Time-resolved ultra-small-angle X-ray scattering beamline(BL10U1)at SSRF

The construction of a new beamline,BL10U1,was completed at the Shanghai synchrotron radiation facility in 2020.This multipurpose beamline was designed to provide X-ray scattering techniques such as ultra-small-angle X-ray scattering(USAXS),small-angle X-ray scattering(SAXS),wide-angle X-ray scattering,and microfocus SAXS(μSAXS)for a broad user community.To realize fast time-resolved USAXS experiments,the beamline adopted an in-vacuum undulator with a total length of 1.6 m as the photon source.An in-house cryogenic-cooled double multilayer monochromator was installed to deliver a photon flux of approximately 10^(13) photons/s at a photon energy of 10 keV.The three-year successful operation of this beamline demonstrated that the monochromator operated smoothly,as expected.BL10U1 has three end stations in succession:USAXS end station,μSAXS end station,and end station for industrial applications.The minimum scattering vector q~0.0042 nm^(-1) at 10 keV can be achieved at the USAXS end station equipped with a 28 m-long and 1.8 m-diameter vacuum flight tube.At theμSAXS end station,a beam spot of less than 10×8μm was achieved for micro-SAXS experiments.In contrast,in situ experimental instruments up to 5 m high and 8 m wide can be mounted at the industrial application end station,which offers industrial scientists the opportunity to use their large industrial equipment.BL10U1 opens up a new capability to investigate phenomena such as non-equilibrium and dynamic processes of materials with a wide length scale from angstroms to micrometers with millisecond time resolution.In this paper,we also report beamline design considerations and commissioning results.

STUDIES ON THE NATURE OF THE MACROMOLECULAR CONDENSED STATE OF "NASCENT" ULTRA HIGH MOLAR MASS POLYETHYLENE

Ultra high molar mass polyethylene(UHPE)powder as polymerized in a slurry process has been studied,in its nascent state,after recrystallization on rapid cooling from the melt and after hot compression molding to a film,by DSC,effect of annealing the recrystallized specimen at 120 similar to 130 degreesC,morphology by polarizing optical microscopy and small angle X-ray scattering.Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains,involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers.On melting,a nematic rubbery state of nanometer size domain resulted.The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC,possibly higher than 300 ℃,the exact temperature is however not sue because of chain degradation at such high temperatures.The recrystallization process from the melt is a crystallization from a nematic rubbery state.The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity.The remelting peak temperature could be returned close to that of the nascent state by annealing at 120~130 ℃.

Temperature-induced Evolution of Micro-structure and Chain Dynamics in Thermoplastic Polyurethane with Low Hard Segment Content as Studied by In Situ Synchrotron SAXS and Time-Domain NMR Experiments

The microstructural evolution of a thermoplastic polyurethane(TPU)with low hard segment content has been monitored utilizing in situ real-time synchrotron small angle X-ray scattering(SAXS)and time-domain nuclear magnetic resonance(NMR)measurements.The TPU is composed of 23 wt% of[4,4-methylenediphenyl diisocyanate(MDI)]-[1,4-butanediol(BD)]chain segments,which form hard domains,as[polytetrahydrofuran(PTHF)]forming soft domains.The number and distribution of monomer units in hard blocks is determined by the successive self-nucleation and annealing thermal fractionation technique.In situ SAXS method reveals heating-induced increase in the spacing of hard and soft domains,while time-domain ^(1)H-NMR characterizes the changes in the phase composition and chain dynamics in these domains.A glassy fraction of short MDI-BD chain segments in hard domains passes through T_(g) above ambient temperature.At higher temperatures,MDI-BD nanocrystals start to melt.Sequence length distribution of MDI-BD chain segments causes a distribution in crystal sizes and wide melting temperature range.The melting is accompanied by the mixing of MDI-BD with PTHF segments in soft domains,and by increase in segmental mobility in these domains.Above 180℃,the TPU melt is homogeneous on the scale above nanometers according to SAXS data.

