Dj. Martin et al., THE EFFECT OF AVERAGE SOFT SEGMENT LENGTH ON MORPHOLOGY AND PROPERTIES OF A SERIES OF POLYURETHANE ELASTOMERS .2. SAXS-DSC ANNEALING STUDY, Journal of applied polymer science, 64(4), 1997, pp. 803-817
A series of eight thermoplastic polyurethane elastomers were synthesiz
ed from 4,4'-methylene diphenyl diisocyanate (MDI) and 1,4-butanediol
(BDO) chain extender, with poly(hexamethylene oxide) (PHMO) macrodiol
soft segments. The PHMO molecular weights employed ranged from 433 g/m
ol to 1180 g/mol. All materials contained 60% (w/w) of the macrodiol.
The materials were characterized by differential scanning calorimetry(
DSC) following up to nine different thermal treatments. In addition, t
hree of the materials were selected for characterization by small-angl
e x-ray scattering (SAXS) following similar thermal treatments. The DS
C experiments showed the existence of five hard segment melting region
s (labelled T1-T5), which were postulated to result from the disorderi
ng or melting of sequences containing one to five MDI-derived units, r
espectively. Evidence for urethane linkage dissociation and reassociat
ion during annealing at temperatures above 150 degrees C is presented.
This process aids in the formation of higher melting structures. Anne
aling temperatures of 80-100 degrees C provided the maximum SAXS scatt
ering intensity values. Materials containing longer soft segments (and
, therefore, longer hard segments) were observed to develop and sustai
n higher melting hard domain structures and also develop maximum avera
ge interdomain spacing values at higher annealing temperatures. Anothe
r additional series of three PHMO-based polyurethanes having narrower
hard segment length distributions, was synthesized and characterized b
y DSC in the as-synthesized and annealed states. The resulting DSC end
otherms provided further evidence to suggest that the T1-T5 endotherms
were possibly due to melting of various hard segment length populatio
ns. (C) 1997 John Wiley & Sons, Inc.