ZnGA-MMT catalyzed the copolymerization of carbon dioxide with propylene oxide

Zinc glutarate (ZnGA) synthesized from zinc oxide and glutarate acid was dispersed on the surface of acid-treated montmorillonite (MMT) in quinoline to prepare ZnGA-MMT catalyst. The results of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) measurements indicated that the ZnGA on the surface of acid-treated MMT had the same crystalline structure as pure ZnGA. Copolymerization between CO₂ and propylene oxide (PO) was carried out under optimized reaction conditions using ZnGA-MMT catalyst, consequently giving poly(propylene carbonate) (PPC) with high molecular weight in a very high yield (115.2 g polymer per gram of ZnGA). The obtained PPCs were investigated using ¹³C NMR and FTIR spectra, showing a completely alternating structure. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) examinations showed the PPCs with a high transition temperature of 38 °C and a very high decomposition temperature (>250 °C) due to the presence of MMT residual in polymer.     

Effect of temperature and nanoparticle type on hydrolytic degradation of poly(lactic acid) nanocomposites

PLA and its nanocomposite films based on modified montmorillonite (CLO30B) or fluorohectorite (SOM MEE) and unmodified sepiolite (SEPS9) were processed at a clay loading of 5 wt% and hydrolytically degraded at 37 and 58 °C in a pH 7.0 phosphate-buffered solution. An effective hydrolytic degradation for neat PLA and nanocomposites was obtained at both temperatures of degradation, with higher extent at 58 °C due to more extensive micro-structural changes and molecular rearrangements, allowing a higher water absorption into the polymer matrix.The addition of CLO30B and SEPS9 delayed the degradation of PLA at 37 °C due to their inducing PLA crystallization effect and/or to their high water uptake reducing the amount of water available for polymer matrix hydrolysis. The presence of SOM MEE also induced polymer crystallization, but it was also found to catalyze hydrolysis of PLA. Concerning hydrolysis at 58 °C, the presence of any nanoparticle did not significantly affect the degradation trend of PLA, achieving similar molecular weight decreases for all the studied materials. This was related to the easy access of water molecules to the bulk material at this temperature, minimizing the effect of polymer crystallinity clay nature and aspect ratio on the polymer degradation.     

Structure and thermal degradation of poly(vinyl chloride) synthesized by various polymerization catalyst

Relationship between the structure and the thermal stability of poly(vinyl chloride) synthesized by various polymerization catalysts was investigated. The Cp∗Ti(OPh)/MAO catalyst, n-butyllithium (n-BuLi), the Cu(0)/TREN/CHBr₃/DMSO catalyst, benzoyl peroxide/N,N-dimethylaniline (BPO/DMA), 2,2’-azobis(2.4-dimethylvaleronitrile) (V-65) was used as the polymerization catalyst. The temperature of 5% weight loss was in the following order; Cp∗Ti(OPh)₃/MAO (280 °C) > n-BuLi (264 °C) > V-65 (249 °C) > Cu(0)/TREN/CHBr₃/DMSO (215 °C) > BPO/DMA (209 °C), and the rate of weight loss was the reverse order of T_−5% in the isothermal degradation of the polymer from 160 °C to 220 °C. The T_−5% value of the polymer obtained from the polymerization with Cp∗Ti(OPh)₃/MAO catalyst increased with an increase of the molecular weight of PVC, in contrast to that PVC obtained with the radical initiator did not depend on the molecular weight of the polymer. The T_−5% value of PVC macromonomer was 285 °C, while the temperature of non-functionalized PVC was 262 °C, respectively. It is clear that the PVC macromonomer had a good thermal stability regardless of low-molecular weight.     

Electron-beam irradiation on poly(propylene carbonate) in the presence of polyfunctional monomers

Poly(propylene carbonate) (PPC) showed predominantly degradation under electron-beam irradiation, accompanied by deterioration of its mechanical performance due to sharp decrease of the molecular weight. Crosslinked PPC was prepared by addition of polyfunctional monomer (PFM) to enhance the mechanical performance of PPC. When 8 wt% of PFM like triallyl isocyanurate (TAIC) was added, crosslinked PPC with a gel fraction of 60.7% was prepared at 50 kGy irradiation dose, which showed a tensile strength at 20 °C of 45.5 MPa, whereas it was only 38.5 MPa for pure PPC. The onset degradation temperature (T_i) and glass transition temperature (T_g) of this crosslinked PPC was 246 °C and 45 °C, respectively, a significant increase related to pure PPC of 211 °C and 36 °C. Therefore, thermal and mechanical performances of PPC could be improved via electron-beam irradiation in the presence of suitable PFM.     

