Effect of center block structure on the physical and rheological properties of ABA block copolymers. Part II. Rheological properties

The effect of the chemical structure of the center block on the rheological properties of ABA block copolymers with polystyrene end blocks has been investigated. The chemical structure of the center blocks investigated in the present paper are polybutadiene, polyisoprene, ethylene/butene copolymer, ethylene/propylene copolymer and polydimethyl-siloxane. The chemical structure of the center block was found to have a pronounced effect on the rheological properties of the ABA block copolymer melts. The long range relaxation times of these block copolymer melts increases with increasing incompatibility between the styrene block and the center block. However, the rheological properties of the block copolymers are not influenced significantly by the glass transition or the entanglement molecular weight of the center block.     

Synthesis,structure, and physical properties of poly(trimethylene terephthalate)-block-poly(caprolactone) copolymers

The series of poly(trimethylene terephthalate)-block-PCLT (PTT-block-PCLT) copolymers with different contents of PTT as rigid, and poly(caprolactone) (PCL) as flexible segments have been synthesized from dimethyl terephthalate (DMT), 1,3-bio-propanediol, and PCL diol) in a two-step process involving transesterification and polycondensation in the melt. The weight amount of flexible PCLT segments varied from 0 (homopolymer PTT), 25, 35 to 45%. The molecular structure of the synthesized copolymers was confirmed by nuclear magnetic resonance and Fourier transform infrared spectroscopy analyses. According to Hoy's method, one confirmed that PTT and PCL are likely miscible, as the difference of the solubility parameters of PTT and PCL block pairs, equals to 3.15 MPa^1/2. Moreover, the phase structure and mutual miscibility for the series of PTT-block-PCLT copolymers was characterized by differential scanning calorimetry, dynamic mechanical thermal analysis, and wide-angle X-ray scattering measurements. In copolymers with 35 and 45 wt % of flexible segments, the crystalline phase is formed during annealing above glass-transition temperature of copolymer. These copolymers during cooling at the standard rate do not crystallize. It was also found that incorporation of PCLT flexible segments, due to the macrophase separated structure, cause the decrease of the melting point and glass-transition temperature, along with the tensile modulus and tensile strength of PTT-block-PCLT copolymers, and at the same time cause an increase in the value of the elongation at break. As a result of copolymerization of PTT with PCLT, one obtained multiblock copolymers with a heterophase structure. By changing the PTT/PCLT ratio, one obtained copolymers that differ in hardness and tensile strength. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47341.     

The influence of diblock copolymers on the structure and properties of polybutadiene-polyisoprene blends

The structure and properties of a ternary polymer system comprised of 1, 4 polybutadiene, cis 1, 4 polyisoprene, and the corresponding 1, 4 polybutadiene/cis 1, 4 polyisoprene diblock copolymer have been investigated. Dynamic mechanical properties were measured as a function of frequency (3.5 to 110 Hz) and temperature (?135 to 40°C). Thermomechanical analysis and transmission electron microscopy provided additional information on the, phase relationships in the various specimens. The blends studied covered the entire triangular composition diagram; both slow solvent evaporation and rapid spin casting techniques were employed in the sample preparation. Results indicate that the BI diblock is a single phase material whereas binary blends of the two homopolymers are two-phase in nature. Ternary blends of the two homopolymers with diblock and binary blends of a single homopolymer with diblock can be one or two phase materials depending on the sample composition and the ratio of B to I units in the diblock. All evidence From the dynamic, thermomechanical and microscopic experiments is used to elucidate the influence of the diblock in these polymer blends.     

The formation, structure and properties of urethane-diacetylene copolymers as optical strain-sensitive surface coatings

Segmented copolyurethanes comprising ductile polyether-urethane (PE-U) and rigid diacetylene-urethane (DA-U) phases, have been prepared via a one-shot, bulk polymerisation process. Subsequent thermal treatment (100 °C/40 h) of the as-prepared linear copolymers effected solid-state topochemical reactions within the DA-U phase, producing crosslinked and intensely coloured materials. The cross-polymerised copolymers had values of T_g between −32°C and 70°C depending on composition, and were elastically isotropic with tensile moduli and strengths ranging, respectively, from 20–1800 MPa, and 8–67 MPa. The copolymers exhibited optical properties similar to those of polydiacetylene single crystals, and produced intense resonance Raman spectra. In particular, the CC triple bond stretching Raman band at ˜ 2080 cm⁻¹ was well defined and shifted to lower frequency under the application of tensile stress/strain. The copolyurethanes may be readily applied as surface coatings to various substrates, and their use as optically stress/strain-sensitive materials (optical strain sensors) is demonstrated.     

