乙酸乙烯酯无乳化剂乳液聚合的影响因素探讨

采用乙酸乙烯酯(VAc)在水中以过硫酸钾(KPS)和亚硫酸氢钠氧化还原体系作为引发剂进行无乳化剂乳液聚合,探讨了引发剂浓度、聚合温度、单体浓度和搅拌速度对聚合速率及转化率的影响。结果表明:当VAc质量分数为30%,KPS:VAc摩尔比为1:2 000,聚合温度10℃,反应时间10 h,搅拌速度80 r/min,时聚合产物聚乙酸乙烯的聚合度达到10 848;当VAc质量分数为35%时,聚合转化率可达到96%,聚合速率与引发剂浓度的0.944次方成正比;当搅拌速度达到200 r/min以上时,搅拌速度对聚合速率以及转化率影的响可以忽略。     

N-苯基马来酰亚胺/苯乙烯/丙烯腈/ɑ-甲基苯乙烯乳液共聚动力学

以十二烷基硫酸钠(SDS)为乳化剂,过硫酸钾(KPS)引发剂引发N-苯基马来酰亚胺/苯乙烯/丙烯腈/ɑ-甲基苯乙烯(PMI/St/AN/-ɑMeSt)进行四元乳液共聚,考察了聚合温度,引发剂浓度,乳化剂浓度,-ɑMeSt浓度对聚合速率的影响。结果表明,共聚体系的表观活化能为84.14 kJ/mol,聚合初始速率同引发剂浓度的0.46次方和乳化剂浓度的0.57次方成正比。乳化剂浓度8.4 m mol/L,引发剂浓度1.8m mol/L,聚合温度75℃,聚合1 h,85℃熟化2 h是较为合理的反应条件。-ɑMeSt的浓度对聚合速率有很大的影响,应控制在0.35 mol/L以下。     

N-苯基马来酰亚胺/苯乙烯/丙烯腈/α-甲基苯乙烯乳液共聚动力学

以十二烷基硫酸钠（SDS）为乳化剂,过硫酸钾（KPS）引发剂引发N-苯基马来酰亚胺／苯乙烯／丙烯腈／α-甲基苯乙烯（PMI／St／AN／α-MeSt）进行四元乳液共聚,考察了聚合温度,引发剂浓度,乳化剂浓度,α-MeSt浓度对聚合速率的影响。结果表明,共聚体系的表观活化能为84．14kJ／mol,聚合初始速率同引发剂浓度的0．46次方和乳化剂浓度的0．57次方成正比。乳化剂浓度8．4mmol／L,引发剂浓度1．8mmol／L,聚合温度75℃,聚合1h,85℃熟化2h是较为合理的反应条件。α-MeSt的浓度对聚合速率有很大的影响,应控制在0．35mol／L以下。     

苯乙烯-丙烯酸乙酯微乳液制备工艺研究

以苯乙烯、丙烯酸乙酯为主要单体,以十二烷基硫酸钠(SDS)和辛基苯酚聚-氧乙烯醚(OP-10)组成混合乳化体系,以过硫酸钾(KPS)为引发剂,采用半连续微乳液聚合的方式制备丙烯酸酯微乳液。考察了单体配比、聚合温度、乳化体系配比、引发剂等因素对乳液性能的影响。当单体配比为m(EA)∶m(MMA)=1∶1、聚合温度为75～76℃、乳化剂用量共计25 g且SDS/OP-10=3∶2、引发剂用量为1.0g,且采取聚合中期补加KPS溶液的方式补加、丙烯酸用量为3%,体系的p H值在7～8时制得的微乳液的产品性能最好。     

苯乙烯/丙烯酸丁酯交联体系乳液聚合动力学研究

以十二烷基苯磺酸钠(SDBS)为乳化剂,过硫酸钾(KPS)引发苯乙烯/丙烯酸丁酯(St/BA)乳液共聚,加入二甲基丙烯酸乙二醇酯(EGDMA)、聚丁二烯生胶(PB)作为交联剂,研究了聚合温度、引发剂浓度、乳化剂浓度、单体配比对聚合速率的影响。实验结果表明,共聚体系的表观活化能为70.67kJ/mol,聚合初始速率与引发剂浓度的0.43次方、乳化剂浓度的0.56次方和单体BA的0.49次方成正比。     

低温乳液聚合制备超高分子量聚乙烯醇

采用一种新型氧化还原引发体系过硫酸钾(KPS)/N,N-二甲基乙醇胺(DMEA),通过低温乳液聚合制备了超高分子量的聚醋酸乙烯酯(PVAc),醇解得超高分子量的聚乙烯醇(PVA)。研究了不同引发剂质量分数、温度和乳化剂浓度对聚合反应的影响。结果表明,实验结果与一般自由基聚合规律一致,但由于醋酸乙烯酯(VAc)自由基本身活性很高,易发生链转移,乳化剂对VAc聚合有一定的缓聚作用。KPS/DMEA引发体系相比常用的KPS/NaHSO_3具有更高的引发反应活性。反应最佳条件如下:反应温度2℃,引发剂质量分数为0.4%,乳化剂质量分数为0.5%,得到PVAc的黏均聚合度为28 940,PVA的黏均聚合度为9 077,支化度为2.19。     

