Advanced Polymeric Materials

Conducting Polymers

1. Polyacetylene

a. Structure

Polyacetylene consists of a long chain of carbon atoms with alternating single and double bonds between them, each with one hydrogen atom. The double bonds can have either cis or trans geometry. The controlled synthesis of each isomer of the polymer, cis-polyacetylene or trans-polyacetylene, can be achieved by changing the temperature at which the reaction is conducted.

b. Preparation

A variety of methods have been developed to synthesize polyacetylene, from pure acetylene as well as other monomers. One of the most common methods uses titanium and aluminum catalysts, known as Ziegler-Natta catalysts, with gaseous acetylene.

c. Application

1. The discovery of polyacetylene as a conductive organic polymer led to many developments in materials science.2. Conducting polymers are of interest for low-cost solution-processing for film-forming polymer3. Both cis andtrans-polyacetylene show high thermal stability

2. Polypyrrole

a. Structure

b. Preparation

a. Most commonly Ppy is prepared by oxidation of pyrrole, which can be achieved using ferric chloride in methanol:

n C4H4NH + 2 FeCl3 → (C4H2NH)n + 2 FeCl2 + 2 HCl

b. Conductive forms of PPy are prepared by oxidation ("p-doping") of the polymer:

(C4H2NH)n + x FeCl3 → (C4H2NH)nClx + x FeCl2

c. Applications

a. PPy and related conductive polymers have two main application in electronic devices and for chemical sensors.b. PPy is also potential vehicle for drug delivery. c. The polymer matrix serves as a container for proteins.

3. Polyaniline

a. Structure

b. Preparation

Although the synthetic methods to produce polyaniline are quite simple, the mechanism of polymerization is probably complex. It can be

described as follows, where [O] is a generic oxidant:

n C6H5NH2 + [O] → [C6H4NH]n + H2O

c. Applications

1. Has three distinct oxidation states with different colors and has an acid/base doping response due to which it is used as an attractive for acid/base chemical vapor sensors, supercapacitors and biosensors.

2. Also used for applications such as actuators, supercapacitors and electrochromics. 3. They are suitable for manufacture of electrically conducting yarns, antistatic coatings, electromagnetic shielding, and flexible electrodes.

High Temperature Polymer

Most organic polymeric materials melt below 200°C and most of them begin to degrade rapidly at temperatures only slightly above 200°C. Thermally stable polymers are generally considered to be those which will withstand much higher temperatures without loss of strength or change of structure. In general we expect these materials to withstand at least 300°C in air and up to 500°C or higher in inert atmospheres. Polymers, which show these properties, are usually highly aromatic in structure, often with heterocyclic units, high melting, sometimes infusible and usually with low solubility in all solvents. This makes their fabrication very difficult and as a consequence limits their usefulness.There are a relatively few polymers which are available commercially as plastics, films, wire-coating polymers, etc. which are stable in the temperature ranges indicated. There are other polymers which have been synthesized and tested in pilot-plant, scale which show promise but are still very expensive and not generally used. Finally there are other classes which have been studied in the laboratory and have not yet reached the development stage.

1. Polyimides

a. Structure

b. Preparation

Several methods are possible to prepare polyimides, among them:

The reaction between a dianhydride and a diamine (the most used method).

The reaction between a dianhydride and a diisocyanate

c. Applications

1. They are used in the electronics industry for flexible cables, as an insulating film onmagnet wire and for medical tubing.

2. The semiconductor industry uses polyimide as a high-temperature adhesive; it is also used as a mechanical stress buffer

3. An additional use of polyimide resin is as an insulating and passivation[4] layer in the manufacture of digital semiconductor

4. Used as bushings, bearings, sockets or constructive parts in demanding applications.

2. Polyarylsulphones

a. Structure

(Draw any one out of it)

b. Preparation

A typical polysulfone is produced by the reaction of a diphenol and bis(4-chlorophenyl)sulfone, forming a polyether by elimination of sodium chloride:

n HOC6H4OH + n (ClC6H4)2SO2 + n Na2CO3 → [OC6H4OC6H4SO2C6H4]n + 2n NaCl + n H2O + n CO2.

The diphenol is typically bisphenol-A or 1,4-dihydroxybenzene. Such step polymerizations require highly pure monomer to ensure high molecular

weight products.

c. Applications

i. Polyarylsulfone is used in the automotive industryii. Polyarylsulfone is used in the electrical and electronics industry

iii. water fittingsiv. Pump impellersv. Microwave Dishes

Biomedical Applications of

1. Hydrogel: - The hydrogel can be defined as a crosslinked polymeric network which has the capacity to hold 2 water within its porous structure

Application of hydrogel in Biocompatibility tests

The biocompatibility of the hydrogels is generally associated with the hydrophilic nature of the same, which helps in washing off the toxic and un-reacted chemicals during synthesis. The presence of water in the system makes it soft and rubbery which offers least frictional irritation and provides a soothing effect when in contact with the physiological system

Application of hydrogel in hydrogels in drug delivery

When the drug bearing hydrogel comes in contact with aqueous medium, water penetrates into the system and dissolves the drug. Diffusion is the main phenomena by which the dissolved drug diffuses out of the delivery systems to the surrounding aqueous medium. Diffusion is defined as the movement of the individual molecules from the region of high solute concentration to a region of low concentration when the systems are separated by a polymeric membrane

Application of hydrogel in wound healingHydrogel is a cross-linked polymer matrix which has the ability to absorb and hold water in its network structure. Hydrogels act as a moist wound dressing material and have the ability to absorb and retain the wound exudates along with the foreign bodies, such as bacteria, within its network structure. In addition to this, hydrogels have been found to promote fibroblast proliferation by reducing the fluid loss from the wound surface and protect the wound from external source necessary for rapid wound healing.

Application of hydrogel in tissue engineeringTissue engineering (TE) is a multidisciplinary approach and involves the expertise of materials science, medical science and biological science for the development of biological substitutes (tissue/ organ). In practice, the patient’s cells are generally combined with a scaffold for generating new tissue. A scaffold can be made up of either ceramic or polymer, which can be either permanent or restorable.

Application of hydrogels for gene delivery

Gene delivery is defined as the incorporation of foreign DNA particles into the host cells and can be mediated by viral and non-viral methods. The non-viral techniques include the use of a gene gun, electroporation and sonication. Of late researchers have started the use of polymers. The use of hydrogel for the delivery of plasmid-beta 1 gene increased the wound healing process in diabetic mouse