Influence of amorphous block on the thermal behavior of well-defined block copolymers based on ε-caprolactone

Abstract

In this work, we studied the thermal characterization of block copolymers based on e-caprolactone. The copolymers were obtained by anionic polymerization techniques, using different co-monomers such as styrene (S) and dimethylsiloxane (DMS). Synthesized copolymers were characterized by H-nuclear magnetic resonance, size exclusion chromatography, and Fourier transform infrared spectroscopy. Isothermal crystallization was performed by differential scanning calorimetry (DSC), and Avrami's theory was employed in order to obtain kinetics parameters of interest, such as the half-life for the crystallization process (t 1/2 ), the bulk crystallization constant (k), and the Avrami's exponent (n). The spherulitic growth was measured by polarized optical microscopy in order to determine the crystallization behavior. Poly(e-caprolactone) block (PCL) crystallization was analyzed by considering the physico-chemical characteristics of the neighboring block, PS or PDMS. The chemical nature of the neighbor block in the PCL-based copolymer affects the kinetics parameters of Avrami's equation, as can be deduced by comparing the values obtained for pure PCL and the studied block copolymers. On the other hand, the apparent thermal degradation activation energies E ad for PCL and block copolymers were determined by Ozawa's method. The incorporation of PDMS instead of PS improves the stability of the resulting copolymer, as it was observed by thermogravimetric analysis.

Thermal Characterization of “Comb‐Like” Block Copolymers Based on PCL Obtained by Combining ROP and RAFT Polymerizations

“…The continuous activation energy curve resulting from the linear heating rate is showed in Figure for PCL and COP5. PCL homopolymer presented an average activation energy value of ∼159 KJ mol −1 ,which is similar to values reported in the literature . Rázga & Petránek and Çekingen et al reported values of activation energy for the degradation process of PHEMA homopolymer of ∼129 KJ mol −1 .…”

“…Finally, a linear PCL homopolymer was synthesized following classical anionic polymerization procedures . This homopolymer was synthesized by using this technique in order to have a perfect control of its molar mass and polydispersity, with the purpose of having a true model PCL homopolymer.…”

“…Briefly, a conventional whole‐sealed glass reactor, a high‐vacuum line, sealed‐glass ampoules of reagents, and glass‐blowing techniques were employed to perform the polymerization. More details for these procedures have been previously reported in the scientific literature …”

Synthesis of Grafted Block Copolymers Based on ε‐Caprolactone: Influence of Branches on Their Thermal Behavior

“…Figures and show the TGA and first‐derivative curves under nitrogen and oxygen atmospheres, respectively. Model PCL showed one thermal event at around 405–410 °C, as it is reported in the literature . As it can be observed, PHEMA incorporation did not affect the maximum degradation rate ( T max ) of the linear polyester (Figure b and Table ), but a decrease in the initial zone between 180 and 350 °C was observed.…”

“…The resulting BSTSE was further purified by column chromatography on silica using petroleum ether as eluent and recrystallized under cold conditions. On the other hand, a model PCL homopolymer was synthesized as reference material by employing classical anionic polymerization as described elsewhere (DP ≈ 100) …”