香菇多糖的成分及其分子量研究

从香菇子实体中用0.9%NaCl水溶液、85%乙醇、热水、1%草酸铵、5%NaOH/0.05%NaBH₄和2%NaOH/2%尿素分别提取出四种杂多糖(L-FⅠ-L-FⅣn)和两种葡聚糖(L-FⅤ和L-FⅥn).红外光谱和高效液相色谱分析结果表明杂多糖主要由葡萄糖、葡萄糖醛酸、木糖、甘露糖、半乳糖和鼠李糖组成,而且按照分离过程的进行多糖中葡萄糖含量递增.由光散射和膜渗透压法研究了多糖的重均分子量Mw、均方根旋转半径2>^1/2、第二维利系数A₂及数均分子量M_n.L-FⅡ、L-FⅢ、L-FⅤ及L-FⅥn的M_w值依次为19.7×10⁴、192.3×10⁴、136.4×10⁴和136.7×10⁴,它们的多分散系数-Mw/-Mn在3～5范围.     

黑木耳酸性杂多糖溶液性质研究

从黑木耳子实体提取出的酸性杂多糖,通过重沉淀分成8个级分,用小角激光光散射和膜渗透压法测得试样在0.5mol/L NaCl/10％镉乙二胺饱和液(C)中的M_w(5.88×10~5)、M_n(1.43×10~5)和A_2值.研究了各个分级试样在3种水溶液中30℃的粘度行为,确立了Mark-Houwink方程为:(A)0.5mol/L NaCl,[η]=0.235 M_w~(0.48);(B)0.2mol Na_2SO_4/0.01 mol/L 磷酸盐缓冲液,[η]=7.61×10~(-2)M_w~(0.57);(C)[η]=6.44×10~(-2) M_w~(0.59).无扰尺寸(S~2)_0/M及K_8为12.9×10~(-18)cm~2·mol/g及0.175cm~3/g.确证该多糖分子在溶液中呈稍刚硬的柔性无规线团状态.     

Molecular weights of polystyrenes in toluene solutions by light scattering. Comparison between classical values and values deduced from a new method

Light scattering measurements in toluene solutions are performed for a series of monodisperse polystyrenes with a molecular weight M_w range from 4×10³ to 8×10⁶. The scattered polarized intensities I_v and the natural depolarization ratios ρ_n are registered with different apparatus at λ=633 or 488 nm and the M_w values are deduced through different formulae. The complete Carr and Zimm formula (CL_a), from I_v and ρ_n, and the usual simplified formula (CL_b), from I_v, are considered for the classical method. An already demonstrated formula is considered for the new method (New). Values of M_w and related parameters do not depend on the experimental systems used but deviations appear when using different formulae. The deviations are generally low (about 10%) but often systematic: M_w(CL_a)<M_w(CL_b)<M_w(New). The most important difference concerns the effect of destructive interferences for M_w>5×10⁵: the new formula leads to a lower increase from θ=90° to θ→0 for M_w values (θ is the observation angle). For instance, in the 8×10⁶ sample, M_w(θ→0)/M_w(θ=90°)=3.6 instead of 6.1, which implies a revision of the usual determination of the radius of gyration, R_g.     

Molecular weight determination from light scattering and refraction in solutions. A new and coherent theoretical equation

The classical theoretical equation allowing for the determination of the solute's molecular weight (M₂) from light scattering (LS) and refractive measurements in diluted solutions is reexamined. Serious theoretical and practical defects in its derivation and application are pointed out, especially about the refraction increment dn/dc. A new theoretical equation is deduced from a more consistent application of the basic molecular orientation formulae to binary liquid mixtures. More adequate additive molecular properties, the specific mean polarizability ( /M and the specific square of the mean polarizability instead of and , are considered with respect to refraction and LS, respectively. Inadequate approximations are avoided and a corrected LS intensity expression is used. The new equation is tested upon several typical mixtures of small molecules from measurements either performed in this work or collected in the literature (for LS perpendicular to the incident beam) to ensure objectivity. Examples of measurements in macromolecule solutions from other authors are also analysed. The new equation is suitable for practical applications, because it is based upon easy relative measurements only, and allows for a reliable determination of the M₂ values in macromolecules. The reasons for which the classic equation leads to realistic values, in spite of its theoretical inconsistency, are also explained.     

