynamic radii in the range from 40 to 120 nm depending on the length and grafting density of the two blocks in diphilic side chains.     

Synthesis and Solution Properties of Loose Polymer Brushes Having Polyimide Backbone and Methylmethacrylate Side Chains

Summary: Graft-copolymers with polyimide backbone and PMMA side chains are synthesized by ATRP of methylmethacrylate on the polyimide macroinitiator. The obtained copolymers, macroinitiator, and cleaved side chains are investigated by ¹H NMR, SEC, static and dynamic light scattering, sedimentation, and viscosimetry in solutions. The synthesized copolymer is relatively loose polymer brushes: the average distance between grafted PMMA chains is ∼11 nm (4 repeat units of the backbone). The hydrodynamic and conformational characteristics of graft-copolymers change on passage from ethylacetate to chloroform due to difference in the thermodynamic quality of the solvents with respect to the copolymer components. The backbone is characterized more extended conformation than individual polyimide macromolecule.     

Small‐angle neutron scattering analysis of bottlebrush backbone and side chain flexibility

Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are determined through small‐angle neutron scattering analysis of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a “grafting‐through” ring‐opening polymerization. Scattering profiles are modeled with the empirical Guinier–Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end‐to‐end distance proportional to N^0.55, while the overall bottlebrush increases in size proportional to N^0.77. These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in solution. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 104–111     

Synthesis and investigation of the solution behavior of graft block copolymers of polyimide and poly(methyl methacrylate)

Graft copolymers with a polyimide backbone and poly(methyl methacrylate) side chains are investigated in dilute chloroform and ethyl acetate solutions via the methods of molecular hydrodynamics and optics. Copolymer samples are prepared through the “grafting from” method via atom-transfer radical polymerization with a multicenter polyimide macroinitiator. In solutions of copolymers with low degrees of functionalization Z (40%), supermolecular structures are formed as a result of interactions between the polyimide backbones. In samples with Z → 100%, the backbone is well screened by side chains; therefore, molecular solutions are formed in both solvents. The hydrodynamic and conformational behavior of samples with high functionalization degrees changes after the transition from ethyl acetate to chloroform owing to the different thermodynamic qualities of the solvents with respect to the copolymer components. In both solvents, the backbone tends to avoid contact with a poor solvent. This effect is more pronounced in the case of ethyl acetate. Macromolecules of the studied graft copolymers are characterized by high equilibrium rigidities (>40 nm) that are 10 times higher than the corresponding characteristics of aromatic polyimides.     

Polysoaps in Backbone‐Selective Solvents: Effects of Side‐Chain Length on Collapse Dynamics

Abstract

Molecular dynamics (MD) simulations of model comb‐graft heteropolymers were performed to understand general mechanistic features of coil‐to‐micelle relaxation after instantaneous quench from a nonselective solvent to solvent conditions selective for the backbone monomers and poor for the side‐chain monomers. The systems considered were single bead‐spring molecules with backbones of 30 monomers and 10 equally spaced side chains of 1, 5, 10, or 20 monomers each, immersed in dense liquids of 20,000 simple solvent particles. We find that the coil‐to‐micelle relaxation time, τ _r , averaged over 50 independent trajectories for each set of topological parameters considered, decreases with increasing side‐chain length. A two‐stage relaxation mechanism is observed: (1) a fast collapse and aggregation of neighboring side chains to form a chain of “protomicelles,” followed by (2) a slow intramolecular aggregation of protomicelles. Fast collapse dominates for molecules with relatively longer side chains due to relatively higher probabilities of initial contacts between side‐chain monomers in different side chains, while slow intramolecular aggregation dominates for molecules with relatively shorter side chains.     

