Triblock Structure Research Articles

Synthesis of copolymers of poly(amino acid)–urethane in N,N-dimethylformamide

The copolymers of poly(amino acid)–urethane (PAU) with multiblock–triblock structures have been synthesized in N,N-dimethylformamide (DMF). The use of triethylamine as an initiator of polymerizing NCA to both terminals of the PAU intermediate having urethane segments and a small amount of PMLG caused gelatinization, while the use of hydrazine gave a fluid solution with a whitish turbidity. Infrared (IR) spectra of the PAU in DMF demonstrated that the PMLG segments in the PAU obtained from TEA had an α-helix structure and PAU from hydrazine had a β-structure in addition to the α-helix structure. The X-ray diffraction pattern showed that the α-helix chains of the PMLG segments in the PAU obtained from hydrazine were oriented. Compared with the PMLG homopolymer, the elastic recovery and adhesion of the PAU significantly increased with a maintenance of a good sense of touch which is a unique quality of PMLG.

The synthesis of poly[6,8-dioxabicyclo[3.2.1]octane-b-(ethylene glycol)-b-6,8-dioxabicyclo[3.2.1]octane] by controlled cationic ring-opening polymerization

The triblock copolymer poly[6,8-dioxabicyclo[3.2.1]octane-b-(ethylene glycol)-b-6,8-dioxabicyclo[3.2.1]octane] was prepared by the controlled cationic ring-opening polymerization of 6,8-dioxabicyclo[3.2.1]octane (6,8-DBO) from a macroinitiator. The macroinitiator, poly(ethylene glycol) (PEG) di(1-chloroethyl ether), was prepared via the addition of HCl to PEG divinyl ether and was characterized with 13C NMR, 1H NMR, and gel permeation chromatography (GPC). Upon preparation, a small fraction of the chain ends underwent a cyclization reaction to form inactive chain ends. When the macroinitiator was used in polymerizations of 6,8-DBO with ZnI2 as an activator, linear kinetic plots were observed, a linear increase in the copolymer molecular weight with conversion was seen, and the molecular weight distributions of the copolymer samples remained constant at about 1.40. Confirmation of the triblock structure of the final product was obtained with 1H NMR spectra, 13C DEPT spectra, and GPC chromatograms. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4081–4087, 2000

Blends of polycarbonate and polysulphone-polydimethyl-siloxane block copolymers: analysis of compatibility and impact strength

The possibility of modifying polycarbonates by using dian (Bisphenol A) polysulphone-polydimethyl siloxane block copolymers having multiblock structure and triblocks with end polydimethyl siloxane or a polysulphone block structure was shown. In triblock copolymers the polydimethyl siloxane blocks have a constant molecular weight equal to 2500, while in polyblocks it was assumed to be 2500 and 10,000. The molecular weight of polysulphone blocks varied between 700 and 9000 in triblocks or between 500 and 4500 in polyblocks. It was found that block copolymers of both multi-and triblock structure with polydimethyl siloxane end blocks of concentration 45-68 wt % are created with PC microheterogenous blends. These blends, in a wide temperature interval (from cryogenic to the glass transition temperature of PC), have high impact strength when multiple crazes are created independently on testing temperature.

Synthesis, characterization and associative properties of triblock and diblock perfluorinated poly(acrylamide)s

A triblock perfluorinated poly(acrylamide) was produced by polymerization of acrylamide at 82 °C in acetonitrile using a difunctional azo-derivative initiator bearing fluorinated groups. The presence of triblock structures was revealed by GPC analyses by changing the nature of the solvent. Fractionation of a poly(acrylamide) sample allowed us to isolate the triblock fractions from the diblock ones. Polymerization with a small amount of initiator led to a sample with few triblock structures compared to a polymerization with a large amount of initiator. It can be concluded from this that acrylamide rather gives disproportionation according to the literature and that triblock formation comes from primary radical termination.