Correlation between microstructure and physical properties in styrene–ethylene copolymers

The structural organization and the physical properties of a new copolymer styrene–ethylene have been analyzed. The composition was 80% of ethylene units, corresponding to 52% in weight, with a distribution of styrene units in the chain implying the absence of styrene–styrene sequences. The length of the polyethylene chains, limited by the insertion of the phenyl group, is not sufficient to allow good crystallization, and in fact the copolymer shows a very low crystailinity, of the order of 5–10%, and a broad melting range, with a peak centered at 120°C. The small crystalline domains are segregated into an amorphous matrix, producing a thermoplastic elastomer. The mechanical properties at large deformation were analyzed at different temperatures. The copolymer shows good elastic properties, in terms of deformation reversibility as well as of energy dissipation in the hysteresis cycles. Also the stress level and the elastic recovery are very good, if compared with others thermoplastic elastomers. © 1995 John Wiley & Sons, Inc.     

硫化硅橡胶交联结构与物理性能关系研究

研究硫化体系、硫化剂用量、基体硅橡胶相对分子质量和交联密度对硫化硅橡胶硬度、压缩应力和柔顺性的影响。结果表明,随着硫化剂用量的增大,硫化硅橡胶的硬度和压缩应力增大;当基体硅橡胶相同时,采用加成硫化体系制备的硫化硅橡胶柔顺性较采用过氧化物硫化体系更好;当采用加成硫化体系时,基体硅橡胶相对分子质量和硫化胶交联密度越小,硫化硅橡胶的柔顺性越好。     

Synthesis and physical properties of liquid‐crystalline copolymers with azobenzene segments

To investigate the effects of photoisomerizable azobenzene segments on the liquid‐crystalline characteristics and thermal properties of polymers, a series of liquid‐crystalline homopolymers and copolymers with azobenzene segments was synthesized. The azobenzene contents of the copolymers were estimated with elemental analysis. The photoisomerization of the azobenzene derivatives was studied with ultraviolet–visible (UV–vis) spectroscopy. The UV–vis absorption of the copolymers was found to be parallel with the content of the azobenzene segments. UV irradiation was found to cause a decrease in the copolymer transmittance around 355 nm due to the photoinduced isomerization from entgegen (E) to zusammen (Z). The phase‐transition temperatures and molecular weights of the polymers were investigated with differential scanning calorimetry and gel permeation chromatography, respectively. The variation in the phase‐transition temperature of the homopolymers before and after UV (365 nm) irradiation was investigated. The bended Z structure was found to disturb the order of the orientation of liquid crystals and to lower the phase‐transition temperature. The appearance of the polymer film was changed from opaque to clear after sufficient UV irradiation. The image recording of the polymer films was achieved after UV irradiation through a mask with pictures. The stability and reliability of the Nematic‐Isotropic phase transition of the homopolymers was evaluated with repeated cycles of 365‐nm UV irradiation and heating at 130°C. After the recycle phase transition was repeated nine times, no significant decay in the response and transmittance could be found. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 2006     

The structure of propylene-ethylene sequential copolymers

Polypropylene is frequently modified by incorporating ethylene during polymerization or by blending with ethylene polymers or copolymers. Such ethylene-containing systems exhibit a very characteristic texture of small particles (globules) superposed on the spherulitic crystallinity of the polypropylene. The nature and occurrence of these particles have been investigated. The conclusion reached is that they contain ethylene polymers, both crystalline and amorphous, and that they can exist in a quiescent melt.     

The structure and physical properties of polypropylene and thermoplastic olefin nanocomposites containing nanosilica

The morphology and physical properties of thermoplastic olefin blend (TPO) based nanocomposites containing nanosilica are reported. Addition of maleated PP resulted in improved filler dispersion within the PP matrix, where the filler resided exclusively. This separated morphology resulted in selective reinforcement of the PP matrix without compromising ductility, as demonstrated by mechanical property characterization. The tensile moduli, impact and flexural properties of TPO/nanosilica composites showed improvements at low loadings of nanosilica, indicating a good balance of stiffness and toughness. The addition of nanosilica into the TPOs decreased the size of the dispersed elastomer phase, which was a factor in the observed improvements of impact strength. Silane-modified nanosilica dispersed more efficiently in the polymer matrix, giving rise to improved impact properties of the TPO composites, compared to the unmodified filler.     

