Formation of copolymers

When a mixture of two (or more) types of monomers is used as starting material in a polymerization reaction, the result can be the formation of a copolymer. However, different monomers differ significantly in their tendency to enter into copolymers. Even some monomers that are very difficult to polymerize alone or do not form polymers at all may participate very easily in the formation of some copolymers. One such example is maleic anhydride that gives easily copolymers with styrene or with vinyl chloride and forms very difficultly a homopolymer. 

In their structure the copolymers may contain the monomeric units randomly, and their overall composition is determined by the composition of the initial feed mixture of monomers (see Section 2.3). Alternating copolymers (a//-copolymers) also are known, where the monomers alternate regularly along the chain. Other types include block polymers where a linear arrangement of groups of one type of monomers is present, graft polymers that have side chain blocks connected to a polymer main chain, per-copolymers where ordered sequences of more than two units are present, etc. 

Copolymers have a very large range of applications in practice since they may possess properties difficult to attain in homopolymers. For this reason, many polymer samples from common sources are copolymers. 

---

The formation of copolymers involves the reaction of (at least) two kinds of monomers. This means that each must be capable of undergoing the same propagation reaction, but is is apparent that quite a range of reactivities is compatible with this broad requirement. We shall examine such things as the polarity of monomers, the degree of resonance stabilization they possess and the steric... 

Ring-Opening Polymerization. Examples of the formation of copolymers by ring-opening reactions are shown in equations 33 and 34... 

Creton, C., Kramer, E.J., Hui, C.-Y. and Brown, H.R., Failure mechanisms of polymer interfaces reinforced with block copolymers. Macromolecules, 25, 3075-3088 (1992). Boucher et al., E., Effects of the formation of copolymer on the interfacial adhesion between semicrystalline polymers. Macromolecules, 29, 774-782 (1996). 

Grafting provides a convenient means for modifying the properties of numerous polymers. It is often required that a polymer possess a number of properties. Such diverse properties may not be easily achieved by the synthesis of homopolymers alone but can be achieved through the formation of copolymers or even terpoly-mers. The formation of graft copolymer with sufficiently long polymeric sequences of diverse chemical composition opens the way to afford speciality polymeric materials. 

During the copolymerization 4 is, therefore, consumed faster, and at the initial stage the copolymers are enriched with 4. At high conversion levels its relative portion in the macromolecules of the copolyner decreases, resulting in the formation of copolymers with non-uniform composition. 

The structural versatility of pseudopoly (amino acids) can be increased further by considering dipeptides as monomeric starting materials as well. In this case polymerizations can be designed that involve one of the amino acid side chains and the C terminus, one of the amino acid side chains and the N terminus, or both of the amino acid side chains as reactive groups. The use of dipeptides as monomers in the manner described above results in the formation of copolymers in which amide bonds and nonamide linkages strictly alternate (Fig. 3). It is noteworthy that these polymers have both an amino function and a carboxylic acid function as pendant chains. This feature should facilitate the attachment of drug molecules or crosslinkers,... 

The following examples, found in R. eutropha, illustrate the formation of copolymers (cf. [37]). With propionic acid as an additional carbon source, the 3-ketothiolase catalyzes the condensation of the propionyl-CoA unit with acetyl-CoA to form 3-ketovaleryl-CoA, which is reduced to 3-hydroxyvalerate moieties and polymerized by the synthase [27]. 

Similar procedures were used in the preparation of the other polymers the use of mixtures of DHTN and DHCH resulted in the formation of copolymers with Tg values intermediate between those of 2 and 12. 

By the formation of copolymers. Alternate isotactic copolymers. . . M,M2M M2. .. of monomers CHA=CHB with CH2=CH2, or of CHA=CHA or CHA=CHB with CHD=CH2 or CHD=CHE are chiral (38, 268, 269). Several examples arc reported in 82-89 (Scheme 18). Chiral copolymers with more complex structure such as. .. M,M,M2M MiM2. . . may be obtained even from two vinyl monomers, as recently demonstrated by WulfF and Hohn (see 53) (93). The copolymers formed by monomer units, which (vide supra) themselves produce chiral homopolymers (270) are also chiral, unless accidental compensation occurs. 

After monomer conversion, apparently further formation of copolymers may be effected by a mechanism of mechanosynthesis in the polymer-polymer system. 

The formation of copolymer by polycondensation reaction was proved by IR analysis. The spectra show absorption band at 1470, 1640, 2990, and 3100 cm-1 characteristic of—C—O—NH— groups, at 3300 cm-1 for imine groups and at 920 cm-1 for primary amine groups. From the point of view of chemical composition, the polycondensation products are composed by a fraction insoluble in... 

Intractable polymers, such as polyvinyl chloride (PVC), may be flexibilized, to some extent, by the formation of copolymers, such as the copolymers of vinyl chloride and vinyl acetate or octyl acrylate, or by the addition of nonvolatile low-molecular-weight compounds (plasticizers) having solubility parameters similar to those of the polymer. Thus PVC is plasticized by the addition of dioctyl phthalate. The flexibility of these products is proportional to the amount of plasticizer added. Copolymers, such as the vinyl chloride-vinyl acetate copolymer, require less plasticizer to obtain the same degree of flexibility. 

