UP resins are made of reinforced fibers like glass, carbon or aramid fibers embedded in a polymer matrix. Unsaturated polyester resins were first developed in the 1930s by reacting glycols with maleic anhydride, which could be cured with a peroxide catalyst to an insoluble solid. These resins are widely used due to their good mechanical properties, corrosion resistance and low weight. Common applications include building materials, sanitary ware, transportation parts like boat hulls, and pipes.

1. USATURATED POLYESTERS
An Introduction
UP Resins are made up of at least two separate components; reinforced fibre and embedding
matrix. Other additives may be used to improve properties or characteristics. Carbon, aramide or
most commonly glass fibres may be used yielding FRP (Fibre Reinforced Plastic) or specifically
GRP (Glass Reinforced Plastics) in the case of glass. Materials basically bridge the gap between
conventional, commodity plastics and specialist engineering plastics. Production takes place by
introducing reinforcement while the resin is in an uncured, liquid state. Such plastics are widely
used in a host of applications where advantage may be taken of their good range of mechanical
properties, corrosion resistance and low weight.
The actual preparation of the first polyester resin is accredited to both Berzelius in 1847 and
Gay-Lussac and Pelouze in 1883. The unsaturated polyester resins used in today’s re-inforced
plastics (RP) are combinations of reactive monomers. Carleton Ellis introduced the idea for the
combination in the 1930’s. Ellis discovered that unsaturated polyester resins made by reacting
glycols with maleric anhydride could be cured to insoluble solids simply by adding a peroxide
catalyst. He applied for a patent on this idea in 1936.
Ellis later discovered that a more useful product could be made by combining the unsaturated
polyester alkyd with such reactive monomers as vinyl acetate or styrene, which makes it easier to
add the catalyst and apply the resin.
The first use of glass fiber reinforced polyester composites was in aircraft ducting, with the first
non-military application in boat hulls. The invention of the pultrusion line allowed development
of unsaturated polyester based materials into new application areas such as oil wells, fishing rods
and electrical insulation devices. The filament winding process further expanded the potential
market for unsaturated polyester resins. This technique was initially developed for making
military rocket cases and nozzle’s; however, potential for use in the making of pipes and storage
vessels was soon recognized.
A new polyester resin material called SMC (Sheet Moulding Compound) was formulated in the
1960s and following this BMC (Bulk Moulding Compounds) or DMC (Dough Moulding
Compounds). These products may be generically referred to as PMCs (polyester moulding
compounds). Compounds of this type contain chopped glass fibres and resin, they offer the
advantage that, during formation, fibres and resins are able to flow under the action of heat and
pressure in a hot press (or compression) moulding system. Systems of this nature facilitate the
moulding of complex details from simple material packs. Cycle times tend to be between two
and ten minutes. High pressures and tooling costs associated with such processes mean those
forming quantities of less than 10,000 tend not to be economic.

2. Physical Properties
The nature of the Unsaturated Polyester means that physical properties are dependant on the
additional materials used, and the conditions of curing, for a specific application. With such
variety available it is best to refer to manufacturers for performance of individual grades.
Cross-linking of linear unsaturatedpolyester
• Involve the reaction between the unsaturated sites in polymer chain and vinyl-type monomer
• As carried commercially, cross-linking of unsaturated polyester is invariably a free radical
reaction
• Two types of initiating systems are commonly employed for this reaction, namely those
effective elevated temperature and those effective at room temperature.
• The most important initiators used at elevated temperatures are peroxides, which liberate
free radicals as a result of thermal decomposition.
• A peroxide which is widely used in this way is benzoyl peroxide.
• Other peroxides include 2,4-chlorobenzoyl peroxide, ditert-butyl peroxide and lauroyl
peroxide
• Mixtures of polyester resin and this type of peroxide are comparatively stable at room
temperature but rapidly cross-link at temperature ranging from about 70 – 150C.
• Such peroxides are used principally in processes employing moulding compositions, when
short curing times are required .
• Initiating systems which are effective at room temperature normally consist of mixtures of a
peroxy compound and an activator (accelerator)
• In the presence of accelerator, the peroxy compound rapidly decomposes without the

3. application of heat into free radicals
• The two most important peroxy materials now used for the “cold” curing of polyester resin
are methyl ethyl ketone peroxide (MEKP) and cyclohexane peroxide.
• In reality, MEKP and cyclohexane peroroxides are hydroperoxides.
• The most common accelerators for MEKP and cyclohexane peroxide are salts of metals which
exhibit more than one valency.
• The most widely used metal of this kind is cobalt, although salts of cerium, iron, manganase,
tin, vanadium also find some application.
• In order to be effective as an accelerator a metal salt must be soluble in the polyester resin .
• The most commonly used salts are naphthenates, which are readily soluble, octoate may also
be used
• The decomposition of a hydroperoxide (ROOH) by a metal salt such as cobalt napthenate to
give free radicals proceeds according to the following:
• The cycle is repeated until all hydro peroxide has been decomposed.
• Cobalt napthenate-methyl-ethyl-ketone peroxide or cyclohexane peroxide systems are very
extensively used in the production of large glass-fiber laminates by hand lay-up and cured at
room temperature.
• It may be noted that the foregoing metal-based accelerators, which are highly reactive
towards hydro peroxides, have little influence on the decomposition of peroxide especially

