Non-Isothermal Degradation Kinetics of Hybrid Copolymers Containing Thermosensitive and Polypeptide Blocks

Abstract

Novel, self-associating hybrid copolymers were synthesized via controlled ring-opening polymerization of -carboxyanhydride of Z-L-lysine (Z-L-Lys-NCA), initiated by amino-functional macroinitiators. A poly(N-isopropylacrylamide) (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 ammoniummediated 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-isopropylacrylamide) 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.

Thermal stability and non‐isothermal kinetics of poly(ethyl cyanoacrylate) nanofibers

“…Even when the influence of the surface area is taken into account, the pre-exponential factor for a solid-phase reaction might range from six to seven orders of magnitude. 26,46 These high values of the pre-exponential factor indicate the presence of a 'loose' complex. The negative values of ΔS ≠ confirm that the activated complex is better structured, or 'organized', than the initial reagent.…”

“…In order to gain a deeper insight into the phenomenon under study, the theory of the activated complex (transition state) of Eyring 23,30,44–47 is applied for evaluation of the basic thermodynamic functions. The general equation 30,46,47 describing this theory is given as follows: where е = 27 183 is the Neper number; χ is the transition factor, which represents unity for monomolecular reactions; k B is the Boltzmann constant; h is the Planck constant; and T p is the peak temperature of the DTG curves at various heating rates. Taking into account that: the thermodynamic functions Δ S ≠ , Δ H ≠ and Δ G ≠ , which well characterize the decomposition process, may be calculated 44,48,49 .…”

“…In the current study, the estimated lifetime (or the time of accelerating ageing t f ) to failure of PECA was defined as the time when the mass loss reaches 5 mass%, i.e. α = 0.05 30,34,46,54 . In the case of the F n mechanism reaction, t f can be assessed by the following equation: …”

“…44 This equation is obtained from the Kissinger method, according to which it is assumed that at a constant value of the activation energy, the peak temperature conversion is approximately constant and f 0 ⊍ p À Á should not depend on the heating rate. 29 In order to gain a deeper insight into the phenomenon under study, the theory of the activated complex (transition state) of Eyring 23,30,[44][45][46][47] is applied for evaluation of the basic thermodynamic functions. The general equation 30,46,47 describing this theory is given as follows:…”

Control over the Process of Thermo-Oxidative Degradation of Polymers in a Solution

“…The problem of studying degradation of polymers by simulation is described in many works of both domestic (Berlin et al, 1978;Bryk, 1989;Koptelov and Milekhin, 2012) and foreign researchers (Ivanova et al, 2012;Browarzik and Koch, 1996;Ziff and McGrady, 1986). Studying of the polymer degradation process in a solution by modeling is described in a relatively small number of studies (Sivalingam and Madras, 2004;Sterling et al, 2001).…”