Molecular weight determination from light scattering and refraction in solutions. A new and coherent theoretical equation

The classical theoretical equation allowing for the determination of the solute's molecular weight (M₂) from light scattering (LS) and refractive measurements in diluted solutions is reexamined. Serious theoretical and practical defects in its derivation and application are pointed out, especially about the refraction increment dn/dc. A new theoretical equation is deduced from a more consistent application of the basic molecular orientation formulae to binary liquid mixtures. More adequate additive molecular properties, the specific mean polarizability and the specific square of the mean polarizability instead of ga and , are considered with respect to refraction and LS, respectively. Inadequate approximations are avoided and a corrected LS intensity expression is used. The new equation is tested upon several typical mixtures of small molecules from measurements either performed in this work or collected in the literature (for LS perpendicular to the incident beam) to ensure objectivity. Examples of measurements in macromolecule solutions from other authors are also analysed. The new equation is suitable for practical applications, because it is based upon easy relative measurements only, and allows for a reliable determination of the M₂ values in macromolecules. The reasons for which the classic equation leads to realistic values, in spite of its theoretical inconsistency, are also explained.     

Coupling of near infrared spectroscopy to automatic continuous online monitoring of polymerization reactions

In situ near infrared (NIR) spectroscopy is performed simultaneously with automatic continuous online monitoring of polymerization reactions (ACOMP) during methyl methacrylate polymerization. ACOMP is an absolute technique that furnishes weight average molecular mass M_w, intrinsic viscosity, monomer conversion, and other characteristics, whereas NIR furnishes monomer conversion data via an empirical calibration. An advantage of in situ NIR is that it furnishes immediate information on the conversion in the reactor, whereas ACOMP relies on continuous withdrawal and dilution of a small stream of reactor fluid, so that there is a lag time of several minutes between what ACOMP reports and what is occurring in the reactor. Simultaneous monomer conversion data from in situ NIR and ACOMP, the latter derived from both refractive index and UV absorption, are compared and found to be in good agreement. The evolution of conversion kinetics and M_w generally conform to the predictions of the Quasi-Steady State Approximation. Having established the agreement between the methods, the path is now open for combining NIR with ACOMP to characterize increasingly complex systems, such as copolymerization with two or more monomeric species, that are not feasible by either technique separately.     

The interaction between sodium dodecylsulfate and the cationic-nonionic random copolymer (3-(2-methylpropionamide)propyl) trimethylammonium chloride–acrylamide of two different charge densities studied using dynamic light scattering and rheometry