Synthesis of degradable molecular brushes via a combination of ring-opening polymerization and click chemistry

Acid-degradable molecular brushes with polycarbonate backbone and densely grafted side chains (∼1.9 SCs per backbone repeating unit) were synthesized for the first time using the grafting-onto method. Extremely efficient copper-catalyzed azide-alkyne cycloaddition click reactions between the polycarbonate backbone containing two pendant azido groups per backbone unit and alkynyl-terminated poly (methyl acrylate) (ay-PMA₇₂, average degree of polymerization DP = 72) SCs were demonstrated to finish in 10 min with a quantitative conversion of the azido groups. Similar grafting efficiencies were also achieved when using alkynyl-terminated polystyrene (ay-PS), poly(ethylene oxide) (ay-PEO), and poly (t-butyl acrylate)-b-polystyrene (ay-PtBA-b-PS) to successfully prepare molecular brushes with high grafting density (>1.8 SCs per backbone repeating unit). Under acidic condition, the polycarbonate backbones were completely degradable and the final degraded product of the molecular brushes was a linear polymer chain with molecular weight two times of the SCs. When a mixture of hydrophobic ay-PS and hydrophilic ay-PEO chains was used, amphiphilic heterobrushes PC-g-(PS-co-PEO) were synthesized, which could self-assemble into micelles or vesicles in selective solvents, depending on the ratio of the two SCs in the brush. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 239–248     

Efficient synthesis of well‐defined amphiphilic cylindrical brushes polymer with high grafting density: Interfacial “Click” chemistry approach

Reported here is a novel approach toward efficient preparation of well‐defined cylindrical brushes polymer (CBPs) with both hydrophobic and hydrophilic side chains connected to the linear backbone by interfacial “click” chemistry in two immiscible solvents. The CBPs with high grafting density of more than 95% and molecular polydispersity (M_w/M_n) less than 1.12 can be readily synthesized using present approach. On contrary, the CBPs synthesized from the “click” reaction in a single solvent in homogenous state have low grafting density of less than 55% and molecular polydispersity (M_w/M_n) more than 1.78. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Solution behavior of polyimide‐graft‐polystyrene copolymers in selective solvents

A polyimide‐graft‐polystyrene (PI‐g‐PS) copolymer with a polyimide backbone and polystyrene side chains was synthesized by the “grafting from” method using styrene polymerization on a polyimide multicenter macroinitiator via ATRP mechanism. The side chain grafting density z = 0.86 of PI‐g‐PS is rather high for graft‐copolymers synthesized by the ATRP method. Molecular characteristics and solution behavior of PI‐g‐PS were studied in selective solvents using light scattering and viscometry methods. In all solvents, the backbone tends to avoid contact with a poor solvent. To describe the conformation and hydrodynamic properties of PI‐g‐PS macromolecules in thermodynamically good solvents for side chains and PI‐g‐PS, the wormlike spherocylinder model is used. Macromolecules of the studied graft‐copolymer are characterized by high equilibrium rigidities (Kuhn segment length >20 nm). In Θ‐conditions, PI‐g‐PS macromolecules may be modeled by a rigid prolate ellipsoid of revolution with a low asymmetry form and a collapsed backbone as the ellipsoid core. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1539–1546     

Conformations of molecular brushes based on polyimide and poly(methyl methacrylate) in selective solvents: Experiment and computer simulation

The effect of solvent quality with respect to main and side chains on the conformations of molecular brushes is investigated by the methods of molecular hydrodynamics and optics as well as by computer simulation. Copolymers with a polyimide backbone and poly(methyl methacrylate) side chains are studied in solvents featuring strongly different thermodynamic qualities (chloroform, ethyl acetate, and 3-heptanone). The studied samples have close total molecular masses and backbone lengths but differ in grafting densities and lengths of side chains: a brush with densely grafted and relatively short side chains versus a brush with loosely grafted but very long side chains. For both types of brushes, similar changes in hydrodynamic behavior with improvement in the solvent quality are found experimentally. Computer simulation shows that these changes have different origins. In the former case, macromolecules are elongated, and their volumes grow simultaneously, while in the latter case, the shape of the macromolecules remains close to spherical and the changes in hydrodynamic parameters are mainly due to an increase in the volume of macromolecules.     

