Effects of sample preparation and flow geometry on the rheological behaviour and morphology of microphase-separated block copolymers: comparison of cone-and-plate and capillary data

The steady shear viscosities of two microphase-separated triblock copolymers, a polystyrene-block-polybutadiene-block-polystyrene copolymer (Kraton 1102) and a polystyrene-block-polyisoprene-block-polystyrene copolymer (Kraton 1107), were measured at various temperatures, using a cone-and-plate rheometer at low shear rates (ca. 0.01–10s⁻¹) and a capillary rheometer at high shear rates (ca. 5–5000 s⁻¹). In order to investigate the effect of sample preparation on the viscosity, specimens of Kraton 1102 were prepared using two different methods: (a) solvent film casting and (b) compression moulding. Samples of Kraton 1107 were prepared only by compression moulding. In the present study we found that (a) for compression-moulded specimens the shear viscosities obtained using a cone-and-plate rheometer did not overlap those obtained using a capillary rheometer, while for solvent-cast specimens there was a reasonably good agreement between the two, and (b) the viscosities of solvent-cast specimens were much lower than those of compression-moulded specimens. This observation was explained with the aid of transmission electron micrographs, which were taken of ultrathin sections cut parallel and perpendicular to the direction of shear. We found from transmission electron micrographs that the application of steady shear flow affected greatly the morphology of Kraton 1102 having cylindrical microdomains of polystyrene phase, whereas it affected little the morphology of Kraton 1107 having spherical microdomains of polystyrene phase. Also measured were the complex shear viscosities of the two block copolymers at various temperatures. We have shown that neither time-temperature superposition nor the Cox-Merz rule is applicable to microphase-separated block copolymers.     

Influence of block molecular weight on the properties of styrene‐ethylenebutylene‐styrene block copolymers

Styrene‐ethylene butylene‐styrene (S‐EB‐S) block copolymers with similar polystyrene contents and varying molecular weights (S‐EB‐S‐1, molecular weight: 8833‐41223‐8833; S‐EB‐S‐2, molecular weight: 15844‐70534‐15844; S‐EB‐S‐3, molecular weight: 26133‐111067‐26133) were used in this study. The domain size of the polystyrene phase marginally increases with an increase in polystyrene segmental weight as observed by atomic force microscopy. Dynamic mechanical measurements of these polymers were carried out over a wide range of temperatures and frequencies. These polymers exhibited three peaks: α, β, and γ in the tan δ‐temperature curve. With increase in the molecular weight of the S‐EB‐S polymers, the α‐transition temperature shifted to higher values, while the β‐ and γ‐transitions remained unaltered. Also, the elastic modulus and storage modulus decreased with increase in the molecular weight. The rheological behavior of the various S‐EB‐S polymers was studied using a Monsanto Processability Tester. These systems exhibited pseudoplastic flow behavior. The shear viscosity of these S‐EB‐S polymers decreased with an increase in the molecular weight from S‐EB‐S‐1 to S‐EB‐S‐3 polymers because of the wall slip and plug flow. The activation energy of the melt flow process was found to vary between 4 and 0.6 kcal/mol in the range of shear rates studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1621–1628, 2000     

Simulation study of the morphologies of energetic block copolymers based on glycidyl azide polymer

The morphologies of energetic block copolymers based on glycidyl azide polymer (GAP) were investigated by dissipative particle dynamics simulation. The results show that the morphologies could be used to qualitatively explain the variation in the mechanical properties of poly(azidomethyl ethylene oxide‐b‐butadiene) diblock copolymers (DBCs) and that bicontinuous (B) phases could effectively improve the mechanical properties. Among our designed DBCs, only GAP–acrylic acid, GAP–acrylonitrile, and GAP–vinyl amide could form B phases at very narrow regions of GAP contents. The triblock copolymers with their linear topologies could maintain the B phases in the broader region of GAP contents. We hope these results can provide help in the design and synthesis of new energetic block copolymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improved mechanical properties of shape‐memory polyurethane block copolymers through the control of the soft‐segment arrangement

High‐performance shape‐memory polyurethane block copolymers, prepared with two types of poly(tetramethylene glycol) (PTMG) used as soft segments, were investigated for their mechanical properties. Copolymers with a random or block soft‐segment arrangement had higher stresses at break and elongations at break than those with only one kind of PTMG. Random copolymers with fewer interchain interactions showed higher elongation than block copolymers. All the copolymers had shape‐recovery ratios higher than 80%. In dynamic mechanical testing, the glass‐transition behavior clearly depended on the soft‐segment arrangement: random copolymers had only one glass‐transition peak, whereas block copolymers showed two separate glass‐transition peaks. Overall, the control of the soft‐segment arrangement plays a vital role in the development of high‐performance shape‐memory polyurethane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2410–2415, 2004     

