Grafting thermal initiated

The trapped radicals, most of which are presumably polymeric species, have been used to initiate graft copolymerization [127,128]. For this purpose, the irradiated polymer is brought into contact with a monomer that can diffuse into the polymer and thus reach the trapped radical sites. This reaction is assumed to lead almost exclusively to graft copolymer and to very little homopolymer since it can be conducted at low temperature, thus minimizing thermal initiation and chain transfer processes. Moreover, low-molecular weight radicals, which would initiate homopolymerization, are not expected to remain trapped at ordinary temperatures. Accordingly, irradiation at low temperatures increases the grafting yield [129]. 

Dialkyl peroxides (continued) colorimetry, 707-8 flame ionization detection, 708 NMR spectroscopy, 708 titration methods, 707 UV-visible spectrophotometry, 707-8 enthalpies of reactions, 153-4 graft polymerization initiation, 706 hydroperoxide determination, 685 peroxide transfer synthesis, 824-5 stmctural characterization, 708-16 electrochemical analysis, 715-16 electron diffraction, 713 mass spectrometry, 714 NMR spectroscopy, 709-11 thermal analysis, 714-15 vibrational spectra, 713-14 X-ray crystallography, 711-13 synthesis... 

In addition to the thermal initiation, the use of peroxides or azo components is a common and well established method to start the chain reaction. Peroxides increase the rate of the polymerization process and improve the grafting efficiency in the case of IPS. More recently, multifunctional peroxides have also been used in order to obtain products with special molecular weight distributions. 

In GPPS systems, these peroxides mainly supplemented the free radicals generated by thermal initiation, whereas in the HIPS process, it was found that they could enhance the grafting of styrene to unsaturated rubbers, such as polybutadiene. Additional benefits of organic peroxide initiators were increased production per unit reactor volume, reduction of styrene oligomers and lower reactor temperatures. The instantaneous removal of peroxide feed to a runaway reactor also provides a safety mechanism. Peroxide-initiated systems have higher reaction rates owing to shorter reactor residence times, so the ability to remove one source of radical initiation quickly is important. 

The grafting of an alternating copolymer on a substrate polymer occurs when the alternating copolymer is prepared under conditions normally used without the substrate polymer. When comonomers that are subject to spontaneous or thermal initiation are polymerized in the presence of a suitable polymer, graft copolymers are formed despite the absence of a radical catalyst (10). 

Synthetic strategies associated with grafting employ various modes of polymerizations, for example, living/controlled techniques, thermally initiated or photoini-tiated polymerizations. Among these, photochemical technique offers a number of advantages. First of all, it can be conducted at room temperature. This is quite remarkable when low manufacturing costs are concerned for mass production, as well... 

Besides, ILs unit could be attached to the sidewall of CNTs by radical grafting, in which acid-oxidation pretreatment of CNTs could be avoided. Chen et al. reported that thermal-initiation free radical polymerization of the IL monomer 3-ethyl-l-vinylimidazolium tetrafluoroborate ([VEIM]BF4] on the CNT surface (Fig. 4.18a] [62]. Then under similar method, the Pt and PtRu nanoparticles with narrow size distribution (average diameter (1.3 0.4] nm for PtRu, (1.9 0.5] nm for Pt] are dispersed uniformly on the CNTs and show better performance in methanol electrooxidation than that without ILs units (Fig. 4.18b]. 

As already stated, grafting may be initiated by thermal or photochemical processes, and we have studied both. Thermal initiation, e.g. with molybdenum hexacarbonyl, normally requires somewhat elevated temperatures,... 

The techniques of graft polymerization have been developed for liquid as well as gas phase. One of the polymerization techniques comprises impregnation of cellulose by a solution of conjugated monomers, followed by soaking in a relevant initiator. Chemical vapor deposition (CVD) of poly(3,4-ethylenedioxythiophene) is another, solvent-less technique, used for thin layer deposition of conjugated polymer on fibers [33]. Three CVD methods have been developed physical vaporization CVD [34, 35], plasma-enhanced CVD [36], and thermally initiated CVD [37, 38]. However, low conductivity is achieved when dopants are not used. 

