Copolymerization thermal initiation

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]. 

In thermal polymerization where the rate of initiation may also vary with composition, an abnormal cross initiation rate may introduce a further contribution to nonadditive behavior. The only system investigated quantitatively is styrene-methyl methacrylate, rates of thermal copolymerization of which were measured by Walling. The rate ratios appearing in Eq. (26) are known for this system from studies on the individual monomers, from copolymer composition studies, and from the copolymerization rate at fixed initiation rate. Hence a single measurement of the thermal copolymerization rate yields a value for Ri. Knowing hm and ki22 from the thermal initiation rates for either monomer alone (Chap. IV), the bimolecular cross initiation rate constant kii2 may be calculated. At 60°C it was found to be 2.8 times that... 

Due to the fact that thermally initiated free radical copolymerization is by far the most routinely employed method for fabrication of organic monolithic stationary phases, the pore formation mechanism is discussed for this particular kind of polymerization. 

The polymerization time as a polymerization parameter for adjustment of the porous properties of thermally initiated copolymers has recently been characterized [111]. A polymerization mixture comprising methylstyrene and l,2-bis(p-vinylbenzyl)ethane as monomers was subjected to thermally initiated copolymerization for different times (0.75, 1.0, 1.5, 2, 6, 12, and 24h) at 65°C. The mixtures were polymerized in silanized 200pm I.D. capillary columns as well as in glass vials for ISEC and MIP/BET measurements, respectively. 

CPT-SO > System. Bulk copolymerization of CPT and SO> takes takes place spontaneously at a remarkable rate even at —15 °C. In comparison with the thermal initiation of p-dioxene and maleic anhydride which proceeds through a similar charge transfer complex at room temperature (13), the interaction between CPT and S02 seems more pronounced, giving the propagating species at a lower temperature. 

More recently, iodonium salts have been widely used as photoinitiators in the polymerization studies of various monomeric precursors, such as copolymerization of butyl vinyl ether and methyl methacrylate by combination of radical and radical promoted cationic mechanisms [22], thermal and photopolymerization of divinyl ethers [23], photopolymerization of vinyl ether networks using an iodonium initiator [24,25], dual photo- and thermally-initiated cationic polymerization of epoxy monomers [26], preparation and properties of elastomers based on a cycloaliphatic diepoxide and poly(tetrahydrofuran) [27], photoinduced crosslinking of divinyl ethers [28], cationic photopolymerization of l,2-epoxy-6-(9-carbazolyl)-4-oxahexane [29], preparation of interpenetrating polymer network hydrogels based on 2-hydroxyethyl methacrylate and N-vinyl-2-pyrrolidone [30], photopolymerization of unsaturated cyclic ethers [31] and many other works. 

The ability of AAm complexes with Cr(III), Er(III) and other metal nitrates to involve other comonomers, such as acrylic or methacrylic acid and maleide anhydride, in spontaneous copolymerization in aqueous solutions has been reported [122]. It was possible to copolymerize transition metal nitrate AAm complexes with maleic acid under frontal conditions by thermal initiation [83]. 

Interfacial copolymerization of hydrophilic vinylethers with hydrophobic maleates can be conducted in direct [79] and in inverse [80] miniemulsions, leading to encapsulation of organic liquids or water, respectively. The concept is based on two monomers that do not homopolymerize and are located in the organic and aqueous phase, respectively. The polymerization is initiated by an interfacially active azoinitiator. Regarding the system for encapsulation of organic liquids, thermal initiation (60°C) leads to coalescence and destabilization of the miniemulsion, and thus lower reaction temperatures (30°C) are required. UV initiation was also used for the generation of stable capsules. 

Kimaro et al. [93] had prepared free-standing membranes by thermally initiated cross-linking copolymerization of styrene monomers followed by leaching of a polyester present as pore former at a concentration of 1.8 wt% in the reaction mixture. SEM pictures suggested the presence of isolated pores with diameters of up to 1 pm at a low density (< 2 %). In line with permeation data, it could be speculated that trans-membrane channels had been obtained, induced by the presence of a removable macromolecular pore former in the reaction mixture. 

Superabsorbent polyacrylates are prepared by means of free-radical-initiated copolymerization of acrylic acid and its salts with a cross-linker (12,13). Two principal processes are used bulk, aqueous solution pol5unerization and suspension polymerization of aqueous monomer droplets in a hydrocarbon liquid continuous phase (14) (see Bulk and Solution Polymerizations Reactors Heterophase Polymerization). In either process, the monomers are dissolved in water at concentrations of 20-40 wt% and the polymerization is initiated by free radicals in the aqueous phase (15). The initiators, freeradical (qv) used include thermally decomposable initiators, reduction-oxidation systems, and photochemical initiators and combinations. Redox systems include persulfate/bisulfite, persulfate/thiosulfate, persulfate/ascorbate, and hydrogen peroxide/ascorbate. Thermal initiators include persulfates, 2,2 -azobis(2-amidinopropane)-dihydrochloride, and 2,2 -azobis(4-cyanopentanoic acid). Combinations of initiators are useful for polymerizations taking place over a temperature range. 

