TIT# Deformation Behavior of PET, PBT and PBT-Based Thermoplastic Elastomers
     as Revealed by SAXS from Synchrotron
AUT# Stribeck, Norbert; Fakirov, Stoyko; Apostolov, Anton A.; Denchev, Zlatan;
     Gehrke, Rainer;
SOU# Macromol. Chem. Phys. (2003), 204(7), 1000-1013
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ABS# The present paper discloses the changes in the nanostructure as revealed
     by small-angle X-ray scattering (SAXS) of synchrotron radiation of
     anisotropic semicrystalline samples of polyester and poly(ether ester)
     type differing in their chemical composition, while subjected to
     controlled progressive elongation. From the group of polyesters
     poly(ethylene terephthalate) (PET), and poly(butylene terephthalate) (PBT)
     were selected. Two PBT-based commercial poly(ether ester)s were also
     studied differing in the molecular weight of their soft segments
     (poly(tetramethylene glycol, PTMG) being 1000 (Arnitel EM550) and 2000
     (Arnitel EM400), respectively. A blend of PBT and EM550 (40/60 by wt.)
     was also characterized. All materials underwent the same sample preparation
     process resulting in highly oriented "bristles" of 1 mm diameter. It was
     found that $\varepsilon _b$, the elongation at break, strongly depends
     on the flexibility of the glycol residues of the materials studied -
     ranging from $\varepsilon _{b}$ = 8% for PET that contains ethylene
     glycol residues, through $\varepsilon _{b}$ = 18% for PBT including the
     more flexible tetramethylene glycol (TMG) up to $\varepsilon _{b}$ = 510%
     for the PEE containing the longest PTMG moieties. During straining the
     relationship between the external elongation $\varepsilon $ and the
     changes in the long spacing L was determined. After relaxation from each
     deformation step the relationship between the tensile set
     $\varepsilon _{r}$ and the long period L was also followed and discussed.
     Such analysis led to a model describing the nanostructure evolution
     during the deformation--relaxation cycle that finally was verified and
     refined utilizing the multidimensional chord distribution function (CDF)
     computed from the anisotropic SAXS patterns.