The effects of complex formation between sodium dodecylsulfate (SDS) and the positively charged (3-(2-methylpropionamide)propyl)trimethyl-ammonium chloride-acrylamide (MAPTAC-AM) copolymer have been studied in dilute and semidilute aqueous solution in the presence of 10 mM NaCl. Two different charge densities of the copolymer have been used in the study: 0.31 and 0.66, corresponding to the proportion of MAPTAC units. Dynamic light scattering (DLS) and rheometry (static low-shear and capillary viscometry) have been performed on the systems at different charge ratios, i.e., SDS/MAPTAC molar ratios, r. Regarding the phase behavior, the maximum binding ratio prior to precipitation differs between the copolymers. A 1.0% w/v solution of SDS/31% MAPTAC-AM is soluble at r = 0.4 , while an SDS/66% MAPTAC-AM solution of 1.0% w/v shows phase separation at this ratio. With excess surfactant, the complex in the former system is resolubilized at r=2.0, whereas the latter system is still phase-separated at r=5.0. DLS results show that, for both copolymers, the hydrodynamic radius, R _h, of the single-chain copolymer-surfactant complex decreases as a function of r, but then increases slightly prior to phase separation. The corresponding hydrodynamic virial coefficient, k _D, changes in the same manner as R _h. The light-scattering data also show that the formation of larger structures is promoted as the polymer concentration is increased from 0.2 to 1.0% w/v. This is shown by the increase in the relative aggregate-to-single coil peak areas in the relaxation time distributions. Both systems have this common trend. The results from rheological measurements support the results from DLS. A reduction in intrinsic viscosity, [η], is observed on increasing r up to phase separation. The major part of the static low-shear measurements showed Newtonian behavior for both systems at different copolymer concentrations (27.6–138 mM), and at different r. These systems, partially ionic polymer/oppositely charged surfactant, present very interesting rheological behavior at relatively high polymer concentrations and at low r values. Their behavior is similar to those of hydrophobically modified polyelectrolytes. Received: 17 June 1998 Accepted: 12 August 1998     

Influence of the repeated extrusion on the degradation of polyethylene. Structural changes in low density polyethylene

The influence of the repeated extrusion on the molecular parameters of low density polyethylene (LDPE) Bralen NA 7-25 was studied. Virgin polyethylene was submitted up to 20 extrusion cycles and the processed samples were fractioned using precipitation fractionation. Non-fractionated samples and the individual polymer fractions were characterized by their weight average molar masses M_w (static light scattering), number average molar masses M_n (osmometry) and limiting viscosity numbers [η] (viscometry). Rheological properties in terms of shear viscosity curve, zero shear viscosity and flow activation energy were also determined by using high pressure capillary rheometer. The course of the changes in molecular parameters of LDPE is influenced both by the initial polymer structure and by the changes induced by the mechano-chemical degradation. The suggested degradation mechanisms during multiple extrusion of Bralen are chain scission predominating in the early stage of processing followed by recombination of macromolecules resulting in crosslinking and formation of microgel, which is clearly notable for the samples extruded 3-20 times.     

SBS嵌段共聚物分子结构对其在溶液中链形态的影响

线形两嵌段 (SB) 苯乙烯-丁二烯嵌段共聚物、线形三嵌段[ (SB) 2]和星形四臂三嵌段[ (SB) 4]的苯乙烯-丁二烯-苯乙烯 (SBS) 嵌段共聚物溶于四氢呋喃 (THF) 和环己烷 (CH) 中, 通过黏度法获得它们的特性黏数并计算其黏度半径 (Rη) ;采用静态激光光散射法研究了它们在溶液中的第二维利系数和均方根旋转半径 (Rg) .由于Rη与其流体力学半径 (Rh) 具有相似性, 所以表征链形态的特征参数ρ (=Rg/Rh) 可通过上述两种方法获得.结果表明, (SB) 4分子在良溶剂THF中表现出柔顺链构象, 在CH中表现为实心球构象; (SB) 2在THF和CH中均为空心球构象;两嵌段SB在THF和CH中均为柔顺链构象.     

Thermal degradation of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) and their blends upon melt processing

Poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) are biodegradable aliphatic polyesters, which being semicrystalline and thermoplastic can be processed by conventional methods. Their blends give interesting materials for industrial packaging applications, due to their increased ductility as PBAT content increases. However, like many aliphatic polyesters, the PLA matrix degrades upon melt processing thus affecting the thermo-mechanical features of the blended material. In this work, we studied the effect of processing at high temperature on the molecular weight distribution, morphology, and thermo-mechanical properties of both homopolymers, as well as the PLA/PBAT 75/25 blend. Notably, different processing conditions were adopted in terms of temperature (range 150-200 °C) and other relevant processing parameters (moisture removal and nitrogen atmosphere). Analysis of PLA/PBAT blends indicated that intermolecular chain reactions took place under strong degradative conditions of PLA, yielding PLA/PBAT mixed chains (copolymers). Increasing amounts of copolymers resulted in improved phase dispersion and increased ductility, as SEM and mechanical tests indicated. Conversely, reduced PLA degradation with less copolymer formation, afforded higher modulus materials, owing to poorer dispersion of the soft phase (PBAT) into the PLA matrix.     