Vinyl chloride-ethylene copolymers: The effect of modest ethylene concentrations on the physical properties of compounds

Vinyl chloride-ethylene copolymers containing from 1.0 to 5.5 wt.% ethylene were synthesized and compounded with DOP plasticizer at levels of 0, 5, 10, 20, 30, and 40 parts per hundred parts of resin. Physical property tests indicated that, as an internal plasticizer, ethylene was 2 to 3 times more efficient than DOP in the range studied. An examination of room temperature modulus as well as brittleness also indicated that crystallinity was still apparent in all copolymers.     

Chemical structure and physical properties of antheraea assama silk

This work deals with the chemical composition, physical structure, and thermal behavior of Antheraea assama silk fibers. The amino acid composition is characterized by the high content of alanine, glycine, and serine. Among the amino acid residues with polar side chains, aspartic acid, arginine, and tyrosine prevail. The birefrigence and isotropic refractive index values are 0.030 and 1.557, respectively. The stress-strain curve shows a yield point at 5% elongation, followed by a region of gradual extensibility. Blongation at break is about 40%. The X-ray diffraction pattern is typical of β silks, with–(ala)_n–repeats in the polypeptide sequences of the crystalline regions. The differential scanning calorimetry curve shows two minor endotherms at 230 and 300°C, before final thermal decomposition at 362°C. The maximum extent of contraction exhibited by the thermomechanical analysis curve is 2%. The surface of degummed fibers shows the presence of longtitudinal strations. The fiber cross section is mostly relliptical. Raw Fibers taken from cocoons show the presence of several crystalline deposits on the surface, identified as crystals of calcium oxalate. © 1994 John Wiley & Sons, Inc.     

顺酐化苯乙烯-丁二烯-苯乙烯嵌段共聚物离聚体的制备及其结构和性能

在甲苯/环己烷混合溶剂体系中考察了顺酐化苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)的制备条件,得到马来酸酐/SBS/过氧化苯甲酰质量比为30/100/1、SBS质量浓度为0.10 g/mL、过氧化苯甲酰/甲苯引发液的滴加时间为10 min及75 ℃下反应4 h的较为理想的反应条件.在此条件下既可以避免凝胶的生成,又可获得较高的接枝率(6.87%).所得顺酐化SBS经氢氧化钠溶液中和后生成钠离聚体,傅里叶变换红外光谱分析证实接枝反应和离聚体的合成均得到预期的产物.差示扫描量热分析结果表明离子化微区的存在使得离聚体在高温段有1个玻璃化转变温度.离聚体的拉伸强度、搭接剪切强度和乳化性能均随顺酐化程度的提高而改善.     

The structure and physical properties of anionically polymerized nylon 6 crosslinked by bislactams

Crosslinked polyamides prepared by copolymerization of ?-caprolactam with bislactams under conditions of activated anionic polymerization proceeding adiabatically below their melting point show differences in physico-mechanical properties. Owing to varying copolymerization rates of bislactams, depending on the position of the connecting bridge of the bislactam in relation to the amido group, copolymers with different morphological structure are formed. The differences in the mechanical properties of the copolymers are explained on the basis of the differences in the morphological structure. This explanation is supported by results obtained by measuring the thermal and dynamic properties.     

The supermolecular structure of ethylene-vinyl acetate copolymers

Summary The supermolecular structures, as measured by small-angle light scattering, were determined as a function of branching content and quenching temperature for a series of ethylene-vinyl acetate copolymers. The morphological pattern that evolved was similar to that of random ethylene-1-alkene copolymers and long-chain branched polyethylenes. The structure of the lamellar crystallites determines whether spherulites develop and how well they are organized. Received: 21 April 1998/Revised version: 6 August 1998/Accepted: 8 August 1998     

Electronic structure and properties of alternating donor-acceptor conjugated copolymers: 3,4-Ethylenedioxythiophene (EDOT) copolymers and model compounds

