Lecture 8 Flashcards
DEF:A large molecule (macromolecule) built up by repetitive
bonding (covalent) of smaller molecules (monomers= A, B, …etc)
Polymer
Polymers could be classified based on:
- chain chemical structure backbone
- monomers type
- Arrangement of monomer
- Structure
- Thermal behaviour & Molecular Forces
- Origin (Sources)
- Mode of polymerization
Polymers are formed by linking monomers through chemical
reaction_____
Polymerization
is represented by chains with two ends.
Linear polymer
have side chains, or branches, of significant
length which are bonded to the main chain at branch points, and are
characterized in terms of the number and size of the branches.
Branched polymer
___have three dimensional
structures in which each chain is connected to all others by a
sequence of junction points and other chains.
Cross-linked or network polymer
Thermal Behaviour between polymerchains:
Thermoplastic
Thermosetting
____These are the linear or slightly branched
long chain molecules capable of repeatedly softening on heating and hardening on cooling.
Thermosplastic
______These polymers are cross linked or heavily branched molecules, which on heating undergo
extensive cross linking in molds and again become infusible.
Thermosetting polymers
Polymers can be classified into two categories based on the
forces of attraction:
Elastomers
Fibers
How does the forces of attraction affect polymer chain:
Forces of attraction bind the polymer chains and affect polymer mechanical properties like tensile strength, elasticity, toughness,
…..etc. which determine polymer applications.
These mechanical properties are governed by intermolecular forces, e.g., van der Waals forces and hydrogen bonds, present in the polymer.
____is a randomly oriented amorphous polymer.
Elastomer
stretches
and then reverts back to its original shape. In these elastomeric polymers, the
polymer chains are held together by the weakest intermolecular forces. These
weak binding forces permit the polymer to be stretched
Elastomers
are the thread forming solids which possess high tensile
strength. These characteristics can be attributed to the strong
intermolecular forces like hydrogen bonding
Fibers
Natural polymers aka:
Bio-polymer
examples of Natural polymers
Proteins, nucleic
acids, polysaccharides,
rubber and resins.
examples of Semi-synthetic
polymers
Cellulose
derivatives as cellulose
acetate and cellulose
nitrate
examples of Synthetic polymers:
Man-made polymers
produced industrially: plastic
(polythene), synthetic fibres
(nylon) and synthetic rubbers
Whats the first synthetic polymer:
organic polymer polyvinylchloride
Methods of preparation of synthetic polymers:
- Addition Polymers
- Condensation polymers
Addition polymers aka:
Chain growth
condensation polymers aka:
Step growth
example of addition polymer:
the formation of polythene from ethene and polypropene from propene
When 2 or more monomers are
involved in the addition polymer, the product is referred to as:
Co-polymer
3 steps involved in polymerization:
- Initiation
- Propagation
- Termination
reactive intermediates used in addition polymer:
reactive intermediate such as free radicals, cation or anions without loss
of small molecules.
The reactive intermediate involved in the polymerization of ethene:
- product: polythene
- reactive intermediate: Benzoyl peroxide initiator that produces phenyl
an important requirment in condesation polymers:
2 functional groups
examples of condensation polymers:
Nylon: formation of amide linkage with water loss
Properties of polymers:
1.Polydispersity:all synthetic polymers and naturally occurring macromolecules possess a range of molecular weights,because there is a range of sizes for polymer chains
2.Thermal behavior:Polymers do not have a sharp melting point because they
are transformed from semi-crystalline to a solid amorphous
phase and subsequently they have a melting range.
3.solubility: Water-soluble polymers have an ability to increase the viscosity of solvents at low
concentrations, to swell or change shape in solution. they are used as suspending
agents, in drug-polymer conjugates and in the formation of soluble macromolecular
drug carriers.
polymers that dont posses polydispersity:
- proteins or naturally occuring macrmolecules
The rate of dissolution of a water-soluble polymer depends on its
molecular weight
solubility property of large water-soluble polymers:
the larger the molecule, the stronger are the forces holding the chains together and more energy is needed to force the chains apart in the solvent
the greater the degree of crystallinity of the polymer, the lower is the___
rate of dissolution
Insoluble polymers or polymers with a low rate of solution are used in:
- To form thin films
- As film coating materials
- As surgical dressings
- As membranes for dialysis or filtration
- As matrices for enveloping drugs to control their release properties
- As packaging materials
Drug entrapped in a micro/nanoparticulate polymer:
- Matrix System:
- Reservoir System
def: Drug is dispersed in an insoluble matrix of rigid non-swellable hydrophobic materials or swellable hydrophilic substances
Matrix system
def: these system are hallow containing inner core of drug surrounded in a water-insoluble polymer membrane
Reservoir system
factors that affect matrix system vs reservoir system:
Matrix system: polymer property, the diffusivity of drug in the matrix, nature of drug and excipients, geometry
Reservoir system: membrane thickness, membrane porosity, chemical nature of membrane material, nature of drug & excipients
How are molecules weighed in polydispersity?
Determined by:
- Chemical Analysis
- Osmotic pressure
- Light-scattering measurements
