Synthesis and fractionation of poly(phenylene methylene)

Poly(phenylene methylene) (PPM) was isolated in a broad range of molar masses by optimization of the catalytic polymerization of benzyl chloride with SnCl₄ or FeCl₃, followed by fractionation by Soxhlet extraction or phase separation in concentrated solutions in poor solvents. Low molar mass products were also obtained by quenching the reaction at moderate monomer conversions. Products with number average molar masses (M_n) ranging from 200 to 61,000 g mol⁻¹ were isolated, the latter being an order of magnitude above the previously reported values. DSC analysis of polymers of different molar masses revealed that the glass transition temperature follows the Flory‐Fox equation reaching a plateau value of 65 °C at a molar mass between 10,000 and 20,000 g mol⁻¹. The onset of decomposition temperature of higher molar mass products proceeds above 450 °C (maximum decomposition rate at 515 °C), according to TGA. Furthermore, the substitution pattern of PPM was discussed by study of chemical shifts of the methylene group by extensive NMR spectroscopy (¹H, ¹³C, DEPT, and HSQC) and by comparison with two mono‐substituted derivatives of PPM—poly(2,4,6‐trimethylphenylene methylene) and poly(2,3,5,6‐tetramethylphenylene methylene)—which were synthesized analogous to PPM. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 309–318     

Ethylene Polymerization over Supported Titanium-Magnesium Catalysts: Heterogeneity of Active Centers and Effect of Catalyst Composition on the Molecular Mass Distribution of Polymer

New experimental approach was used for analysis of molecular weight distribution (MWD) of polymers produced over titanium-magnesium catalysts (TMC). Polymers were fractionated on to fractions with narrow MWD (polydispersity (PD) values Mw/Mn ≤ 2). Then some of these fractions were combined to get the minimal quantity of fractions with PD values close to 2 (Flory components). It was found that three fractions corresponding to three groups of active centers are sufficient for proper fitting experimental MWD curve for PE obtained over TMC with different Ti content and with different hydrogen concentration in polymerization.     

Microwave‐assisted suzuki coupling reaction for rapid synthesis of conjugated polymer–poly(9,9‐dihexylfluorene)s as an example

Long reaction period (dozens of hours) is often required for the synthesis of conjugated polymers by palladium‐catalyzed Suzuki polymerization reaction. This work shows that microwave can accelerate Suzuki polymerization to realize the ultra‐rapid synthesis of conjugated polymers, here poly(9,9‐dihexylfluorene)s (PDHFs) as an example. The effects of reaction conditions on the polymerization have been systematically investigated, including the mode of microwave irradiation, microwave power, reaction temperature, reaction time, solvents, catalyst species, and catalyst concentrations. Compared with the conventional heating method (oil bath) for the synthesis of PDHFs (48 h, M_w = 20,000 g/mol), Suzuki polymerization under optimized microwave condition can yield PDHFs with higher molecular weight (M_w = 40,000 g/mol) in a much shorter time (14 min). The structures of obtained PDHFs samples are fully characterized spectroscopically, demonstrating well‐defined PDHFs have been prepared through microwave‐assisted (MA) Suzuki polymerization reaction. In addition, the mechanism of MA Suzuki polymerization is proposed preliminarily. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

正交试验法优化制备用于小分子物质分离的聚(甲基丙烯酸缩水甘油酯-二乙烯基苯)型整体柱

以甲基丙烯酸缩水甘油酯(GMA)为单体,二乙烯基苯(DVB)为交联剂,以环己醇和正十二醇为致孔剂,过氧化苯甲酰(BPO)为引发剂,直接以50 mm×4.6 mm色谱柱为模具,通过原位聚合制备聚(GMA-DVB)型整体柱。以GMA和DVB的体积比、环己醇和十二醇的体积比以及BPO占聚合物的质量分数为三因素,以分离苯和乙苯等小分子物质时的半峰宽分离度(R1/2)为考察指标,进行三因素三水平的正交试验,通过测定整体柱的比表面积、孔径和孔容分布对其进行表征。结果表明,制备整体柱的最优配方为V(GMA): V(DVB): V(环己醇): V(正十二醇)=0.825:0.825:1.32:2.03, BPO的质量分数为0.7%。应用所制备的整体柱分离苯和乙苯等小分子物质,理论塔板数达到37000塔板/m, R1/2值达到7.14,完全达到基线分离,分离时间小于10 min。该方法制备整体柱的重复性好,柱效较高,基本满足商品化要求。     

