Synthesis, properties, and applications of polycaprolactone-polydimethylsiloxane-polycaprolactone triblock copolymers

Abstract

Poly(ε-caprolactone)–polydimethylsiloxane–poly(ε-caprolactone) (PCL-PDMS-PCL) triblock copolymers with block lengths in 1,000 – 32,000 g/mol range were synthesized by the ring-opening polymerization of ε-caprolactone using aminopropyl terminated PDMS oligomers as initiators. Reactions were carried out in bulk or solution at 125±5 ºC using tin octoate catalyst. Products obtained in high yields were characterized by FTIR, GPC, DSC, AFM, SEM, XRD, OM and water contact angle measurements. Effect of the copolymer composition and the molecular weight of the PDMS and PCL blocks on; (i) microphase separation and copolymer morphology, (ii) crystallization of PCL segments, and (iii) surface properties of the copolymers were investigated. Regardless of the block lengths, all copolymers displayed microphase separated morphologies. The extent of microphase separation, resultant morphology and sizes of the microphases were strongly dependent on copolymer composition and block lengths of PCL and PDMS. Crystalline PCL microphase was observed in all copolymers, which increased as a function of PCL content and molecular weight. All copolymers displayed hydrophobic surfaces as determined by static water contact angle measurements. Hydrophobicity improved with an increase in the PDMS block length. Copolymer morphologies were also obtained by computational studies at the molecular and mesoscopic levels via density functional theory (DFT) and dissipative particle dynamics (DPD) methods respectively. Computational results obtained were in very good agreement with the microphase morphologies determined by AFM studies. PCL-PDMS-PCL copolymers can be used as reactive oligomers or surface or bulk modifying additives for polymeric systems. We evaluated them as a processing aid in the melt extrusion of polyolefins, where they improved the extruder output substantially. They were also used as surface modifying additives for electrospun polyacrylonitrile fibers and silica modified epoxy networks, which led to the formation of superhydrophobic surfaces.