Get Android App. Get iOS App. What is not true about polymers? Polymers Report Error. Solution: Polymers have high molecular weights.
Questions from Polymers. Many techniques have been developed to determine the molecular weight of polymer [ 8 ]. Which technique to use is dependent on many factors such as the size of the polymer, the ease of access and operation of the equipment, the cost of the analysis, and so on.
For polymer molecular weight is less than 50,, its molecular weight can be determined by the end group analysis. The methods for end group analysis include titration, elemental analysis, radio active tagging, and spectroscopy. Infrared spectroscopy IR , nuclear magnetic resonance spectroscopy NMR , and mass spectroscopy MS are commonly used spectroscopic technique.
The 2 in the numerator takes into account that two end groups are being counted per molecule. The acid number is defined as the number of milligrams of base required to neutralize 1 g of polyester which is used to monitor the progress of polyester synthesis in industry.
Schematic representation of a membrane osmometer [ 2 ]. Plot of reduced osmotic pressure versus concentration [ 2 ].
Zimm plot of light-scattering data of polymer [ 2 ]. Schematic of a laser light scattering photometer [ 2 ]. Schematic of cone-plate rotational viscometer [ 2 ]. Simple illustrations of the principle of gel permeation chromatography GPC [ 9 ]. Adapted from I. Campbell, Introduction to Synthetic Polymers, Oxford, , p. The right peak is PS.
The peak of copolymer is shifted to the left due to the addition of P2VP. How many paper clips does one need to string together?
In general, the viscosity of polymer is reduced by increasing temperature. This is the basis for all weather multi viscosity motor oils. Discuss the value of knowledge of the molecular weight and distribution of a polymer to the polymer scientist and engineer. Which method would you use to obtain this information on a routine basis in the laboratory and in the production respectively?
Which method would you use to obtain this information for a new polymer type which is not previously known? What would be the number average, weight average molecular weight and polydispersity of a sample of polypropylene that consists of 5 mol of unit propylene and 10 mol of 10, unit propylene? Titration of the reaction mixture with 0.
What is the number average molecular weight of the polyester? Would this method be suitable for determining any polyester? Explain how one might experimentally determine the Mark-Houwink-Sakurada constants K and a for a given polymer. If the PDI of polystyrene is larger than 1. Please calculate the end-to-end distance of a polymer with molecular weight of 1 million and intrinsic viscosity of 2. What is the solution behavior of this polymer?
Skip to main content Skip to sections. This service is more advanced with JavaScript available. Advertisement Hide. Polymer Size and Polymer Solutions. Authors Authors and affiliations Wei-Fang Su. Chapter First Online: 09 October This process is experimental and the keywords may be updated as the learning algorithm improves. Download chapter PDF. To have strong durable mechanical properties, the polymer has to have molecular weight much larger than 10, for structural applications.
However, for thin film or other special application, low molecular weight polymer or oligomer sometime is adequate. As shown in Fig. HDPE is an excellent electrical insulator. Films made from LDPE stretch easily and are commonly used for wrapping. LDPE is insoluble in water, but softens and swells on exposure to hydrocarbon solvents.
It swells to more than double its size in nonpolar organic solvents like toluene, eventually dissolving, but is impermeable to water. The C 5 H 8 monomer isoprene is a volatile liquid b. Cotton absorbs water readily, but is unaffected by immersion in toluene or most other organic solvents.
Cellulose fibers may be bent and twisted, but do not stretch much before breaking. The monomer of cellulose is the C 6 H 12 O 6 aldohexose D-glucose. To account for the differences noted here we need to consider the nature of the aggregate macromolecular structure, or morphology , of each substance. Because polymer molecules are so large, they generally pack together in a non-uniform fashion, with ordered or crystalline-like regions mixed together with disordered or amorphous domains.
In some cases the entire solid may be amorphous, composed entirely of coiled and tangled macromolecular chains. Crystallinity occurs when linear polymer chains are structurally oriented in a uniform three-dimensional matrix. In the diagram on the right, crystalline domains are colored blue. Increased crystallinity is associated with an increase in rigidity, tensile strength and opacity due to light scattering.
