Droplet synthesis of well-defined block copolymers using solvent-resistant microfluidic device

Well-defined diblock copolymers were synthesized via an exothermic RAFT route by a droplet microfluidic process using a solvent-resistant and thermally stable fluoropolymer microreactor fabricated by a non-lithographic embedded template method. The resulting polymers were compared to products obtained from continuous flow capillary reactor and conventional bulk synthesis. The droplet based microreactor demonstrated superior molecular weight distribution control by synthesizing a higher molecular weight product with higher conversion and narrow polydispersity in a much shorter reaction time. The high quality of the as-synthesized block copolymer PMMA-b-PS led to a generation of micelles with a narrow size distribution that could be used as a template for well-ordered mesoporous silica with regular frameworks and high surface areas.     

Grafting of polymers with controlled molecular weight onto ultrafine silica surface

To graft polymers with controlled molecular weight and narrow molecular weight distribution, the grafting of polymers onto ultrafine silica surface by the termination of living polymer cation with amino groups introduced onto the surface was investigated. The introduction of amino or N-phenylamino groups onto the silica surface was achieved by the treatment of silica with γ-aminopropyltriethxysilane or N-phenyl-γ-aminopropyltrimethoxysilane. It was found that these amino groups on silica are readily reacted with living poly(isobutyl vinyl ether) (polyIBVE), which was generated with CF₃COOH/ZnCl₂ initiating system, and polyIBVE with controlled molecular weight and narrow molecular weight distribution is grafted onto the surface. By the termination of living poly(2-methyl-2-oxazoline), which was generated with methyl p-toluenesulfonate initiator, with amino groups on silica, polyMeOZO was also grafted onto the surface. The percentage of grafting of polymer onto the silica surface decreased with increasing molecular weight of the living polymer, because the steric hindrance of silica surface increases with increasing molecular weight of living polymer. Polymer-grafted silica gave a stable dispersion in a good solvent for grafted chains. © 1995 John Wiley & Sons, Inc.     

Synthesis,doping, and processing of high molecular weight poly(o-methoxyaniline)

High molecular weight poly(o-methoxyaniline) was synthesized using a novel method in which the polymerization occurs in the presence of a neutral salt. The molecular weight of the polymer was greatly affected by the quenching procedure employed to conclude the polymerization. Conventional doping of the base form of poly(o-methoxyaniline) produced a yellow coloration of the doping solution and polymer degradation. It was found that the molecular weight of the polymer decreased significantly after washing or doping with certain aqueous acid media. The gelation conditions of N-methyl pyrrolidinone (NMP) solutions and film preparation were also investigated for polymers of various molecular weights. The gelation time in NMP decreased drastically with the increase in the polymer molecular weight (the same for solution concentration and temperature), until a critical point was reached after which its decrease was very slow. Flexible, free-standing, and stretchable films were readily obtained from the higher molecular weight polymers. Good quality doped gel films with conductivity of up to 1 S/cm were obtained under optimized doping conditions. © 1994 John Wiley & Sons, Inc.     

Theoretical studies on the degradation of ladder polymers

The random degradation of four- and six-membered ring ladder polymers was simulated on a digital computer by utilizing a Monte Carlo model. The degradation was compared with that of a single-chain linear polymer undergoing an identical degradation reaction. Significant differences in the change in molecular weight as a function of time were noted between the ladder polymer and the single chain polymer. Similar studies were conducted with imperfect ladder polymers which had occasional missing bonds in the ladder structure. These imperfections produced a marked drop in molecular weight at a given time compared with the perfect ladder polymer.     

PMMA-containing ITX Residues and its Initiation for Synthesizing PMMA-b-PSt Copolymer

In virtue of the reversible coupling and cleaving mechanism involved isopropylthioxanthone (ITX), a precursor of poly(methyl methacrylate) ended with ITX residues (PMMA-ITXH) was firstly synthesized through the photopolymerization of methyl methacrylate (MMA) initiated by a binary system of ITX and ethyl-p-dimethyl amino benzoate (EDAB), and secondly, applying this precursor as a macroinitiator, block copolymer of poly(methyl methacrylate) and polystyrene (PMMA-b-PSt) was produced through a thermal activated radical polymerization of styrene (St) at a temperature above 80°C. The content of incorporation of the reduced ITX groups in the precursor was estimated by UV-vis spectrum analysis and the results indicated that it was greatly influenced by the ITX concentration in system. The presence of EDAB could promote the polymerization and result in high monomer conversions and low molecular weight of polymers with wide distributions, but had no evident effect on the incorporation of reduced ITX moieties in polymer. Furthermore, more monomer supplied in system was advantageous for the production of high molecular weight of polymers and provided apparently low content of reduced ITX residues in polymer. Using a selected precursor of PMMA-ITXH with a moderate level of reduced ITX residues, molecular weight and its distribution, the bulk polymerization of St was initiated. FTIR spectrum analysis and GPC measurement confirmed the formation of block copolymer of PMMA-b-PSt.     

