‘Living’ free radical graft copolymers,II: Structure

Poly(vinyl chloride)–n-propyl xanthate (PVC–nPX) macroinitiators with 3 to 14 bonded xanthate groups per molecule were synthesized using PVC and potassium n-propyl xanthate. The reaction took place rapidly between 30 and 45°C. Ultraviolet (UV) and nuclear magnetic resonance studies confirmed the presence of xanthyl groups on these macroinitiators. The PVC–nPX macroinitiators were grafted by methyl methacrylate under UV irradiation of 254, 302 and 336 nm producing graft copolymers and homopolymers. The molecular weights increased with increasing conversion, which is consistent with a ‘living’ polymerization process. The active species in these polymerizations are believed to be macroradicals and xanthyl radicals.     

Radical polymerization of styrene by a hexa‐substituted‐ethane type thermal iniferter

The bulk polymerization of styrene (St) initiated with a hexa‐substituted‐ethane type initiator, diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS), was investigated. It was found that DCDPS served as a thermal iniferter for polymerization of St and the polymerization had some characteristics in common with living radical polymerization, ie, both the yield and the molecular weight of the resulting polymers increased with increasing reaction time. The resultant polystyrene can act as a macroinitiator for chain‐extension polymerization of St or for radical polymerization of methyl methacrylate to give a block copolymer. © 2001 Society of Chemical Industry     

Networks of partially hydrogenated cis-1,4-polybutadiene and ‘rigid rods’

Networks of ‘flexible’ and ‘rigid’ chains were synthesized. As ‘flexible’ component we have used different partially hydrogenated cis-1,4-polybutadiene. The ‘rigid’ component was synthesized from bis(1,2,4-triazoline-3,5-dione)s and biscyclohexadienes via repetitive Diels-Alder reaction. A slight excess of bis(1,2,4-triazoline-3,5-dione)s leads to polymers with 1,2,4-triazoline-3,5-dione end groups, which can easily react with the partially hydrogenated cis-1,4-polybutadiene. The influence of the extent of hydrogenation and the amount of crosslinker on the mechanical and thermal behaviour is described.     

Poly(ethylene oxide)‐block‐polystyrene copolymers obtained by radical polymerization involving chain‐transfer processes

Poly(ethylene oxide)‐block‐polystyrene (PEO–PSt) block copolymers were prepared by radical polymerization of styrene in the presence of iodoacetate—terminated PEO (PEO‐I) as a macromolecular chain‐transfer agent. PEO‐I was synthesized by successively converting the OH end‐group of α‐methoxy ω‐hydroxy PEO to chloroacetate and then to the iodoacetate. The chain‐transfer constant of PEO‐I was estimated from the rate of consumption of the transfer agent versus the rate of consumption of the monomer (C_{tr, PEO‐I} = 0.23). Due to the involvement of degenerative transfer, styrene polymerization in the presence of PEO‐I displayed some of the characteristics of a controlled/‘living’ process, namely an increase in the molecular weight and decrease of polydispersity with monomer conversion. However, because of the slow consumption of PEO‐I due to its low chain‐transfer constant, this process was not a fully controlled one, as indicated by the polydispersity being higher than in a controlled polymerization process (1.65 versus < 1.5). The formation of PEO–PSt block copolymers was confirmed by the use of size‐exclusion chromatography and ¹H NMR spectroscopy. Copyright © 2004 Society of Chemical Industry     

Radical thermo‐ and sonopolymerization of methyl methacrylate initiated by iodobenzene 1,1‐diacetate

The efficiency of iodobenzene 1,1‐diacetate or (diacetoxyiodo)benzene (DAIB) as a thermo‐ and sono‐initiator of methyl methacrylate (MMA) in radical bulk polymerization is tested. The polymerization kinetics and molecular‐mass characteristics support an assumption for a combined polymerization mechanism including a classical bimolecular termination with chain transfer reaction and iniferter quasi‐living polymerization. In addition to the equilibrium formation and degradation of the ‘dormant’ polymer ends, other possible decomposition reactions of the hypervalent iodine bond are the probable reason for the deviation of this polymerization from the iniferter polymerization mechanism. These reactions bear some similarity to the two‐step addition–fragmentation chain transfer mechanism of controlled radical polymerization. The application of the poly(MMA) obtained as a macroinitiator is evidence of ‘dormant’ chain end formation. © 2001 Society of Chemical Industry     

