Compatibilization efficiency of styrene‐butadiene block copolymers as a function of their block number

Effect of block number in linear styrene‐butadiene (SB) block copolymers (BCs) on their compatibilization efficiency in blending polystyrene (PS) with polybutadiene (PB) was studied. Di‐, tri‐, or pentablocks of SB copolymers as well as their combinations were blended with the mentioned homopolymers; supramolecular structure determined by small angle X‐ray scattering method (SAXS), morphology using scanning electron microscopy (SEM) combined with image analysis (IA), and stress transfer characteristics of the blends were chosen as criteria of compatibilization efficiency of the copolymers used. It was proved that the addition of SB BCs led to remarkably finer phase structure and substantially higher toughness of PS/PB blends. Triblock copolymer showed to be the compatibilizer with higher efficiency than diblock, pentablock, and the di/triblock copolymer mixture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The preparation of some block copolymers

The reactivity of the double bonds in p-divinylbenzene toward anionic reagents is much greater than is the residual double bond in the divinylbenzene unit incorporated in a polymer chain. Thus it is possible to add to a “living” polymer a few divinylbenzene units before appreciable crosslinking occurs. Each of these units will have a vinyl group conjugated with a phenyl ring and will be comparable in reactivity to styrene. If the reaction is stopped at this point by the addition of methanol, the molecular weight of the product is essentially that of the original living polymer. These polymers may then be copolymerized through these active double bonds with any monomer with which styrene may be copolymerized, to form block or graft-like copolymers. The copolymerizations may be effected by any of the methods applicable to styrene, i.e., free radical, cationic, or anionic. Such copolymerizations have been attempted with methyl methacrylate, butyl acrylate, vinyl chloride, vinylidene chloride, vinyl acetate, butadiene, isobutene, and propene, usually successfully.     

The role of taut tie molecules on the mechanical properties of gel-spun UHMWPE fibres

Summary Gel-spun hot-drawn UHMWPE fibres are known to display a high tensile modulus and strength. These properties are treated in a simple morphological model, explaining the approach of nearly the crystal modulus for fibres attaining only a fraction of the theoretical tensile strength and elongation at break.Creep experiments on irradiated gel-spun UHMWPE fibres serve as an additional test for the application of the model.     

Elastic moduli of highly stretched tie molecules in solid polyethylene

The elastic properties of interlamellar bridges in semicrystalline polyethylene (PE) were estimated from the molecular-mechanics calculations on the assumption that the energy loading of a chain backbone represents the principal deformation mechanism. The calculations result in the force-length functions featuring abrupt discontinuities due to sequential annihilation of the defects by the conformational transitions. The correlation of the chain elastic moduli E with the concentration of defects in the chain and with the chain extension ratio x were established. The distribution functions ζ(E) of Young's moduli of interlamellar bridges in semicrystalline PE were calculated by using the literature data on the chain length distributions of tie molecules. The impact of the distribution function of moduli ζ(E) on the overall elastic response of solid PE materials was examined, particularly in cases of the stacked lamellae morphology involving so-called hard elastic PE.     

The opto-mechanical behaviour of diacetylene-containing segmented block copolymers

Summary The effects of mechanical deformation on the optical properties of segmented copolyurethanes have been studied using resonance Raman spectroscopy. Linear elastomeric and glassy copolyurethanes, each containing diacetylene-urethane (DA-U) hard segment domains dispersed in a continuous polyether-urethane (PE-U) matrix, were prepared in bulk and themally cross-polymerised in the solid state. The crosslinked copolymers produced intense Raman spectra in which the triple bond stretching Raman band at ∼2080 cm^-1 is well defined and shifts to lower frequency under the application of tensile stress. Shifts in Raman spectra have been used to monitor stress concentrations around defects such as holes and notches machined into copolyurethane sheets. The copolyurethanes are readily applied as surface coatings to various subtrates, and their use as optically stress/strain-sensitive materials (optical strain sensors) is demonstrated.     

The effect of radiation on comb block copolymers

In order to increase the plasma etch resistance of photoresists, comb-shaped block copolymers have been prepared with radiation resistant sidechains and radiation sensitive backbones. The sidechains were polystyrene, and the backbones were poly(methyl methacrylate) or poly(alkene sulphones). It was found possible to synthesize these block copolymers with up to 50% of the radiation resistant sidechains by anionic grafting for poly(methyl methacrylate). In the case of the polysulphones, an initial polystyrene containing a terminal alkene group was synthesized. This was copolymerized with the alkene and sulphur dioxide by a radical reaction. The radiation sensitivity of the copolymers was then studied.     

