Copolymerization of cyclic monomers

Many copolymers have been prepared from cyclic monomers. These can form through ring-opening copolymerizations of monomers with similar functional groups as well as with different ones. Some cyclic monomers can also copolymerize with some linear monomers. Only a few copolymers of cyclic monomers, however, are currently used industrially. 

The composition of the copolymers depends upon the reaction conditions, the counter ions, the solvents, and the reaction temperatures. The initiator system can be very important when cyclic monomers with different functional groups are copolymerized. Also, if different propagating centers are involved in the propagation process, copolymerizations can be very difficult to achieve. 

Prominent among copolymers of cyclic ethers are interpolymers of oxiranes with tetrahydrofuran. Thus, ethylene oxide copolymerizes with tetrahydrofuran with the aid of boron trifluoride-ethylene glycol catalytic system [200]. The resultant copolyether diol contains virtually no unsaturation. 

Another example is a copolymer of allyl glycidyl ether with tetrahydrofuran formed with antimony pentachloride catalyst [201]  

In addition to the above, liquid copolymers form from 1,3-dioxolane with ethylene oxide, when boron trifluoride is used as the catalyst [1]. Also, a rubbery copolymer forms from tetrahydrofuran and 3,3-diethoxycyclobutane with phosphorus pentafluoride catalyst [202]. A 3,3-bis(chloromethyl) oxacyclobutane copolymerizes with tetrahydrofuran with boron fluoride or with ferric chloride catalysis. The product is also a rubbery material [1]. 

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Anionic copolymerization of cyclic monomers occurs only between similar monomer pairs. Random copolymers are not formed between vinyl monomers and epoxides or lactones198 because the propagating species are very different. Thus, the success of the copolymerization of cyclic disulfide and nitropropylene was an exceptional case... 

Although the literature contains much on copolymerizations of cyclic monomers, including data on monomer reactivity ratios, the reader is cautioned that most of the data are less reliable than corresponding data for radical copolymerizations of alkenes (Chap. 6). The... 

Figure 2. Schematic illustration of radical ring-opening copolymerization of cyclic monomers with vinyl monomers.

Discuss copolymerizations of cyclic monomers giving several examples. 

In the lipase-catalyzed ring-opening copolymerization of cyclic monomers, the first example with lactones involved 5-VL and e-CL, using a lipase PF catalyst [98]. 

Aliphatic/aromatic. Copolymerization of aliphatic monomers (terpenes, cyclic C5, and acyclic C5) with the aromatic C9 petroleum stream is used to produce... 

Polymerization equilibria frequently observed in the polymerization of cyclic monomers may become important in copolymerization systems. The four propagation reactions assumed to be irreversible in the derivation of the Mayo-Lewis equation must be modified to include reversible processes. Lowry114,11S first derived a copolymer composition equation for the case in which some of the propagation reactions are reversible and it was applied to ring-opening copalymerization systems1 16, m. In the case of equilibrium copolymerization with complete reversibility, the following reactions must be considered. 

Cationic copolymerization of cyclic ethers, formals, esters and anhydrides has been thoroughly studied in recent years and sufficient information about it is now available. The propagating species involved in the cationic copolymerization of these oxacyclic monomers are believed to be the oxonium ions in most cases, but their detailed nature is dependent on monomer structure. From their copolymerization behavior, these monomers can be arranged in the following order of increasing car-bocationic character of the propagating species ... 

Detailed information on the copolymerization of cyclic trifluoropropylmethyl-siloxane trimer and octamethylcyclotetrasiloxane is also very limited in the open literature26 27 . Recently, preparation of various amine terminated (dimethyl-tri-fluoropropyl,methyl)siloxane oligomers with varying molecular weights and backbone compositions has been reported 69115 ll7). Table 11 shows various properties of the oligomers produced as a function of composition. These types of modification play very important roles in determining the solubility characteristics and hence the compatibility of resultant polysiloxanes with other conventional organic monomers... 

Nearly all synthetic polymers are synthesized by the polymerization or copolymerization of different "monomers." The chain growth process may involve the addition chain reactions of unsaturated small molecules, condensation reactions, or ringopening chain-coupling processes. In conventional polymer chemistry, the synthesis of a new polymer requires the use of a new monomer. This approach is often unsatisfactory for Inorganic systems, where relatively few monomers or cyclic oligomers can be Induced to polymerize, at least under conditions that have been studied to date. The main exception to this rule is the condensation-type growth that occurs with inorganic dl-hydroxy acids. 

Duda A, Libiszowski J, Mosnacek J, Penczek S (2005) Copolymerization of cyclic esters at the living polymer-monomer equilibrium. Macromol Symp 226 109-119... 

