Characterization of semicrystalline random copolymers by small-angle neutron scattering

A new method is introduced to determine the degree of partitioning of noncrystallizable comonomer units (B units) between the two phases of a semicrystalline random copolymer. The method is based on the comparison of the intensities of small-angle neutron and x-ray scattering (SANS and SAXS, respectively). By this technique two quantities can be evaluated: the difference Δρ of the mass densities between the crystalline and the disordered regions, and the concentration fluctuations of the B units in the two phases. It is found that SANS is very sensitive to the presence of small amounts of B units if their scattering length is sufficiently different from that of the A units. This will be the case for copolymers with B units, in which a hydrogen is substituted by another atom. But in addition it can also be achieved generally by deuteration of the comonomer units. So a wide range of copolymer systems can be studied by this method. The capability of the method was proved by measurements on chlorinated polyethylene and on 1,3,5-trioxane–1,3-dioxolane copolymers. Both copolymers are distinguished by a random distribution of the co-units. The results show that even at relatively low concentrations x_B of the comonomer units a remarkable fraction of the B units is incorporated into the crystalline A phase and that this fraction rises if x_B is increased.     

Crystallization of markoffian copolymers

An equilibrium theory is proposed for crystallization of (A, B) binary copolymers whose comonomeric unit sequences are statistically described by conditional pair probabilities P_AA, P_AB, P_BA, and P_BB. These are linked to the product of the reactivity ratios by r = r_Ar_B = (P_AAP_BB)/(P_ABP_BA). Three cases are considered here, (i) B units are rejected from the crystals, (ii) cocrystallization of A and B comonomeric units is possible in the full range of compositions within a single crystal structure (copolymer isomorphism), (iii) cocrystallization takes place either in a poly(A)-type or in a poly(B)-type structure, depending on composition (copolymer isodimorphism). For case (i) crystallization the theory demonstrates, according to expectation, that alternating copolymers (r = 0) produce the largest melting point depression, whereas in case (ii) they give rise to the smallest composition difference between the crystals and the liquid. The theory developed here further illustrates that for binary copolymers which are isodimorphic (case iii), a phase diagram is obtained similar to that for a classical binary system of small molecules.     

Lateral ordering during self-organization of statistical multiblock copolymers

The self-organization of statistical multiblock and Bernoulli AB copolymers is studied. The initial ensemble is generated via the polymer-analogous reaction A→B that proceeds with the accelerating effect of neighboring B units. In a two-dimensional model, the reaction is performed in a rectangle composed of stretched chains. Then, the rectangle is closed into a cylinder, so that ring chains are located on its side surface. The self-organization of the ensemble is simulated via the successive rotation of each upper ring over the lower ring until arrangement with the maximum (in modulus) energy of attraction between chains is attained. Self-organization by energy is accompanied by lateral ordering: the sizes of clusters—accumulations of the one-type units—and mean heights H _A (H _B) of stems—columns consisting of A or B units perpendicular to chains—increase. The ratio between the values of H _A, as well as H _B, for ordered and initial ensembles is independent of the average composition of the system and as a rule increases as the length of blocks increases and the length of chains decreases. Features of generation of the ensemble of short chains and their ordering are revealed. It is shown that, during ordering of multiblock copolymers, the probabilistic properties (the stochastic behavior) of the ensemble are disturbed. The self-organization of statistical multiblock copolymers in a three-dimensional model is investigated via rotation of rings in the torus of the rectangular cross-section. The effects of various factors on self-organization by energy and local ordering in 2D and 3D models are similar; however, the efficiency of ordering in the three-dimensional system is always lower because, in this case, arrangements with the maximum energy of attraction simultaneously to two neighboring chains, rather than to one, are implemented for the majority of chains.     

