The molecular mobility at the interface of poly(dimethylsi1oxane) [PDMS]/nylon-6 block copolymers was investigated using dynamic mechanical analysis (DMA) and solid-state deuterium NMR.Using DMA, Tg depression of the nylon matrix was observed with increasing PDMS content, and the mechanical loss peaks were broadened to lower temperature. When the room-temperature line spectra of solid-state deuterium NMR were compared for nylon-6 homopolymer and PDMS/nylon-6 diblock copolymer, a clear difference was observed; a peak associated with highly mobile nylon was observed in the block copolymer spectrum. This high mobility peak was observed even at -50 "C. Using a selectively deuterated triblock copolymer, the origin of this peak was shown to arise from a shell of softened nylon in the vicinity of PDMS domains. This softening effect was lost at -80 "C where PDMS domains can crystallize. This softened shell is not only from the compositionally mixed interfacial zone but also from a fraction of the pure nylon region surrounding the interfacial zone.

Small specimens of nylon 6/PDMS compositions were screened for relative levels of toughness using a micromechanical testing device. Measurements were made of the total crack length emanating from pre‐cut notches in a specially designed specimen. At room temperature, cracks propagated readily in nylon 6 homopolymer and somewhat more slowly in a composition containing 4 wt% PDMS; at 10 and 28 wt% PDMS the cracks were blunted in a diffuse whitened zone and did not propagate through the specimens. At −40°C, the 10 wt% blend appeared to be as tough as the 4 wt% blend at room temperature.

Crystallized chains of nylon 6 lie parallel to the interfaces of the microphase-separated morphology of a nylon 6/PDMS diblock copolymer. Orienting the morphology in the melt using plane strain compression enabled the nylon chain direction to be determined through a combination of transmission electron microscopy, small-angle X-ray scattering and wide-angle X-ray scattering pole figure analysis. Processing at temperatures above the nylon 6 melting point serves to orient the microphase-separated morphology of the melt; the nylon 6 chain orientations are then largely dictated by thermodynamic considerations that apply to chains crystallizing within the confines of a microphase separated melt.

ABSTRACT:Crystallized chains of nylon 6 lie parallel to the interfaces of the microphase-separated morphology of a nylon 6/PDMS diblock copolymer. Orienting the morphology in the melt using plane strain compression enabled the nylon chain direction to be determined through a combination of transmission electron microscopy, small-angle X-ray scattering and wide-angle X-ray scattering pole figure analysis. Processing at temperatures above the nylon 6 melting point serves to orient the microphase-separated morphology of the melt; the nylon 6 chain orientations are then largely dictated by thermodynamic considerations that apply to chains crystallizing within the confines of a microphase separated melt.

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