Characterization of the PMMA- and PEO-, di- and triblock copolymers, by light scattering, SEC and vapour pressure osmometry

The aggregation of block copolymer dissolved in methyl ethyl ketone (MEK) as well as toluene was observed. The aggregation of molecules leads to micelles and clusters of micelles. Between micelles and clusters a dynamical equilibrium exists. Inside the micelles lyophobic chains of PEO are combined and the outer layer of micelles is formed by lyophilic chains of PMMA. This is observed particularly in samples with triblock or diblock structure and high portions of PEO. In these cases, there are great differences between molecular weights obtained by light scattering, SEC or vapour pressure osmometry (VPO). We introduce a factor A to study the relation of the PEO content in diblock or triblock structure, and the measured M w .

Synthesis, characterization, and physical properties of new copolymers of poly(amino acid)-urethane?copolymers of ?-methyl-L-glutamate-N-carboxyanhydride and urethane prepolymer

New copolymers of amino acid and urethane (PAU), in which a polyurethane segment was combined with poly(γ-methyl-L-glutamate) (PMLG) of various contents, were synthesized by the copolymerization of the polyurethane prepolymer (UPP) having isocyanate groups at both terminals of the chain and γ-methyl-L-glutamate-N-carboxyanhydride (NCA) to improve the elastic recovery and adhesion of PMLG for application of PMLG to synthetic leather. The copolymerization of the UPP with NCA was carried out by applying the reactivity of isocyanate and the polymerization mechanism of NCA using the primary amine and tertiary amine as initiators. Infrared (IR) and 13C-NMR spectra of these PAUs as well as the chemical analysis of the PAU intermediates showed that the PAUs would have a multiblock–triblock structure: namely, the PAUs consisted of the block copolymer segments of urethane and a small amount of PMLG at the center of the copolymer chain and most of the PMLG at both terminals of the copolymer chain. The elastic recovery and adhesion of these PAUs were significantly larger than those of the PMLG with the maintenance of a good sense of touch, which was a unique asset of PMLG. Furthermore, it was found that the PAUs had intermediary moisture permeability between that of PMLG and polyurethane. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 383–389, 1999

Synthesis, characterization, and physical properties of new copolymers of poly(amino acid)–urethane—copolymers of γ‐methyl‐L‐glutamate‐N‐carboxyanhydride and urethane prepolymer

New copolymers of amino acid and urethane (PAU), in which a polyurethane segment was combined with poly(γ-methyl-L-glutamate) (PMLG) of various contents, were synthesized by the copolymerization of the polyurethane prepolymer (UPP) having isocyanate groups at both terminals of the chain and γ-methyl-L-glutamate-N-carboxyanhydride (NCA) to improve the elastic recovery and adhesion of PMLG for application of PMLG to synthetic leather. The copolymerization of the UPP with NCA was carried out by applying the reactivity of isocyanate and the polymerization mechanism of NCA using the primary amine and tertiary amine as initiators. Infrared (IR) and 13C-NMR spectra of these PAUs as well as the chemical analysis of the PAU intermediates showed that the PAUs would have a multiblock–triblock structure: namely, the PAUs consisted of the block copolymer segments of urethane and a small amount of PMLG at the center of the copolymer chain and most of the PMLG at both terminals of the copolymer chain. The elastic recovery and adhesion of these PAUs were significantly larger than those of the PMLG with the maintenance of a good sense of touch, which was a unique asset of PMLG. Furthermore, it was found that the PAUs had intermediary moisture permeability between that of PMLG and polyurethane. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 383–389, 1999

Dynamics and Rheology in Aqueous Solutions of Associating Diblock and Triblock Copolymers of the Same Type