The ceiling temperature constraint in the homopolymerization of alphamethyl styrene (AMS) can be circumvented by copolymerization with acrylonitrile (AN) to prepare multicomponent random microstructures that offer higher heat resistance than SAN. The feasibility of a thermal initiation of free radical chain polymerization is evaluated by an experimental study of the terpolymerization kinetics of AMS-AN-Sty. Process considerations such as polyrates, molecular weight of polymer formed, sensitivity of molecular weight, molecular weight distribution, and kinetics to temperature were measured. 

Obtaining polyrotaxanes by the statistical method through polymerization of various monomers in the presence of macrocycles was attempted by Maciejewski who investigated the thermal radical copolymerization of vinylidene chbride, methyl methacrylate (MMA), acrylonitrile (AN), acrylamide, and thdr mixtures with ace-tonaphtylene in aqueous and dimethylformamide solutions in the presence of p-cyclodextrin or of its acylic derivative. All these attempts failed, however. Only, when copolymerization was initiated by y-radiation with an exposure dose of 5 Mrad, did some of the above-listed monomers form polymers exhibiting optical activity. However, the rotation of the initial p-cyclodextrin was 162°, while that of the obtained products only l°-6°. Such a small polarization plane rotation angle could result only from an insignificant amount of macrocycles in the synthesized compounds. Therefore, for the purpose of a more successful synthesis of cyclodextrin-based rotaxanes, a number of researchers tried to introduce elements of directionality into... 

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... 

As was shown in the early 1970s, alkalis and their derivatives were able to catalyze the polymerization ofMSCBs at 5-90°C, but the reaction proceeded at a low rate and led to polysiltrimethylenes with molecular weights much smaller than those of polymers prepared under thermal initiation. With the use of this method, the polymerization of MSCBs with various substituents (hydrocarbon and carbofunctional) [52] and the copolymerization ofMSCBs [23] can be realized. 

Using typical parameter values for styrene homopolymerization at 80°C, reaction times of the order of magnitude of 100 h are needed to have = 0.05. Even if it can be shown that low polydispersity values can be achieved also at higher values (>0.2-0.3) [72, 73], these values cannot be accepted in copolymerization. While increased reaction temperatures and thus propagation rates generally should promote smaller dead chain contents [compare Eq (55)], in the case of styrenic copolymers this leads to limited improvements only, since undesired side reactions negatively affecting the polymer quality (such as chain transfer and thermal initiation) become more and more important. 

Considering cyclopentene as representative of the cyclic olefins, the kinetics of its copolymerization with MA was investigated.The copolymerization rate data showed a maximum rate at approximately 40 mol % MA. An Arrhenius plot of the rate data and interpretation of the results yielded an overall activation energy of 24.2 0.35 kcal/mol. No thermal initiation was detected for the C4-C8 olefin-MA copolymerizations. 

The effects of adding nonpolymerizable and polymerizable electron donors, such as anthracene, naphthalene, cyclohexene, and dihydrofuran, to the styrene-MA copolymerization system has received substantial study by Tsuchida and coworkers.The ability of these additives and styrene to complex with MA follows the order anthracene > naphthalene > styrene > cyclohexene > dihydrofuran. Naphthalene addition reduced the overall activation energy, increased the rate of thermal initiation and propagation slightly, and increased the rate of copolymerization. In addition, the rate maxima shifted from compositions poor in styrene toward equivalence. Because... 

Since the equilibrium constant for the CTC of this pair is very small (Chapter 10 Appendix), the CTC concentration condition can be approximated as i [Mi][M2] (Sec. 10.3.1). If only the CTC copolymerized the rate should be directly proportional to [Mi], assuming [Mi] = [M2]. The experimental data collected showed that the initiation rate (/ ,) was proportional to [Mi], which contradicts the concept of a thermal-initiation mechanism. On the other hand, if it is assumed that the part of the order with respect to [Mi] in excess of 1 represents a higher-order initiation reaction, then the order with respect to monomer contributing to polymerization initiation should be 2. In any case, the results of [MJ are not clear as to whether it is the contribution of the CTC to the growth reaction or the fit that is a result of polymerization initiation. 

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... 

Three-membered rings are also formed in the copolymerization of sulfur dioxide with bicyclo[2.2.1]heptadiene (11-8) (/, 162). Thermal initiation of this copolymerization is reported to give only 1,5-homoconjugative addition polymerization 134). The white, powdery polymer produced at 150 C is more thermally stable and alkali-resistant than the low-temperature radical-initiated polymer. Elemental analyses were consistent with a 1 1 alternating copolymer structure. 

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