Optical and swelling properties of macroscopic “single crystals” of an S–B–S copolymer. II. Samples possessing a cylindrical morphology

A study is reported of the anisotropic swelling behavior of “single crystal” samples of an S–B–S two-phase copolymer, Kraton K102, on imbibing a selective swelling agent. This material consists of a hexagonal array of polystyrene cylinders in a matrix of polybutadiene. Initially the material expands reversibly, perpendicular to the cylinders. Low-angle x-ray studies show that this corresponds to expansion of the hexagonal lattice and indicates lateral expansion of the matrix material. Birefringence changes can be broadly ascribed to the changes in form birefringence. Subsequently, irreversible expansion occurs along the rod direction. x-ray diffraction studies combined with electron microscopy indicate a transformation of the cylindrical microstructure into a more complex arrangement. This often appears to be an arrangement of spheres, packed on a hexagonal or square lattice, but this cannot completely account for the x-ray results. Some micrographs suggest the existence of a more complex network of the polystyrene microphase units.     

Tearing energy study of “oriented and relaxed” polystyrene in the glassy state

To study the effect of processing history, molecular weight/molecular weight distribution, and thermal history on solid state properties (in particular fracture properties and orientation), carefully characterized polydisperse and monodisperse polystyrene samples were drawn above T_g and the orientation frozen in. The objective was to simulate the incidental orientation of polymer chains after processing, molding, and so forth (e.g., injection or compression, blow molding) as a result of melt flow. A series of polystyrene samples was produced by hot drawing at temperatures of 113 and 148 °C, followed by a relaxation period, and then a quench to below T_g. The level of segmental orientation imposed in the samples was determined by birefringence measurements. The tear energy of the sheets was measured at 20 °C by tearing along the draw direction, ultimately giving a value for the fracture energy, G_3C. Samples of high draw ratio and low segmental orientation were unexpectedly found to have highly anisotropic fracture properties despite the low level of optical anisotropy. The fracture properties also depended significantly on whether the samples were drawn with or without lateral constraint. The results are compared with measurements of isotropic samples and the findings of a previous investigation utilizing SANS and birefringence. Modeling the drawing conditions at the chain level using a recent nonlinear tube theory explains how birefringence alone is an inadequate measure of molecular orientation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 377–394, 2007     

Block polymers from isocyanate-terminated intermediates. II. Preparation of butadiene–ϵ-caprolactam and styrene–ϵ-caprolactam block polymers

Polystyrene–nylon 6 and polybutadiene–nylon 6 block copolymers have been prepared from isocyanate-terminated prepolymers. From extraction and fractionation data the products obtained were found to be mixtures of both homopolymers and pure block copolymer. The polybutadiene–nylon 6 copolymers are extremely pliable at ambient temperatures even at high ?-caprolactam contents (70–80 wt-%). This is true even though these copolymers show a crystalline melting point at 213°C similar to poly-?-caprolactam. Presumably this unusual behavior occurs because of the nature of the synthesis which renders the butadiene portion of these copolymers the continuous phase. Plasticity measurements indicate that pliability is dependent on the molecular weight of the block poly-?-caprolactam.     

Orientation of cylindrical microdomains of triblock copolymers by in situ stress–strain‐ birefringence measurements

The orientation behavior of polystyrene‐block‐hydrogenated polyisoprene‐block‐polystyrene (SEPS) with cylindrical microdomains of polystyrene (PS) dispersed in the rubbery segments was investigated by simultaneous measurements of stress and birefringence during uniaxial stretching. The stress increased sharply with strain below the yield strain and then it gradually increased. In contrast, the birefringence changed little below the yield strain, increased sharply with strain above the yield strain up to a strain of 0.5, and then gradually increased. The characteristic birefringence behavior is attributed to the form birefringence induced by the orientation and the parallel arrangement of the cylindrical microdomains associated with the orientation of the rubbery segments. The orientation function of the cylindrical microdomains f evaluated by analyzing the form birefringence agrees well with that obtained from the SAXS result. The f was almost zero below the yield strain and it increased sharply with strain up to a strain of 0.5 and then was constant above a strain of 0.5. These results suggest that the orientation of the cylindrical microdomains occur above the yield strain up to a strain of 0.5 and that the orientation does not increase above a strain of 0.5 in spite of the continuous orientation of the rubbery ethylene–propylene segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 715–723, 2009     

Influence of molecular architecture of S–S/B–S triblock copolymers on rheological properties