Conformation of oligo(ethylene glycol) grafted poly(norbornene) in solutions: A small angle neutron scattering study

The conformation of newly synthesized amphiphilic poly(methoxyoligo(ethylene oxide) norbornenyl esters) macro-homopolymers in dilute solutions of toluene-d8 and D₂O was investigated by small angle neutron scattering (SANS). The macro-homopolymers consist of a polynorbornene (PNB) backbone with a degree of polymerization (DP) of 50, and each repeat unit has a grafted ethylene glycol (EG) side chain with an average DP of 6.6. The hydrophobic backbone and hydrophilic side chains interact differently with solvents of different polarity, which makes the polymer conformation very sensitive to the solvent quality. It was found that in a 0.5 wt.% toluene solution the polymers assume coil-like conformation and gradually contract and become more compact with increasing polymer concentration. In D₂O, the conformation of the polymers were studied at different concentrations: 0.1, 0.5, 1.0 and 2.0 wt.% and at different temperatures: 25, 44, 60 and 74 °C. The polymers are partially contracted in D₂O and their shape can be described by the form factor of a rigid cylinder. The second virial coefficient A₂ was extracted at three temperatures (25, 44 and 60 °C) and the theta point was estimated to be reached at ∼45 °C. The attractive interactions between the polymers in D₂O increase with temperature, which leads to the polymer-solvent phase separation at the cloud point temperature (CPT). The polymer conformation remains virtually temperature independent below the CPT and at 74 °C polymers collapse and form compact structures with water soluble side chains in the shell.     

Grafting of living poly(ethylene oxide) onto polystyrene via aromatic nucleophilic displacement of activated nitro groups

Polystyrene of M?_ω = 2.2 × 10⁴ was alkylated with 4-nitrophthalimidomethyl groups as grafting sites. Several backbone polymers with various degrees of grafting sites (G = 2–100%) were prepared and characterized by elemental analysis, IR, ¹H- and ¹³C-NMR, and viscosity measurements. “Living” poly(ethylene oxide) with narrow molecular-weight distribution was prepared in the presence of 15-crown-5, and grafted onto the 4-nitrophthalimidomethylated polystyrene. The nitro displacement reaction was fast and the grafting yield was quantitative (100%). The graft copolymers are highly soluble in water and in organic solvents. The intrinsic viscosities of the graft copolymers are higher than those of the backbone polymers. The intrinsic viscosities show an initial increase followed by a decrease as the degree of grafting increase.     

Structure and molecular motion of poly(ethylene oxide) chains adsorbed on a silica-tethered poly(methyl methacrylate) by the spin label method

The spin-label method was used to study the structure and molecular motion of poly(ethylene oxide) (PEO) chains adsorbed on a silica-tethered poly(methyl methacrylate) (PMMA). Spin-labelled PEO with a narrow molecular weight distribution, having number averaged molecular weight (M _N)=6.0×10³, was adsorbed on the surface of the silica-tethered PMMA with various grafting ratios in carbon tetrachloride solution at 35?°C. ESR spectra were measured at various temperatures after the samples were completely dried. The ESR spectra are composed of two spectra arising from spin-labels attached to “train” and “tail” segments, which are strongly and weakly interacted with the silica surface, respectively. The fractional amount of the “tail” segments increases extremely with the grafting ratio of PMMA. Molecular mobility of the PEO chains estimated from the temperature dependence of the ESR spectra also decreases significantly with the grafting ratio of PMMA. Structure and molecular motion of the PMMA chains tethered on the silica were also studied using the spin-labelled PMMA. Consequently, parts of the PEO segments penetrate into the PMMA chains and is adsorbed on the silica surface (“train” segments), whereas parts of the PMMA segments protrude from the surface. The other PEO segments are entangled with the tethered PMMA chains (“tail” segments).     

Simulation of Copolymer Bottle-Brushes

Summary: The structure of bottle-brush polymers with a rigid backbone and flexible side chains is studied in three dimensions, varying the grafting density, the side chain length, and the solvent quality. Some preliminary results of theoretical scaling considerations for one-component bottle-brush polymers in a good solvent are compared with Monte Carlo simulations of a simple lattice model. For the simulations a variant of the pruned-enriched Rosenbluth method (PERM) allowing for simultaneous growth of all side chains in the Monte Carlo sampling is employed. For a symmetrical binary (A,B) bottle-brush polymer, where two types (A,B) of flexible side chains are grafted with one chain end to the backbone in an alternating way, varying repulsive binary interactions between unlike monomers and the solvent quality, it is found that phase separation into an A-rich part of the cylindrical molecule and a B-rich part can occur only locally. Long range order (in the direction of the backbone) does not occur, and hence the transition from the randomly mixed state of the bottle-brush to the phase-separated structure is strongly rounded, in contrast to the corresponding mean field predictions of a sharp transition to a “Janus cylinder” phase-separated structure. This lack of a phase transition can be understood from an analogy with spin models in one dimension. By estimating the correlation length for this phase separation along the backbone as a function of side chain length and solvent quality, we present strong evidence that no sharp phase transition occurs.     