Conformational behavior of styrene–p-chlorostyrene triblock copolymers in dilute solutions. I. Composition dependence of conformational behavior

Dilute solution properties of (styrene-p-chlorostyrene) triblock copolymers in various solvents were studied over a wide range of molecular weight and composition. Viscosity and osmotic pressure results indicate that the conformational behavior of the B_mA_nB_m and A_mB_nA_m copolymers (A = styrene; B = p-chlorostyrene; m and n denote the number of units) are similar in nonselective solvents such as toluene and 2-butanone, but different in selective solvents such as carbon tetrachloride and cumene. Short-range and long-range interaction parameters of the block copolymers were determined by applying the Stockmayer–Fixman method to viscosity data and also by application of the equation relating the osmotic virial coefficient and the excluded volume. The results show that the unperturbed dimensions of the block copolymers vary linearly with composition, and long-range interaction parameters in nonselective solvents can be expressed by those of the parent homopolymers, the chemical composition, and values of the interaction parameter β_AB between styrene and p-chlorostyrene monomeric units.     

Effect of the nature of an organoaluminum activator on catalytic properties of phenoxyimine zirconium complexes in homo- and copolymerization reactions of ethylene

Catalytic properties of the phenoxyimine zirconium complexes, viz., bis[N-(3,5-di-tert-butylsalicylidene)anilinato]zirconium(IV) dichloride (1) and its fluorinated analog, bis[N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinato]zirconium(IV) dichloride (2), were studied. Ethylene homopolymerization and copolymerization of ethylene with α-olefins were chosen as catalytic reactions, and various organoaluminum compounds served as activators: commercial polymethylalumoxane (MAO) containing ∼35 mol.% of trimethylaluminum (TMA), MAO purified from TMA (“dry” MAO), and “classical” organoaluminum compounds, namely, TMA and triisobutylaluminum (TIBA). Complex 1 is not activated by “dry” MAO but is efficiently transformed into the catalytically active state by commercial MAO, “conventional” TMA, and TIBA. These processes give low-molecular-weight polyethylenes (PE) characterized by high values of polydispersity indices and by polymodal curves of gel permeation chromatography (GPC). The order of decreasing the efficiency of activation for the cocatalysts is MAO > TIBA > TMA. Fluorinated complex 2 exhibits a high activity after its treatment with MAO and “dry” MAO, the activity is much lower upon mixing with TIBA, and complex 2 is inactive when using TMA. In the copolymerization of ethylene with hex-1-ene and dec-1-ene, complex 1 treated with MAO is highly active but gives a low level of insertion of the comonomer (1–2 mol.% in the copolymer). Complex 2 activated with “dry” MAO is more efficient in the copolymerization of ethylene with propylene or hex-1-ene but, like complex 1, it does not produce copolymers with a high content of the comonomer. The both catalysts provide the insertion of α-olefin as isolated units separated by extended sections of the chain consisting of ethylene units.     

Reactions ofn-hexane andn-nonane on Pt catalysts and hydrogenating off hydrocarbonaceous adspecies after reaction

n-Hexane andn-nonane were reacted on Pt black, 6% Pt/SiO₂, 0.8% Pt/KL zeolite and a 0.6% industrial Pt/Al₂O₃ catalyst. Selectivities were compared at ∼10% conversion. After reaction, the catalyst was exposed to H₂ and the hydrocarbons leaving the catalysts were analyzed. The amount of hydrocarbons left the catalysts decreased in the sequence Pt black>Pt/SiO₂>Pt/KL>Pt/Al₂O₃. The composition of removed hydrocarbons gave important—although indirect—information on the possible state of “hydrocarbonaceous deposits” during catalysis.     

