Structure and Thermomechanical Properties of Polyurethane Block Copolymers with Shape Memory Effect

Abstract

Shape memory polyurethane (PU) block copolymers composed of 4,4′-methylenebis-(phenylisocyanate), poly(tetramethylene glycol), and 1,4-butanediol as a chain extender were synthesized by a two-step process. FT-IR spectra showed that carbonyl peak appearing at 1700 cm -1 increased with higher hard segment content, whereas another carbonyl peak at 1730 cm -1 decreased. It suggests that hard segments get more aggregated to form domains in the PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of PU, such as maximum stress, tensile modulus, and elongation at break. Especially, maximum stress, tensile modulus, and elongation at break increased significantly at 30 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content. Finally, 80-95% of shape recovery was obtained at 30-45 wt % of hard segment content, and the control of hard segment content in PU block copolymers is very important in determining their physical properties.

Efeito da concentração de segmentos rígidos nas propriedades físico-mecânicas, químicas e na morfologia de elastômeros microcelulares de poliuretano

“…Esse comportamento é explicado pela maior interação entre os segmentos rígidos promovida pelo aumento na quantidade de segmento rígido [22] , e também pela mais alta temperatura de transição vítrea (Tg) dos segmentos rígidos, comparada à dos segmentos flexíveis [23] . O aumento na quantidade do segmento de maior Tg promoveu um aumento na dureza dos EMPU desenvolvidos.…”

“…Entretanto, observou-se uma tendência de redução no alongamento na ruptura com o aumento do percentual de segmento rígido presente nos EMPU. Resultado similar foi obtido por Lee e colaboradores [22] . Segundo esses autores, o aumento do percentual de segmentos rígidos torna o estiramento dos PUs mais difícil, devido ao fato desses segmentos estarem unidos por interações do tipo ligações de hidrogênio.…”

“…Como o segmento rígido atua como uma carga reforçante no PU [1,2] , um aumento na percentual do mesmo implica em um aumento na interação entre os segmentos [22] . Isso implica em uma maior resistência ao rasgo dos EMPU.…”

Electroactive shape memory performance of polyurethane composite having homogeneously dispersed and covalently crosslinked carbon nanotubes

“…Transmission electro microscopy (TEM) measurements were carried out in order to observe the morphology of the nanotubes by using TEM-2000FX2 (JEOL), while the surface topology and the current images of the spin-coated samples were obtained by contact-mode atomic force microscopy (AFM) (Seiko Instruments Inc., SPA-300HV + SPI-3800N). Finally, the shape memory test of the composite films was carried out within a controlled thermal chamber, as described in our previous report [17]. The electroactive shape memory properties of shape recovery and shape retention were evaluated by applying constant electric voltage while monitoring the temperature and the length of the samples [16].…”

“…A comparison of these two methods might be useful for finding an effective way of controlling the dispersion structures of the tubes within the 3 polymer matrix as well as the electroactive memory of electrically conductive polymeric composites. In order to achieve this goal, we chose a polyurethane block copolymer as the polymer matrix due to its excellent shape memory, which is caused by the phase separation between hard and soft segments and thermo-responsive transitions corresponding to soft segments [17], together with acid-treated multi-walled carbon nanotubes (MWCNTs) as the reinforcing filler rather than carbon black [18].…”