Synthesis of Well-defined Long Chain Branched Polyethylene via Anionic Polymerization Combined with Graft-onto Method

Comb-like polyethylene(PE) was prepared via anionic polymerization combined with “graft-onto” process. The polybutadiene(PB) backbone underwent hydroxylation at 1,2-vinyl groups to obtain a controlled number of hydro- xyl groups along the main chain. After the translation of hydroxyl groups to tosyl groups, a nucleophilic substitution by living anionic PB chains was achieved. The comb PE was finally obtained by the hydrogenation of the obtained unsaturated comb polymer. Since the living anionic polymerization was used to prepare the backbones and the branch chains, molecular weight to molecular weight distribution(M_w/M_n<1.5) can be well-controlled in the final comb polymer, including the average number and length of branches.     

The synthesis and properties of a series of novel side-chain liquid crystal polymers based on the Baylis-Hillman reaction

A new methodology is described, based on the Baylis-Hillman reaction, by which thermally stable side-chain liquid crystal (SCLC) polymers can be prepared incorporating a variety of functional groups along the polymer backbone. This methodology also allows a polar group, especially hydroxyl, to be inserted adjacent to the point of attachment of the spacer group to the polymer backbone. The spatial arrangement of the hydroxyl and functional groups is not only conducive to the formation of liquid crystalline phases but may also influence the tacticity of the polymer backbone.     

Dynamic cross‐links to facilitate recyclable polybutadiene elastomer with excellent toughness and stretchability

A facile cross‐linking strategy of using small molecules as physcial crosslinkers to facilitate recyclable polybutadiene (PB) elastomer with excellent toughness and stretchability is demonstrated. Carboxylic acid groups were incorporated along the PB backbone via thiol‐ene reaction, and then the polymer can be cross‐linked by ionic hydrogen bonds between the carboxylic acid groups from PB and the amine groups of the cross‐linkers. The ionic hydrogen bonds can dynamiclly break and reconstruct upon deformation, thus endowing the resultant polymer with not only high toughness and stretchability (～1800%), but also good self‐recovery and enhanced damping properties. Remarkably, the dynamically cross‐linked PB elastomer can be thermally recycled owing to the thermal reversibility of the ionic hydrogen bonds and the mechanical properties can be largely recovered after reprocessing. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1357‐1366     

Long‐chain branched ROMP polymers

This article describes the construction of branched ROMP‐polymer architectures via polycondensation of AB_n‐type macromonomers. For this convergent strategy, a polymer was synthesized that carries several hydroxyl‐groups along the polymer chain and one carboxylic acid group at the chain end. An esterification reaction between these functional groups yielded long‐chain branched polymers. The polymers were analyzed by NMR and SEC to monitor the condensation reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Mechanistic studies on ceric-thiourea-initiated polymerization of methyl methacrylate in acid-aqueous media from end group analysis

The mechanism of the redox polymerization of methyl methacrylate in acid-aqueous medium was studied for ceric-thiourea initiator system by analysis of polymer end groups using the dye partition method. Polymerization at room temperature and at pH 2.30 with this initiator system incorporates mostly amino end groups in the polymers to the extent of 1.18-1.31 and a small amount of hydroxyl end group not exceeding 0.08 per polymer molecule. Under the same pH condition, a higher polymerization temperature increases the amine end group content to 2.17-2.30 and hydroxyl end group content to 0.14-0.18 per polymer molecule. A lower polymerization temperature (5°C), or a lower pH (ca. 1) of the reaction medium, produces polymers with exclusively amine end groups, hydroxyl end groups being totally absent. At pHs greater than 3, amine end group incorporation decreases significantly, with simultaneous increase in hydroxyl incorporation. On the basis of end group results the initiating radical has been identified and the mechanism of initiation has been suggested. The possible mode of termination has also been discussed.     

凝胶渗透色谱多孔硅胶吸附问题的研究

本文以端基为羟基的聚二甲基硅氧烷为测试样品,甲苯为淋洗液,研究了凝胶色谱柱填料多孔硅胶的表面羟基含量等与吸附效应的关系。说明采用对硅胶进行表面处理和在淋洗液中加入吸附抑制剂的方法,不能避免吸附。建议采用端基封闭剂(如三甲基氯硅烷)处理聚合物的活性端基——羟基的方法,解决吸附问题。     

Synthesis of telechelic anthraquinone‐functionalized polybutadiene via ROMP and study of its photo‐oxidation and UV crosslinking behaviors

