磁场对聚乙烯基萘敏化AIBN引发苯乙烯本体光聚合反应的影响

<正> 近年来,Turro等人发现,外磁场能提高一些由油溶性酮类化合物(如二苄基酮)为引发剂的乳液聚合体系的分子量,并且显著地影响所生成聚合物的立体构型,因而引起了人们的注意。     

聚环氧乙烷大单体与丙烯酸乙酯的共聚及其规整接枝共聚物的表征

 本工作研完了末端为甲基丙烯酸酯型的聚环氧乙烷大单体与丙烯酸乙酯的溶液自由基共聚。结果表明,大单体接枝效率和共聚物分子量受单体总浓度、投料比、大单体分子量及引发剂等的影响,接枝效率最高可达90％以上,分子量可在5-15×10⁴范围内变化。丙烯酸乙酯与大单体共聚的竞聚率为0.83。共聚物用萃取法精制后,用IR、¹H-NMR、裂解色谱、GPC和膜渗透压计等进行了表征。证实产物有预期的规整接枝共聚物结构。平均接枝数为2—11。     

INFLUENCES OF MOLECULAR WEIGHT AND BRANCHING PARAMETER OF LACQUER POLYSACCHARIDE ON THE GROWTH OF LEUCOCYTES

A method of determining branching parameter of lacquer polysaccharide wasestablished by acid-base back-titration of terminal uronic acid of branches. The branchingfactors obtained are in agreement with the values determined by colorimetric method withcarbazole and the results estimated by using Zimm-Stockmayer equation from viscositydata. Influences of molecular weights and branching factors of five fractions of lacquerpolysaccharide on the bioactivities were studied. The results show that the polysaccharideshave bioactivities in motivating the growth of leucocytes, and the effect increases with thedecrease of molecular weight and branching factor in the range studied (17×10~4 >M_w>4×10~4).     

蒸气压渗透计的结构对仪器常数的影响

<正> 蒸气压渗透计(VPO)依其结构不同,分为探头下垂式蒸气室和探头站立式蒸气室两类。关于仪器常数K是否随溶质的分子量范围的不同而变化的问题,已引起人们的注意,但报道的结果并不一致。因仪器、标样及纯度、操作方法的不同,难以判断其误差。为了便于比较,本文选用VPO仪中具有代表性二类仪器,对同一标样进行了标定。     

铁体系催化丁二烯聚合的研究——Ⅲ.聚丁二烯的分子量调节及性能

<正> 顺丁橡胶与丁苯橡胶在性能上的差别,在于其分子主链上缺少象苯基那样的侧基。而中乙烯基聚丁二烯的分子主链上有相当数量的乙烯基侧基,它弥补丁顺丁胶的不足之处。故日益受到人们的注意。目前,已工业化的中乙烯基聚丁二烯所用的催化剂为烷基锂体系,其聚合物除了1,2-结构外,其余部分反-1,4结构占多数。我们在前文曾经报     

A STUDY OF LOW-TEMPERATURE CRYSTALLIZATION BEHAVIOR THE cis-1,4 POLYBUTADIENE PREPARED WITH RARE-EARTH CATALYST SYSTEM

The effects of molecular weight and temperature on crystallization processes at low tempera-ture for cis-1,4 polybutadiene prepared with rare-earth catalyst (Ln-PB) have been studied by WAXDmethod. In the range of molecular weight from     

SYNTHESES OF THE SOLUBLE,HIGH MOLECULAR WEIGHT AND LADDERLIKE POLYPH ENYLSILSESQUIOXAN E AND COPOLYMETHYLPHENYLSILSESQUIOXANES BY PREAMMINOLYSIS METHOD

Soluble, high molecular weight (MW) and ladderlike polyphenylsilsesquioxane (LPPSQ) and its copolymers, ladderlike random and block copolymethyiphenylsilsesquioxanes(LR-PMPSQ and LB-PMPSQ)have been prepared by preamminolysis, hydrolysis and polycondensation reactions. The preparation method can be carried out easily at the temperature below 95℃with high yield of 95 %, instead of the conventional way by using high-boiling solvent and any reaction activator or by precipitation with methanol. Three kinds of ladderlike polymers have been characterized. The MW's of the polymers reached to 10~6 without noticeable gelling. The scheme for synthetic route has been proposed.     

Morphology of polytetrafluoroethylene prepared by radiation-induced emulsion polymerization

The original morphology of polytetrafluoroethylene prepared by radiation-induced emulsion polymerization was studied by electron microscopy. The morphology depends on molecular weight, which in turn depends on polymerization conditions, especially the emulsifier concentration. The molecular weight decreases with increasing emulsifier concentration. The morphology changes with molecular weight roughly as follows: fibrils below 10⁵, rods between 10⁵ and 5 × 10⁵, and granular particle above 10⁶. The crystallinity is high for all morphologies.     

