Abstract
Novel, self-associating hybrid copolymers were synthesized via controlled ring-opening polymerization of N-carboxyanhydride of Z-L-lysine (Z-L-Lys-NCA), initiated by amino-functional macroinitiators. A poly(N-isopropylacry-lamide) (PNIPAm)-based macroinitiator containing 10 mol% of polyoxyethylene grafts and a terminal primary amine group in the form of ammonium hydrochloride (PNIPAm-g-PEО) was synthesized and used to initiate the ammonium- mediated ring-opening polymerization of NCA described by Dimitrov and Schlaad [1]. Thus, hybrid copolymers ((PNIPAm-g-PEO)-b-PLys) with controlled molar-mass characteristics and functionality were obtained. The potential applications of PNIPAm-based copolymers in the systems for controlled drug release, immobilization of enzymes and protein purification have aroused great interest in the studies of their properties and behaviour. The thermal stability and thermodynamic properties of the copolymers obtained were studied. The differential thermal analysis of polyfunctional hybrid copolymers (PNIPAm-g-PEO)-b-PLys) showed that thermooxidative destruction occurs in two stages: primary, of the unstable fragments (grafted chains of PEO); and secondary, of the main polymer chains of poly(N-isopropylacry-lamide) and poly(L-lysine). The kinetics of thermal degradation was evaluated and the values of the activation energy of the degradation process, changes of Gibbs free energy, enthalpy and entropy for the formation of the activated complex were also calculated.
Highlights
The synthesis of polypeptide-based hybrid block copolymers is an area that has been under study for the past three decades
The purpose of this study is to evaluate the thermal stability of novel hybrid copolymers containing thermosensitive and polypeptide blocks, as well as to establish the most appropriate mechanism of the thermal degradation and to calculate the kinetic parameters characterizing this process
Self-associating hybrid copolymers containing thermosensitive and polypeptide blocks were synthesized via controlled ring-opening polymerization of NCA of Z-Llysine (Z-L-Lys-NCA), initiated by amino-functional macroinitiators [13]
Summary
The synthesis of polypeptide-based hybrid block copolymers is an area that has been under study for the past three decades. The vast improvements in carboxyanhydride (NCA) of α-amino acid polymerizations allow the synthesis of hybrid block copolymers of controlled characteristics (molar mass, sequence, composition and molar-mass distribution). Such well-defined materials will greatly assist the identification of new self-assembled structures using ordered polypeptide segments as well as yield new materials with a wide range of tunable properties [2]. The presence of functional groups along the chains could lead to significant changes in their behavior in the solid state and in solution [6]. Subsequent transformations of these groups may further lead to polymers with desired functionalities [7,8]
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