A photophysical study of the interactions in poly(styrene-4-sulphonate)–n-butylvinylether block and random copolymers

Interactions between the moieties responsible for the conformations and hydrophobic microdomains in poly(styrene-4-sulphonate) (PSS) and its copolymers with n-butylvinylether (BVE) were studied by their emission spectra and the lifetimes of the phenyl groups and pyrene used as a photochemical probe. The emission spectra of PSS shows bands due to dimers and higher aggregates as well as the characteristic excimer band. At low concentrations, the random copolymers have spectra similar to that of the free monomer, whereas the block copolymers have spectra like that of PSS. At higher concentrations, the random copolymer also shows these excimer bands, due to interchain interactions. Results from the emission of pyrene prove that the behaviour of the copolymers with approximately 40% BVE seems to be relatively independent of having random or block configurations. Except at low concentrations (<0.05 g/dl), where the block copolymer already has a conformation with “stable” hydrophobic microdomains, both types of copolymers behave similarly. There is an initial aggregate equilibrium between individual chains and aggregates, associated with a relocation of the probes. At higher concentrations, both copolymers suffer a severe change in conformation, due to the formation of “stable” hydrophobic microdomains, resulting from interchain interactions. In both cases the lifetimes of pyrene are of the order of 240 ± 10 ns. Received: 27 August 1998 Accepted: 11 January 1999     

Architectural effects on the stability limits of ABC block copolymers

The random phase approximation has been used to extend the Leibler theory for the stability limit of a homogeneous melt of A–B diblock copolymers to examine the onset of microphase and macrophase separation in a variety of ABC block copolymer systems. The stability limit is located by the divergence of the collective structure factor of the melt. We introduce and analyze three models for ABC block copolymers: linear triblocks, random comb copolymers where a fixed number of A and B teeth are placed randomly along a C backbone, and statistical comb copolymers, with A or B teeth spaced regularly, but with sequences constructed using a two parameter Markov process. We compute order-disorder stability boundaries for the segregation strength parameter _χABN at threshold as a function of _χACN, _χBCN, composition, and other model parameters, and compare the results for the three different architectural models. An interesting “reentrant order-disorder transition” is located in several model phase diagrams, and is associated with a peculiar situation in which more incompatibility causes less segregation. In the case of statistical combs, macrophase separation into two liquid phases can be favored over microphase separation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 849–864, 1997     

A local spin evaluation into the active site models of [2Fe2S] ferrodoxin [Fe<Subscript>2</Subscript>S<Subscript>2</Subscript>(SR)<Subscript>4</Subscript>]<Superscript>2−</Superscript> (R=—H, —CH<Subscript>3</Subscript>)

To test the feasibility of local spin theory of Davidson and Clark for ferrodoxin clusters, the models [Fe₂S₂(SR)₄]²⁻ (R=—H, —CH₃) are chosen for evaluation. This purpose is realized by calculating the local spin expectation values 〈S _A·S _B〉, 〈S _A ² 〉, and m _A and discussing the connection between these expected values and the Heisenberg spin model (HSM) and the Noodleman broken-symmetry approach. In practical calculation, the spin-unrestricted Hartree-Fock (UHF) and spin-polarized density functional theory (DFT) are used and the calculational qualities of these two methods are also discussed. In addition, the theoretical magnetic coupling constants J _AB of these models are calculated by various computational schemes for comparison with both theoretical and experimental results previously reported. Supported by the Doctorial Initial Foundations of Hainan Normal University (Grant No. 13140252)     

Synthesis of a “memory tripeptide” (Arg—Glu—Arg,RER) and the Kabachnik—Fields reaction with di- and tripeptides as a method for the synthesis of phosphorus-containing peptide analogs

Methods for the synthesis of potential “twin-drugs” containing fragments of the glutamate receptor antagonist and cognitive function enhancing oligopeptides were developed. The “memory tripeptide” Arg—Glu—Arg (RER) containing the tripeptide sequence of a protein APP_328–330, a gB-amyloid precursor, was synthesized. A method for the synthesis of gA-aminophosphonates with oligopeptides as the amine component of the one-pot three-component Kabachnik—Fields reaction was developed. A method for the synthesis of phosphonopeptides by the introduction of gA-aminophosphonates into the peptide chain was proposed.     

