Copolymerization with the feeding of one of the comonomers: Cationic activated monomer copolymerization of ε‐caprolactone with ethylene oxide

The cationic copolymerization of ε‐caprolactone with ethylene oxide (EO) under the conditions of activated monomer polymerization, that is, with a low‐molecular‐weight diol as an initiator and BF₃ etherate as a catalyst, was studied. To ensure the uniform composition of the resulting copolymers (telechelic oligodiols), the copolymerization was conducted with incremental feeding of the EO comonomer, which was more reactive in the cationic process. ¹H NMR analysis of samples isolated at different stages of the copolymerization indicated that the average composition of the copolymer was indeed nearly constant over the course of the copolymerization. Matrix‐assisted laser desorption/ionization time‐of‐flight spectra of the products revealed, however, that for the same degree of polymerization, macromolecules containing different numbers of EO units were present. The observed distribution was compared with the distribution simulated under the assumption that the probability of incorporating a given unit depended only on the feed composition (nearly constant during the copolymerization). With this assumption, a good agreement between the observed and simulated spectra was obtained. This indicated that, even when the optimum conditions for the formation of a uniform copolymer were created, the individual macromolecules differed in composition because of the statistical character of the copolymerization. The results of differential scanning calorimetry analysis were compatible with such a conclusion; two melting peaks appeared on differential scanning calorimetry curves when a sample was heated immediately after fast cooling, and this may indicate the presence of different types of crystallites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3788–3796, 2005     

Conventional free-radical and RAFT copolymerization of poly(ethylene oxide) containing macromonomers

Conventional free-radical and RAFT copolymerization of poly(ethylene oxide) substituent containing methacrylate macromonomers, PEO₅MEMA and PEO₄₅MEMA, was studied by the use of ¹H NMR spectroscopy for an analysis of residual monomers. From the monomer consumption curves, several parameters including monomer conversion, instantaneous copolymer composition and reactivity ratios of the monomers were evaluated. Reactivity ratios of PEO₅MEMA and MAA estimated by non-linear approach of error-in-variables model and presented as joint confidence regions were constant during conventional free-radical and RAFT copolymerizations of the above monomers but were slightly affected by the RAFT process. Reactivity ratio of PEO₄₅MEMA was found to be lower than that of PEO₅MEMA and varied during copolymerization: increased with conversion in conventional free-radical copolymerization and slightly (without confidence) decreased in the RAFT process. RAFT copolymerization of PEO₄₅MEMA and MAA enabled to synthesize comb copolymers with low composition distribution and more homogeneous distribution of PEO side chains along the mainchain. Under copolymerization with MAA, PEO₄₅MEMA behaved like typical macromonomer with appropriate steric hindrance while the behavior of PEO₅MEMA was similar to that of a low-molecular methacrylate.     

Some newer concepts on ethylene/α-olefin copolymerization on heterogeneous Ziegler-Natta catalysts

Unsteady diffusion kinetics, recently advanced by this laboratory, is applied to the examination of some polymerization and molecular chain structure problems. Hitherto deemed “anomalous” phenomena, such as the faster rate of copolymerization of ethylene/α-olefin than the homopolymerization of ethylene and the enrichment in the incorporation of a higher α-olefin in its copolymerization with ethylene by a lower α-olefin, are reasonably explained by unsteady diffusion of monomers. Molecular chain structure of copolymers, such as compositional heterogeneity and its dependence on comonomer incorporation originates from the difference in diffusion coefficients of the monomers. A copolymer composition equation taking into consideration the unsteady diffusion was developed. In cases where simulated curves were compared with experimental curves, good agreements were found.     

基于单体的Q和e值绘制二元共聚双曲线*

采用Matlab中的Plot函数,首次以单体的Q、e值为中间变量,绘制出二元共聚双曲线。将二元共聚物组成曲线F1-f1和F2-f2同时呈现在一个图上,使隐含的第二单体的共聚行为可视化,有助于加深学习者对二元共聚的理解。     

