Cationic amino-containing N-isopropyl- acrylamide–styrene copolymer latex particles: 1-Particle size and morphology vs. polymerization process

 Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering (QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle morphology information were inferred for discussion of the polymerization mechanism of this system. Received: 21 August 1997 Accepted: 22 October 1997     

Phase behaviour and microstructures of microemulsions (I)

By the orthogonal design, the optimal formation conditions for the middle-phase microemulsions in the system dioctadecyldimethylammonium chloride (DODMAC)/ sodium dodecyl sulfate (SDS)/n-butanol/n-hep-tane/brine were obtained as follows: W_DODMAC: W_SDS = 1:4-1:5,C _π-butanol (%) = 11.0-12.0, andC _NaCl (%) = 3.25 Investigations have been made on the effects of the concentrations of NaCl and n-butanol (l.0%-14.0%), the ratios ofWDODMAC: to W_SDS, and the kinds of alcohols (n-propanol, n-butanol, and n-pentanol) on the formation, the phase behaviour, the ultralow interfacial tensions, the optimal salinity (S^*), and the length of salinity (δS). Some rules and data were worked out about the formation and characteristics of the middle-phase microemulsions. The mi-crostructures of the middle-phase microemulsions were also studied by using FT-IR, ESR, and freeze fracture electron microscopy techniques. The results from the three methods show that the microstructures of the middlephase mi-croemulsions undergo the change from O/W to bicontinuous (B.C.) and to W/O. The distribution rule of the orga-nized molecule assemblies in the middle-phase microemulsions is conducible to constructing the model of microemulsion systems, to recognizing the microstructures of the middle-phase microemulsions, and to setting forth the relationship between the microstructures and macro-properties of rnicroemulsions. Project supported by the Niltional Natural Science Foundation of China and the Chinese Postdoctoral Science Foundation.     

Dispersion polymerization of methyl methacrylate: Mechanism of particle formation

The mechanism for the formation of micron-size polymer particles in the dispersion polymerization of methyl methacrylate was investigated by applying dynamic light scattering to monitor the evolution of the average particle size in the early stages of the polymerization. In addition, the contributions of physically adsorbed stabilizer and graft copolymer were evaluated by measuring the bound, unbound (adsorbed), and free stabilizer, and by determining the amount of added stabilizer required in seeded dispersion polymerizations. Twenty nanometer particles (termed nuclei) were the smallest particles detected and are considered to be formed by aggregation of growing polymer chains precipitating from solution as they exceed their critical chain length. Aggregation of these nuclei with themselves and their aggregates continues until mature and stable particles are formed. This occurs when sufficient stabilizer occupies the particle surface which includes both the polymeric stabilizer [poly(vinylpyrrolidone)] and its graft copolymer which is created in situ. The effects of process variables are discussed based on this mechanistic picture of the dispersion polymerization process. © 1994 John Wiley & Sons, Inc.     

The effect of (natural) polyols on the initial colour of heavy metal- and zinc-free poly(vinyl chloride)

The propensity of (natural) polyols dispersed in heavy metal- and zinc-free PVC sheets to improve the initial colour, e.g. the colour during the first minutes of exposure to high processing temperatures (short-term stability), has been investigated. It is shown using W(Lab) values that the initial colour improves upon addition of polyols containing primary hydroxyl groups. The polyols act as HCl scavengers, presumably via an acid-catalysed S_N2 substitution of the primary hydroxyl groups by chloride ions. In contrast, polyols with only secondary or tertiary hydroxyl groups accelerate the thermal degradation of PVC. Notwithstanding, the efficacy of the (natural) polyols containing primary hydroxyl groups will be reduced if the polyol is susceptible to competitive acid-catalysed intramolecular cyclodehydration reactions under the processing conditions. This is substantiated by a comparison of the behaviour of mannitol and 3,4-di-O-methyl-d-mannitol. The methylated derivative, which is less prone to undergo intramolecular cyclodehydration, improves the initial colour of heavy metal- and zinc-free PVC sheets more significantly than mannitol itself.     

