The thermal stability of several crystal polymorphs in polyamide 11 (PA11) and polyamide 6 (PA6) has been investigated by means of in situ X-ray experiments. In the case of PA11, δ′ and α′ phases display a Brill transition far below the melting point. Both phases transform into a (pseudo)-hexagonal HT δ phase above 100 °C. The latter turns back into the most stable α′ phase upon cooling. PA6 exhibits similar thermally induced crystal transitions. In situ X-ray investigations refute the occurrence of a β → α transition upon heating, whereas the existence of a pseudohexagonal HT phase is suggested as in PA11. For both polymers, the present study underlines the major role of crystal perfection of the most stable α phase on the existence of a Brill transition. The combination of in situ structural information with thermal analysis allows to propose a thermodynamic scheme to describe the Brill transition in both polyamides.

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The plastic behavior of polyamide‐6 (or nylon‐6) films under uniaxial and biaxial tensile drawing is studied in relation to structural features. Quenched films in the mesomorphic β form are more ductile than films in the predominant stable α form. Films in the major γ crystalline form are intermediate between films in the β and α forms. Under uniaxial drawing, a great part of the β phase undergoes strain‐induced phase change into the α form, involving strain hardening of the material. The β→α phase change is more pronounced above 120 °C because of additional thermal reorganization. The γ form that is thermally stable up to 200 °C also undergoes a strain‐induced phase change above 120 °C, but the reorganization is much less important than for the β phase. Biaxial drawing can only be achieved below 120 °C with quenched films. This is likely due to the high mechanical anisotropy of the H‐bonded sheetlike structure of both the α and γ phases that is suspected to develop catastrophic splitting under a normal stress component, notably above 120 °C because of the collapse of the paraffin‐like van der Waals interactions between the sheets. The disordered distribution of the H bonds in the mesomorphic β structure of the quenched films is more appropriate for biaxial drawing. The strain‐induced β→α phase reorganization, which might have been a serious prejudice, proved to be much reduced during biaxial drawing below 120 °C. The mechanism of the strain‐induced phase change is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1224–1236, 2001

The crystallization behavior and the crystalline structure of nylon6-clay nanocomposites are investigated with regard to the processing conditions and thermal treatment. Microextruded bulk samples as well as blown films are under concern. The often reported nucleating effect of the clay particles is shown to strongly depend on the processing parameters prior to the solidification step, namely, the shear intensity which promotes self-nucleation and the temperature of the melt which regulates the density of these unstable nuclei. The MMT content influences the crystallization kinetics and the crystalline structure via the shear amplification phenomenon which increases the densities of both the shear-induced and the MMT-induced nuclei. The MMT platelets also turned out to hinder the crystal growth. The cooling rate plays a major role on the final crystalline structure by shifting the crystallization temperature in the specific growth range of either the Ror the γ-crystal forms of the nylon6 matrix. Blown films corroborate the findings from microextruded samples regarding the competition between nucleation and growth in the resulting crystalline form of the nylon6 matrix. Besides, the strong texturing of the nanocomposite films provides information on the local arrangement of the chains and crystal unit cell on the MMT platelets.

Well-defined dopamine end-functionalized polymers were synthesized by employing the reversible addition–fragmentation chain transfer (RAFT) polymerization technique. tert-Butyl acrylate, N-isopropylacrylamide, and styrene monomers were polymerized in the presence of azobis (isobutyronitrile) and a new catechol-based biomimetic RAFT agent incorporating a trithiocarbonate unit. All RAFT polymerizations exhibited pseudofirst-order kinetics, a linear increase of the number-average molar mass (M n SEC) with conversion and narrow molar mass distributions (polydispersity <1.2). The resulting homopolymers exhibited the electroactive catechol and the ω-trithiocarbonyl end groups. Subsequent immobilization of dopamine end-functionalized polymers on titanium surfaces was monitored by using a surface plasmon resonance (SPR) sensor, and the resulting films were characterized by contact angle, infrared ATR spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS).

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The thermal behavior of polyamide 6/amorphous polyamide blends has been investigated as a function of blend composition and temperature. Crystal phase nature and stability are probed by a combination of thermal analysis, X‐ray diffraction and Fourier transform infrared spectroscopy. Ductility appears to be strongly affected by the addition of the amorphous polyamide, but the corresponding decrease of the yield stress, either taken at the same draw temperature or under a comparable state of mobility of the amorphous phase, may not be simply accounted for by the reduction of overall ordered phase content.

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