Emulsion copolymerization of tribromophenyl maleimide with styrene

Emulsion copolymerization of Tribromophenyl Maleimide (TBPMI) and styrene was conducted by semi-batch and batch processes. The effects of monomer composition and copolymerization method on copolymerization rate, molecular weight and molecular weight distribution, latex particle size and size distribution, glass transition temperature (T_g), thermal stability and mechanical properties were investigated. A kinetic study has shown that the rate of copolymerization in the batch process increased with increasing TBPMI content in the monomer feed. For the semi-batch polymerized samples, molecular weight decreased and molecular weight distribution increased with increasing TBPMI content in the monomer feed. For the batch polymerized samples, molecular weight also decreased but no obvious tendency was observed for the molecular weight distribution when TBPMI content increased. Compared with the batch copolymers, the semi-batch copolymers have a higher molecular weight at the same initial monomer mixture composition. Latex particle size decreased, while particle size distribution slightly increased with increasing TBPMI content in both semi-batch and batch latices. The semi-batch samples exhibit only a single T_g, the value of which increses linearly with increasing TBPMI content. For the batch copolymers, two T_gs were found, reflecting a mixture of styrene-rich and TBPMI-rich copolymer chains. TGA results indicate that the thermal stability of the semi-batch copolymers increased with increasing TBPMI concentration. Young's and flexural moduli increased, while tensile and flexural strengths decreased by increasing the TBPMI content for both the semi-batch and batch specimens. The semi-batch specimens have higher tensile and flexural strenghts than the batch ones.     

Functional and surface-active membranes from poly(vinylidene fluoride)-graft-poly(acrylic acid) prepared via RAFT-mediated graft copolymerization

Poly (vinylidene fluoride) (PVDF) with "living" poly (acrylic acid) (PAAc) side chains (PVDF-g-PAAc) was prepared by reversible addition-fragmentation chain transfer (RAFT)-mediated graft copolymerization of acrylic acid (AAc) with the ozone-pretreated PVDF. The chemical composition and structure of the copolymers were characterized by elemental analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The copolymer could be readily cast into pH-sensitive microfiltration (MF) membranes with enriched living PAAc graft chains on the surface (including the pore surfaces) by phase inversion in an aqueous medium. The surface composition of the membranes was determined by X-ray photoelectron spectroscopy. The morphology of the membranes was characterized by scanning electron microscopy. The pore size distribution of the membranes was found to be much more uniform than that of the corresponding membranes cast from PVDF-g-PAAc prepared by the "conventional" free-radical graft copolymerization process. Most important of all, the MF membranes with surface-tethered PAAc macro chain transfer agents, or the living membrane surfaces, could be further functionalized via surface-initiated block copolymerization with N-isopropylacrylamide (NIPAAM) to obtain the PVDF-g-PAAc-b-PNIPAAM MF membranes, which exhibited both pH- and temperature-dependent permeability to aqueous media.     

Analysis of Linear Methods for Determining Copolymerization Reactivity Ratios. III. Linear Graphic Method for Evaluating Data Obtained at High Conversion Levels

If copolymerizations are carried to high conversions, the determination of copolymerization parameters involves significant computational difficulties because the exact integrated form of the copolymerization equation has to be applied. A simple method has been developed to transform experimental data, even at high conversions, to be used in the differential form of copolymerization equation. In this method an average monomer composition is assigned to the corresponding experimental average copolymer composition. The proposed approximation extends the use of our linearization technique previously developed for low conversions. It was established that this method yields highly reliable results for practically.     

The multiple melting endotherms from poly(butylene terephthalate)

The melting behavior of poly(butylene terephthalate) (PBT) has been investigated, and a simulation has been performed to determine whether the multiple melting endotherms observed during the thermal analysis of PBT can be explained by the simultaneous melting and recrystallization of an initial distribution of crystal melting temperatures that contains only one maximum and two inflection points. Specimens that were cooled at constant rates from the melt showed between one and three melting endotherms upon heating in a differential scanning calorimeter (DSC). The position and breadth of the crystallization exotherms upon cooling from the melt and small-angle x-ray scattering showed that as the cooling rate is increased, the distribution of melting temperatures broadens and shifts to lower temperatures. By combining temperature-dependent recrystallization with an initial distribution of melting temperatures, simulated DSC curves were produced that agreed well with experimental DSC curves. In instances of triple peaked curves, the high temperature peak was due to crystals formed during the scanning process, and the middle and low temperature peaks were due to crystals originally present in the material. Satisfactory agreement between the experimental and simulated curves was found without considering additional crystallization from the amorphous regions during the scanning process.     