The associative character of monodisperse amphiphilic copolymers of the same type, one with a diblock (DB) structure (hydrophobic tail on one end) and the other with a triblock (TB) structure (hydrophobic tails on both ends), has been studied in aqueous solution. The macroscopic properties of these systems have been investigated by rheological methods and correlated to properties on the microscopic level, as revealed from pulsed field gradient NMR and dynamic light-scattering (DLS). The results suggest that, in aqueous solution, both polymers associate, but the thickening effect is much more pronounced for TB due to the gradual formation of bridges between the micellar-like clusters as the concentration increases. This connectivity effect has been surveyed by mixing the polymers in different proportions. The rheological measurements showed that the concentration induced viscosification effect is considerably stronger for TB than that for the DB system; the dynamic moduli were, even at the highest TB concentration, successfully fitted to a single Maxwell element over the experimentally accessible frequency window. The NMR self-diffusion data revealed a much stronger slowing down of the dynamics for the TB system, and a gradually broader distribution of self-diffusion coefficients was observed for this polymer as the concentration increased. The DLS results for all the solutions, except for those of the two highest TB concentrations, indicate initially an exponential decay (always diffusive) followed by a stretched exponential at longer times. For the two highest TB concentrations an additional very slow stretched exponential mode appears in the profile of the correlation function. The slow mode exhibits an approximately q3 (q is the wave vector) dependence for all the DB solutions and for the dilute TB solutions, while at higher TB concentrations this mode becomes q independent (the viscoelastic effect). The very slow mode shows a strong q dependence (q5). The overall picture that emerges from this study is that, at low or moderate TB concentrations and over the considered concentration range for DB, the solution consists of a collection of large clusters of various sizes, slightly interconnected to each other, while at higher TB concentrations the structure of the solution is changed to a transient network, where the connectivity is provided by bridging chains.

Study of butadiene rubber mastication and mixing with carbon black

A thermomechanical method was applied to study the topological and molecular structure of SKD butadiene rubber masticated and mixed with carbon black. Triblock structure (two amorphous blocks and one a pseudocrystalline structure) of a studied raw rubber and rubber compound networks were found. A ratio of these morphology structures changes during mastication. After mastication, a low-temperature block has two glass transition temperatures that shows its more complex structure than that in raw rubber. This shows deep transformations taking place during the mastication process. Despite applying high shear forces and heating during mixing with carbon black in a filled BR compound, we present three structures characteristic for BR. However, introduction of carbon black changes the topological structure of polybutadiene. A part of both amorphous blocks grows. A part of a crystalline structure lowers from 88% after 2.5 min of mixing to 54% after 20 min of compounding. The molecular weight distribution of the chains between the junctions of the network and parts of low-temperature and high-temperature amorphous blocks, and pseudocrystalline structures in architecture of the rubber network were also calculated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 729–737, 1999

A facile synthesis of hydrophobically end-capped poly(oxymethylene-co-polyethylene oxide) by controlled step condensation

A very easy one-step and ambient temperature method for the direct synthesis of water-soluble associative triblock poly(ethylene oxide) (PEO) polymers is described. It involves the step polymerization of PEO chains with activated dihalides such as dichloromethane in the presence of potassium hydroxide powder. The addition of selected amounts of poly(ethylene oxide)-stearyl ether allows the degree of polymerization to be controlled and hydrophobically end-capped poly(oxymethylene-co-polyethylene oxide) structures to be obtained in a large range of molecular weights. These triblock structures are comparable to the well-known hydrophobically end-capped urethane polymers (HEUR) demonstrating interesting associative properties in water.

Tricontinuous Double Gyroid Cubic Phase in Triblock Copolymers of the ABA Type

We report the synthesis and morphological characterization of two triblock copolymers of the ABA type, where A is polystyrene (PS) and B polyisoprene (PI). The volume fraction of the minority component, PS or PI, is approximately 1/3. Cubic microdomain morphologies, already found in diblock and star block copolymers with the same composition range, are observed for the first time in the case of linear triblock copolymers. The two ABA triblocks are on opposite sides of the phase diagram, which signifies that both the A end blocks and the B midblock are capable of forming the interconnected double network structure. Investigation of the morphology was done via birefringence, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Birefringence measurements showed each triblock structure to have isotropic optical properties. The characteristic ratio of the observed Bragg peaks, q2/q1, was approximately / for each sample, indicating a set of eight possible cubic space groups. TEM data showed an interconnected tricontinuous microdomain structure. Since the two triblocks have essentially complementary structures (PS = 0.32 in one and PI = 0.36 in the other), the TEM images of OsO4-stained thin sections are complementary and the diffraction patterns of the images are approximately equal according to Babinet's principle. Examination of high-symmetry projections demonstrated p6mm, p4mm, and c2mm symmetry present in the TEM images. Comparison with the 〈111〉, 〈100〉, and 〈110〉 projections of the eight cubic space groups satisfying the SAXS data eliminated all but the Fm3̄m and Ia3̄d groups as possible structures. Due to the observed connectivity of the structure, the Fm3̄m structure could be eliminated by inspection of possible network structures and the resultant symmetries. Computer simulations of a model structure (double gyroid) based on level surfaces with Ia3̄d symmetry and their Fourier transforms showed excellent agreement with the high-symmetry projections and their respective optical transforms.