Conformation of ionizable poly Para phenylene ethynylene in dilute solutions

The conformation of dinonyl poly para phenylene ethynylenes (PPEs) with carboxylate side chains, equilibrated in solvents of different quality have been studied using molecular dynamics simulations. PPEs are of interest because of their tunable electro‐optical properties, chemical diversity, and functionality which are essential in wide range of applications. The polymer conformation determines the conjugation length and their assembly mode and affects electro‐optical properties which are critical in current and potential uses. This study investigates the effect of carboxylate fraction on PPEs side chains on the conformation of chains in the dilute limit, in solvents of different quality. The dinonyl PPE chains are modeled atomistically, where the solvents are modeled both implicitly and explicitly. Dinonyl PPEs maintained a stretched out conformation up to a carboxylate fraction f of 0.7 in all solvents studied. The nonyl side chains are extended and oriented away from the PPE backbone in toluene and in implicit good solvent, whereas in water and implicit poor solvent, the nonyl side chains are collapsed toward the PPE backbone. Rotation around the aromatic ring is fast and no long range correlations are seen within the backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 582–588     

Comb copolymer cylindrical brushes containing semiflexible side chains: a Monte Carlo study

The off‐lattice Monte Carlo method is applied to investigate the equilibrium conformations of isolated comb copolymer cylindrical brushes in an athermal solution. The molecules considered consist of a flexible backbone, which is densely grafted with semiflexible side chains. The study focuses on the influence of the degree of intrinsic stiffness, λ_side, of the side chains on the conformational behavior of the molecules. It is demonstrated that with a fixed side chain length, M, the local length scale conformational fluctuations of the backbone increase as a function of λ_side. However, the persistence length, λ, of the cylindrical brush increases considerably with the side chain stiffness, indicating that the backbone becomes more extended at the large length scale. Moreover, as a function of λ_side, there is an increase in the ratio λ/D of the persistence length and the diameter, D, of the brush. This behavior is in good agreement with recent theoretical predictions and provides important new insight in the latest experimental observations.     

Influence of the Molecular Polyimide Brush on the Gas Separation Properties of Polyphenylene Oxide

A new hybrid gas separation membrane was prepared from poly(2,6-dimethyl-1,4-phenylene oxide) modified with graft copolyimide with side poly(methyl methacrylate) chains. The changes in the membrane structure on introducing up to 15 wt % modifier were evaluated by atomic force microscopy and density measurements. The microphase separation in modified polyphenylene oxide films was demonstrated. Introduction of graft copolyimide leads to an increase in the density of the hybrid films. The gas transport properties of the membranes were evaluated for H₂, CO₂, O₂, O₄, and N₂. Introduction of up to 10 wt % modifier does not noticeably alter the permeability of the hybrid membranes to all the gases but increases the selectivity in gas separation.

     

Luminescent mesogen jacketed poly(1‐alkyne) bearing lateral terphenyl with hexyloxy tail

Mesogen jacketed liquid crystalline poly(1‐alkyne) and poly(1‐phenyl‐1‐alkyne) linked pendants of terphenyl mesogens with hexyloxy tails at the waist position (? {RC?C? [(CH₂)₃OOC‐terpheyl‐(OC₆H₁₃)₂]}_n? , where R?H, PHATP(OC6)2 ; R?C₆H₅, PPATP(OC6)2 ) were synthesized. The influences of structural variations on the thermal, mesomorphic, and luminescent properties were investigated. Polymerizations of all monomers are carried out by WCl₆‐Ph₄Sn catalysts successfully. The polymers are stable (T_d ≥ 340 °C) and soluble in common solvents. The monomers and polymers show enantiotropic SmA phases in the heating and cooling processes, and the lateral side chains of the mesogenic units are perpendicular to the main chain. The “jacket effect” of chromophoric terphenyl core “shell” around the main chain also contributes to polymers with high photoluminescence, and the pendant‐to‐backbone energy transfer path is involved in the luminescence process of this polymers. In comparison with monosubstituted polyacetylene PHATP(OC6)2 , the disubstituted polyacetylene PPATP(OC6)2 shows better photoluminescence in both THF solution and film, and exhibited about 40 nm red‐shifted than PHATP(OC6)2 , indicating that the “jacket effect” of terphenyl mesogens forces poly(1‐phenyl‐1‐alkyne) backbone to extend in a more planar conformation with a better conjugation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

