Kun-Yuan Qiu

Synthesis and characterization of mesoporous titania and silica-titania materials by urea templated sol-gel reactions

Abstract Mesoporous titania and mesoporous silica–titania materials have been successfully synthesized by using organic compound urea as template (or pore-forming agent) via sol–gel reactions of tetrabutyl titanate alone and with tetraethyl orthosilicate, respectively, followed by removing the urea by extraction with water. The pore parameters and morphology were characterized by N 2 adsorption–desorption measurement, powder X-ray diffraction and transmission electron microscopy. The pore diameters of synthesized titania, up to 5.5 nm, were larger than those mesoporous titania materials prepared by other nonsurfactant compounds reported previously by us. The pore diameters of silica–titania materials decreased with the increase of Si/Ti ratio from 1/100 to 2/1 under the same template concentration.

Synthesis of star-shaped poly(d,l-lactic acid-alt-glycolic acid) with multifunctional initiator and SnOct2 catalyst

Abstract d , l -3-methylglycolide (MG) was successfully polymerized with multifunctional initiator (trimethylolpropane (TMP) or pentaerythritol (PTOL)) and stannous octoate (SnOct 2 ) catalyst in bulk at 110°C. The effects of molar ratios of monomer to initiator, monomer to catalyst and monomer conversion on the molecular weight of polymer were studied. For the homopolymerization of MG with TMP initiator and SnOct 2 catalyst, the molecular weight of polymer increases from 6840 to 35 010 with the molar ratio of monomer to initiator (45–450), and the molecular weight distribution is from 1.15 to 1.35. The results indicate that in the homopolymerization of MG, the molecular weight of polymer is proportional to the molar ratio of monomer to initiator and the monomer conversion. The molar ratio of monomer to catalyst has no influence on the molecular weight of polymer at least within the range of 500–4000. 1 H NMR spectra of the resulting polymers obtained from the homopolymerization of MG show that the homopolymerization of MG with TMP or PTOL initiator and SnOct 2 catalyst produced two types of three-arm or four-arm star-shaped polymers. The bulk ring-opening homopolymerization of MG proceeds through a “coordination–insertion” mechanism and follows the selective acyl–oxygen bond cleavage reaction. 13 C NMR spectroscopy indicates that the obtained poly( d , l -lactic acid-co-glycolic acid) (50:50, in molar ratio; d , l -PLGA50) has an alternating structures of lactyl and glycolyl units.

Preparation of mesoporous silica materials with non-surfactant hydroxy-carboxylic acid compounds as templates via sol–gel process

Abstract Mesoporous silica materials with pore sizes of 2–6 nm have been prepared through the sol–gel reactions of tetraethyl orthosilicate (TEOS) in the presence of hydroxy-carboxylic acid compounds, including citric acid (CA), malic acid (MA), tartaric acid (TA) and lactic acid (LA), as templates or pore-forming agents, followed by extraction with ethanol to remove the template molecules. The materials are characterized by infrared spectroscopy, nitrogen adsorption–desorption tests, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the materials prepared at template concentrations of 40–60 wt% have large surface areas (ca. 900 m 2 /g) and pore volumes (ca. 1.0 cm 3 /g). The mesoporosity arises from interconnecting channels and pores with, however, disordered channel arrangements. The pore diameters and pore volumes increase as the template concentration is increased. The mesoporous materials retain high surface areas and pore volumes with a little change in pore diameters upon calcination at 773 K for 6 h.

Organic-inorganic hybrid materials: relations of thermal and mechanical properties with structures

Abstract Two series of polymethacrylate-silica covalent hybrid materials, i.e., poly[methyl methacrylate-co-3-(trimethoxysilyl)propyl methacrylate]-silica (PMCM-SiO 2 ) and poly(2-hydroxyethyl methacrylate)-silica (PHEMA-SiO 2 ), have been synthesized via two different sol-gel routes. The materials are highly transparent to visible light. Rapid formation of covalent bonds between the polymer and silica components during the sol-gel reactions prevents thermodynamically induced organic-inorganic phase separation. The presence of organic components does not alter the condensations of silanol groups. When extracted with an organic solvent, compositions of the hybrid materials remained largely unchanged. Bulk density and hardness of the materials can be controlled between those of the pure silica and polymers by varying the compositions. The hardness is not significantly affected by the molecular weight of PMCM polymers. The glass transition of the polymer components in all the hybrid materials is much less pronounced than that of pure polymer, as indicated by lower Tan δ peak values and smaller changes in storage modulus. As the silica content is increased, the T g increases for the PHEMA-SiO 2 hybrids while it remains essentially the same for the PMCM-SiO 2 materials. As the silica content is increased, both the storage modulus and thermal stability of the hybrids are improved.

Synthesis of Mesoporous Silica Materials via Nonsurfactant Templated Sol-Gel Route by Using Mixture of Organic Compounds as Template

Mesoporous silica materials have been successfully prepared by employing a mixture of β-cyclodextrin and urea as a template in a HCl-catalyzed sol-gel process, followed by extraction with water. The obtained materials are characterized by nitrogen adsorption-desorption measurements, powder X-ray diffraction patterns and transmission electron microscopy. The changes of the pore parameters depend on both the weight ratio of β-cyclodextrin and urea and the template content in the final silica composite. The effects of the mixture as template (or pore-forming agent) on the physicochemical properties of the two synthesized systems, with different weight ratio and same template content, as well as varied template content and fixed weight ratio, were investigated in this paper. The results show that the hydrogen bonding interactions between β-cyclodextrin and urea molecules or urea aggregates, the urea-holding β-cyclodextrin molecules themselves as well as inorganic species are the driving force in the formation of mesoporous silica materials.

