Copolymers of Two or More Monomers

Ziegler-NattaCatalysts 1230 26-5 Natural and Synthetic Rubbers 1230 26-6 Copolymers of Two or More Monomers 1232 26-7 Condensation Polymers 1232 26-8 Polymer Structure and Properties 1236 EssentialTerms 1239 Study Problems 1240... 

The morphology of copolymers of two or more monomers with a statistical and alternating configuration of the different monomers is determined by the morphology of the related homopolymers. Occasionally, they can reveal a weak phase separation between the components. One example is SAN if the composition does not follow the azeotropic composition (76 mol% S, 24 mol% AN) see Fig. 1.3 and also Fig. 1.55 in Part 11. 

Gradient copolymers are defined as copolymers of two or more monomers, whose composition profile varies along the chain, reflecting variation in monomer concentrations as conversion proceeds. As a conseqnence, gradient copolymers combine the properties of the homopolymers in a way that depends on the nature of the composition profile. 

The T of a polymer can be altered by the copolymerization of two or more monomers. The approximate T value for copolymers can be calculated from a knowledge of the weight fraction W of each monomer type and the T (in degees kelvin) of each homopolymer (12). 

Statistical copolymers are formed when mixtures of two or more monomers are polymerized by a radical process. Many reviews on the kinetics and mechanism of statistical copolymerization have appeared1 9 and some detail can be found in most text books on polymerization. The term random copolymer, often used to describe these materials, is generally not appropriate since the incorporation of monomer units is seldom a purely random process. The... 

Mixtures of two or more monomers can polymerize to form copolymers. Many copolymers have been developed to combine the best features of each monomer. For example, poly(vinyl chloride) (called a homopolymer because it is made from a single monomers) is brittle. By copolymerizing vinyl chloride with vinyl acetate, a copolymer is obtained that is flexible. Arrangement of the monomer units in a copolymer depends on the rates at which the monomers react with each other. Graft copolymers are formed when a monomer is initiated by free radical sites created on an already-formed polymer chain. 

Block copolymer synthesis from living polymerization is typically carried out in batch or semi-batch processes. In the simplest case, one monomer is added, and polymerization is carried out to complete conversion, then the process is repeated with a second monomer. In batch copolymerizations, simultaneous polymerization of two or more monomers is often complicated by the different reactivities of the two monomers. This preferential monomer consumption can create a composition drift during chain growth and therefore a tapered copolymer composition. 

Copolymerisation is the process in which a mixture of two or more monomers gets polymerised to yield a product. The product obtained is known as a copolymer. A copolymer product contains some units of each type of monomer and is different from a physical mixture of individual polymer molecules formed by different monomers. It is not always possible to make a copolymer with any two or more monomers. When two monomers A and B are copolymerised the rate of polymerisation is determined by concentration of monomers. Four different propagation reaction can occur for copolymerisation of A and B. AA, AB, BB, BA". 

The range of properties of polymers can be greatly extended and varied by copolymerization of two or more monomers. The effects of radiation on copolymers would be expected to show similarities to the homopolymers, but major differences from linear relationships are often experienced. Aromatic groups in one monomer frequently show an intramolecular protective effect so that the influence of that monomer may be much greater than its mole fraction. The Tg of a copolymer is normally intermediate between the homopolymers, except for block copolymers, and this can cause a discontinuity in radiation degradation at a fixed temperature. 

The term statistical copolymer is proposed here to embrace a large proportion of those copolymers that are prepared by simultaneous polymerization of two or more monomers in admixture. Such copolymers are often described in the literature as random copolymers , but this is almost always an improper use of the term random and such practice should be abandoned. 

Copolymers are composed of two or more monomers. Source-based names are conveniently employed to describe copolymers using an appropriate term between the names of the monomers. Any of half a dozen or so connecting terms may be used depending on what is known about the structure of the copolymer. When no information is known or intended to be conveyed, the connective term co is employed in the general format poly(A-co-B), where A and B are the names of the two monomers. An unspecified copolymer of styrene and methyl methacrylate would be called poly[styrene-co-(methyl methacrylate)]. 

By copolymerization we understand the mutual polymerization of two or more monomers, with the resulting macromolecules containing repeating units of all the participating monomers. Depending on the distribution of the monomers in the macromolecules one differentiates four types of copolymers (nomenclature of copolymers see Sect.1.2) ... 

