Polymers; They are high molecular weight compounds formed by connecting a large number of molecules with chemical heads in an orderly fashion. "Poly" is a Latin word that means "many". Polymers are formed by the combination of units called monomers. A simple example is Polystyrene. Polystyrene is formed by the combination of many styrene monomers.
Polymers; They are high molecular weight compounds formed by regular bonding of many molecules with chemical bonds. "Poly" is a Latin word that means "many". Polymers are formed by the combination of units called monomers. A simple example of this is Polystyrene. As seen above, polystyrene containing a large number of this monomer is obtained by polymerization of the styrene monomer.
Organic chemists randomly synthesized high molecular weight substances in some experiments in the mid-nineteenth century. Since the second half of this century, researches on polymers have been developed and new polymer types have been developed. The pioneer of this field is German chemist Herman Stauding. Herman Stauding described for the first time the effect of polymerization conditions on polymer formation. Stauding received the Nobel Prize in 1953 for his work in this field of chemistry.
Researchers working in this field for the first time started by imitating natural polymers and in 1930 Wallace Carothers succeeded in synthesizing Nylon. Since the second world war, many polymer laboratories have been produced and many polymers have also started to be produced on an industrial scale. Industrial organic chemists, on the other hand, shifted to the field of polymer chemistry and started to work in this direction. As a result, numerous polymer types are used for various purposes in a wide range of applications today. The formulas of some commonly used polymers and the monomers from which they were synthesized are shown below.
Polymers can be classified according to their structure. If a polymer consists of repeating a single monomer unit, it is called a homopolymer. Examples are polyethylene obtained from ethylene and polystyrene obtained from styrene.
If the polymer molecule consists of the combination of two different monomers, it is called a copolymer. We can divide the types of copolymers into three.
1. Sequential copolymer
3. Irregular copolymer
Polymer chains, whether homopolymer or copolymer, can exist in three different forms.
Molecular Weights of Polymers
Physical properties of polymers are related to molecular weight. For this reason, they must have a certain molecular weight in order to show the physical properties expected from polymers.
Generally, as the molecular weight increases, the intermolecular attraction in the structure increases and this affects the mechanical and thermal properties of the polymer. Molecular weights of polymers can be determined by methods such as gel permeation chromatography, viscometric measurement, osmotic pressure and light scattering.
Synthesis of Polymers
Free Radical Polymerization
It is the type of chain polymerization that runs on radicals. Free radical polymerization consists of three stages.
Initially, monomer molecules are converted into radicals using various methods. Radical formation is provided by heat, photochemical, radiation or various initiators. For this purpose, the most common method to create radicals in the environment is to add an external initiator to the environment. The initiator creates a radical and initiates the polymerization process by double-attacking the vinyl group. Various peroxides, diazo compounds and redox pairs are used as initiators.
The most commonly used peroxide initiator is benzyl peroxide. This initiator is easily decomposed by heat to form free radicals. In the figure below, benzyl peroxide is broken down by the effect of heat and transformed into two free radicals.
Then, the radicals formed in the initiation phase attack the double bond in the monomer molecule and initiate polymerization. In the figure, the radicals formed from the initiator break one of the double heads in the ethylene molecule and form a new radical, thus initiating the polymerization reaction.
Then, the radicals formed in the bonding phase attack the double bond in the monomer molecule and initiate polymerization. In the figure, the radicals formed from the initiator break one of the double bonds in the ethylene molecule and form a new radical, thus initiating the polymerization reaction.
The new radicals formed cause the polymer chain to grow by reacting with the monomers in the environment.
As the polymerization progresses, the polymer chain grows and the molecular weight increases. At this stage of the polymerization, the number of monomers in the environment has decreased. Therefore, the radicals in the environment begin to wither.