New conductive thermoplastic elastomers. Part II. Physical and chemical‐physical characterization

To overcome the problems relevant to the low processbility and scarce mechanical properties of polyaniline, in a previous work we have proposed the synthesis of elastomeric conducting copolymers prepared by grafting polyaniline (EB) or sulfonated polyaniline (SPAN) chains to the backbone of a carboxylated segmented polyurethane (PEUA). In the present work the physical and chemical‐physical properties of the copolymers are investigated. As evidenced by thermal (DSC) and dynamo‐mechanical (DMTA) characterization, the introduction of EB or SPAN in the matrix enhances the hard‐soft phase segregation effect, because of the strong tendency of the conductive polymer chains to aggregate. Moreover, the EB and SPAN chains, grafted to the polyurethane backbone, acting as reinforcing filler, give rise, compared with the mechanical properties of the insulating matrix, to an increase of the Young modulus and a decrease of the tensile set. When the copolymers are HCl doped their electrical conductivity increases many orders of magnitude, reaching values of about 10^?3 Ω^?1 cm^?1. The conductivity, measured along the deformation direction, may be further increased by stretching the copolymer films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1259–1264, 2002     

Influence of S/B middle block composition on the morphology and the mechanical response of polystyrene-poly(styrene-co-butadiene)-polystyrene triblock copolymers

Polystyrene-poly(styrene-co-butadiene)-polystyrene triblock copolymers (PS-P(S-co-B)-PS) having different styrene contents (from 30 wt.% to 80 wt.%) in the statistical copolymer middle block and different block architectures (20-60-20 and 30-40-30) were characterised to study the influence of S/B middle block composition and segregation strength on the morphology and mechanical behaviour. The morphological investigations, i.e. TEM and SAXS, exhibited ordered lamellar and lamellar-like morphologies for both block architectures at low styrene contents between 30 wt.% and 50 wt.% in the S/B middle block. The increase in the styrene content in the middle block to 70 wt.% resulted in phase separated structures without long range order due to the enhanced miscibility between the PS and P(S-co-B) phase as observed from dynamic mechanical analysis. Further it was observed that the glass transition of the butadiene-rich phase is mainly determined by the S/B composition of the statistical copolymer block as confirmed by the Fox-equation. The alteration of the glass transition of the PS-rich phase and the observed PS-softening with raise in styrene content might be correlated to the increasing interphase width due to the enhanced miscibility as shown by calculations based on a simple model for diblock copolymers. Tensile testing revealed a transition from ductile to semi-ductile to brittle behaviour that strongly depends on the styrene content in the S/B middle block, chain architecture and the resulting morphology. Block copolymers (BCPs) with lamellar structure exhibited ductile behaviour with extensive strain hardening, whereas BCPs forming segregated structures without long range order were semi-ductile or brittle depending on the type of block architecture and on the hard-phase content. The transition in the mechanical behaviour was confirmed by fracture mechanical investigations based on the essential work of fracture approach and SEM-characterizations.     

Synthesis and characterization of rubbery highly fluorinated siloxane–imide segmented copolymers

The synthesis and characterization of a series of poly(siloxane–imide) block (or segmented) copolymers obtained by copolymerization of amine‐terminated polydimethylsiloxane with fluorinated aromatic compounds containing anhydride and amine functionality are reported. New fluorinated block copolymers have been synthesized to obtain organophilic polyimides potentially interesting for molecular membrane separations. The new aspects of this work relative to the literature are (1) a comparison of solution and solid‐state approaches in the imidization step to generate the target poly(siloxane–imide) copolymers and (2) exploration of new compositions involving fluorinated aromatic polymers derived from added diamine compounds. It is shown that the copolymer properties can be tailored from glassy to rubbery materials by varying the amount and the type of oligosiloxane used; the transition between glassy and rubbery properties is characterized at a siloxane content of 60 wt%. As a main result, it is shown that the solid‐state approach for inducing the cyclo‐imidization step is the more efficient one for synthesizing polymers with good mechanical properties, when the amount of siloxane block is increased in the copolymer series. Physical and chemical methods (thermogravimetric analysis, Fourier transform infrared spectroscopy, viscosity measurements) were used to characterize the copolymer properties obtained according to the two different synthesis routes. The obtained siloxane–imide copolymers are well soluble in a large variety of moderately polar solvents and exhibit very good thermal stability up to 400 °C. Hence the prepared copolyimides would seem to be promising candidates as organophilic membranes as well as gas permeation membranes. © 2012 Society of Chemical Industry     

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.     

