Alternating copolymer example

In the Type II case, the copolymerization tends toward an alternating arrangement of monomer units. Curve II of Figure 1 shows an example of an alternating copolymer that has an azeotropic copolymer composition, ie, a copolymer composition equal to the monomer feed at a single monomer feed composition. This case is analogous to a constant Foiling mixture ia vapor—Hquid equihbria.T) III... 

Alternating copolymers have the monomers of one type alternating in a regular manner with the monomers of the other, regardless of the composition of the reactants. For example, an alternate copolymer of vinyl acetate and vinyl chloride could be represented as ... 

The only known instance of ring-opening polymerization with these compounds is also the only report on the successful polymerization of 2,5-dihydrofuran74 in which this compound was cationically copolymerized with epichlorhydrin (rx 0, r2 0), propylene oxide (r, 0, r2 0) and 3,3-bischloromethyl oxacyclobutane (/ ] 0, r2 = 1.6). It was shown that all the copolymers obtained possessed a certain degree of unsaturation which was attributed to the presence of open units from 2,5-dihydrofuran. Thus, for example the alternating copolymer with epichlorhydrin had the following structure (IR spectra, Cl content. C=C analysis) ... 

The metathesis of alkyl- or aryl-substituted cycloalkenes provides a route to certain perfectly alternating copolymers. For example, metathesis of 5-methylcyclooctene leads to a polymer that may be considered as a... 

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. 

Copolymers are polymers made up of more than one type of repeating unit (Fig. 19.14). One example is nylon-66, in which the repeating units are formed from 1,6-diaminohexane, H2N(CH2)(lNH2, and adipic acid, HOOC(CH2)4COOH. They form an alternating copolymer, in which acid and amine monomers alternate. 

Cationic copolymerization of other monomers which do not polymerize by themselves often yields alternating copolymers. Some examples are254,2SS) ... 

Step polymerisations tend to be carried out using two different bifunctional molecules so that these give rise to molecules which are essentially copolymers. For example, nylon 6,6 is prepared from hexamethylenediamine and adipic acid it thus consists of alternating residues along the polymer chain and may be thought of as an alternating copolymer. 

Alternating copolymers, as illustrated in Fig. 5.8 b), are generally made by condensation polymerization of two different monomers. Such copolymers display regularity and are capable of crystallizing under the appropriate conditions. Examples of such copolymers include nylons 66 and 610, and various types of polyurethane. 

A similar technique was applied to the synthesis of AB and ABA block copolymers containing random and alternating copolymer sequences [178-180]. For example poly(St-ra dora-MMA)-hZock-poly(VAc), poly(VAc-hZock-poly(St-ran-dora-MMA)-hZock-poly(VAc), poly(St)-foZoc/c-poly(DiPF-aZMBVE), poly(IBVE-aZf-MAn)-hZock-poly(St)-hZock-poly(IBVE-aZf-MAn), poly(St)-hZock-poly(EA)-random-AA), and poly(St)-hZock-poly(EA-ra dora-AA-random-MMA) were synthesized [178]. 

Another example of efficient Forster energy transfer in Eu3+ complexes of fluorene copolymers (similar to the alternating copolymers described in Scheme 2.49) was demonstrated by Huang and coworkers [414] for random copolymers. They synthesized copolymers 336 with a different ratio between the fluorene and the benzene units in the backbone and converted them into europium complexes 337 (Scheme 2.50) [414]. The complexes 337 were capable of both blue and red emission under UV excitation. In solution, blue emission was the dominant mode. However, the blue emission was significantly reduced or completely suppressed in the solid state and nearly monochromatic (fwhm 4 nm) red emission at 613 nm was observed. 

Some particularities of the extraction of ions from an aqueous organic phase, and of the phase catalyzed polyetherification will be summarized. These will represent the fundamentals of our work on the synthesis of some novel classes of functional polymers and sequential copolymers. Examples will be provided for the synthesis of functional polymers containing only cyclic imino ethers or both cyclic imino ethers as well as their own cationic initiator attached to the same polymer backbone ABA triblock copolymers and (AB)n alternating block copolymers and a novel class of main chain thermotropic liquid crystalline polymers containing functional chain ends, i.e., polyethers. 

More complex polysaccharides play important roles in connective tissues and elsewhere. For example, hyaluronic acid is universally present in connective tissues of animals, as well as in their vitreous and synovial fluids. It helps to provide the fluids present in joints with shock-absorbing and lubricating properties. Unlike cellulose, chitin, starch, and glycogen, hyaluronic acid contains two different monomers glucose and N-acetylglucosamine alternate in the structure. Thus, hyaluronic acid is a regular alternating copolymer ABABABA —... 

The copolymer described by Eq. 6-1, referred to as a statistical copolymer, has a distribution of the two monomer units along the copolymer chain that follows some statistical law, for example, Bemoullian (zero-order Markov) or first- or second-order Markov. Copolymers formed via Bemoullian processes have the two monomer units distributed randomly and are referred to as random copolymers. The reader is cautioned that the distinction between the terms statistical and random, recommended by IUPAC [IUPAC, 1991, in press], has often not been followed in the literature. Most references use the term random copolymer independent of the type of statistical process involved in synthesizing the copolymer. There are three other types of copolymer structures—alternating, block, and graft. The alternating copolymer contains the two monomer units in equimolar amounts in a regular alternating distribution ... 

The resulting copolymer can contain at most 50 mol% M2 units, even at high concentration of M2 in the monomer mixture. This applies, for example, to maleic anhydride, and especially to such monomers as molecular oxygen or sulfur dioxide where, independent of the comonomer used, essentially alternating copolymers are obtained, with almost equal amounts of the two components. 

Finally, it should be mentioned that there exist two other routes for the synthesis of copolymers. First the partial chemical conversion of homopolymers (see Sect. 5.1), for example, the partial hydrolysis of poly(vinyl acetate). Secondly, by homopolymerization of correspondingly built monomers. An example for these macromolecular compounds, sometimes called pseudo-copolymers, is the alternating copolymer of formaldehyde and ethylene oxide synthesized by ringopening polymerization of 1,3-dioxolane. 

Most often, the extent of completely alternating copolymer formation, expressed as 100% C02 linkages or 50% C02 content, is very high. With regards to the selectivity of the coupling reaction for copolymer versus cyclic carbonate production, two observations are consistently found, regardless of the catalyst. First, aliphatic epoxides are more prone to cyclic carbonate formation than alicyclic epoxides for example, PO affords propylene carbonate more readily than CHO provides cyclohexene carbonate. Second, in either instance, since it has been shown that the activation barriers for cyclic carbonate production are higher... 

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