Characterization of styrene-ethylene oxide and methyl methacrylate-styrene block copolymers by light scattering

Several polystyrene-poly(ethylene oxide)-polystyrene (PS-PEO-PS) and poly(methyl methacrylate)-polystyrene-poly(methyl methacrylate) (PMMA-PS-PMMA) block copolymers, synthesized by free-radical polymerization, were studied in various solvents by using a light-scattering technique. The copolymers, which have different lengths of central blocks, had molecular weights within the range 3.0 × 10⁴ to 1.6 × 10⁶. It was found that almost all of them were confirmed as block copolymers from the variation of the product $\text{M}{}_{\mathrm{<mtext>app</mtext>}}\text{〈S}{}^2{}_{\mathrm{<mtext>app</mtext>}}\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ with $\text{W}{}_{\mathrm{<mtext>A</mtext><mtext>v</mtext><mtext>A</mtext>}}\text{v}$, although they were rather heterogeneous. The copolymer compositions determined either from the additivity of the refractive index increments of its constituent parts and the copolymer or from ultra-violet analysis were in excellent agreement with each other.     

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.     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 2. Type PEP copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(ethylene oxide)/poly(propylene oxide) type PEP block copolymers with E-block length 48 chain units and P-block lengths 0 to 7 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. Both extended-chain and once-folded-chain crystalline lamellae are found, the former with thickness about 32 E chain units and the latter with thickness about 21 E chain units. Compared with the specific volume of supercooled melt of the same composition the specific volume of the polymer in the amorphous lamellae is lower in the extended-chain polycrystals and higher in the once-folded-chain polycrystals. The melting points of the copolymers are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 37 to 55°C compared with T⁰_m = 76°C. This is due to the large positive free energy of formation from the melt of the crystalline/amorphous end interface (σ_o) and the amorphous layer (σ_a). For extended-chain polycrystals we find σ_o 3 kJ/mol and σ_a 3.5 kJ/mol; for once-folded-chain polycrystals we find σ_o 6 kJ/mol and σ_a 2 kJ/mol. We also find σ_o,x = 2.5 kJ/mol for a completely extended-chain end interface and σ_o,f = 10 kJ/mol for a completely folded-chain end interface.     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 1. Type PE copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(propylene oxide)/poly(ethylene oxide) type PE block copolymers with E-block length 40 chain units and P-block lengths 0 to 11 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. The crystalline lamella thickness is found to be about 25 E chain units, i.e. the crystals are predominantly of extended-chain type. The specific volume of the polymer in the amorphous lamellae is found to be lower than that of polymer of corresponding composition in the supercooled melt. The melting points are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 47 to 51°C compared with T⁰_m = 76°C. This is due to the positive free energy of formation from the melt of the amorphous layer (σ₅ 3.5 kJ/mol) and the crystalline/amorphous) interface (σ_o 3 kJ/mol).     

Organized structures in amorphous styrene/cis-1,4-isoprene block copolymers: low angle X-ray scattering and electron microscopy

It is shown that amorphous styrene/cis-1,4-isoprene block copolymers form organized structures in concentrated solutions as well as in the solid state. The effects of the nature and the concentration of the solvent, the composition of the copolymer and the temperature on the parameters determined by low angle X-ray scattering and electron microscopy are discussed. It is observed that, independent of the nature or concentration of the solvent, a given block copolymer exhibits only one ordered structure which may be lamellar or hexagonal.     

Small-angle X-ray investigations of defined multiblock (b-styrene-bisphenol a carbonate) copolymers

The separation of phases in defined multiblock (b-styrene-bisphenol A carbonate) copolymers was analyzed by small-angle X-ray scattering. It was found that these copolymers form typical microdomain structures. For copolymers containing 0.34 and 0.47 wt.-parts polycarbonate (PC) the microdomains are arranged in the face-centred cubic macronetwork. The distance between domains decreases with increasing concentration of polycarbonate. The copolymer containing 0.767 PC has lamellar structure. The thickness of the domain-boundary interphase was quantitatively estimated by analyzing a systematic deviation of the scattering curves at large angle tail from the Porod's law. The thickness of the transition layer decreases with increasing concentration of polycarbonate.     

X-ray diffraction studies of ABA propylene–ethylene block copolymers

ABA triblock copolymers of propylene and ethylene, where the central block is a random copolymer of ethylene and propylene and the A blocks are either isotactic polypropylene or polyethylene, are described. Structural changes induced by stretching at room and elevated temperatures are reported. WAXS was used to monitor these changes. The results indicate theat block copolymers were synthesized and that different combinations of mechanical properties may be obtained by varying the type and length of the A blocks and adjusting the monomer ratio in the random B block.     

