A heteropolymer or copolymer is a polymer derived from two (or more) monomeric species, as opposed to a homopolymer where only one monomer is used. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds [1] Copolymerization refers to methods used to chemically synthesize a copolymer.
Commercially relevant copolymers include ABS plastic, SBR, Nitrile rubber, styrene-acrylonitrile, styrene-isoprene-styrene (SIS) and ethylene-vinyl acetate. Acrylonitrile butadiene styrene or ABS, ( Chemical formula (C8H8· C4H6·C3H3Nn is Styrene-Butadiene ( SBR) is an Elastomeric Copolymer consisting of Styrene and Butadiene. Nitrile rubber or Buna-N, is a Synthetic rubber Copolymer of Acrylonitrile (ACN and Butadiene. Styrene acrylonitrile resin is a Copolymer Plastic consisting of Styrene and Acrylonitrile. Ethylene vinyl acetate (CAS# 24937-78-8 also known as EVA) is the copolymer of Ethylene and Vinyl acetate.
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Types of copolymers
Since a copolymer consists of at least two types of constitutional units (not structural units), copolymers can be classified based on how these units are arranged along the chain. In Polymer chemistry, a structural unit is a building block of a Polymer chain and related to the Repeat unit. In Polymer chemistry, a structural unit is a building block of a Polymer chain and related to the Repeat unit. [2] These include:
- Alternating copolymers with regular alternating A and B units (2)
- Periodic copolymers with A and B units arranged in a repeating sequence (e. g. (A-B-A-B-B-A-A-A-A-B-B-B)n
- Random copolymers (or Statistical Copolymers) with random sequences of monomer A and B (3)
- Block copolymers comprised of two or more homopolymer subunits linked by covalent bonds (4). The union of the homopolymer subunits may require an intermediate non-repeating subunit, known as a junction block. Block copolymers with two or three distinct blocks are called diblock copolymers and triblock copolymers, respectively.
Copolymers may also be described in terms of the existence of or arrangement of branches in the polymer structure. Linear copolymers consist of a single main chain whereas branched copolymers consist of a single main chain with one or more polymeric side chains.
Other special types of branched copolymers include star copolymers, brush copolymers, and comb copolymers.
A terpolymer is a copolymer consisting of three distinct monomers. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other The term is derived from ter (Latin), meaning thrice, and polymer. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds
Graft copolymers
Graft copolymers are a special type of branched copolymer in which the side chains are structurally distinct from the main chain. The illustration (5) depicts a special case where the main chain and side chains are composed of distinct homopolymers. However, the individual chains of a graft copolymer may be homopolymers or copolymers. Note that different copolymer sequencing is sufficient to define a structural difference, thus an A-B diblock copolymer with A-B alternating copolymer side chains is properly called a graft copolymer.
For example, suppose we perform a free-radical polymerization of styrene in the presence of polybutadiene, a synthetic rubber, which retains one reactive C=C double bond per residue. Radical polymerization is a type of Polymerization in which the Reactive center of a polymer chain consists of a radical. Polybutadiene is a Synthetic rubber that is a Polymer formed from the Polymerization of the Monomer 13-butadiene. Elastomer Synthetic rubber is any type of artificially made Polymer material which acts as an Elastomer. We get polystyrene chains growing out in either direction from some of the places where there were double bonds, with a one-carbon rearrangement. Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene Or to look at it the other way around, the result is a polystyrene backbone with polybutadiene chains growing out of it in both directions. This is an interesting copolymer variant in that one of the ingredients was a polymer to begin with.
As with block copolymers, the quasi-composite product has properties of both "components". A heteropolymer or copolymer is a Polymer derived from two (or more Monomeric species as opposed to a Homopolymer where only one monomer is Composite materials (or composites for short are engineered Materials made from two or more constituent materials with significantly different physical or chemical In the example cited, the rubbery chains absorb energy when the substance is hit, so it is much less brittle than ordinary polystyrene. The product is called high-impact polystyrene, or HIPS.
