Polymers PDF

Physical Pharmacy Polymers Dr.Khalid T Maaroof 1 Introduction Polymers are substances of high molecular weight made up of repeating monomer units. Examples: Proteins (monomer is amino acid) Polysaccharide (monomer is saccharide)  Introduction The...

Physical Pharmacy Polymers Dr.Khalid T Maaroof 1 Introduction Polymers are substances of high molecular weight made up of repeating monomer units. Examples: Proteins (monomer is amino acid) Polysaccharide (monomer is saccharide)  Introduction The word “polymer” means “many parts.” the physical and mechanical properties of the polymer can be tailor-made. HOW? Polymer categories  Polymer categories – based on composition Polymers in which all the monomeric units are identical are referred to as homopolymers; those formed from more than one monomer type are called copolymers.  Polymer categories – based on linkage and structure Polymers can be: Linear or Branched Have crosslinking or not Crystalline or amorphous Entangled polymers? secondary bonding Linear Branched Cross-Linked Network  Branched or linear polymers Polymers can be branched or linear. When branched they can form networks of polymers. Branched chains can freely move, which offers the polymer a low melting temperature. On the other hand, linear chains have a higher chance of approaching each other in their solid state, which increases their crystallinity and melting temperature.  Polymer crosslinking linear or branched chains may be joined by crosslinks. The chains are chemically linked and will be restricted from moving depending on the level of cross-linking. Very highly cross-linked polymers are very rigid (three dimensional) structures that degrade at high temperatures before their chains start to move (why they do not melt?). If a polymer is cross-linked, its solubility will be sacrificed at the expense of swellability. Polymer crosslinking  Gels Gels are formed when crosslinked polymers are added to solvents (most commonly water). The polymers do not dissolve in the solvent but instead swell. Incorporation of the solvent in to the structure of the polymers leads to the formation of the gel. Polymers used for preparation of gels are called gelling agents (eg: carbapol) Gels  Crystalline and amorphous polymers Polymers are rarely 100% crystalline as it is difficult for all regions of all chains to become aligned. crystalline region amorphous region  Pharmaceutical application of polymers The pharmaceutical applications of polymers range from their use as binders in tablets to viscosity and flow controlling agents in liquids, suspensions and emulsions. Polymers can be used as film coatings to mask the unpleasant taste of a drugs. To enhance drug stability To modify drug release characteristics [controlled release (e.g. extended, pulsatile and targeted) enhanced stability and improved bioavailability.]  Characteristics of ideal polymer system Inert and compatible with environment. Nontoxic. Easily administrable. Easy and inexpensive to fabricate the dosage form. Good mechanical strength. An example for polymer based technologies in drug delivery. Questions?