Photo-controlled/living radical polymerization mediated by 2,2,6,6-tetramethylpiperidine-1-oxyl in inert atmospheres

The photo-controlled/living radical polymerization of methyl methacrylate using a nitroxide mediator was established in an inert atmosphere. The bulk polymerization was performed at room temperature using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator and (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate as the accelerator by irradiation with a high-pressure mercury lamp. The photopolymerization in a N₂ atmosphere produced a polymer with a comparatively narrow molecular weight distribution; however, the experimental molecular weight was slightly different from the theoretical molecular weight. The Ar atmospheric polymerization also provided a polymer with the molecular weight distribution similar to that of the polymer obtained by the N₂ atmospheric polymerization. These inert atmospheric polymerizations more rapidly proceeded to produce polymers with narrower molecular weight distributions than the vacuum polymerization. The livingness of the Ar atmospheric polymerization was confirmed on the basis of the first-order time–conversion plots and conversion–molecular weight plots.     

聚γ-缩水甘油醚氧丙基三甲氧基硅烷的合成与表征

采用双金属氰化络合物催化剂(DMC)催化γ-缩水甘油醚氧丙基三甲氧基硅烷(KH560)开环聚合,合成出结构规整的均聚产物PKH560.通过FTIR2、9Si-NMR1、H-NMR对聚合物的结构进行表征.结果表明,以DMC为催化剂,可以实现KH560的开环聚合,合成出分子量较大的目标产物PKH560.凝胶渗透色谱与多角度激光联用仪(GPC/MALLS)测得该聚合物PKH560的数均分子量大于1×104,分子量分布介于1.10与1.35之间;分析不同聚合时间PKH560的数均分子量与单体转化率之间的关系可知,聚合物的数均分子量Mn与单体转化率呈线性增长关系,聚合物的分子量分布较窄(Mw/Mn=1.10~1.35),表明该聚合反应具有活性聚合的特征.     

Endgroup analysis of isolated poly(methyl methacrylate) from graft copolymers of wool

In order to elucidate the termination mechanism in the graft copolymerization of methyl methacrylate to unreduced and reduced wool fibers, graft copolymers were prepared by means of the LiBr–K₂S₂O₈ redox sytem without homopolymer or with K₂S₂O₈ only with homopolymer at 30°C. The graft polymers (PMMA) were isolated almost completely from the wool trunk by an HCI-digestion method, leaving a few amino acid residues on the end of the graft polymers. Dinitrophenylation of the isolated polymer was carried out by various methods. The spectral features were almost the same as for dinitrophenylated amino acids of the usual type such as valine, leucine, and methionine, with a maximum in ultraviolet light at 340–345 mμ. From colorimetric analysis of the number of dinitrophenylated amino acid endgroups and the measurement of the average molecular weight of the isolated polymers, the number of amino acid endgroups linked to the graft polymers was calculated to be about one and two per polymer chain in reduced and unreduced wool, respectively, independent of the reaction system, graft-on, and molecular weight of graft polymers. From these facts, it was suggested that the most of isolated polymers are the truly grafted polymers. Also, the termination reactions have been explained as follows. In the unreduced wool, the restriction of mobility of the radical end might be expected, for the confinement of growing chains in wool fibers. This would be favorable to termination by recombination rather than by the disproportionation, since the former has a lower activation energy than the latter. Thus, the formation of intra- or intermolecular crosslinks might be considered between polypeptide chains. On the other hand, in the reduced wool, the mobility of graft polymers might be considered to be greater than that of unreduced wool because of its open structure. Therefore, termination would be principally by disproportionation between graft polymer radicals.     