Polymerization of methyl methacrylate with a thermal iniferter: Diethyl 2,3‐dicyano‐2,3‐di(p‐tolyl)succinate

A hexa‐substituted ethane type compound, diethyl‐2,3‐dicyano‐2,3‐di(p‐tolyl)succinate (DCDTS), was successfully synthesized and used for initiation of methyl methacrylate (MMA) polymerization. The reaction demonstrated the characteristics of a “living” polymerization; i.e., both the yield and the molecular weight of the resulting polymers increased linearly with increasing reaction time, the molecular‐weight distribution of PMMA obtained was ～1.60 and almost unaffected by the conversion, and the resultant polymer can be chain extended by adding fresh MMA. End group analysis of the resultant PMMA confirmed that DCDTS behaves as a thermal iniferter for MMA polymerization. A block copolymer was prepared from the resultant PMMA, which contains a hexa‐substituted C? C bond functional end group. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2566–2572, 2001     

Synthesis of three‐arm poly(ethylene glycol) by combination of controlled anionic polymerization and ‘click’ chemistry

Poly(ethylene glycol) (PEG) is an important water‐soluble polymer, which is widely used in the biomedical field because of its good biodegradability, biocompatibility and permeability. It is usually synthesized by anionic polymerization of ethylene oxide but side reactions lead to the formation of some oligomers. High molecular weight PEG can be obtained, however, through coordinated anionic polymerization. Recently a novel controlled anionic polymerization based on the initiating system ammonium bromide/trialkylaluminium was reported. Related studies have shown that the controlled anionic polymerization allows the synthesis of linear polyethers with low dispersity in a wide range of molecular weights at ambient temperature. Unfortunately, so far this controlled anionic polymerization has not been used to synthesize polymers with complex architectures. In the work reported here, controlled anionic polymerization was combined with ‘click’ chemistry for the first time to synthesize polyethers with multiple arms. Firstly, controlled anionic polymerization was employed to synthesize a linear bromine‐terminated PEG (PEG‐Br) using ethylene oxide as the monomer and tetraoctylammonium bromide/triisobutylaluminium as the initiating system at room temperature. The terminal bromine in the PEG thus synthesized was then converted into an azide group by the reaction of PEG‐Br and sodium azide. A trifunctional linking agent was also prepared by the reaction of trimethylolpropane and propiolic acid. By using ‘click’ chemistry, a three‐arm PEG was finally obtained through the reaction of the azide‐terminated PEG and the trifunctional linking agent. The chemical structure of the polymer thus synthesized was characterized using infrared spectroscopy, NMR spectroscopy, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and size‐exclusion chromatography with multi‐angle laser light scattering. It was found that the synthesized polyether possesses the designed structure. Considering the wide applicability of controlled anionic polymerization and ‘click’ chemistry, their combination is a valuable way to synthesize various polyethers with multiple arms. Copyright © 2009 Society of Chemical Industry     

The Effect of Initiators and Reaction Conditions on the Polymer Syntheses by Atom Transfer Radical Polymerization

The controlled/“living” radical polymerization of methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and styrene by atom transfer radical polymerization (ATRP) is reported. The effect of initiators and reaction conditions on the ATRP results was investigated. Controlled polymerizations with predictable molecular weights were performed on MMA at 40^○C and 80^○C using a CuCl/bipyridine (bipy) catalyst system in conjunction with 1-bromoethyl benzene as the initiator. The addition of a polar solvent was necessary to decrease the polymerization rate and afford low polydispersity materials. The ATRP processes followed a first-order kinetics with respect to the monomer concentration. The molecular weights of the resulting polymers were very close to their calculated values and increased with the conversion. The ATRP results of styrene showed a similar trend and revealed that CuBr/bipy or CuBr/PMDETA was a more suitable catalyst system than CuCl/bipy. In addition, it was found that controlled polymerizations could be readily carried out both in a nonpolar solvent or in bulk. Furthermore, by using the bromine-terminated polymer as the macroinitiator, diblock copolymers of PSt-b-PMMA, PSt-b-PHEMA, PMMA-b-PSt, and PMMA-b-PHEMA could be obtained. Thermal analysis and X-ray diffraction studies confirmed the amorphous structures of the resulting polymers.     