Chain polymerization can work through free radicals as well as ions and coordination complexing agents. The mechanism by which a vinyl monomer is polymerized depends on the group on the substrate. For example, halogenated vinyls (such as vinyl chloride, etc.) and vinyl esters are polymerized only with radicals. If electron donating groups are attached to the vinyl monomer, only cationic polymerization is possible.
Ionic polymerization generally involves heterogeneous systems in which catalysts are in a separate phase. Its reaction rate is much faster than radical polymerization. In some cases the polymerization process takes place at very low temperatures to control the reaction rate.
Condensation polymers are obtained by reacting similar or different poly-functional monomers, usually removing a small molecule. The most important condition here is that the monomers are poly-functional. Monomers bearing at least two of the functional groups such as OH, COOH, NH2, etc. can be esterified, amidated, etc. They form condensation polymers by removing small molecules with such reactions. Polyurethanes such as urethane formation from which polyurethanes are obtained and caprolactam ring opening from which nylon 6 is obtained, such as direct addition of monomers without small molecule release, are also generally considered within this group.
In this type of polymerization, the monomer is directly polymerized at a certain temperature and pressure after a suitable initiator has been added into it. The most important feature of this process is that highly pure polymers can be produced. In the process, the product formed as a result of polymerization, post-production separation, purification, etc. It does not require such processes, it can be sold directly. In addition, since it requires cheaper machinery and equipment than other processes, it is considered a simple and economical process.
The most important disadvantage of this process is that the resulting heat cannot be easily removed from the environment, so temperature control is difficult. This aspect should be particularly important in radical polymerization. Such polymerizations are strongly exothermic and the immediate formation of high molecular weight polymer molecules causes a rapid increase in ambient viscosity. Temperature control becomes extremely difficult. Local temperature increases can cause gas formation, even violent explosions, as a result of polymer degradation and boiling of the monomer.
This polymerization technique is widely used in the industry to produce large quantities of polymers. As a result of this polymerization, depending on the polymerization conditions, particles with a diameter of 50/1000 micrometers with or without porosity are obtained. There are two phases in suspension polymerization.
- Monomer phase
- dispersion phase
If a polymer is to be used for suspension polymerization, the first property to be considered is the solubility of the monomer in the dispersion phase. The solubility of the monomer in the dispersion phase should be very low. For this purpose, hydrophobic liquids such as oil and petroleum ether are used for hydrophilic monomers. Water is also used as the dispersion phase for hydrophobic monomers. Monomer droplets contain the initiator dissolved in their structure. Heat etc. The polymerization reaction is started with the effects. As a result of the reaction, every single drop of monomer turns into a polymer particle.
The biggest problem that can be encountered in suspension polymerization is the accumulation of particles by sticking to each other. To prevent this, stabilizers are added to the dispersion phase that can keep the particles stably. Particle diameter varies depending on the stabilizer used and the mixing speed of the medium.
In emulsion polymerization, there are two phases that do not mix with each other. The monomer phase is dispersed as emulsion in the dispersion phase. Unlike suspension polymerization, here the initiator is dissolved in the dispersion phase. By using various emulsifying agents, the monomer phase is kept stable in the emulsion state in the dispersion phase. The most widely used of these is sodium dodecylsulfate. With this polymerization technique, uniform spherical particles around 1 micrometer are obtained.
With this polymerization technique, uniform spherical polymer particles between 1-10 micrometers are obtained. The characteristic of dispersion polymerization is that the monomer phase dissolves in the dispersion phase, but the polymer formed at the end of the polymerization process is not dissolved in the dispersion phase.