The influence of middle and outer block composition of symmetric triblock copolymers consisting of a polystyrene–polybutadiene (S/B) random middle block and two polystyrene (PS) outer blocks on morphology and rheological behavior has been investigated. Master curves are obtained by shifting the experimental data measured at different temperatures using time‐temperature superposition principle, the validity of which was confirmed in the linear viscoelastic regime. The rheological properties are observed to be strongly influenced by the relative composition of the S‐SB‐S triblock copolymers. Increasing the S/B ratio from 1:1 to 1:2 in the middle block has lead to a change in morphology from wormlike to lamellar, which is also accompanied with broad and sharp tan δ peaks in the dynamic mechanical measurements, respectively. The storage and loss modulus have been observed to increase with the increase in PS contents in the outer blocks and PB content in the middle block. The triblock copolymer with wormlike structure showed terminal linear viscoelastic behavior, whereas the ones with lamellar morphology showed nonterminal flow behavior in the similar low‐frequency regime. The relaxation modulus (G_t) has been observed to increase four times when the S/B ratio is increased from 1:1 to 1:2, whereas it increases threefold when the PS‐content in the outer block was increased by just 8 wt %. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2776–2788, 2006     

A process–structure–property study of anisotropic PMDA-ODA films

A practical methodology for the correlation and prediction of the process–property performance of advanced materials is developed. The model polymer studied is PMDA-ODA polyimide. The connecting link between the process and the properties is the structural state of the polymer. An essential ingredient for a quantitative characterization of the system is a knowledge of its phase state and intrinsic molecular properties. The intrinsic molecular properties define the limiting performance properties available to the polymer. Anisotropic films and sheets produced by five different fabrication processes are examined. Maps of the molecular symmetry axis, the orientation function, and the thickness distributions of two 50-in.-wide sheets fabricated differently are measured nondestructively for process comparison. Four other film fabrication processes are examined and their three-dimensional orientation states determined and correlated. A three-dimensional orientation function triangular plot permits simultaneous representation of the different fabrication processes on the same figure and allows the investigator to choose the most economic and efficient fabrication route. The structure–property study includes the structural correlation and intrinsic molecular property determination of the anisotropic coefficient of thermal expansion (CTE), the anisotropic mechanical moduli and compliances, and the anisotropic dielectric constants. 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 777–788, 1997     

On the deformation mechanisms of oriented PET and PP films under load

Uniaxially orienred semicrystalline poly(ethylene terephthalate) (PET) and poly(propylene) (PP) films were loaded parallel to draw direction at various temperatures. Changes in the submicroscopical structure of the films under load were examined by small and wide-angle x-ray scattering (SAXS; WAXS) and birefringence measurements. WAXS measurements reveal a decrease of the initial high orientation of the chains in the crystallites during deformation. Simultaneously, an increase of the birefringence was detected, indicating an orientation of chains in the amorphous regions. The alteration of the long period reflections in the SAXS patterns give strong evidence that lamellar stacks with different orientation angles according to load direction are present. Depending on the orientation of stacks, the contribution of lamellar separation to sample deformation alters, giving rise to different amounts of density changes in the stacks. Absolute intensity measurements of SAXS using a Kratky apparatus reveal that lamellar separation occurs preferentially below or in the range of the glass-transition temperature at small strain. With increasing strain and temperatures above the glass-transition slip deformation mechanisms become more important. The formation of microvoids was observed at strain near to elongation at break below or in the range of glass-transition temperature.     

Dynamic birefringence of oligostyrene: A symptom of “polymeric” mode

The dynamic birefringence and the dynamic viscoelasticity of an oligostyrene, A1000, whose molecular weight (M_w = 1050) was comparable to the Kuhn segment size, M_K, were examined near and above the glass‐transition temperature in order to characterize polymeric features of very short chains with M ∼ M_K. The complex shear modulus, G*(ω), was similar to that for supercooled liquids: No polymeric modes such as the Rouse mode were detected at low frequencies of viscoelastic spectrum. On the other hand, the strain‐optical coefficient was found to be negative in the terminal flow zone and positive in the glassy zone. Because the negative birefringence of polystyrene is originated by polymeric modes associated with chain orientation, the present results indicate that polymeric modes exist and become dominant for birefringence in the terminal flow. The data were analyzed using a modified stress‐optical rule: The modulus and the strain‐optical ratio were separated into polymeric (rubbery) and glassy components. The total modulus, G*(ω), was mostly due to the glassy component, G_G*(ω), resulting in the positive birefringence. G_G*(ω) for A1000 agreed with that for high M polystyrenes when compared at a comparable reduced frequency scale. The polymeric component, G_R*(ω), giving rise to the negative birefringence was lower than G_G*(ω) over the whole frequency range but its contribution to the birefringence exceeded that of the glassy component at low frequencies because of the larger optical anisotropy and longer characteristic relaxation time of the former. The limiting modulus of G_R* at high frequencies was about 3 times lower than that for high M polystyrenes, indicating that the main‐chain orientation of the oligostyrene on instantaneous deformation was reduced compared with that of high M polystyrenes. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 954–964, 2000     

