Studies on thermal and morphological properties of 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane-epoxy-bismaleimide matrices

A new cyanate ester monomer, 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane has been synthesized and characterized. Epoxy modified with 4, 8 and 12% (by weight) of cyanate ester were made using epoxy resin and 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane and cured by using diaminodiphenylmethane. The cyanate ester modified epoxy matrix systems were further modified with 4, 8 and 12% (by weight) of bismaleimide (N,N′-bismaleimido-4,4′-diphenylmethane). The formation of oxazolidinone and isocyanurate during cure reaction of epoxy and cyanate ester blend was confirmed by IR spectral studies. Bismaleimide-cyanate ester-epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. Thermal studies indicate that the introduction of cyanate ester into epoxy resin improves the thermal degradation studies at the expense of glass transition temperature. Whereas the incorporation of bismaleimide into epoxy resin enhances the thermal properties according to its percentage content. However, the introduction of both cyanate ester and bismaleimide influences the thermal properties according to their percentage content. DSC thermogram of cyanate ester modified epoxy and bismaleimide modified epoxy show unimodel reaction exotherms. The thermal degradation temperature and heat distortion temperature of the cured bismaleimide modified epoxy and cyanate ester-epoxy systems increased with increasing bismaleimide content. The morphology of the bismaleimide modified epoxy and cyanate ester-epoxy systems were also studied by scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd.     

Influence of the Epoxy/Acid Stoichiometry on the Cure Behavior and Mechanical Properties of Epoxy Vitrimers

Bisphenol A epoxy resin cured with a mixture of dimerized and trimerized fatty acids is the first epoxy vitrimer and has been extensively studied. However, the cure behavior and thermal and mechanical properties of this epoxy vitrimer depend on the epoxy/acid stoichiometry. To address these issues, epoxy vitrimers with three epoxy/acid stoichiometries (9:11, 1:1 and 11:9) were prepared and recycled four times. Differential scanning calorimetry (DSC) was used to study the cure behavior of the original epoxy vitrimers. The dynamic mechanical properties and mechanical performance of the original and recycled epoxy vitrimers were investigated by using dynamic mechanical analysis (DMA) and a universal testing machine. Furthermore, the reaction mechanism of epoxy vitrimer with different epoxy/acid stoichiometry was interpreted. With an increase in the epoxy/acid ratio, the reaction rate, swelling ratio, glass transition temperature and mechanical properties of the original epoxy vitrimers decreased, whereas the gel content increased. The recycling decreased the swelling ratio and elongation at break of the original epoxy vitrimers. Moreover, the elongation at break of the recycled epoxy vitrimers decreased with the epoxy/acid ratio at the same recycling time. However, the gel content, tensile strength and toughness of the original epoxy vitrimers increased after the recycling. The mechanical properties of epoxy vitrimers can be tuned with the variation in the epoxy/acid stoichiometry.     

Structure,Properties and Biodegradation of Some Bacterial Copoly(hydroxyalkanoate)s

This article describes the relationships between not only comonomer-unit compositions but also their distributions and structures as well as properties for bacterial copoly(hydroxyalkanoate)s, including poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxy-propionate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxy-butyrate-co-4-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-mercapto-propionate). It was found that as-produced copoly(hydroxy-alkanoate)s have broad comonomer-unit compositional distributions, which we can control to some degree. The structure and properties of copoly(hydroxy-alkanoate)s depend not only on the chemical structure and the comonomer-unit composition but also on the comonomer-unit compositional distribution.     

Synthesis and Properties of Hydrogels Based on Chitosan and Poly(Vinyl Alcohol) Crosslinked by Genipin

Semi‐interpenetrating polymeric networks of chitosan and poly(vinyl alcohol) [PVA] were prepared by varying the ratio of the constituents. The hydrogels were crosslinked using genipin, a naturally occurring nontoxic cross‐linking agent. The swelling behavior of these hydrogels was studied by immersing the films in deionized water at various temperatures and in buffer solutions of different pH. The states of water in the hydrogels, swollen at 25°C and pH 7, were determined using Differential Scanning Calorimetry (DSC). The swelling behavior of the gels was found to be dependent on temperature and pH of the medium. The amount of freezing water in the swollen hydrogels increased, whereas the amount of nonfreezing bound water remained more or less the same with increasing PVA concentration.     

