Conformational behavior of comb-like polyelectrolytes in selective solvent: computer simulation study

In this work, we present molecular dynamics simulations of comb-like polyelectrolytes in selective solvent. The studied polymers have a neutral backbone and polyelectrolyte side chains. The solvent is poor for the backbone and the theta solvent for the side chains. The polymers are modeled on a coarse-grained level with implicit solvent. The simulations show that the comb-like polyelectrolytes tend to form intramolecular self-organized structures of the pearl necklace type. This type of conformational behavior has been predicted by Borisov and Zhulina (Borisov, O. V.; Zhulina, E. B. Macromolecules 2005, 38, 2506) for neutral comb-like copolymers in selective solvent. The present study shows that comb-like polyelectrolytes in selective solvent exhibit the same type of behavior; however, it can be controlled by one additional parameter, the degree of dissociation of the grafts. The local conformational characteristics are studied using the ensemble-averaged bond angle cosines as functions of monomer position in the chain, which reveal structural details invisible by other means.     

Effects of polar group saturation on physical gelation of amphiphilic polymer solutions

Monte Carlo simulation on the basis of the comblike coarse grained nonpolar/polar (NP) model has been carried out to study the polar group saturation effect on physical gelation of amphiphilic polymer solutions. The effects of polar group saturation due to hydrogen bonding or ion bridging on the sol-gel phase diagram, microstructure of aggregates, and chain conformation of amphiphilic polymer solutions under four different solvent conditions to either the nonpolar backbone or the polar side chain in amphiphilic polymer chains have been investigated. It is found that an increase of polar group saturation results in a monotonically decreased critical concentration of gelation point, which can be qualitatively supported by the dynamic rheological measurements on pectin aqueous solutions. Furthermore, various solvent conditions to either the backbone or the side chain have significant impact on both chain conformation and microstructure of aggregates. When the solvent is repulsive to the nonpolar backbone but attractive to the polar side chain, the polymer chains are collapsed, and the gelation follows the mechanism of colloidal packing; at the other solvent conditions, the gelation follows the mechanism of random aggregation.     

Synthesis and characterization of semifluorinated polymers and block copolymers

The goal of the investigation presented here was to evaluate the influence of semifluorinated side chains on the bulk structure and the surface properties of polysulfones with different chain structure. Thus, segmented block copolymers consisting of polysulfone and semifluorinated aromatic polyester segments as well as polysulfones having semifluorinated side chains randomly distributed over the polymer backbone were synthesized and characterized. Oxydecylperfluorodecyl side chains were used because of their strong tendency for self-organization. The influence of the chain architecture on the self-organization as well as on the surface properties, particularly the wetting behavior, was examined. It could be shown that despite of the higher self-organizing tendency of block copolymers the surface properties of both polymer types are comparable and depend only on the concentration of side chains.     

Conformational Aspects and Intramolecular Phase Separation of Alternating Copolymacromonomers: A Computer Simulation Study

Summary: Using the bond fluctuation model (BFM), simulations have been performed on molecular bottle brushes with two chemically different types of side chains. In the first part of this work, rigidity of the backbone is imposed. The influence of solvent quality and side chain length on the intramolecular phase separation of side chain material, leading to Janus cylinders, has been investigated and compared to theoretical predictions. In the second part of this work, the restriction of rigidity for the backbone is relaxed. In a poor solvent, the side chain material collapses into a globular state. Several globules containing each one type of side chain material are connected together by backbone material. When imposing different solvent conditions for both types of side chains, a bending of the backbone is found as predicted by theory and observed in very recent experiments.

Comparison between typical snapshots in θ solvent. The side chain length is 25 beads. Dark and light coloured side chains repel each other.     