片晶装饰技术研究高分子液晶向列相的向错

采用片晶装饰技术和四氧化钉染色技术相结合在透射电镜下研究了热致性高分子液晶的向错结构，在一种热致性聚芳酯的冻结液晶态中观察到了向错强度分别为Ｓ＝±１／２和Ｓ＝±１的两类共六种的向错形态，以及每个向错与其相邻向错之间相互联结和相互作用的状态．     

Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. I. Free quenching

The residual birefringence distributions in polycarbonate disks quenched in a liquid bath under various conditions are determined. Unbalanced distributions of approximately parabolic shape are obtained in the cross-sections in general. A systematic influence of the initial quench temperature on the imblance of the birefringence distributions is observed, with higher initial temperatures leading to a strong shift of birefringence in the positive direction. The systematic variation of the birefringence distribution with quenching conditions is interpreted in terms of a stress and an orientation contribution. The distributions are predicted correctly by a numerical program making use of the linear stress-optical rule with a different stress-optical coefficient above and below the glass-transition temperature. The contribution of molecular orientation is distinguished experimentally from the stress contribution by annealing experiments. © 1993 John Wiley & Sons, Inc.     

Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. II. Effects of sectioning

Birefringence distributions in cross-sections of quenched polycarbonate disks are investigated. The effects of the introduction of new surfaces by sectioning are studied by using different cross-section widths, by quenching rod-shaped specimens, and by measuring the birefringence with oblique incident light. The experimental results are confirmed by numerical calculations of stress distributions in rods with varying aspect ratios. Stress release by appropriate sectioning is used to distinguish between stress and orientation contribution to birefringence. It is found that cutting cross-sections leads to a major stress redistribution in the width direction. This does not affect the birefringence measurement, but the decrease of the stress level in the long direction needs to be taken into account. The molecular orientation in the quenched samples cannot be explained only by the effect of transient thermal stresses above the glass transition. There is another orientation contribution, most likely related to stress relaxation below T_g. © 1993 John Wiley & Sons, Inc.     

Kinetics of mesophase formation and crystallization in poly(diethylsiloxane)

Optical and calorimetric studies of the kinetics of mesophase formation and crystallization in poly(diethylsiloxane) have been conducted. The mesomorphic phase is found to grow from the isotropic melt in the form of lamellar domains about 2 μm thick in the temperature range 293–307 K. According to birefringence data, macromolecules in the mesomorphic lamellae are perpendicular to the end faces. The kinetics of mesophase formation obey the Avrami equation with the morphological parameter n close to 2 (it is equal to 1.75 ± 0.05), which corresponds to the two-dimensional growth of the mesomorphic phase from athermal nuclei. The limiting conversion of the isotropic melt was shown to be temperature-dependent. This is likely to be connected with a change in the number of nuclei with temperature. The crystallization of polymer from the mesomorphic state occurs with retention of the optical texture of the sample. The process proceeds not as a sporadic crystallization of individual mesomorphic lamellae but as a growth of the nucleated crystalline regions via a consecutive incorporation of adjacent crystallizing lamellae.     

Molecular orientation of rigid‐rod polyimide films characterized by polarized attenuated total reflection/fourier transform infrared spectroscopy

The variations in the molecular orientation of uniaxially drawn rigid‐rod polyimide films were systematically characterized in all three dimensions with polarized attenuated total reflection/Fourier transform infrared spectroscopy. The second‐order orientation coefficients were directly deduced from the anisotropy in IR absorptions of particular bands. With the draw ratio increasing, the state of the molecular orientation changed from being nearly planar to completely uniaxial via biaxial orientation, and the degree of orientation was much larger than that of a semirigid polyimide having an ether linkage at the same draw ratio, which originated from the rigid‐rod structure. In addition, the imide planes were rotationally oriented to the out‐of‐plane direction of the film geometry. Furthermore, the relationship between the molecular chain orientation and the in‐plane birefringence in the biaxial orientation state was examined. The intrinsic birefringence was estimated from biaxial orientation films to be 0.33 at a wavelength of 1307 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 418–428, 2003     

Microstructural investigation of high‐speed melt‐spun nylon 6 fibers produced with variable spinning speeds