Telechelic anthraquinone‐functionalized polybutadiene (AQ‐PB‐AQ) was synthesized by ring opening metathesis polymerization to achieve homogeneous dispersion of AQ groups in the polymer matrix. It was observed that the AQ end groups act as a sensitizing group resulting in photo‐induced crosslinking and oxidation reaction at the olefin groups in the PB. The process was confirmed by comparing the polymer's mass loss and Fourier transform infrared (FTIR) spectra with those of telechelic diacetoxy‐functionalized PB (AcO‐PB‐OAc) which did not show any difference before and after ultraviolet irradiation. Homogeneity of the AQ groups in PB matrix results in rapid crosslinking of PB in a short period of time (<4 min) while a simple blend of AQ methyl ester in AcO‐PB‐OAc matrix did not show such behavior. Photo‐oxidative reaction has concurrently occurred during the crosslinking reaction. Generation of  OH,  OOH, and carbonyl groups in the matrix during the photo‐oxidation was verified by FTIR, elemental analysis, and water contact angle measurements. A plausible mechanism for the process was proposed in which the photo‐sensitized AQ groups abstract hydrogen from the PB chain to yield reactive radical species, initiating oxidative crosslinking, and degradation of PB or reduction of AQ to hydroanthraquinone species. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1249–1258     

Thermal and photo-degradation of unstabilized ABS

Thermal- and photo-stabilities of unstabilized acrylonitrile-butadiene-styrene terpolymer, ABS, have been investigated by i.r. spectroscopy. Degradation of ABS samples is initiated by attack on the polybutadiene (PB) component; oxidation products containing hydroxyl and carbonyl groups are produced. The effect of prior thermal processing is to introduce into the polymer hydroperoxides arising from oxidative destruction of PB-unsaturation; these hydroperoxides act as catalysts during subsequent u.v. irradiation. The insolubility of degraded samples of ABS is associated with the formation of cross-linked structures and occurs mainly in the PB segment. It is concluded that the degradation characteristics of ABS are essentially those of the polybutadiene component.     

Graft Polymerization of Vinyl Monomers Onto Carbon Black by Use of the Redox System Consisting of Ceric Ions and Carbon Black Carrying Alcoholic Hydroxyl Groups

The radical graft polymerization of vinyl monomers onto carbon black initiated by a redox system consisting of ceric ion and carbon black having alcoholic hydroxyl groups was investigated. The introduction of alcoholic hydroxyl groups onto the carbon black surface was achieved by the reaction of carbon black with alcoholic hydroxyl radicals, formed by the reaction of alcohol with benzoyl peroxide. The rate of the polymerization of acrylamide (AAm) initiated by the redox system was found to increase in the following order of hydroxyl groups: 1-hydroxyoctyl < 1-hydroxypropyl < 1-hydroxyethyl < hydroxymethyl < 1-hydroxy-1-methylethyl. In the redox polymerization, poly-AAm was effectively grafted onto carbon black by propagation of the polymer from the radical formed by the reaction of ceric ions with the alcoholic hydroxy groups. The percentage of grafting increased with increasing conversion. By use of this redox system, poly(acrylic acid), polyacrylonitrile, and poly(N-vinyl-2-pyrrolidone) could be grafted onto carbon black, but poly(methyl methacrylate) and polystyrene could not be so grafted. The graft polymerization of AAm by use of a redox system consisting of ceric ion and PVA-grafted carbon black was also investigated.     

Metallation of unsaturated polymers and formation of graft copolymers

The use of N,N,N′,N′-tetramethylethylenediamine (TMEDA) is known to enhance the metallation of capability of butyllithium. It has been found that this TMEDA–BuLi reagent smoothly metallates olefins in high yields at 50°C in less than 4 hr by replacement of allylic hydrogen. This reaction has been applied to unsaturated polymers such as polybutadiene and polyisoprene. The resulting products have lithium atoms scattered along the chain. The amount of lithium on the chain can be varied over wide limits. Each lithium atom on the chain can act as a site for grafting or adding functional groups to the base polymer. Thus, this method allows the preparation of polymers having controlled amounts of branching as well as the introduction of functional groups into the polymer. Through the use of this metallation technique, polymers containing styrene and butadience grafts are specifically reported. In addition, polymers containing hydroxyl or carboxyl groups along the backbone are prepared by using this technique.     

A straight way to regioselectively functionalized polysaccharide esters

The topic of this contribution ID a novel method for regioselective esterification of starch, similar polysaccharides and cyclodextrines avoiding protecting or activating groups. A broad spectrum of polysaccharides could be acylated selectively at the C-2 position of the AGU. The reaction principle ID based on a transesterification of a carboxylic acid vinyl ester with the hydroxyl groups of the polymer ID the presence of a low molecular salt. The interaction of the reaction participants and the solution state of the polysaccharides enable this selective functionalization. The structure characterization of the new polysaccharide derivatives ID carried out by NMR spectroscopy, especially the HMBC technique, after a complete esterification of the free hydroxyl groups with a suitable carbon acid anhydride.     

