Influences of the initiation and termination reactions on the molecular weight distribution and compositional heterogeneity of functional copolymers: an application of Monte Carlo simulation (original) (raw)
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Protein-like copolymers: computer simulation
Physica A: Statistical Mechanics and its Applications, 1998
The notion of protein-like AB copolymers is introduced. Such copolymers can be generated with the help of the "instant image" of a dense homopolymer globule by assigning that the monomeric units closer to the globular surface are of A type, while the core is formed by the B type units. After that the primary structure of the chain is ÿxed, and one introduces di erent interaction potentials for A and B units. In doing so, we have in mind mainly aqueous systems and analogy with globular proteins, therefore A units are regarded as hydrophilic, and B units as hydrophobic. By means of Monte Carlo simulation using the bond uctuation model we study the coil-globule transition for a protein-like copolymer upon the increase of attraction of hydrophobic B units, and compare the results with those for random AB copolymers. From the analysis of the primary structure of protein-like copolymers one can see that the "degree of blockiness" of the protein-like sequence is higher than for random copolymers, therefore the copolymers with the "random-block" primary structure are generated for comparison as well (the average length of A and B sequences being the same as for protein-like copolymers). It is shown that the coil-globule transition in protein-like copolymers occurs at higher temperatures, is more abrupt and has faster kinetics than for random copolymers with the same A=B composition and for random-block copolymers with the same A=B composition and "degree of blockiness". The globules of protein-like copolymers exhibit a dense micelle-like core of hydrophobic B units stabilized by the long dangling loops of hydrophilic A units. Apparently, a protein-like copolymer "inherits" some of the properties of the "parent globule" which is re ected in the special long-range correlations in primary structure.
Journal of Non- …, 2008
We present a lattice Monte Carlo study of a series of block copolymer chains in selective solvents of varying quality, first using a diblock chain of the length of N=32N=32 with a 16–16 microarchitecture, and then – two multiblock chains of N=64N=64 and N=128N=128, with (8–8)4(8–8)4 and (16–16)4(16–16)4 microarchitectures, respectively. We report a variety of thermodynamic and structural properties, such as energy, specific heat, end-to-end distance and radius of gyration both for the whole chain and for individual blocks. The simulations have demonstrated that a multiblock copolymer in a selective solvent exhibits protein-like behavior undergoing a two-step transition, first from a swollen state to a secondary ‘pearl-necklace’ state and then to a tertiary super-globular state as the solvent quality decreases, i.e. upon cooling. We have found that mean-squared end-to-end distances of multiblock chains decrease as the temperature is reduced, as expected.
Polymer Science Series A, 2007
The coil-globule transition in copolymers composed of amphiphilic and hydrophilic monomer units has been studied by the computer simulation technique. It has been shown that the structure of globules formed in such systems substantially depends on the rate at which the solvent quality worsens. The globule resulting from slow cooling is cylindrical, and its core contains a large amount of hydrophilic groups. The globule formed upon rapid cooling takes the helical conformation, in which all hydrophilic groups are displaced to the periphery. One helix turn of such globules contains 3-5 units. In both cases, the backbone of the polymer chain forms a typical zigzag-shaped structure with an average angle between neighboring bond vectors of about 60 ° . This fact implies that globules of copolymers consisting of amphiphilic and hydrophilic units comprise secondary structure components.
Industrial & Engineering Chemistry Research, 2008
Vapor pressure data (at 50°C) of solutions of poly(methyl methacrylate) [PMMA], polystyrene [PS], and poly(styrene-ran-methyl methacrylate) [P(S-ran-MMA)], with different weight fractions f of styrene units, in either CHCl 3 , acetone [AC], methyl acetate [MeAc], or toluene [TL] were evaluated with respect to the dependence of the Flory-Huggins interaction parameter on polymer concentration and on f. For all solutions under investigation, varies considerably with the composition of the mixture, and only for four of them [CHCl 3 /PS, AC/PMMA, MeAc/PS, and TL/P(S-ran-MMA) f ) 0.5] is this dependence linear; another four systems exhibit a minimum [CHCl 3 /PMMA, CHCl 3 /P(S-ran-MMA) f ) 0.5, TL/PMMA, and TL/PS], and only one [MeAc/PMMA] shows a maximum. With the exception of CHCl 3 /P(S-ran-MMA) and f ) 0.5, the
Charged designed copolymers in the presence of multivalent counterions: a molecular dynamics study
New Journal of Physics, 2004
We present the results of molecular dynamics simulations of charged proteinlike hydrophobic-hydrophilic (HP) copolymers in a dilute salt-free solution with multivalent counterions under poor solvent conditions. The primary sequence of these copolymers is constructed such that they can self-assemble into a segregated core-shell microstructure thus resembling some of the basic properties of globular proteins. The results are compared with those obtained earlier for the system containing monovalent counterions. The processes of coilto-globule transition, aggregation of polyions, and counterion condensation are studied in detail as a function of temperature. The main attention is paid to the influence of the counterions of different charge on the aggregation of the copolymers. It is found that multivalent counterions considerably increase the aggregation of the chains, which form in their presence the finite-size aggregates built up from several polyions. However, the striking feature of the aggregation is that this process does not appear to lead to macroscopic phase separation. The mechanism that prevents the phase separation is discussed.