4. those used for curing polyester at elevated temperature
• However, peroxide do decompose rapidly at room temperature into free radicals in the
presence of tertiary amines.
• Amines such as dimethylaniline, diethylaniline, and dimethyl-p-toluidine react violently with
benzoyl peroxide or tertiary amine.
• Polyester resin cured with benzoyl peroxide-tertiary amine tend to discolour and craze on
ageing
• The reaction between benzoyl peroxide and tertiary amine is thought to proceed via a one-
electron transfer from nitrogen, as shown in the following example involving dimethylaniline:
• The cross-linking of an unsaturated polyester by means of a vinyl monomer such as styrene
may be represented
• The average value of n in the structure may be deduced from both spectroscopic and
degradation studies.
• Both the spectroscopic and degradation studies indicate that in a typical cured general
purpose polyester resin the cross-links contain 1-3 styrene units.
• Determination of the molecular weight of the polymer enables estimation of the average of
chains linked together by a continuous cross-link
• Typically such copolymers have Mn ~2500 which indicates that each continuous styrene-
fumarate copolymer chains passes through 6-10 cross-link sites in the un-degraded cured
polyester.
• It will be noted that the cross-linking of linear unsaturated polyester by vinyl monomers does
not involve the elimination of any volatile by-products.

5. • Hence, it is possible to cure the resin without the application of pressure.
• It is also possible to cure the resins without the application of heat, they are very useful in the
manufacture of large structure such as boat hulls
UnsaturatedPolyesters resinProperties of cross-linkedpolymers
• Cross-linked unsaturated polyesters are rigid, infusible and insoluble.
• There are so many varieties of polyester resins now commercially available that it is difficult
to give typical values for physical properties of cured materials.
• Furthermore, polyester resin are mostly used in conjunction with glass fibre and the physical
properties of the final product greatly depend on the type and quantity of glass fibre
incorporated.
• Cross-linked polyesters have good heat stability, showing little weight loss up to about 200°C.
• The mechanical strength of general purpose materials begins to decline at about 100°C and
the maximum service temperature of glass-fibre laminates and mouldings is about 150°C; for
heat resistance grades of resins these temperature are of the order of 160°C and 200°C.
• The electrical insulating properties of cured polyester are satisfactory for many purposes but
the polar nature of the ester group results in a relatively high power factor and dielectric
constant and so the use of the resins in high frequency applications is limited.
• Cross-linked polyesters are resistant to a wide range of organic solvents but they are attacked
by chlorinated hydrocarbons (e.g. chloroform, ethylene dichloride and trichloroethylene),
esters (e.g. ethyl acetate) and ketones (e.g. acetone and MEK).
• The ester groups in the polymer provide sites for hydrolytic attack and strong alkalis cause

6. appreciable degradation.
• The polymer is, however, resistant to most inorganic and organic acids, with exception of
strong oxodising acids.
Applications
UP Resins are widely used in a host of applications where advantage may be taken of their good
range of mechanical properties, corrosion resistance and low weight.
Un-reinforced versions are most commonly used for clear casting resins, coatings, buttons, body
fillers, work-surfaces (such as polyester marble), polyester concrete (for applications such as
road drainage) and in the manufacture of Gel Coats (applied to composite materials to improve
the surface finish).
The largest market for reinforced polyester resin (composite materials) is the building and
sanitary ware market; here the material finds usage as structural parts (e.g. replacement of
concrete clad steel), cladding panels, sheeting (e.g. for pre-fabricated buildings), roofing tiles,
pipes and also for applications such as bathroom furniture (e.g. baths and shower trays).
The Transport market makes significant usage of UP Resins. Since the materials tend to lend
themselves to lower volume applications it is most commonly used in aeroplanes, trucks, buses
and coaches. Established markets include parts such as bumper beams, body panels, sunroof
frames, catalytic converter heat shields, dashboard carriers, seat structures, battery supports and
spring systems. In addition to weight reduction, polyester parts have the opportunity to reduce
painting costs (should composite parts require painting, however, a conductive primer coat or in-
mould coating, with lower paint transfer efficiency and lower rates of work means that part price

7. overtakes costs associated with electro-galvanised steel). Polyester parts also provide good
corrosion resistance properties.
Rail cars, rolling stock and shipping containers are also manufactured using UP resin
composites. The marine market is also heavily reliant on UP Resins, principally for the
manufacture of luxury boat hulls.
Other markets for UP Resins include the caravan panel market and the material is widely used in
storage vessels (where the chemical resistance of the material is highly valued).
REFERENCES
1: http://www.shepchem.com/Products/Unsaturated-Polyester-Resins.aspx#sthash.PSB8n502.dpuf.
2:

8. JOMO KENYATTA UNIVERSITY OFAGRICULTURE AND
TECHNOLOGY
NAME: PAUL NDISI KEVIN
REG NO: SC 233-1252/2013
COURSE: BSC INDUSTRIAL CHEMISTRY
UNIT: SCH 2442 POLYMER PROCESSING
TASK: ASSINMENT 1
TITLE: UNSATURATED POLYESTER
LECTURER: DR. P. MWANGI
DATE ISSUE: 09/9/2016 DATE DUE: 23/9/2016