Synthesis of mikto‐topology star polymer containing one cyclic arm

Well‐defined mikto‐topology star polystyrene composed of one cyclic arm and four linear arms was synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu‐catalyzed azide‐alkyne cycloaddition (CuAAC) click reaction. First, the bromine‐alkyne α,ω‐linear polystyrenes containing four hydroxyl groups protected with acetone‐based ketal groups were synthesized by ATRP of styrene using a designed initiator. Then, the bromine end‐group was converted to the azide and the linear polystyrene was cyclized intra‐molecularly by the CuAAC reaction. The four hydroxyl groups were released by deprotection and then esterified with 2‐bromoisobutyryl bromide to produce a cyclic polymer bearing four ATRP initiating units. By subsequent ATRP of styrene to grow linear polymers with the cyclic polystyrene as a macroinitiator, the mikto‐topology star polymers were prepared. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Characterization and formation mechanism of the precipitates generated by irradiation of dicyclohexano-18-crown-6 aqueous solution

Dicyclohexano-18-crown-6 (DCH18C6) aqueous solution was irradiated using ⁶⁰Co source and precipitates containing yellow transparent blocks (PA) and powders (PB) were obtained. TGA analysis confirms that both PA and PB have higher thermal stability than DCH18C6. Both DSC and GPC results suggest that PA might be oligomer and PB were ultrahigh molecular weight polymers. The FTIR spectra indicate that both PA and PB have similar chemical structures containing carboxyl and hydroxyl groups. By using scavengers, it was found that the formation of PA and PB is attributed to the radiation-induced radical polymerization of DCH18C6, and ·OH radical produced by water radiolysis might be a critical species for the formation of PA and PB. These studies help to understand the radiation chemistry behavior of DCH18C6 in the reprocessing of nuclear fuel.     

Synthesis of well‐defined comb‐like graft (co)polymers by nucleophilic substitution reaction between living polymers and polyhalohydrocarbon

A series of graft (co)polymers were synthesized by nucleophilic substitution reaction between iodinated 1,2‐polybutadiene (PB‐I, backbone) and living polymer lithium (side chains). The coupling reaction between PB‐I and living polymers can finish within minutes at room temperature, and high conversion (up to 92%) could be obtained by effectively avoiding side reaction of dimerization when living polymers were capped with 1,1‐diphenylethylene. By virtue of living anionic polymerization, backbone length, side chain length, and side chain composition, as well as graft density, were well controlled. Tunable molecular weight of graft (co)polymers with narrow molecular weight distribution can be obtained by changing either the lengths of side chain and backbone, or the graft density. Graft copolymers could also be synthesized with side chains of multicomponent polymers, such as block polymer (polystyrene‐b‐polybutadiene) and even mixed polymers (polystyrene and polybutadiene) as hetero chains. Thus, based on living anionic polymerization, this work provides a facile way for modular synthesis of graft (co)polymers via nucleophilic substitution reaction between living polymers and polyhalohydrocarbon (PB‐I). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

最小二乘—红外光谱法定量测定羟基化合物

根据羟基伸缩振动吸收带的特性，用最小二乘法有效消除了溶液中羟基间的缔合作用对测定结果的影响。此方法已用于聚合物中羟基含量的测定。     

Ionic Polymerization of 1,2-Butylene Oxide: NMR Study of the Reaction Products

An NMR study on the reaction products of the ionic polymerization of 1,2-butylene oxide has been carried out. Polymers prepared via a cationic mechanism by using a trityl salt as the initiator are built up of repeat monomer units, and the propagation reaction follows Bernoullian statistics. Polymers prepared via an anionic mechanism with the use of sodium metal as initiator, on the other hand, are not made up of repeat monomer units, and the propagation reaction follows a first-order Markov statistics. In the cationic polymers the mean chemical shifts of the triads and tetrads move upfield on replacing m dyads by r dyads; however, the pentads move downfield on changing m by r. In the anionic polymers the mean chemical shifts for the triads and tetrads of the ethyl group along with the pentads of the methine protons move upfield whereas tetrads associated with the remaining methylenes move downfield on replacing m dyads by r dyads as well as on replacing 0-C6H4CI2 by CCU or DMSO-de as the solvent for recording the spectrum. The anionic polymer M-b, which is rich in double bonds and hydroxyl groups, has relatively lower values for the geminal couplings J_AB and the vicinal couplings J_AX.and J_BX as compared to those obtained with polymer M-a, which has practically no double bonds and very few (if any) hydroxyl groups. The appearance of the methylene protons in polymer M-b as well as the coupling constants J_AB., J_AX, and J_Bxvary on changing the solvent from O-C6H4Cl2 to CCh or DMSO-de.     

