Abstract
A series of novel Si–O–Si crosslinked organic/inorganic hybrid semi-crystalline polymers with shape memory properties was prepared from alkoxysilane-terminated poly(butylene succinate) (PBS) by water-induced silane crosslinking under organic solvent-free and catalyst-free conditions. The hydrolyzation and condensation of alkoxysilane end groups allowed for the generation of silica-like crosslinking points between the polymeric chains, acting not only as chemical net-points, but also as inorganic filler for a reinforcement effect. The resulting networks were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic-mechanical analysis (DMA) and tensile and shape memory tests to gain insight into the relationship between the polymeric structure, the morphology and the properties. By controlling the molecular weight of the PBS precursor, a fine tuning of the crosslinking density and the inorganic content of the resulting network was possible, leading to different thermal, mechanical and shape memory properties. Thanks to their suitable morphology consisting of crystalline domains, which represent the molecular switches between the temporary and permanent shapes, and chemical net-points, which permit the shape recovery, the synthesized materials showed good shape memory characteristics, being able to fix a significant portion of the applied strain in a temporary shape and to restore their original shape above their melting temperature.
Highlights
Due to increasing concerns for sustainable development and the impact of materials on the environment, bio-degradable and bio-based polymers have attracted intensive interest in the past few decades [1]
The molecular weights of poly(butylene succinate) (PBS) diols were varied by varying the polycondensation time [22], and they were determined by 1H NMR spectroscopy (Figure 1a) calculating the degree of polymerization (Dp) as described in the Experimental Section
This method permits one to obtain, under organic solvent-free and catalyst-free conditions, covalently crosslinked PBS-based Shape memory polymers (SMPs), with Si–O–Si domains behaving as net-points necessary for shape memory behavior
Summary
Due to increasing concerns for sustainable development and the impact of materials on the environment, bio-degradable and bio-based polymers have attracted intensive interest in the past few decades [1]. Concerning a possible way of chemical crosslinking, silane grafting or copolymerization or endcapping and subsequent water-crosslinking of polymers have received much attention in recent years, for industrial applications, and in fundamental research, because of various advantages, such as easy processing, low capital investment and the favorable properties of the processed materials [15,16]. Crosslinking reactions of alkoxysilane-terminated poly(butylene succinate) (PBS) In this scenario, the organic-inorganic hybrid materials have recently received increasing attention in the field of SMPs, because of their improved mechanical properties together with the possibility of easy and fine tuning of the shape memory performance through the modification of suitable structural factors of the networks [18,19,20,21]. The crosslinked materials, having Si–O–Si domains acting as net-points, and as inorganic filler for reinforcement, were investigated for their molecular architecture and characterized in terms of thermal properties, dynamic-mechanical properties and shape-memory behavior, exploiting their melting temperature for the activation of the recovery process
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