J. S. Lin

The gamma phase of high-molecular-weight polypropylene: 1. Morphological aspects

Abstract A high-molecular-weight polypropylene ( M w = 83000, M w M n = 3.0 ) has been crystallized isothermally as a function of pressure at a constant supercooling of 50°C. Wide-angle X-ray diffraction (WAXD) shows that the X-ray diffraction spectrum of the γ phase is identical to that reported for low-molecular-weight polymers, with the exception that the peaks are broader. Calculations of the γ content using WAXD show the nearly 100% γ phase is formed at 2 k bar, but a mixture of γ and α crystals are formed at lower crystallization pressures. Small-angle X-ray scattering (SAXS) studies show that γ lamellae are approximately one-half the thickness of α lamellae produced at an equivalent supercooling. Morphological studies conducted using transmission electron microscopy of carbon replicas of permanganically etched surfaces confirm the thin nature of the lamellae and demonstrate their inherent waviness. Unlike α crystals, γ lamellae do not form cross-hatched textures. A model is proposed, involving γ α lamellae and epitaxy during the growth process, to account for all the observable morphological data.

Crystallization induced microstructure of crystalline/crystalline poly(vinylidenefluoride)/poly(3-hydroxybutyrate) blends probed by small angle X-ray scattering

Abstract The lamellar morphology of a melt-miscible blend consisting of two crystalline constituents, poly(vinylidene fluoride) (PVDF) and poly(3-hydroxybutyrate) (PHB), has been investigated by small angle X-ray scattering (SAXS). Owing to the proximity of melting points, PVDF and PHB crystallized over essentially the same temperature range, and consequently created a crystalline/crystalline state with the morphology characterized by the spatial arrangement of PVDF and PHB lamellae. Irrespective of the crystallization temperatures ( T c ), the SAXS patterns revealed the presences of two lamellar stack (LS) domains, where one contained mainly PVDF lamellae (PVDF LS domain) and the other primarily consisted of PHB lamellae (PHB LS domain). The interlamellar (IL) regions of both LS domains were found to contain mixed amorphous PVDF and PHB. The blends crystallized at higher T c exhibited smaller SAXS invariants. This observed T c dependence was connected with the disparity in crystallization kinetics that gave rise to different LS domain sizes at different T c s.

Crystalline memory effect in isothermal crystallization of syndiotactic polypropylenes: effect of fusion temperature on crystallization and melting behavior

In this manuscript, studies on the crystalline memory effect in syndiotactic polypropylene (s-PP) were focused on the effect of prior melt annealing on the subsequent isothermal crystallization kinetics, crystalline structure, lamellar morphology, and subsequent melting behavior using a combination of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS) techniques. On partial melting, choices of the fusion temperature used to melt the samples played an important role in determining the overall rate of isothermal crystallization, while they had no effect on the resulting values of the apparent crystallinity content, the long period, the lamellar thickness, and the low-melting peak temperature.

X-ray scattering studies of thin films of photosensitive polyimides

Abstract Using the techniques of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS), the morphology of polyimide thin films thermally imidized from several photosensitive polyimide (PSPI) precursors has been investigated and compared with that of the thin films prepared from the corresponding poly(amic acid) precursors: poly(4,4′-oxydiphenylene pyromellitimide) (PMDA-ODA), poly( p -phenylene biphenyltetracarboximide) (BPDA-PDA) and poly(4,4′-oxydiphenylene benzophenonetetracarboximide) (BTDA-ODA). The WAXD results indicate that regardless of the precursor origin, the BTDA-ODA polyimide is amorphous, whereas the other polyimides exhibit a molecular order. For both the PMDA-ODA and the BPDA-PDA, the molecular order is relatively higher in the films prepared from the PSPI precursors than in those from the corresponding poly(amic acid)s, indicating that during thermal imidization, the photosensitive groups play an important role to improve the mobility of the polymer chains, which may be critically needed to make better molecular packing, in spite of their bulkiness having the potential to hinder the molecular packing. In Lorentz-corrected SAXS analyses, a long period (130–156 A mean periodicity) was observed for all the polyimides except the PMDA-ODA. In particular, the microstructure in the BPDA-PDA could be described by an extended chain-based two-phase (ordered and less ordered phase) model with diffuse boundaries because of its high chain rigidity. In addition, the Guinier SAXS analyses indicate the presence of voids in all the polyimide films, regardless of the precursor origin. The size of voids was 251–349 A in radius, depending upon the type of polyimide.