Synthesis of polyesters-perfluoropolyethers block copolymers

Summary Multiblock-(A-B)_n-copolymers containing polyester segments together with perfluoropolyether (PFPE) segments have been prepared by polymerizing dimethyl terephthalate (DMT), or an equimolar mixture of DMT and dimethyl isophthalate (DMI), with ethylene glycol (EG) in the presence of different telechelic perfluoropolyethers in various amounts (5–30 wt%), using Tl(OBu)₄ as the catalyst. Fomblin ZDEAL (a-COOCH₃ terminated PFPE), Fomblin ZDOL (a PFPE having-CH₂OH terminal groups), and Fomblin ZDOLTX (a PFPE having-CH₂O(CH₂CH₂O)_yH terminal groups) were used as telechelic PFPEs. Fomblin ZDOLTX gave the best results: the highest yield in block copolymer (less sensitive to hydrolysis with respect to block copolymers prepared from the other PFPEs), a longer average length of polyester segments, and a relatively low fraction of PFPE lost by distillation during polymerization.     

Single-chain scattering in heterogeneous block copolymers

Diblock copolymers consisting of polystyrene (S) attached to a polybutadiene (B) block (which is either hydrogenous or perdeuterated) have been synthesized and blended in such a way that the microphase-separated S and B domains have equal scattering-length densities, thus eliminating the component of small-angle neutron scattering (SANS) due to the domain structure. Two samples were studied: one with small spherical polybutadiene microdomains whose size was in essential agreement with calculations assuming equilibrium, and a second one of larger molecular weight in which the sphere size, while larger, was considerably smaller than predicted from equilibrium theory. The SANS spectra of these samples were analysed to give the radii of gyration R_g and molecular weights M_w of the labelled polybutadiene blocks from plots of I^?1versusQ² and least-square fits to the single-chain scattering function proposed by Debye. Results for the first sample agreed with the molecular weight obtained from chromatography and u.v. absorption and with the R_g found in bulk polybutadiene of similar M_w. The SANS estimates of both M_w and R_g for the second sample were anomallously large; these deviations may be due to (a) non-Gaussian conformations of the polybutadiene chains imposed by the nonequilibrium state of the microdomain, or (b) clustering of the deuterated polybutadiene chains within the microdomain due to small isotopic differences in chemical potential, enhanced by the larger M_w. Observations on other systems suggest that the second effect is the dominant one.     

Controlling the phase behavior of block copolymers via sequential block growth

Block copolymers remain one of the most extensively investigated classes of polymers due to their abilities to self-organize into various nanostructures and modify polymer/polymer interfaces. Despite fundamental and technological interest in these materials, only a handful of experimental phase diagrams exist due to the laborious task of preparing such diagrams. In this work, two copolymer series are each synthesized from a single macromolecule via sequential living anionic polymerization to yield molecularly asymmetric diblock and triblock copolymers systematically varying in composition. The phase behavior and morphology of these copolymers are experimentally interrogated and quantitatively compared with predictions from mean-field theories, which probe copolymer phase behavior beyond current experimental conditions.     

Alkaline degradation of styrene-acrylonitrile copolymers and formation of block copolymers

The styrene-acrylonitrile (SAN) copolymer, dissolved in dimethylsulfoxide (DMSO), has been degraded in the presence of some bases such as KOH and potassium-t-butoxide at room temperature. The addition of 4-vinylpyridine or propyleneoxide which can be anionically polymerized, has led to the production of copolymers. Their composition has been studied by IR, elemental analysis, and fractionation techniques. The presence of groups in the degraded products has been explained by a scission mechanism which gives rise to anions useful for the formation of block polymers.     

Importance of tie molecules in preventing polyethylene fracture under long-term loading conditions

Brittle-type slow crack fracture is the dominant mode of failure in polyethylene pipe used for natural gas distribution. Constant tensile load testing of polyethylene pipe sections indicates a link between this mode of failure and environmental stress cracking. Interlamellar fracture can occur in both the presence and absence of an accelerating environment. The fibre deformation process is reviewed, describing the role of amorphous entangled tie molecules in preventing slow crack-type fracture. Relative resistance to slow crack brittle failure is explained in terms of this model for various materials tested.     

