STUDIES ON POLY (CAPROLACTONE-CO-DIMETHYL SILOXANE) COPOLYMERS FOR THERMORESPONSIVE SHAPE MEMORY APPLICATIONS

Abstract

Polycaprolactone – polydimethylsiloxane – polycaprolactone (PCL-PDMS-PCL) triblock copolymer is a type of polymer that consists of three distinct polymer segments arranged in a linear structure. Polycaprolactone is biodegradable polyester that has gained attention due to its unique properties such as low melting point, good mechanical strength, and biocompatibility. It has found various applications in fields such as biomedical engineering, drug delivery, tissue engineering and 3D printing. PDMS is a type of silicone polymer with unique characteristics, including low surface energy, excellent thermal stability, and high hydrophobicity. PDMS exhibits good biocompatibility, chemical resistance, and low toxicity, making it suitable for various applications such as biomedical devices, microfluidic systems, and coatings. The PCL segments act as "end blocks" as well as "hard blocks" due to their relatively higher glass transition temperature (Tg) and more rigid nature. On the other hand, the PDMS segment acts as a "soft block" due to its lower Tg and more flexible nature. The arrangement of PCL-PDMS-PCL triblock copolymer results in a unique material with tunable properties. By adjusting the length of each polymer block, the mechanical, thermal, and surface properties of the copolymer can be tailored. The shape memory triblock photocrosslinked copolymeric films of varying poly(ɛ caprolactone) (PCL) chain length and constant polydimethylsiloxane (PDMS) content are synthesized. The effect of PCL chain length on structural, rheological, mechanical, thermal and shape memory properties of triblock copolymeric films is studied. The structural properties are analysed by X-ray diffraction (XRD) and optical microscope. Discrete crystal morphology is observed with increase in PCL chain length. Viscoelastic and mechanical properties are evaluated for the films of PCL and copolymers. Thermal properties are evaluated by differential scanning calorimetry (DSC) using non-isothermal and isothermal xviii modes. The crystallinity and crystal melting point of triblock polymer increases with increase in PCL chain length. The crystallization kinetics of triblock PCL-PDMS-PCL copolymeric films is studied with the help of Avrami model and Lauritzen-Hoffman (LH) model. The three-dimensional growth of PCL crystals is observed in triblock copolymers. Inclusion of PDMS block resulted in longer crystallization time, higher energy barrier and affects the crystal growth rate of PCL block, which further affect the shape fixity and shape recovery ratio accordingly. The soil burial degradation behavior of PCL-PDMS-PCL triblock copolymer films is studied to understand its landfill effect and degradation mechanism. The microlevel, macrolevel and structural changes in the samples of homopolymer and triblock copolymer are analyzed before and after soil burial test. Microlevel changes are determined by evaluation of morphological properties with digital camera, optical microscope (OM) and scanning electron microscope (SEM) images and found that degradation of copolymer films enhanced with increase in PCL chain length. A Macrolevel structural changes are examined by Fourier transform infra-red spectroscopy (FTIR) and DSC crystallinity. The soil burial degradation mechanism is proposed for PCL-PDMS-PCL tri-block copolymer films on the basis of results obtained.