Isothermal crystallization kinetics of grafted block copolymers based on ε-caprolactone

NINAGO, MARIO; REDONDO, FRANCO LEONARDO; DE FREITAS, AUGUSTO G. O.; MURARO, PAULO I. R.; GIACOMELLI, CRISTIANO; CIOLINO, ANDRÉS E.; VILLAR, MARCELO A.

Sevilla

Simposio; Frontiers in Polymer Science 2017; 2017

Frontiers in Polymer Science

Grafted ?comb-like? block copolymers based on hydroxyethylmethacrylate and ε-caprolactone, P(HEMA-co-HEMA-g-PCL)-b-PCL, were obtained through simultaneous ?grafting through? and ?grafting from? methods in a one-pot reaction by combining radical addition fragmentation transfer (RAFT) and ring opening polymerization (ROP) reactions. Copolymers were characterized by SEC, FTIR and TGA analyses. The isothermal crystallization kinetics of a linear PCL and grafted copolymers were performed by DSC at different crystallization temperatures. Samples were heated from15 to 90 °C at 10 °C min-1, and were rapidly cooled (60 °C min-1) to selected crystallization temperatures for the PCL block. Isothermal crystallization experiments were carried out between 16 and 24 °C, by using a 2 °C step (Figure 1). An analysis, based on Avrami?s theory, was applied to describe the isothermal crystallization process in order to obtain kinetics parameters of interest, such as the half-life for the crystallization process (t1/2), the bulk crystallization constant (k), and the Avrami?s exponent (n). Avrami?s exponent values were  3 for linear PCL exhibiting a spherical growing, whereas for copolymers it was obtained n values in the range of 1.7?2.8 indicating that PCL block in the copolymers crystallizes in two dimensions (disk and cylindrical). Besides, spherulitic growth rate, crystallization rate, and activation energy (Ea) of the copolymers were affected by the length of PCL branches. From TGA analysis, degradation events associated to both PCL and PHEMA were observed. A reduction in the maximum degradation temperature was also observed in all samples studied regarding the value of linear PCL.