A detailed analysis of the Raman spectrum of syndiotactic
polystyrene, sPS, in the region
600−850 cm-1 has been undertaken. As
sPS exhibits considerable polymorphism, spectra of various
preparations including melt-crystallized sPS (α/β form),
solvent-crystallized sPS (γ/δ forms), and quenched
glassy material were studied. The ν1 vibration of
the phenyl ring (ring breathing mode) has been shown
to manifest itself through the presence of two peaks resulting from
local conformational changes in the
alkyl backbone. The peak centred around 773
cm-1 has been assigned to an all-trans
backbone sequence
whereas the higher frequency feature at ∼798
cm-1 is attributed to mixed trans/gauche
conformations.
For comparison the spectrum of atactic polystyrene was also
studied, and the presence of a weak shoulder
is assigned to a syndiotactic all-trans component within the polymer.
Further study of a cross section of
molded material exhibiting a skin/core structure reveals the continuous
way in which the relative size,
position, width, and intensity of these features vary with changing
crystallinity.
SynopsisTwo kinds of ultrahigh-molecular-weight linear polyethylene (UHMW PE), together with conventional high-density polyethylene (HDPE), were subjected to 0 irradiation, and changes in their properties were monitored. Elastic modulus increased steadily with dose for all materials, as did the yield stress. A dramatic rise of density with dose was observed in the UHMW P E specimens accompanied by a corresponding increase in heat of fusion, x-ray crystallinity, and peak melting temperature. The magnitude of such changes in HDPE was much smaller. In UHMW P E specimens, the x-ray long period simultaneously decreased but crystal thickness remained constant. No changes in long period occurred in HDPE. The effects are attributed to the scission of tie molecules in UHMW P E followed by a growth in the perfection of the crystal lamellae, and suggest a method for assessing the tie-molecule content of such materials.
Syndiotactic polystyrene (sPS) has been found to
exhibit two distinct vibrational peaks in
the Raman spectrum corresponding to the ν1 vibrational
mode. These features have been assigned to
the symmetric phenyl ring breathing mode coupled to the polymer
backbone. It has been shown that the
presence of long all-trans sequences gives rise to a peak at
∼773 cm-1, whereas less well-defined
trans/gauche conformations result in a separate peak at ∼798
cm-1. With increasing levels of
crystallinity,
the integrated intensity of the former feature grows at the expense of
the high-frequency feature. The
use of a series of annealed isotropic films of glassy sPS of increasing
crystallinity and molten sPS has
made it possible to examine the precise relationship between these two
features and other neighboring
vibrational peaks. The level of crystallinity within each sample
has been determined independently using
wide-angle X-ray scattering, differential scanning calorimetry, and
infrared spectroscopic measurements.
It has been found that the relative area under the
all-trans ν1 band can be directly related to
the crystalline
volume fraction within each sample. It is proposed that this Raman
vibrational feature centered around
773 cm-1 can be used as a quantitative
measure of crystallinity for sPS once the contribution from
the
all-trans sequences in the melt is subtracted from the
spectrum.
Titanium metal was subjected to two surface treatments (alkaline peroxide etch and chromic acid anodization) and resulting oxide morphology examined by high-resolution scanning electron microscopy in a Jeol 100-CX STEM. The effects of treatment time in alkaline peroxide upon oxide morphology were followed and parallel mechanical measurements made on the strengths of adhesive bonds between the metal and an epoxy resin. These strengths were measured after a standard environmental exposure, namely 120 h in water at 80 ~ C. As time-of-treatment increases, a micro-porous oxide layer is developed and adhesive strength rises to a maximum. Prolonged treatment with alkaline peroxide produces a drastic fall in adhesive strength accompanied by gross etching of the metal surface without changes in the oxide morphology. The loss of adhesive durability in this case is therefore attributable to surface chemistry effects rather than morphological changes.
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