Question

5. When termination is by chain transfer, what is the relationship of average degree of

polymerization DP) and the kinetic chain length? Compare and contrast dendrimers with

block copolymer micelles, globular proteins, inorganic nanoparticles in terms of attributes and

hkely utlity in the following applications:(a) drug delivery; (b) homogenous catalysis, and(c)

solubilization.

6. When a dilute solution of block copolymers undergoes micellization, ie, some numbers

of

chains aggregate into a(usually spherical) assembly to shield one block from the solvent it does

not lke, the light scattering intensity increases. In fact, if micellization is induced by changing

temperature at a fixed conlentration the ratio of the intensity after micellization to that before

micellization is a good estimate of the average aggregation number of the micelles. Explain this

observation.+

Answer 1

Degree of polymerisation is given by,

DP = 1/1-P.

Kinetic chain length is given by the propagation step which will be divided by initiation step.

But when the reaction goes towards completion, the concentration of monomer become equal to zero and then the kinetic chain length is equal to the number average degree of polymerization of the polymer. That means , kinetic chain length is an average quantity.

Dendrimers are synthetic macromolecules which is composed of repetitive layers of branching units. These branching units emerges from a central core.

Dendrimers are characterized by two ways :

1) By tunable size,

2) By the precise number of peripheral groups.

These peripheral groups determines the physiochemical properties and functions of dendrimers.

Dendrimers have high multivalency, functional surface and globular architecture. This globular architecture have nanometer size diameter which makes it suitable for wide range of applications.

a) Application of dendrimer In drug delivery:- one of the famous dendrimer is GATG (gallic acid triethylene glycol). The presence of terminal azide groups In GATG dendrimer and PEG (poly ethylene glycol) dendritic block copolymers makes it efficient to attach with variety of ligands for biomedical relevance. Due to this the resulting functionalized dendrimers have application In drug delivery and gene delivery. Dendrimers are used as an antiviral agents . This is also used for the treatment of neurodegenerative diseases and In diagnosis.

b) Application of dendrimers In homogeneous catalysis:- dendrimers In homogeneous catalysis is used as non - chiral dendritic transition metal complexes. For example: kharasch addition of ccl4 to methacrylate is catalysed by Ni(II) , CO/Alkene polymerisation catalysed by Pd(II) and rhodium catalyzed hydroformylation reaction etc.

c) The third application is solubilization. Dendrimers have potential application In enhancing solubility of poorly soluble drugs. Because dendrimers have hydrophilic exteriors and interiors as well which are responsible for its unimolecular micelle nature to increase the solubility for drug delivery.