Polymers Large molecules copolymers

Table 10 contains some selected permeabiUty data including diffusion and solubiUty coefficients for flavors in polymers used in food packaging. Generally, vinyUdene chloride copolymers and glassy polymers such as polyamides and EVOH are good barriers to flavor and aroma permeation whereas the polyolefins are poor barriers. Comparison to Table 5 shows that the large molecule diffusion coefficients are 1000 or more times lower than the small molecule coefficients. The solubiUty coefficients are as much as one million times higher. Equation 7 shows how to estimate the time to reach steady-state permeation t if the diffusion coefficient and thickness of a film are known. 

A polymer is a large molecule (macromolecule) constructed from many smaller structural units called monomers. When only one species of monomer is used to build a macromolecule, it is known as a homopolymer, two species a copolymer, three species a terpolymer. 

Migrating antistats are satisfactory solutions in many cases, but inherendy dissipating polymers (IDPs) or conductive polymers added to POs induce permanent antistatic/ESD properties. Two main advantages of these materials are usually dted in the literature (1) IDPs are large molecules that are not consumed, so they provide stable antistat/ESD properties over time and (2) IDPs do not bloom to the surface, so they cannot be "wiped off" and do not affect other surface properties. They are also usually clear, thermally stable, and some are much less affected by humidity than migrating antistats. Permanent polymeric antistats are usually conductive block copolymers that form continuous conductive networks when added to a polymer matrix. Many IDPs are not compatible with POs the ones discussed below are compatible [6-16,6-20, 6-28). 

Synthetic polymers are large molecules which are made up of many repeating subunits. Synthetic polymers can be classified as linear or branched, depending on their structure (Mendes et ah, 2013). Examples of branched polymers are dendrimers whereas block copolymers are linear polymers (Mendes et ah, 2013). 

Graft copolymer (8.6) Material whose molecules contain large segments of one type of molecule grafted onto or attached to chains of a second type of polymer. The graft copolymer will display properties of each of the constiment polymers. 

Polymers are produced via polymerisation techniques, such as anionic, cationic, step-growth and so on, which result in the formation of large molecules from monomers. The use of one type of monomer results in a homopolymer, whereas the use of two or more different monomers leads to the formation of copolymers. Polymerisation is usually controlled by the addition of a catalyst or initiator, and polymers produced by these techniques are thermoplastic in nature. 

The term polymer describes materials which are large molecules. They are also called resins and macromolecules by industrialists and academics respectively. The main classes of polymers are plastics, elastomers (or rubbers), fibres and films. Polymers are effect chemicals—that is, they fulfil a particular application. Originally they were made—or accidentally discovered as in the case of polyethylene (PE) or polytetrafluoroethylene (PTFE)—and end-uses found for them. However, increased knowledge of properties such as toughness and strength together with experience gained with fillers and plasticizers, makes it possible to predict the properties of new polymers, copolymers or blends to the extent that the new polymeric materials are manufactured to serve a particular application. 

Polymers are large molecules made of many repeating units called monomers. A copolymer consists of two or more different monomers. 

Thus a polymer is a substance consisting of large molecules formed by the joining together of simple molecules that are known as monomers where two or more monomers are involved the resultant product is known as a copolymer. As an example, polymerization of ethylene forms a... 

The importance of the copolymer concept to polymer science and engineering can not be overemphasized. Essentially, it was the realization of various methods to incorporate two or more compositionally different repeating units into the large molecules that provided practically unlimited versatility to macromolecular synthesis... 

Polymers are, by definition, molecules composed by a large number of small chemical units, the monomers. Above, we have discussed A- and B-homopolymers, assuming that all A-polymers are composed of the same single A-monomer, and B-polymers by another specific B-monomer. Such chemical equality is often the situation in synthetic polymers, as for example polyethylene purely composed of -CH2- ethylene monomers. Many natural polymers, on the other hand, are composed of several different monomers example of these include proteins, which are polymeric chains composed of different amino acids such polymers are termed copolymers. 

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