Blends of bisphenol-A polycarbonate and acrylic polymers: II. PC/acrylic copolymers as a new route for compatibilization

An acrylic polymer containing acid and anhydride units, referred to as reactive polyglutarimide (RPGI), has been used to react with PC. The reaction has been previously determined as an acidolysis of the carbonate bond which breaks the PC chain in two parts. One of those two parts remains free while the other one is grafted on the acrylic backbone. We have found that the anhydride units could also react with the carbonate bonds. In this case the PC macromolecule would also be broken in two parts, which would, however, both be grafted on the acrylic backbone. The reaction has been performed in solution in order to keep good contact between the reacting units. The influence of temperature and concentration on the grafting ratio has been studied. The best experimental conditions were determined in order to obtain a grafted copolymer where the acrylic backbone only supports, on the average, one PC side chain through acid reaction or two PC chains through anhydride reaction. Indeed, these two types of reactions could not be isolated. The efficiency of this copolymer as emulsifier has been studied in solution cast blends as well as in melt mixed blends. The copolymer strongly affects the microstructure in solution cast blends where films containing 30 wt % of PC have become transparent. However, the dispersed phase size of solvent cast blends could be highly influenced by the casting conditions related to solvent trapping. In melt mixed samples, the copolymer also reduces significantly the dispersed phase size, but no transparent blends have been observed so far. These results were compared with those given in the literature describing the efficiency of a synthesized copolymer which has a more complicated structure. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 735–747, 1997     

On the shape of bottle-brush macromolecules: systematic variation of architectural parameters

We measured the form factor of bottle-brush macromolecules under good solvent conditions with small-angle neutron scattering and static light scattering. The systems under investigation are brushes, synthesized via the grafting-from route, built from a poly(alkyl methacrylate) backbone to which poly(n-butyl acrylate) side chains are densely grafted. The aim of our work is to study how the systematic variation of structural parameters such as the side chain length and backbone length change the conformation of the polymer brushes in solution. All spectra can be consistently described by a model, considering the bottle-brush polymers as flexible rods with internal density fluctuations. Parameters discussed are (1) the contour length per main chain monomer l(b), (2) the fractal dimension of the side chains Ds, as well as (3) the fractal dimension D, and (4) the Kuhn length lambdak of the overall brush. l(b)=0.253+/-0.008 nm is found to be independent of the side chain length and equal to the value found for the bare main chain, indicating a strongly stretched conformation for the backbone due to the presence of the side chains. The fractal dimension of the side chains is determined to be Ds=1.75+/-0.07 which is very close to the value of 10.588 approximately 1.70 expected for a three-dimensional self-avoiding random walk (3D-SAW) under good solvent conditions. On larger length scales the overall brush appears to be a 3D-SAW itself (D=1.64+/-0.08) with a Kuhn-step length of lambdak=70+/-4 nm. The value is independent of the side chain length and 46 times larger than the Kuhn length of the bare backbone (lambdak=1.8+/-0.2 nm). The ratio of Kuhn length to brush diameter lambda(k)d>or=20 determines whether lyotropic behavior can be expected or not. Since longer side chains do not lead to more persistent structures, lambda(k)d decreases from 8 to 4 with increasing side chain length and lyotropic behavior becomes unlikely.     

多嵌段高分子的溶解性和分子形状的蒙特卡罗研究

利用 Ｍｏｎｔｅ Ｃａｒｌｏ 方法模拟了两组分多嵌段高分子链在稀溶液中的行为,着重探讨了不同的嵌段长度对高分子性质的影响．研究中以自避的分子链为研究对象,分别考察了稀溶液中该分子链的溶解性、分子线团形状和嵌段单元的空间分布,与嵌段长度的关系．结果表明,在相同溶剂条件下,嵌段序列的长度对共聚高分子溶解性有较大影响,嵌段序列长度与溶解性能具有非单调的变化规律．该分子链在溶剂中的形状同样受到嵌段序列长度的影响．嵌段间的相互作用能的差别越大,则高分子的溶解性和形状对嵌段长度的依赖性就越显著     

PSt-g-PEO两亲接枝共聚物溶液的性质

两亲共聚物是指分子结构中同时具有对两种相结构都有亲和性的聚合物,一般指分子结构中同时含有亲油和亲水基团的共聚物,研究两亲共聚物在选择性溶剂中的形态及聚集态结构,对于其作为表面活性剂,增溶剂,生物医药材料,以及固体微胶束的研究都具有重要的理论和实际意义。[1-3]／     