良溶剂中接枝型聚两性电解质单链构象的布朗动力学模拟

采用布朗动力学研究了在良溶剂中荷电平衡的接枝聚两性电解质(GPA)的单链构象转变行为,讨论了主链链长、支链数及电荷密度对GPA分子链构象转变的影响.研究发现,随着静电相互作用的增强,GPA分子链构象转变过程由线团、主链与支链间的折叠、链段塌缩和电荷配对形成偶极子与四极子等4个阶段构成.与线型聚两性电解质不同,GPA存在的额外支链间空间排斥与静电排斥作用随着分子结构的变化而改变,并影响构象转变行为.在强静电相互作用下,良溶剂中的GPA链由于溶剂化作用会再伸展,以保证偶极子完全配对成四极子.减小主链长度或电荷密度或增加支链数目都会增大体系的排斥力和主链的刚性,阻滞分子链的塌缩,并使得分子链再伸展的幅度增大.     

Synthesis of a “molecular rope curtain”: Preparation and characterization of a sliding graft copolymer with grafted poly(ethylene glycol) side chains by the “grafting onto” strategy

A sliding graft copolymer (SGC) with poly(ethylene glycol) (PEG) side chains was prepared by ester formation between terminal carboxyl groups of oxidized PEG methyl ether with molecular weight of 2000 (mPEG2000‐COOH) and hydroxyl groups of a polyrotaxane consisting of PEG and cyclodextrins (CDs). Formation of the SGC structure was confirmed by ¹H NMR, attenuated total reflectance Fourier‐transformed infrared, and gel permeation chromatography. The SGC was soluble in good solvents of PEG and insoluble in poor solvents of PEG. Estimation of the number of grafted mPEG chains suggested a “rope‐curtain” like structure, in which an mPEG chain is connected to each CD ring. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Combination of “living” nitroxide-mediated and photoiniferter-induced “grafting from” free-radical polymerizations: From branched copolymers to unimolecular micelles and microgels

We report on solution properties of lightly grafted copolymers composed of polystyrene (PS) backbone (degree of polymerization of PS backbone, N_b=95) and variable length of poly(tert-butyl methacrylate) P(tBuMA) side chains (degree of polymerization of side chains, N_sc=14-222) at fixed number of grafting sites n = 11 and polydispersity index (M_w/M_n) ranging from 1.05 to 2.63. Synthesis of these graft copolymers is based on a novel synthetic route [Gromadzki D, Makuška R, Netopilík M, Holler P, Lokaj J, Janata M, et al. Eur Polym J 2008;44:59-71] involving two independent controlled/“living” polymerization mechanisms, namely nitroxide-mediated radical polymerization (NMP) for the synthesis of the backbone and photoinduced “grafting from” iniferter process for building of P(tBuMA) branches. The viscosity-related contraction factors g^′<1 confirmed high degree of branching of the studied graft copolymers. Dilute solutions of graft copolymers in non-selective solvent (THF), examined by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and viscometry, revealed a transition from comb-like conformation through wormlike-star to a microgel architecture under increasing number of monomeric units in side chains. These data were further supported by the structure factors R_η/R_h and R_g/R_h obtained by independent measurements and extrapolated to infinite dilution. Persistence lengths of the samples exhibiting comb-like topology were larger compared to linear polystyrene backbone and P(tBuMA) side chains in THF suggesting stiffening of the main chain with increasing size of the attached side chains. Unimolecular micelles were detected by DLS and SAXS in solvent selective for grafts, tert-amyl alcohol.