Influence of electron beam radiation on mechanical and thermal properties of styrene‐butadiene‐styrene block copolymer

Electron beam crosslinking of elastomers is a special type of crosslinking technique that has gained importance over conventional chemical crosslinking method, because the former process is fast, pollution free, and simple. The technique involves the impingement of high‐energy electrons generated from electron accelerators and the subsequent production of free radicals on target elastomers. These radicals result in crosslinking of elastomers via radical–radical coupling. In the process, some chain scission may also take place. In this work, a high‐vinyl (～ 50%) styrene‐butadiene‐styrene (S‐B‐S) block copolymer was used as the base polymer. An attempt was made to see the effect of electron beam radiation on the mechanical and thermal properties of the block copolymer. Radiation doses were varied from 25 to 300 kGy. Mechanical properties like tensile strength, elongation at break, modulus at different elongations, hardness, tear strength, crosslink density, and crosslink to chain scission of the irradiated samples were studied and compared with those of unirradiated ones. In this S‐B‐S block copolymer, a relatively low‐radiation dose was found effective in improving the level of mechanical properties. Differential scanning calorimeter and dynamic mechanical analyzer were used to study the thermal characteristics of the irradiated polymer. Influence of a stabilizer at different concentrations on the properties of S‐B‐S at varied radiation doses were also focused on. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of comonomer incorporation on morphology and thermal and mechanical properties of blends based upon isotactic metallocene–polypropene and random ethene/1‐butene copolymers

Blends of isotactic polypropene (i‐PP) with random ethene/1‐butene (EB) copolymers containing 10, 24, 48, 58, 62, 82, and 90 wt % 1‐butene were prepared in order to examine the influence of the EB molecular architecture on the morphology development as well as on the thermal and mechanical properties. Compatibility between i‐PP and EB increased with increasing 1‐butene content in EB to afford single‐phase blends at a 1‐butene content exceeding 82 wt %. The morphology was investigated using AFM and TEM. Improved compatibility accounted for enhanced EB dispersion and interfacial adhesion. Highly flexible as well as stiff blends with improved toughness were obtained. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 838–848, 1999     

Enhanced crystallization rate and mechanical properties of poly(l‐lactic acid) by stereocomplexation with four‐armed poly(ϵ‐caprolactone)‐block‐poly(d‐lactic acid) diblock copolymer

Poly(l ‐lactic acid) (PLLA) was blended with a series of four‐armed poly(? ‐caprolactone)‐block ‐poly(d ‐lactic acid) (4a‐PCL‐b ‐PDLA) copolymers in order to improve its crystallization rate and mechanical properties. It is found that a higher content of 4a‐PCL‐b ‐PDLA copolymer or longer PDLA block in the copolymer lead to faster crystallization of the blend, which is attributed to the formation of stereocomplex crystallites between PLLA matrix and PDLA blocks of the 4a‐PCL‐b ‐PDLA copolymers. Meanwhile, the PDLA block can improve the miscibility between flexible PCL phase and PLLA phase, which is beneficial for improving mechanical properties. The tensile results indicate that the 10% 4a‐PCL_5k‐b ‐PDLA_5k/PLLA blend has the largest elongation at break of about 72% because of the synergistic effects of stereocomplexation between enantiomeric PLAs, multi‐arm structure and plasticization of PCL blocks. It is concluded that well‐controlled composition and content of 4a‐PCL‐b ‐PDLA copolymer in PLLA blends can significantly improve the crystallization rate and mechanical properties of the PLLA matrix. © 2017 Society of Chemical Industry     

Influence of addition of styrene–ethylene/butylene–styrene copolymer on rheological,mechanical, and tribological properties of polyamide nanocomposites

