HPC is non ionic semisynthetic polymer.
Hydroxypropyl cellulose is also commonly known as hydroxypropyl methylcellulose (HPMC) or hypromellose which is a coating agent and film-former and used as an inactive ingredient in the pharmaceutical industry. It has also been used as a rate-controlling polymer for sustained-release dose forms in pharmaceutical industry.
HPC is an ether of cellulose. In HPC some of the hydroxyl groups in the repeating glucose units have been hydroxypropylated which forms -OCH2CH(OH)CH3 groups using propylene oxide. The average number of substituted hydroxyl groups per glucose unit is referred to as the degree of substitution (DS).
In some cases hydroxypropyl group when added contains a hydroxyl group, this can also be etherified during preparation of HPC. In such case the number of moles of hydroxypropyl groups per glucose ring, moles of substitution (MS), can be higher than 3.Complete substitution for HPC is 3.
Since cellulose is very crystalline in nature, HPC must have an MS about 4 in order to have a good solubility in water. HPC has a combination of hydrophobic and hydrophilic groups, so it has a lower critical solution temperature (LCST) at 45 °C. At temperatures below the LCST, HPC is readily soluble in water; above the LCST, HPC is not soluble.
HPC have ability to form liquid crystals and many mesophases according to its concentration in water. Such mesophases include isotropic, anisotropic, nematic and cholesteric.