Chemical Industries Technologies Ⅰ
Chapter 12-continued:
Synthetic Petroleum-Based Polymers
Dr. Asma Eskhan
1
Chapter 12: Synthetic Petroleum-Based Polymers
Outline:
• Thermoplastics
➢ Polyethylene, Polypropylene, Polyvinyl Chloride, Polystyrene
• Thermosetting Plastics
➢Polyurethanes
• Synthetic Rubber
➢Butadiene, Styrene-Butadiene Rubber (SBR), Nitrile Rubber (NBR),
Polyisoprene, Butyl rubber, Thermoplastic Elastomers.
• Synthetic Fibers
Synthetic Rubber
• Synthetic rubbers (elastomers) are long-chain polymers with special
chemical and physical as well as mechanical properties.
• These materials have chemical stability, high abrasion resistance,
strength, and good dimensional stability.
• Many of these properties are imparted to the original polymer through
crosslinking agents and additives.
• An important property of elastomeric materials is their ability to be
stretched at least twice their original length and to return back to nearly
their original length when released.
• Natural rubber is an elastomer constituted of isoprene units. These units
are linked in a cis-1,4-configuration that gives natural rubber the
outstanding properties of high resilience and strength.
Synthetic Rubber
• Vulcanization of rubber is a chemical reaction by which elastomer chains
are linked together. The long chain molecules impart elasticity, and the
crosslinks give load supporting strength.
• Synthetic rubbers include elastomers that could be crosslinked such as
polybutadiene, polyisoprene, and ethylene-propylene-diene terepolymer.
• It also includes thermoplastic elastomers that are not crosslinked and are
adapted for special purposes such as automobile bumpers and wire and
cable coatings. These materials could be scraped and reused.
• However, they cannot replace all traditional rubber since they do not have
the wide temperature performance range of thermoset rubber.
• The major use of rubber is for tire production. Non-tire consumption
includes hoses, footwear, molded and extruded materials, and
plasticizers.
Synthetic Rubber
• Vulcanization of rubber is a chemical reaction by which elastomer chains
are linked together. The long chain molecules impart elasticity, and the
crosslinks give load supporting strength.
• Synthetic rubbers include elastomers that could be crosslinked such as
polybutadiene, polyisoprene, and ethylene-propylene-diene terepolymer.
• It also includes thermoplastic elastomers that are not crosslinked and are
adapted for special purposes such as automobile bumpers and wire and
cable coatings. These materials could be scraped and reused.
• However, they cannot replace all traditional rubber since they do not have
the wide temperature performance range of thermoset rubber.
• The major use of rubber is for tire production. Non-tire consumption
includes hoses, footwear, molded and extruded materials, and
plasticizers.
Butadiene Polymers and Copolymers
• Butadiene could be
polymerized using free
radical initiators or ionic or
coordination catalysts.
• When butadiene is
polymerized in emulsion
using a free radical initiator
such as cumene
hydroperoxide, a random
polymer is obtained with
three isomeric
configurations, the 1,4-
addition configuration
dominating:
Butadiene Polymers and Copolymers
• Polymerization of butadiene using anionic initiators (alkyllithium) in a
nonpolar solvent produces a polymer with a high cis configuration.
• A high cis-polybutadiene is also obtained when coordination catalysts are
used.
Properties and Uses of Polybutadiene
• cis-1,4-Polybutadiene is characterized by high elasticity, low heat buildup,
high abrasion resistance, and resistance to oxidation.
• However, it has a relatively low mechanical strength. This is improved by
incorporating a cis, trans block copolymer or 1,2-(vinyl) block copolymer
in the polybutadiene matrix.
• Also, a small amount of natural rubber may be mixed with polybutadiene
to improve its properties.
• trans 1,4-Polybutadiene is characterized by a higher glass transition
temperature (Tg = –14°C ) than the cis form (Tg = –108°C ). The polymer has
the toughness, resilience, and abrasion resistance of natural rubber (Tg = –
14°C ).
Styrene-Butadiene Rubber (SBR)
• Styrene-butadiene rubber (SBR) is the most widely used synthetic rubber.
• It can be produced by the copolymerization of butadiene (≈ 75%) and
styrene (≈ 25%) using free radical initiators.
• The micro-structure of the polymer is 60–68% trans, 14–19% cis, and 17–
21% 1,2–.
