水性丙烯酸改性环氧醇酸树脂的制备及性能研究

为了提高水性醇酸涂料的防腐性和耐候性,本文以 E-20环氧树脂和亚麻油酸反应制备环氧酯,并与苯甲酸、季戊四醇、苯酐反应制备环氧改性醇酸树脂,进一步采用丙烯酸类单体对制备的环氧改性醇酸树脂进行改性,制备了性能优异的水性丙烯酸改性环氧醇酸树脂,以制备的水性丙烯酸改性环氧醇酸树脂为成膜物质,设计了水性防腐涂料,讨论了脂肪酸的种类、环氧树脂的种类及用量、环氧酯的酯化度、改性单体的比例、助溶剂等因素对树脂性能的影响。结果表明：环氧树脂可以提高涂层的防腐性能,丙烯酸酯类单体可以提高涂层的耐候性、耐水性和耐盐雾性。     

耐高温丙烯酸酯压敏胶的研制

以丙烯酸丁酯(BA)和丙烯酸-2-乙基己酯(2-EHA)为软单体、甲基丙烯酸甲酯(MMA)为硬单体、环氧树脂(EP)为改性单体、丙烯酰胺(AM)为内交联剂、过氧化苯甲酰(BPO)为引发剂以及乙酸乙酯/乙醇为混合溶剂,采用溶液聚合法制备出一种耐高温溶剂型丙烯酸酯PSA(压敏胶)。研究了单体、引发剂和交联剂等对PSA性能的影响。结果表明:当w(2-EHA)=20%、w(MMA)=13%、w(BPO)=0.5%和w(AM)=0.6%时,PSA的综合性能相对最好;当w(EP)=5%时,PSA的耐高温性能显著提高。     

水性环氧丙烯酸接枝共聚物的合成与表征

环氧树脂EP因其价格低廉、综合性能优异,被广泛应用于涂料、粘结剂等行业,但由于相似相溶的原则,只有有机溶剂才能溶解环氧树脂,使其水性化研究一直被研究者所重视。文章用夺H型引发剂过氧化苯甲酰(BPO)诱导环氧树脂上"活泼H"产生C自由基,使其与丙烯酸类单体发生自由基共聚,达到接枝改性的目的,实现环氧树脂水性化;同时,用傅立叶红外光谱(FT-IR)、凝胶渗透色谱(GPC)、酸值对产物进行了分析与表征。研究发现:当m(环氧树脂)∶m(丙烯酸单体)=7∶3、BPO含量占总量3.3%、酸值60 mg KOH/g时,可制得一种接枝率较高、性能优异的水性环氧丙烯酸接枝共聚物(EAG)体系。     

丙烯酸酯接枝改性环氧树脂乳液的合成与性能研究

以BA(丙烯酸丁酯)为软单体、St(苯乙烯)为硬单体、EP(环氧树脂)为基体、APS(过硫酸铵)为引发剂和三乙烯四胺为固化剂,采用乳液聚合法合成了丙烯酸酯接枝改性EP乳液。研究结果表明:当反应温度为80℃、m(BA)∶m(St)=1∶1、n(环氧基)∶n(氨基)=1∶1、w(引发剂)=0.8%、w(乳化剂)=4%和w(EP)=25%(均相对于单体总质量而言)时,合成的丙烯酸酯改性EP乳液具有良好的综合性能,其稳定性及涂膜强度均满足应用要求。     

环氧树脂改性丙烯酸酯乳液的制备与性能研究

以甲基丙烯酸甲酯(MMA)、丙烯酸(AA)、丙烯酸丁酯(BA)和苯乙烯(St)为共聚单体,自制的环氧树脂(EP)乳液为改性剂,SDBS(十二烷基苯磺酸钠)/OP-10(烷基酚聚氧乙烯醚)为阴/非离子型复合乳化剂,过硫酸铵(APS)为引发剂,采用预乳化法制得EP改性丙烯酸酯乳液。研究结果表明:当m(SDBS)∶m(OP-10)=1.0∶1、m(软单体)∶m(硬单体)=5∶5、w(OP-10/SDBS)=4%、w(APS)=0.6%、w(改性剂)=10%(均相对于混合单体总质量而言)和反应温度为70~80℃时,制得的EP改性丙烯酸酯乳液具有良好的综合性能(如单体转化率大于95%、乳液的Ca~(2+)稳定性良好、胶膜吸水率小于5.0%和附着力为1级)。     