Amorphous polymers are usually less rigid, weaker and more easily deformed. They are often transparent. Three factors that influence the degree of crystallinity are: i Chain length ii Chain branching iii Interchain bonding. As noted earlier, HDPE is composed of very long unbranched hydrocarbon chains. These pack together easily in crystalline domains that alternate with amorphous segments, and the resulting material, while relatively strong and stiff, retains a degree of flexibility.
In contrast, LDPE is composed of smaller and more highly branched chains which do not easily adopt crystalline structures. This material is therefore softer, weaker, less dense and more easily deformed than HDPE. As a rule, mechanical properties such as ductility, tensile strength, and hardness rise and eventually level off with increasing chain length. The nature of cellulose supports the above analysis and demonstrates the importance of the third factor iii.
To begin with, cellulose chains easily adopt a stable rod-like conformation. These molecules align themselves side by side into fibers that are stabilized by inter-chain hydrogen bonding between the three hydroxyl groups on each monomer unit.
Consequently, crystallinity is high and the cellulose molecules do not move or slip relative to each other. The high concentration of hydroxyl groups also accounts for the facile absorption of water that is characteristic of cotton. Natural rubber is a completely amorphous polymer. Unfortunately, the potentially useful properties of raw latex rubber are limited by temperature dependence; however, these properties can be modified by chemical change.
The cis-double bonds in the hydrocarbon chain provide planar segments that stiffen, but do not straighten the chain. If instead, the chains of rubber molecules are slightly cross-linked by sulfur atoms, a process called vulcanization which was discovered by Charles Goodyear in , the desirable elastomeric properties of rubber are substantially improved.
The following illustration shows a cross-linked section of amorphous rubber. By clicking on the diagram it will change to a display of the corresponding stretched section.
The more highly-ordered chains in the stretched conformation are entropically unstable and return to their original coiled state when allowed to relax click a second time. On heating or cooling most polymers undergo thermal transitions that provide insight into their morphology. These are defined as the melt transition, T m , and the glass transition, T g.
T m is the temperature at which crystalline domains lose their structure, or melt. As crystallinity increases, so does T m. T g is the temperature below which amorphous domains lose the structural mobility of the polymer chains and become rigid glasses. T g often depends on the history of the sample, particularly previous heat treatment, mechanical manipulation and annealing. It is sometimes interpreted as the temperature above which significant portions of polymer chains are able to slide past each other in response to an applied force.
The introduction of relatively large and stiff substituents such as benzene rings will interfere with this chain movement, thus increasing T g note polystyrene below. The introduction of small molecular compounds called plasticizers into the polymer matrix increases the interchain spacing, allowing chain movement at lower temperatures. The outgassing of plasticizers used to modify interior plastic components of automobiles produces the "new-car smell" to which we are accustomed.
T m and T g values for some common addition polymers are listed below. Note that cellulose has neither a T m nor a T g. Rubber is a member of an important group of polymers called elastomers. Elastomers are amorphous polymers that have the ability to stretch and then return to their original shape at temperatures above T g. This property is important in applications such as gaskets and O-rings, so the development of synthetic elastomers that can function under harsh or demanding conditions remains a practical goal.
At temperatures below T g elastomers become rigid glassy solids and lose all elasticity. A tragic example of this caused the space shuttle Challenger disaster.
The unexpectedly low temperatures on the morning of the launch were below this T g , allowing hot rocket gases to escape the seals. Symmetrical monomers such as ethylene and tetrafluoroethylene can join together in only one way.
Monosubstituted monomers, on the other hand, may join together in two organized ways, described in the following diagram, or in a third random manner. Most monomers of this kind, including propylene, vinyl chloride, styrene, acrylonitrile and acrylic esters, prefer to join in a head-to-tail fashion, with some randomness occurring from time to time. The reasons for this regioselectivity will be discussed in the synthetic methods section. If the polymer chain is drawn in a zig-zag fashion, as shown above, each of the substituent groups Z will necessarily be located above or below the plane defined by the carbon chain.
