八甲基环四硅氧烷与氨取代基有机硅单体的共聚动力学Ⅱ模型考核与结果讨论

对前文 (I)的共聚动力学模型进行了分析与简化 ,并分别通过对各影响因素的单因素实验和多因素相互作用实验对模型进行了进一步的考核 ,确定了模型参数并通过模型对聚合动力学行为作了说明     

八甲基环四硅氧烷改性苯丙乳液的动力学研究

用八甲基环四硅氧烷(D4)改性丙烯酸丁酯(BA)-苯乙烯(St)乳液,得到了稳定的改性苯丙乳液.研究了该聚合体系的动力学特征,讨论了加料方式、反应温度、D4加入量对聚合速率的影响.结果表明:采用预乳化半连续滴加法,聚合速率比间歇加料法平缓、单体转化率较高;当D4用量在3%～8%时,聚合速率和转化率随其增加稍有降低;反应温度由65℃升高到80℃,聚合速率和转化率都相应提高.     

相反转法制备有机硅阴离子乳液

研究了八甲基环四硅氧烷(D4)的开环乳液聚合,讨论了温度、催化剂、乳化剂用量对反应速率、转化率及乳液稳定性的影响,优选的制备条件为:在复配乳化剂质量比m(SDBS)∶m(OP-10)为3∶2~1∶1、用量为1%~2%(对单体质量,下同)时,通过相反转法对D4进行预乳化,采用连续聚合法得到了固体质量分数为40%、带蓝光半透明、无“漂油”的有机硅阴离子乳液.     

阳离子有机硅柔软剂的合成及应用

以D4、1631、1227和水为原料,以KOH为催化剂,合成阳离子有机硅柔软剂,探讨了温度、催化剂用量、搅拌速度、乳化剂用量和乳化剂比例对八甲基环四硅氧烷转化率的影响。结果表明催化剂用量为1%,温度为80℃,搅拌速度为300～350r/min,乳化剂用量为7.4%,乳化剂比例1631∶1227=3.5∶1是合成最佳条件;自制柔软剂的粒径在62.8nm左右,且对织物白度基本没有影响,对织物柔软性和撕裂强力的改善与商品柔软剂相当,对织物的亲水性影响比商品柔软剂小。     

酸白土催化体系开环八甲基环四硅氧烷的研究及机理探讨

Cationic ring opening polymerization of octamethylcyclotetrasiloxane （Da） initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments.Higher temperature was found beneficial for the reaction process while stirring intensity beyond a certain level showed no obvious effect on the reaction rate. Polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance （IH-NMR） and gel perneation chromotography. The width of molecular mass distribution was found ranging between 1.2 and 1.4, which is extraordinarlly narrow compared with that of cationic polymerizations reported elsewhere （〉 1.9）. The results were believed due to the absence of free proton and counter ion which simplifies the polymerization process and the huge steric hindrance provided by bentonite particles which keeps the propagation of polysiloxane onto the surface of bentonite particles in a much more regular way. A feasible mechanism is proposed and seems to be supported well by experiments. Additionally, from the results of α, ω-dihydrogen terminated polysiloxanes prepared, the possibility of applying this potential environmentally friendly heterogeneous catalyst in industrial polymerization of cyclosiloxanes is anticipated.     

Anionic polymerization of octamethylcyclotetrasiloxane in aqueous emulsion I: Preliminary results and kinetic study

The synthesis of poly(dimethylsiloxane) (PDMS) by anionic polymerization of octamethylcyclotetrasiloxane (D₄) in aqueous emulsion using an emulsifying agent acting also as initiator (benzyldimethyldodecylammonium hydroxide) is described. Stable emulsions of α,ω-dihydroxy PDMS with an easily controlled molar mass (up to 15 000), a low polydispersity index and high yields were obtained. The amount of cyclics formed (essentially D₄ to D₇) is lower than that observed in bulk. Kinetics analysis and computerized simulations are in good agreement with a reaction scheme involving simultaneous polyaddition/polycondensation processes. At high monomer consumption, polycondensation predominates leading to a broadening of the molecular weight distribution (MWD). The apparent rate constants of initiation, propagation and condensation at various temperatures and the corresponding activation energies were determined.     

