Polymers
6. POLYMERS and elastomers
Lecture no. 1
Objectives: Definition, Functionality, Classification of high polymers – based on origin, molecular structure.
6.1.1. DEFINITION:
The word polymer is derived from the two greek words, poly and meros, meaning many and parts or units respectively. Polymers are macro molecules formed by linking smaller molecules repeatedly, called monomers.
Examples:
Polythene is formed by linking a large number of ethene (or ethylene) molecules together as shown below.
Similarly polystyrene is formed by linking styrene molecules together.
The number of repeating units (n) in the chain, so formed is called as the degree of polymerization.
Polymers with high degree of polymerization are called high polymers and these have very high molecular weights (104 to 106).
Polymers with low degree of polymerization are called oligomers.
6.1.2. FUNCTIONALITY:
Polymerization is a process, which allows simple and low molecular mass compounds to combine and form a complex, high molecular mass compound. For this, each low molecular mass compound should have the capability to react at least with two other molecules of the same or some other compound. In other words, they should have a functionality of at least two. So, the functionality of a compound is the number of reactive sites or bonding sites.
The reactive functional groups are like –OH, -COOH, NH2, -SH, -NCO, etc.,
Examples: CH3CH2OH one reactive - OH group is present so functionality is one (i.e., monofunctional)
CH3COOH monofunctional CH3 (CH2)4 (CH2) NH2 monofunctional HO CH2 CH2 OH two – OH groups are present, so bifunctional CH2 (COOH)2 bifunctional H2N CH2 (CH2)4 (CH2) NH2 bifunctional
HOOC CH2 CH (COOH) CH2 COOH trifunctional
Some compounds, however, do not contain any reactive functional groups, but the presence of double or triple bonds in the molecule bestows polyfunctionality on them. e.g.,
Lecture no. 1
Objectives: Definition, Functionality, Classification of high polymers – based on origin, molecular structure.
6.1.1. DEFINITION:
The word polymer is derived from the two greek words, poly and meros, meaning many and parts or units respectively. Polymers are macro molecules formed by linking smaller molecules repeatedly, called monomers.
Examples:
Polythene is formed by linking a large number of ethene (or ethylene) molecules together as shown below.
Similarly polystyrene is formed by linking styrene molecules together.
The number of repeating units (n) in the chain, so formed is called as the degree of polymerization.
Polymers with high degree of polymerization are called high polymers and these have very high molecular weights (104 to 106).
Polymers with low degree of polymerization are called oligomers.
6.1.2. FUNCTIONALITY:
Polymerization is a process, which allows simple and low molecular mass compounds to combine and form a complex, high molecular mass compound. For this, each low molecular mass compound should have the capability to react at least with two other molecules of the same or some other compound. In other words, they should have a functionality of at least two. So, the functionality of a compound is the number of reactive sites or bonding sites.
The reactive functional groups are like –OH, -COOH, NH2, -SH, -NCO, etc.,
Examples: CH3CH2OH one reactive - OH group is present so functionality is one (i.e., monofunctional)
CH3COOH monofunctional CH3 (CH2)4 (CH2) NH2 monofunctional HO CH2 CH2 OH two – OH groups are present, so bifunctional CH2 (COOH)2 bifunctional H2N CH2 (CH2)4 (CH2) NH2 bifunctional
HOOC CH2 CH (COOH) CH2 COOH trifunctional
Some compounds, however, do not contain any reactive functional groups, but the presence of double or triple bonds in the molecule bestows polyfunctionality on them. e.g.,
References: - 1. Engineering Chemistry by “ Jain & Jain. 2. Engineering Chemistry by A.K. Pahari, B.S. Chauhan 3. Engineering Chemistry by” R.V. Gadag & A. Nithayananda Shetty. 4. Shalaby, S.W. Biomedical Polymers; Hanser: New York (1994). 5. Uhrich, K.E. et al. Chem. Rev., 99, 3181 (1999). 6. Dobrzynski, P. et al. Macromolecules, 32, 4735 (1999).