Polymers are additives used widely in pharmaceutical systems for numerous objectives, i.e. as suspending, emulsifying and flocculating agents, adhesives, and for packaging and coating materials. Polymers are made up of repeating monomer units with a high molecular weight. Their chemical reactivity depends on the chemistry of their monomer units, but their properties depend mainly on how the monomers are assembled together. Nearly all polymers exist with a range of molecular weight and for convenience the reported molecular weight of a polymer is the average molecular weight. In agree with Florence & Attwood, 2003 water soluble polymers have the capability to increase the viscosity of solvents at low concentrations, to swell in solutions and …show more content…
The kinetics of the gel layer formation depends on the external parameters like temperature, molecular weight of the polymer, and pH of the solution. HPMC was the subject of many studies. The Ph. Eur. describes hypromellos, as a partly O-methylated and O-(2-hydroxypropylated) cellulose. It is available in several grades that vary in viscosity and extent of substitution. Grades may be distinguished by appending a number indicative of the apparent viscosity, inmPas, of a 2% w/w aqueous solution at 20°C. Hypromellose defined in the USP 32 specifies the substitution type by appending a four-digit number to the nonproprietary name: e.g. hypromellose 1828. The first two digits refer to the approximate percentage content of the methoxy group (OCH3).These two digits refer to the approximate percentage content of the hydroxypropoxy group (OCH2CH(OH)CH3), calculated on a dried basis. It contains methoxy and hydroxypropoxy groups conforming to the limits for the various types of hypromellose. Molecular weight is approximately 10000–1500000. Hypromellose (INN), short for hydroxypropyl methylcellulose (HPMC), is a semisynthetic, inert, viscoelastic polymer used as excipient in eye drops, as well as an excipient and controlled-delivery component in oral medicaments, found in a variety of …show more content…
Evidence suggests that the chemistry of hypromellose encourages a strong, tight gel formation compared to other cellulose derivates. As a result, drug-release rates have been sustained longer with hypromellose than with equivalent levels of methylcellulose (MC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC) or carboxymethylcellulose (CMC). For these reasons, hypromellose is very often the polymer of choice over other cellulose