Conformation of comb‐like liquid crystal polymers in isotropic solution probed by small‐angle neutron scattering

The conformational characteristics of a comb‐like side‐chain liquid crystal polysiloxane (SCLCP), dissolved in deuterated chloroform, were evaluated by small‐angle neutron scattering (SANS) measurements over a wide q range. SANS studies were carried out on specimens with constant backbone length (DP = 198) and variable spacer length (n = 3, 5, and 11), and with constant spacer length (n = 5) and variable DP (45, 72, 127, and 198). The form factor P(q) at high q was analyzed using the wormlike chain model with finite cross‐sectional thickness (R_c) and taking into account the molecular weight polydispersity. The analysis generated values of persistence length in the range l_p = 28–32 Å, considerably larger than that of the unsubstituted polysiloxane chain (l_p = 5.8 Å), with contour lengths per monomer comparable to the fully‐extended polysiloxane backbone (l_m = 2.9 Å). This indicates a relatively rigid SCLCP chain due to the influence of the densely attached mesogenic groups. The SCLCP with n = 11 is more flexible (l_p = 28 Å) than those with n = 3 and n = 5 (l_p = 32 Å). The cross‐sectional thickness increases with spacer length, R_c ～ n^0.21±0.02 (3 ≤ n ≤ 11), and the contour length per monomer decreases with increasing spacer length, l_m ～ n^?0.35±0.01. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2412–2424, 2006     

Microstructure and morphology of self‐assembling multiblock poly(ethylene‐1‐butene)‐n copolymers in solution studied by wide‐Q small‐angle neutron scattering and microscopy

Multiblock ethylene‐1‐butene copolymers (PEB‐n) with graded ethylene content (where n is the number of ethyl branches per 100 backbone carbons) represent efficient cold filter plugging point (CFPP) depressants for crude oils and middle distillates. The aggregation behavior and the interaction with wax molecules of a tetrablock PEB‐2.6/PEB‐6.0/PEB‐10.9/PEB‐13.2 and triblock PEB‐6.5/PEB‐8.9/PEB‐10.1 copolymers in decane solutions were investigated over a wide temperature range by combining different small‐angle neutron scattering techniques and optical microscopy. The experimental results revealed in the decrease of temperature formation and evolution of multisized structural levels showing a hierarchical organization on the length scale from 1 nm up to 10 μm. One‐dimensional polymer aggregates arising as initial structures associate and branch that lead to the occurrence of complex macroaggregates with diffusive interfaces and sizes of several microns. The one‐dimensional copolymer structure shows longitudinal density modulation and micellar‐like substructures in neat polymer solutions. When wax is added, this structure becomes more homogeneous in decrease of temperature as a consequence of the cocrystallization of wax and copolymer. The wax crystallization in board‐like objects of much smaller size than required by the CFPP criterion of oil and refinery industry (filter mesh size of 45 μm) is templated and controlled by the assembling features of the crystalline–amorphous PEB‐n multiblock copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Review of polystyrene diffusion studies in latex particles by small‐angle neutron scattering

This paper reviews small‐angle neutron scattering (SANS) and some results from direct nonradiative energy transfer (DET), for the observation of the diffusion coefficients of polystyrene chains at latex interfaces. To compare SANS with DET, doubly labeled polystyrene with deuterium and fluorescence groups were synthesized, showing that while SANS and DET produce comparable data in terms of diffusion coefficients, both results differ in detail, each having their own advantages. Chain confinement, ionic end groups, and short branch effects on interdiffusion were studied. Large polymer chains confined in small particles have non‐Gaussian shapes that store rubber elastic energy. Rapid, non‐diffusion relaxation is inhibited because the density would be required to become less than normal. Hence confinement effects on the diffusion rate are not significant. Using the DET method, ionic end‐groups were found to increase the early‐time apparent interdiffusion coefficients during film formation. The early‐time apparent diffusion coefficients of polystyrene with varying end‐groups were found to increase as follows: The higher apparent diffusion coefficients of the chains with ionic groups are presumably due to a surface segregation of the end‐groups caused by the polar, aqueous environment during latex synthesis. The interdiffusion behavior of sulfite‐ended polystyrene (M_n ? 300 000 g/mol) with H‐ends, one sulfite end, and two sulfite ends were compared via SANS and DET. The diffusion coefficients of polystyrene with one or two sulfite end groups were five times and ten times lower than that of polystyrene, respectively. The ionic end group effects on the reduced diffusion coefficients are interpreted as the competition between enhancement by the surface segregation of end groups and reduction by end group aggregation. Noting that sulfate end groups diffused faster, while sulfite end groups diffused slower, the effect is complex, and not yet fully resolved. Diffusion coefficients of polystyrene with branches were studied by DET. Short branches work to decrease the T_g and hence increase the diffusion coefficients. However, after the experimental temperature, T, is converted to a normalized temperature, T‐T_g, the diffusion coefficients are found to be almost independent upon the number of branches and the length of branches. The branch length ranged from one‐carbon to 40 carbons. Side chains of entanglement molecular weight or longer may be required to significantly reduce the diffusion coefficient. Copyright © 2002 John Wiley & Sons, Ltd.     