To develop new tribomaterials for mechanical sliding parts, investigations were carried out on the influence of adding styrene–ethylene/butylene–styrene block copolymer (SEBS) on the rheological, mechanical, and tribological properties of polyamide 6 (PA6) nanocomposite, which is a commercial product of layered silicate (clay) filled polyamide 6 (PA6/Clay). Two kinds of block copolymers, unmodified SEBS (SEBS) and maleic anhydride‐grafted SEBS (SEBS‐g‐MA), were added with PA6/Clay nanocomposite. Dynamic viscoelastic properties in the molten state of these nanocomposites and their tensile, impact, and tribological properties of these nanocomposites were evaluated. Dynamic viscoelastic properties were found to increase with the addition of SEBS and were influenced, in particular, by block copolymers containing SEBS‐g‐MA. Influence of the addition of SEBS on mechanical properties of these systems differed for each mechanical property. Although tensile properties decreased with SEBS, Izod impact properties were improved with the addition of SEBS‐g‐MA. Tribological properties were improved with the addition of block copolymer, and the influence of the amount of addition was higher than the type of block copolymer used. These results indicate that new tribomaterials developed have sufficient balance amongst moldability, mechanical, and tribological properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Optimization of the property profile of poly‐L‐lactide by synthesis of PLLA‐polystyrene–block copolymers

Diblock and triblock copolymers of poly‐L ‐lactide (PLLA) and polystyrene (PS) were synthesized and the mechanical properties of these copolymers studied. Free radical polymerization of styrene in the presence of 2‐mercaptoethanol as functional chain transfer agent produced mono‐functionalized PS‐blocks which were used as macroinitiators in the subsequent ring opening polymerization (ROP) of L ‐lactide to produce the diblock copolymers. Furthermore a α‐ω‐bishydroxyl functionalized PS‐block was synthesized by RAFT, which was then engaged as bifunctional initiator for the ROP of L ‐lactide to provide the triblock copolymers PLLA‐PS‐PLLA. Through the copolymerisation and high molar masses, it was possible to achieve an improved mechanical property profile, compared with pure PLLA, or the analogous blends of PLLA and PS. A weight fraction of PS of 10–30% was found to be the optimal range for improving the heat deflection temperature (HDT), as well as mechanical properties such as ultimate tensile strength or elongation at break. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Biodegradable elastomers based on ABA triblocks: influence of end‐block crystallinity on elastomeric character

ABA triblock copolymers, based on biodegradable monomers, namely ε‐caprolactone (CL) and L ‐lactide (LLA), were synthesized and studied. The end‐blocks were mostly poly(L ‐lactide) while the middle segments were a random copolymer of PCL and PLLA. Synthesis of these copolymers was performed by varying the end‐block segment length while retaining a fixed middle‐block segment length and vice versa. Nuclear magnetic resonance studies confirmed the designed structure of the copolymers and their thermal properties were studied with differential scanning calorimetry. Mechanical and thermomechanical properties were determined with an Instron tester and by dynamic mechanical analysis, respectively. The elastomeric character of the copolymers was verified by cyclic test as well as by creep and recovery measurements. Changes made to the middle‐ and end‐block segment lengths had a significant influence on the mechanical properties of the copolymers, especially their extendibility and recoverability. An increase in the crystallinity of the end‐blocks in the copolymers caused a drop in their elastomeric character. In cyclic testing, under conditions of 50% and 150% strain, copolymers with low end‐block crystallinity could recover more than 85% whereas copolymers with high crystallinity showed reduced recovery values as low as 60%. Copyright © 2011 Society of Chemical Industry     

Preparation and characterization of polystyrene–poly(ethylene oxide) amphiphilic block copolymers via atom transfer radical polymerization: Potential application as paper coating materials

Poly(ethylene oxide) (PEO) monochloro macroinitiators or PEO telechelic macroinitiators (Cl‐PEO‐Cl) were prepared from monohydroxyfunctional or dihydroxyfunctional PEO and 2‐chloro propionyl chloride. These macroinitiators were applied to the atom transfer radical polymerization of styrene (S). The polymerization was carried out in bulk at 140°C and catalyzed by Copper(I) chloride (CuCl) in the presence of 2,2′‐bipyridine (bipy) ligand (CuCl/bipy). The amphiphilic copolymers were either A‐B diblock or A‐B‐A triblock type, where A block is polystyrene (PS) and B block is PEO. The living nature of the polymerizations leads to block copolymers with narrow molecular weight distribution (1.072 < M_w/M_n < 1.392) for most of the macroinitiators synthesized. The macroinitiator itself and the corresponding block copolymers were characterized by FTIR, ¹H NMR, and SEC analysis. By adjusting the content of the PEO blocks it was possible to prepare water‐soluble/dispersible block copolymers. The obtained block copolymers were used to control paper surface characteristics by surface treatment with small amount of chemicals. The printability of the treated paper was evaluated with polarity factors, liquid absorption measurements, and felt pen tests. The adsorption of such copolymers at the solid/liquid interface is relevant to the wetting and spreading of liquids on hydrophobic/hydrophilic surfaces. From our study, it is observed that the chain length of the hydrophilic block and the amount of hydrophobic block play an important role in modification of the paper surface. Among all of block copolymers synthesized, the PS‐b‐PEO‐b‐PS containing 10 wt % PS was found to retard water absorption considerably. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4304–4313, 2006     

