Abstract
Tailor-made, linear, and “comb-like” poly(ε-caprolactone)-based copolymers were synthesized by employing a combination of controlled polymerization techniques. Poly(dimethylsiloxane-block-ε-caprolactone) copolymers (SCL#) were synthesized by a combination of anionic and ring-opening polymerization (ROP), whereas “comb-like” poly(hydroxyethylmethacrylate-co-(hydroxyethylmethacrylate-graft-ε-caprolactone)-block-ε-caprolactone) (HEMACL#) were synthesized through simultaneous ROP and reversible addition fragmentation chain transfer (RAFT) polymerization. Copolymers were characterized by hydrogen nuclear magnetic resonance (1H-NMR), size exclusion chromatography (SEC), and Fourier transform infrared (FTIR) spectroscopy. All polymers exhibited narrow molar masses distributions (Mw/Mn<1.54), and their thermal properties were analyzed by isothermal crystallization kinetics (Avrami’s theory, by using differential scanning calorimetry (DSC)) and by employing modulated thermogravimetric analysis (MTGA). The macromolecular structure exerts a noticeable effect on the PCL block behavior when compared to the PCL homopolymer, at least for the temperature range studied (16–24°C): less differences in thermal properties were observed for linear block copolymers, whereas for “comb-like” graft copolymers their final crystallization capacity strongly depends on the presence of branches. For both sets of copolymers, the decrease in the resulting melting temperatures and the increase in the half-life crystallization time values might be useful processing parameters, particularly if these copolymers are planned for using as an alternative source of 3D printing or electrospinning materials.
Highlights
During the last decades, the development of new polymerization techniques has noticeably increased the potential of polymer materials to expand their uses [1]
International Journal of Polymer Science (RDRP) techniques, such as atom transfer polymerization (ATRP), nitroxide-mediated polymerization (NMP), and reversible addition-fragmentation chain-transfer (RAFT) polymerization, are well-established, and their uses in the synthesis of macromolecules are widely employed in synthetic laboratories worldwide
Its polymerization was performed by using tin(II) octanoate (Sn(Oct)2, Aldrich) as catalyst, following the procedure previously reported by Satti et al [42]. 2Hydroxyethyl(methacrylate) (HEMA, Aldrich), diphenyl phosphate (DPP), 1,1′-azobis(cyclohexanecarbonitrile) (Vazo catalyst 88, Aldrich, 98%), toluene (Aldrich), methanol (Química Industrial), dimethylformamide (DMF), chloroform (Aldrich), deuterated chloroform (CDCl3), and petroleum ether were used without any further purification. 2(Benzylsulfanylthiocarbonylsulfanyl)ethanol (BSTSE, chain transfer agent for RAFT polymerization and hydroxyl initiator for ring-opening polymerization (ROP)) was prepared following a one-pot procedure, purified by column chromatography on silica using petroleum ether as eluent and recrystallized under cold conditions, as it was previously described [20, 43, 44]
Summary
The development of new polymerization techniques (which involve less sophisticated procedures from a practical point of view) has noticeably increased the potential of polymer materials to expand their uses [1]. Graft and block copolymers have received the attention of polymer scientists due to their attractive macromolecular characteristics and properties. This interest lies on the combination of thermodynamically incompatible macromolecular species linked together, which imposes restrictions regarding their properties and final applications. The processability of these materials is a crucial point that will justify their further uses In such a sense, many processing parameters such as viscosity-temperature dependence, glass-transition temperature, thermal stability, and melting temperature of semicrystalline blocks or segments are critical to decide whether or not using them [4]
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