Impact of low‐molecular mass components (oligomers) on the glass transition in thin films of poly(methyl methacrylate)

Commercial polydisperse atactic poly(methyl methacrylate) (PMMA) exhibits a decreased glass transition temperature (T_g) when the film thickness is less than ～60 nm, whereas more model atactic PMMA shows an increased T_g in thin films supported on clean silicon wafers. NMR indicates no difference in tacticity, so the divergent thin film behavior appears related to the relative distribution of molecular mass. Extraction of some low molecular weight PMMA components from the commercial sample results in a significant modification of the thin film T_g compared with the initial PMMA fraction. The extracted sample exhibits initially a slight decrease in T_g as the film thickness is reduced below ～60 nm, but then T_g appears to increase for films thinner than 20 nm. These results illustrate the sensitivity of polymer thin film properties to low‐molecular mass components and could explain some of the contradictory reports on the T_g of polymer thin films that exist in the literature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Effect of reaction conditions on the molecular weight and polydispersity of linear poly(arylene ether phosphine oxide)s prepared from an AB monomer

A thorough study of the polymerization behavior of 4‐fluoro‐4′‐hydroxytriphenyl‐phosphine oxide, 2 , under nucleophilic aromatic substitution reactions has been carried out. The synthesis of 2 was achieved in excellent yields by the reaction of bis(4‐fluorophenyl)phenylphosphine oxide, 1 , with one equivalent of potassium hydroxide in DMSO/water. The structure and purity of 2 were confirmed via ¹H, ¹³C, and ³¹P NMR spectroscopy along with elemental analysis. Polymerization reactions of 2 in NMP or DMSO at 180 °C provided the corresponding linear poly(arylene ether phosphine oxide)s, PAEPOs, with number average molecular weights, M_n, ranging from 11,700 to 36,500 Da. All of the polymer samples were completely soluble in chloroform, tetrahydrofuran, DMSO, NMP, and DMAc. The polymerization reactions were accompanied by a competing intramolecular process that resulted in the formation of cyclic oligomeric species that were removed via a final precipitation from methanol. Analysis using ³¹P NMR spectroscopy and size exclusion chromatography (SEC) confirmed that the majority of the lower molecular weight cyclic species were removed via this process. The polymer samples formed tough films when chloroform solutions were slowly evaporated on a glass slide. The PAEPO samples prepared in this study exhibited excellent thermal stability with T_d (5%) values between 503 and 542 in air while the glass transition temperatures ranged from 223 to 237 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2099–2106, 2006     

Liquid chromatography at the critical condition: Thermodynamic significance and influence of pore size

Liquid chromatography at the critical condition (LCCC) is a high performance liquid chromatography (HPLC) technique that lies between size exclusion chromatography and adsorption-based interaction chromatography, where the elution of polymers becomes independent of polymer molecular weight. At LCCC, the balance between the entropic exclusion and the enthalpic adsorption interactions between polymers and stationary phases results in the simultaneous HPLC elution of polymers regardless of molecular weight. Using C18-bonded silica chromatographic columns with 5 μm particle size and different average pore size (diameter = 300 Å, 120 Å, 100 Å, and 50 Å), we report (1) the thermodynamic significance of LCCC conditions and (2) the influence of column pore size on the determination of critical conditions for linear polymer chains. Specifically, we used mixtures of monodisperse polystyrene samples ranging in molecular weight from 162 to 371,100 g/mol and controlled the temperature of the HPLC columns at a fixed composition of a mobile phase consisting of 57(v/v)% methylene chloride and 43(v/v)% acetonitrile. It was found that, at the fixed mobile phase composition, the temperature of LCCC (T_LCCC) is higher for C18-bonded chromatographic columns with larger average pore size. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2533–2540, 2009     

Multidimensional analytical protocols for the fractionation and analysis of complex polyolefins

Although produced from simple monomers that contain just carbon and hydrogen, polyolefin have complex molecular structures that are characterized by distributions in molar mass, chemical composition, and branching. Accordingly, a variety of advanced analytical techniques are needed for the comprehensive characterization of the molecular heterogeneity of polyolefins. These include different fractionation, spectroscopic, and thermal analysis methods. Very frequently, method couplings such as two-dimensional liquid chromatography or the coupling of crystallization- and column-based techniques are required. This review presents the current state of the art in multidimensional analysis of complex polyolefins. It discusses methods for bulk analysis as well as different analytical and preparative fractionation protocols. For different types of polyolefins it is shown that a preparative fractionation according to chemical composition/branching or molar mass helps to reduce the molecular complexity of the sample. Sample libraries can be obtained that may have narrow distributions regarding one molecular parameter. A detailed investigation of such library samples regarding other (broadly distributed) molecular parameters helps to fully explore the molecular heterogeneity of a complex sample.     

