Solution polymerization of ε‐caprolactone (ε‐CL) was performed using four different initiators namely: tin(II) octanoate (Sn(Oct)2)/ethanolamine, aluminium Schiff's base complex‐HAPENAlOiPr, lithium diisopropyl amide (LDA) and aluminium isopropoxide. The reaction conditions varied with the initiator used. LDA gave rise to the most rapid polymerization with the highest amount of cyclic species as detected by 13C NMR. However, no cyclic species were detected when HAPENAlOiPr was used as initiator. The tin(II) octanoate/ethanolamine system lead to an α,ω‐dihydroxy‐polycaprolactone (PCL). The copolymerization of ε‐CL was then performed with the hard to oligomerize γ‐butyrolactone using the four initiators. GPC (Gel Permeation Chromatography) analyses showed the formation of copolymers. The highest incorporation of polybutyrolactone (PBL) in the copolymer was obtained using HAPENAlOiPr as evidenced by 1H NMR. 13C NMR indicated the presence of pseudoperiodic random copolymers with short blocks of PCL whose block length varied with initiator used. The longest and shortest block length were obtained using Sn(Oct)2 and HAPENAlOiPr respectively as calculated from 13C NMR. The reactivity ratios were determined using the Finemann‐Ross method at low conversion with HAPENAlOiPr as initiator. The values obtained, rCL = 19.4 and rBL = 0.11, confirmed the presence of long blocks of CL units in the copolymer.
The synthesis and detailed characterization of racemic 3-methyl-1,4-dioxan-2-one (3-MeDX) are reported. The bulk ringopening polymerization of 3-MeDX, to yield a poly(ester-ether) meant for biomedical applications, in the presence of various initiators such as tin(II) octanoate, tin(II) octanoate/n-butyl alcohol, aluminium tris-isopropoxide and an aluminium Schiff base complex (HAPENAlO i Pr) under varying experimental conditions is here detailed for the first time. Polymerization kinetics were investigated and compared with those of 1,4-dioxan-2-one. The studies reveal that the rate of polymerization of 3-MeDX is less than that of 1,4-dioxan-2-one. Experimental conditions to achieve relatively high molar masses have been established. Thermodynamic parameters such as enthalpy and entropy of 3-MeDX polymerization as well as ceiling temperature have been determined. Poly(D,L-3-MeDX) is found to possess a much lower ceiling temperature than poly(1,4-dioxan-2-one). Poly(D,L-3-MeDX) was characterized using NMR spectroscopy, matrix-assisted laser desorption ionization mass spectrometry, size exclusion chromatography and differential scanning calorimetry. This polymer is an amorphous material with a glass transition temperature of about −20 • C.
Synthesis of random copolymers by the nonsequential polymerization of 1,4-dioxan-2-one with D,L-3-methyl-1,4-dioxan-2-one was first investigated using a range of classical initiators. Experimental conditions such as temperature and initiator concentrations were varied to achieve reasonable monomer conversions and molar masses. In general, copolymers were slightly enriched in 1,4-dioxan-2-one. On the basis of block lengths of the respective (co)monomer sequences, it is proposed that the copolymer consists of longer blocks of dioxanone units and a pseudoperiodic pattern with a random distribution of MeDX units. The thermal properties of the copolymer changed significantly with the percentage of MeDX units incorporated. A copolymer with 8% mole percent of MeDX units exhibits a T m of 95.5°C, which is about 15°lower than PDX homopolymer. A range of (PEG) m -b-[(PDX)-co-(PMeDX)] n block copolymers was also successfully prepared using R-methoxy-ω-hydroxy-PEG as macroinitiator. The amphiphilic character of these copolymers is also here demonstrated with spherical core-shell micelles having an average size of 25-30 nm as determined by TEM. The tunable biodegradability characteristics of the hydrophobic core make these polymers interesting candidates as nanocarriers in controlled drug delivery.
Introduction: Because tissue engineering scaffolds serve as a temporary environment until new tissue can be formed, their mechanical performance, thermal properties, and biocompatibility are critical for maintaining their functionality. The goal of this study was to electrospin scaffolds from copolymers containing varying amounts of 1,4-Dioxan-2-one (DX) and D,L-3-Methyl-1,4-dioxan-2-one (DL-3-MeDX), and characterize their mechanical and thermal properties. Methods and Results: Image tool analysis of scanning electron micrographs revealed the presence of DL-3-MeDX causes the fiber diameter of the scaffold to decrease as compared to polydioxanone (PDO). Uniaxial tensile testing revealed increasing amounts of DL-3-MeDX in the copolymer decreases scaffold peak stress, strain at break and toughness. Modulated differential scanning calorimetry was used for thermal analysis of the scaffolds and showed that increasing amounts of DL-3-MeDX causes a decrease in the melting as well as crystallization temperatures. Conclusion: Based on the results of the mechanical and thermal properties of these copolymer scaffolds, it is evident that these constructs could be functional in a variety of biomedical engineering applications.
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