Synthesis of well-defined, polymer-grafted silica nanoparticles via reverse ATRP

The surface grafting onto ultrafine silica via reverse ATRP of methyl methacrylate initiated by peroxide groups introduced onto the surface and conventional ATRP of Styrene initiated by the hybrid nanoparticles were investigated. The introduction of peroxide groups onto the silica surface was achieved by the reaction of hydrogen peroxide with chlorosilyl groups, which were introduced by the treatment of silica with thionyl chloride. Well-defined polymer chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polymer layer. The polymerization was closely controlled in solution at quite low temperature such as 70 °C. In both cases, linear kinetic plots, linear plots of molecular weight (M_n) versus conversion, in hydrodynamic diameter with increasing conversion, and narrow molecular weight distributions (M_w/M_n) for the grafted polymer samples were observed. Hydrolysis of silica cores by hydrofluoric acid treatment enabled characterization of cleaved polymer using GPC. Ultrathin films of hybrid nanoparticles were examined using TEM and AFM.     

Thermal degradation of polystyrene in the presence of hydrogen by catalyst in solution

For the first time, low temperature degradation (170-240 °C) of polystyrene in benzene is carried out in the presence of hydrogen using iron(III) oxide catalyst. The effect of temperature, catalyst loading and polymer loading on degradation are studied in hydrogen atmosphere. Degradation is also carried out at different initial hydrogen partial pressure. The time dependent molecular weight is calculated using viscosity average method. It is found that the degradation is enhanced considerably in the presence of hydrogen and followed random degradation chain scission. A random degradation kinetic model of Kelen [Kelen T. Polymer degradation. New York: Van Nostrand Reinhold Company; 1983.] is used to estimate the degradation rate constants. Empirical correlations are proposed to account for the effect of catalyst loading and initial hydrogen partial pressure on degradation. The true thermal degradation rate constants are calculated using these proposed correlations at given catalyst loading and initial hydrogen partial pressure with varying temperature. The frequency factor and activation energy are also determined using Arrhenius equation considering the true thermal degradation rate constants.     

Regio‐regular structure high molecular weight poly(propylene carbonate) by rare earth ternary catalyst and Lewis base cocatalyst

Lewis base modification strategy on rare earth ternary catalyst was disclosed to enhance nucleophilic ability of active center during copolymerization of carbon dioxide and propylene oxide (PO), poly(propylene carbonate) (PPC) with H‐T linkages over 83%, and number–average molecular weight (M_n) up to 100 kg/mol was synthesized at room temperature using Y(CCl₃OO)₃‐ZnEt₂‐glycerine catalyst and 1,10‐phenanthroline (PHEN) cocatalyst. Coordination of PHEN with active Zinc center enhanced the nucleophilic ability of the metal carbonate, which became more regio‐specific in attacking carbon in PO, leading to PPC with improved H‐T linkages. Moreover, the binding of PHEN to active Zinc center also raised the carbonate content of PPC to over 99%, whereas the PPC from common rare earth ternary catalyst was about 96%. Unlike the highly regio‐regular structure PPC but with relatively low molecular weight recently reported in the literature, our high molecular weight regio‐regular PPC did show significant improvement in thermal and mechanical performances. PPC with H‐T linkages up to 83.2% showed glass transition temperature (T_g) of 43.3 °C, while T_g of PPC with H‐T linkages of 69.7% was only 36.1 °C. When H‐T connectivity was raised from 69.7 to 83.2%, the modulus of PPC showed a 78% increase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4451–4458, 2008     

Phenanthrene degradation in subcritical water

Subcritical water (<374 °C and <221 bar) has unique characteristics such as dramatically decreased dielectric constant, surface tension, and viscosity with increasing temperature, allowing for dissolution and reaction of organics in high-temperature water to occur. Additionally, the dissociation constant of water at temperatures of 200-300 °C is three orders of magnitude greater than that of ambient water, which may also contribute to the reactivity of subcritical water with certain organic compounds. In this study, the degradation and oxidation of phenanthrene in subcritical water were investigated. Both deionized water and water with 3% hydrogen peroxide were used in the degradation and oxidation studies. The effect of temperature on degradation efficiency has been determined with a temperature range of 100-350 °C. When the temperature was increased from 150 to 350 °C, the amount of phenanthrene degraded varied from 6 to 243 μg in each milliliter of deionized water. However, these quantities were increased to 195 μg at 150 °C and 3680 μg at 350 °C in each milliliter of water with 3% hydrogen peroxide. Several degradation products including phenol, benzoic acid, and ketones were identified by using gas chromatography/mass spectrometry (GC/MS).     

