Connecting free volume with shape memory properties in noncytotoxic gamma‐irradiated polycyclooctene

Abstract

ABSTRACT:The free volume holes of a shape memory polymer have been analyzed considering that the empty space between molecules is necessary for the molecular motion, and the shape memory response is based on polymer segments acting as molecular switches through variable flexibility with temperature or other stimuli. Therefore, thermomechanical analysis (TMA) and positron annihilation lifetime spectroscopy (PALS) have been applied to analyze shape recovery and free volume hole sizes in gamma-irradiated polycyclooctene (PCO) samples, as a noncytotoxic alternative to more conventional PCO crosslinked via peroxide for future applications in medicine. Thus, a first approach relating structure, free volume holes and shape memory properties in gamma-irradiated PCO is presented. The results suggest that free volume holes caused by gamma irradiation in PCO samples facilitate the recovery process by improving movement of polymer chains and open possibilities for the design and control of the macroscopic response. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1080-1088 KEYWORDS: free volume; gamma-irradiated polycylooctene; noncytotoxic polymers; positron annihilation lifetime spectroscopy; shape memory polymers INTRODUCTION Polycyclooctene (PCO) is a semicrystalline polymer that can be obtained by ring-opening metathesis polymerization (ROMP), and demonstrates outstanding shape memory properties by crosslinking the macromolecular chains. Employing commercial PCO, magneto-active polymers, 1 thermoresponsive polymers, 2 shape memory composites, 3 triple-shape memory polymers, 4 and selfrepair systems 5 have been developed. Based on the reversibility of the effect, shape memory polymers are categorized in one-way SMPs (1W-SMPs) and two-way SMPs (2W-SMPs). In the first case, 1W-SMPs, after the recovery process, it is necessary to program again the material to obtain a new transition between the temporary and the permanent shape. In the second case, 2W-SMPs, the transition between the temporary shape and the permanent one is reversible (reversing the supplied stimulus, temporary or permanent shape can be obtained). As it has been previously described, 6-9 PCO has shown both effects.

Influence of the soft segment nature on the thermomechanical behavior of shape memory polyurethanes

“…The fixing ( R f ) and recovery ( R r ) ratios were calculated for each sample using Eqs. and . …”

Polymeric Shape-Memory Micro-Patterned Surface for Switching Wettability with Temperature

“…TMA was also conducted in tension mode on the DMA-1 from Mettler Toledo in the temperature range of −10 to 80 °C at a heating rate of 4 °C min . TMA measurements were made following a similar procedure to that reported earlier [30], where the increase of the sample length was recorded as a function of temperature (Figure 3). This temperature range was selected according to the melting temperature previously calculated from calorimetric analysis [26] and corroborated here by DMTA measurements.…”

“…Shape fixity ratio (Rf) and shape recovery ratio (Rr) for all performed experiments were calculated according to [30] and the obtained values are listed in Table 3. Previously, the sample is heated without force to 80 °C in order to allow relaxation of the polymer chains, so initial conditions are fixed (sample dimensions and temperature).…”

Shape memory behaviour of a gamma-irradiated commercial polycyclooctene.

“…For that, samples shaped as strips with a cross-section area of 4 mm x 1.5 mm and initial clamps distance of 20 mm was employed. Taking into account the melting temperatures of the samples (Table 1), we thought appropriately to perform the thermomechanical experiments in the temperature range of 30-80º C [17]. The analysis were conducted on a Mettler Toledo DMA-1 at a heating rate of 4º C min -1 , recording the increase of the sample length as a function of temperature (Figure 5).…”