Analytical and Bioanalytical Chemistry, 2010
We present a method by which to obtain the absolute, chemical-heterogeneity-corrected molar mass (M) averages and distributions of copolymers and apply the method to a gradient random copolymer of styrene and methyl methacrylate in which the styrene percentage decreases from approximately 30% to 19% as a function of increasing molar mass. The method consists of separation by size-exclusion chromatography (SEC) with detection using multi-angle static light scattering (MALS), differential viscometry (VISC), differential refractometry (DRI), and ultraviolet absorption spectroscopy (UV) and relies on the preferential absorption of styrene over methyl methacrylate at 260 nm. Using this quadruple-detector SEC/MALS/UV/ VISC/DRI approach, the percentage of styrene (%St) in each elution slice is determined. This %St is then used to determine the specific refractive index increment, corrected for chemical composition, at each elution slice, which is then used to obtain the molar mass at each slice, corrected for chemical composition. From this corrected molar mass and from the chemical-composition-corrected refractometer response, the absolute, chemical-heterogeneity-corrected molar mass averages and distribution of the copolymer are calculated. The corrected molar mass and intrinsic viscosity at each SEC elution slice are used to construct a chemical-heterogeneity-corrected Mark-Houwink plot. The slice-wise-corrected M data are used, in conjunction with the MALS-determined R G,z of each slice, to construct a conformation plot corrected for chemical heterogeneity. The corrected molar mass distribution (MMD) of the gradient copolymer extends over an approximately 30,000 g/mol wider range than the uncorrected MMD. Additionally, correction of the Mark-Houwink and conformation plots for the effects of chemical heterogeneity shows that the copolymer adopts a more compact conformation in solution than originally concluded.
New Journal of Physics, 2004
We propose a computer model describing the synthesis of proteinlike copolymers in a polar solution via irreversible polymerization of hydrophobic and hydrophilic monomers with simultaneous globule formation. In the model, growing chain macroradical, polymerizing monomers, and the preferential absorption of hydrophobic monomers in the core of the globule are taken into account explicitly. The effect of monomer concentrations and reaction rate on the conformational properties and primary copolymer sequences is investigated. We find that, under certain conditions, the resulting copolymers can form proteinlike globules with hydrophobic core wrapped in a hydrophilic envelope. Also, a gradient structure of primary sequences of the copolymers is revealed. Such sequences are formed due to both a change in the chain conformation and a continuous redistribution of comonomers between the globule and the solution in the course of the polymerization.
Supramolecular Copolymers: Structure and Composition Revealed by Theoretical Modeling
Journal of the American Chemical Society
Supramolecular copolymers, non-covalent analogues of synthetic copolymers, constitute a new and promising class of polymers. In contrast to their covalent counterparts, the details of their mechanism of formation, as well as the factors determining their composition and length, are still poorly understood. Here, the supramolecular copolymerization between two slightly structurally different benzene-1,3,5-tricarboxamide (BTA) monomers functionalized with either oligodimethylsiloxane (oDMSi) or alkyl side chains is unraveled by combining experimental and theoretical approaches. By applying the "sergeant-and-soldiers" approach using circular dichroism (CD) experiments, we are able to obtain detailed insights into the structure and composition of these supramolecular copolymers. Moreover, we observe an unexpected chiral induction upon mixing two independently CD-silent solutions of the achiral (soldier) and chiral (sergeant) monomers. We find that the subtle differences in the chemical structure of the two monomers impact their homopolymerization mechanism: whereas alkyl-BTAs cooperatively self-assemble, oDMSi-BTAs self-assemble in an isodesmic manner. The effect of these mechanistic differences in the supramolecular copolymerization process is investigated as a function of the composition of the two monomers and explicitly rationalized by mathematical modeling. The results show that, at low fractions of oDMSi-BTA sergeants (<10 mol%), the polymerization process is cooperative and the supramolecular helicity is biased toward the helical preference of the sergeant. However, at higher fractions of oDMSi-BTA sergeant (>25 mol%), the isodesmic assembly of the increasing amounts of sergeant becomes more dominant, and different species start to coexist in the copolymerization process. The analysis of the experimental data with a newly developed theoretical model allows us to quantify the thermodynamic parameters, the distribution of different species, and the compositions and stack lengths of the formed supramolecular copolymers existing at various feed ratios of the two monomers.