There are very few reported copolymerizations between cyclic monomers and carbon-carbon double-bond monomers. Such copolymerizations would require a careful selection of the monomers and reaction conditions to closely match the reactivities of the different monomers and propagating centers. The almost complete absence of successes indicates that the required balancing of reactivities is nearly impossible to achieve. There are a few reports of copolymerizations between carbon-carbon double-bond monomers and cyclic ethers or acetals [Higashimura et al., 1967 Inoue and Aida, 1984 Yamashita et al., 1966],... 

In contrast to the copolymerization of cyclic carbonates, the molecular weights are lower in the epoxide copolymerization 6,41 43). We assume that this is due to the presence of proton donors in the reaction mixture. They occur as impurities in epoxides 19,20) or anhydrides, moisture in all components of the copolymerization system, or their presence is a consequence of the high rate of hydrolysis of cyclic anhydrides 21). Proton donors added to the monomer feed remarkably decrease the molecular weight42 even in the copolymerization of ethylene glycol carbonate at 200 °C. Under these conditions, when recyclization of phthalic acid takes place 64) and the released C02 can tear off moisture to the gas phase, the molecular weight Mv decreases without proton donors from 45200 to 7100 in the presence of 5% phthalic acid or ethylene glycol or to 9300 in the presence of 15% water42,54. ... 

Aziridines represent another group of cyclic monomers that are capable of copolymerizing with C02 to potentially provide useful polymeric materials, namely polyurethanes. Early studies of the reactions of aziridines with C02 led to the production of cyclic urethanes [72] and polymers [73, 74], but the polymeric product was shown to consist of both urethane and amine linkages, as depicted in Equation 8.7. However, because the rate of homopolymerization of aziridines is similar to that of the copolymerization of aziridines and C02, the urethane linkages were limited to -30%. 

Although homopolymerization of cyclopentene results in 1,3 enchainment of the monomer units in copolymerization, blocks of cyclic monomer units are rarely observed as a consequence of the unfavorable copolymerization parameters. The isolated cyclopentene units maybe incorporated in a cis-1,2 or cis-1,3 fashion, with their ratio dependent on the catalyst used (238-240). Thus, ethylene compensates for the steric hindrance at the a carbon atom of the growing chain after insertion of the cyclopentene. 

One of the so far not very numerous group of cyclic monomers able to polymerize and to copolymerize with styrene, methyl methacrylate, etc. under the effect of peroxides is spiroorthocarbonate [307],... 

In studies of the kinetics of copolymerization of cyclic compounds the Mayo—Lewis equations [150] for kinetics of copolymerization have been applied, often with deserved caution. Many monomer reactivity ratios have been derived in this way. A large number of them have been summarized previously [7, 151] and we will not repeat them here nor attempt to update the lists. Instead we shall concentrate on some of the factors that seem to be important in regulating the copolymerizations and on some of the newer approaches that have been suggested for dealing with the complicated kinetics and give only a few examples of individual rate studies. 

In copolymerizations of cyclic ethers, too, basicity of the monomers seems to correlate well with the reactivity ratios determined from copolymer composition. Recently, Saegusa et al. [54] have pointed out that the apparent values of the monomer reactivity ratios in cyclic ether copolymerizations may be more influenced by the exchange... 

The heat of polymerization of a number of cyclic monomers is lower than that of unsaturated monomers, causing extensive reversibility of the propagation steps. Thus, Scheme (15-1) has to be complemented with reversible steps and this leads to a completely different functional dependence of d[MJ/d[M2] (= [mj/fmj, i.e. copolymer composition) on [M,]/[M2] (monomer feed). This is certainly the case with cyclic monomers with heats of copolymerization equal to or lower than 40 kJ mole-1. 

The attack on the endocyclic carbon leads to crosspropagation whereas attack on the exocyclic group is merely an exchange of one active species for another with expulsion of a monomer molecule. In the copolymerization of cyclic ethers, like THF and OXP, this reaction has been quantitatively studied. For the tetrahydro-furanium cation kexo/kendo = 2 10-2, whereas for the oxepanium cation kexo/kendo = 0.5 and, therefore, the exo-attack cannot be neglected 8). 

The radical copolymerization of cyclic ketene acetal with various vinyl monomers such as styrene, MMA, vinyl acetate, and methyl vinyl ketone could afford the copolymers with ester groups in the main chain (26-28). These copolymers showed enzymatic degradability and photodegradability and are applicable as environmentally degradable materials. 

The free radical polymerizations of cyclic ketene acetals have recently evoked a lot of interest (10-13). TTie oly(e-caprolactone) (PCL) can be synthesized by free radical ring opening polymerization (10). The copolymerization of its monomer, 2-methylene-l,3-dioxepane (MDO), with some vinyl monomers resulted in an aliphatic ester backbone, as well as the pendant functional groups from the vinyl monomers (10). By free radical polymerization of MDO and the vinyl monomers vinylphosphonic acid (VPA), dimethylvinylphosphonate (VPE) and acrylic acid (AA), we synthesized a series of biodegradable copolymers including PCL... 

Figure 28.3 Chainwise copolymerization of epoxy monomers with cyclic anhydrides.

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