Molecular motion of isolated polybutadiene chains tethered on the fresh surface of polytetrafluoroethylene

The polybutadiene (PBD) chains tethered on the fresh surface of a polytetrafluoroethylene (PTFE) were produced by a block copolymerization of PTFE with 1,3-butadiene in vacuum at 77 K. The extremely low segmental density of the tethered chains was estimated by a spin labelling technique. The tethered chains can be regarded as ‘isolated polymer chains’. The PBD tethered chain has an unpaired electron at the chain end. We studied the molecular mobility of the PBD tethered chains by electron spin resonance (e.s.r.) spectroscopy, using the PBD chain end radical as a probe. The site exchange motion between two conformations at the chain end was observed in the temperature range 77–173 K and the rate of the exchange motion was determined by spectral simulations. The tethered chains are mobile even below 218 K which is a glass transition temperature of 1,4-PBD in the bulk. The high mobility of the PBD chains tethered on the PTFE surface is attributed to: the PBD chains have a very large space around the chains because of an extremely low segmental density on the PTFE surface. © 1997 Elsevier Science Ltd.     

Effect of substrate on gradient domain morphology formed in acrylate copolymer/fluoro-copolymer blends

The effect of the substrate on the gradient domain morphology was investigated for immiscible blends of poly(2-ethylhexyl acrylate-co-acrylicacid-co-vinylacetate) [P(2EHA-AA-VAc)] and poly(vinylidene fluoride-co-hexafluoro acetone) [P(VDF-HFA)]. The blends were prepared on substrates of poly(dimethyl siloxane) (PDMS) coated on a liner and of poly(tetrafluoro ethylene) (PTFE) from a THF solution by coating. The chemical compositions and the cross-sectional morphology of the surface (surface in contact with air) and bottom (surface in contact with substrate) sides were examined by attenuated total reflection Fourier transform infrared spectroscopy and scanning electron microscopy. The P(2EHA-AA-VAc)/P(VDF-HFA) (50/50), (30/70) blends prepared on PDMS revealed a gradient domain morphology, whereas the (50/50) and (30/70) blends prepared on PTFE formed a sea-island type of phase separation structure. On the other hand, when the P(2EHA-AA-VAc)/P(VDF-HFA) (70/30) blend was prepared on PTFE, P(2EHA-AA-VAc) and P(VDF-HFA) components segregated at the surface and the bottom, respectively. We concluded that the affinity between P(VDF-HFA) and the substrates strongly influenced the formation of the gradient domain morphology and the surface segregation of P(2EHA-AA-VAc).