分别含有质子给体和质子受体的丙烯酸酯共聚物在溶液中的特殊相互作用研究

用粘度法和光散射法研究了分别具有质子给体 (Protondonor)和质子受体 (Protonacceptor)官能团的丙烯酸酯共聚物在溶液中的相互作用 .从粘度增长因子和聚合物在溶液中理想增比粘度的关系基础上提出了一个新的相互作用参数ka,研究了质子给体聚合物和质子受体聚合物在甲苯中的特殊相互作用 ,讨论了丙烯酸酯含量和酯烷基长度对组分间相互作用的影响 .结果表明 ,组分间的特殊相互作用随着丙烯酸长碳链酯含量和酯烷基长度的增加而增强 .光散射的结果表明ka 能够用于表征共混体系中的特殊相互作用     

Micellar behavior of a well-defined dendritic polymer (PS2PI)3: the effects of architecture and solvent selectivity

The micelles formed when a dendritic polymer of polystyrene (PS) and polyisoprene (PI), having the overall structure (PS₂PI)₃, were examined in two solvents, dimethylformamide (DMF) and dimethylacetamide (DMA). Both solvents are good solvents for polystyrene and non-solvents for polyisoprene. The aggregation behavior was studied by a combination of static and dynamic light scattering and viscometry. In both systems star-like micelles were formed which followed the hard sphere model. The aggregation number was much lower for the micelles formed in DMA. The polymer-solvent interaction parameters indicate that the interactions are stronger between both PS-DMA and PI-DMA than for either polymer block with DMF. The effects of solvent selectivity are exacerbated by the structure of the polymer. With each polymer molecule contributing six soluble arms to the micelle, in the better solvent (DMA) increased repulsive interactions between the extended polystyrene lead to lower aggregation numbers.     

木质素基高效减水剂GCL1-JB的分子量测定

分别采用静态光散射法（SLS）和凝胶渗透色谱法（GPC）测定了木质素基高效减水剂GCL1-JB的分子量（Mw）.由于GCL1-JB直接溶于水中存在聚电解质效应和聚集现象,SLS法测得的分子量（Mw,SLS）远大于GPC测得的分子量（Mw,GPC）.为了通过SLS测得GCL1-JB的真实Mw,在GCL1-JB溶液中加入NaCl来屏蔽GCL1-JB的聚电解质效应,并采用0.45 m的微孔滤膜滤除GCL1-JB聚集体.GCL1-JB的动态光散射测试中存在2个扩散峰：快模式峰和慢模式峰.快模式峰对应GCL1-JB的单分子行为,而慢模式峰对应GCL1-JB的聚电解质效应和GCL1-JB聚集体.GCL1-JB动态光散射的慢模式峰随着NaCl的不断加入和进一步的过滤处理而逐渐减弱.当NaCl在溶液中的浓度达到0.1 mol/L,动态光散射的慢模式峰完全消失.在没有慢模式峰存在的条件下利用SLS测得GCL1-JB的绝对分子量为121300,这个分子量被认为是GCL1-JB单分子的真实分子量.然而该条件下SLS法测得的Mw,SLS仍然比GPC法测得的Mw,GPC大,这是由于GCL1-JB与GPC标样NaPSS的构象差异引起的.GCL1-JB的分子构象比NaPSS的更卷曲,所以用NaPSS作为GPC标样得到Mw,GPC比GCL1-JB的真实分子量小.本研究提出了一种利用SLS准确测量GCL1-JB的Mw的方法,对存在聚电解质效应和聚集现象的木质素及其衍生产物的绝对分子量测定具有普遍的借鉴意义.