TEMPO／BPO引发苯乙烯聚合反应的研究

由三丙酮胺经改进的Ｗｏｌｆ－Ｋｉｓｈｎｅｒ还原反应首先合成了２,２,６,６－四甲基哌啶,再参照Ｒｏｚａｎｔｚｅｖ报道的方法将２,２,６,６－四甲基哌啶氧化制备了２,２,６,６－四甲基哌啶－１－氧稳定氮氧自由基（ＴＥＭＰＯ）,研究了ＴＥＭＰＯ的存在对过氧化苯甲酰引发苯乙聚合反应的影响,分子量分布指数（ＭＷ／Ｍｎ）为１．１９－１．３５的窄分散的聚苯乙烯。     

Nitroxide‐mediated ‘living’ free radical synthesis of novel rod–coil diblock copolymers with polystyrene and mesogen‐jacketed liquid‐crystal polymer segments

The synthesis of rod–coil diblock copolymers with narrow polydispersity was achieved for the first time by TEMPO‐mediated ‘living’ free radical polymerization of styrene and 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene. The block architecture of the two diblock copolymers thus prepared, MPCS‐block‐St (5400/2400) and MPCS‐block‐St (10 800/8700), was confirmed by GPC, ¹H and ¹³C NMR and DSC studies. The liquid‐crystalline behaviour of the copolymers was studied by DSC and polarized optical microscope. It was observed that both copolymers showed two distinct glass transitions, corresponding to polystyrene and poly(‐2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene). Above the glass transition temperature of rigid block, liquid‐crystalline phase was formed. The clearing point of the phase is higher than the polymer decomposition temperature. © 2000 Society of Chemical Industry     

‘Smart’ corrosion inhibiting coatings

Under certain conditions, the driving force of corrosion produces protective oxide films, a process typically referred to as passivity. In cases where passivity is difficult to achieve, for example, for Al alloys in neutral NaCl solutions, it is conceivable that a ‘smart’ coating can be micro- or nano-engineered to use the energy of the corrosion to generate ‘on demand’ a corrosion inhibitor for stopping or slowing corrosion at defects. Work at Rockwell Scientific provides evidence that anionic inhibitors for the oxygen reduction reaction (ORR), when used as dopants for conducting polyaniline (PANI) films, inhibit corrosion of a Al 2024-T3 substrate at a scribe. In effect, the scribe polarizes the PANI causing it to release the inhibitor.     

‘Living’ radical polymerization of styrene with AIBN/FeCl3/PPh3 initiating system via a reverse atom transfer radical polymerization process

Well‐defined polystyrenes with an α‐C(CH₃)₂(CN) and an ω‐chlorine atom end‐groups, and narrow polydispersity (M_n = 3000–4000 g mol⁻¹, M_w/M_n = 1.3–1.4) have been synthesized by a radical polymerization process using 2,2′‐azobisisobutyronitrile(AIBN)/FeCl₃/PPh₃ initiation system. When the ratio of [St]₀:[AIBN]₀:[FeCl₃]₀:[PPh₃]₀ is 200:1:4:12 at 110 °C, the radical polymerization is ‘living’, but the molecular weight of the polymers is not well‐controlled. The polymerization mechanism belongs to a reverse atom transfer radical polymerization (ATRP). Because the polymer obtained is end‐functionalized by a chlorine atom, it can then be used as a macroinitiator to perform a chain extension polymerization in the presence of CuCl/2,2′‐bipyridine catalyst system via a conventional ATRP process. The presence of a chlorine atom as an end‐group was determined by ¹H NMR spectroscopy. © 2000 Society of Chemical Industry     

活性自由基聚合的分类及原子转移自由基聚合的研究进展

阐述了活性自由基聚合的产生背景和基本概念,介绍了活性自由基聚合的分类,描述了原子转移自由基聚合的研究进展。     

原子转移自由基聚合研究进展

原子转移自由基聚合(ATRP)反应是实现活性聚合的一种颇为有效的途径,可以合成分子量可控、分子量分布窄的各种聚合物.介绍了ATRP的研究进展,包括ATRP反应的特点、聚合反应机理、应用、研究现状及前景展望.     