The effect of radiation-induced cross-linking on the relaxation of taut tie molecules during annealing of drawn LDPE

Shrinkage, retractive stress, and infrared dichroism of the drawn low-density polyethylene (LDPE) as-drawn and irradiated by ⁶⁰Co-ray have been measured under different annealing conditions. The shrinkage and the disorientation of the irradiated sample was undergone more rapidly than that of unirradiated one as the temperature was continuously increased, surpassing a certain value, and a higher degree of shrinkage and disorientation was achieved finally for the irradiated sample when the samples were annealed with free ends. For the samples heated isothermally with fixed ends, the retractive stress went through a maximum and then attenuated to a limited value, and the degree of such a stress attenuation for the unirradiated sample was much more than that for the irradiated sample. These results show that the taut tie molecules (TTMs) in drawn PE can relax by the pulling of chain segments out of crystal blocks that they anchored in at elevated temperatures higher than the α transition and also by the displacing of microfibrils if the samples were annealed with free ends. The cross-links produced by irradiation prohibit the former process. It was further observed that the dependence of the average extinction coefficient of the band at 2016 cm^?1 on that of the band at 1894 cm^?1 is related to irradiation and annealing conditions, which has also been explained by the relaxation of TTMs and the function of irradiation-induced cross-linking on the relaxation. © 1993 John Wiley & Sons, Inc.     

The preparation of block copolymers of styrene and methacrylic acid

A new method of preparing block copolymers of styrene and methacrylic acid is described. It is based upon use of the anionically initiated “living chain” method to prepare block copolymers of styrene and methyl methacrylate, with subsequent hydrolysis of the methyl methacrylate block to methacrylic acid.     

Adhesive properties of star-shaped block copolymers

Star-shaped block copolymers were used as heat activated adhesives in glass to glass joints. The branches consisted in either AB or ABA poly(styrene-b-isoprene) block copolymers. Tensile shear strengths of simple lap joints were measured for star block copolymers differing in the length or in the number of branches. Values higher than those of the corresponding linear species were obtained. These results were related to the presence of chemical junction points created by coupling the linear copolymers.     

Glass transitions of some block copolymers

A number of block and graft copolymers have been prepared from several vinyl monomers, and their glass transition temperatures measured. The series included polar, nonpolar and polar-nonpolar pairs. It was found in all cases except one that the glass transition temperatures were close to those found for the individual homopolymers. The exception was a block copolymer of styrene and α-methylstyrene, the only pair whose homopolymers would give clear mixed solutions in a mutual solvent.     

极性化SBS的环氧化改性

以甲酸和过氧化氢为氧化剂对极性化SBS(SBSVP)进行了环氧化改性。通过环氧含量、双键减少量以及副反应程度的测定,讨论了影响SBSVP环氧化反应的主要因素:n甲酸/n过氧化氢、反应温度、反应时间、SBSVP的质量分数。得到了SBSVP环氧化的适宜条件:SBSVP质量分数10%,n甲酸∶n过氧化氢=1∶1,反应温度60℃,反应时间2.5 h,所得产物的环氧基质量分数为11.1%。     

Properties of block versus random copolymers

Physical and mechanical properties of block copolymers are compared and correlated with the corresponding random copolymers. The important properties of melting point, transition temperatures, tensile strength, modulus, and elastic properties depend upon the structural arrangement of the molecular units comprising the polymer strecture. All available data suggest overwhelmingly that properties of block copolymers are superior to those of random copolymers. A block copolymer can have properties characteristic of each of the homopolymers from which it is derived as well as a set of properties due to the polymer strcture as a whole. Block copolymers have an advantage over random copolymers in that a crystalline polymer can be modified without significant reduction of its melting point, modulus, tensile strength, and elastic properties, and by suitable selection of a second component it affords a means of “building in” a particular property.     

Preparation of organophosphorus polyurethane block copolymers

The preparation of an organophosphorus polyurethane block copolymer of poly-(ethylene oxide) (PEO) and poly(bis-p-carboglycoxyphenyl phenyl phosphine oxide) (PCGPPO) as well as the respective homopolyurethanes is described. The properties of the prepared polymers (melting point, intrinsic viscosity, solubility, and chemical composition) have been determined. Results of thermal and infrared analyses of these polymers are also reported.     

Viscoelastic properties of homogeneous block copolymers

The molecular theory of Rouse-Bueche-Zimm has been modified to predict the viscoelastic behavior of homogeneous block copolymers. The model consists of beads and springs whose magnitudes correspond to the types of blocks in the polymer. Maximum relaxation times can be computed by this model. Viscoelastic data for poly(styrene-b-α-methyl styrene-b-styrene), poly(α-methyl styrene-b-styrene-b-α-methylstyrene) and poly(styrene-b-α-methyl styrene) were determined by stress relaxation methods. The results compare favorably with those predicted by the theory.     

Synthesis of diacetylenic-butadiene-acrylic acid block copolymers

Synopsis This paper describes the synthesis and post-polymerization in solution of a copolymer 1,3-butadiene-acrylic acid modified with diacetylenic pendant groups. The products were characterized by UV, IR and NMR spectorscopy.