Effect of electron beam radiation on tensile and viscoelastic properties of styrenic block copolymers

The effect of electron beam (E‐beam) radiation on a series of styrenic block copolymers (SBCs) was investigated. These SBCs included newly developed poly(styrene‐block‐isoprene/butadiene‐block‐styrene) (SIBS), poly(styrene‐block‐butadiene‐block‐styrene) (SBS), and poly(styrene‐block‐isoprene‐block‐styrene) (SIS). The tensile properties, stress relaxation, molecular weight, and dynamical mechanical properties were studied. Generally, the crosslink density and tensile moduli of SBCs increased with increasing of E‐beam radiation dose. The tensile strength of SIBS and SIS was shown to first decrease at lower E‐beam radiation dose (<120 kGy) and then increase at higher radiation dose (>190 kGy). The tensile strength of SBS was significantly decreased at high E‐beam radiation dose (>190 kGy). This was attributed to the differences between entanglement before E‐beam radiation and the homogeneity of the crosslink network after exposure. POLYM. ENG. SCI., 54:2979–2988, 2014. © 2014 Society of Plastics Engineers     

Structure-property relations of segmented block copolymers with liquid-liquid demixed morphologies

Poly(propylene oxide) based polyether(ester-amide)s (PEEA) with non-crystallisable amide segments were synthesized and their structure-property relations studied. These model segmented block copolymers were used to gain insight in the structure-property relations of block copolymers with liquid-liquid demixed morphologies, also present in segmented polyurethanes. The poly(propylene oxide) used had a molecular weight of 2300 g/mol and was end capped with 20 wt% ethylene oxide. The non-crystallisable amide segments are based on an amorphous polyamide: poly(m-xylylene isophthalamide) and the repetitive length (x) of the amide segment was varied from 1 to 10. Phase separation in these PEEA's occurred by liquid-liquid demixing when the length (x) of the non-crystallisable amide segment was higher than 2 (x>2). TEM experiments showed spherical structures at two size scales, 5-10 nm domains (nano-domains) and 30-500 nm domains (sub-micron domains), both dispersed in a polyether matrix. The size and volume fraction of these spherical domains were found to increase with increasing the amide segment length. The modulus of the materials increased moderately with increasing amide segment content (increasing amide segment length x). The compression and tensile sets values of these PEEA's were found to decrease with increasing amide segment length, thus these PEEA's behave also more elastic at longer amide contents (thus also at higher modulus). Giving time these liquid-liquid demixed segmented block copolymers recovered completely.     

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.     

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.     

Morphology and properties of crystalline polyester-siloxane block copolymers

A new series of crystalline (AB)_n type multiblock copolymers based on crystalline poly(hexamethylene sebacate) (HMS) and amorphous poly(dimethylsiloxane) (DMS) has been prepared, and their solid state properties have been examined. The copolymers range from 0-69 wt percent DMS, and they crystallize in spherulitic textures when cast in films from solution or the melt. As the DMS concentration in the copolymers increases, the spherulite sizes decrease, but only a very small melting point depression is observed. Available evidence suggests extensive microphase separation in the bulk of the solid state. Surface characterization of the copolymers indicates that phase separation is also prevalent at the polymer-air interface. The block copolymers and polyblends have critical surface tensions of wetting very similar to DMS homopolymer.     

Synthesis and properties of amphiphilic thermo-sensitive block copolymers

Octadecyl acrylate (ODA) as hydrophobic monomer and N-isopropylacryamide (NIPAAm) as hydrophilic monomer were chosen to synthetize the thermo-sensitive block copolymers PODA_x-PNIPAAm_y-PODA_x (BAB-type) via reversible-addition-fragmentation chain transfer (RAFT) polymerization, the block copolymers could self-assemble to flower-like micelles in aqueous solution with hydrophobic PODA as the inner core and stabilized by hydrophilic PNIPAAm as the outer shell. The characterizations of the micelles such as surfactivity, thermo-sensitivity, micelle hydrodynamic radius (R _h ) and polydispersity index (PdI) were demonstrated by surface tension technique, UV-Vis, and dynamic light scattering (DLS) measurements, respectively. The longer the hydrophilic chain was, the higher the critical micellization concentration (CMC) would be, and the higher content of the PODA was, the lower the lower critical solution temperature (LCST) would be. The average R _h remained at about 100 nm below LCST, but decreased sharply to about 42 nm and kept constant when reaching and above LCST, which meant the non-aggregation of BAB type block copolymers. The micelle was homogeneous with the small PdI within the range of research. B_0.5mA_24mB_0.5m had the largest capacity to encapsulate lipophilic Sudan Red IV model drugs and the drug loading efficiency was 9.76%.     