Thermal diffusion and molecular weight calibration of poly(ethylene-co-vinyl acetate)s by thermal field-flow fractionation

Copolymer characterization is accomplished with respect to measurement of thermal diffusion coefficient (D_T) and molecular weight determination by thermal field-flow fractionation. The examined copolymers are the eight poly(ethylene-co-vinyl acetate)s [P(E-V)] having different compositions of vinyl acetate ranging from 25 to 70% and the molecular weight from 110,000 to 285,000, and three polyvinyl acetate standards as component homopolymer. The carrier solvents are tetrahydrofuran, toluene, and chlorobenzene which have different viscosities and thermal conductivities. Measured D_T values vary from 1.36 × 10^?8 to 5.97 × 10_?8 cm²/(s . K) which are dependent on the composition of copolymers and types of carriers. These values increase linearly with the increase of weight percent of vinyl acetate. It is possible to estimate D_T values of polyethylene from the extrapolated intercept in the plots of D_T vs. vinyl acetate wt % of copolymer. Tetrahydrofuran is found to be the appropriate carrier solvent for the separation of P(E-V) copolymers since D_T varies greatly with the increase of wt % in THF. Attempts are made to correlate the measured retention data with molecular sizes of copolymers for the construction of the molecular weight calibration curve. Good correlations (r² ≥ 0.931) are found in which D/D_T values of polymers vary inversely with the product of hydrodynamic volume by weight ratio of vinyl acetate. Based on this relationship, the unknown molecular weight of copolymer sample can be determined from component homopolymers for which standards are readily available. © 1995 John Wiley & Sons, Inc.     

高效液相色谱法测定食品中的香豆素

介绍了用反相高效波相色谱（RP－HPLC）测定食品中香豆素含量的方法。样品用无水乙醚萃取,在40℃水浴上用氮气吹干,残留物用V（甲醇）：V（水）=9：1反萃取,用RP－HPLC定量分析。方法最小检出限为0.015mg／L,在2～10mg／L范围内有良好的线性关系,测定准确、重现性好,回收率为97.6％～100．8％,方法可行。     

Characterisation of poly(N-isopropylacrylamide) by asymmetrical flow field-flow fractionation, dynamic light scattering, and size exclusion chromatography

Asymmetrical flow field-flow fractionation (AsFIFFF) was used to determine the hydrodynamic particle sizes, molar masses, and phase transition behaviour of various poly(N-isopropylacrylamide) (PNIPAM) samples synthesised by reversible addition--fragmentation chain transfer (RAFT) and conventional free radical polymerisation processes. The results were compared with corresponding data obtained by dynamic light scattering (DLS) and size exclusion chromatography (SEC). Agreement between the three methods was good except at higher molar masses, where the molar mass averages obtained by SEC were much lower than those obtained by AsFIFFF and light scattering. The aggregation of the polymers, which are thermally sensitive, was studied by DLS and AsFIFFF at various temperatures. In deionised water there was an abrupt change in the particle size due to phase separation at approximately equal to 32-35 degrees C. The critical temperatures determined by AsFIFFF were 3-5 degrees C higher than those obtained by DLS.     

Chromatographic characterization of amphiphilic di‐ and tri‐block copolymers of poly(ethylene oxide) and poly(ε‐caprolactone)

Amphiphilic di‐ and tri‐block copolymers based on poly(ethylene oxide) as a hydrophilic segment and poly(ε‐caprolactone) as a hydrophobic part are synthesized by the ring‐opening polymerization of ε‐caprolactone while using poly(ethylene glycol)s and methoxy poly(ethylene glycol)s of varying molar masses as macro‐initiators. The synthesized block copolymers are characterized with respect to their total relative molar mass and its distribution by size exclusion chromatography. Liquid chromatography at critical conditions of both blocks is established for the analysis of individual block lengths and tracking presence of unwanted homopolymers of both types in the block copolymer samples. New critical conditions of polycaprolactone on reversed phase column are reported using organic mobile phase. The established critical conditions of polycaprolactone extended the applicable molar mass range significantly compared to already reported critical conditions of polycaprolactone in aqueous mobile phase. Block copolymers are also analyzed at critical conditions of poly(ethylene glycol). Complete analysis of the di‐ and tri‐block copolymers at corresponding critical conditions provided a fair estimate of molar mass of non‐critical block besides information regarding presence of homopolymers of both types in the samples.     

