Radiation-chemical synthesis of tetrafluoroethylene telomers and their use for preparation of thin protective fluoropolymer coatings

The specific features and possibilities of preparation of protective coatings and composite materials based on fluoromonomers using high-energy rays (⁶⁰Co γ-rays, fast electrons) were analyzed. The emphasis was placed on synthesis and application of tetrafluoroethylene telomers in acetone. The structure and properties of telomers were examined by IR and NMR spectroscopy, as well as by X-ray diffraction analysis and diathermy. The radiation initiation allows preparation of new products with a broad spectrum of functional properties and opens wider prospects for technological application of fluoromonomers.     

Radiation-chemical processes for fabrication of protective coatings and composite materials with the use of fluorinated monomers

The feasibility and the specific features of fabrication of protective coatings and composite materials on the basis of fluorinated monomers with the use of high-energy radiation (⁶⁰Co γ-rays, fast electrons) are analyzed. The consideration is focused on the radiation-chemical synthesis of tetrafluoroethylene telomers, their practical application, and modification of polymeric and inorganic materials by means of low-temperature postradiation polymerization and liquid-phase graft polymerization of fluorinated monomers. Radiation initiation makes it possible to prepare new products with a broad range of functional properties and to design novel technologies with the use of fluorinated monomers.     

A short review of radiation-induced raft-mediated graft copolymerization: A powerful combination for modifying the surface properties of polymers in a controlled manner

Surface grafting of polymeric materials is attracting increasing attention as it enables the preparation of new materials from known and commercially available polymers having desirable bulk properties such as thermal stability, elasticity, permeability, etc., in conjunction with advantageous newly tailored surface properties such as biocompatibility, biomimicry, adhesion, etc. Ionizing radiation, particularly γ radiation is one of the most powerful tools for preparing graft copolymers as it generates radicals on most substrates. With the advent of living free-radical polymerization techniques, application of γ radiation has been extended to a new era of grafting; grafting in a controlled manner to achieve surfaces with tailored and well-defined properties. This report presents the current use of γ radiation in living free-radical polymerization and highlights the use of both techniques together as a combination to present an advance in the ability to prepare surfaces with desired, tunable and well-defined properties.     

Calorimetric study of the low-temperature postradiation polymerization of tetrafluoroethylene in the presence of reduced graphite oxide

Low-temperature postradiation polymerization of tetrafluoroethylene in the presence of carbon material obtained by explosive exfoliation of graphite oxide has been studied by the technique of calorimetry. The process results in tetrafluoroethylene grafting onto modified graphite oxide to form a new composite containing ～40–65% polytetrafluoroethylene.     

Postradiation polymerization of tetrafluoroethylene on mineral supports at low temperatures

The low-temperature graft polymerization of tetrafluoroethylene (TFE) on mineral supports (SiO₂, Al₂O₃, TiO₂, and activated charcoal) has been investigated by the microcalorimetry, ESR, and IR spectroscopy techniques. It has been shown that polymerization of TFE is initiated by radical ion centers formed upon radiolysis of the support. The initiation stage includes the interaction of a radical ion particle of the support with a monomer molecule yielding a growing neutral radical. The radical growth of polymer chains has been confirmed by the appearnce of the ESR spectrum of terminal fluoroalkyl radicals ～CF₂?CF₂, and the covalent C-Si bonds of the polymer with the support have been detected by means of IR spectroscopy. The efficiency of the low-temperature graft polymerization depends on the monomer sorption and the sorbent nature: the highest efficiency is observed for Al₂O₃ and, then, macroporous glasses; grafting proceeds to the least extent (yield below 5%) on the carbon supports, which do not the form radical ion centers during radiation activation.     

Participation of an excited monomer in the propagation reaction of the γ-ray induced polymerization of ethylene

In the polymerization of ethylene, the reactivity of the growing radical produced by γ-radiation was compared with that of the radical from 2,2′-azobisisobutyronitrile. The radicals produced in the polymerization at around room temperature were long-lived irrespective of the method of initiation. However, it was found that the radical produced by γ-radiation became unreactive to ethylene when the reaction system was not exposed to γ-rays. Irradiation with γ-rays or ultraviolet light in a region below about 3900 Å was required for its chain growth. On the other hand, the radical from AIBN was always reactive, and the reactivity was little changed by γ-radiation or by the presence of a trace amount of radiolysis products of ethylene. In explaining of these characteristic differences between the nature of these radicals produced by two different methods of initiation, some other information on their reactivity was reviewed, and the participation of an excited ethylene in a dimer form was proposed, as for the propagation reaction of the γ-ray-induced polymerization.     