The electronic structure and properties of 3,4-ethylenedioxythiophene (EDOT) based alternating donor-acceptor conjugated copolymers and their model compounds were studied by the density functional theory (DFT) at the B3LYP level with 6-31G or 6-31G** basis set. The acceptors investigated include thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), thiadiazolothienopyrazine (TPD), quinoxaline (BP), benzothiadiazole (BD), pyrazinoquinoxaline (BPP), benzobisthiadiazole (BDD), and thiadiazoloquinoxaline (BDP). The torsional angle, intramolecular charge transfer, bridge bond length, and bond length alternation were analyzed and correlated with the electronic properties. It was found that the geometries of the donor-acceptor materials were significantly affected by the ring size and intramolecular charge transfer. The HOMO level, LUMO level, and band gap of the model compounds were well correlated with the acceptor strength. However, the electronic properties of the copolymers did not vary systematically with the acceptor strength due to the change in geometry from model compound to polymer. The aromatic geometry of EDOT-TP model compound is transformed to quinoid in the corresponding copolymer and results in a small band gap (E_g) of 0.97 eV. Large intramolecular charge transfer and the small bond length alternation in the EDOT-BDP copolymer resulted in an E_g of 0.7 eV. Hence, these two polymers could have potential applications for transparent conductors or photovoltaic devices. The small effective masses and large HOMO and LUMO bandwidths of PEDOT-TP and PEDOT-BDP make them potential materials for ambipolar thin film transistors. The theoretical results suggest that both the acceptor strength and the stable geometry contribute significantly to the electronic properties of alternating donor-acceptor conjugated copolymers.     

Correlating chemical structure and physical properties of vegetable oil esters

The influence of FA ester chemical structures on the rheology and crystallization temperature of those compounds was evaluated using methyl, n-butyl, n-octyl, and 2-ethyl-1-hexyl FA esters with different chain lengths and different degrees of unsaturation. The rheological properties were analyzed in a high-precision rheometer at various temperatures, and the crystallization temperatures were determined by DSC. Esters produced from the esterification of pure FA and from the transesterification of vegetable oils (i.e., soybean, corn, linseed, and babassu coconut oils) were evaluated. The length of the FA chain was shown to have a marked influence on the viscosity and crystallization temperature of the systems, whereas branching affected only the crystallization temperature to a significant extent. The viscosity and crystallization temperature of the systems were also influenced by the degree of unsaturation. One double bond was shown to increase viscosity, whereas two or three double bonds caused a decrease in the viscosity of the systems. Unsaturation lowered the crystallization temperature in all cases, regardless of the number of double bonds. From all the oils studied, methyl esters from babassu coconut oil presented the lowest crystallization temperatures.     

Synthesis and properties of two kinds of amphiphilic graft copolymers with well-defined structure

Polyacrylamide with well-defined polystyrene grafts (PAM-g-PS) and poly(methacrylic acid) with well-defined poly(methyl methacrylate) grafts (PMAA-g-PMMA) were synthesized via macromer techniques. Polymerization conditions and reactivity ratios for the copolymerizations were studied. The graft copolymers were purified by extractions and characterized with IR spectra. Structural parameters of PMAA-g-PMMA were determined by measurement of number average molecular weight of both macromers and copolymers. Both kinds of the graft copolymers are amphiphilic, exhibiting good emulsifying properties. When PAM-g-PS was mixed with PMAA-g-PMMA in a molar ratio of PAM/PMAA = 1, an intermolecular complex membrane was formed. This behaves as a chemical valve; its permeability can be controlled reversibly by changing the pH value. © 1994 John Wiley & Sons, Inc.     

Porous structure and rheological properties of hydrogels of highly water-absorptive cellulose graft copolymers

The porous structures of the highly swollen hydrogels of cellulose—acrylamide graft copolymers were studied by the solute exclusion technique. For these hydrogels, the cumulative volume of pores up to 560 Å in pore width was between 450 and 850 mL/g, and was between 20 and 30% of the total pore volume. With an increasing in the amount of crosslinker added in the grafting procedure, the cumulative pore volume up to 560 Å decreased. Furthermore, larger pores shrunk preferentially. In the range of concentration from 0.003 to 0.3%, the viscosity of the hydrogels increased remarkably with an increase in concentration. The concentration dependence of the viscosity showed a transition at about 0.03%, which corresponded to the reciprocal of the water retention values for each copolymer. At concentrations over 3%, fluidity of the hydrogels was lost and the water swollen copolymers became viscoelastic. This dynamic viscoelasticity remained essentially unchanged in the temperature range of 20 to 80°C. The dynamic viscoelasticity was dependent on the concentration, but the concentration dependence was smaller than that of the viscosity. The larger the amount of the crosslinker added, the larger the value of dynamic modulus became.