giass ture (Tg) is the temperature range where a polymer chain gains of the polymer chains depends on (1) the presence of stiffening ated in the polymer backbone and (2) the presence of functional backbone. These functional groups attached to the polymer back For example, polyethylene terephthalate (PET) has a higher glass tra ene adipate. The terephthalic acid moiety in polyethylene ably an inflexible unit. Furthermore, the terephthalic acid moie e and restricts polymer chain mobility. On the other hand, the ene adipate is flexible; thus, making the polymer backbone chains pendant groups in the glass transition temperature is very evident n temperatures of low density polyethylene (LDPE) and polyvinyl al higher glass transition temperature than LDPE attributed to the p OH) which can form strong hydrogen bonds with other polymer ch

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Properties of Polymers
The properties of the polymers are usually governed by its structure. One such important
property of polymers that is being analysed is the glass transition temperature. The glass transition
temperature (Tg) is the temperature range where a polymer chain gains segmental motion. The
flexibility of the polymer chains depends on (1) the presence of stiffening and flexibilizing groups
incorporated in the polymer backbone and (2) the presence of functional groups attached to the
polymer backbone. These functional groups attached to the polymer backbone is called pendant
groups. For example, polyethylene terephthalate (PET) has a higher glass transition temperature than
polyethylene adipate. The terephthalic acid moiety in polyethylene terephthalate (PET) is
considerably an inflexible unit. Furthermore, the terephthalic acid moiety stiffens the polymer
backbone and restricts polymer chain mobility. On the other hand, the adipic acid moiety in
polyethylene adipate is flexible; thus, making the polymer backbone chains more freely mobile. The
effect of pendant groups in the glass transition temperature is very evident by comparing the glass
transition temperatures of low density polyethylene (LDPE) and polyvinyl alcohol (PVA). PVA has a
relatively higher glass transition temperature than LDPE attributed to the presence of the hydroxyl
group (-OH) which can form strong hydrogen bonds with other polymer chains. Whereas in LDPE,
each polymer chains can only interact with each other via the much weaker London dispersion forces.
The glass transition temperature of polymers also increase due to polymer backbone symmetry and
the presence of crosslinks. Adding additives such as plasticizers, on the other hand, decreases the
glass transition temperatures of polymers.
Table. Approximate glass transition temperatures (Tg) for selected polymers
Glass Transition
Polymer
Chemical Structure
Temperature (Tg)
OH
Polyethylene Adipate
223
Polyethylene
Terephthalate (PET)
342
in
нн
Low density
148
polyethylene (LDPE)
Polyvinyl Alcohol (PVA)
358
НО
Another important property of polymers is its melting temperature. Melting temperature (Tm)
is the temperature range in which the whole polymer chains become mobile. Synonymous to Tg, the
melting temperature is higher for polymers having stiffening groups in the backbone and pendant
groups that may form stronger intermolecular forces of attraction.
Transcribed Image Text:Properties of Polymers The properties of the polymers are usually governed by its structure. One such important property of polymers that is being analysed is the glass transition temperature. The glass transition temperature (Tg) is the temperature range where a polymer chain gains segmental motion. The flexibility of the polymer chains depends on (1) the presence of stiffening and flexibilizing groups incorporated in the polymer backbone and (2) the presence of functional groups attached to the polymer backbone. These functional groups attached to the polymer backbone is called pendant groups. For example, polyethylene terephthalate (PET) has a higher glass transition temperature than polyethylene adipate. The terephthalic acid moiety in polyethylene terephthalate (PET) is considerably an inflexible unit. Furthermore, the terephthalic acid moiety stiffens the polymer backbone and restricts polymer chain mobility. On the other hand, the adipic acid moiety in polyethylene adipate is flexible; thus, making the polymer backbone chains more freely mobile. The effect of pendant groups in the glass transition temperature is very evident by comparing the glass transition temperatures of low density polyethylene (LDPE) and polyvinyl alcohol (PVA). PVA has a relatively higher glass transition temperature than LDPE attributed to the presence of the hydroxyl group (-OH) which can form strong hydrogen bonds with other polymer chains. Whereas in LDPE, each polymer chains can only interact with each other via the much weaker London dispersion forces. The glass transition temperature of polymers also increase due to polymer backbone symmetry and the presence of crosslinks. Adding additives such as plasticizers, on the other hand, decreases the glass transition temperatures of polymers. Table. Approximate glass transition temperatures (Tg) for selected polymers Glass Transition Polymer Chemical Structure Temperature (Tg) OH Polyethylene Adipate 223 Polyethylene Terephthalate (PET) 342 in нн Low density 148 polyethylene (LDPE) Polyvinyl Alcohol (PVA) 358 НО Another important property of polymers is its melting temperature. Melting temperature (Tm) is the temperature range in which the whole polymer chains become mobile. Synonymous to Tg, the melting temperature is higher for polymers having stiffening groups in the backbone and pendant groups that may form stronger intermolecular forces of attraction.
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