有机硅/丙烯酸酯共聚乳液的耐热性能

以八甲基环四硅氧烷、乙烯基三甲氧基硅烷、丙烯酸丁酯、甲基丙烯酸甲酯、丙烯酸等为原料，采用种子乳液聚合法合成了高有机硅含量的有机硅／丙烯酸酯接枝共聚物。利用红外光谱表征了有机硅丙烯酸酯共聚物的结构，利用热重分析测试了共聚物的热分解温度。结果表明，丙烯酸酯聚合物上成功地引入了有机硅链节，且耐热性能得到很大地提高。     

Kinetics of the Anionic Ring Opening Polymerization of Cyclosiloxanes Initiated with a Superbase

Kinetics of the anionic ring opening polymerization of octamethylcyclotetrasiloxane, D₄, and hexamethylcyclotrisiloxane, D₃, in toluene solution initiated by hexapyrrolidinediphosphazenium hydroxide, P₂Pyr₆ ⁺OH^– were studied. Reactions are first order both in monomer and in initiator. The specific rate of the D₃ polymerization is higher than that of D₄ by about 2–3 orders of magnitudes. Activation energies are 18.1 kcal mol^–1 for D₄ and 11 kcal mol^–1 for D₃. The back-biting reaction leading to decamethylcyclopentasiloxane, D₅, was followed in the polymerization of D₄. This reaction is retarded by the presence of monomer. The kinetics is interpreted in terms of a mechanism in which the active propagation center appears mostly as a monomer separated ion pair, which is also the intermediate in the propagation step.     

高粘度甲基硅油的合成及其拼混数学模型

在催化剂四甲基氢氧化铵作用下,以八甲基环四硅氧烷(D4)和六甲基二硅醚(MM)为原料合成了高粘度甲基硅油。考察了催化剂用量、反应物中起始水分以及封头剂的加入温度及加入量等因素对产品粘度的影响。其最佳反应条件为:催化剂用量为m(催化剂)∶m(D4)=8.0×10-5∶1,水分控制在0.5%~1.0%,封头剂的加入温度为85~90°C,封头剂的用量为m(封头剂)∶m(D4)=1.0×10-3。在此条件下,得到粘度(5.5~6.0)×102Pa.s的甲基硅油。并通过对不同粘度的甲基硅油进行拼混试验,建立了甲基硅油粘度拼混数学模型为m1logμ1 m2logμ2=(m1 m2)logμ3,拼混得到的甲基硅油其粘度的实测值与计算值相对误差小于3%。     

Prenatal Octamethylcyclotetrasiloxane Exposure Impaired Proliferation of Neuronal Progenitor,Leading to Motor,Cognition, Social and Behavioral Functions

Cyclic siloxane octamethylcyclotetrasiloxane (D4) has raised concerns as an endocrine-disrupting chemical (EDC). D4 is widely used in detergent products, cosmetics, and personal care products. Recently, robust toxicological data for D4 has been reported, but the adverse effects of D4 on brain development are unknown. Here, pregnant mice on gestational day 9.5 were treated daily with D4 to postnatal day 28, and the offspring mice were studied. The prenatal D4-treated mice exhibited cognitive dysfunction, limited memory, and motor learning defect. Moreover, prenatal D4 exposure reduced the proliferation of neuronal progenitors in the offspring mouse brain. Next, the mechanisms through which D4 regulated the cell cycle were investigated. Aberrant gene expression, such as cyclin-dependent kinases CDK6 and cyclin-dependent kinase inhibitor p27, were found in the prenatal D4-treated mice. Furthermore, the estrogen receptors ERa and ERb were increased in the brain of prenatal D4-treated mice. Overall, these findings suggest that D4 exerts estrogen activity that affects the cell cycle progression of neuronal progenitor cells during neurodevelopment, which may be associated with cognitive deficits in offspring.