Ivan Navarro-Baena

Synthesis of PLLA-b-PCL-b-PLLA linear tri-block copolymers and their corresponding poly(ester-urethane)s: effect of the molecular weight on their crystallisation and mechanical properties

With the general objective to design polymer based materials with specific thermal and mechanical properties, a systematic study on the crystallinity and the mechanical properties of synthesized linear tri-block copolymers based on poly(L-lactic acid) and poly(e-caprolactone) and of their corresponding poly(ester-urethane)s has been performed. In particular, eleven tri-block copolymers were synthesized varying both the molecular weight of the blocks as well as the relative content of each block in the copolymer, focusing the attention on the relationship between their chemical compositions and their tailored final properties in order to tune them taking into account their possible applications (i.e. as shape memory materials). From them, eleven poly(ester-urethane)s were synthesized by condensation with hexamethylene diisocyanate (HDI). The chemical composition of the synthesized polymers was studied and correlated with their thermal and crystalline properties obtained by both dynamic scanning calorimetry (DSC) and small angle X-ray diffraction (SAXS) experiments. The relationship between their crystalline structure, thermal and mechanical properties with the molecular weight as well as with the relative content of each comonomer in the copolymers and the amount of HDI in the poly(ester-urethane) was analysed. The results obtained demonstrate that these bio tri-block copolymers and the corresponding poly(ester-urethane)s can be tailored with interesting crystalline and mechanical properties. Future applications as shape memory systems are thus envisaged.

Shape memory polymers: properties, synthesis and applications

Abstract: Shape memory materials are able to change their shape in a controlled way upon application of an external stimulus such as temperature, light, application of electric or magnetic fields, etc. Due to their scientific and technological relevance, our aim is to review shape memory polymers, briefly introducing metals and ceramics. Polymeric materials show a wide range of relevant properties such as processability, versatility and biocompatibility, among others, characteristics that are responsible for the amplified interest in recent years in the shape memory field. With their cheaper cost and wide application spectrum, this review also reports the numerous advantages of shape memory polymers over alloys and ceramics, which are driving current research trends.

Influence of the processing parameters on the electrospinning of bio-plymeric fibers

The main aim of this research is the production of different biopolymeric fibers by electrospinning and the determination of the optimum working parameters for each polymer analyzed. In particular, three different biopolymers have been studied: poly(lactic acid) (PLA), poly(e-caprolactone) (PCL) and a synthesized poly(ester-urethane) based on a synthesized PLA-b-PCL-b-PLA tri-block copolymer. This research is focused on the analysis of the influence of the processing parameters, such as the concentration and flow-rate of the polymer solution and the applied voltage, as well as the physico-chemical properties of the polymers used, on the fiber formation and crystallization behavior. Therefore, the optimum working conditions for each polymer were determined and related to the final properties of the electrospun fibers in terms of geometry, homogeneous morphology and crystallinity.

Crystallization behavior of diblock copolymers based on PCL and PLLA biopolymers

This paper aims to increase the knowledge on the crystallinity features of diblock copolymers based on poly(∊-caprolactone) (PCL) and poly(l-lactic acid) (PLLA). Six diblock copolymers have been synthesized starting from a synthesized PCL with a molecular weight of around 5000 g mol−1, varying the molecular weight of the PLLA block. The crystalline unit cells for both PCL and PLLA blocks have been studied with wide-angle X-ray diffraction analysis. The effects of the copolymer composition on the crystalline cell parameters as well as on the degree of crystallinity and the crystallite sizes, determined using the Scherrer equation, are discussed. The double-crystalline nature of the diblock copolymer was confirmed by small-angle X-ray scattering experiments. This technique was also used to study the melting behavior of the copolymers by studying the variation of the diffraction spectra with temperature. The effects of PCL chains on the packing of the PLLA lamellae are discussed. Finally, the crystallization behavior was studied by differential scanning calorimetry analysis, performing experiments at different crystallization temperatures and studying the results by fitting the experimental data with an Avrami-type equation. The influence of each block on the crystallization parameters of the other block are discussed. This study allows a better understanding of the effects of the chemical structure on the crystalline behavior of these block copolymers, leading to the possibility to tailor the materials for specific applications.