核/壳型含硅苯丙乳液的合成与研究

以甲基丙烯酸甲酯(MMA)和苯乙烯(St)为核单体,丙烯酸丁酯(BA)、丙烯酸(AA)和γ-(2,3-环氧丙氧)丙基三甲氧基硅烷(KH-560)为壳单体,制备出具有核/壳型结构的含硅苯丙乳液。采用激光粒度分析法、差示扫描量热法(DSC)、红外光谱(FT-IR)法和透射电镜(TEM)等测试手段,研究了软硬单体配比、乳化剂、引发剂和交联剂KH-560用量对乳液及其胶膜性能的影响。研究结果表明,当w(引发剂)=0.5%、m(BA)∶m(St)∶m(MMA)=1.5∶0.5∶1.0、w(混合乳化剂)=3.0%和w(KH-560)=16%时,制取的含硅苯丙乳液稳定性好、平均粒径小且分布较窄,适度交联可提高乳胶膜的耐水性和硬度。     

苯乙烯协助甲基丙烯酸缩水甘油酯固相接枝改性聚丁烯-1

以过氧化苯甲酰(BPO)为引发剂,甲基丙烯酸缩水甘油酯(GMA)为单体,苯乙烯(St)为共单体,通过固相接枝改性聚丁烯-1(PB-1),考察了反应温度、单体用量、共单体用量和引发剂用量对接枝反应的影响。实验研究表明:在GMA用量5%、BPO用量0.3%、n(GMA)/n(St)=1的条件下,100℃反应2 h后得到接枝率为4.8%的改性产物。共单体St的加入有利于GMA接枝到PB-1大分子链上,并在一定程度上抑制了PB-1的降解。     

带环氧基丙烯酸树脂改性环氧树脂防腐涂料的性能

利用自由基聚合法合成了带环氧基丙烯酸树脂,并对其结构进行了表征,研究了引发剂和链转移剂用量对带环氧基丙烯酸树脂黏度的影响。将带环氧基丙烯酸树脂与环氧树脂按1∶9的质量比混合,复配防腐颜料及填料制备改性环氧树脂防腐涂料,并测定了其层间附着力和防腐蚀性能。结果表明:单体发生完全聚合,且聚合物带环氧基;随着引发剂和链转移剂用量的增加,带环氧基丙烯酸树脂的黏度下降;与纯环氧树脂防腐涂料相比,改性环氧树脂防腐涂料的层间附着力更高,n(MMA)∶n(BA)∶n(GMA)为6.00∶3.00∶0.475和6.00∶3.00∶1.000的涂料配方耐盐雾性和电化学阻抗更优。     

丙烯酸酯改性环氧树脂乳液合成与性能研究

以St(苯乙烯)为介质,首先将AA(丙烯酸)和环氧树脂E-44进行酯化,然后采用预乳化方法,以酯化产物、St、BA(丙烯酸丁酯)为单体,通过乳液聚合制备了单组分丙烯酸酯改性的环氧树脂乳液,探讨了乳化剂和引发剂用量等对乳液性能的影响。研究结果表明:当环氧树脂用量为25%,n(E-44)∶n(AA)=1∶1.3,m(BA)∶m(St)=6∶4,引发剂用量为0.6%,乳化剂用量为4%时,乳液性能稳定且具有良好的涂膜性能;酯化过程中采用单体St为溶剂,避免了采用其他有机溶剂带来的污染问题,同时单组分结构设计赋予了乳液良好的施工便利性。     