Mathematical modeling of crystallization analysis fractionation (Crystaf) of polyethylene

Four polyethylene samples (PE) with different molecular weight distributions (MWD) were analyzed by crystallization analysis fractionation (Crystaf) at several cooling rates to investigate the effect of MWD and cooling rate on their Crystaf profiles. Using these results, we developed a mathematical model for Crystaf that considers crystallization kinetic effects, which are ignored in all previous Crystaf models. The Crystaf model we proposed can fit the experimental Crystaf profiles of the 4 polyethylene resins very well. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2749–2759, 2006     

(2-甲基丙烯酰胺)乙氧基-2-甲基丙烯酸乙二醇单酯基质分子印迹手性分离介质的合成与表征

通过甲基丙烯酰氯和二甘醇胺反应设计合成了一种交联剂(2-甲基丙烯酰胺)乙氧基-2-甲基丙烯酸乙二醇单酯,以自行合成的(2-甲基丙烯酰胺)乙氧基-2-甲基丙烯酸乙二醇单酯为交联剂,丙烯酰胺为功能单体,合成了一种用于手性分离的N-叔丁氧羰酰-L-色氨酸(N-Boc-L-Trp,N-[(tert-butoxy)carbonyl]-tryptophan)的分子印迹聚合物。评价了该分子印迹聚合物作为高效液相色谱柱填料对N-叔丁氧羰酰-色氨酸(N-Boc-Trp)的手性拆分能力。结果表明:当检测波长为280 nm,流动相为V(甲醇)∶V(水)=80∶20,流速0.8 mL/min时,该填料实现了对N-Boc-Trp外消旋混合物的手性拆分,显示出良好的选择识别性能。     

Ethylene polymerization behavior of Cr(III)‐containing montmorillonite: Influence of chromium compounds

Montmorillonite was treated with Cr(NO₃)₃, Cr(acetate)₃, and Cr(acac)₃ to give three catalyst precursors, Cr‐MMT‐1 , Cr‐MMT‐2 , and Cr‐MMT‐3 , respectively. Application of these catalysts to the ethylene polymerization reaction revealed Cr‐MMT‐1 to be much more reactive than the other two while the molecular weight distributions of the polymers were practically the same. Elemental analysis, XRD, and TEM measurements suggested that chromium occupied the interlayer section in Cr‐MMT‐1 and mostly the outer surface region for the other two catalysts. Aluminosilicate‐supported Cr catalysts exhibited reactivity similar to that of Cr‐MMT‐2 and Cr‐MMT‐3 . However, more of the low‐molecular‐weight polymer was formed. These data suggested that there is a relationship between the sites of the Cr ions and catalytic reactivity, and between supporting solid identity and molecular weight distribution of the polymer. The use of n‐Bu₂Mg and Et₂Zn in the place of Et₃Al led to lower activity but gave polymers of narrower molecular weight distribution, with more of the high‐molecular‐weight material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2272–2280, 2009     

Synthesis,characterization and molecular weight studies of certain soluble poly(3-alkylthiophene) conducting polymers

Soluble conducting polymers of 3-hexylthiophene, 3-octylthiophene, 3-decylthiophene and 3-dodecylthiophene were synthesized by constant potential electrolysis. The resultant polymers were characterized by cyclic voltammetry, ultraviolet spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Molecular weights were studied with gel permeation chromatography on solutions of the polymers in toluene. Surface properties were investigated by scanning electron microscopy. Substituent groups lengths have been found to strongly influence the electronic properties of the resultant polymers. Poly(3-hexylthiophene) has shown the highest conductivity, with the highest degree of polymerization. The conductivity and the degree of polymerization values decrease as the substituent chain length increases.H.B. Mark Jr.: deseased     

Gamma irradiation of electrospun poly(ε‐caprolactone) fibers affects material properties but not cell response