Liquid crystalline side‐group block copolymers with triblock structure: Investigations on the influence of the block arrangement on the morphology and the LC‐phase behavior

Liquid crystalline side‐group block copolymers with triblock structure: Investigations on the influence of the block arrangement on the morphology and the LC‐phase behavior

Liquid crystalline side-group block copolymers with triblock structure: Investigations on the influence of the block arrangement on the morphology and the LC-phase behavior

Liquid crystalline triblock copolymers with LC inner block and amorphous outer blocks have been synthesized by living anionic polymerization and investigated using DSC, TEM, and small-angle x-ray diffraction. All samples of poly[styrene-block-2-(3-cholesteryloxycarbonyloxy) ethyl methacrylate-block-styrene] (PS-b-PChEMA-b-PS) show liquid crystalline behavior and phase separation between the blocks. Compared to triblock copolymers with PS inner block (PChEMA-b-PS-b-PChEMA) and diblock copolymers (PS-b-PChEMA) the LC block copolymers with PS outer blocks have the same properties. The LC behavior and the morphology do not depend on the block arrangement ; they are only influenced by the volume fractions of the blocks. Those samples in which the liquid crystalline subphase is not continuous (spheres) only a nematic phase was found, whereas in all samples with a continuous liquid crystalline subphase, the smectic A phase of the homopolymer was observed.

Diblock and triblock semifluorinated n-alkanes: preparations, structural aspects and applications

The results of several recent studies on a new family of compounds consisting of linear semifluorinated n-alkanes with a diblock or triblock structure are reviewed. Special emphasis is laid on their morphology and structural characteristics in the crystalline state and on their phase transitions either in the solid or in the crystalline liquid state, surface activity in organic solvents and the formation of a gel-like phase. Recently proposed applications for these compounds are also reported.

Synthesis and thermal properties of poly(2,2-dimethyltrimethylene carbonate)-block-poly(tetrahydrofuran)-block-poly(2,2-dimethyltrimethylene carbonate)

Alkalimetal salts (Li +, K +) and metal-free salts ([(CH 3) 2N] 3S +, Bu 4N +) of hydroxytelechelic poly(THF) were used as initiators for the anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC). With both systems triblock copolymers were obtained with a monomodal distribution of molecular weights, with one exception. Copolymers with equal length of the poly(DTC) block and increasing molecular weight of the initiating block show the following features: (i) no influence at low molecular weights of the initiator ( M n = 650 ); (ii) plasticizing effect in the range 1000 < M n < 2600 ; (iii) two phase systems at M n > 2600 . The triblock structure of the copolymers was established by degradation of the poly(THF) middle block under acidic conditions with subsequent 1H-NMR and GPC analysis.

Efficient syntheses of the triblock copolymer styrene‐b‐tetrahydrofuran‐b‐styrene by coupling of preformed blocks

AbstractThe triblock copolymer styrene‐b‐tetrahydrofuran‐b‐styrene was prepared from commercially available hydroxyl‐terminated poly(tetrahydrofuran), Mn = 1,650 and mono‐hydroxyl‐terminated polystyrene, Mn = 7,600. Poly(tetrahydrofuran) blocks were first chain extended by reaction by with 1.1 equivalents 4,4′‐diphenylmethane diisocyanate (MDI) and subsequently end capped with 20% excess of hydroxyl‐terminated polystyrene. Gel permeation chromatography revealed clearly the success of the end capping step to give triblock copolymer mixed with a small amount of excess polystyrene. 1H NMR revealed a gross composition by weight of 50% styrene, 41% tetrahydrofuran, and 9% MDI. DSC revealed a 5°C elevation of the PTHF glass transition and a 15°C lowering of PS glass transition temperature as compared with those of the individual component blocks. These values along with behavior of films as a tough elastomer are consistent with triblock structure and microphase separated morphology. The polymer does not flow readily below 125°C which is well above Tg of the polystyrene domains.