Terpolymerization of acrylonitrile,styrene, and 2,3-dibromopropyl acrylate

The terpolymerization of acrylonitrile with styrene and 2,3-dibromopropyl acrylate in emulsion and dimethyl formamide solution was investigated. Polymerizations, when stopped at low conversions, yielded terpolymers that showed good agreement between experimental and theoretical copolymerization composition data, calculated from the Alfrey-Goldfinger equation. The relationship between monomer feed and terpolymer compositions is displayed on triangular coordinate graphs proposed by Slocombe. By using a computer program the lines of unique composition and binary azeotropic composition for both systems were established. In the case of emulsion polymerization the azeotropic ternary point was determined at a molar ratio for acrylonitrile/styrene/2,3-dibromopropyl acrylate of 0.27/0.61/0.12. The experimental results of emulsion terpolymerization fit the calculated curves satisfactorily over a wide range of monomer compositions up to high conversions. The influence of 2,3-dibromopropyl acrylate on the thermal and flammability characteristics of the terpolymers is described.     

Determination of chain transfer constant to dodecanethiol in styrene/methyl methacrylate and butyl acrylate/methyl methacrylate copolymerization and effect of chain length on composition and stereochemical configuration of copolymers

Free radical copolymerization of styrene/methyl methacrylate (S/MMA) and butyl acrylate/methyl methacrylate (BA/MMA) in the presence of n-dodecanthiol (DDT) has been studied at 60°C in a 3 mol/L benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator. Overall chain transfer constant to DDT has been determined for both copolymerization systems, as a function of monomer feed composition using complete molecular weight distribution and the Mayo method. Overall transfer coefficients have values which are dependent on both monomer feed composition and individual comonomer transfer values. Composition, sequence distribution, and stereoregularity of copolymers obtained are, in our experimental conditions, independent of copolymer molecular weight. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2913–2925, 1998     

Controlled Composition in Emulsion Copolymerization Application to Butadiene-Acrylonitrile Copolymers

Abstract

The use of gas chromatographic analysis of the actual monomer mixture at fixed time intervals to monitor the composition of copolymers in emulsion copolymerization has been described previously. The design has been now improved by the insertion of a dilution cell to avoid flocculation problems in the loop carrying the reaction medium from the reactor to the injection kit of the chromatograph. Then the copolymerization can be monitored up to completion. This system has been applied to the copolymerization of butadiene and acrylonitrile, and constant composition runs have been compared to the batch. Two main differences are observed. (1) Constant composition copolymers show a unique glass transition interval of limited width instead of two or at least one broad temperature interval for the copolymer produced in batch. (2) In the monitored copolymerizations, the production of insoluble gels is delayed and sometimes totally avoided. The production of the gels is related to the formation of 1,2-butadiene units which appear to be preferentially present in long sequences of butadiene units. The cross-linking process involves the consumption of the pendent vinyl groups by copolymerization with the monomers.     

Microemulsion copolymerization of styrene and acrylonitrile with n‐butanol as the cosurfactant

The microemulsion copolymerization of styrene and acrylonitrile in an n‐butanol/cetyltrimethylammonium bromide/oil/water microemulsion system was studied. The solubilization sites of the two monomers were determined with an NMR technique. The results showed that the solubilization behaviors of the two monomers were quite different. Most of the styrene was solubilized in the palisade layer of the microemulsion, whereas the acrylonitrile had an equilibrium distribution in the aqueous phase and palisade layer of the microemulsion. The reactivity ratios of styrene and acrylonitrile in the microemulsion system were different from those in other media. The effect of the monomer feed composition on the copolymerization kinetics was investigated, and the mechanism of nucleation of the latex particles was examined. The experimental results showed that the copolymerization loci were changed from the microemulsion droplets to the aqueous phase when the concentration of acrylonitrile in the monomer feed reached approximately 80%; this could be further proved by the effect of the monomer feed composition on the copolymerization kinetics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 203–216, 2005     

乙烯基单体／N-苯基马来酰亚胺共聚物组成分布测定原理及应用

共聚物分子量往往根据溶液性质来测定 ,而组成变化对高分子溶液的性质有影响 .如果共聚物组成不随分子量而变化 ,则认为组成分布均匀 .用化学或光谱方法得到的共聚物组成只是一个平均值 ,不能完全表征组成分布情况 .根据溶液性质差异进行分级 ,需选择合适的溶剂 沉淀剂体系 ,且操作时间长 .采用薄层色谱法所需时间亦长 ,且由于存在扩散效应而掩盖真实的共聚物组成分布 .自从凝胶渗透色谱 (ＧＰＣ)出现后 ,将紫外吸收光谱 (ＵＶ)或红外吸收光谱仪与示差折光仪 (ＤＲ)串联 ,一个对组成敏感 ,一个对浓度 (共聚物总量 )敏感 ,将组成变化和分子量…     

