Synchrotron small-angle X-ray scattering (SAXS) was used to investigate the microphase structure and microphase separation kinetics of two segmented polyurethanes with 4,4'-diphenylmethyl diisocyanate (MDI) and l,4'-butanediol (BD) as the hard segment and poly(tetramethylene oxide) (PTMO) and poly (propylene oxide) end-capped with poly (ethylene oxide) (PPO-PEO) (M" ~2000) as the soft segments. A more complete phase separation was observed in the PTMO based sample although PTMO and PPO-PEO have almost identical solubility parameters. This phase separation behavior could be explained as due partially to a kinetic factor. The microphase separation kinetics from quenching a sample in the melt state to lower annealing temperatures could be described by a relaxation process. A single-relaxation time process was observed for the PTMO based sample. By variation of the soft segment molecular weight from 1000 to 2000, the relaxation time was reduced from ~103 to 64 s. This behavior strongly supports our argument that in a segmented polyurethane, hard segment mobility, system viscosity, and hard segment interactions are the three controlling factors. In the PPO-PEO-based sample a double-relaxation time process was observed. One of the relaxation times was 54 s while the other secondary process was 1.48 X 103 s.

No abstract

No abstract

synopsisA series of low-density polyethylene extruded films was examined quantitatively by the birefringence, infrared dichroism, and x-ray pole figure techniques. The birefringence ranges from mildly positive to mildly negative with increasing severity of quenching conditions. The x-ray data show that the birefringence is largely due to the contribution of oriented crystallites, the amorphous orientation being quite low. The crystal orientation functions suggest equal degrees of a and c axis orientation parallel to the machine direction at low quenching rates, and increasing a axis orientation as the quenching rate increases, coupled with a shift in the c axis from parallel to perpendicular orientation. These results are confirmed by infrared dichroism data. The relative degree of a and c axis orientation ultimately reached is intermediate between that predicted by Keller's type I and type I1 models, but approximates the orientation previously observed in laboratory films prepared by oriented crystalhiation at 100% elongation. The crystalline orientation may be explained by the modified row orientation structure of Keller and Machin. However, the data can also be reconciled with that of spherulitic entities observed in samples crystallized at 2650% stretch. It is suggested that these spherulites may possess a combination type I1 and screw dislocation morphology in the equatorial and polar regions, respectively. Such a structure differs from the row structure in that the latter implies that the amount of polar material is negligible compared to the equatorial material. It is recognized, however, that orientation data cannot unambiguously decide between these alternatives.

The x-ray pole figure technique has been applied to the study of orientation in polyethylene. Wilchinsky-type orientation functions of the form 〈cos2φhkl, q〉 are determined as well as pole figures. These functions are shown to be related to the crystalline contributions to birefringence and infrared dichroism. A new method of presenting these functions on an equilateral triangle plot is introduced. Equations are presented for calculating the orientation functions for weakly diffracting [hkl] planes for materials of the orthorhombic, tetragonal, hexagonal, and cubic systems. The method of analysis is applied to various polyethylene samples, including a unidirectionally recrystallized sample (I) and to crosslinked film recrystallized at low orientation (II), and at higher orientation (III). The resulting data are interpreted in terms of various morphological models and are also correlated with birefringence. The data on (I) are consistent with a model of random orientation of a and c about the b axis. In (II) and (III) the row nucleation model and the a-axis orientation model are both inadequate. For (II) a diffusely oriented helix model is suggested; for (III) a screw dislocation model of crystal growth, with the screw axes parallel to the stretch direction, is proposed.