Kinetics and mechanism of the grafting of 2-(dimethylamino)ethyl methacrylate onto hydrocarbon substrates

The kinetics of grafting a basic monomer, 2-(dimethylamino)-ethyl methacrylate (DMAEMA) to hydrocarbon substrates have been investigated. These systems were chosen as models for the grafting of a homopolymerizable monomer to polyolefins such as polyethylene. The reactions with squalane and n-eicosane were initiated by an organic peroxide, 2,5-dimethyl 2,5 dit-butylperoxy)-3-hexyne; grafting yields become significant at high reaction temperatures and low monomer concentrations. In squalane, the order of reaction with respect to monomer increased from about 1.1 for 0.22?0.44M DMAEMA to almost 2 at 0.69M DMAEMA; the order with respect to initiator was 0.56. The overall activation energy in the 130?160°C temperature range was, however, surprisingly low, 42±5 kJ mol^?1. When analytical data were used to separate the overall rate into those for grafting and homopolymerization, different kinetic paths were observed for the competing reactions. These results are interpreted in terms of two different mechanisms; intramolecular chain transfer plays an important role in grafting, while depropagation becomes a major factor in homopolymerization at temperatures above 150°C. © 1995 John Wiley & Sons, Inc.     

The effect of the counterion composition on the chain restriction in the cationic polymerization of isobutylene

The effects of the nature of halogens in the initiatingtert-butyl halide-aluminum-containing Lewis acid system on the number average molecular weightM _n and the structure of end groups of polyisobutylene macromolecules obtained in the cationic polymerization of isobutylene in hexane at -78 °C were studied. An increase inM _n is observed in the transition from chlorine to bromine and iodine, accompanied by a decrease in the fraction of end C=C groups and an increase in the relative content of C-Hal groups (Hal = Cl, Br, and I). When atoms of different halogens are present in the counterion, more bulky atoms preferentially participate in the formation of the end groups. The results are interpreted within the framework of the principle of hard and soft acids and bases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1184–1187, May, 1996.     

The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H₂C?N(CH₃)₂]⁺ and [N(CH₃)₃]^+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

三苄基氯化锡及其衍生物的合成

三苄基氯化锡最初用格氏法制得。Keiti等曾报道由锡和苄基氯直接制备,这时溶剂对反应的影响很大:用水作溶剂时得到三苄基锡;用甲苯作溶剂时得到二苄基二氯化锡;用正丁醇作溶剂时三苄基氯化锡的产率只有61％。在反应体系中加入KI、KBr或H_3PO_4等催化剂,三苄基氯化锡的产率也只有60％。本文用DMF作溶剂,AlCl_3-I_2作催化剂,并首次在反应体系中加入镁、锌、铝和钠等使副产物氯化亚锡还原成活性很高的金属锡,后者再与等基氯反应,可使三苄基氯化锡的产率提高到91.3％。文中还报导三种尚     

The effect of the amphiprotic nature of human hair keratin on the adsorption of high charge density cationic polyelectrolytes

Adsorption of the cationic polymers poly(methacrylamidopropyltrimethyl ammonium chloride) (PMAPTAC) and poly(1,1-dimethylpiperidinium-3,5-diallylmethylene chloride) (PDMPDAMC) on human hair was studied by measurements of the amount of polymer adsorbed and by the streaming potential method. Results reflect the amphoteric nature of the keratin surface and show that the excess of anionic sites at pH values above 4 is the main driving force for the adsorption of cationic polyelectrolytes. Lowering the pH below 4 or addition of neutral salt (KCl) reduces the amount of adsorbed polymer. It was shown that the adsorption of cationic polymer in the concentration range 0.01 to 0.1 % and at neutral pH reverses the overall character of the surface from anionic to cationic. Keratin fibers modified in this manner do not exhibit amphoteric character and bear excess positive charge in the pH range 2–9.5. The value of the amount of the polymer adsorbed at saturation concentration (2 mg/g) as well as the lack of molecular weight effect in the range (5 · 10⁴ – 10⁶) on the amount of polymer adsorbed suggest that polymer chains adopt a rather extended conformation on the fiber surface. Some data concerning the formation of a complex between adsorbed cationic polymer and anionic detergents or polyelectrolytes are also presented.     

Ti接枝MCM-41催化剂的结构设计及化学亲和选择性研究

 用二氯化钛茂作为活性物种的来源，利用Si－MCM－41催化剂表面羟基的反应性，得到了Ti接枝MCM－41催化剂的两种结构模型．结构表征结果表明，Ti接枝MCM－41催化剂不仅长程结构好，孔径分布均一，而且催化剂表面活性中心含量高．两种结构模型催化剂上芳烃羟化反应性能表明，Ti接枝MCM－41催化剂表面的亲水／憎水性可以在较宽的范围内调变，从而可实现控制芳烃羟化的化学亲和选择性．另外，研究结果还表明，Ti接枝MCM－41催化剂具有很好的活性稳定性．