• Currently, more SBR is produced by copolymerizing the two monomers
with anionic or coordination catalysts.
• The formed copolymer has better mechanical properties and a narrower
molecular weight distribution.
• Block copolymers of butadiene and styrene may be produced in solution
using coordination or anionic catalysts.
Styrene-Butadiene Rubber (SBR)
• Butadiene polymerizes first until it is consumed, then styrene starts to
polymerize.
• SBR produced by coordinaton catalysts has better tensile strength than
that produced by free radical initiators.
• The main use of SBR is for tire production. Other uses include footwear,
coatings, carpet backing, and adhesives.
Nitrile Rubber (NBR),
also known as nitrile butadiene
rubber
• Nitrile rubber is a copolymer of butadiene and acrylonitrile.
It has the special property of being resistant to hydrocarbon liquids.
• The copolymerization occurs in an aqueous emulsion.
• When free radicals are used, a random copolymer is obtained.
• Alternating copolymers are produced when a Zieglar-Natta catalyst is employed.
• Molecular weight can be controlled by adding modifiers and inhibitors.
• When the polymerization reaches approximately 65%, the reaction mixture is
vacuum distilled in presence of steam to recover the monomer.
• The ratio of acrylonitrile/butadiene could be adjusted to obtain a polymer with
specific properties.
Nitrile Rubber (NBR)
• Increasing the acrylonitrile ratio increases oil resistance of the rubber but
decreases its plasticizer compatibility.
• NBR is produced in different grades depending on the end use of the
polymer.
• Low acrylonitrile rubber is flexible at low temperatures and is generally
used in gaskets, O-rings, and adhesives.
• The medium type is used in less flexible articles such as kitchen mats and
shoe soles.
• High acrylonitrile polymers are more rigid and highly resistant to
hydrocarbons and oils and are used in fuel tanks and hoses, hydraulic
equipment, and gaskets.
Polyisoprene
• Natural rubber is a stereoregular
polymer composed of isoprene units
attached in a cis configuration.
• This arrangement gives the rubber
high resilience and strength.
• Isoprene can be polymerized using
free radical initiators, but a random
polymer is obtained.
• As with butadiene, polymerization of isoprene can produce a mixture of isomers.
• Stereoregular polyisoprene is obtained when Zieglar-Natta catalysts or anionic
initiators are used. The most important coordination catalyst is αTiCl3 cocatalyzed
with aluminum alkyls.
• The polymerization rate and cis content depends upon Al/Ti ratio, which should be
greater than one. Lower ratios predominantly produce the trans structure.
Polyisoprene
Properties and Uses of Polyisoprene
• Polyisoprene is a synthetic polymer (elastomer) that can be vulcanized by
the addition of sulfur.
• cis-Polyisoprene has properties similar to that of natural rubber. It is
characterized by high tensile strength and insensitivity to temperature
changes, but it has low abrasion resistance. It is attacked by oxygen and
hydrocarbons.
• trans-Polyisoprene is similar to Gutta percha, which is produced from the
leaves and bark of the sapotacea tree. It has different properties from the
cis form and cannot be vulcanized. Few commercial uses are based on
trans-polyisoprene.
• Important uses of cis-polyisoprene include the production of tires,
specialized mechanical products, conveyor belts, footwear, and
insulation.
Butyl Rubber
• Butyl rubber is a copolymer of isobutylene (97.5%) and isoprene (2.5%).
The polymerization is carried out at low temperature (below –95°C ) using
AlCl3 cocatalyzed with a small amount of water.
• The product is a linear random copolymer that can be cured to a
thermosetting polymer. This is made possible through the presence of
some unsaturation from isoprene.
• Butyl rubber vulcanizates have tensile strengths up to 2,000 psi, and are
characterized by low permeability to air and a high resistance to many
chemicals and to oxidation.
• These properties make it a suitable rubber for the production of tire inner
tubes and inner liners of tubeless tires.
Butyl Rubber
Thermoplastic Elastomers
• Thermoplastic elastomers (TPES), as the name indicates, are plastic
polymers with the physical properties of rubbers.
• They are soft, flexible, and possess the resilience needed of rubbers.
However, they are processed like thermoplastics by extrusion and
injection molding.
• TPE’s are more economical to produce than traditional thermoset
materials because fewer steps are required to manufacture them than to
manufacture and vulcanize thermoset rubber.
• An important property of these polymers is that they are recyclable.
