Free radical conventional

That the Poisson distribution results in a narrower distribution of molecular weights than is obtained with termination is shown by Fig. 6.11. Here N /N is plotted as a function of n for F= 50, for living polymers as given by Eq. (6.109). and for conventional free-radical polymerization as given by Eq. (6.77). This same point is made by considering the ratio M /M for the case of living polymers. This ratio may be shown to equal... 

Poly(acrylic acid) and Poly(methacrylic acid). Poly(acryHc acid) (8) (PAA) may be prepared by polymerization of the monomer with conventional free-radical initiators using the monomer either undiluted (36) (with cross-linker for superadsorber appHcations) or in aqueous solution. Photochemical polymerization (sensitized by benzoin) of methyl acrylate in ethanol solution at —78° C provides a syndiotactic form (37) that can be hydrolyzed to syndiotactic PAA. From academic studies, alkaline hydrolysis of the methyl ester requires a lower time than acid hydrolysis of the polymeric ester, and can lead to oxidative degradation of the polymer (38). Po1y(meth acrylic acid) (PMAA) (9) is prepared only by the direct polymerization of the acid monomer it is not readily obtained by the hydrolysis of methyl methacrylate. 

Copolymers of VDC can also be prepared by methods other than conventional free-radical polymerization. Copolymers have been formed by irradiation and with various organometaHic and coordination complex catalysts (28,44,50—53). Graft copolymers have also been described (54—58). 

As discussed in Section 7.3, conventional free radical polymerization is a widely used technique that is relatively easy to employ. However, it does have its limitations. It is often difficult to obtain predetermined polymer architectures with precise and narrow molecular weight distributions. Transition metal-mediated living radical polymerization is a recently developed method that has been developed to overcome these limitations [53, 54]. It permits the synthesis of polymers with varied architectures (for example, blocks, stars, and combs) and with predetermined end groups (e.g., rotaxanes, biomolecules, and dyes). 

Acrylamide readily undergoes polymerization by conventional free radical methods, ionizing radiation, ultrasonic waves, and ultraviolet radiation. The base-cata-lized hydrogen transfer polymerization of acrylamide yields poly-/3-alanine (Nylon 3) a water insoluble polymer that is soluble in certain hot organics. All current industrial production is believed to be by free radical polymerization. 

Acrylamide is polymerized by the conventional free radical initiators, e.g., peroxides [27,28], redox pairs [29-33], and azo compounds [34]. Electro-chemical initi-... 

Autoacceleration in the polymerization of MA poses a serious problem [21-23]. Saini et al. [24] attempted to polymerize MA by using /3-PCPY as the initiator with a view to minimize the difficulties experienced due to this phenomenon. The findings led to the conclusion that -PCPY can be used to obtain 19.5% conversion of MA without gelation due to autoacceleration, which is nearly double the conversion obtained by using the conventional free radical initiator (AIBN) in the same experimental conditions. 

Kobetaki et a/. 89 642 have examined the combination of conventional free radical and NMP to prepare PBMA-Woci-PS and the combination of anionic and NMP to prepare PB-6/oc -PS. 

Radiolytic ethylene destruction occurs with a yield of ca. 20 molecules consumed/100 e.v. (36, 48). Products containing up to six carbons account for ca. 60% of that amount, and can be ascribed to free radical reactions, molecular detachments, and low order ion-molecule reactions (32). This leaves only eight molecules/100 e.v. which may have formed ethylene polymer, corresponding to a chain length of only 2.1 molecules/ ion. Even if we assumed that ethylene destruction were entirely the result of ionic polymerization, only about five ethylene molecules would be involved per ion pair. The absence of ionic polymerization can also be demonstrated by the results of the gamma ray initiated polymerization of ethylene, whose kinetics can be completely explained on the basis of conventional free radical reactions and known rate constants for these processes (32). An increase above the expected rates occurs only at pressures in excess of ca. 20 atmospheres (10). The virtual absence of ionic polymerization can be regarded as one of the most surprising aspects of the radiation chemistry of ethylene. 

The above discussion has been based on conventional free-radical catalysis. There has been substantial research on long-lived free radicals that can give a living polymer without the severe cleanliness requirements of anionic polymerizations. Unfortunately, it has not yet had commercial success. 

