Physical Pharmacy: Polymers Introduction

Introduction to Polymers

• Polymers are substances of high molecular weight made up of repeating monomer units.
• Examples of polymers include proteins (monomer is amino acid) and polysaccharides (monomer is saccharide).
• The word "polymer" means "many parts".
• The physical and mechanical properties of polymers can be tailored-made.

Polymer Categories

• Polymers can be categorized based on composition into homopolymers and copolymers.
• Homopolymers are formed from identical monomeric units, while copolymers are formed from more than one monomer type.
• Polymers can also be categorized based on linkage and structure into linear, branched, cross-linked, crystalline, amorphous, and entangled polymers.

Branched or Linear Polymers

• Polymers can be branched or linear, and branched polymers can form networks of polymers.
• Branched chains can freely move, which offers the polymer a low melting temperature.
• 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, which restricts their movement.
• Very highly cross-linked polymers are very rigid (three-dimensional) structures that degrade at high temperatures before their chains start to move.
• If a polymer is cross-linked, its solubility will be sacrificed at the expense of swellability.

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 into the structure of the polymers leads to the formation of the gel.
• Polymers used for preparation of gels are called gelling agents (e.g., carbapol).

Crystalline and Amorphous Polymers

• Polymers are rarely 100% crystalline as it is difficult for all regions of all chains to become aligned.
• Polymers can have both crystalline and amorphous regions.

Pharmaceutical Applications 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 drug.
• Polymers can enhance drug stability, modify drug release characteristics, and improve bioavailability.

Characteristics of Ideal Polymer System

• Inert and compatible with the environment.
• Nontoxic.
• Easily administrable.
• Easy and inexpensive to fabricate the dosage form.
• Good mechanical strength.
• Example: polymer-based technologies in drug delivery.