1. Chemical Composition of
Rubber
Subject: Rubber Technology (3132602)
B.E. Sem 3 (Rubber Technology)
Prepared by:
Prof. Priyanka Chavda
Rubber Technology Department
L. D. College of Engineering

2. Content
 Chemical Composition of Polymer Molecule
 CARBON
 HYDROGEN
 OXYGEN
 NITROGEN
 HALOGEN
 SULFUR
 SILICON
 PHOSPHORUS
 METALS
 Polymeric ingredients in final polymer composition

3. CARBON
 The most important element in organic chemistry and polymer chemistry, and
forms all or most of the main chain in most polymer molecules.
 Neither electropositive nor electronegative, and the C-C bond by itself is
completely neutral and very stable, as we see in diamond and graphite.
 The energy and strength of the C-C bond are quite sufficient for thermal stability
and for ultraviolet light stability.
 Attachment of other elements to the carbon atom introduces polarity into the C-C
bond and thus lowers its stability.
 Most of the effects upon polymer properties are due to the attachment of these
other elements to the carbon.
 In the C=C double bond the two pairs of electrons between two carbon atom can
be accommodated electrically with good stability.

4.  This make the C=C double bond very reactive with oxygen, halogens, ozone and
hydrogen halides, reactions which are important in the utilization of rubber.
 When the C=C double bond is in the alpha position at the end of the molecule, it is
very often polymerizable by free radical or ionic mechanisms, particularly with
application of appropriate initiators. This is important in monomer casting.
 The alpha carbon (Cα) in organic molecules refers to the first carbon atom that
attaches to a functional group, such as a carbonyl. The second carbon atom is
called the beta carbon (Cβ), and the system continues naming in alphabetical
order with Greek letters.
 In aromatic structure, the unsaturation of the C=C double bond is completely
stabilized by resonance, and these aromatic structure provides high thermal
stability in polymer molecules.

5. HYDROGEN
 After carbon , hydrogen is the next most common element in organic chemistry
and in polymer structure.
 While it forming bonds with C , this C-H bonds are more reactive than the perfectly
balanced C-C bond and produces chemical reactivity or instability in the polymer
molecule.
 In the absence of oxygen , the energy of C-H bond is provide thermal and
ultraviolet stability,
 it undergoes substitution reaction which forms chlorinated polymer by halogenation
reaction.
 The aliphatic C-H bond has low surface energy, low surface tension, low adhesion
and low friction.
 The aromatic C-H bond is quite stable, but still permits reactions and has moderate
surface tension , producing less lubricity and higher adhesion.

6.  When the aromatic ring is activated by some groups such as phenolic hydroxyl or
amine, these greatly activate C-H bonds in the para and ortho position.
 When H is attached to elements other than carbon , it becomes much more
reactive but when H attached with O in hydroxyl groups may be highly reactive.
 This is important in formation of cellulose ester, polyesters, and polyvinyl.

7. OXYGEN
 Oxygen is the most common element in organic chemistry and in polymer structure.
 It is much more electronegative than carbon and hydrogen.
 The presence of oxygen atom in polymer structure also frequently produces high
surface energy and surface tension.
 The stability of the C-O-C bonds depends very much upon the groups to which it is
attached in aromatics.
 The C=O carbonyl bond is resonating structure which effect the polarity and reactivity of
adjacent groups.
 It absorbs ultraviolet light strongly in the range of 2800 – 3200 angstrom and this can
cause instability of the polymer towards ultraviolet light aging.
 The -CO2- group in polymers and in the side chain of polymers made from ester type
monomers is quiet sensitive to hydrolysis.
 The O-O bond of peroxides is very unstable.
 The presence of such weak O-O peroxide bond in the polymer structure makes it
particularly sensitive to thermal degradation.

8. Nitrogen
 Nitrogen in third most common element in organic chemistry.
 It is intermediate between carbon and oxygen in periodic table, so it is electronegative in nature.
 Bonds between carbon and Nitrogen are fairly strong but also provide fairy polar, providing strong
adhesion to polar substance.
 About bond,- C N = Nitrile bonds, which is presence in ABS and SAN resins, acrylic fiber.
 Nitrile rubber is strongly polar and unshared pair of electrons on the Nitrogen highly exposed and
available for very strong Hydrogen bonding.
 When acrylonitrile polymers are burned it is possible that HCN has may be released, forming very
toxic conditions N H bond It is fairly reactive, while is important in polymerization of polyamides and
in the cure of urethane, urea and melamine resins.
 Modification of the properties of nylon.
 O=C-N-H in polyamides introduced polarity and powerful Hydrogen bond.
 This responsible for water absorption and moderately moist absorption.
 It is also responsible for very high surface energy and surface tension which are useful in
adhesives.