高固含量苯丙微乳液的制备与性能研究

以苯乙烯(St)、甲基丙烯酸甲酯(MMA)和丙烯酸丁酯(BA)为共聚单体,丙烯酸(AA)为功能单体,反应型乳化剂(DNS-86)、十二烷基硫酸钠(SDS)和壬基酚醚磺基琥珀酸酯钠盐(OS)为复合乳化剂,采用种子乳液聚合法制备了粒径小、耐水性好且固含量为50%的苯丙微乳液。研究结果表明:当w(引发剂)=0.7%、m(MMA+St)∶m(BA)∶m(AA)=5.0∶4.7∶0.3、w(St)=15%~25%、m(DNS-86)∶m(SDS+OS)=3∶2且w(复合乳化剂)=5%时,高固含量苯丙微乳液的综合性能良好。     

Compact Swelling in Bi1.4Pb0.6Sr2Ca2Cu3.6Oy During the Formation of High-Tc Superconducting Phase

Compact swelling in Pb-doped Bi-Sr-Ca-Cu-O superconductor has been studied by observing the effects of the size of calcined powders, volatilization of materials, and sintering of high- T _c (2223) powders. The bulk density increases at the early stage of sintering, for about 20 h, and then decreases. Densification occurs when the low- T _c (2212) phase and a liquid phase exist, whereas dedensification occurs with the formation of the 2223 phase regardless of the presence of the liquid. Gas evolution from specimens does not appear to be responsible for compact swelling. Compact swelling is explained by anisotropic growth of thin, platelike 2223 grains in random orientation. When 2223 grains grow in a preferred direction, compact swelling is suppressed.     

Synthetic routes to nanoscale BxCyNz architectures

B_xC_yN_z nanoscale materials, hybrids of h-BN and graphite, have been recently synthesised using various techniques. Here, we present the latest advances in the synthesis and characterisation of B-C-N nanotubes and nanofibres. In particular, we focus on layered BC₂N, BN, BC and CN_x systems, reviewing their production methods as well as their structural and electronic properties. These materials may find important applications in the fabrication of nanotransistors, robust nanocomposites, conducting polymers, storage components and field emission sources.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.     

(Bi1/2Na1/2)TiO3–Ba(Cu1/2W1/2)O3 Lead-Free Piezoelectric Ceramics

(Bi_1/2Na_1/2)TiO₃ with 0–6 mol% Ba(Cu_1/2W_1/2)O₃ (BNT-BCW), a new member of the BNT-based group, has been prepared following the conventional mixed oxide route. The compacted bodies were sintered at 1130°C for 2 h to get dense ceramics. The addition of BCW into BNT ceramics facilitated the poling process because of a reduction in leakage current. 0.995BNT·0.005BCW ceramics exhibit a relatively high piezoelectric constant ( d ₃₃= 80 × 10⁻¹² C/N) and a relatively low dielectric loss (tan δ= 1.5%). Increased amount of BCW was found to increase the dielectric constant and loss of BNT-BCW ceramics and to suppress the grain growth. During sintering, some BCW diffuses into the lattice of BNT to form a solid solution and some remains on the grain boundaries.     

Structure Evolution from Pb(Mg1/3Nb2/3)O3 to La(Mg2/3Nb1/3)O3

The crystal structure of lanthanum-modified lead magnesium niobates having composition (Pb_{1− x} La _x ) (Mg_{(1+ x )/3}-Nb_{(2− x )/3})O₃ with X = 0 to 1 was investigated by X-ray powder diffraction. It was found that the fundamental reflections from perovskite structure remain in the whole range of composition. The superlattice reflections from the A(B'_1/2-B"_1/2)O₃ ordered structure are also well preserved for La content greater than 50 at.%; however, a series of extra peaks of mixing indices appears, with intensities gradually enhanced with the increase of La content. For the complete substitution of Pb by La, a splitting of some reflections can be observed in the diffraction pattern. The results indicate that the crystal structure evolves continuously with the La content, from disordered cubic perovskite of space group Pm 3 m for X = 0, to ordered cubic perovskite of space group Fm 3 m for X = 0.5, distorted cubic perovskite of space group Pa 3 for 0.5 < X < 0.9, and finally to a rhombohedral perovskite, possibly belonging to the space group R 3 , for X ≥ 0.9. In the evolution of structure, a linear reduction of the lattice constant of the perovskite cell from 4.048 to 3.964 Å was observed.