Living/controlled radical polymerization of styrene with a new initiating system : DCDPS/FeCl3/PPh3

The living/controlled radical polymerization of styrene was investigated with a new initiating system, DCDPS/FeCl3/PPh3, in which diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS) was a hexa-substituted ethane thermal iniferter. The polymerization mechanism belonged to a reverse atom transfer radical polymerization (ATRP) process. The polymerization was controlled closely in bulk (at 100 °C) or in solution (at 110 °C) with a high molecular weight and quite narrow polydispersity (Mw/Mn = 1.18 ∼ 1.28). End-group analysis results by 1H NMR spectroscopy showed that the polymer was ω-functionalized by a chlorine atom, which also was confirmed by the result of a chain-extension reaction in the presence of a FeCl2/PPh3 or CuCl/bipy (2,2′-bipyridine) catalyst via a conventional ATRP process.

Nickel-mediated living radical polymerization of styrene in conjunction with tetraethylthiuram disulfide

The radical polymerization of styrene initiated with tetraethylthiuram disulfide (TD)/nickel (II) chloride (NiCl2)/triphenylphosphine (PPh3) was of living nature via a one-electron redox reaction between nickel(II) and (III) species. The mechanism belonged to reverse atom transfer radical polymerization (reverse ATRP). The living essence was affected by the molar concentration of the initiator and catalyst. With the feed ratio of [MMA]0/[TD]0 equal to 1000/1, the kinetics was of first order on the monomer. The values of number-average molecular weights measured by gel permeation chromatography (GPC) of resulting polymers were in close agreement with those calculated by the assumption that one living radical generated one polymer chain, and molecular weight distributions were as low as 1.34. α-S2CNEt2 and ω-Cl were demonstrated to end-cap the polymer chain. PSt-b-PMMA could be produced by the polymerization of MMA initiated with the resulting PSt-Cl/CuCl/bpy through a normal ATRP procedure.

Preparation of poly(methyl acrylate-co-itaconic anhydride)/SiO2 hybrid materials via the sol-gel process : The effect of the coupling agent, inorganic content, and nature of the catalyst

Transparent poly(methyl acrylate-co-itaconic anhydride)/SiO2 hybrid materials were prepared from methyl acrylate-itaconic anhydride copolymer and tetraethoxysilane (TEOS) with the coupling agent (3-aminopropyl)triethoxysilane (APTES) via a sol–gel process. The covalent bonds between the organic and inorganic phases were introduced by the in situ aminolysis of the itaconic anhydride units with APTES forming a copolymer bearing a triethoxysilyl group. These groups subsequently were hydrolyzed with TEOS and allowed to form a network. These reactions were monitored by Fourier transform infrared analysis. The amount of APTES had a dramatic influence on the gel time and sol fraction. The effect of APTES, the inorganic content, and the nature of the catalyst on the thermal properties and morphology of the hybrid materials were studied by differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and atomic force microscopy.

Synthesis of Mesoporous Silica Materials via Nonsurfactant Urea-Templated Sol-Gel Reactions

Mesoporous silica materials with pore diameters of 2 to 6 nm have been prepared using urea as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate, followed by removing the urea molecules by extraction with methanol or water. Characterization results from nitrogen sorption isotherm, powder X-ray diffraction, and transmission electron microscopy indicate that the materials have large specific surface areas (e.g., 600 m2/g) and pore volumes (e.g., 0.8 cm3/g) as well as narrow pore size distributions. The mesoporosity is arisen from interconnecting wormlike channels and pores of regular diameters. As the urea concentration is increased, the nitrogen sorption isotherms of the silica matrices transform from the reversible type I to the type IV form with type H2 hysteresis, along with increases in the diameter and volume of the pores.

Living polymerization of D,L-3-methylglycolide initiated with bimetallic (Al/Zn) μ-oxo alkoxide and copolymers thereof

D,L-3-Methylglycolide (MG) was successfully polymerized with bimetallic (Al/Zn) μ-oxo alkoxide as an initiator in toluene at 90 °C. The effect of the initiator concentration and monomer conversion on the molecular weight was studied. It is shown that the polymerization of MG follows a living process. A kinetic study indicated that the polymerization approximates the first order in the monomer, and no induction period was observed. 1H NMR spectroscopy showed that the ring-opening polymerization proceeds through a coordination–insertion mechanism with selective cleavage of the acyl–oxygen bond of the monomer. On the basis of 1H NMR and 13C NMR analyses, the selective cleavage of the acyl–oxygen bond of the monomer mainly occurs at the least hindered carbonyl groups (P1 = 0.84, P2 = 0.16). Therefore, the main chain of poly(D,L-lactic acid-co-glycolic acid) (50/50 molar ratio) obtained from the homopolymerization of MG was primarily composed of alternating lactyl and glycolyl units. The diblock copolymers poly(ϵ-caprolactone)-b-poly(D,L-lactic acid-alt-glycolic acid) and poly(L-lactide)-b-poly(D,L-lactic acid-alt-glycolic acid) were successfully synthesized by the sequential living polymerization of related lactones (ϵ-caprolactone or L-lactide). 13C NMR spectra of diblock copolymers clearly show their pure diblock structures.