A <Superscript>1</Superscript>H NMR study of radical copolymerization of <Emphasis Type="Italic">N</Emphasis>-vinylsuccinimide with <Emphasis Type="Italic">n</Emphasis>-butyl acrylate in dimethyl sulfoxide

Kinetic features of radical copolymerization of N-vinylsuccinimide with n-butyl acrylate in dimethyl sulfoxide were studied by ¹H NMR spectroscopy. The dependences of the running concentrations of the monomers and of the “instant” and overall compositions of the copolymers on the reaction time were determined. The limiting conversions were established for correct analysis of the kinetic features of copolymerization at essentially different relative activities of the monomers. The copolymerization constants and the probability of alternation of the units in the copolymer chains were calculated. Original Russian Text E.V. Sivtsov, A.I. Gostev, N.A. Lavrov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 10, pp. 1679–1682.     

Tuning block copolymer phase behavior with a selectively associating homopolymer additive

We use polymer random phase approximation (RPA) theory to calculate the microphase separation transition (MST) spinodal for an AB + C diblock copolymer–homopolymer blend where the C homopolymers are strongly attracted to the A segment of the copolymers. Our calculations indicate that one can shift the MST spinodal value of the A ? B segmental interaction parameter (χ_ABN)_S to significantly lower values [i.e., (χ_ABN)_S < 10.5] upon the addition of a selectively attractive C homopolymer. For a sufficiently attractive C homopolymer, (χ_ABN)_S can be pushed to negative values, indicating microphase separation in what would appear to be a completely miscible diblock copolymer. Furthermore, we show that microphase separation can occur in diblock copolymer–homopolymer blends where the segmental interactions between all polymer constituents are attractive. By tuning the value of (χ_ABN)_S with a homopolymer additive, one is therefore able to tune the effective copolymer segregation strength and thus dramatically affect the blend phase behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2083–2090, 2009     

Copolymerization behavior of direct polycondensation of AB2 and AB monomers that forms hyperbranched aromatic polyamide copolymers

The copolymerization behavior of the one‐step direct polycondensation of 3,5‐bis‐(4‐aminophenoxy)benzoic acid (AB₂ monomer) and 3‐(4‐aminophenoxy)benzoic acid (AB monomer) was investigated by IR and ¹³C NMR measurements. IR measurements revealed that the content of the AB₂ units in the polymer was higher in the early stages of polymerization. ¹³C NMR spectra of the polymers indicated that the number of dendritic units increased slowly with increasing reaction time. The stepwise copolymerization of the AB₂ and AB monomers was also carried out, and the structure was analyzed by ¹³C NMR measurements. Copolymer synthesized stepwise by adding AB₂ monomer first (polymer II ) had more dendritic units and less terminal units as compared with the one‐step copolymer (polymer I ). Copolymer synthesized stepwise by adding AB monomer first gave a resulting copolymer (polymer III ) composed of long AB chains. The solubility of the stepwise copolymers was low, and the inherent viscosity was high in comparison with the one‐step copolymer as a result of the difference in architecture of the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3304–3310, 2001     

Segmentation of Heteropolymer Sequences Specifying Subsequences with Different Composition and Statistical Properties

We have studied the segmentation of two‐letter AB heterosequences composed of subsequences with different composition and distribution of A and B monomer units along the chain. Our approach is based on the segmentation function S(k) introduced in the present work and on the Jensen–Shannon divergence measure determined with respect to the probabilities of the lengths of uniform blocks of A and B monomer units. It is shown that the function S(k) is extremely sensitive to the sequence statistics. Even visual analysis of S(k) allows judgment on some features of sequence statistics. In particular, function S(k) is constant for random copolymers, it is an oscillating function for random block copolymers and shows monotonic growth up to some constant value for proteinlike copolymers. However, due to significant fluctuations observed for short sequences, the function S(k) can be effectively used only for segmentation of a heterosequence composed of very long subsequences. On the other hand, we find that the Jensen–Shannon divergence measure does not allow one to judge the type of statistics, but is extremely efficient for segmentation of a heterosequence. Therefore, the two introduced functions, being mutually complementary, provide an effective approach for recognizing and segmentation of heterosequences. As an example, the methods developed are applied for concatenating sequences of different proteins.