The equatorial small‐angle scattering during the straining of poly(ether ester) and its analysis

A method for the quantitative analysis of two‐dimensional (2D) small‐angle X‐ray scattering (SAXS) patterns with fiber symmetry by successive information filtering is proposed and applied to a series of images recorded during a straining experiment of a two‐phase polymer sample at a synchrotron beamline. The studied equatorial scattering is similar to the frequently discussed void scattering, but originates from an ensemble of rodlike soft domains (needles) in the sample, orientated in the direction of strain. The intensity is extracted and projected onto the equatorial plane, the ideal two‐phase structure is extracted, and the 2D chord distribution is computed. This curve describes a 2D two‐phase morphology made from needle cross‐sections embedded in matrix material. Because interparticular correlation is found to be weak in the chord distribution, pure particle scattering is assumed. Modeling the needle cross‐sections by circular disks leads to a simple theory, which allows the deconvolution of a disk diameter distribution from the chord distribution. It is shown how parameters of the disk diameter distribution can be computed without deconvolution. For the selected poly(ether ester) thermoplastic elastomer the study of the soft domain needles indicates strain‐induced hardening. While for low elongation ϵ the soft needles are more compressible than the microfibrillar matrix, saturation is observed for ϵ > 2.5. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 975–981, 1999     

Microwave‐assisted suzuki coupling reaction for rapid synthesis of conjugated polymer–poly(9,9‐dihexylfluorene)s as an example

Long reaction period (dozens of hours) is often required for the synthesis of conjugated polymers by palladium‐catalyzed Suzuki polymerization reaction. This work shows that microwave can accelerate Suzuki polymerization to realize the ultra‐rapid synthesis of conjugated polymers, here poly(9,9‐dihexylfluorene)s (PDHFs) as an example. The effects of reaction conditions on the polymerization have been systematically investigated, including the mode of microwave irradiation, microwave power, reaction temperature, reaction time, solvents, catalyst species, and catalyst concentrations. Compared with the conventional heating method (oil bath) for the synthesis of PDHFs (48 h, M_w = 20,000 g/mol), Suzuki polymerization under optimized microwave condition can yield PDHFs with higher molecular weight (M_w = 40,000 g/mol) in a much shorter time (14 min). The structures of obtained PDHFs samples are fully characterized spectroscopically, demonstrating well‐defined PDHFs have been prepared through microwave‐assisted (MA) Suzuki polymerization reaction. In addition, the mechanism of MA Suzuki polymerization is proposed preliminarily. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Multivariable structural characterization of semicrystalline polymer blends by small‐angle light scattering

A new multi‐variable‐measurement approach for characterizing and correlating the nanoscale and microscale morphology of crystal‐amorphous polymer blends with melt‐phase behavior is described. A vertical small‐angle light scattering (SALS) instrument optimized for examining the scattering and light transmitted from structures ranging from 0.5 to 50 μm, thereby spanning the size range characteristic of the initial‐to‐late stages of thermal‐phase transitions (e.g., melt‐phase separation and crystallization) in crystal‐amorphous polymer blends, was constructed. The SALS instrument was interfaced with differential scanning calorimetry (DSC), and simultaneous SALS/DSC/transmission measurements were performed. We show that the measurement of transmitted light and SALS under H_V (cross‐polarized) optical alignments during melting can be used to reliably measure the thermodynamic (e.g., crystal melting and melt‐phase separation temperatures) and structural variables (e.g., crystalline fraction within the superstructures and volume fraction of superstructures) necessary for describing the multiphase behavior of crystal‐amorphous blends in one combined measurement. We also evaluate the orientation correlations of crystalline volume elements within the superstructures. Our results indicate that simultaneous measurement of transmitted light can provide a reliable estimate of the total scattering from density and orientation fluctuations and the melt‐phase separation temperature of polymer blends. For solution‐cast poly(?‐caprolactone)/poly(D,L‐lactic acid) blends, our multivariable measurements during melting provide the parameters necessary to generate a crystal–liquid and liquid–liquid phase diagram and characterize the solid‐state morphology. This opens up the challenge to explore use of our vertical SALS instrument as a rapid and convenient method for developing structure–property relationships for crystal‐amorphous polymer blends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2714–2727, 2002     

