Abstract
A novel well-defined linear poly(ε-caprolactone) (P1) containing terminal azobenzene and ethyne groups was successfully synthesized through tin-catalyzed ring-opening polymerization of ε-caprolactone in the presence of N,N′-bis(2-hydroxyethyl)-4-(3-ethynylphenylazo)aniline (BHA) in bulk. Subsequent reactions allowed the synthesis of the corresponding bromoester end-functionalized polymer (P2), which was converted into AB2 type polymer (P3) containing terminal azide groups with NaN3. Consequently, hyperbranched poly(ε-caprolactone) (HPCL) was prepared with AB2 macromonomer (P3) by “click” chemistry under the catalysis of CuSO4·5H2O/sodium ascorbate/H2O. The structure of the resultant HPCL was characterized by gel permeation chromatography (GPC), proton nuclear magnetic resonance (1H-NMR), ultraviolet-visible (UV-Vis) spectroscopy and fourier transform infrared spectroscopy (FT-IR). Thermal and crystallization properties of P1 and HPCL were further studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarised optical microscopy (POM). These results indicated that the crystallinity of HPCL was slightly lower than that of P1 due to the hyperbranched structure of HPCL. Additionally, the photo-induced trans-cis isomerization behaviors of BHA, P1 and HPCL containing terminal azobenzene were investigated in chloroform solution, and the photoisomerization rate constant (kexp) of small molecule (BHA) was nearly three times faster than that of polymers P1 and HPCL, which was due to the sterically hindering effect of the polymer-chain configuration.
Highlights
In recent years, biodegradable aliphatic polyesters have attracted considerable research attention, and are widely applied in the specialty biomedical areas, as well as in the environmental and marine fields [1,2]
Compared with dendrimers obtained from step-by-step synthesis, hyperbranched polymers could be considered as irregular analogues of the dendrimers with narrow polydispersity and predictable molecular weights [16], hyperbranched polymers can be synthesized by direct one-pot polymerization based on functional ABx-type (x ≥ 2) monomers [17,18], which were better suited for application in highly functionalized globular production
Poly(ε-caprolactone) (PCL) containing terminal azobenzene and ethyne groups was synthesized through tin-catalyzed ring-opening polymerization of ε-caprolactone (CL) in the presence of
Summary
Biodegradable aliphatic polyesters have attracted considerable research attention, and are widely applied in the specialty biomedical areas (such as drug delivery materials), as well as in the environmental and marine fields [1,2]. Chemistry had attracted much attention because of its high efficiency, quantitative yield and selectivity under mild reaction conditions [25,26,27] This novel method had been successfully applied in the area of polymer materials with different topologic structures, including linear, block, and star-shaped polymers and dendrimers [28,29,30,31,32,33,34]. Owing to steric hindrance of the polymer-chain configuration, the photoisomerization rate constant (kexp) of HPCL was much lower than that of the small molecule (BHA) This process could provide a useful alternative method for synthesizing a well-defined HPCL containing terminal functional group in the presence of a branch point
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