液晶聚芳醚酮的结构与性能研究

以联苯二酚、取代对苯二酚及含氟酮单体为原料 ,通过亲核取代反应 ,合成了系列具有液晶性的新型聚芳醚酮 .研究了聚合物分子结构与性能之间的关系 .由于结晶相是从有序的液晶相转化形成的 ,故侧基含量的增加对液晶聚合物的融熔转变温度无显著影响 .聚合物的液晶稳定性受侧基影响较大 ,含极性侧基的氯取代聚合物的液晶温区比含大空阻侧基的聚合物的液晶温区小得多 ,说明空间几何因素比极性因素对液晶稳定性的影响大 .不同分子量聚合物有不同的液晶有序结构 ,低分子量聚合物具有高有序液晶结构 ,而高分子量聚合物只有低有序的向列相结构 .     

Effects of Sericite Modified by Macromolecular Dispersant on the Thermal,Mechanical and Electrical Properties of the NR/SBR Composites

A new hydrosoluble macromolecular dispersant and modifier, poly(ethylene glycol)-maleic anhydride-acrylic acid (PEG-MA-AA) terpolymer was synthesized via ring-opening reaction and free radical polymerization. The chemical structure of the PEG-MA-AA terpolymer was confirmed by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance spectroscopy (NMR), and its average molecular weight was determined by gel permeation chromatography (GPC). Modified sericite (MSE) was synthesized from sericite (SE) by the surface modification with PEG-MA-AA. The NR/SBR/MSE composites were prepared via the blending of the modified sericite and NR/SBR rubber. The thermal, mechanical and electrical properties of the composites were investigated by TGA, tensile test machine and high-insulation resistance meter. The results showed that the thermal stability and the mechanical and electrical insulation properties of NR/SBR/MSE composites were improved significantly. SEM also revealed that modified sericite possessed good dispersibility.     

生物可降解共聚物聚丁二酸/对苯二甲酸丁二醇酯(PBST)的序列结构及结晶性研究

制备了高分子量的聚丁二酸丁二醇酯,并通过与对苯二甲酸二甲酯的无规共聚调节其生物可降解性及力学性能,得到了具有优良机械性能和不同生物降解速度的一系列共聚物,并对共聚物序列结构、热力学性能、结晶性进行了研究.结果表明,该共聚物为无规共聚物,PBS和PBT分别结晶.共聚物的结晶熔点符合无规共聚物的Flory方程.     

Exploration of the Crystal Structure and Thermal and Spectroscopic Properties of Monoclinic Praseodymium Sulfate Pr2(SO4)3

Praseodymium sulfate was obtained by the precipitation method and the crystal structure was determined by Rietveld analysis. Pr₂(SO₄)₃ is crystallized in the monoclinic structure, space group C2/c, with cell parameters a = 21.6052 (4), b = 6.7237 (1) and c = 6.9777 (1) Å, β = 107.9148 (7)°, Z = 4, V = 964.48 (3) ų (T = 150 °C). The thermal expansion of Pr₂(SO₄)₃ is strongly anisotropic. As was obtained by XRD measurements, all cell parameters are increased on heating. However, due to a strong increase of the monoclinic angle β, there is a direction of negative thermal expansion. In the argon atmosphere, Pr₂(SO₄)₃ is stable in the temperature range of T = 30–870 °C. The kinetics of the thermal decomposition process of praseodymium sulfate octahydrate Pr₂(SO₄)₃·8H₂O was studied as well. The vibrational properties of Pr₂(SO₄)₃ were examined by Raman and Fourier-transform infrared absorption spectroscopy methods. The band gap structure of Pr₂(SO₄)₃ was evaluated by ab initio calculations, and it was found that the valence band top is dominated by the p electrons of oxygen ions, while the conduction band bottom is formed by the d electrons of Pr³⁺ ions. The exact position of ZPL is determined via PL and PLE spectra at 77 K to be at 481 nm, and that enabled a correct assignment of luminescent bands. The maximum luminescent band in Pr₂(SO₄)₃ belongs to the ³P₀ → ³F₂ transition at 640 nm.     