The dinitrobenzyl tosylate, (15) triphenylsulfonium hexafluoroarsenate (16), and triphenylsulfonium triflate (17) were prepared as described in the literature. The monomers, 4-t-butoxycarbonyloxy-a-methylstyene (t-BOC-a-methylstyrene), and 4-t-butoxycarbonyloxystyrene (t-BOC-styrene) and their respective homopolymers, TBS and TBMS were prepared as described in the literature (12,14). TBSS was prepared by conventional, free-radical methods (13,18). The composition of this polymer (ratio of SO2 to t-BOC styrene) is controlled by changing the polymerization temperature and/or initiator concentration (Table II). 

One alternative to the tetrafluoroethylene-based backbones of the previously discussed materials is the use of styrene and particularly its fluorinated derivatives to form PEMs. As extensively reported in the literature, styrenic monomers are widely available and easy to modify, and their polymers are easily synthesized via conventional free radical and other polymerization techniques. 

Polyols. Typical polyols used in automotive topcoats Include acrylic copolymers and polyesters which have varied number of hydroxyl groups. Acrylic copolymers ranging in number average molecular weight from 1,000 to 10,000 and containing 15-40% by weight of a hydroxy functional comonomer such as hydroxyethyl acrylate have been studied. The acrylic copolymers were prepared by conventional free radical solution polymerization. 

Some early polymerizations reported as Ziegler-Natta polymerizations were conventional free-radical, cationic, or anionic polymerizations proceeding with low stereoselectivity. Some Ziegler-Natta initiators contain components that are capable of initiating conventional ionic polymerizations of certain monomers, such as anionic polymerization of methacrylates by alkyllithium and cationic polymerization of vinyl ethers by TiCLt-... 

Markl et al.92 have obtained heterocyclohexa-2,5-dienes (51), by cycloaddition of arylphosphines, arylarsines, and dialkylstannanes with acetylene derivatives in the presence of 18-crown-6 and benzene. The technique is superior to the conventional free radical method (benzene, AIBN) or to the method employing a strong base (BuLi, THF, or NH2Na,NH3). 

Fig. 5. Copolymerization of methyl methacrylate and styrene in tetrahydrofuran (O) and in N,N-dimethyl formamide ( ). Solid line represents copolymer composition produced by conventional free-radical initiators...

Poly(acrylic acid) and Poly(rnethacrylic acid). Poly(acrylic acid) (PAA) may be prepared by polymerization of the monomer with conventional free-radical initiators using the monomer either undiluted (widi cross-linker for superadsorber applications) or in aqueous solution. Photochemical polymerization (sensitized by benzoin) of methyl acrylate in ethanol solution at —78°C provides a syndiotactic form that can be hydrolyzed to syndiotactic PAA. 

Although the acetylene derivatives Co2(CO)6(C6H5C=CCOOH) and Co3(CO)9(H)(CH=CC6H5) were also found to initiate polymerization in the presence of CC14) Co2(CO)8 was found to be not only inactive, but actually to inhibit polymerization in the presence of conventional free radical initiators. The unusual behavior of dicobalt octacarbonyl may be related to its greater reactivity. The reaction with carbon tetrachloride has been studied by Dent et al. (22a) and Ercoli et al. (26a) who isolated a complex C1C [Co(CO)3]3. This could arise from a series of C—Cl cleavage reactions... 

Today, the majority of all polymeric materials is produced using the free-radical polymerization technique [11-17]. Unfortunately, however, in conventional free-radical copolymerization, control of the incorporation of monomer species into a copolymer chain is practically impossible. Furthermore, in this process, the propagating macroradicals usually attach monomeric units in a random way, governed by the relative reactivities of polymerizing comonomers. This lack of control confines the versatility of the free-radical process, because the microscopic polymer properties, such as chemical composition distribution and tacticity are key parameters that determine the macroscopic behavior of the resultant product. 

A PP macromonomer with a methacryloyl end group was synthesized, and was used to prepare PMMA-g-PP graft copolymers by conventional free radical copolymerization [104]. Vinylidene-terminated PP (Mn = 1000) was converted into terminally hydroxylated PP (PP-OH) by a combination of the hydroboration reaction of the unsaturated group and oxidation reaction. Resulting PP-OH was reacted with methacryloylchloride to synthesize termi-... 

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