Fabrication of electrospun fibrous scaffolds as future medical devices is being widely researched, with particular emphasis given to their material properties and effect on cell response and differentiation. However, the vast majority of these scaffolds are sterilized via nonmedically approved methods, including submersion in ethanol and exposure to UV light. Although these techniques are adequate for laboratory‐based research, they are not sufficient for human implantation. In this case, regulatory approved, medical grade sterilization is required. In this study, we report the effects of gamma irradiation, a regulatory approved technique, on electrospun poly(ε‐caprolactone) fibers. Fabricated fibers were separately subjected to different dosages of irradiation ranging from 0 to 45 kGy and then assessed for their physicochemical properties. Gamma irradiation affected fiber properties irrespective of dosage. A dose‐dependent decrease in polymer molecular weight was observed and an increase in melting point and crystallinity reported. Similarly, irradiation had a significant effect on mechanical properties with greatest decrease in tensile strength (68%) for fibers exposed to 40 kGy. The method of sterilization had no effect on cell response. Seeded tenocytes attached to all fibers and elongated parallel to the underlying fiber direction. The results demonstrate the importance of incorporating medical grade sterilization procedures early in the research projects time line to assist translation from bench to clinic. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Effect of chemical modifications on the electronic structure of poly(3‐hexylthiophene)

The widespread use of poly(3‐hexylthiophene) (P3HT) in the active layers of organic solar cells indicates that it possesses chemical stability and solubility suitable for such an application. However, it would be desirable to have a material that can maintain these properties but with a smaller bandgap, which would lead to more efficient energy harvesting of the solar spectrum. Fifteen P3HT derivatives were studied using the Density Functional Theory. The conclusion is that it is possible to obtain compounds with significantly smaller bandgaps and with solubility and stability similar to that of P3HT, mostly through the binding of oxygen atoms or conjugated organic groups to the thiophenic ring. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013     

聚噻吩的光电化学研究

导电聚合物是由一些具有共轭π键的聚合物经化学或电化学掺杂后形成的导电率可从绝缘体延伸到导体范围的一类高分子材料。其中噻吩及其衍生物具有导电率高、环境稳定性好、成膜性好、禁带宽度小等特点,是用做光伏电池的理想材料。相继报道的有聚3-甲噻吩[1]、聚3-己基噻吩[2],聚(3-十一烷基-2,2’-并噻吩)[3]等。对于聚噻吩的光电化学性质的研究,在国际上很少见报道,国内尚未见报道,本文对聚噻吩(PTh)的光电化学性质进行了研究。1实验部分1.1仪器与试剂光电化学实验采用带石英窗口的三电极电解池,工作电极为ITO/PTh膜电极,参比电极为饱和…     

化妆品中8种呋喃香豆素的高效液相色谱法检测及质谱确证

建立了同时测定化妆品中8种呋喃香豆素类化合物(8-羟基补骨脂素、补骨脂素、异补骨脂素、8-甲氧基补骨脂素、5-甲氧基补骨脂素、三甲沙林、欧前胡素和异欧前胡素)的高效液相色谱分析方法及液相色谱-串联质谱确证方法。膏霜类、水剂类、香波类、散粉类、唇膏类等不同类型的化妆品样品分别经适宜的提取溶液进行超声提取,提取液以离心处理后,取上清液经微孔滤膜过滤后测定。采用Agilent Zorbax SB-Phenyl色谱柱(250 mm×4.6 mm, 5 μm)分离,以甲醇-乙腈-水三元流动相梯度洗脱,流速1.0 mL/min,柱温30 ℃,检测波长250 nm。8-羟基补骨脂素的定量限为0.25 mg/kg,补骨脂素、异补骨脂素、8-甲氧基补骨脂素、5-甲氧基补骨脂素、三甲沙林、欧前胡素、异欧前胡素的定量限为0.5 mg/kg。在低、中、高3种加标水平下,8种待测组分的平均回收率为85.0%～105.8%,相对标准偏差为0.41%～7.90%。采用本方法在一日内不同时间点(6个时间点,每隔1 h测定一次)和不同日期(6 d内)测定混合标准溶液,得到8个目标物峰面积的日内精密度均小于1%,日间精密度均小于2%。该方法准确、简便、快速,适用于不同类型化妆品中8种呋喃香豆素类化合物的测定。