高分子量二氧化碳-环氧丙烷共聚物的合成条件研究

利用新型多配体负载戊二酸锌来催化二氧化碳和环氧丙烷合成高分子量聚碳酸(1,2-丙二醇).通过研究反应时间和反应压力对产率以及产物的结构和性能的影响来对反应条件进行了优化.结果表明在反应压力为5.2MPa,反应时间为40h时所得聚合物的数均分子量大于23×104,玻璃化转变温度达到38℃,拉伸强度达到31MPa.     

The influence of biotic and abiotic factors on the rate of degradation of poly(lactic) acid (PLA) coupons buried in compost and soil

Poly(lactic) acid (PLA) is a compostable biopolymer and has been commercialised for the for the manufacture of short-shelf life products. As a result, increasing amounts of PLA are entering waste management systems and the environment; however, the degradation mechanism is unclear. While hydrolysis of the polymer occurs abiotically at elevated temperature in the presence of water, potential catalytic role for microbes in this process is yet to be established. In this study, we examined the degradation of PLA coupons from commercial packaging at a range of temperatures (25°, 37°, 45°, 50° and 55 °C) in soil and compost and compared with the degradation rates in sterile aqueous conditions by measuring loss of tensile strength and molecular weight (Mw). In addition, in order to assess the possible influence of abiotic soluble factors in compost and soil on degradation of PLA, degradation rates in microorganism-rich compost and soil were compared with sterile compost and soil extract at 50 °C. Temperature was determined to be the key parameter in PLA degradation and degradation rates in microorganism-rich compost and soil were faster than in sterile water at temperatures 45° and 50 °C determined by tensile strength and Mw loss. Furthermore, all tensile strength was lost faster after 30 and 36 days in microorganism-rich compost and soil, respectively, than in sterile compost and soil extract, 57 and 54 days, respectively at 50 °C. Significantly more Mw, 68% and 64%, was lost in compost and soil, respectively than in compost extract, Mw, 53%; and in soil extract, 57%. Therefore, degradation rates were faster in microorganism-rich compost and soil than in sterile compost and soil extract, which contained the abiotic soluble factors of compost and soil at 50 °C. These comparative studies support a direct role for microorganisms in PLA degradation at elevated temperatures in humid environments. No change in tensile strength or Mw was observed either 25° or 37 °C after 1 year suggesting that accumulation of PLA in the environment may cause future pollution issues.     

Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions

Selective oxidation of sulfides to sulfoxides and sulfones with hydrogen peroxide under organic solvent-free conditions was demonstrated by the MWW-type titanosilicate zeolite catalyst. Sulfides were oxidized smoothly to give sulfoxides with good selectivities at ambient temperature using 1.0–1.2 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst. Especially, the Ti-MWW with an interlayer-expanded structure (Ti-IEZ-MWW) catalyst showed high activity with good chemoselectivity for the oxidation of various sulfides. The catalyst is recyclable for at least five cycles, and the only byproduct is water. Sulfides were directly oxidized to give sulfones in high yields by 2.5 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions.     

The reciprocal influence between ion transport and degradation of PA66 in acid solution

Transport behavior of acid solution through polyamide was studied by measuring element distribution in cross section, pH, and ion concentration. Degree of degradation that related to the decreasing of molecular weight and flexural strength was observed in order to study the influence of acid solution on the polyamide 66 (PA66) degradation. The permeation mechanism of acid solution can be explained: at first water penetrates into polyamide and it is followed by acid. In this process, water does not affect the molecular weight at 50 °C but only reduces the polyamide strength by plasticization. Moreover, proton (H⁺) has contributed to the anion transport and degradation of polyamide by the hydrolytic reaction. Proton attacks the polyamide chain, and scission of chain occurs, and reacts with anion to form other material substance. This process affects the decrease of molecular weight and the significant loss of polyamide strength. Analysis results from ion concentration measurement shows that the amount of proton and anion transport into deionized waterside was imbalance, which probably due to the different mobility between proton and anion or formation of other material substance by reaction of anion and PA66 bond. Such information is not only necessary for the investigation of hydrolytic degradation of polymer and prediction of lifetimes for a protective polymer lining/coating to chemical attack, but may also be helpful towards gaining a deeper insight into the processes of degradation of other polymer.     

