1. Conducting Polymers:

Polymeric materials has been synthesized which possess electrical conductivities on par with metallic conductors. Such polymers are called conducting polymers.

Conductivities as high as $1.5\times 10^7 ohm^{-1}m^{-1}$ have been attained in these polymeric materials.

On a volume basis, this value is equal to one-fourth of the conductivity of copper, or is twice it’s conductivity on the basis of weight.

INTRINSIC CONDUCTING POLYMER:

• It is a polymer whose backbones or associated groups consist of delocalized electron-pair or residual charge.
• Such polymers essentially contain conjugated$\pi$-electrons backbones, which is responsible for electrical charge.
• Overlapping of orbitals over the entire backbone results in the formation of valence bands as well as conduction bands, which extends over the entire polymer molecule.
• Presence of conjugated$\pi$-electron in a polymer increases its conductivity to a larger extent. For example: Poly-p-phenylene, polyquinoline, polyaniline, polypyrrole, etc.

DOPED CONDUCTING POLYMER:

• It is obtained by exposing a polymer to a charged transfer agent in either gas phase or in solution.
• Intrinsically conducting polymers possess low conductivity, but these possess low ionisation potential and high electron affinities, so these can be easily oxidised or reduced.

Consequently, the conductivity of intrinsically conducting polymer can be increased by creating either positive or negative charges on the polymer backbone by oxidation or reduction.

This technique is called doping. It is of the two types

1. p-doping
2. n-doping

Examples:

(i)

$\text{(C}_2\text{H}_2)_n + 2\text{FeCl}_3 \rightarrow \text{(C}_2\text{H}_2)_n^+\text{FeCl}_4^- + \text{FeCl}_2$

Where,

$\text{(C}_2\text{H}_2)_n$-Polyacetylene

$ \text{(C}_2\text{H}_2)_n^+\text{FeCl}_4^- $-Lewis acid

$2\text{(C}_2\text{H}_2)_n + 3\text{I}_2 \rightarrow 2[\text{(C}_2\text{H}_2)_n ^+\text{I}_3^-]$

(ii)

$...-\text{CH}=\text{CH}-\text{CH}=\text{CH}-... + \text{B} \xrightarrow{Reduciton} ...-\text{CH}=\text{CH}-{\text{CH}}=\text{CH}-...\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{B}^+$

2. Polymers in medicine and surgery

Polymers for medical applications:

1. Polymers for artificial joints
2. Bioabsorbable polymers for surgical applications
3. -Adhesives for medical applications

(i) Polymers for artificial joints

There are several regenerative treatments, but joint replacement with an artificial joint is the most common and effective treatment

The artificial joint has a sliding interface using a combination of a hard material against a soft material.

Hard material: Metallic femoral head

Soft material: polytetra-fluoroethylene (PTFE) shell

Cement material: Cold curing acrylic cement (polymethylmethacrylate)

The soft material made of polytetra-fluoroethylene (PTFE), then it was replaced by high density polyethylene (HDPE) and later by ultra hogh molecular polythere (UHMWPE)

UHMWPE was chosen because of its low friction coefficient, high resistance to wear, high impact resistance, high ductility and stability in the body.

(ii) Bioabsorbable polymers for surgical applications

Polymeric materials and composites have been used in medical applications; tissue replacement; support of tissues and delivery of drugs

Based on their behaviour in living tissue, polymeric biomaterials can be divided into

1. Biostable
2. Bioastable (biodegradable)

(iii) Adhesives for medical applications

Bioabsorbable sutures are used in the fixation of bone fractures, closure of soft tissue wound etc.