INVESTIGATION ON THE RELATIONSHIP BETWEEN INTRINSIC VISCOSITY AND MOLECULAR WEIGHT OF POLY (VINYL CHLORIDE-DIETHYL MALEATE)

A poly (vinyichloride-diethyl maleate) copolymer has been fractionated by repeated precipitation method. All fractions and the unfractionated sample have been characterized by viscometry, dynamic osmometry, Zimm static osmometry, light scattering and gel permeation chromatography. After correction for polydispersity, a [η]～M relationship for monodisperse polymer solutions has been obtained:[η]=1.99×10~(-3)M~(0.87) (ml/g, at 25℃, in cyclohcxanone)For the copolymer solution in THF, the second virial coefficient A_2 decreases as the molecular weight increases. The relationship isA_2=2 slope ((?)_n RT)~(-1/2).     

DETERMINATION OF BRANCHING DISTRIBUTION IN HIGH cis-1,4-POLYBUTADIENE BY GPC AND AUTOMATIC VISCOMETRY

Based on the methods reported by Ambler and Kraus, a method has been developed for the determination of long-chain branching distribution in polymers by the combined use of GPC and intrinsic viscosity data of polymer fractions. In this method, g_i, λ_i, G_i, m_i, the weight percentage of polymer that is branched, etc. can be used simultaneously to characterize the distribution, degree and content of branching in polymers. Some relations between molecular weight polydispersity and branching polydispersity in Nickel-based high cis-1,4-polybutadiene samples are discussed. It was found that the number of long branches λ. per unit molecular weight is a function of molecular weight and all of the samples are highly branched at a molecular weight of about 10~6.     

Gel permeation chromatographic characterization of sodium hyaluronate and its fractions prepared by ultrasonic degradation

Summary High-molecular-weight sodium hyaluronate isolated from rooster combs was degraded by ultrasonication. The molecular weight of hyaluronate and its polydispersity was determined by gel-permeation chromatography. During 75-min treatment the molecular weight value decreased from 1.39×10⁶ Da to 2.25×10⁵ Da while the polydispersity of the molecular weight increased from 1.29 to 2.36. The reciprocal value of the square of the hyaluronate's molecular weight was linearly proportional to the time of ultrasonication.     

Use of gel-permeation chromatography in the determination of the composition of two-polymer mixtures

The possibility of evaluating with acceptable accuracy the composition of a two-polymer mixture which is well separated by GPC, was studied by using mixtures of high molecular weight polybutadiene (M?_w = 4.5 × 10⁵) and low molecular weight polyiso-butylene (M?_n in the range of 10³). It was concluded that a satisfactory evaluation of the composition of a polymer mixture can be achieved, provided that the variations of the refractive index with the molecular weight are taken into account for the low molecular weight polymer (the polyisobutylene).     

场流分级的机内浓缩和再进样方法

<正> 除制备色谱外,一般色谱和场流分级的进样量都是很小的,而溶质层在经过色谱柱或场流分级柱槽后由于分离以及加宽效应浓度又要大大降低,因此,所得级分中溶质的含量极少。如需把所得级分做再进样,则必须在同一条件下重复收集同一集分,经浓缩后再进     

Radiation-induced homogeneous polymerization of ethylene in cyclohexane

The radiation-induced polymerization of ethylene in cyclohexane was carried out in a reactor of 100 ml capacity under a range of temperature of 25–150°C, dose rate of 4.1 × 10⁴–2.9 × 10⁵ rad/hr, pressure of 200 kg/cm², and amount of cyclohexane of 20–90 ml. The polymerization was found to proceed at a steady state from the beginning. The polymerization rate is maximum at ca. 50 ml of cyclohexane. The dose rate exponent of the polymerization rate was 0.6 at every temperature from 25 to 150°C. The polymer molecular weight is in the range of 10³–10⁴, independent of dose rate, and decreases with increasing amount of cyclohexane. The molecular weight distribution is unimodal and narrow. Kinetic analysis of these results indicates that the polymerization proceeds via a simple scheme of homogeneous polymerization and the polymer molecular weight was determined by the chain transfer reaction which takes place mostly with cyclohexane. The unimodal and narrow molecular weight distribution is also consistent with the homogeneous polymerization scheme.     

SYNTHESIS AND CHARACTERIZATION OF FOUR-ARMED BLOCK POLY(STYRENE-b-p-NITROPHENYL METHACRYLATE)PREPARED BY THE ATRP METHOD*

A novel tetrafunctional initiator, C [CH_2O (CH_2)_3 OOCCH(Br)CH_3]_4 (1), was synthesized through the reaction oftetraol with α-bromopropionyl chloride, and then was used as initiator of atom transfer radical polymerization (ATRP) in thepreparation of 4-armed polystyrene (PSt) with narrow polydispersity. The structure, molecular weight and molecular weightdistribution (MWD) of each arm were studied by ~1H-NMR and GPC data of hydrolyzed products of the 4-armed PSt. TheATRP of St using 1/CuBr/bpy as initiator system is of "living" character based on the following evidence: narrow MWD,constant concentration of chain radical during the polymerization, control of molecular weight by the molar ratio of monomerconsumed to 1. The 4-armed poly(St-b-p-nitrophenyl methacrylate) [poly(St-b-NPMA)] was prepared by the ATRP ofNPMA using 4-armed PSt with terminal bromine as the initiator, and characterized by FT-IR, ~1H-NMR spectra and GPCcurves. The micelles with PSt as core, and PNPMA as shell were formed by dropping DMSO into a solution of 4-armedpoly(St-b-NPMA) in DMF, as proved by laser light scatter (LLS) method.     