Size exclusion chromatography of branched polymers: Star and comb polymers

Monte Carlo simulations were conducted to estimate the elution curve of size exclusion chromatography (SEC). The present simulation can be applied to various types of branched polymers, as long as the kinetic mechanism of nonlinear polymer formation is given. We considered two types of detector systems, (1) a detector that measures the polymer concentration in the elution volume to determine the calibrated molecular weights, such as by using the differential refractive index detector (RI), and (2) a detector that determines the weight‐average molecular weight of polymers within the elution volume directly, such as a light scattering photometer (LS). For polydisperse star polymers, both detector systems tend to give a reasonable estimate of the true molecular weight distribution (MWD). On the other hand, for comb‐branched polymers, the RI detector underestimates the molecular weight of branched polymers significantly. The LS detector system improves the measured MWD, but still is not exact. The present simulation technique promises to establish various types of complicated reaction mechanisms for nonlinear polymer formation by using the SEC data quantitatively. In addition, the present technique could be used to reinvestigate a large amount of SEC data obtained up to the present to estimate the true MWD.     

Molecular weight distribution of metallocene polymerization with long chain branching using a binary catalyst system

In metallocene polymerization, termination by β-hydride elimination generates polymer chains containing unsaturated vinyl groups at their chain ends. Further polymerization of these macromonomers produces branched polymers. Material properties of the branched polymers not only depend on molecular weight and branching density, but also on chain structure. This work presents analytical expressions to predict the bivariate distribution of molecular weight and branching density for polymer chains having dendritic and comb structures. It is shown that when a single metallocene catalyst is used the formation of dendritic polymers is favored with only a very small fraction of highly branched chains assuming comb structure. The use of a binary catalyst system is therefore proposed to obtain high content of comb polymers. One catalyst generates macromonomers and the other yields in-situ branching. It is found that the comb polymers give much narrower molecular weight distributions than dendritic polymers with same branching densities.     

Synthesis and thermal properties of a new class of high-temperature polyamides from hexahydrobenzodipyrrole

A series of polyamides was synthesized by the interfacial polycondensation of 1,2,3,5,6,7-hexahydrobenzo [1,2-c:4,5-c′] dipyrrole with isophthalic, terephthalic, oxydibenzoic, sebacic and adipic acid chlorides. High molecular weight polymers with inherent viscosities ranging from 0.4 to 2.3 dl/g were obtained. Polymerization with isophthaloyl chloride gave the highest molecular weight polymer in this series. These polyamides melt between 350°C and 475°C, depending on structural differences as determined by differential scanning calorimetry (DSC). Rapid weight loss in these polymers was observed in the range of 350–400°C under thermogravimetric analysis in a nitrogen atmosphere. All these polyamides are susceptible to photooxidative degradation. The results were compared with Nomex polymer poly(1,3-phenylene isophthalamide).     

α,α-二溴甲苯引发的苯乙烯原子转移自由基聚合研究

自从Ｍａｔｙｊａｓｚｅｗｓｋｉ等[1,2 ] 发现原子转移自由基聚合 (ＡＴＲＰ)以来 ,寻求新的双多官能引发剂是该领域的重要研究方向之一[3～ 7] .2 0 0 0年 ,我们[8]曾报道了α ,α 二溴乙酸乙酯可作为丙烯酸酯ＡＴＲＰ的双官能引发剂 ,并基于其两端增长的活性聚合性质合成了ＰＳ ｂ ＰＢＡ ｂ ＰＳ和ＰＭＭＡ ｂ ＰＢＡ ｂ ＰＭＭＡ两种三嵌段共聚物 .与此同时 ,Ｈｏｃｋｅｒ等[9] 通过比较氯化苄与α ,α 二氯甲苯引发的苯乙烯ＡＴＲＰ的聚合速度 ,认为α ,α 二氯甲苯是苯乙烯ＡＴＲＰ的双官能引发剂 .当我们参照上述结果 ,用α ,α 二…     

Monte Carlo simulation of size exclusion chromatography for branched polymers formed through free‐radical polymerization with chain transfer to polymer

The elution curves of size exclusion chromatography (SEC) for branched polymers formed through free‐radical polymerization that involves chain transfer to polymer were theoretically investigated by using a Monte Carlo method. We considered two types of measured molecular weight distribution (MWD), (1) the calibrated MWD relative to standard linear polymers, and (2) the MWD obtained by using a light scattering photometer (LS) in which the weight‐average molecular weight of polymers within the elution volume is determined directly. It was found that the calibrated MWD clearly underestimates the high molecular weight tail, and the measured distributions are narrower than the true MWD. On the other hand, the present simulation results showed that the LS method gives reasonable estimates of the true MWDs. The mean square radius of gyration of the polymer molecules having the same molecular weight was also investigated. The radii of gyration showed clear deviation from the Zimm‐Stockmayer equation^[1] because of the non‐random nature of branched structure and the difference in the primary chain length distribution.     