两亲性接枝共聚物在选择性溶剂中自组装行为的模拟研究

利用粗粒化分子动力学(CGMD)方法研究了两亲性接枝共聚物在不同选择性溶剂中的自组装行为. 分析了主链刚性及链长对自组装结构的影响. 研究结果表明, 当溶剂对主链为良溶剂而对支链为不良溶剂时, 两亲性接枝共聚物随主链刚性的增加自组装形成花状胶束、 花桥状胶束及桥状胶束, 并且组分比例对自组装结构影响很大; 随着链长的增加, 柔性链出现单花状胶束到多花状胶束的转化. 当溶剂对主链为不良溶剂而对支链为良溶剂时, 可得到近球形或椭球形核壳状胶束及束状结构; 不同链长时, 柔性接枝共聚物链均只能得到近球形的单核壳状胶束.     

Synthesis,dynamic light scattering,and luminescence properties of copolymers containing iridium(III) bisterpyridine in the side chain

Supramolecular block‐random copolymers containing [Ir(terpy)₂]³⁺ in the side chain were synthesized via postfunctionalization of a P(S‐b‐AC_terpy) block copolymer. Absorbance and emission spectra compared to a model compound show that the polymer backbone has a minor effect on the polymer absorbance but produces a larger shift for the phosphorescence signals to higher wavelength. Dynamic light scattering of the metal complex containing copolymer studied in various solvents showed monomodal aggregation with decreasing aggregate size as the solvent dielectric constant increased. The copolymer precursor P(S‐b‐AC_terpy) shows multimodal aggregation in different solvents with the major population consisting of single chains. This difference in behavior between the two polymers is attributed to the electrolytic nature of the complex and the amphiphilicity induced by the charged metal complex. Supramolecular copolymers like these will continue to have interesting self‐organizational properties and may find applications in multicomponent systems for photoinduced charge separation processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1109–1121, 2007     

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     

Conformational studies of bottle-brush polymers absorbed on a flat solid surface

The adsorption of a bottle-brush polymer end-grafted with one chain end of its backbone to a flat substrate surface is studied by Monte Carlo simulation of a coarse-grained model, that previously has been characterized in the bulk, assuming a dilute solution under good solvent conditions. Applying the bond fluctuation model on the simple cubic lattice, we vary the backbone chain length N(b) from N(b)=67 to N(b)=259 effective monomeric units, the side chain length N from N=6 to N=48, and set the grafting density to σ=1, i.e., parameters that correspond well to the experimentally accessible range. When the adsorption energy strength ? is varied, we find that the adsorption transition (which becomes well-defined in the limit N(b)→∞, for arbitrary finite N) roughly occurs at the same value ?(c) as for ordinary linear chains (N=0), at least within our statistical errors. Mean square end-to-end distances and gyration radii of the side chains are obtained, as well as the monomer density profile in the direction perpendicular to the adsorbing surface. We show that for longer side chains the adsorption of bottle-brushes is a two-step process, the decrease of the perpendicular linear dimension of side chains with adsorption energy strength can even be nonmonotonic. Also, the behavior of the static structure factor S(q) is analyzed, evidence for a quasi-two-dimensional scaling is presented, and consequences for the interpretation of experiments are discussed.     

Random copolymerization of macromonomers as a versatile strategy to synthesize mixed-graft block copolymers

The random copolymerization of norbornene-functionalized macromonomers was explored as a method of synthesizing mixed-graft block copolymers (mGBCPs). The copolymerization kinetics of a model system of polystyrene (PS) and poly(lactic acid) (PLA) macromonomers was first analyzed, revealing a gradient composition of side chains along the mGBCP backbone. The phase separation behavior of mGBCPs with PS and PLA side chains of various backbone lengths and side chain molar ratios was investigated, and increasing the backbone length was found to stabilize the phase-separated nanostructures. The graft architecture was also demonstrated to improve the processability of the mGBCP, compared to a linear counterpart. Investigations of mGBCPs comprised of polydimethylsiloxane and poly(ethylene oxide) side chains exemplified the diverse self-assembled morphologies, including a Frank-Kasper A15 phase, that can be obtained with mGBCPs synthesized by random copolymerization of macromonomers. Lastly, a ternary mGBCP was synthesized by the copolymerization of three macromonomers.     

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.     

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.     

聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质的研究

采用核磁共振 (NMR)、动态激光光散射 (DLS)、透射电子显微镜 (TEM )等方法研究了规整性聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质 ,研究表明两亲接枝共聚物在选择性溶剂中可形成球状胶束 ,溶液的浓度、温度和聚合物结构等因素影响其胶束的大小、形态     

Géométrie de micelles à deux compartiments hydrophobes

We discuss a “comb block copolymer” with a hydrophilic backbone (N polar heads), Nf/2 side chains of type A, and Nf/2 side chains of type B. Imposing an area per head and a volume per side chain, we predict various conformations based on two spherical portions. In certain cases, two distinct conformations are permitted by this criterion: the best one should minimise the A/B interfacial energy. We also discuss “multiplets” (p polymers per double micelle) and “necklaces” (k double micelles for one polymer chain).     

An Efficient Approach for Preparing Giant Polypeptide Triblock Copolymers by Protein Dimerization

An efficient and convenient approach for preparing a giant polypeptide–poly(ethylene oxide) triblock copolymer architecture of defined structure and composition is reported. This copolymer consists of two long polypeptide chains derived from bovine serum albumin of distinct lengths with stabilizing poly(ethylene oxide) side‐chains, a connecting poly(ethylene oxide) block, and the presence of secondary structure elements along the polypeptide backbone. It is synthesized from the abundant plasma protein serum albumin and the polypeptide backbone is fully biodegradable. This approach represents a convenient and efficient strategy for preparing giant polypeptide‐based block copolymers of defined structure via a semi‐synthetic strategy. Such high‐molecular‐weight, biodegradable copolymers are attractive for various biomedical applications     

Computer simulation of bottle-brush polymers with flexible backbone: good solvent versus theta solvent conditions

By molecular dynamics simulation of a coarse-grained bead-spring-type model for a cylindrical molecular brush with a backbone chain of N(b) effective monomers to which with grafting density σ side chains with N effective monomers are tethered, several characteristic length scales are studied for variable solvent quality. Side chain lengths are in the range 5 ≤ N ≤ 40, backbone chain lengths are in the range 50 ≤ N(b) ≤ 200, and we perform a comparison to results for the bond fluctuation model on the simple cubic lattice (for which much longer chains are accessible, N(b) ≤ 1027, and which corresponds to an athermal, very good, solvent). We obtain linear dimensions of the side chains and the backbone chain and discuss their N-dependence in terms of power laws and the associated effective exponents. We show that even at the theta point the side chains are considerably stretched, their linear dimension depending on the solvent quality only weakly. Effective persistence lengths are extracted both from the orientational correlations and from the backbone end-to-end distance; it is shown that different measures of the persistence length (which would all agree for Gaussian chains) are not mutually consistent with each other and depend distinctly both on N(b) and the solvent quality. A brief discussion of pertinent experiments is given.     

Conformational properties and dynamics of molecular bottle‐brushes: A cellular‐automaton‐based simulation

Extensive computer simulation was performed using the bond‐fluctuation model and cellular‐automaton (CA)‐based simulation technique to probe the equilibrium structure and dynamical behavior of comb‐branched polymers in which the flexible side chains of a given length are placed regularly along the backbone and the number of branches increases linearly with total molecular weight. By applying very efficient CA algorithm – the “lattice molecular dynamics” (LMD) method – we have been able to study the properties of sufficiently large structures (up to 5880 monomeric units). Depending on the length of main and side chains as well as on interbranch spacing, we have calculated mean chain dimensions, local fractal dimensionalities, particle scattering functions, time autocorrelation functions, etc. The following main conclusions may be drawn from the results presented in our study: (i) The critical exponent, governing the mean size of the main chain, remains unchanged from its value known for a 3d self‐avoiding walk (SAW). On the other hand, two‐dimensional branched macromolecules with one‐sided branches are effectively in a collapsed state even under conditions of a good solvent, forming specific helical superstructures. (ii) Comparison of the simulated data with the predictions of the scaling model indicates that the latter is valid in describing the mean dimensions of the backbone as a function of side‐chain length and interbranch spacing. (iii) The excluded volume interaction between side chains dramatically slows down the relaxation of the backbone chain.