Polyethylene WAXS measurements

Since the solid-state structure formed in block copolymers with homogeneous melts is driven by crystallization, the kinetics of lamellar-scale structure formation might be expected to parallel those of crystallization at the unit-cell level. In the same poly(ethylene-6-(ethylene- / -propylene)) diblock copolymer system, the time evolution of the copolymer crystallinity calculated based on the observed SAXS peaks, as illustrated in Figure 11.16, overlaps with that calculated based on the WAXS data. Since SAXS measures the development of diblock copolymer microstructure on the tens-of-nanometers scale, while WAXS measures polyethylene crystallization on the angstrom scale, the observation that the SAXS data track the WAXS data indicates that the formation of the lamellar microstructure in these diblock copolymers is indeed driven by crystallization, rather than by microphase separation between chemically incompatible blocks [115]. 

For semicrystalline isotropic materials a qualitative measure of crystallinity is directly obtained from the respective WAXS curve. Figure 8.2 demonstrates the phenomenon for polyethylene terephthalate) (PET). The curve in bold, solid line shows a WAXS curve with many reflections. The material is a PET with high crystallinity. The thin solid line at the bottom shows a compressed image of the corresponding scattering curve from a completely amorphous sample. Compared to the semicrystalline material it only shows two very broad peaks - the so-called first and second order of the amorphous halo. 

Effect of RMM on the tensile impact strength of linear polyethylene. A normal polymer with a distribution of RMM was split into a number of fractions each fraction had a particular RMM. The tensile impact strength of each fraction was measured. The tensile impact strength increases with RMM. The experiment quantifies the common experience that paraffin wax (which can be looked upon as a polyethylene with less than 200 CHj units in the molecule) is a brittle solid, with a toughness incomparably less than that of polyethylene. (After L. H. Tung. S. P. E. Conference Proceedings (1958) p. 959.)... 

A semicrystalline polymer such as polyethylene consists of at least two components solid crystals surrounded by an amorphous phase. The mobility of the chains in the orthorhombic crystal phase is negligible, whereas it is appreciable in the amorphous phase at room temperature. The crystal phase gives broad resonance lines, whereas considerably narrower lines are associated with the mobile amorphous phase. Detailed analysis of many polyethylene samples has shown that the NMR line profiles cannot be explained by these two components alone. A third component with intermediate mobility needs to be introduced in the model. Crystallinity data obtained by resolution of the proton spectrum or spectrum into these three components are in fair agreement with crystallinity data by X-ray diffraction and density measurements, and NMR can also assess an intermediate phase. The latter is not revealed by WAXS or density measurements. 

Observations of infrared dichroism on pol3rmeric systems were first made about 1950 using pols peptides (53,54). Fraser (55,56) developed its use to measure orientation in polymers quantitatively and establish a relationship of dichroic ratio D to the Hermans orientation factor equivalent to equation 2. The first infrared dichroism studies on polyethylene were performed in 1954 by Stein and co-workers (57,58). The article (58) discusses the determination of uniaxial orientation in polyethylene films using wide-angle x-ray (wax) diffraction, birefringence, and infrared dichroism, and explicitly states the interrelation of the former two measurements through... 

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