Block Copolymers
A special kind of copolymer is called a "block copolymer". Block copolymers are made up of blocks of different polymerized monomers. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other For example, PS-b-PMMA is short for polystyrene-b-poly(methyl methacrylate) and is made by first polymerizing styrene, and then subsequently polymerizing MMA from the reactive end of the polystyrene chains. Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene Methyl methacrylate is an Organic compound with the formula CH2=C(CH3CO2CH3 Styrene, also known as vinyl benzene as well as many other names (see table is an Organic compound with the Chemical formula C6H5CH=CH2 This polymer is a "diblock copolymer" because it contains two different chemical blocks. You can also make triblocks, tetrablocks, multiblocks, etc. Diblock copolymers are made using living polymerization techniques, such as atom transfer free radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT), ring-opening metathesis polymerization (ROMP), and living cationic or living anionic polymerizations. In Polymer chemistry, living polymerization is a form of Addition polymerization where the ability of a growing Polymer chain to terminate has ATRP or Atom Transfer Radical Polymerization is a Polymerization reaction involving free radicals. RAFT or Reversible addition&ndashfragmentation chain transfer is a form of living radical polymerization. Ring-opening metathesis polymerization (ROMP is a type of Olefin metathesis Polymerization that produces industrially important products In Polymer chemistry, living polymerization is a form of Addition polymerization where the ability of a growing Polymer chain to terminate has
Phase separation
Block copolymers are interesting because they can "microphase separate" to form periodic nanostructures, as in the styrene-butadiene-styrene block copolymer shown at right. The polymer is known as Kraton and is used for shoe soles and adhesives. Glue or adhesive is a compound that adheres or bonds two items together Owing to the microfine structure, the transmission electron microscope or TEM was needed to examine the structure. The butadiene matrix was stained with osmium tetroxide to provide contrast in the image. Osmium tetroxide is the Chemical compound with the formula OsO4 The material was made by living polymerization so that the blocks are almost monodisperse, so helping to create a very regular microstructure. In Polymer chemistry, living polymerization is a form of Addition polymerization where the ability of a growing Polymer chain to terminate has A collection of objects are called monodisperse or monosized if they have the same size shape and mass The molecular weight of the polystyrene blocks in the main picture is 102,000; the inset picture has a molecular weight of 91,000, producing slightly smaller domains. The molecular mass (abbreviated m of a substance, more commonly referred to as molecular weight and abbreviated as MW, is the Mass of one Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene
Microphase separation is a situation similar to that of oil and water. An oil is a substance that is in a viscous Liquid state ( "oily") at ambient temperatures or slightly warmer and is Water is a common Chemical substance that is essential for the survival of all known forms of Life. Oil and water are immiscible - they phase separate. With two immiscible blocks, block copolymers undergo a similar phase separation. Because the blocks are covalently bonded to each other, they cannot demix macroscopically. In "microphase separation" the blocks form nanometer-sized structures. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a Depending on the relative lengths of each block, several morphologies can be obtained. Sufficiently different block lengths lead to nanometer-sized spheres of one block in a matrix of the second (for example PMMA in polystyrene). Poly(methyl methacrylate ( PMMA) or poly(methyl 2-methylpropenoate is a Thermoplastic and transparent Plastic. Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene By using less different block lengths, a cylinder geometry can be obtained. Blocks of similar length form stripes (often called lamellae in the technical literature). Between the cylindrical and lamellar phase is the gyroid phase. A gyroid is an infinitely connected triply periodic Minimal surface discovered by Alan Schoen in 1970 The nanoscale structures created from block copolymers could potentially be used for creating devices for use in computer memory, nanoscale-templating and nanoscale separations. In Psychology, memory is an organism's ability to store retain and subsequently retrieve information
Polymer scientists use thermodynamics to describe how the different blocks interact. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " The interaction parameter, also called "chi" gives an indication of how different, chemically, the two blocks are and whether or not they will microphase separate. Flory-Huggins solution theory is a Mathematical model of the Thermodynamics of Polymer Solutions which takes account of the great dissimilarity Chi ( Uppercase Χ, Lowercase χ; Χι He is the 22nd letter of the Greek alphabet, pronounced as in English If the product of chi and the degree of polymerization is large (greater than 10. 5), the blocks will microphase separate. If the product of chi and the degree of polymerization is too small (less than 10. 5), the different blocks are able to mix.
Copolymer equation
An alternating copolymer has the formula: -A-B-A-B-A-B-A-B-A-B-, or -(-A-B-)n-. The molar ratios of the monomer in the polymer is close to one, which happens when the reactivity ratios r1 & r2 are close to zero, as given by the Mayo-Lewis equation also called the copolymerization equation:[3]
![\frac {d\left [M_1 \right]}{d\left [M_2\right]}=\frac{\left [M_1\right]\left (r_1\left[M_1\right]+\left [M_2\right]\right)}{\left [M_2\right]\left (\left [M_1\right]+r_2\left [M_2\right]\right)}](../../../../math/d/e/a/dea8c560dd0363f25dc92f414a5b64f6.png)
where r1 = k11/k12 & r2 = k22/k21
Copolymer engineering
Copolymerization is used to modify the properties of man-made plastics to specific needs, for example to reduce crystallinity, modify glass transition temperature or to improve solubility. The Mayo-Lewis equation or copolymer equation in Polymer chemistry describes the distribution of Monomers in a Copolymer: Taking into consideration The glass transition temperature, T g is the temperature at which an Amorphous solid, such as Glass or a Polymer, becomes brittle It is a way of improving mechanical properties, in a technique known as rubber toughening. Many Thermoplastics such as Polystyrene and PMMA are brittle when stressed a property which limits applications Elastomeric phases within a rigid matrix act as crack initiators, and so increase the energy absorption when the material is impacted for example. Acrylonitrile butadiene styrene is a common example. Acrylonitrile butadiene styrene or ABS, ( Chemical formula (C8H8· C4H6·C3H3Nn is
External links
- http://www.chem.rochester.edu/~chem421/copoly.htm
- Block Copolymers: Institute of Physical & Theoretical Chemistry, University of Regensburg, Regensburg, Germany
- Distance learning course in polymers
- Polymer structures
See also
References
- ^ Odian, G. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Tholin (after the Greek word for muddy is a Heteropolymer formed by solar Ultraviolet irradiation of simple Organic compounds such as Methane Principles of Polymerization, 4th Ed. , Wiley-Interscience, Hoboken, NJ 2004, Ch. 6. ISBN 0-471-27400-3
- ^ IUPAC. "Glossary of Basic Terms in Polymer Science". Pure Appl. Chem. 1996, 68, 2287-2311
- ^ Copolymerization. I. A Basis for Comparing the Behavior of Monomers in Copolymerization; The Copolymerization of Styrene and Methyl MethacrylateFrank R. Mayo and Frederick M. Lewis J. Am. Chem. Soc.; 1944; 66(9) pp 1594 - 1601; doi:10.1021/ja01237a052
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