The structural details of high‐speed melt‐spun nylon 6 fibers at spinning speeds ranging from 4500 to 6100 m/min were investigated by solid‐state proton nuclear magnetic resonance (¹H NMR) spectroscopy, density and birefringence measurements, differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). The analyses of the proton spin‐lattice relaxation times in the rotating frame and correlation times confirmed the existence of three different phases, the immobile crystalline, intermediate rigid amorphous, and mobile amorphous regions, in the fiber sample. At spinning speeds lower than 5200 m/min, the portion of the crystalline phase increased at the expense of the rigid amorphous region and then reached a plateau afterward, from which the mobile amorphous portion increased. Combined analyses of density and birefringence measurements, DSC, and XRD in conjunction with NMR results indicated that the formation of the γ crystal became predominant compared to that of the α crystal. The orientation factor of the crystalline phase increased slightly with increasing spinning speed, whereas the amorphous orientation factor decreased because of the increase of the purely amorphous region. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1285–1293, 2000     

A concept for bifocal contact‐ or intraocular lenses: liquid single crystal hydrogels (“LSCH”)

The synthesis of liquid single crystal hydrogels (“LSCH”) in suitable molds offers an innovative concept to realize bifocal contact‐ or intraocular‐lenses. LSCH combine the properties required for applications as bifocal ophthalmic lenses: the soft and water‐containing hydrogel enables oxygen permeation and exhibits high birefringence due to the liquid crystalline phase structure built up by rigid rod‐like amphiphiles. Via a photo‐initiated crosslinking reaction of aqueous solutions of monomeric lyotropic liquid crystalline amphiphiles in the macroscopically ordered liquid crystalline state, we obtain optically uniaxially ordered and transparent LSCH. The orientation process and the phase structure of the anisotropic hydrogel is analyzed by deuterium NMR‐spectroscopy. Copyright © 2002 John Wiley & Sons, Ltd.     

Study of crystalline orientation in drawn ultra-high–molecular weight polyethylene films

A wide-angle x-ray diffraction (WAXD) study of the development of molecular orientation in the crystalline phase of ultra-high–molecular weight polyethylene films prepared by the gelation–crystallization method is presented. WAXD scans of the undrawn films show that the lamellae are oriented in the plane of the films. Upon drawing at 130°C, the orientation of the molecular chains changes from the direction normal to the film surface (ND) to the elongation direction. The decrease of the 200/020 intensity ratio at low draw ration (λ <10) indicates that double orientation develops during the transformation from the lamellar to the fibrillar morphology, with the a-axis oriented parallel to ND. The orientation distributions of the 110, 200, 020, and 002 planes of the orthorhombic unit cell of polyethylene were studied and characterized by the coefficients of a Legendre polynomial series. At a draw ratio of 4.5, the second-order coefficient, 〈P₂(cos χ〉, already gets close to its limiting value, but it is shown that higher order coefficients of the polynomial series can be used to describe the evolution of the orentation, even up to λ = 50. The coefficients relative to the molecular chain orientation, 〈P_n(cos χ)〉_c, can be calculated from different crystalline reflections. Curve-fitting calculations were made in order to improve the correlation between the results obtained from the orientation distribution of the 110, 020, and 002 planes. A Person VII function was found to give a better fit of the experimental curves than Gaussian or Lorentzian equations. © 1993 John Wiley & Sons, Inc.     

Macrophase‐separation in binary blends of symmetric polystyrene‐polybutadiene diblock copolymers

Binary blends of compositionally symmetric polystyrene‐polybutadiene diblock copolymers are investigated as a function of chain length ratio and blend composition using small‐angle neutron scattering. Three different low molar mass copolymers were blended with a high molar mass copolymer. The results are related to the theoretical phase diagram put forward by M. W. Matsen (J. Chem. Phys. 103 , 3268 (1995)). The conditions for macrophase‐separation are established, an observed asymmetry of the lamellae rich in long copolymers is discussed and the variation of the lamellar thickness with the volume fraction of short chains in the one‐phase state is compared with theoretical predictions.     

Partitioning of polystyrene between incompatible phases and distributional effects in the system polystyrene–polybutadiene–toluene

The average molecular weights and the molecular weight distributions of polystyrene (PS) in the conjugate incompatible phases of the ternary system of PS and polybutadiene with toluene as solvent were studied at 23°C. Gelpermeation chromatography, with ultraviolet and differential refractive index detectors, was used for analyzing the compositions of the conjugate phases and for obtaining the molecular weight averages of PS in the phases. Both narrow and broad molecular weight distribution (MWD) polymer samples were used. The effect of broad MWD polymers is seen as one of narrowing the shape of the binodal, thus effectively increasing the compatible region. The molecular weight averages of PS in the two conjugate phases do not vary significantly in the case of the narrow MWD PS sample while for broad MWD samples the average molecular weight of PS is found to be higher in the PS-rich phase than in the polybutadiene-rich phase for tie lines closer to the plait point indicating a partitioning or redistribution of the molecular weight species of PS between the incompatible phases.