Measurements of single chain form factors by small-angle neutron scattering from polystyrene blends containing high concentrations of labelled molecules☆

Abstract A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow.

Morphology and ordering behavior of a poly(styrene)-b-poly(ferrocenyldimethylsilane) diblock copolymer

Abstract The thermal behavior and morphology of a diblock copolymer of polystyrene and poly(ferrocenyldimethylsilane) (PFS) ( M n =36 000, φ PS =0.308) have been surveyed using small angle X-ray scattering and transmission electron microscopy. As cast films are partly crystalline. The crystal structure is seriously perturbed by the propensity of the molecules to microphase segregation. After annealing above the glass transition temperature of polystyrene both crystallization and definition of the microphase separated domains are improved. The system forms an ordered microphase segregated structure once annealed above the melting temperature of the PFS block. Even then both cylindrical and spherical morphologies are observed and annealing times of a few days do not force the system to develop the long range order generally associated with carefully annealed polystyrene- b -polydiene polymers of comparable molecular weight.

Small-angle X-ray scattering studies of crystallization in crosslinked linear polyethylene

Abstract The results of a comprehensive small-angle X-ray scattering study of linear polyethylene crosslinked using a peroxide have been combined with a study of the crystallization kinetics to obtain a generalized picture of the effects of limited mobility and comonomer content on crystallization. It is shown that there are three regions of behaviour: (i) an initial region in which the crosslinks are soluble in the crystal to a certain limiting composition; (ii) a region in which the lamellar thickness decreases in a continuous manner with increasing crosslink density; and (iii) a region where the lamellar thickness is virtually independent of crosslink density. The results are interpreted using the Sanchez-Eby theory, the Andrews theory and regime theory to generate a comprehensive description of the behaviour.

Isothermal melt crystallization and melting behaviour of syndiotactic polypropylene

The lamellar morphological information and subsequent melting behaviour of syndiotactic polypropylene (s-PP) samples isothermally crystallized at crystallization temperatures ranging from 30 to 95 °C have been investigated using a combination of wide-angle X-ray diffraction (WAXD), small- angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) techniques. Three known methods for determining the equilibrium melting temperature Tm °, namely the Gibbs-Thomson extrapolation, the linear Hoffman-Weeks extrapolation and the non-linear Hoffman-Weeks extra- polation, have been employed to evaluate this important thermodynamic parameter, and the results obtained are compared. Finally, an estimate of the equilibrium melting temperature for a perfect s-PP sample (T m °) 100% is given. # 2000 Society of Chemical Industry

Microphase-separated poly(styrene-b-isoprene)n multiblock copolymers with constant block lengths

Abstract Linear multiblock copolymers, like their diblock analogues, are capable of ordering into periodic microstructures when the blocks are sufficiently incompatible. In this work, a series of four linear poly(styrene-b-isoprene)n (SI)n (1 ≤ n ≤ 4) multiblock copolymers with nearly equal block lengths has been synthesized via living sequential anionic polymerization. All of the copolymers are microphase-separated, as discerned by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), and exhibit lamellar morphologies in which the microdomain periodicity decreases with n. This behaviour suggests that the middle blocks contract the microdomains along the lamellar normal. Microstructural characteristics are compared with predictions from formalisms proposed for linear multiblock copolymers and, along with conformational considerations, are used to interpret the thermal and tensile properties of the copolymers.

The National Center for Small-Angle Scattering Research

The National Center for Small-Angle Scattering Research is a user-dedicated facility supported by the National Science Foundation and the Department of Energy under an interagency agreement. The two main facilities available to users are the NSF constructed 30-m small-angle neutron scattering instrument (SANS) and the 10-m DOE constructed small-angle x-ray scattering camera (SAXS). Test measurements carried out on ATPase in H2O and in D2O buffer indicate that the SANS facility is capable of providing meaningful data on a wide variety of biological systems. Details of work carried out on the instrument by Uberbacher, Olins, and Bunick, on the binding of HMG proteins to nucleosomes, are presented in a separate poster. (Research sponsored by the National Science Foundation under interagency agreement No. 40-637-77 under Union Carbide Corporation contract W-7405-ENG-26 with the U.S. Department of Energy.)