In summary, the acid-catalyzed condensation polymerization of sugars in methyl sulfoxide results in the formation of copolymers of the sugars with formaldehyde. The glycosyl residues probably occur in blocks, instead of being evenly separated by methylene bridges. The polymers are highly branched, and the glycosyl residues appear to be substituted in a random fashion. 

Terpolymers made from two different olefins and CO are known. They were first described in Brubaker s initial patent and involved the free radical initiated terpolymerization of CO and C2H with another olefin such as propylene, isobutylene, butadiene, vinyl acetate, diethyl maleate or tetrafluoroethylene More recently, in another patent, Hammer has described the free radical initiated terpolymerization of CO and C2H with vinyl esters, vinyl ethers or methyl methacrylate 26Reaction temperatures of 180-200 °C and a combined pressure of 186 MPa were employed. Typically a CO QH4 olefin molar ratio of 10 65 25 was observed in the terpolymers. In other patents, Hammer 27,28) has described the formation of copolymers with pendant epoxy groups by the free radical initiated polymerization of CO, QH4, vinyl acetate and glycidyl methacrylate. Reaction conditions similar to those stated above were employed, and a typical CO C2H vinyl acetate glycidyl methacrylate molar ratio of 10 65 20 5 was observed in the product polymer. 

X-ray examination of cellulose, which had been y-irradiated, showed no change in the degree of crystallinity of the cellulose (2, 5). Similarly, x-ray examinations of cellulose copolymers have not demonstrated conclusively that the formation of copolymers decreased the crystallinity of cellulose (54, 55, 57). 

There are several ways of using the olefin metathesis reaction to generate copolymers. Occasional reference has been made earlier to the formation of copolymers. Here we give further illustrations. For the ADMET copolymerization of linear dienes, see Section VII.C. 

The same authors report the formation of copolymers and terpolymers of tetramethylene urea, 7-butyrolactone, and ethylene carbonate or 1,2-propylene carbonate <2004MM6755>. 

The alicyclic epoxide, limonene oxide, which is obtained from a renewable resource has shown modest activity compared to CHO for reaction with C02 to provide a copolymer. This significant decrease in reactivity is presumably due to the steric influence of a disubstitution at one of the ipso carbon centers. Of course, in either highly selective reaction, where complete formation of copolymer or cyclic carbonate occurs, the process displays 100% atom economy. The environmental attractiveness of this process is further enhanced by the fact that reactions are generally carried out in the absence of an organic cosolvent, that is, in C02-swollen epoxide solutions. 

An Interpretative review of the reactions initiated by macrocellulosic free radicals with vinyl monomers to yield block and graft copolymers of fibrous cellulose was made. Macrocellulosic radicals are usually formed by interactions with radiation or chemical redox systems. Important factors in these heterogeneous reactions are lifetimes and accessibilities of the radicals and interactions of solutions of monomer with fibrous cellulose. Changes in organochemical, macromolecular, and morphological structures in cellulosic fibers through formation of copolymers are made. 

To prove formation of copolymers with regular disposition of cyclic fragments in macromolecular backbone, some copolymers were fractionated into several fractions. Results of the ultimate analysis have indicated that the values detected for fractions coincide with the calculated ones, which rep-resents direct proof of the regular structure of copolymers. 

From the experimental results (Fakirov, 1999) and taking into account the experimental conditions used for the coreactive blending (275-290 °C, a treatment time of 45 min, the presence of a transesterification catalyst), one has to assume the occurrence of intensive chemical interactions. It is also to be expected that these reactions will lead not only to the formation of copolymers, but will also result in a more or less complete randomization of the sequential order of the repeating units (eq. (5.8)). If this is the case, the initially two-component blends should be converted into one-component ones. The latter represent one-phase systems (copolymeric material) whenever randomization (i.e. amorphization) takes place. That this occurs can be concluded from the DSC curves shown in Fig. 5.6. In contrast to the homopolymer PET the blends do not crystallize and they exhibit only one glass transition temperature. 

In conclusion, when working with blends of condensation polymers, one always has to take into account the possibility of chemical interaction and the formation of copolymers. The extent of this reaction is important because it is possible to obtain a one-component, as well as a one-phase, system when the blocky sequential order is converted to a random one. Such systems are very appropriate for the verification of relationships reflecting the effect of composition on various properties since they are free from other factors. Finally, in such cases one is dealing with copolymers distinguished by the creation of new chemical bonds, not with blends, although initially two or more homopolycondensates are mixed. 

Figure 7.36 shows that natural graphite Irom Siberia can be used to synthesize copolymers with different properties.An increase in the specific surface area results in the formation of copolymers with shorter blocks. By varying the structure of the filler and its concentration, one is able to tailor copolymers to a desired structure. 

The conductivity of the PAn/HA emeraldine salts (ES) is dependent upon the temperature9 as well as humidity and, hence, polymer water content.10-11 In general, attachment of functional groups decreases the conductivity, whereas the formation of copolymers between aniline and functionalized aniline results in polymers with intermediate conductivity. In addition, the preparation conditions,12-13 particularly as... 

---