Synthesis of amino acid based covalently cross-linked polymeric gels using tetrakis(hydroxymethyl) phosphonium chloride as a cross-linker

Abstract

This work reports the design and synthesis of side-chain amino acid containing cross-linked polymer gels with high mechanical strength. The Boc-leucine methacryloyloxyethyl ester (Boc-Leu-HEMA) has been polymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization to obtain the corresponding polymer, P(Boc-Leu-HEMA). After Boc group deprotection under acidic condition and pH neutralization amino groups remain in the polymer side chain, which were reacted with tetrakis(hydroxymethyl) phosphonium chloride (THPC) to obtain chemically cross-linked gels. The mechanical properties of gels have been studied by rheological measurements, which reveal that mechanical strength increases as weight% of polymer in solution, cross-linking density and polarity of solvents increases, and decreases as molecular weight of polymers increases. A plateau of storage modulus (G′) over a wide range of angular frequency demonstrates that viscoelastic property of gels is independent of angular frequency. Field emission scanning electron microscopy (FE-SEM) studies of cross-sectioned gels validate rheological observation that as the G′ values of gel increases, porosity of gel decreases.