Latexes are usually copolymer systems of two or more monomers, and their total solids content, including polymers, emulsifiers, stabilizers etc. is 40-50% by mass. Most commercially available polymer latexes are based on elastomeric and thermoplastic polymers which form continuous polymer films when dried [88]. The major types of latexes include styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), polyacrylic ester (PAE) and epoxy resin (EP) which are available both as emulsions and redispersible powders. They are widely used for bridge deck overlays and patching, as adhesives, and integral waterproofers. A brief description of the main types in current use is as follows [87]. 

As is well known from free radical copolymerization theory, the composition of the copolymers will depend only on the propagation reaction. The relative ability of monomer to add to a growing chain is influenced by the nature of the last chain unit and by the relative concentration. Generally, chain transfer to monomer by polymer radicals will occur to an appreciable extent, and the final product will be made up of homopolymers, multisegment block copolymers, and branched and grafted structures. In the presence of two or more monomers,... 

Copolymer A polymeric material formed by the reaction of two or more monomers. 

Sequential Oxidation of DMP and DPP. The usual approach to formation of block copolymers is by the sequential polymerization of two or more monomers or by linking together preformed homopolymer blocks. In view of the importance of the redistribution process in the oxidative coupling of phenols there can be no assurance that successive polymerization of two phenols will yield block copolymers under any conditions. It is certain, however, that block copolymers can be formed only if the conditions are such that polymerization of the second monomer is much faster than redistribution of the added monomer with the polymer previously formed from the first. The extent of redistribution is followed conveniently by noting the effect of added monomer on solution viscosity, as indicated by the efflux time from a calibrated pipet. 

Copolymerization. Introducing a comonomer (one of the compounds comprising the monomer) with known glass transition temperature, Tgl, into a polymer with known Tg 2 to form a copolymer (a polymer comprised of two or more monomers) can affect the glass transition temperature. If the two homopolymers (polymer... 

Grafted block copolymers of activated cellulose (cell ) are formed by immersing the activated cellulose in a solution of two or more monomers (M and m). Typical reactions include ... 

Random copolymer—A copolymer that has a random sequence of two or more monomer units. 

Propagation in a mixture of two or more monomers, as any other chemical reaction, is determined by thermodynamic and kinetic factors. Either a mixture of homopolymers or, more often a copolymer is formed with varying monomer order in the chains. The propagation of two... 

Now, if a mixture of two (or more) monomers is allowed to undergo polymerization, there is obtained a copolymer a polymer that contains two (or more) kinds of monomeric units in the same molecule. For example ... 

The most important industrial applications of radical reaction to date are used for the manufacture of polymers. Around 108 tonnes (or 75%) of all polymers are prepared using radical processes. These are chain reactions in which an initial radical adds to the double bond of an alkene monomer and the resulting radical adds to another alkene monomer and so on. This addition polymerisation is used to make a number of important polymers, including poly(vinyl chloride) (PVC), polystyrene, polyethylene and poly(methyl methacrylate). Copolymers can also be easily prepared starting from a mixture of two or more monomers. These polymers have found widespread use as they possess a range of chemical and mechanical properties (such as strength and toughness). 

In the preceding chapter we have considered free-radical polymerizations where only one monomer is used to produce a homopolymer. However, chain polymerizations can be carried out with mixtures of two or more monomers to form polymeric products that contain two or more different structures in the polymer chain. This type of chain polymerization process in which two or more monomers are simultaneously polymerized is termed a copofymerization and the product is a copolymer. It is important to note that the copolymer is not an alloy of two or more homopolymers but contains units of all the different monomers incorporated into each copolymer molecule. The process can be depicted, for copolymerization of two monomers, as... 

We have considered so far free-radical polymerizations where only one monomer is used and the product is a homopdlymer. The same type of polymerization can also be carried out with a mixture of two or more monomers to produce a polymer product that contains two or more different mer units in the same polymer chain. The polymerization is then termed a copolymerization and the product is termed a copolymer. Monomers taking part in copolymerization are referred to as comonomers. The simultaneous polymerization of two monomers is known as binary copolymerization and that of three monomers as ternary copolymerization, and so on. The term multicomponent copolymerization embraces all such cases. The relative proportions of the different mer units in the copolymer chain depend on the relative concentrations of the comonomers in the feed mixture and on their relative reactivities. This will be the main subject of our discussion in this chapter. 

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