RAFT polymerization has also been applied to the modification of fluoropolymers, PVDF in particular [90-92], The peroxides generated on the ozone-pretreated PVDF facihtated the thermally initiated graft copolymerization of poly(ethylene glycol methacrylate) (PEGMA) in the RAFT-mediated proeess. RAFT polymerization involves a reversible addition-fragmentation cycle, in which transfer of a dithioestCT... 

General methods of obtaining functionalized HRs with carboxylic groups include thermal grafting with initiators forming free radicals, or with cationic catalysts of the Friedel-Crafts type. Also included are cationic co-oligomerization of unsaturated hydrocarbons or of some Diels-Alder adducts (obtained from dienic hydrocarbons) with MA or other filodienes with carboxylic functions [155,1561. 

Maleic anhydride grafting (cont.) poly(styrene-co-divinylbenzene), 694 poly(styrene-co-isobutylene), 675, 689 poly(styrene-co-nfialeic anhydride), 676, 679 poly(vinyl acetate), 676, 694 poly(vinyl acetate-co-vinyl fluoride), 678 poly(vinyl alkyl ethers), 675, 679, 692, 701 poly(vinyl chloride), 683, 692, 693, 695, 702 poly(vinylidene chloride), 691 poly(vinyl toluene-co-butadiene), 689 radical—initiated, 459-462, 464-466, 471, 475, 476 radiation—initiated, 459, 461, 466, 471, 474 redox-initiated, 476 rubber, 678, 686, 687, 691, 694 to saturated polymers, 459-466, 475, 476 solvents used 460-463, 465, 466, 469, 474-476 styrene block copolymers, 679 tall oil pitch, 678, 697 terpene polymers, 679, 700 thermally-initiated, 462, 464-467, 469, 476 to unsaturated polymers, 459, 466-474 vapor-phase techniques, 464, 474, 475 to wool fibers, 476 Maleic anhydride monomer acceptor for complex formation, 207-210 acetal copolymerization, 316 acetone CTC thermodynamic constants, 211 acetone photo-adduct pyrolysis, 195, 196 acetylacetone reaction, 235 acetylenic photochemical reactions, 193-196 acrylamide eutectic mixtures, 285 acylation of aromatic acids, 97 acylation of aromatics, 91, 92 acylation of fused aromatics, 92, 95, 97, 98 acylation of olefins, 99 acylation of phenols, 94-96 acylic diene Diels-Alder reactions, 104-111, 139 addition polymer condensations, 503-505 adduct with 2-cyclohexylimino-cyclopentanedi-thiocarboxylic acid, 51 adducts for epoxy resins curing, 507-510 adduct with 2-iminocyclopentanedithiocarboxylic acid, 51... 

This example illustrates a graft polymerisation in which colloid stabilisation and both Redox and thermal initiation techniques are employed. The reaction in effect takes place in two stages, with the vinyl acetate polymerisation taking place before the acrylic monomers are polymerised. 

The grafting reactions initiated by free radicals discussed here have generally been identifiable, at least in part, by ESR spectroscopy. Other methods include chemical oxidation of cellulose by thermal decomposition of peroxides, ultrasonic radiation, electric-arc discharge (also called corona discharge), electrolysis, mechanical milling and oxidation of products of chemical reactions in the presence of vinyl monomers. Chemical modification of cellulose, e,g. by diazotization and thiocar-bonation, increases the rate of oxidation and of graft copolymer formation in the presence of vinyl monomers. ... 

In graft copolymerization using an initiator, grafting occurs preferentially via the primary radicals, whereas in thermal graft copolymerization grafting is initiated by polymer radicals [24,25]. 

When 4-(mercaptoacetamido)diphenylamine [60766-26-9] (39) is added to EPDM mbber and mixed in a torque rheometer for 15 minutes at 150°C, 87% of it chemically binds to the elastomer (24). The mechanical and thermal stress placed on the polymer during mixing mptures the polymer chain, producing radicals that initiate the grafting process. 

Grafting reactions onto a polymer backbone with a polymeric initiator have recently been reported by Hazer [56-60]. Active polystyrene [56], active polymethyl methacrylate [57], or macroazoinitiator [58,59] was mixed with a biopolyester polyhydroxynonanaate [60] (PHN) or polybutadiene to be carried out by thermal grafting reactions. The grafting reactions of PHN with polymer radicals may proceed by H-abstraction from the tertier carbon atom in the same manner as free radical modification reactions of polypropylene or polyhy-droxybutyratevalerate [61,62]. 

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