Small-angle light scattering studies of macrophase separation in segmented polyurethane block copolymers

Quantitative small-angle light scattering (SALS) analysis is carried out on two similar segmented polyurethane block copolymers. The polyurethane prepared from toluene diisocyanate, is optically transparent, while a polyurethane prepared using the same soft segment, but with 4-4′ diphenyl methane diisocyanate, scatters light appreciably. SALS investigation of the latter sample shows clearly that the scattering arises from the presence of long-range density fluctuations. Analysis of the density fluctuations is accomplished with the Debye-Bueche theory for random two-phase systems, incorporating a correction for the effects of multiple scattering. Application of this procedure leads to a correlation length of 4200 nm; corresponding well with the structure observed in optical photo-micrographs. The occurrence of phase separation during polymerization is discussed as a possible origin for the observed macrophase structure.     

Oxidation effect on templating of metal oxide nanoparticles within block copolymers

Amphiphilic norbornene-b-(norbornene dicarboxylic acid) diblock copolymers with different block ratios were prepared as templates for the incorporation of iron ions using an ion exchange protocol. The disordered arrangement of iron oxide particles within these copolymers was attributed to the oxidation of the iron ions and the strong interactions between iron oxide nanoparticles, particularly at high iron ion concentrations, which was found to affect the self-assembly of the block copolymer morphologies.     

Surface active block copolymers: I. The preparation and some surface active properties of block copolymers of tetrahydrofuran and ethylene oxide

A new type of surface active block copolymer (TE type) having the general formula HO(C₂H₄O)_x(CH₂. CH₂CH₂CH₂O)_y-(C₂H₄O)_zH, was obtained by addition of ethylene oxide to polyoxytetramethylene glycols with molecular weight of 1000-3400. TE types in which the polyoxyethylene sections comprised more than 20–25% of the total weight are soluble in water, and the relation between cloud point and oxyethylene content for TE types was similar to that for propylene oxide-ethylene oxide block copolymers (Pluronics). Some surface active properties of TE types were examined in comparison with those of Pluronics and some other surfactants. The surface tension, foaming and antifoaming properties of TE types were comparable to those of Pluronics. Although the wetting power of TE types was poor, their suspending power (for carbon black) was superior to that of Pluronics in both aqueous and nonaqeuous media. The addition of TE types to some conventional detergents enhanced significantly their detergency. TE types showed a remarkable demulsifying action, on addition to some W/O emulsions.     

Studies on the synthesis of block copolymers of acrylonitrile and ethylene oxide

The synthesis of polyacrylonitrile–poly(ethylene oxide) block copolymers was carried out with the use of modified initiator containing azo groups, being a product of reaction between poly(ethylene oxide) (mol wt 6000) with azobisisobutyronitrile. Effects of initiator concentration, temperature, and synthesis time on the yield, composition, and intrinsic viscosity of the copolymers were examined. To confirm the segmental structure of the obtained products, precipitation, fractionation, gel permeation chromatography, infrared, and ¹H nuclear magnetic resonance methods were used. © 1993 John Wiley & Sons, Inc.     

Small-angle X-ray scattering investigations of fractal dimensions of hybrid inorganic organic network (ceramers) based on tetraethylorthosilicate and polytetramethylene oxide

Over the last 2 years the sol gel technique has become very popular because of its ability to yield multicomponent inorganic glasses at low temperatures. More recently techniques to incorporate functionlized organic species into a sol gel network of metal alkoxides have been developed and studied in our laboratory as well as others. Most of these studies have focussed on the structure-property behavior of these materials, with an emphasis on understanding the properties in terms of the level of microphase separation that occurs during the network buildup in these systems. While much has been gained in this respect, the desire exists to characterize better the structure of the inorganic phase in such systems, and in this respect, utilization of small-angle X-ray scattering profiles can provide information about this structure through fractal analysis. The work discussed here focuses specifically on the fractal character of specific ceramer materials produced as a result of the reaction between tetraethylorthosilicate and end-functionalized polytetramethylene oxide. It is shown that the cosolvent system utilized to compatibilize the reactants plays a very important role in development of the structure of the inorganic phase in these hybrid materials.     

Bisphenol-A-polycarbonate-bisphenol-A-polysulfone block copolymers

Multiblock , block copolymers of bisphenol-A-polycarbon ate and bisphenol-A-polysulfone were prepared by three different synthesis routes. The in situ method consisted of forming the polycarbonate block in the presence of hydroxyl terminated polysulfone oligorner. The coupled oligomer technique utilized phosgene to link up the two preformed oligomers to high molecular weight. In one case, a perfectly alternating block copolymer was formed by reacting a ～9, 000 M _n chloroformate terminated polycarbonate with a ～9, 000 M _n hydroxyl terminated polysulfone. Block sizes from ～4, 000 to ～26, 000 were investigated. The oligomers and copolymers were characterized by potentiometric titrations and UV end group analysis. Membrane osmometry and gel permeation chromatography were also employed. Dynamic mechanical behavior of solvent cast and compression molded films was assessed via rheovibron measurements. The copolymers were ductile and transparent and displayed essentially only a single intermediate glass transition temperature, that is, microphase separation was not observed. This is in contrast to simple physical blends of the homopolymers or oligomers, which are opaque and display two glass transition temperatures.     