Ethylene polymerization studies with supported cyclopentadienyl,arene, and allyl chromium catalysts

Highly active catalysts for low pressure ethylene polymerization are formed when chromocene, bis (benzene)- or bis (cumene)-chromium or tris- or bis (allyl)-chromium compounds are deposited on high surface area silica-alumina or silica supports. Each catalyst type shows its own unique behavior in preparation, polymerization, activity, isomerization, and response to hydrogen as a chain transfer agent. The arene chromium compounds require an acidic support (silicaalumina) or thermal aging with silica to form a highly active catalyst. At 90°C polymerization temperature arene chromium catalysts produced high molecular weight polyethylene and showed, in contrast to supported chromocene catalysts, a much lower response to hydrogen as a chain transfer agent. An increase in polymerization temperature caused a significant decrease in polymer molecular weight. Addition of cyclopentadiene to supported bis (cumene)-chromium catalyst led to a new catalyst which showed a chain transfer response to hydrogen typical of a supported chromocene catalyst. Polymerization activity with tris- or bis (allyl)-chromium appears to depend on the divalent chromium content in the catalyst. Changes in the silica dehydration temperature of supported allyl chromium catalyst have a significant effect on the resulting polymer molecular weight. High molecular weight polymers were formed with catalysts that were prepared using silica dehydration temperatures below about 400°C. Dimers, trimers, and oligomers of ethylene were usually formed with catalysts that were prepared on silica dehydrated much above 400°C. The order of activity of the different types of catalysts was chromocene/silica > chromocene/silica-alumina > bis (arene)-chromium/silica-alumina ? allyl chromium/silica.     

Synthesis and characterization of high molecular weight poly(1,2-propylene carbonate-<Emphasis Type="Italic">co</Emphasis>-1,2-cyclohexylene carbonate) using zinc complex catalyst

Using supported multi-component zinc dicarboxylate catalyst,poly（1,2-propylene carbonate-co-1,2-cyclohexylene carbonate）（PPCHC） was successfully synthesized from carbon dioxide（CO₂） with propylene oxide（PO） and cyclohexene oxide（CHO）.The conversion of epoxides dramatically increased up to 89.7%（yield:384.2 g of polymer per g of Zn） with increasing reaction temperature from 60℃to 80℃.The optimized reaction temperature is 80℃.The chemical structure,the molecular weight,as well as thermal and mechanical properties of the resulting terpolymers were investigated extensively. When CHO feed content（mol%） is lower than 10%,the PPCHC terpolymers have number average molecular weight（M_n） ranging from 102×10³ to 202×10³ and molecular weight distribution（MWD） values ranging from 2.8 to 3.5.In contrast to poly（propylene carbonate）（PPC）,the introduction of small amount of CHO leads to increase in the glass transition temperature from 38.0℃to 42.6℃.Similarly,the mechanical strength of the synthesized terpolymer is greatly enhanced due to the incorporation of CHO.These improvements in mechanical and thermal properties are of importance for the practical application of PPC.     

In vitro and in vivo degradation of an injectable bone repair composite

In vitro and in vivo degradation behaviors of an injectable bone regeneration composite (IBRC) which comprised of nano-hydroxyapatite/collagen (nHAC) particles in alginate hydrogel carrier were investigated. In vitro degradation quantitative testing indicated that the alginate had a faster degradation rate in simulated body fluid (SBF) than in deionized water at 37 °C. Similarly, IBRC also had a higher degradation rate in SBF than in deionized water at 37 °C, which was evaluated by alginate molecular weight measurement, mechanical properties test and degradation kinetics evaluation. But molecular weight of alginate degraded slower in IBRC than that in aqueous solution. In vitro results showed that degradation medium SBF had influence on degradation of alginate molecules. In the in vivo degradation study, surprisingly, there was no obvious decreasing of molecular weight of alginate from 0 to 8 weeks. IBRC degraded mostly after 24 weeks implantation and was replaced by connective tissue. No fibrous capsule and acute inflammatory reaction were found during the observed 24 weeks after IBRC implantation. There is only a mild short-term inflammatory response in rat dorsum muscle. These results indicated that IBRC had a controllable degradability and biocompatibility. Therefore, IBRC may be a promising degradable material for bone repair and bone tissue engineering.     

Protein release from interpenetrating polymer network hydrogels triggered by endogenous biomarkers

A biocompatible drug delivery system with a high-sensitive stimuli-responsive behavior is reported. Calcium alginate hydrogels interpenetrated with polyvinyl alcohol–diboronate polymer network (IPN) effectively respond to the presence of hydrogen peroxide through oxidative degradation of boronate esters. The degradation of the IPN entails the reopening of the original alginate pores, resulting in a 5–9 times increase in release rates of encapsulated proteins with molecular masses ranging from 16.7 to 66 kDa. The release can be triggered by hydrogen peroxide concentrations as low as 50 μM in the bulk solution. Alternatively, hydrogen peroxide can also be generated inside the hydrogels by incorporation of oxidase enzymes in the presence of their substrates, such as lactate, glucose, or hypoxanthine, which can serve as biomarkers of certain physiological disorders.     