Adsorption kinetics of NIPAM-based polymers at the air-water interface as studied by pendant drop and bubble tensiometry

The adsorption of N-isopropylacrylamide (NIPAM) based thermoresponsive polymers at the air-water interface was investigated by using drop and bubble shape tensiometry. The molecular weight dependence of polymer adsorption rate was studied by using narrowly distributed polymer fractions (polydispersity < 1.2) that were prepared by solvent:nonsolvent fractionation. The time-dependent surface tension profiles were fitted to the Hua-Rosen equation and the t values obtained were applied for interpretation of the kinetic data. It was found that the rate of polymer adsorption increased as the molecular weight of the polymer decreased. The relationship between polymer surface concentration and surface tension was determined by applying the pendant drop as a Langmuir-type film balance. From this relationship, the kinetics of polymer adsorption determined experimentally was compared with the adsorption rates predicted by a diffusion-controlled adsorption model based on the Ward-Tordai equation. The predicted adsorption rates were in good agreement with what was found experimentally. The dependence of the adsorption rate on the molecular weight of polymers can be satisfactorily described within the diffusion-controlled model.     

Self-organization-induced three-dimensional honeycomb pattern in structure-controlled bulky methacrylate polymers: Synthesis, morphology, and mechanism of pore formation

Here we report, for the first time, a novel molecular design for three-dimensional honeycomb structures through a self-organization of hydrogen-bonded bulky anchoring group in a methacrylic polymer backbone. The polymerizable monomer design includes a methacrylic double bond linked to various hydrophobic anchoring units such as ethane, n-decane, tricyclodecane (TCD), and adamantane via a hydrogen-bonded cycloaliphatic urethane linkage. The structures of the polymers were confirmed by nuclear magnetic resonance (NMR) and the molecular weights of the polymer were determined by gel permeation chromatography (GPC). The methacrylate polymers having tricyclodecane and adamantane bulky anchoring groups self-organized to produce three-dimensional honeycomb patterns in tetrahydrofuran-water solvent mixture at ambient conditions, whereas its linear analogues (ethane, n-decane) failed to produce any micropattern. The scanning electron microscopy (SEM) analysis of the above-prepared polymer films revealed that the structure of the polymer played a major role in the formation of the honeycomb patterns. The solution Fourier transform infrared (FTIR) measurements confirmed that the bulky tricyclodecane and adamantane polymers have strong hydrogen-bonding interaction compared to that of their linear analogues, which is the driving force for the micropatterns. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the bulky polymers revealed that the polymers exist as vesicles or micelles in the solution, which leads to the formation of the honeycomb pattern. The honeycomb pattern formation in the bulky polymer systems suggests that two cooperative factors such as hydrogen-bonding interaction and hydrophobicity of bulky anchoring units are necessary to induce three-dimensional honeycomb structures. To investigate the effect of molecular weights and its distribution on the self-organization process, both benzoyl peroxide (BPO) initiated free radical and atom transfer radical polymerization (ATRP) techniques were employed for the polymerization. Micropores formed irrespective of differences in molecular weight and polydispersity index (PDI); however, the pore size distribution was influenced by both molecular weights and PDI. Low molecular weight samples afforded polydisperse pores with the ATRP samples with more narrow PDI producing pores with large dimensions. The approach has also been investigated for polystyrene-bulky methacrylic copolymer, and the results revealed that uniform honeycomb patterns were produced for copolymers having more than 50 mol % incorporation of bulky units.     

Synthesis of ultra‐high‐molecular‐weight poly(α‐olefin)s by thiobis(phenoxy)titanium/modified methylaluminoxane system

Polymerization of 1‐butene with thiobis(phenoxy)titanium dichloride (TBPTiCl₂) with modified methylaluminoxane (MMAO) yielded atactic and regioirregular poly(1‐butene) with low molecular weight. However, productivity was increased and the yielded polymer structure was changed when water‐modified MMAO (WM‐MMAO) was used as a cocatalyst. The molecular weight of obtained polymer with TBPTiCl₂/WM‐MMAO was dramatically increased and reached over 9 million g/mol. Poly(1‐butene) produced by this catalytic system was almost regioregular and slightly isotactic. 1‐Hexene and 1‐octene were also polymerized by this catalytic system. In all cases, the ultra‐high‐molecular‐weight polymers were obtained. These results showed that the modified structure of the MMAO cluster by water affects the productivity, molecular weight, regioregularity, and stereoregularity of yielded polyolefins. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1107–1111, 2004     