Segmentation function S(k, l, x) as a function of parameter k and starting number x of “window” for a sequence composed of elastin and ribonuclease sequences.     

Microphase Separation within a Comb Copolymer with Attractive Side Chains: A Computer Simulation Study

Computer simulation modelling of a flexible comb copolymer with attractive interactions between the monomer units of the side chains is performed. The conditions for the coil‐globule transition, induced by the increase of attractive interaction, ε, between side chain monomer units, are analysed for different values of the number of monomer units in the backbone, N, in the side chains, n, and between successive grafting points, m. It is shown that the coil‐globule transition of such a copolymer corresponds to a first‐order phase transition. The energy of attraction (ε) required for the realisation of the coil‐globule transition decreases with increasing n and decreasing m. The coil‐globule transition is accompanied by significant aggregation of side chain units. The resulting globule has a complex structure. In the case of a relatively short backbone (small value of N), the globule consists of a spherical core formed by side chains and an enveloping shell formed by the monomer units of the backbone. In the case of long copolymers (large value of N), the side chains form several spherical micelles while the backbone is wrapped on the surfaces of these micelles and between them.     

Hyperbranched copolymers made from A2, B2 and BB′2type monomers (iv)

The new approach for synthesis of hyperbranched polymers from commercially available A₂ and type monomers was extended to synthesize hyperbranched copolymers. In this work, hyperbranched copoly(sulfone-amine) was prepared by copolymerization of divinyl sulfone (A₂) with 4,4′-trimethylenedipiperidine (B₂) and N-ethylethylenediamine (BB’₂). During the reaction, secondary-amino groups of B₂ and BB’₂ monomers react rapidly with vinyl groups of A₂ monomers within 35 s, generating a type of intermediate containing one vinyl group and two reactive hydrogen atoms. Now the intermediates can be regarded as a new type monomer, which further polymerizes to form hyperbranched copoly(sulfone-amine). The polymerization mechanism was investigated with FTIR and LC-MSD. The degree of branching (DB) of hyperbranched copolymers increased with decreasing the ratio of 4, 4′-trimethylenedipiperidine to N-ethylethylenediamine, so DB can be controlled. When the initial mole ratio of B₂ to BB′₂was equal to or higher than four,r≥4, resulted copolymers were semi-crystalline, while copolymers withr3 were amorphous.     

Star-shaped block copolymers. III. Surface and interfacial properties

Surface and interfacial activities of A(B)₂ star-shaped block copolymers, where B is a polyoxirane block and A a polydiene or polyvinyl block, have been measured at 20°C. The surface tension of organic solvents is only slightly lowered by these copolymers, whereas a significant surface activity is noted in water. Interfacial tensions are dependent on both the nature of the organic solvent (aliphatic or aromatic hydrocarbons) and the molecular parameters of the copolymers; 50% polyoxirane seems to be the composition of maximum surface activity. The role played by the molecular architecture [A-B or A(B)₂] of the copolymers is demonstrated. The same limiting interfacial tension is obtained on increasing the concentration of diblock [A-B] or star-shaped block [A(B)₂] copolymer. The limiting value is, however, attained at significantly lower concentration with the star-shaped copolymers. Their ability to fill the interface is accordingly higher.     

Theory of cluster self-organization for crystal-forming systems: A model of transition from disodered to ordered systems