凝胶色谱法测定顺丁橡胶平均分子量及其分布的研究

通过一系列的条件试验,包括样品浓度、样品量及流动相流速对柱效的影响,确定了最佳的凝胶色谱（ＧＰＣ）试验条件;采用普适校正法将聚苯乙烯（ＰＳ）标定曲线转换成顺丁橡胶（ＰＢ）标定曲线,并对Ｍａｒｋ－Ｈｏｕｗｉｎｋ方程式中Ｋ,α值的选择进行了讨论;采用４种分子量加宽方程对色谱柱加宽效应进行改正计算,通过比较,选定适合本试验系统的加宽效应的改正方法;用粘度法测得的顺丁橡胶特性粘度（η）吻合ＧＰＣ所测得特性粘度值,证明了方法的可靠性。     

Characterization of novel optically active conjugated polyarylenes and poly(aryleneethnylene)s by a combination of off-line static and dynamic light scattering with gel permeation chromatography

By combining the offline static and dynamic laser light scattering (LLS) and gel permeation chromatography (GPC) results of a broadly distributed polymer sample, we were able to characterize a series of chiral binaphthyl-based polyarylenes and poly(aryleneethnylene)s in THF at 25°C. For each of the samples, we obtained not only the weight-average molar mass M_w, the second virial coefficient A₂ and the z-average translational diffusion coefficient 〈D〉, but also two calibrations: V = A + Blog(M) and D = k_D M^−αD, where V, D, and M are the elution volume, the translational diffusion coefficient and the molar mass for monodisperse polymer chains, respectively, and A, B, k_D, and α_D are four calibration constants. Using these calibrations, we estimated the molar mass distributions of these novel polymers. We showed that using polystyrene to calibrate the GPC columns could lead to a smaller M_w. Our results indicate that all the polymers studied have a rigid chain conformation in THF at 25°C and the introduction of the —NO₂ groups into the monomer can greatly promote the polymer solubility in THF.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2615–2622, 1998     

Small‐angle neutron scattering analysis of bottlebrush backbone and side chain flexibility

Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are determined through small‐angle neutron scattering analysis of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a “grafting‐through” ring‐opening polymerization. Scattering profiles are modeled with the empirical Guinier–Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end‐to‐end distance proportional to N^0.55, while the overall bottlebrush increases in size proportional to N^0.77. These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in solution. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 104–111     

Crystallization and chain conformation of semicrystalline and amorphous polymer blends studied by wide‐angle and small‐angle scattering

We examine the crystallization and chain conformation behavior of semicrystalline poly(ethylene oxide) (PEO) and amorphous poly(vinyl acetate) (PVAc) mixtures with wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and small‐angle neutron scattering (SANS) experiments. For blends with PEO weight fractions (wt_PEO) greater than or equal to 0.3, below the melting point of PEO, the WAXD patterns reveal that crystalline PEO belongs to the monoclinic system. The unit‐cell parameters are independent of wt_PEO. However, the bulk crystallinity determined from WAXD decreases as wt_PEO decreases. The scattered intensities from SAXS experiments show that the systems form an ordered crystalline/amorphous lamellar structure. In a combination of WAXD and SAXS analysis, the related morphological parameters are assigned correctly. With the addition of amorphous PVAc, both the average amorphous layer thickness and long spacing increase, whereas the average crystalline layer thickness decreases. We find that a two‐phase analysis of the correlation function from SAXS, in which the scattering invariant is linearly proportional to the volume fraction of lamellar stacks, describes quantitatively the crystallization behavior of PEO in the presence of PVAc. When wt_PEO is close to 1, the samples are fully spaced‐filled with lamellar stacks. As wt_PEO decreases from 1.0 to 0.3, more PVAc chains are excluded from the interlamellar region into the interfibrillar region. The fraction outside the lamellar stacks, which is completely occupied with PVAc chains, increases from 0 to 58%. Because the radius of gyration of PVAc with a random‐coil configuration determined from SANS is smaller than the average amorphous layer thickness from SAXS, we believe that the amorphous PVAc chains still persist with a random‐coil configuration even when the blends form an ordered structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2705–2715, 2001     

Synthesis and characterization of poly(L‐lactide)s and poly(D‐lactide)s of controlled molecular weight