Temperature‐responsive Catalyst for the Coupling Reaction of Carbon Dioxide and Propylene Oxide

The selective synthesis of polypropylene carbonate (PPC) and cyclic propylene carbonate (CPC) from coupling reaction of CO₂ and propylene oxide (PO) is a long term pursuing target. Here we report that a temperature controllable porphyrin aluminum catalyst using 5,10,15,20‐tetra(1,2,3,4,5,6, 7,8‐octahydro‐1,4:5,8‐dimethanoanthracen‐9‐yl)porphyrin as ligand, once in conjunction with suitable onium salt, achieved single cycloaddition or copolymerization reaction. Only cycloaddition reaction happened at temperature above 75 °C to produce 100% CPC, whereas copolymerization became dominant to afford PPC with selectivity over 99% at 25 °C, and the obtained PPC showed over 99% carbonate linkage and 92% head‐to‐tail structure. Based on systematic analysis of the electronic and steric feature in the porphyrin ligand, it was found that the electronic feature of the substituent in porphyrin ligand was decisive for PPC selectivity, porphyrin ligand bearing strong electron‐donating substituents displayed a significantly reduced tolerance towards increased temperature with respect to PPC formation. Therefore, temperature‐responsive catalyst could be designed by suitable modification in porphyrin ligand, and such accurate synthesis of target product by one catalyst may create a useful and facile platform for selective PPC or CPC production.     

Studies on the atom transfer radical polymerization of a maleimide AB* monomer and modification of the halogen end groups

The atom transfer radical polymerization (ATRP) of an AB* monomer, N-(4-α-bromobutyryloxy phenyl)maleimide (BBPMI), was conducted using the complex of CuBr/2,2′-bipyridine as catalyst. The study of kinetics of polymerization and the growth behavior of macromolecules show that the polymerization proceeds rapidly in first 1 h and then slows down. The decrease in the rate of polymerization is ascribed to the poor reactivity of maleimide radicals from A* to initiate the polymerization of maleimide double bonds. The molecular weight of the resulting polymer also increases with the dosage of catalyst. The coincidence of molecular weight determined by hydrogen proton nuclear magnetic resonance spectroscopy (¹H NMR) and gel permeation chromatography (GPC) proves that the resulting polymer is of linear structure, which is further verified by ¹³C NMR measurement and high performance liquid chromatography (HPLC) analysis of the hydrolysate of the resulting polymer. The stabilization modification of the halogen end groups of the resulting polymer by free-radical chain transfer reaction was attempted under ATRP condition. Isopropyl benzene was employed as the chain transfer agent. Indeed, the modified polymer with carbon-bromine bonds conversion of 40.7% shows enhanced thermal stability. The initial weight loss temperature has been increased from 193 to 243 °C. On the other hand, the atom transfer radical copolymerization of BBPMI with styrene resulted in the formation of hyperbranched polymer.     

Synthesis and biodegradation studies of 1,3-propanediol based aliphatic poly(ester carbonate)s

A series of poly(ester carbonate)s were obtained from adipic acid, 1,3-propanediol and diethyl carbonate in the presence of catalyst Ti(OBu)₄ by polycondensation and transestrification process. The amount of monomeric composition was varied in order to get the polymer of different composition. The structure, average molecular weight and physical properties of poly(ester carbonate) were characterized by FT-IR, ¹H NMR, solubility, solution viscosity, gel permeation chromatography, differential scanning calorimetry and XRD analysis. Biodegradability of poly(ester carbonate)s was investigated by hydrolytic (pH 7.2 and 11.5), enzymatic using Rhizopus delemar lipase at 37 °C and soil burial test. The biodegradation rate observed was more for poly(ester carbonate) containing 40% and 10% of diethyl carbonate due to their low crystallinity.     

H2O2氧化降解海藻酸钠的研究

低分子量海藻酸钠在生物医学领域显示出越来越多的优势,以H2O2为氧化剂对海藻酸钠进行了降解研究。结果表明：随着溶液pH值的降低、反应温度的升高及H2O2用量的增加,氧化产物的表观粘度下降,降解速度加快,Cu2+和Fe2+等金属离子的存在加快了海藻酸钠的降解。GPC结果表明海藻酸钠被氧化降解后,分子量下降,分布变宽。FTIR显示,降解前后海藻酸钠的糖环结构没有改变,主要是开裂海藻酸钠的β-(1,4)糖苷键。