Effect of molecular weight upon the heterogeneous nucleation of crystallization in polypropylene

The effect of basic aluminium dibenzoate upon the supercooling of polypropylene fractions of molecular weight 9.2 × 10³-1.25 × 10⁶ was determined by differential thermal analysis. The response to heterogeneous nucleation within the precision of the method used appears to be only slightly dependent, if at all, upon the molecular weight of the polymer.     

SURFACE STRUCTURE OF THE MICELLE OK AN AMPHOTERIC AMPHIPHILE DERIVED FROM LYSINE

ABSTRACT

Micelle structure in aqueous colloid of an amphoteric amphiphile N^αN^α-dimethyl-N^? -lauroyl lysine (DMLL), which was derived from lysine, was studied through light scattering, SAXS and a rheological method. The critical micelle concentration of the colloid system is 216 UM and the weight average molecular weight of the micelle is 2.40 × 10⁴, i.e. the aggregation number is 67.4. The diameter of the micelle is about 43.4 Å and the spherical micelle is likely to be retained in a concentration up to about 20 %, The SAXS measurements show that the electron density Fluctuation in the micelle is almost negligible and that the surface area of the micelle is approximately 3.5 times larger than that of a completely smooth sphere.     

IR STUDY ON MONOMOLECULAR PARTICLE AGGLOMERATES OF POLYSTYRENE OBTAINED BY FREEZE-DRYING OF ITS DILUTE SOLUTION

The monomolecular particle agglomerates of polystyrenes were obtained by freeze-drying of its very dilutesolutions of 1.3×10~(-5)-2.0×10~(-5) g/mL in benzene: cylcohexane (100:1) solvents, and they were annealed at roomtemperature for hundred days before use. According to ~(13)C-NMR measurement the polystyrenes should be practically atactic.The number average molecular weights of the samples are 2.80×10~3, 2.00×10~4, and 1.55×10~6, respectively. The freeze-dried aPS with a molecular weight higher than 10~4 show two new IR absorption bands at 1098 and 1261 cm~(-1), which areabsent in the normal aPS and freeze-dried styrene oligomer. It was also found that the low molecular weight samples canonly form powders, whereas the freeze-dried aPS with higher molecular weight form a mixture of powders and fibrils, ofwhich the longer fibrils show a much stronger 1261 cm~(-1) band than the shorter fibrils and the powder. It seems that the1261 cm~(-1) band corresponds to the stacking behavior of monomolecular particles.     

ON THE KINETICS AND MECHANISM OF THE COPOLYMERIZATION OF ACRYLONITRILE WITH STYRENE IN THE PRESENCE OF COPPER CHLORIDE

The copolymerization of styrene (St) and acrylonitrile (AN) complexed with CuCl_2 monomer by a free radicalmechanism was performed using benzoyl peroxide as an initiator at 65℃ under N_2 atmosphere for 150 min. The rate ofpolymerization (R_p) was found to increase linearly with the concentration (in mol/L) of CuCl_2, AN and St through scalingrelations. The activation energy of the copolymerization process in the presence and absence of CuCl_2 was found to be46.5 kJ/mol and 102 kJ/mol, respectively. The viscosity average molecular weigh of the copolymer and the k_p~2/k_t ratio weredctermired to further assess the accelerating effect of CuCl_2 on the copolymerization process. The copolymerization processin the presence of CuCl_2 has a radical complex mechanism.     

Radiation-induced degradation and crosslinking of poly(ethylene oxide) in solid state

The effects of g-irradiation on solid poly(ethylene oxide) (PEO) of an initial weight-average molecular weight of 6.3^.10⁵ Da were investigated by gel permeation chromatography and viscometry. The parameters studied were changes in number- and weight-average molecular weight, molecular weight distribution and viscosity of PEO in aqueous solution. Irradiation of poly(ethylene oxide) powder in the presence of oxygen leads to the dominance of chain scission reactions. Their high radiation-chemical yield [G(scission) » 2.5^.10^-6 mol/J] indicates the occurrence of effective chain reactions. Upon irradiation in vacuum, crosslinking and scission occur side-by-side and the changes in molecular weight are less pronounced in the studied dose range (up to 20 kGy). Scission dominates for doses up to ca. 15 kGy, while for higher doses intermolecular crosslinking gains in importance. The competition between these processes seems to depend not only on the applied dose but also to be influenced by the inhomogenity of the material (molecular weight and/or possibly the crystallinity). Parallel occurrence of scission and crosslinking leads to the broadening of the molecular weight distribution.