Effects of pH During the Base Catalyzed Reaction of Two-Step Acid/Base Catalyzed Process on the Microstructures and Physical Properties of Poly(dimethylsiloxane) Modified Silica Xerogels

Poly(dimethylsiloxane) (PDMS) modified silica xerogels were prepared by two-step acid/base catalyzed sol-gel process. By keeping the acid amount and hydrolysis period in acidic environment fixed, and adding different amounts of base to the sol afterwards, attempts had been made to study the effect of the different amounts of base catalyst on the micro-structure and physical properties of the prepared ORMOSILs. DTA, SEM, BET, FTIR were performed to characterize the derived specimens. The microstructure and physical properties are greatly influenced by the amount of base added to the sol. With increasing base content the crystallite size and porosity increase and the pore size distribution takes a broad spectrum. Whereas, the glass transition temperature seems to decrease with increasing of base catalyst amount. This is explained in terms of the change in the relative amounts of hydrolysis and condensation reactions due to the addition of different amount of base catalyst, which predominantly influences the condensation reactions. The results are reported in this communication along with possible explanations behind the observations.     

A Comprehensive Investigation of the Structural,Thermal, and Biological Properties of Fully Randomized Biomedical Polyesters Synthesized with a Nontoxic Bismuth(III) Catalyst

Aliphatic polyesters are the most common type of biodegradable synthetic polymer used in many pharmaceutical applications nowadays. This report describes the ring-opening polymerization (ROP) of l-lactide (L-LA), ε-caprolactone (CL) and glycolide (Gly) in the presence of a simple, inexpensive and convenient PEG200-BiOct₃ catalytic system. The chemical structures of the obtained copolymers were characterized by ¹H- or ¹³C-NMR. GPC was used to estimate the average molecular weight of the resulting polyesters, whereas TGA and DSC were employed to determine the thermal properties of polymeric products. The effects of temperature, reaction time, and catalyst content on the polymerization process were investigated. Importantly, the obtained polyesters were not cyto- or genotoxic, which is significant in terms of the potential for medical applications (e.g., for drug delivery systems). As a result of transesterification, the copolymers obtained had a random distribution of comonomer units along the polymer chain. The thermal analysis indicated an amorphous nature of poly(l-lactide-co-ε-caprolactone) (PLACL) and a low degree of crystallinity of poly(ε-caprolactone-co-glycolide) (PCLGA, X_c = 15.1%), in accordance with the microstructures with random distributions and short sequences of comonomer units (l = 1.02–2.82). Significant differences in reactivity were observed among comonomers, confirming preferential ring opening of L-LA during the copolymerization process.     

ChemInform Abstract: Electronic Structure,Elastic Anisotropy,Thermal Conductivity and Optical Properties of Calcium Apatite Ca5(PO4)3X (X: F,Cl or Br).

The structural properties, phase stability, electronic structure, elastic properties, and optical properties of Ca₅(PO₃)₄F (FA), Ca₅(PO₃)₄Cl (ClA) and Ca₅(PO₃)₄Br (BrA) are studied by DFT calculations with the generalized gradient approximation.     

Li(NTO)(H2O)2的热分解行为及其结构与性质的关系研究

摘要在水中合成了3-硝基-1,2,4．三唑-5-酮(NTO)的锂盐Li(NTO)(H2O)2,利用DSC,TG／DTG和IR方法研究了其金属配合物的热分解机理,并用Kissinger法、Ozawa法、积分法和微分法对标题配合物进行了非等温动力学研究,得到了热分解反应的动力学参数,确定了热分解第一阶段的动力学方程及配合物的热爆炸临界温度(Tb)为289．33℃．采取RHF／6-31G,DFT-RB3LYP／6-31G方法对标题化合物进行了几何全优化,并对其成键情况、电荷分布和化合物的稳定性进行了分析．     

(NiV13O38)7-的电子结构和催化性质的探讨

使用SCC－DV－Xα方法研究了高钒杂多化合物（NiV13O38）7-的电子结构，并探讨了它的催化性质·结果表明，（NiV13O38）7-是一种比Keggin结构更强的催化剂。分析了该阴离子中的键的强弱关系，认为配位数越少的氧与V形成的键越强．并分析了前线轨道HOMO，LUMO的组成，从而得出它的催化活性中心是Ni，V、一配位端氧，二、三配位桥氧，五配位中心氧的结论。     

Effect of Incorporating Aromatic and Chiral Groups on the Dielectric Properties of Poly(dimethyltin esters)

High‐dielectric constant materials are critical for numerous applications such as photovoltaics, photonics, transistors, and capacitors. There are numerous polymers used as dielectric layers in these applications but can suffer from having a low dielectric constant, small band gap, or ferroelectricity. Here, the structure–property relationship of various poly(dimethyltin esters) is described that look to enhance the dipolar and atomic polarization component of the dielectric constant. These polymers are also modeled using first principles calculations based on density functional theory (DFT) to predict such values as the total, electronic, and ionic dielectric constant as well as structure. A strong correlation is achieved between the theoretical and experimental values with the polymers exhibiting dielectric constants >4.5 with dissipation on the order of 10⁻³–10⁻².

