Two types of three-arm or four-arm star-shaped hydroxy-terminated poly( -caprolactone) (PCL) were successfully synthesized via the ring-opening polymerization of -caprolactone (CL) with multifunctional initiator, such as trimethylolpropane (TMP) or pentaerythritol (PTOL), and stannous octoate (SnOct 2) catalyst in bulk at 110 °C. The number-average molecular weight of PCL is proportional to the molar ratio of monomer to initiator. 1 H NMR spectroscopy of the resulting PCL indicates that it contains a primary hydroxy end group in each arm. The star-shaped PCL with hydroxy end groups can be used as a macroinitiator for block copolymerization with DL-3-methylglycolide (MG) using SnOct2 catalyst in bulk at 115 °C. 1 H NMR spectra of the resulting block copolymers show that the molecular weights and the unit compositions of the block copolymers were controlled by the molar ratios of MG monomer to hydroxy groups of PCL and MG to CL in feed, respectively. Moreover, the molecular weights of the resulting block copolymers linearly increased with the increase of the molar ratios of MG to CL in feed. The molecular weight distributions of the block copolymers were rather narrow (M w/Mn ) 1.09-1.26). 13 C NMR spectra of the resulting block copolymers clearly show their diblock structures, that is, PCL as the first block and poly(DL-lactic acid-alt-glycolic acid) (DL-PLGA50) with alternating structures of lactyl and glycolyl units as the second block. Therefore, two types of three-arm or four-arm star-shaped diblock copolyesters comprising the first block PCL and the second block DL-PLGA50 were successfully synthesized via the sequential ring-opening polymerization of CL with multifunctional initiator and SnOct2 catalyst and then followed by copolymerization with MG.
The synthesis of mesoporous silica materials has been achieved with d-glucose as a nonsurfactant pore-forming agent in the sol−gel reactions of tetraethyl orthosilicate under basic or near neutral (pH 6) conditions. Regardless of the pH values of the medium, transparent and monolithic glucose-containing silica gels could be obtained. d-Glucose was removed by water extraction to afford silica materials with high specific surface area of ∼800 m2/g, pore volume of ∼0.5 cm3/g, and narrow pore distribution with BJH pore diameter of 3.2−3.5 nm, indicative of the mesoporosity. As the glucose concentration is increased in the synthesis, these pore parameters generally increase, and the N2 sorption isotherms gradually transform from reversible type I to type IV-like isotherms with H2 hysteresis. At low glucose concentrations (<36 wt %), both micropores and mesopores contribute to the porosity of the materials. However, at high glucose concentrations (36−64 wt %), mesopores are dominant. The characteristics of pore structures are similar to those for the materials obtained under acid catalysis. The aggregation or assembly of the aggregates of the glucose molecules and their hydrogen-bonding interactions with the silicate species might direct the mesophase formation.
Well-defined poly(methyl methacrylate) (PMMA) with an α-hydrogen atom and an ω-chlorine atom as the end groups has been synthesized by bulk polymerization of MMA at 95 °C using a new initiation system, 1,1,2,2-tetraphenyl-1,2-ethanediol (TPED)/FeCl3/PPh3. The conversion of polymerization reached to ∼100%. The molecular weight of PMMA obtained was high and the polydispersity index was quite narrow (e.g., M n = 171 800; M w/M n = 1.13). The polymerization of MMA exhibited some “living”/controlled radical polymerization characteristics. The mechanism of polymerization was proposed as a reverse atom transfer radical polymerization (ATRP). The presence of the hydrogen and the chlorine atoms as end groups of the PMMA obtained was determined by 1H NMR spectroscopy.
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