9. HALOGENS
 The halogen elements in group VII of the periodic table are the most negative
elements known, and also have the smallest atomic radius.
 Fluorine :
 Fluorine is the most negative and smallest of the halogens almost as small as
hydrogen.
 The C-F bond has very low surface energy giving low surface tension, high
lubricity and nonwetting properties to a high degree. These properties are useful in
stain-proofing fabrics, nonstick cooking utensils. Mold lubricants and self-
lubricating bearing surface.
 The C-F bond is chemically very stable and it has high thermal and ultraviolet light
stability this stability is useful in gasket and in high temperature plastics and
elastomers.

10.  Chlorine :
 Chlorine is slightly less negative and larges than fluorine, but still forms quite
strong covalent bonds with carbon.
 Chlorine provides flame resistance. The high polarity and surface energy of the C-
Cl bond also produce high surface tension and adhesion.
 Chlorine creates strong polarity and perhaps some hydrogen bonding, thus
provides both strength and plasticizer compatibility in PVC.
 Higher atomic weight produces polymer of higher specific gravity.
 High polarity and surface energy of C-Cl bond produces high surface tension and
adhesion.
 Bromine :
 Bromine is considerably larger and less electronegative than chlorine.
 It forms fairly stable bonds with carbon, but splits out easily under the influence of
heat or ultraviolet light, usually causing discoloration.

11.  Only by adding small amounts of bromine in polymer gives high degree of flame
resistance.
 Iodine :
 Iodine is the largest and least electronegative of the halogens, and the bonds it
forms with carbon are quite unstable, so that it is hardly ever found in polymer
molecules.
 If it could be firmly bound, it would probably provide high density, high flame-
resistance.
 According to size :
F < Cl < Br < I
 According to electronegativity :
F > Cl > Br > I

12. SULFUR
 Sulfur is fairly similar to oxygen in its chemical properties, but less electronegative
and larger in size.
 The sulfide link aliphatic polymers is quite sensitive to atmospheric or chemical
oxidation.
 Steric hindrance of the benzen rings are more than sufficient to protect the sulfide
group against oxidation in aromatic polymers.
 The -Sx- group of polysulfide rubbers is fairly weakly bonded and fluid, providing
the chemical reactivity which is useful in equilibration and vulcanization.
 The -SO2- group in polymeric sulfones is itself quite stable, and the oxygens
projecting from it each have two pairs of unshared electrons to donate for the
strong hydrogen bonding to adjacent molecules.

13. SILICON
 Silicon is more electropositive and larger than carbon.
 Si-Si bonds and Si-H bonds are unstable and reactive.
 The Si-C bond in organosilane is very stable, due to this silicon polymers
are useful as high temperature elastomers.
 The Si-OH silanol bond is very reactive and polymerizes rapidly to form
silicones.
 The Si-O-R organosilixane bond is also quite reactive and polymerizes or
reacts with substrates readily.
 The Si-O-Si bond in both glass and silicon polymers is very stable to heat.
Its is useful in the preparation of silicone polymers.

14. PHOSPHORUS
Slightly more electropositive than nitrogen.
Produces the greatest flame retardant effect.
The P-O-C bond provides useful structures for
incorporation into polyether, polyesters and
polyurethane.
The P-C bond accompanied by high toxicity and it is
not commonly used in production of polymers.

15. METALS
 A variety of metallic elements are occasionally useful in polymer structure.
 Sodium ions commonly used in ionomers to provide fairly strong
thermoplastic cross-link which combiner processability and toughness in
the final polymer.
 Polymer containing high concentration of sodium carboxylate side groups
are soluble in water and used for thickening food latex paints.
 Several group-II metal are frequently used in vulcanization of elastomer
particularly magnesium, calcium and zinc.
 Calcium also proving cross-links when calcium acrylate is polymerization
for soil stabilization.
 Addition at metals in polymer well increases the price of polymer.

16. MONOMERIC INGREDIENTS IN THE FINAL
POLYMER COMPOSITION
It may be either:
(1)Impurities remaining from the original polymerization
reaction
(2)Monomeric additives purposely introduced during
compounding to modify composition and final
properties

17. Impurities remaining from the original
polymerization reaction
Impurities
Monomer
Solvent
Water
Chloride Ion
Catalysts and In initiators
Dispersant

18. Monomeric additives purposely introduced during
compounding to modify composition and final
properties
 Plasticizer
 Stabilizers
 Reinforcements and Fillers
 Cross-linking agents
 Foaming agents
 Flame retarders
 Lubricants
 Antistatic
 Biocides
 Colors