Francesco de Candia

Three-block copolymers: morphologies and stress - strain properties of samples prepared under various experimental conditions

Abstract The structural and morphological characterization of a styrene-butadiene-styrene thermoelastic three-block copolymer (Kraton 1101) is reported together with the stress-strain properties of specimens prepared with different techniques (compression moulding, extrusion, solution casting). The influences of the extrusion and of the annealing treatment at high temperature on the morphology (and therefore on the stress-strain properties) are considered in detail because the structure of the specimen becomes particularly simple; it consists of polystyrene cylinders arranged along the extrusion direction and embedded into the rubbery matrix. The rods along the axis lead to a continuous polystyrene phase, so that the plugs exhibit the Mullins and hardening effects already observed for other copolymers. Films cast from toluene are also investigated; the rate of evaporation of the solvent shows a remarkable influence on the morphology of the material and, of course, on its physical properties. An explanation for the hardening effects at high values of deformation is also suggested, supported by optical birefringence measurements on compression moulded specimens after strain.

Correlation between physical-mechanical properties and morphological features of cruciform styrene - butadiene block copolymers

Abstract The structural and morphological characterization of a cruciform styrene-butadiene block copolymer of the (SB)4Si type is reported together with the stress-strain properties of films prepared by compression moulding. The influence of the compression on the morphology (and therefore on the mechanical properties) are considered in detail because the structure of the specimen becomes particularly simple; it consists of polystyrene cylinders arranged perpendicularly to the compression plane. The rods lead to a semi-continuous polystyrene phase, so that the film exhibits the Mullins and hardening effects already observed for linear three block copolymers. Explanations for these phenomena are given, supported by optical observations and by electron microscopical views of sections cut after deformation.

Synthesis and physical behaviour of poly(amidoether) block copolymers

Abstract Random multiblock polyamide-polyether copolymers containing 13–30 wt% of polyether have been synthesized by a two-step procedure from adipoyl chloride, 1,6-diaminohexane and two α,ω-dihydroxy-poly(ethylene oxides) having M n =600 and 1550 g mol−1. The compositions and architectures of the copolymers were determined by elemental analysis and by 1H nuclear magnetic resonance spectroscopy. Thermal analysis showed the presence of a main crystalline component that thermal parameters indicated as polyamidic. Transport properties were analysed using water vapour as permeant; they indicated a permeability much higher than in polyamide-6,6 and suggested the presence in the amorphous component of a domain structure in which polyether volume elements are segregated from a polyamide matrix. Thermomechanical and dynamic mechanical analyses suggested that flexible polyether sequences increase the overall flexibility of the copolymer chains.

Synthesis and Characterization of Alternating Polyesteramides

Aliphatic and partially aromatic alternating polyesteramides were prepared from appropriate bisesteramides and aliphatic diols of various chain length. An investigation of their thermal and viscoelastic behaviour showed that the Tm and Tg values of such polyesteramides are those to be expected for a system with intermediate properties between those of the two homopolymers. A discussion of the experimental Tm values in terms of group contributions is presented.

Correlation between morphology and stress-strain properties of three block copolymers: 2. The hardening effect of the second deformation

Abstract The discussion of the correlation between morphology and stress-strain properties of linear three block copolymers is centralized on the hardening effect which comes out at the highest values of the extension ratio when a deformation immediately follows another one. The experimental results support the hypothesis that this phenomenon is due to a kinetic effect. A model is proposed which involves the recovery of the original molecular conformations of the elastic central blocks of the chains between two successive deformations; on this basis the hardening is explained assuming that elastic chains partly stretched are present in the specimen.