羟基的区别定量分析

从原理、可操作性、测定范围等方面论述了伯、仲、叔羟基的定量分析方法,并对化学动力学法、红外光谱法、紫外光谱法、极谱法和各种核磁法进行了综合比较。各种方法各有优势,宜根据实际条件进行选择,其中仪器分析法尤其是核磁法代表了羟基定量分析法的发展方向。     

Role of Functional Groups in the Monomer Molecule on the Radical Polymerization in the Presence of Graphene Oxide. Polymerization of Hydroxyethyl Acrylate under Isothermal and Non-Isothermal Conditions

Functional groups in a monomer molecule usually play an important role during polymerization by enhancing or decreasing the reaction rate due to the possible formation of side bonds. The situation becomes more complicated when polymerization takes place in the presence of graphene oxide since it also includes functional groups in its surface. Aiming to explore the role of functional groups on polymerization rate, the in situ bulk radical polymerization of hydroxyethyl acrylate (HEA) in the presence or not of graphene oxide was investigated. Differential scanning calorimetry was used to continuously record the reaction rate under both isothermal and non-isothermal conditions. Simple kinetic models and isoconversional analysis were used to estimate the variation of the overall activation energy with the monomer conversion. It was found that during isothermal experiments, the formation of both inter- and intra-chain hydrogen bonds between the monomer and polymer molecules results in slower polymerization of neat HEA with higher overall activation energy compared to that estimated in the presence of GO. The presence of GO results in a dissociation of hydrogen bonds between monomer and polymer molecules and, thus, to higher reaction rates. Isoconversional methods employed during non-isothermal experiments revealed that the presence of GO results in higher overall activation energy due to the reaction of more functional groups on the surface of GO with the hydroxyl and carbonyl groups of the monomer and polymer molecules, together with the reaction of primary initiator radicals with the surface hydroxyl groups in GO.     

Polycarbonate-modified epoxies. I. Studies on the reactions of epoxy resin/polycarbonate blends prior to cure

An epoxy resin based upon the diglycidyl ether of bisphenol-A was modified with poly(bisphenol A carbonate) (PC). Prior to aromatic amine cure, the possible reactions in the epoxy resin/PC blend were investigated using GPC and FTIR techniques. It was shown that at 150°C, the epoxy resin acted as a plasticizer and promoted the crystallization of PC. In addition, a transesterification between the secondary hydroxyl groups in the epoxy resin with the carbonate groups in PC occurred. This reaction resulted in degraded PC chains with phenolic hydroxyl end groups. There was no evidence of reaction of epoxide groups at 150°C in this blend. At 200°C, the secondary hydroxyl groups acted as a catalyst converting most of the aromatic–aromatic carbonates to the aromaticndash;liphatic and aliphaticndash;aliphatic carbonates through transesterification. At this elevated temperature, the secondary hydroxyl groups were regenerated by the addition reaction between the epoxide groups and the phenolic hydroxyl end groups, either from the transesterification or the hydrolysis of PC. This addition reaction combining the PC chains and epoxy chains eventually resulted in a crosslinked polymer if the extent of reaction was high. Thus, by using a melt blending process at high temperature, e.g., 200°C, a copolymer network structure of PC-modified epoxy could be formed. The fracture toughness should be increased by increasing the capability for plastic deformation due to the incorporation of PC chains into the network; results will be reported in a future study. © 1996 John Wiley & Sons, Inc.     

Degradation of poly(ethylene terephthalate)/clay nanocomposites during melt extrusion: Effect of clay catalysis and chain extension

Organoclays with various contents of hydroxyl groups and absorbed ammonium were prepared and compounded with poly(ethylene terephthalate) (PET), forming PET/clay nanocomposites via melt extrusion. Dilute solution viscosity techniques were used to evaluate the level of molecular weight of PET/clay nanocomposites. Actually, a significant reduction in PET molecular weight was observed. The level of degradation depended on both the clay structure and surfactant chemistry in organoclays. The composites, based on clay with larger amount of hydroxyl groups on the edge of clay platelets, experienced much more degradation, because the hydroxyl groups acted as Brønsted acidic sites to accelerate polymer degradation. Furthermore, organoclays with different amounts of absorbed ammonium led to different extents of polymer degradation, depending upon the acidic sites produced by the Hofmann elimination reaction of ammonium. In addition, the composite with better clay dispersion state, which was considered as an increasing amount of clay surface and ammonium exposed to the PET matrix, experienced polymer degradation more seriously. To compensate for polymer degradation during melt extrusion, pyromellitic dianhydride (PMDA) was used as chain extender to increase the intrinsic viscosity of polymer matrix; more importantly, the addition of PMDA had little influence on the clay exfoliation state in PET/clay nanocomposites.