Olefins alternating copolymers

It has been discovered that styrene forms a linear alternating copolymer with carbon monoxide using palladium II—phenanthroline complexes. The polymers are syndiotactic and have a crystalline melting point - 280° C (59). Shell Oil Company is commercializing carbon monoxide a-olefin plastics based on this technology (60). 

In this section wc consider systems where the radical formed by propagation can eyclizc to yield a new propagating radical. Certain 1,4-dicncs undergo cyclocopolymerization with suitable olefins. For example, divinyl ether and MAH are proposed to undergo alternating copolymerization as illustrated in Scheme 4.19.167 These cyclo-copolymerizations can he quantitative only for the case of a strictly alternating copolymer. This can be achieved with certain electron donor-electron acceptor pairs, for example divinyl ether-maleic anhydride. 

Alternating copolymers of ethylene with olefins containing double bonds in the cis configuration, like ds-2-butene, cyclopentene, cycloheptene,115 and norbomene,116 have been described. Recently also copolymers of carbon monoxide with styrene and styrene derivatives, having syndiotactic117 and isotactic118 configurations, have been synthesized and characterized. 

Another class of "chain scission" positive resists is the poly(olefin sulfones). These polymers are alternating copolymers of an olefin and sulfur dioxide. The relatively weak C-S bond is readily cleaved upon irradiation and several sensitive resists have been developed based on this chemistry (49,50). One of these materials, poly(butene-l sulfone) (PBS) has been made commercially available for mask making. PBS exhibits an e-beam sensitivity of 1.6 pC cm-2 at 20 kV and 0.25 pm resolution. 

Though important results have already been obtained in the carbonylation of olefins, the field still remains open. Development of more active, efficient and stable catalysts based also on less expensive metals will make the carbonylation processes more attractive. Carbonylation of less common olefins, including functionalised ones, has to be explored in more depth. Other important targets are the efficient living copolymerisation, the multiple olefin insertion producing non-alternating copolymers and the selective synthesis of unsaturated products like acrylates and methacrylates. 

PBS (Figure 30) is an alternating copolymer of sulfur dioxide and 1-butene. It undergoes efficient main chain scission upon exposure to electron beam radiation to produce, as major scission products, sulfur dioxide and the olefin monomer. Exposure results first in scission of the main chain carbon-sulfur bond, followed by depolymerization of the radical (and cationic) fragments to an extent that is temperature dependent and results in evolution of the volatile monomers species. The mechanism of the radiochemical degradation of polyolefin sulfones has been the subject of detailed studies by O Donnell et. al. (.41). 

The other major class of positive resists is based on polyfolefin sulfones) which are alternating copolymers of sulfur dioxide and the respective olefin having the general structure. 

Free-radical polymerization of a 1 1 mixture of dimethyl fumarate and vinyl acetate, resulting in a highly regular alternating copolymer, illustrates the importance of substitution on the properties of both the free radical and the olefinic substrate [139] ... 

The rates and orientation of free radical additions to fluoroalkenes depend upon the nature of the attacking radical and the alkene, but polar effects again are important For instance, methyl radical adds 9 5 times faster to tetrafluoroethylene than to ethylene at 164 °C, but the tnfluoromethyl radical adds 10 times taster to ethylene [7551 The more favorable polar transition states combine the nucleophilic radical with the electron deficient olefin 17 and vice versa (18) These polar effects account for the tendency of perfluoroalkenes and alkenes to produce highly regular, alternating copolymers (see Chapter starting on page 1101)... 

Preferred olefins in the polymerisation are one or more of ethylene, propylene, 1-butene, 2-butene, 1-hexene, 1-octene, 1-pentene, 1-tetradecene, norbornene and cyclopentene, with ethylene, propylene and cyclopentene. Other monomers that may be used with these catalysts (when it is a Pd(II) complex) to form copolymers with olefins and selected cycloolefins are carbon monoxide (CO) and vinyl ketones of the general formula H2C=CHC(0)R. Carbon monoxide forms alternating copolymers with the various olefins and cycloolefins. 

Lewis acids have long been known to influence free radical polymerizations [117]. They have been particularly important in copolymerizations of hydrocarbon olefins with electron-poor monomers such as acrylates or acrylonitriles. In this way strictly alternating copolymers can be synthesized from monomer pairs which in the absence of Lewis acids would give more random copolymers. The Lewis acid complexes with the electron pair of the acceptor group of the acrylate or acrylonitrile to form the more electrophilic complexed monomer, which then copolymerizes in alternating fashion with the electron-rich hydrocarbon olefin. 

The outcome of charge-transfer polymerizations has been systematized by Iwatsuki and Yamashita in their penetrating early review [130]. They arrived at a correlation of polymerization behavior with the value of the EDA complex equilibrium constant, Keq, With weak donor and acceptor olefins, no spontaneous polymerization takes place, while the addition of a radical initiator results in a random or an alternating copolymer depending on the value of Keq. As the donor and acceptor strength of the olefins increases, spontaneous initiation rates for radical copolymerization increase and with even stronger donor and acceptor olefins, ionic homopolymerization takes place (cationic and/or anionic). 

The interactions of a-olefins or styrene with sulfur dioxide (16) or a-olefins (24, 58, 78), frans-stilbene (64), styrene (1,63), p-dioxene (52), 2,2-dimethyl-l,3-dioxole (17), or alkyl vinyl ethers (1, 63) with maleic anhydride yield charge transfer complexes which are stable and generally readily detectable either visually or by their ultraviolet absorption spectra. However, under the influence of a sufficiently energetic attack in the form of heat or free radicals, the diradical complexes open, and alternating copolymers are formed. 

This copolymer is apparently an essentially completely alternating copolymer resulting from the greater electron-donating power of the isoprene compared with that of an olefin. 

Hirooka has proposed that the products are alternating copolymers produced through complex copolymerization and that the latter process differs from that of Imoto and Otsu (30, 33, 34) in which a free radical initiator is necessary for the random copolymerization of olefins with acrylonitrile or methyl methacrylate in the presence of zinc chloride. 

In later communications (27, 28) Hirooka reported that in addition to acrylonitrile, other conjugated monomers such as methyl acrylate and methyl methacrylate formed active complexes with organoaluminum halides, and the latter yielded high molecular weight 1 1 alternating copolymers with styrene and ethylene. However, an unconjugated monomer such as vinyl acetate failed to copolymerize with olefins by this technique. 

Title Synthesis of A,B-Alternating Copolymers by Olefin Metathesis Reactions of Cyclic Olefins or Olefinic Polymers with an Acyclic Diene... 

Alternating copolymers have been previously synthesized via metathesis polymerization by Grubbs et al. using ring-opening insertion metathesis polymerization (ROIMP) [120,121]. Here, a fast ROMP polymerization of a cyclic olefin... 

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