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Metal alloying is widely used to improve metal properties, and while many polymers used today are relatively pure (e.g., polystyrene, nylon), an increasing number are mixtures of two or more polymers. One reason for doing so, as with metals, is to broaden the range of properties. The main practical issue is that homopolymers blend poorly, and even where blends are possible, as in some thermoplastics, phase separation can occur easily. Copolymerization, a process that polymerizes a mixture of monomers, is frequently used to solve this problem. Because of the possibility of branching, structural isomerism within a single monomer, and the way the different repeat units can be added together, it provides a much wider range of structures than mixing homopolymers. Furthermore, composition and, of course, molecular mass can be varied to achieve the desired balance of properties in the finished product.
Overview
Manipulation of the order of repeat units along the length of the chain is a central problem in copolymerization. As an example, consider the copolymerization of two monomers, A and B. The chain could begin with either a molecule of A or a molecule of B, and there are always two options for which monomer molecule will be attached at each subsequent addition. Because a copolymer is made up of at least two different types of constituent units (also known as structural units), copolymers can be classified according to how these units are arranged along the chain. Linear copolymers, which include alternating copolymers, statistical copolymers, and block copolymers, are made up of a single main chain. Branched copolymers are made up of a single main chain and one or more polymeric side chains, and they can be grafted, star-shaped, or have other architectures.
Copolymerization
Typically, a copolymer is a polymer derived from more than one monomer species in polymer chemistry. Copolymerization is the polymerization of monomers into copolymers. Now, we can say that bipolymers are copolymers created by the copolymerization of two monomer species. Terpolymers and quaterpolymers are those formed from three and four monomers, respectively.
Promotional copolymers include acrylonitrile butadiene styrene (ABS), styrene/butadiene co-polymer (SBR), nitrile rubber, styrene-acrylonitrile, styrene-isoprene-styrene (SIS), and ethylene-vinyl acetate, which are all formed by chain-growth polymerization. Another method of production is step-growth polymerization, which is used to create the nylon-12/6/66 copolymer of nylon 12, nylon 6, and nylon 66, as well as the copolyester family.
Examples of copolymer
The general examples of copolymers includes polyethylene-vinyl acetate (PEVA), nitrile rubber, and acrylonitrile butadiene styrene.
The copolymer of ethylene and vinyl acetate is being called ethylene-vinyl acetate (EVA), also known as polyethylene-vinyl acetate (PEVA). The weight percent of vinyl acetate typically ranges between 10 and 40%, with the remainder being ethylene. There are three types of EVA copolymer, which differ in their vinyl acetate (VA) content and how they are used. Vinyl acetate modified polyethylene refers to an EVA copolymer based on a low proportion of VA (approximately up to 4%). It is a copolymer that is processed as a thermoplastics material in the same way that low density polyethylene is. It has some of the properties of low density polyethylene, but with increased gloss (suitable for film), softness, and flexibility. The material is generally thought to be non-toxic.
Nitrile rubber is said to be a synthetic rubber which derived from acrylonitrile (ACN) and butadiene. It is also being known as nitrile butadiene rubber, NBR, Buna-N, and acrylonitrile butadiene rubber. Perbunan, Nipol, Krynac, and Europrene are some brand names. This rubber is unique in that it is resistant to oil, gasoline, and other chemicals. In the automotive and aerospace industries, NBR is used to make fuel and oil handling hoses, seals, grommets, and self-sealing fuel tanks. It is used to make protective gloves in the nuclear industry. The high temperature stability of NBR from 40 to 108 °C (40 to 226 °F) makes it an ideal material for aeronautical applications. Nitrile butadiene is also used in the manufacturing of moulded goods, footwear, adhesives, sealants, sponges, expanded foams, and floor mats.
Acrylonitrile butadiene styrene is indeed a tough and impact-resistant copolymer. It is considered as a thermoplastic composed of three monomers: acrylonitrile, butadiene, and styrene. Acrylonitrile is made from propylene and ammonia, which gives it thermal stability and chemical resistance. ABS is tough due to the presence of butadiene, a byproduct of ethylene production from steam crackers. Styrene is made by dehydrogenating ethyl benzene, which increases its rigidity and is used to make dash boards, wheel covers, pipe, door handle, bumpers, automotive trim, interior and exterior panel applications.
Types of copolymerization
Copolymers are classified according to their structure. Those with a single chain are known as linear copolymers, while those with polymeric side chains are known as branched copolymers.
Linear copolymers: Linear copolymers, which would include alternating copolymers, statistical copolymers, and block copolymers, are made up of a single main chain. Through spontaneous or sequential ATRP of two or more monomers with precise control of molar mass, composition, and functionality, a wide range of copolymers can be prepared. For the first time in a radical process, the use of a difunctional initiator enables the preparation of functional homo-telechelic polymers with almost any desired chain end functionality. The reaction ratio of co-monomers in a CRP is very similar to the values found in free radical copolymerization, though there are some factors that affect CRP processes with intermittent activation, such as differences in repetitive activation or deactivation and adequate time for complete system re-equilibration, which can result in different rates of comonomer consumption.
Branched copolymers: Branched copolymers are made up of a single main chain and one or more polymeric side chains, and they can be grafted, star-shaped, or have other architectures. Nonlinear copolymer architectures can take a variety of forms. Brush copolymers and comb copolymers are two common types of branched copolymers, in addition to the grafted and star polymers discussed below.
Graft copolymers are really a type of branched copolymer in which the side chains differ structurally from the main chain. Typically, the main chain is formed from one type of monomer (A), and the branches are formed from a different monomer (B), or the side-chains have constitutional or configurational features that differ from those found in the main chain.
A graft copolymer’s individual chains can be homopolymers or copolymers. Because different copolymer sequencing is sufficient to define a structural difference, an A-B diblock copolymer with A-B alternating copolymer side chains is correctly referred to as a graft copolymer. Polystyrene chains, for example, can be grafted onto polybutadiene, a synthetic rubber with one reactive C=C double bond per repeat unit. Polybutadiene is dissolved in styrene, which is then polymerized using free radicals. Growing chains of polystyrene can add across the double bonds of rubber molecules, forming polystyrene branches. Graft copolymers are created by combining ungrafted polystyrene chains and rubber molecules.
Copolymers account for a sizable portion of commercial polymers. They differ in terms of both the composition and distribution of the various monomers along the backbone. The monomers can have similar or very different physical properties, resulting in a wide range of copolymers with a wide range of properties and end-uses.
FAQs
What is the difference between polymerization and copolymerization?
Polymerization is the chemical reaction of bonding together multiple identical units (monomers) to form a polymer, while copolymerization is the polymerization of multiple monomers to form a copolymer.
What are copolymers used for?
Block copolymers are frequently used in adhesives, surfactants, membranes, foams, and cosmetics.
Why is copolymer better than homopolymer?
Copolymers have typically outperformed homopolymer POMs in terms of centreline porosity, property retention over a longer period of time, and slightly lower crystallinity. Lower crystallinity results in a lower melting temperature for copolymer, and a lower melting temperature results in a faster cycle time and higher productivity.