Consequently we can identify three configurational isomers of such polymers. If all the substituents lie on one side of the chain the configuration is called isotactic. If the substituents alternate from one side to another in a regular manner the configuration is termed syndiotactic. Finally, a random arrangement of substituent groups is referred to as atactic. Examples of these configurations are shown here.
Many common and useful polymers, such as polystyrene, polyacrylonitrile and poly vinyl chloride are atactic as normally prepared. Customized catalysts that effect stereoregular polymerization of polypropylene and some other monomers have been developed, and the improved properties associated with the increased crystallinity of these products has made this an important field of investigation.
The following values of T g have been reported. The properties of a given polymer will vary considerably with its tacticity. Thus, atactic polypropylene is useless as a solid construction material, and is employed mainly as a component of adhesives or as a soft matrix for composite materials.
In contrast, isotactic polypropylene is a high-melting solid ca. All the monomers from which addition polymers are made are alkenes or functionally substituted alkenes.
The most common and thermodynamically favored chemical transformations of alkenes are addition reactions. Many of these addition reactions are known to proceed in a stepwise fashion by way of reactive intermediates , and this is the mechanism followed by most polymerizations. A general diagram illustrating this assembly of linear macromolecules, which supports the name chain growth polymers , is presented here. Indeed, cases of explosively uncontrolled polymerizations have been reported.
Virtually all of the monomers described above are subject to radical polymerization. Since this can be initiated by traces of oxygen or other minor impurities, pure samples of these compounds are often "stabilized" by small amounts of radical inhibitors to avoid unwanted reaction. When radical polymerization is desired, it must be started by using a radical initiator , such as a peroxide or certain azo compounds. The formulas of some common initiators, and equations showing the formation of radical species from these initiators are presented below.
By using small amounts of initiators, a wide variety of monomers can be polymerized. One example of this radical polymerization is the conversion of styrene to polystyrene, shown in the following diagram. Low-density polyethylene LDPE —the squishy material that plastic bags and wrap like the kind you might wrap your sandwich in —is an example. The resulting polymer is stronger and has a higher density. An example is high-density polyethylene HDPE , used to make things like plastic bottles, food containers and plumbing pipes.
In contrast to thermoplastic polymers are thermosetting polymers. It is useful, though, for things like car tyres, since a tyre that melts in the heat is going to make for a pretty interesting drive to the beach. Glues and electrical components are also thermosetting polymers. As well as the arrangement of molecules, the properties of a polymer are also determined by the length of the molecular chain.
In a nutshell, longer equals stronger. This is because, as a molecule gets longer, the total binding forces between molecules are greater, making the polymer chain stronger. When more than a thousand carbon atoms line up in a chain of ethylene monomers, for example, the resulting polymer, polyethylene, is strong and flexible.
Developments in synthetic polymers go way beyond plastic bags and drink bottles. Flexible, electricity-conducting polymers may be the next big thing. Into virtual reality VR? In the not-too-distant future, you might be able to ditch the chunky goggles and pop in a pair of contact lenses instead, thanks to very thin, electricity-conducting polymer coatings. Australian scientists have also been working on lightweight, flexible solar cells which can be cheaply printed with polymer inks using a conventional printer.
Cities of the future could see a multitude of surfaces—buildings, cars, even clothing—made of this power-generating material. Thanks to a plethora of cheap, disposable products and packaging, plastics often get a bad rap pardon the pun for their impact on the environment—and rightly so. But new discoveries in materials science—from solar cells to biodegradable plastics made of natural materials—also hold out the promise of a more sustainable future. Polymers: from DNA to rubber ducks Expert reviewers.
What do DNA, rubber ducks and weird seventies raincoats have in common? What is a polymer? One way of thinking about polymers is like a chain of connected-up paperclips. A polymer is a large molecule made up of smaller, joined-together molecules called monomers.
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