Synthesis of Star-Shaped Polymers via Coordination of Bipyridyl-Terminated Polyoxyethylene with Metal Ions

Abstract

This paper describes the synthesis of various star-shaped polymers by means of complexation of bipyridyl-terminated polyoxyethylene with Ru(II) ion. Three kinds of bipyridyl-terminated polyoxyethylenes of different molecular weights were prepared from the corresponding polyoxyethylene monomethyl ethers with narrow molecular weight distributions. Bipyridyl was found to be introduced quantitatively at the end of the polymers based on the results of UV spectra. The formation of a star-shaped polymer was carried out by the reaction of RuCl₃ with three equivalents of bipyridyl-terminated polyoxyethylene. The UV spectrum of the star-shaped polymer obtained supported the formation of a typical Ru(II) tris(bipyridyl) complex. From the results of GPC, the star-shaped polymer obtained had a higher molecular weight than the pre-polymer and showed a narrow molecular weight distribution. In the case of a Ni(II) or a Co(II) complex, however, the star-shaped polymer was found to be dissociated into three linear prepolymers under the conditions of GPC measurement.     

Photo-controlled/living radical polymerization of 2-(dimethylamino)ethyl methacrylate using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as a mediator

The photo-controlled/living radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) was attained using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator and (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) (r-AMDV) as the initiator. The bulk polymerization of DMAEMA produced a polymer with a comparatively narrow molecular weight distribution below 1.6. The first-order time conversion plots showed a linear increase. The molecular weight of the resulting polymer also increased with an increase in the monomer conversion. The molecular weights of the resulting polymers were in good agreement with the theoretical molecular weights. A linear correlation was also obtained for the plots of the molecular weight vs. the reciprocal of the initial concentration of r-AMDV. The GPC analysis demonstrated the living nature of the polymerization based on the fact that the curves were shifted to the higher molecular weight side without deactivation as the conversion increased.     

From Living to “Immortal” Polymerization

Aluminum porphyrin is an excellent initiator for the living polymerizations of a wide variety of monomers such as epoxide, β-lactone, δ-lactone, ε-lactone, and lactide, and also for the alternating copolymerization of epoxide and cyclic acid anhydride or carbon dioxide, to give polymers and copolymers with narrow molecular weight distribution. Aluminum porphyrin was recently found to initiate also the living polymerization of methacrylic ester. In the polymerizations of epoxides and lactones initiated with aluminum porphyrin in the presence of an appropriate protic compound, polymers with narrow molecular weight can be obtained with the number of the polymer molecules more than those of the initiator. This fact demonstrates the “immortal” nature of the polymerization due to unusual reactivities of aluminum prophyrin.     

Solution Polymerization of Acrylonitrile Catalyzed by Sodium Triethylthioisopropoxyaluminate: A Polyacrylonitrile with High Structural Regularity

A new catalyst for the polymerization of acrylonitrile has been found by reacting sodium aluminum tetraethyl with a stoichiometric amount of oxygen, alcohols, or mercaptans, etc. The catalyst prepared by reacting NaAlEt₄ with RSH remains active at temperatures as low as ?78°C., polymerizing acrylonitrile into high molecular weight polymers with high conversions. At ?78°C., the propagating chain remains active over a period of days, and the chain length increases with time or conversion. At high conversions the molecular weight of the polymer is directly proportional to the concentration of the monomer, the catalyst concentration being kept constant. The efficiency of the catalyst expressed as the ratio of the number of the polymer molecules produced to the number of the sulfur atoms used is in excess of 80%. The weight-average molecular weight of the polymer measured by light scattering is roughly equal to the number-average molecular weight determined by sulfur analysis assuming only onesulfur atom in each polymer molecule. Although the data given here are only qualitative in nature, it is nevertheless evident that this system bears great resemblances to anionic polymerizations resulting in “living polymers.” The polymer obtained with the NaAlEt₃S(i-Pr) catalyst at ?78°C. differs from free-radical polyacrylonitrile in exhibiting substantially lower solubility, higher melting point, and higher rate of crystallization than that for the free-radical polymer. The polymer is also free from structural mpurities; it does not cause fluorescence in dilute solutions and has no absorption peak at 265 mμ; both these effects are produced by impurities in free-radical polyacrylonitrile. It is concluded that the polymer reported here is more regular in structure than free-radical polyacrylonitrile.