High molecular weight poly(L ‐lactide)s (PLLAs) and poly(D ‐lactide)s (PDLAs) were synthesized in toluene at 70 °C by ring‐opening polymerization of optically pure L ‐lactide and D ‐lactide, using tin(II) 2‐ethylhexanoate (SnOct₂) and 2‐(2‐methoxyethoxy)ethanol as initiator and coinitiator, respectively. Under these conditions, polarimetry as well as ¹³C NMR spectroscopy indicated that the synthesized poly(lactide)s (PLAs) are more than 99% isotactic. The molecular weight was successfully controlled by adjusting the monomer‐to‐initiator molar ratio. Gel permeation chromatography and MALDI‐TOF mass spectrometry analyses showed that the polydispersity index of the PLAs is below 1.1. Moreover, MALDI‐TOF spectra showed two different chain distributions, one characterized by an even number of lactic acid repeat units and the other by an odd number of lactic acid repeat units. The second distribution, indicative of the presence of intermolecular transesterification reactions, appears at the very beginning of the polymerization and its intensity increases with the polymerization time. Finally, a reversible reaction kinetic model was used to determine the monomer equilibrium concentration ([M]_eq = 1.4 ± 0.5%) and the propagation rate constant (k_p = 14.4 ± 0.5 L mol^?1 h^?1) of the polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1944–1955, 2007     

Central small‐angle diffuse scattering from fibers is made of two components

Small‐angle X‐ray and neutron scattering from materials with fibrous texture generally includes a central diffuse scattering that is either diamond‐shaped or shaped like a two‐bladed propeller. The central scattering from fibers of polyacrylonitrile, nylon, and poly(ethylene terephthalate) and in particular the changes seen during deformation and heating have been examined. The result is that all types of central scattering from fibers are best described as having two distinct components, where these components are an extended equatorial streak and an inner nearly isotropic scattering. They arise respectively from objects that do and do not become aligned or elongated during fiber production. Examples of objects that do not become aligned are small spherical voids and solid particles. Objects that do become aligned include internal phase boundaries, and the surfaces of the fibers themselves. The equatorial streak arises from an assembly of such elongated objects preferentially oriented along the fiber axis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Ethylene polymerization reactions with multicenter Ziegler‐Natta catalysts—Manipulation of active center distribution

This article describes ethylene/1‐hexene copolymerization reactions with a supported titanium‐based, multicenter Ziegler‐Natta catalyst. The catalyst was modified by pretreating its solid precursor with AlEt₂Cl and with similar organoaluminum chlorides, Al₂Et₃Cl₃, AlEtCl₂, and AlMe₂Cl. Testing of the untreated and the pretreated catalysts in copolymerization reactions under standard reaction conditions demonstrated that the modifying agents produce two changes in the catalyst. First, the pretreatment significantly reduces the reactivity of active centers that produce high molecular weight, highly crystalline copolymer components with a low 1‐hexene content. Second, the pretreatment noticeably increases the reactivity of active centers that produce low molecular weight copolymer components with a high 1‐hexene content. The first effect is caused by Lewis acid‐base interactions of the modifiers with the active centers, whereas the second (activating) effect is due to the removal of catalyst poisons (organosilicon compounds generated in the process of the catalyst synthesis) by AlEt₂Cl. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4219–4229, 2010     

Synthesis and characterization of arborescent (hyperbranched) polyisobutylenes from the 4‐(1,2‐oxirane‐isopropyl)styrene inimer

The synthesis of the novel inimer (initiator‐monomer) 4‐(1,2‐oxirane‐isopropyl)styrene EPOIM and the copolymerization of this inimer with isobutylene (IB) to form arborescent polyisobutylene (PIB) is described. Polymerizations were accomplished by use of TiCl₄ coinitiator and the effect of reaction conditions was investigated. Size exclusion chromatography (SEC) was used demonstrate EPOIM incorporation across the whole molecular weight distribution. The average number of branch points (B) per chain measured by use of selective link destruction increased with increasing EPOIM/IB ratio and decreased with [TiCl₄]. Large scale polymerizations were carried out based on results from small scale polymerizations. Architecture analysis carried out through use of branching parameters based on the radii of gyration R_g and hydrodynamic radii R_h measured by multidetector SEC corroborated the proposed arborescent architecture. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5847–5856, 2007     

Characterization of Polymers by Liquid Chromatography

Liquid chromatography (LC) is well established for the comprehensive characterization of complex macromolecules with multiple distributions. Hyphenated chromatographic methods in their various forms are currently one of the most promising and powerful methods for the fractionation and characterization of complex sample mixtures in different property coordinates. Modern detector technologies open up new ways to investigate various properties with high sensitivity even in the low concentration ranges used in chromatography. This paper discusses possibilities and applications for the advanced characterization of macromolecules.     