Solid state properties of xylenyl ether-aryl ether sulfone triblock copolymers

Summary The morphology and mechanical properties of a series of xylenyl ether-aryl ether sulfone ABA triblock copolymers were studied, where the A represents the xylenyl ether block (PXE) and the B represents aryl ether sulfone block (PSF). The copolymers investigated were composed of PXE block lengths of 16,000 or 23,000 g/mol together with aryl ether sulfone oligomers with molecular weights ranging from 5,000 to 20,000 g/mol. Both homo- and heterogeneous morphologies were observed depending on the composition of the copolymers. The copolymers with the high polysulfone block lengths showed higher phase demixing. The triblock copolymers showed the expected tough ductile mechanical properties, as judged by the high elongations (50–165%).     

Mechanical properties–morphology relationships in nano‐/microstructured epoxy matrices modified with PEO–PPO–PEO block copolymers

Epoxy‐based blends containing poly(ethylene oxide)‐co‐poly(propylene oxide)‐co‐poly(ethylene oxide) (PEO–PPO–PEO) block copolymers with different PEO/PPO molar ratios have been investigated in order to analyze the effect of the generated morphologies and interactions between components on the mechanical properties of the blends. Mechanical, morphological and dynamic mechanical analyses indicate that the observed increase of flexural modulus can be related to the decrease of free volume. In modified systems that remain miscible, an increase of flexural modulus, strength and fracture toughness can be observed. Also, macrophase‐ and microphase‐separated systems show an increase of fracture toughness but not of flexural modulus and strength at low contents of block copolymers. Copyright © 2007 Society of Chemical Industry     

Compatibilisation of polystyrene-polyolefin blends

Summary The impact properties of 1:1 polyolefin-polystyrene blends compatibilised with a series of hydrogenated styrene-butadiene block copolymers of various structures have been studied with a view to establishing a structure-property realationship. The most effective compatibiliser in this context appears to be a low molecular weight triblock (Kraton G1652). Addition of only 5% Kraton G1652 affords a ca. three-fold improvement in the impact strength for a 1:1 PP/PS blend over the uncompatibilised blend and leads to near HIPS impact strength for a 1:1 LDPE/PS blend. This compatibiliser is as effective as a high molecular weight tapered diblock and appears to be substantially more effective than either low molecular weight diblocks or a higher molecular weight triblock.     

Morphology and micromechanical deformation behavior of styrene–butadiene block copolymers. III. Binary blends of asymmetric star block copolymer with general‐purpose polystyrene

The correlation between morphology, mechanical properties, and micromechanical deformation behavior of the blends consisting of an asymmetric styrene/butadiene star block copolymer (ST2‐S74, total styrene volume content Φ_PS = 0.74) and general‐purpose polystyrene (GPPS) was investigated using transmission electron microscopy and uniaxial tensile testing. Addition of 20 wt % of GPPS to the block copolymer resulted in a drastic reduction in strain at break, indicating the existence of critical PS lamella thickness D_c. Above D_c lamellar block copolymers displayed a transition from ductile to brittle behavior, substantiating the mechanism of thin layer yielding proposed for lamellar star block copolymers. The blends showed a variety of deformation structures ranging from classical crazelike zones to those with internal shearlike components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1208–1218, 2004     

Copolymers of N‐methylpyrrole and 3,4‐ethylenedioxythiophene: structural,physical and electronic properties

The structural, electric and electronic properties of copolymers derived from mixtures of N‐methylpyrrole and 3,4‐ethylenedioxythiophene (EDOT) with various concentration ratios have been investigated and, additionally, compared with those of the corresponding homopolymers. The electropolymerization kinetics of all the generated copolymers and the homopolymers was examined in terms of current productivity using chronoamperometry. The chemical structure of the linkages between adjacent monomers and the microstructure of the chains were investigated using Fourier transform infrared spectroscopy and quantum mechanical calculations, respectively. The results indicate that the linkages between monomeric units formed during the anodic copolymerization are of the α–α type, while the microstructure of the copolymers depends on the EDOT content. Theoretical calculations were also used to examine the electronic properties of the systems under study, while the conductivity and the electrical stability were studied using the sheet‐resistance method. Interestingly, the electric properties are consistent with the random and block microstructures predicted for the copolymers with low and high EDOT content, respectively. Copyright © 2006 Society of Chemical Industry