Copolymerisation radicalaire du méthacrylate de méthyle et du chlorure de vinylidène avec ou sans dérive de composition

Two sets of methylmethacrylate-vinylidene chloride copolymers were prepared via radical copolymerization in dimethylformamide. The first set is carried out in batches. Gas-chromatographic analysis of samples allows a kinetic study from which the reactivity ratios r_M - 2.73 and r_C - 0.24 are derived. For the second set a new apparatus, briefly described, has been used. It permits to keep constant the composition of the monomer mixture, through addition of methyl methacrylate, monitored by a chromatographic analysis. The two sets of copolymers are analyzed using nuclear magnetic resonance (60 MHz) leading to the triad distribution, from which the reactivity ratios are derived. Owing to the composition drift, the method cannot be applied to the first set of copolymers; but in that case, it is possible to calculate the triad distribution, the knowledge of the reactivity ratios, and the calculation fits quite well the experimental results.     

Peculiarities of N-vinylpyrrolidone copolymerization with vinyl acetate in the presence of tributylborane and 1,4-benzoquinone

Copolymerization of N-vinylpyrrolidone with vinyl acetate in the presence of tributylborane and 1,4-benzoquinone has been investigated. The curves of copolymer composition and relative reactivity of monomers were obtained. An introduction of tributylborane in the monomer mixture leads to the formation of complex with N-vinylpyrrolidone. Molecular weight of the copolymers and the rate of the copolymerization decreases with the addition of tributylborane and 1,4-benzoquinone compare to conventional copolymerization initiated by dicyclohexyl peroxydicarbonate. The curve of the copolymer composition acquires an S-shape. Triad composition of the copolymers differs from the theoretical values. The reason for the observed pheno mena is realization of the effect of preferential solvation (bootstrap-effect).

     

活化/失活反应对原子转移自由基共聚产物微观结构的影响

提出了一个可以处理原子转移自由基共聚及其产物微结构的模型,采用计算机模拟产生了包括活化/失活反应的ATRcP稳态增长反应链,得到了有关链段分布的信息.模拟发现,含有休眠过程的ATRcP产物与常规的自由基的相比组成结构和序列结构完全一致,即活化/失活反应不影响ATRcP产物的微组成与微序列结构.     

HEMA-NVP-St三元共聚体系研究Ⅲ.均化剂对共聚物组成均一性的影响

用溴化钾-溴酸钾滴定法测定双键含量,元素分析法测定共聚物组成。讨论了HEMA-NVP-St三元共聚体系在不同反应程度时共聚物组成的变化,以及在此三元共聚体系中引入均化剂后,少量均化剂对共聚体系组成均一性的影响。发现在HEMA-NVP-St三元共聚体系中加入均化剂,对共聚反应的反应动力学影响不大,但对共聚物的组成均一性有较大影响。它的加入使三元共聚物中的链节比分布(即不同反应程度时,产物的累积平均组成)向较均一的方向发展。结合红外光谱、电子显微镜等实验证据,从微观结构上探讨了约化剂的作用。阐明均化剂改善了反应体系的相容性,从而得到组成分布较为均一的共聚产物。     

TiCl_4/MgCl_2催化丙烯/1-辛烯共聚合研究

本文用TiCl_4/MgCl_2-Al(i-Bu)_3催化剂进行丙烯/1-辛烯共聚合,研究发现引入少量共聚单体1-辛烯时,能提高丙烯的聚合活性。30℃时,测得共聚合竟聚率为r_丙=5.63,r_辛=0.32。共聚物的结晶度和己烷不溶物含量随其1-辛烯含量的增加而迅速下降。X射线衍射及~(13)C-NMR测定结果表明,共聚物的己烷可溶部分为非结晶的无规共聚物,己烷不溶部分是具有镶嵌着半个1-辛烯单体单元的长嵌段聚丙烯链结构的结晶性共聚物。