     

基于[(Tp)Fe(CN)3]-氰根桥联异金属三核配合物的合成、晶体结构及磁性

采用[(Tp)Fe(CN)3]-(Tp=hydrotris(pyrazolyl)borate)与[NiL](ClO4)2(L=3,10-bis(2-bydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetra-decane)反应,合成了氰根桥联的异金属三核配合物[NiL][(Tp)Fe(CN)3]2·4H2O(1),并对其结构和磁性进行了研究.该化合物晶体属于正交晶系,Pbca空间群.配合物1中,Ni(Ⅱ)大环与2 [(Tp)re(CN)3]-通过氰根桥联,形成近似直线的三核结构.Ni原子的配位采取六配位稍畸变的八面体构型.其中大环配体上的4个N原子占据赤道平面而桥联氰根的2个N原子占据轴向位置.磁性测定表明在2-300 K的温度范围内,Ni(Ⅱ)和Fe(Ⅲ)之间通过桥联的氰根产生弱的铁磁相互作用.用哈密顿函数H=-2J(SFel·SNi SFe2·SNi)对其XMT-T曲线进行了拟合,得到1的朗德因子g=2.35和交换常数J=8.13 cm-1.最后,对配合物的结构与磁性的关系进行了讨论.     

基于[(Tp)Fe(CN)3]-氰基桥联双核配合物的合成、结构和磁性研究

采用[TpFe^Ⅲ(CN)₃]^-作为构筑基块，合成并表征了一个氰基桥联双核配合物[(Tp)Fe^Ⅲ(CN)₃Cu^Ⅱ(bpy)₂]ClO₄·CH₃OH (1)。对化合物1进行了晶体结构分析，其晶胞参数为a=0.904 26(5) nm，b=1.352 56(7) nm，c=1.556 02(8) nm，α=106.08(1)°，β=95.79(1)°，γ=91.01(1)°，P1空间群。在这个化合物中，[TpFe^Ⅲ(CN)₃]通过其中1个氰基与[Cu(bpy)₂]²⁺桥联，而另外2个氰基未参与配位。磁性研究表明，在化合物1中，Cu(Ⅱ)与Fe(Ⅲ)离子之间表现为铁磁相互作用。用哈密顿函数H=-2JS_FeS_Cu对其χ_MT-T曲线进行了拟合，得到1的朗德因子g=2.34和交换常数J=5.52 cm^-1。     

Kinetic Studies on Star Polymerization of Styrene,MA and MMA Using New Three and Four Arm Chain Transfer Agents (CTAs): The Role of R-Group Structure Present in the CTA on RAFT Polymerization

Polystyrene, poly(methylacrylate) and poly(methyl methacrylate) four and three-arm stars were synthesized by Reversible Addition Fragmentation chain-Transfer (RAFT) polymerization by using two new dithioester-derived chain transfer agents [CTA or R-S-(C = S)Z]), CTA-1 and CTA-2. CTA-1 is a four arm CTA while CTA-2 is a three-arm CTA. These were easily synthesized from commercially available reagents and were characterized by spectroscopic techniques such as ¹H-NMR, ¹³C-NMR, IR and mass spectrometry. It is demonstrated that the two new CTAs enable the growth of arms away from the core (i.e., core first approach). An attempt has been made to study the effect of the structure of the R-group, which is present as the core in the CTA, on the polymerization, by analyzing the detailed kinetics. This study suggests that CTA-2, with a benzylic R group, enables the controlled star polymerization of styrene while CTA-1, with a R group similar in structure to the propagating radical derived from the polymerization of methyl acrylate (MA), enables the controlled polymerization of MA although to a lesser extent. This study also reveals that the temperature of free radical initiated RAFT (star) polymerization should be chosen in such a way that it is a compromise between reasonable rate of homolysis of the initiator and the CTA (R-group).