Initiation, Development and Stabilization of Cavities during Tensile Deformation of Semicrystalline Polymers

By using polybutene-1 as a typical example, we illustrate the initiation, development and stabilization of cavities in the sample during tensile deformation. Samples with the same crystallinity, long spacing and crystalline lamellar thickness but very different sizes of spherulites were prepared via changing the melt history. Dimension of cavities during stretching the samples was determined by in situ ultra small angle X-ray scattering techniques. It turned out that the size of the cavities was bigger in the sample with larger spherulites than the one with smaller spherulites. The results show clear evidence of initiating cavities within crystalline phase at the grain-boundary of crystalline blocks, growing of cavities passing through parallel stacked lamellar crystals and amorphous layers and finally stablized by tilted lamellae at both ends of the plate-like cavities within the spherulites.

中国改革开放以来的高分子物理和表征研究

本综述介绍了改革开放四十多年来中国大陆学者在高分子物理和表征领域所取得的部分成就.按照时间顺序,分别从概念的突破、理论的发展和技术的创新三个方面选取具有代表性研究成果进行简短的介绍,以期展示当代中国学者在这一基础研究领域所表现出来的拼搏意志和创新精神,激励新一代学者共同努力,勇攀科学高峰,为国民经济和社会发展作出更大的贡献.

Fractionation of Polyolefin Elastomer by a Modified SSA Technique

As an important part of semicrystalline polymer materials,polyolefin elastomers are widely used,and the in-depth analysis of their molecular chain structure information is of great significance to promote their rapid development.We show in this work an effort in characterizing a commercial polyolefin elastomer of ethylene/1-octene copolymer by a modified successive self-nucleation and annealing(SSA)technique.A small amount of linear polyethylene was blended with the ethylene/1-octene copolymer serving as nucleation agent during SSA.It turned out that a tiny fraction of linear polyethylene can significantly promote the crystallization of the copolymer during cooling from different annealing temperatures and increase the melting temperature of the fractions so that providing apparent methylene sequence length much closer to the real value than obtained by traditional SSA technique.

PHASE BEHAVIOR OF CHARGE STABLIZED COLLOID DISPERSION WITH ADDED WATER SOLUBLE POLYMERS

Demixing and colloidal crystallization in the mixture of charge stabilized colloidal poly（methyl methacrylate） particles and soluble poly（ethylene oxide） were investigated by means of synchrotron small-angle X-ray scattering （SAXS） technique. Phase diagram of the mixture was obtained based on visual inspection and SAXS results. The phase behavior is determined as a function of the concentration of the polymer as well as the volume fraction of the colloidal particles. The system shows a one phase region when the concentration of the polymer is low, whereas a two-phase region is present when the concentration of the polymer is larger than a critical concentration at certain volume fraction of the colloids. Interestingly, a face centered cubic colloidal crystalline structure was formed under certain conditions, which has been rarely observed in experiments of colloid-polymer mixtures with competing interactions.

Preparation and Properties of High-performance Polyimide Copolymer Fibers Derived from 5-Amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole

A series of polyamic acid copolymers(co-PAAs) with para-hydroxyl groups was synthesized using two diamine monomers,namely p-phenylenediamine(p-PDA) and 5-amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole(m-pHBOA), of different molar ratios through copolymerization with 3,3′,4,4′-biphenyltetracarboxylic dianhydride(BPDA) in N,N-dimethyacetamine(DMAc). The co-PAA solutions were used to fabricate fibers by dry-jet wet spinning, and thermal imidization was conducted to obtain polyimide copolymer(coPI) fibers. The effects of the m-pHBOA moiety on molecular packing and physical properties of the prepared fibers were investigated.Fourier transform infrared(FTIR) spectroscopic results confirmed that intra/intermolecular hydrogen bonds originated from the hydroxyl group and the nitrogen atom of the benzoxazole group and/or the hydroxyl group and the oxygen atom of the carbonyl group of cyclic imide. As-prepared PI fibers displayed homogenous and smooth surface and uniform diameter. The glass transition temperatures(Tgs) of PI fibers were within 311-337 °C. The polyimide fibers showed 5% weight loss temperature(T5%) at above 510 °C in air. Twodimensional wide-angle X-ray diffraction(WXRD) patterns indicated that the homo-PI and co-PI fibers presented regularly arranged polymer chains along the fiber axial direction. The ordered molecular packing along the transversal direction was destroyed by introducing the m-pHBOA moiety. Moreover, the crystallinity and orientation factors increased with increasing draw ratio. Small-angle X-ray scattering(SAXS) results showed that it is beneficial to reduce defects in the fibers by increasing the draw ratio. The resultant PI fibers exhibited excellent mechanical properties with fracture strength and initial modulus of 2.48 and 89.73 GPa, respectively, when the molar ratio of p-PDA/m-pHBOA was 5/5 and the draw ratio was 3.0.