Structure and properties of shape-memory polyurethane block copolymers

Segmented polyurethanes containing soft segments with lower molecular weight exhibit shape-memorizing properties. Structure and properties of shape-memorizing polyurethanes (S-PUs) were studied. S-PUs are characterized by a rather high glass transition temperature: T_g of S-PUs is usually in the range of 10–50°C. A Pplot of 1/T_m against–In X_A is approximately linear, indicating that the hard segments are randomly distributed along the molecular chain. S-PUs with a hard segment of 67–80 mole % form negative spheruiites; they give a faint scattering maximum in a small-angle X-ray diffraction pattern. On the other hand, S-PUs with a hard segment of 50 mole % form fine birefringent elements, giving diffuse scattering in its SAXD pattern. A cyclic test of an S-PUs above T_g indicates that the residual strain increases and the recovery strain decreases with increasing cycle and maximum strain. It has been suggested by dynamic mechanical investigation that the shape-memorizing property of the S-PUs may be ascribed to the molecular motion of the amorphous soft segments. © 1996 John Wiley & Sons, Inc.     

Micromechanical properties of polyether block amide copolymers

A series of polyether block amide copolymers based on poly(tetramethylene oxide) of molecular weight 1000 or 2000 and polyamide 12 of molecular weight between 600 and 4000 with varying PE/PA weight ratio (from 80 to 20%) were studied by using dynamic mechanical spectroscopy and differential scanning calorimetry. Dynamic mechanical experiments showed three main relaxation peaks related to, the subglass transition of the soft segments, the glass transition of the soft segments, and the glass transition of the hard segments. A quench, carried out on a 70% PA copolymer from 110 to 15°C, leads to a decrease in the storage modulus. This result should be related to the destruction of physical ties.     

Physical properties of isobutylene based block copolymers

Physical, mechanical and thermal properties of a new class of isobutylene based model block copolymers are studied and contrasted with those of traditional thermoplastic elastomers based on polydienes and saturated polydienes (polyolefins) such as Kraton (or Vector) and Kraton G block copolymers. Melt state rheological and dynamic mechanical measurements confirm that thermodynamic interactions between polystyrene (S) and polyisobutylene (iB) or poly‐p‐tert‐butylstyrene (tbS) and iB are comparable to, if not larger than, those between S and polybutadiene (B) or S and ethylene/butene‐1 copolymer (EB). Physical properties for the S‐iB‐S and tbS‐iB‐tbS block copolymers, particularly the injection‐moldability and cut‐growth characteristics, are found to be considerably different from those found for the S‐B‐S and S‐EB‐S systems. We attribute this behavior to the longer entanglement chain length of iB compared with those for B and EB.     

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     

Rheological characteristics and morphologies of styrene–butadiene–maleic anhydride block copolymers

Studies on the morphologies and rheological characteristics of two styrene–butadiene–maleic anhydride block copolymers (SBMa) have been performed. The transmission electron microscopy micrographs show that the morphologies of SBMa change from matrix–island structure to co‐continuous structure. Curves for dynamic modulus varied with frequency (ω) show obvious solid‐like behavior in the low ω region, which is typical for ordered block copolymers or networked materials. Van Gurp–Palmen plots have been used to exploit the thermorheological complexity of two copolymers. The master curves of two copolymers have been acquired through time–temperature superposition principle, and the plateau modulus (G) have been obtained from G′ at ω, where the loss tangent (tan δ) approaches a minimum. Meanwhile, Williams–Landel–Ferry equation has been used to evaluate the free volume parameters. The relaxation time spectra of two copolymers have been calculated and fitted with modified Baumgaertel–Schausberger–Winter model. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dynamic mechanical and thermomechanical properties of silicone-polycarbonate block copolymers

Representative random, alternating block copolymers of polydimethylsiloxane (PDMS) and bisphenol-A-polycarbonate (BPAPC) were studied by thermomechanical and dynamic mechanical techniques. Data on glass transition temperatures (T_g), heat-deflection temperatures (T_d), Vicat softening temperatures (T_s), coefficients of linear expansion (α), stress-strain, and stress relaxation for four PDMS-BPAPC block co-polymers are presented. The effect of casting films from mixed n-hexane-methylene chloride solution on the thermomechanical and dynamic mechanical properties was also studied.     

Synthesis,characterization, crystalline morphologies and hydrophilicity of A4BA4 nonlinear block copolymers

Novel, well‐defined A₄BA₄ nonlinear block copolymers [poly(?‐caprolactone)]₄‐block‐poly(propylene oxide)‐block‐[poly(?‐caprolactone)]₄ (PCL₄‐b‐PPO‐b‐PCL₄) with eight arms were synthesized by ring‐opening polymerization. An investigation of melting and crystallization demonstrated that the values of crystallization temperature, melting temperature and degree of crystallinity of PCL₄‐b‐PPO‐b‐PCL₄ were enhanced with an increase of PCL chain length. At the same time, the crystallizability of PCL segments was influenced by the star‐shaped structure of the copolymers and the amorphous PPO segments in the copolymers. Furthermore, PCL₄‐b‐PPO‐b‐PCL₄ showed crystalline morphologies that were different from that of linear PCL according to polarized optical microscopy. Moreover, the hydrophilicity of the copolymers could be improved and adjusted by the star‐shaped structure and the alteration of the relative content of the PCL and PPO segments in the copolymers.© 2013 Society of Chemical Industry     

Time-dependent flow of quasi-linear viscoelastic fluids

Transient flow behavior of an incompressible quasi-linear viscoelastic fluid under suddenly applied constant pressure as well as under a periodic pressure gradient was investigated using a three-parameter relaxation function. In the light of these solutions, the roll of viscoelastic relaxation in the overshooting of volumetric flow rate and the effect of viscoelastic parameters on the mean square velocity profile are discussed.     