High-efficient surface tailoring via reverse atom transfer radical polymerization and reversible addition-fragmentation chain-transfer polymerization in an aqueous system initiated by a monocenter redox pair

The commonly used multi-center initiation methods always lead to the formation of quantities of homopolymer in the surface tailoring based on reverse atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization. In this study, a monocenter redox pair constructed of silica bearing tert-butyl hydroperoxide groups and ascorbic acid (SiO₂-TBHP/AsAc) was applied to substitute the commonly used initiation method of R-supported RAFT grafting polymerization. All the propagating radicals were restricted on the surface of solid particles during the whole procedure theoretically, resulting in a higher grafting efficiency of 95.1% combined with the “controllable” feature at 10 h. This redox pair was also used to initiate the reverse ATRP in miniemulsion successfully with a grafting efficiency of 86.3% at 10 h. The grafting efficiency obtained under this monocenter initiation method was significantly higher than that of the frequently reported surface modification by reverse ATRP and RAFT polymerization. In addition, the high-efficient surface tailoring was traced and confirmed by nuclear magnetic resonance, Fourier transform infrared, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission electron microscopy, and other analysis tests. The advantage of this monocenter redox pair will open a new avenue for the potential “high-efficient” surface tailoring of various materials.     

Radiation-Induced Polymerization of Tetrafluoroethylene

Polymerization of tetrafluoroethylene was carried out in bulk at low temperatures by initiation with γ-rays from a ⁶⁰ Co source. It was found that a remarkable postpolymerization takes place even in the liquid phase. Kinetical analysis has been made of the in-source and postpolymerizations. An activation energy of 2.7 kcal/mole was obtained for the in-source polymerization and 10.3 kcal/mole for the postpolymerization. The long lifetime of polymer radicals in the liquid phase at -78°C seems to be due to the slow recombination rate of the polymer radicals, based on the rodlike shape of the polymer radicals.     

Graft polymerization of vinyl monomers onto cellulose in presence of soda lime glass. I

Sodium bisulfite–soda lime glass has proved to be a good initiator for polymerization and graft polymerization onto cellulose of some vinyl monomers. A scheme dealing with the mechanism of initiation has been proposed assuming trapping of the bisulfite radical inside the glass frame-work to form a so-called sulfur-impregnated solid. Such a solid has paramagnetic properties and acts on the vinyl monomers and cellulose as any free-radical-producing source thus leading to polymerization and graft polymerization onto cellulose. Other radicals containing sulfur, such as sulfite, sulfate, and persulfate failed to give such property with soda lime glass. With the sodium bisulfite–soda lime glass system the reactivity decreases in the order methyl methacrylate > ethyl acrylate > acrylonitrile which is inconsistent with the arrangement of acceptor monomers with decreasing electron-donating ability. This may reflect interference of the addition reaction which may take place between the monomer and bisulfite and the rate of which may depend on the activation energy of the monomer.     

Photopolymerization of tetrafluoroethylene in solution of hexafluoropropylene trimer in the presence of long-lived perfluoroallyl radicals

Conclusions In photolysis of tetrafluoroethylene in a solution of the hexafluoropropylene trimer containing long-lived perfluoroallyl radicals, the following processes can take place: 1) phototransformation of these radicals into active perfluoroalkyl radicals and their recombination, and participation in initiation of photopolymerization of tetrafluoroethylene; the formation of the long-lived perfluoroalkyl radical on addition of a molecule of solvent to the propagating radical and the formation of a long-lived radical captured by the propagating chain compete with these processes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2698–2702, December, 1987.     

Rational Design of Biomolecules/Polymer Hybrids by Reversible Deactivation Radical Polymerization (RDRP) for Biomedical Applications

Hybrids, produced by hybridization of proteins, peptides, DNA, and other new biomolecules with polymers, often have unique functional properties. These properties, such as biocompatibility, stability and specificity, lead to various smart biomaterials. This review mainly introduces biomolecule-polymer hybrid materials by reversible deactivation radical polymerization(RDRP), emphasizing reverse addition-fragmentation chain transfer(RAFT) polymerization, and nitroxide mediated polymerization(NMP). It includes the methods of RDRP to improve the biocompatibility of biomedical materials and organisms by surface modification. The key to the current synthesis of biomolecule-polymer hybrids is to control polymerization. Besides, this review describes several different kinds of biomolecule-polymer hybrid materials and their applications in the biomedical field. These progresses provide ideas for the investigation of biodegradable and highly bioactive biomedical soft tissue materials. The research hotspots of nanotechnology in biomedical fields are controlled drug release materials and gene therapy carrier materials. Research showed that RDRP method could improve the therapeutic effect and reduce the dosage and side effects of the drug.Specifically, by means of RDRP, the original materials can be modified to develop intelligent polymer materials as membrane materials with selective permeability and surface modification.     