聚丙烯酸钠高吸水剂的合成和性能评价

以丙烯酸（从）共聚单体,分别以过硫酸钾（KPS）和N,N-亚甲基双丙烯酰胺（NMBA）为引发剂和交联剂,采用水溶液聚合法合成聚丙烯酸钠高吸水性树脂。评价了SAP在蒸馏水的吸水速率及SAP在水中的保水能力。探讨了单体浓度（M）、引发剂浓度（I）、交联剂浓度（C）、聚合温度（℃）对SAP在自来水中吸水倍率的影响。结果表明：在AA浓度为40％：交联剂N,N′-亚甲基双丙烯酰胺质量分数为单体总量的0．035％;引发剂质量分数为0．10％;聚合温度为80℃;合成得到的高吸水性树脂吸蒸馏水率达到1050g／g。     

ASPAA/MMA/AN三元共聚物的合成与表征

在合成N-[4-(磺酰胺)苯基]丙烯酰胺(ASPAA)单体,并进行结构表征的基础上,以N,N-二甲基甲酰胺为溶剂,过氧化苯甲酰为引发剂,采用自由基溶液聚合合成了ASPAA／甲基丙烯酸甲酯／丙烯腈三元共聚物,用IR和^1H—NMR图谱确认了结构。共聚结果表明85℃和95℃,引发剂浓度1．0％～1．5％时,聚合初期速率较高;共聚物分子量随聚合温度和引发剂浓度增加而降低。随ASPAA含量的增加,共聚物的玻璃化温度和酸值均升高,并通过ASPAA含量来调节。     

双官能团引发剂引发甲基丙烯酸甲酯的聚合速率

研究了双官能团引发剂2,5-双(2-乙基己酰过氧化)-2,5-二甲基己烷（TX-141）引发甲基丙烯酸甲酯（MMA）的自由基聚合动力学,考察了引发剂浓度、聚合温度对聚合动力学的影响.结果表明：该体系的聚合活化能为91 kJ•mol^-1左右,计算得到TX-141引发剂的分解活化能为140 kJ•mol^-1左右,与实验值接近;TX-141引发剂的反应级数约为0.72,说明MMA聚合终止基元反应中单基和双基终止并存.同时与相似半衰期的过氧化二苯甲酰（BPO）比较,发现当TX-141引发剂浓度为BPO的1/2时,两者在各个聚合温度下的聚合动力学曲线几乎相同;但相对分子质量有明显增加,随聚合转化率增加,TX-141与BPO引发的聚合物数均分子量之比从1.2变化到1.33;由TX-141引发的聚合物低转化率时DSC曲线出现放热峰,而高转化率以及BPO引发的聚合物则没有.说明双官能团引发剂TX-141引发聚合时,在低转化率下TX-141引发剂的2个过氧键没有全部断裂,随聚合进行,断裂程度加深.     

室温离子交联苯丙乳液合成及性能研究

以苯乙烯(St)、丙烯酸丁酯(BA)和丙烯酸(AA)为单体,过硫酸钾(KPS)为引发剂,采用乳液聚合方法通过离子交联合成了室温交联型苯丙乳液。考查了聚合温度、引发剂用量、乳化剂用量对聚合稳定性和乳液性能的影响,同时研究了Zn~(2+)/AA配比和软硬单体配比对胶膜性能的影响。结果显示,在80℃、KPS用量为0.4%、乳化剂用量为2.0%~3.5%时,乳液具有较好聚合稳定性以及粒径单分散性;随配比中醋酸锌用量增加,胶膜的干燥时间缩短,吸水性减小,而拉伸强度有适当提高;随体系中硬单体含量增加,胶膜的干燥时间增加,而硬度和拉伸强度则逐渐提高,吸水性变小。     

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.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.     

Participation of lewis base on vinyl chloride polymerization with Al(C2H5)3CCl4 catalyst system

The polymerization of vinyl chloride has been investigated using an $\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3\text{CCl}{}_4$ catalyst system in the presence of various Lewis bases. Effective Lewis bases are γ-butyrolactone, diglyme and diethylenetriamine which are multidentate. The rate of polymerization is dependent not only on the basicity of the Lewis base used but also on a coordination number of one. The latter is the predominant factor. For the effect of polymeric amines, a tentative hypothesis is discussed.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Synthesis and Characterization of Ti0.33Ta0.33Nb0.33C and Ti0.33Ta0.33Nb0.33CxN1-x Whiskers

Ta_0.33Ti_0.33Nb_0.33C and Ta_0.33Ti_0.33Nb_0.33C _x N_{1− x} whiskers were synthesized via a carbothermal vapor-liquid-solid growth mechanism in the temperature range 900°-1450°C in Ar or N₂. The optimum temperature was 1250°C. Whiskers were obtained in a yield of 70-90 vol%. The whiskers were 0.5–1 µm in diameter and 10–30 µm in length. The starting materials that produced the highest whisker yield were: TiO₂, Ta₂O₅, Nb₂O₅, C, Ni, and NaCl. C was added to reduce the oxides, and Ni to catalyze whisker growth. NaCl was used as a source of Cl for vapor-phase transportation of Ta and Nb oxochlorides and Ti chlorides to the catalyst. The catalyst metal was recycled several times during the synthesis and was transported as NiCl₂( g ) according to thermodynamic calculations. The rate of formation and the chemical composition of the whiskers depended on the synthesis temperature, the choice of catalyst, and the atmosphere. At low temperatures, the whiskers were enriched in Nb and Ta, whereas the Ti content increased with increased synthesis temperature.