Radical Polymerization of n-BMA Using a Di-Site Phase Transfer Catalyst

The di-site phase transfer catalyzed radical polymerization of butyl methacrylate with the phase transfer catalyst N,N′-diheptyl-N,N,N′,N′-tetramethyl-1,2-ethanediammonium dibromide (DHTMEDADB) was carried out in an aqueous-organic biphase system at 60 ± 1°C under nitrogeneous atmosphere at fixed pH and ionic strength. A suitable kinetic scheme has been proposed and its significance was discussed. The polymers obtained were investigated and characterized (FTIR, ¹H-NMR and XRD studies).     

原子转移自由基聚合法（ATRP）制备聚丙烯酰胺

以苄基氯为引发剂,氯化亚铁为催化剂,三苯基膦为配体研究了丙烯酰胺在N,N-二甲基甲酰胺中的原子转移自由基聚合,考察了聚合时间、催化剂与配体的摩尔配比、温度等因素对单体转化率、分子量的影响。结果表明：80℃下,[AM]/[C6H5CH2Cl]/[FeCl2]/[PPh3]=100/1/0.5/1时,聚丙烯酰胺分子量随单体转化率增加线性增大,ln[[MM]]0与聚合时间呈线性关系,温度对聚合特征有较大影响。     

Living Radical Polymerization and Molecular Imprinting: Improving Polymer Morphology in Imprinted Polymers

Living radical polymerization (LRP) techniques and their ability to improve the morphology of crosslinked polymer networks by controlling polymer chain growth are reviewed. Recent successes in the creation of improved molecularly imprinted polymer networks are also discussed. LRP offers the ability to control molecular weight, polydispersity, and tacticity while reducing microgel formation in polymers created via free‐radical polymerization (FRP). The improved network architecture of polymers created via LRP has great potential, especially when considering imprinted networks which have traditionally been plagued by heterogeneity in network morphology and binding affinities. Using LRP can considerably improve template recognition and further delay template transport in imprinted polymers.

     

Atom transfer radical copolymerization of methyl methacrylate with N‐cyclohexylmaleimide

Atom transfer radical polymerization has been applied to simultaneously copolymerize methyl methacrylate (MMA) and N‐cyclohexylmaleimide (NCMI). Molecular weight behaviour and kinetic study on the copolymerization with the CuBr/bipyridine(bpy) catalyst system in anisole indicate that MMA/NCMI copolymerization behaves in a ‘living’ fashion. The influence of several factors, such as temperature, solvent, initiator and monomer ratio, on the copolymerization were investigated. Copolymerization of MMA and NCMI in the presence of CuBr/bpy using cyclohexanone as a solvent instead of anisole displayed poor control. The monomer reactivity ratios were evaluated as r_NCMI = 0.26 and r_MMA=1.35. The glass transition temperature of the resulting copolymer increases with increasing NCMI concentration. The thermal stability of plexiglass could be improved through copolymerization with NCMI. © 2000 Society of Chemical Industry     

壳聚糖的自由基聚合修饰改性

综述了普通自由基聚合和原子转移自由基聚合(ATRP)反应对壳聚糖及其衍生物进行修饰改性的研究现状。着重介绍了ATRP技术在壳聚糖接枝改性方面的应用。     

Novel alumina ‘KK Leaf Structures’ as catalyst supports

A method has been devised in which alumina can be formed into a layer of thin leaf-like structures that have a thickness of 0.2–0.8 μm. This consists of a process in which aluminium iso-propoxide is transformed into a sol–gel and then: frozen (−195 °C), freeze-dried (−60 °C), and finally calcined (450 °C). These special conditions lead to the formation of a structure that is named: ‘KK Leaves’.

After calcining at 450 °C, the leaves have a specific surface area of 282 m²/g, an average pore size of 2.8 nm, and exhibit a curly shape. The structure has the appearance of a loosely packed (but ordered) collection of thin curly leaves with fine ribs resembling leaf veins on trees and plants. They would readily act as a support, e.g., for a catalyst, or adsorbents, or act as a membrane filter.