Solution properties of poly(dimethyl siloxane)

The solution properties of poly(dimethyl siloxane) (PDMS) were studied with light scattering (LS), gel permeation chromatography/light scattering (GPC/LS), and viscometry methods. PDMS samples were fractionated, and the weight‐average molecular weights, second virial coefficient, and the z‐average radius of gyration of each fraction were found according to the Zimm method with the LS technique. In this work, the molecular weight range studied was 7.5 × 10⁴ to 8.0 × 10⁵. Molecular weights and molecular weight distributions were determined by GPC/LS. The intrinsic viscosities of these fractions were studied in toluene at 30 °C, in methyl ethyl ketone (MEK) at 20 °C, and in bromocyclohexane (BCH) at 26 °C and 28 °C. The Mark–Houwink–Sakurada relationship showed that toluene was a good solvent, and MEK at 20 °C and BCH at 28 °C were θ solvents for PDMS. The unperturbed dimensions were calculated with LS and intrinsic viscosity data. The unperturbed dimensions, expressed in terms of the characteristic ratio, were found to be 6.66 with different extrapolation methods in toluene at 30 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2678–2686, 2000     

Solution characterization of the novel organometallic polymer poly(ferrocenyldimethylsilane)

A series of four well‐defined poly(ferrocenyldimethylsilane) (PFS) samples spanning a molecular weight range of approximately 10,000–100,000 g mol⁻¹ was synthesized by the living anionic polymerization of dimethyl[1]silaferrocenophane initiated with n‐BuLi. The polymers possessed narrow polydispersities and were used to characterize the solution behavior of PFS in tetrahydrofuran (THF). The weight‐average molecular weights (M_w ) of the polymers were determined by low‐angle laser light scattering (LALLS), conventional gel permeation chromatography (GPC), and GPC equipped with a triple detector (refractive index, light scattering, and viscosity). The molecular weight calculated by conventional GPC, with polystyrene standards, underestimated the true value in comparison with LALLS and GPC with the triple detection system. The Mark–Houwink parameter a for PFS in THF was 0.62 (k = 2.5 × 10⁻⁴), which is indicative of fairly marginal polymer–solvent interactions. The scaling exponent between the radius of gyration and M_w was 0.54, also consistent with marginal polymer–solvent interactions for PFS in THF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3032–3041, 2000     

Small‐angle x‐ray scattering study of thermoreversible poly(vinyl chloride) gels

Poly(vinyl chloride) (PVC)/bis(2‐ethylhexyl)phthalate (DOP) gels were prepared at room temperature from tetrahydrofuran solutions of PVC and DOP. PVC/DOP gels of different molecular weights at various PVC concentrations (c) were investigated with small‐angle X‐ray scattering (SAXS). The mean distance between two neighboring inhomogeneities (D) and two characteristic lengths, the intrainhomogeneity distance (d₁) and interinhomogeneity distance (d₂), were evaluated from Bragg's law and the distance distribution function, respectively. Both D and d₂ can be expressed by a power‐law relation (e.g., D and d₂ ∝ c^?0.5). After a period of rapid cooling to 25 °C from the sol state, the structural evolution was examined with time‐resolved SAXS measurements. An Avrami analysis with the SAXS invariant data revealed that the growth kinetics of PVC/DOP gels was one‐dimensional growth from predetermined nuclei, regardless of c. These results suggest that the PVC/DOP gels are constructed from a fibrillar structure that forms gel structures at high concentrations or low temperatures. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2340–2350, 2001     

Capillary flow behavior of worm‐like micelles studied by small‐angle X‐ray scattering and small angle light scattering

A novel capillary flow device has been developed and applied to study the orientation of worm‐like micelles, among other systems. Small‐angle X‐ray scattering (SAXS) data from micelles formed by a Pluronic block copolymer in aqueous salt solution provides evidence for the formation of worm‐like micelles, which align under flow. A transition from a rod‐like form factor to a less persistent conformation is observed under flow. Flow alignment of worm‐like micelles formed by the low molar mass amphiphile system cetyl pyridinium chloride+sodium salicylate is studied for comparative purposes. Here, inhomogenous flow at the micron scale is revealed by streaks in the small‐angle light scattering pattern perpendicular to the flow direction. Copyright © 2006 John Wiley & Sons, Ltd.