The current state of ideas concerning the self-organization of crystal-forming systems where long-range order spontaneously appears in the arrangement of nanolevel structural units of any nature (micro- and macromolecules or atomic clusters) that initially existed in a dynamic state as a chaotic mixture is considered. Three partially overlapping stages of self-organization of a system accepted in physical models of “order-disorder” kinetic transitions are matched to those used in supramolecular chemistry. An algorithmically constructed model of transition from disordered to hierarchically ordered systems is considered. The geometrical and topological modeling of density fluctuations of n-atomic species (clusters) An in a crystal-forming medium is carried out. A specific set of An clusters with block-diagonal connectivity matrices is recognized. These types of clusters (S ₃⁰), having “sectional” or “hierarchic” partition, are defined as precursors of crystal structures that are capable of evolving most rapidly to give rise to a long-range order in structures. For an S ₃⁰ ring cluster shaped as a triangle, geometrical and topological modeling is carried out for all of the eight topologically and symmetrically possible types of S ₃¹ primary chains built of S ₃⁰ using theory of one-dimensional symmetry groups. Thirty three structural variants of morphologically and topologically different types of S ₃² micronets described by two-dimensional groups of symmetry are considered. Algorithms are presented for combinatorial and topological analysis to search for precursor clusters and restore a three-dimensional net of covalent and noncovalent bonds in a crystal structure by the matrix (cluster) self-assembly mechanism. The model advanced is universal. Examples of self-assembly of a series of cluster-assembled structures of AB₂ alloys of the unique Friauf-Laves family (which counts in 1400 of binary and ternary compounds) are given: for MgCu₂ (cF24) (with its superstructures of ZrCu ₅ and MgSnCu₄ types), MgZn₂ (hP12), and MgNi₂ (hP24) (from AB₂ or A₂B + B₃ three-atom clusters); for ZrZn₂₂ icosahedral structures (from a suprapolyhedral cluster built of a ZrZn₁₆ Friauf polyhedron and two ZnZn₁₂ icosahedra); NaCd₂ (from one A cluster with 61 atoms and two B clusters with 63 atoms); and for a bimolecular compound C₇₈H₃₀ (which is formed of fullerene C₆₀ and a C₂₈H₃₀ molecule). The scenario of formation of self-curving nets with icosahedral symmetry is considered: to form a B₁₂ icosahedron from two isomers with n = 3, a C₂₀ dodecahedron from two isomers with n = 5, and C₆₀ fullerene from pentagonal clusters with n = 5.     

Model block copolymers with complex architecture

The synthesis of non linear block copolymers of the type (BA)₂B (3-miktoarm star copolymer), (BA)₃B (4-miktoarm star copolymer), (BA)₃B(AB)₃ (super H-shaped), B₂AB₂ (H-shaped) and (B,A)A(B,A) (π-shaped), where A is polyisoprene 1,4 and B is polystyrene was performed using anionic polymerization techniques and suitable chlorosilane chemistry. Characterization data showed that the samples are molecularly and compositionally homogeneous. TEM, SAXS and SANS were used to study the microphase behavior of the copolymers. For all samples, the results were analyzed in the frame of the theoretical predictions given by Milner and taking into account the results from previous studies on the A₂B and A₃B miktoarm star copolymers.     

三嵌段共聚物和两嵌段共聚物在水溶液中共混自组装成多室胶束结构的耗散粒子动力学模拟(英文)

利用耗散粒子动力学模拟研究了在水溶液中混合不同的线形三嵌段共聚物AxByCz和线形两嵌段共聚物AmBn对多室胶束的形貌多样性的影响.通过改变线形的三嵌段共聚物和两嵌段共聚物的链长来寻找多室胶束的形成条件.由线形三嵌段共聚物和线形两嵌段共聚物的不同混合形成的多室胶束结构是多种多样的,例如"蠕虫状"胶束、"汉堡包"胶束、"球上球"胶束、"核-壳-壳"胶束等等.多室胶束的整体形貌和内部结构的控制都可以从线形三嵌段共聚物和两嵌段共聚物的二元共混得到.为了表征获得的多室胶束结构,我们计算了密度图和成对分布函数图.在此工作中,可以获得和观察到复杂的多室胶束.结果表明,简单地混合线形的三嵌段共聚物和线形的两嵌段共聚物是一个控制多室胶束形貌和结构的有效方法,在工程实验中可以更简单更经济地形成多室胶束结构.因此,在设计新的多室胶束方面,聚合物共混仍然是未来值得更加关注的一个话题.