All-conjugated block copolymers

All-conjugated block copolymers of the rod-rod type came into the focus of interest because of their unique and attractive combination of nanostructure formation and electronic activity. Potential applications in a next generation of organic polymer materials for photovoltaic devices ("bulk heterojunction"-type solar cells) or (bio)sensors have been proposed. Combining the fascinating self-assembly properties of block copolymers with the active electronic and/or optical function of conjugated polymers in all-conjugated block copolymers is, therefore, a very challenging goal of synthetic polymer chemistry. First examples of such all-conjugated block copolymers from a couple of research groups all over the world demonstrate possible synthetic approaches and the rich application potential in electronic devices. A crucial point in such a development of novel polymer materials is a rational control over their nanostructure formation. All-conjugated di- or triblock copolymers may allow for an organization of the copolymer materials into large-area ordered arrays with a length scale of nanostructure formation of the order of the exciton diffusion length of organic semiconductors (typically ca. 10 nm). Especially for amphiphilic, all-conjugated copolymers the formation of well-defined supramolecular structures (vesicles) has been observed. However, intense further research is necessary toward tailor-made, all-conjugated block copolymers for specific applications. The search for optimized block copolymer materials should consider the electronic as well as the morphological (self-assembly) properties.     

Acrytonitrile block copolymers

Summary Acrylonitrile was polymerized by an insertion process on being added to solutions containing the adduct of the reaction of tetrakis(dimethylamino) titanium (T4) and azobisisobutyronitrile (AIBN). The obtained azo-linked polyacrylonitrile has appropriate initiating functionality for a subsequent vinyl polymerization.     

Chiorosulfonated block copolymers

Rubber-phase chlorosulforiated polystyrene-poly-(ethylene-butene-1)-polystyrene block copolymers were prepared by reaction of the block copolymer in solution with SO₂ and C1₂. Sample compositions ranged up to 7 weight percent sulfur and 29 weight percent chlorine contents as determined by X-ray fluorescence and infrared spectroscopy. A series of chlorosulfonated derivatives of an analogue of the elastomeric midblock were prepared and analyzed in similar fashion. A comparison of dynamic mechanical and dielectric behavior of solvent cast films of the block copolymer and midblock polymer materials indicates the existence of sulfonyl chloride dipole-dipole complexes in the solid state. Further evidence for the presence of such aggregates was obtained from analysis by Fourier-transform infrared spectroscopy. It appears that polystyrene domains in the block copolymer materials hinder this aggregation up to moderate concentrations of the sulfonyl chloride group as compared with the relatively unrestrained aggregate formation in the analogue midblock materials. At high levels of substitution, the formation of dipole aggregates disrupts the integrity of the polystyrene domain structure in the block copolymer materials, resulting in a reduction in mechanical strength.     

Synthesis and characterization of block copolymers based on natural rubber and polypropylene oxide

Segmented block copolymers from different grades of hydroxyl terminated liquid natural rubber (HTNR) (M _n 3000, 8800, 10,000, and 17,000) and polypropylene oxide (PPO) (M _n 1000, 2000, 3000, and 4000) have been synthesized and characterized by spectral analysis, thermal analysis, scanning electron microscopy (SEM), and mechanical testing. The glass transition temperature of NR block was found to be at about ?64°C, which is independent of the PPO whose transition is around 15°C. The thermogravimetric analysis (TGA) shows that the thermal degradation of the samples proceeded in two steps characteristic of the immiscible components. The inability of PPO segments to provide physical crosslinking and the subsequent formation of hard domains is reflected in the low tensile properties and tear properties. The amorphous nature of the PPO phase and its immiscibility with NR phase are evidenced by the SEM studies. The effect of molecular weight of PPO as well as HTNR on the properties of the block copolymers has also been discussed. © 2006 Wiley Periodicals, Inc. JAppl Polym Sci 103: 909–916, 2007     

Cellulose containing block copolymers

Summary Solution properties of trimethylcellulose-poly(oxytetramethylene two and star block copolymers with defined molecular weights are reported. The solubility behavior of the concerned block copolymers is mainly governed by the solubility of the trimethylcellulose blocks. The solubility parameters for TMC and POTM indicate that both polymers are incompatible with each other. This is confirmed by the appearance of phase separation in concentrated solutions of corresponding blends even in nonselective solvents. Intrinsic viscosities of the block copolymers are reported and compared to corresponding polymer blend solutions.