International Abbreviated Names of Some Polymers
. ABS Acrylonitrile-butadiene-styrene copolymer
. AMMA Acrylonitrile-methyl methacrylate copolymer
. ANM Acrylic ester-acrylonitrile copolymer
. BR Polybutadiene
. BT Poly (1-butene)
. CA Cellulose acetate
. CAB Cellulose acetobutyrate
. CF Cresol-formaldehyde resin
. CHR Polyepichlorohydrin
. CL Poly (vinyl chloride) fiber
. CPVC Chlorinated poly (vinyl chloride)
. CR Polychloroprene
. EEA Ethylene-ethyl acrylate copolymer
. EP Epoxy resin
. EPDM Ethylene-propylene-diene elastomer
. EVA Ethylene-vinyl acetate copolymer
. FE Fluorine containing elastomer
. GEP Glass fiber reinforced elastomer
. GFK Glass fiber reinforced plastic
. IIR Butyl rubber
. LDPE Low density polyethylene
. LLDPE Linear low density Polyethylene
. MA Modacrylic fiber
. MF Melamine-formaldehyde solution
. MOD Modacrylic fiber
. NBR Acrylonitrile-butadiene elastomer
. NR Natural rubber
. PA Polyamide
. PAC Polyacrylonitrile fiber
. PAN Polyacrylonitrile
. PBMA Poly (butyl methacrylate)
. PCF Poly (trifluorochlorethylene) fiber
. PCTFE Poly (trifluorochlorethylene) fiber
. PDAP Poly (diallyl phthalate)
. PDMS Poly (dimethyl siloxane)
. PE Polyethylene
. PEO Poly (ethylene oxide)
. PES Polyester fiber
. PETP Poly (ethylene terephthalate)
. PF Phenol-formaldehyde resin
. PFEP Tetrafluoroethylene-hexafluoropropylene
. PIB Polyisobutylene
. PL Poly ethylene
. PMMA Poly (methyl methacrylate)
. PO Phenoxy resin
. POM Polyoxy methylene
. POR Propylene oxide-allylglycidyl ether elastomer
. PP Polypropylene
. PPO Poly (phenylene oxide)
. PS Polystyrene
. PSB Styrene-butadiene copolymer
. PST Polystyrene fiber
. PTF Poly (tetrafluoroethylene) fiber
. PTFE Poly (tetrafluoroethylene)
. PU Polyurethane fiber
. PUA Poly urea fiber
. PVA Poly (vinyl ether)
. PVAC Poly (vinyl acetate)
. PVAL Poly (vinyl alcohol)
. PVB Poly (vinyl butyral)
. PVC Poly (vinyl chloride)
. PVCA Vinyl chloride-vinyl acetate copolymer
. PVDC Poly (vinylidene chloride)
. PVDF Poly (vinylidene chloride)
. PVF Poly (vinyl fluoride)
. PVFM Poly (vinyl formal.)
. PVM Vinyl ether-vinyl chloride copolymer
. SAN Styrene-acrylonitrile copolymer
. SBR Styrene-butadiene elastomer
. VMQ Silicone
. UF Urea-formaldehyde resin
. UP Unsaturated polyester
PHYSICAL PROPERTIES OF SOLVENTS
SOLVENT CURING TIME BOILING POINT (° C) FLASH POINT (° C) DENSITY
Toluol 2.1 111 4 0.87
Xylen (Xylol) 0.6 137 27 0.86
Heptane 9.0 98 4 0.68
Hexan 4.3 69 -22 0.66
Methyl Alcohol 5.9 64 11 0.79
Ethyl Alcohol 3.2 78 11 0.79
Isopropyl Alcohol 2.3 82 12 0.79
Butyl Alcohol 0.5 118 29 0.81
Ethyl glycol 0.2 195 111 1.12
Acetone 11.5 56 -15 0.79
MEK 5.7 80 -7 0.80
MIBK 1.6 118 23 0.80
Methyl Acetate 11.8 57 -10 0.92
Ethyl Acetate 6.2 77 -4 0.90
Butyl Acetate 1.0 126 22 0.88
Drying time is given as Butyl Acetate = 1. Solvents below 1 are used as retarding and solvents above 1 are used as accelerators. It is necessary to be as cautious as possible when adding retarding solvent to inks. However, in hot weather, retarding solvent is required.