Viscoelastic properties of heterophase blends of homopolymers and block copolymers

Stress relaxation and dynamic mechanical measurements were carried out for two types of heterophase polyblends. One is obtained by blending homopolymers of butadiene and styrene (high impact polystyrene or HIPS); the other by blending homopolymer of butadiene with a triblock copolymer of styrene-butadiene-styrene (SBS/B). It was found that for HIPS, time temperature superposition is difficult, and the shift factors cannot be adequately interpreted by a reasonable model. For SBS/B it is impossible to carry out superposition. Modulus-temperature and loss tangent curves determined by dynamic mechanical experiments indicate the presence of new transition near ?40°C. Possible mechanisms giving rise to this new transition are discussed.     

Physical properties of block copolymers of polydimethyl siloxane and polycarbonate

A detailed study of the physical properties of alternating block copolymers of polydimethyl siloxane and bisphenol-A polycarbonate is presented. The results suggest that the mechanical and optical properties of such materials are dependent upon the presence of associated regions as well as the nature of the chain between such regions. Dielectric, infrared, and DSC data as well as the stress and birefringence strain behavior are presented.     

Preparation and water sorption properties of cellulose-polypropylene glycol block copolymers

A series of cellulose-polypropylene glycol block copolymers have been prepared by techniques described previously. The chain extension reactions used for their preparation were confirmed by i.r. and intrinsic viscosity data. The water sorption of films of the blocks was determined and the results, calculated on the cellulose content, compared with various forms of pure cellulose. It was found that lower crystallinity of the blocks was indicated by the higher water sorption values. As the size of the cellulose blocks was decreased the water sorption also decreased but the smallest block sample gave a higher value. It is believed that the polypropylene glycol blocks exert a restraining influence on the water sorption which is eventually overcome by the decrease in the crystallinity of the cellulose blocks as their size decreases.     

偶氮嵌段共聚物合成、自组装与光响应性

含偶氮苯基团的嵌段共聚物兼具偶氮聚合物和嵌段共聚物的特点,可自组装形成具有特殊光响应性能的各种纳米/亚微米结构,在光信息存储、传感器、药物输送、光控智能材料等领域有重要的应用前景。本文对本课题组近年来在含强推拉电子型偶氮生色团的嵌段共聚物合成、自组装与光响应性方面的研究工作进行简要综述。     

Structure and properties of oil extended styrene butadiene block copolymers

The relationships between mechanical properties and structure of rapidly spin cast styrene-butadiene-styrene (SBS) block copolymers diluted with two different types of mineral oil are discussed. Small angle X-ray scattering (SAXS) measurements indicate that both oils go mainly into the rubbery polybutadiene phase. While during rapid spin casting the paraffinic oil improves the phase separation of polystyrene (PS) and polybutadiene (PB), the opposite is true for the aromatic oil. The measurements also suggest that the oils cause a preferential swelling of the superstructure along the longitudinal direction of the cylindrical PS domains. From this, it can be concluded that a larger number of interconnecting PB chains is present in the cross direction than in the longitudinal one. With increasing oil content, a further decrease of interconnecting chains in the latter direction may be the reason for the decrease of the tensile modulus. Furthermore, above a critical value of dilution (33 wt percent for paraffinic oil, 50 wt percent for the aromatic one), more and more spherical domains are formed instead of the cylindrical ones. This morphological transition explains the step present in the double logarithmic plot of the large strain tensile modulus as a function of oil dilution.     

Microstructural influences on volumetric properties of styrene-butadiene-styrene block copolymers

A water-displacement method was used to measure the specific volume of three styrene-butadiene-styrene (SBS) block copolymers over the temperature range 4°C to 65°C. The polymers contained 0.268. 0.293, and 0.482 weight fraction polystyrene, varied in molecular weight, and are known to be phase-separated at these temperatures. Coefficients of thermal expansion were also obtained and found to be constant over this temperature range. Results are compared with various models of composite behavior, the most successful of which is the linear mixing rule which gives good predictions over this composition range. Deviations for specific volume are negative, and for expansion coefficient positive, from the linear rules. More complex behavior is suggested, however, and this is interpreted in terms of microstructural characteristics. Some apparent contradictions in data reported by other workers are explained. Results are presented also for samples stretched uniaxially up to 300 percent strain; only slight evidence of dilation is seen at 22°C. but increase of the expansion coefficient is more apparent.