Effect of polymerization conditions on the molecular weight of polystyrene grafted onto silica in the radical graft polymerization initiated by azo or peroxyester groups introduced onto the surface

The effect of polymerization conditions on the molecular weight of polystyrene grafted onto silica obtained from the radical graft polymerization initiated by azo and peroxyester groups introduced onto the surface was investigated. The molecular weight of polystyrene grafted onto silica obtained from the radical graft polymerization initiated by surface azo and peroxyester groups decreased with decreasing monomer concentration and polymerization temperature. The molecular weight of polystyrene was found to be controlled to some extent by the addition of a chain transfer agent. The molecular weight of grafted chain on silica surface obtained from the graft polymerization initiated by surface radicals formed by photodecomposition of azo groups was considerably smaller than that by thermal decomposition. The number of grafted polystyrene in photopolymeriztion, however, was much larger than that in thermal polymerization. These results are explained by the blocking of surface radicals formed on the silica surface by previously grafted polymer chain: when the decomposition of surface azo and peroxyester groups proceed instantaneously at the initial stage of the polymerization, the number of grafted polymer chains increased.     

Adsorption complexes ‘zeolite–cationic surfactant’: properties and surface activity in a polymer composite material based on ultra-high-molecular-weight polyethylene

We investigated the adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) to zeolite from premicellar and micellar solutions, as well as some properties of the organically modified zeolite surface and the nature of its interfacial interaction with ultra-high-molecular-weight polyethylene (UHMWPE) in a UHMWPE-based polymer composite material (PCM). The formation mechanism of mono- and bimolecular adsorption layers of cetyltrimethylammonium cation and bromide anion to the clinoptilolite (Cli) surface was proposed, and the thermodynamic and kinetic characteristics of adsorption were determined. The surface texture of organically modified zeolite was studied by instrumental methods; the thermal stability limits of CTAB adsorption layers to zeolite surface and their decomposition behavior in inert and oxidizing media were established. The evaluation of the deformation and strength properties, the study of the supramolecular structure, and the calculation of the thermodynamic and kinetic parameters of the PCM crystallization process revealed that the filing with organically modified Cli increases the UHMWPE surface activity and improves their compatibility.     

Graft copolymers by acyclic diene metathesis and atom transfer radical polymerization techniques

Precise graft copolymer architectures were achieved by combining the macromonomer technique with the acyclic diene metathesis (ADMET) reaction. These well‐defined copolymer structures were the result of proper monomer design before metathesis polymerization. Features such as length of the graft, nature, and concentration of the graft site along the backbone were manipulated via the combination of living atom transfer radical polymerization methods with ADMET chemistry. Furthermore, the physical behavior of these materials was altered such that they presented dissimilar thermal properties of either the homopolymers or random copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2816–2827, 2003     

On the role of oil-soluble initiators in the radical polymerization of micellar systems

Polymerization in micellar systems is a technique which allows the preparation of ultrafine as well as coarse latex particles. This article presents a review of the current literature in the field of radical polymerization of classical monomers in micellar systems initiated by oil-soluble initiators. Besides a short introduction to some of the kinetic aspects of emulsion polymerization initiated by water-soluble initiators, we mainly focus on the kinetics and the mechanism of radical polymerization in o/w and w/o micellar systems initiated by classical oil-soluble initiators. The initiation of emulsion polymerization of an unsaturated monomer (styrene, butyl acrylate,...) by a water-soluble initiator (ammonium peroxodisulfate) is well understood. It starts in the aqueous phase and the initiating radicals enter the monomer-swollen micelle. The formed oligomeric radicals are surface active and increase the colloidal stability of the disperse system. Besides, the charged initiating radicals might experience the energetic barrier when entering the charged particle surface. The locus of initiation with oil-soluble initiators is more complex. It can partition between the aqueous-phase and the oil-phase. Besides, the surface-active oil-soluble initiator can penetrate into the interfacial layer. The dissolved oil-soluble initiator in the monomer droplet can experience the cage effect. The small fraction of the oil-soluble initiator dissolved in the aqueous phase takes part in the formation of radicals. The oligomeric radicals formed are uncharged and therefore, they do not experience the energetic barrier when entering the polymer particles. We summarize and discuss the experimental data of radical polymerization of monomers initiated by oil-soluble initiators in terms of partitioning an initiator among the different domains of the multiphase system. The inhibitor approach is used to model the formation of radicals and their history during the polymerization. The nature of the interfacial layer and the type of oil-soluble initiator including the surface active ones are related to the kinetic and colloidal parameters. The emulsifier type and reaction conditions in the polymerization are summarized and discussed.     