Limited Fraction of Crystallized Side Chains in Bottlebrush Poly(n-alkyl methacrylate)s

Crystallinity of bottlebrush polymers due to side chain crystallization has been considered to be related to the length of the side chains only under the assumption of complete participation of crystallization by all sidechains.Recent experimental results revealed that in poly(n-alkyl methacrylate)s a fraction of side chains could not crystallize due to constraints imposed by the trapped main chain entanglements and required expansi on of main chain-main chain distanee.This result renders the original simplified con sideration of the origin of crystallinity in bottlebrush polymers questionable.In this work,we introduce a new parameter f_(c),the fraction of crystallizable side chains,to better describe the crystallinity of bottlebrush polymers.A lin earrelati on ship between the meltingenthalpy and the number of alkyl groups in side chains for bottlebrush polymers reported repeatedly indicates that f_(c) remains essentially unchanged when bottlebrush polymers had the same main chain structure and grafting degree but different side chain lengths.The slope of the above-mentioned linear relationship is thus △H_(CH2)xf_(c),where △H_(CH2) stands for the melting enthalpy of one mole alkyl group packed into the crystal.With a known value of f_(c),it is possible to estimate the value of △H_(CH_(2)).In case of poly(n-alkyl methacrylate)s,we estimated △H_(CH_(2)) of hexagonal crystal being at most 5.74 kJ/mol with the knowledge of possibly smallest f_(c) of 0.67 obtained from small angle X-ray scattering data.Therefore,the crystallinity of bottlebrush polymer would be calculated based on the equati on X_(c)=f_(c)×N_(c)/N with N and N_(c) being the nu mber of alkyl groups in a side chain and those packed in the crystalline structure,respectively.Both chemical structure and grafting degree of bottlebrush polymers affect f_(c).

Advantage of Preserving Bi-orientation Structure of Isotactic Polypropylene through Die Drawing

The isotactic polypropylene(iPP) usually shows a unique parent-daughter lamellae structure in which the parent and daughter lamellae are against each other with a near perpendicular angle(80° or 100°). Inducing a high fraction of oriented cross-hatched structure in iPP during processing is desirable for designing the bi-oriented iPP products. We processed a commercial iPP via tensile-stretching and die-drawing to evaluate the structural evolution of oriented parent-daughter lamellae. It turned out that the die-drawing process had an advantage in attaining a high fraction of oriented cross-hatched structure of iPP, as compared to the free tensile stretching. Besides, the presence of α-nucleating agents affected the formation of oriented parent-daughter lamellae in the die-drawn samples whereas such influence diminished in the free stretched ones. It was found that the confined deformation inside the die led to the well-preserved oriented cross-hatched structure in the die-drawn iPP.

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene γ Form

The crystallization behavior of syndiotactic polystyrene（s PS） γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl＇s crystallization theory. On the basis of the differential scanning calorimetric results, it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness, which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization. Further temperature dependent small-angle X-ray scattering（SAXS） measurement revealed the evolution of the γ form lamellae upon heating until phase transition, involving three different regimes： lamellae stable region（25-90 °C）, melt-recrystallization region（90-185 °C） and pre-phase transition region（185-195 °C）. As a result, recrystallization line, equilibrium recrystallization line and melting line were developed for the s PS γ form crystallization process. Since the melt of γ form involved a γ-to-α/β form phase transition, the melting line was also denoted as the phase transition line in this special case. Therefore, the equilibrium crystallization temperature and melting（phase transition） temperatures were determined at around 390 and 220 °C on the basis of the thermodynamic phase diagram of the s PS γ form.