用原子转移自由基方法合成新型大分子偶联剂

表面活性剂工业作为精细化工中一个重要分支目前正处于良好发展时期,具有特殊功能“大分子桥”的大分子偶联剂由于其独特的结构,多用作复合材料,在理论和实际应用中都得到了广泛而深入的研究,接枝型大分子偶联剂由性质差别很大的主链和支链组成,具有清晰的结构及独特的性能,     

Surface‐initiated atom transfer radical polymerization from porous poly(tetrafluoroethylene) membranes using the C?F groups as initiators

This work reports the surface‐initiated atom transfer radical polymerization (ATRP) from hydrogen plasma‐treated porous poly(tetrafluoroethylene) (PTFE) membranes using the C? F groups as initiators. Hydrogen plasma treatment on PTFE membrane surfaces changes their chemical environment through defluorination and hydrogenation reactions. With the hydrogen plasma treatment, the C? F groups of the modified PTFE membrane surface become effective initiators of ATRP. Surface‐initiated ATRP of poly(ethylene glycol) methacrylate (PEGMA) is carried out to graft PPEGMA chains to PTFE membrane surfaces. The chain lengths of poly(PEGMA) (PPEGMA) grafted on PTFE surfaces increase with increasing the reaction time of ATRP. Furthermore, the chain ends of PPEGMA grown on PTFE membrane surfaces then serve as macroinitiators for the ATRP of N‐isopropylacrylamide (NIPAAm) to build up the PPEGMA‐b‐PNIPAAm block copolymer chains on the PTFE membrane surfaces. The chemical structures of the modified PTFE membranes are characterized using X‐ray photoelectron spectroscopy. The modification increases the surface hydrophilicity of the PTFE membranes with reductions in their water‐contact angles from 120° to 60°. The modified PTFE membranes also show temperature‐responsive properties and protein repulsion features owing to the presence of PNIPAAM and PPEGMA chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2076–2083, 2010     

表面光接枝聚合反应新进展

表面性能对高分子材料应用至关重要,但多数聚烯烃材料表面惰性,需对表面进行改性或功能化．紫外光引发表面光接枝聚合反应具有诸多优势,因而获得广泛应用．作者以本实验室近年的研究为基础,结合这一领域国际上的部分重要研究成果,概述了实施表面光接枝聚合反应的一些新方法：控制,活性表面光接枝聚合、自引发光接枝聚合、暗区表面光接枝聚合、表面光接枝-交联聚合以及表面小分子光化学反应等．     

Graft and block copolymers with polysiloxane and vinyl polymer segments

A convenient new process to make silicone/organic block and graft copolymers has been recently demonstrated. This dual copolymerization process combines conventional condensation polymerization of the siloxane segments with free radical polymerization of the organic vinyl polymer segments. The copolymerization process is relatively simple and economical compared with other copolymerization techniques as it uses commonly available starting materials and available process equipment. Silicone segments containing alkene side chains or end-groups are prepared in the usual way by polycondensation using an acid or base catalyst. The double bonds of the alkene groups are oxidized to carbonyls which are then used to initiate vinyl monomer polymerization and link the siloxane with the vinyl segments. This initiation step is based on a redox system of copper^(II) salts which generates free radicals on the alpha carbons next to the carbonyl groups. This copolymerization process is relatively fast and proceeds at high yields.     

Intensification of Preparation of Modified Polycaproamide Fiber

A procedure was developed for graft polymerization of dimethylaminoethyl methacrylate onto polycaproamide using a redox system whose components are added to the reaction mixture sequentially. A scheme of radical graft polymerization of dimethylaminoethyl methacrylate onto polycaproamide was suggested. The properties of the copolymers were studied. The materials based on modified polycaproamide show promise as chemisorbents.