| name | properties |
| carboxypolymethylene (carbomer) (carbopol) | 1-used as suspending agent ,binding in tablets ,and in formulation of prolonged-acting tablets. 2-it is high Mwt polymer of acrylic acid ,cross-linked with allyl sucrose and contain high proportion of cooH group 3-its aq. Soln is acidic and sol in water 4-its viscousity is low so when neutralize soln it become very viscous (bet. pH 6-11) form salt (responsible for high viscousity 5-electrolytes reduce viscousity so you must add high conc of polymer where ionizable drugs are present.(to compensate decrease in viscousity) |
| cellulose derevative (as cellulose itself not water sol) | |
| ethylcellulose | 1-ethyl ether( ethoxy gr.oc2h5)_ of cellulose contain 44-51% of ethoxy gr. 2-insol. In water but sol in chloroform & alc 3-posiible to form water sol grades with lower degree of substitution (decrease no of ethoxy gr). |
| commercial methyl cellulose | 1-prep by heterogenous reaction of 1/2 -oH gr. In chain And methyl gr. 2-methylated groups are not evenly distributed throughout the polymer chains (regions are of high density) |
| methylcellulose | 1-methyl ether of cellulose contain 29% of methoxyl gr 2-slowly sol in water 3-4% soln of MC of Mwt 4500 has gel point of about 50c(good viscousity) but ts defect is sol. in cold water4-low viscousity grades are used as emulsifiers for liq parrafin & other mineral oils 5-high viscousity grades used as thickening agents in medicated jellies and in suspention 6-evenly distibuted due to methylation of all oH gr.7-poorly sol in cold water so wetting by hot water then dispersing in cold water |
| sod carboxy methylcellulose' | 1-sol in water at all temps because of cooH gr (acidic) 2-viscousity depend on pH 3-viscousity decreased below pH 5 (acidic) or above 10(alkaline) so kept in pH neutral {bet 5-10} to give highly viscous soln 4-addn of heavy metal ions (al,zn,fe+2) causes decrease in viscousity |
| ethylmethyl cellulose | 1-contain ethyl & methyl gr sol in water .hydroxyethylcellulose 1-is sol in hot and cold water but does not gel 2-used in opthalmic solns (prolongation of effect of drug) hydroxypropylmethylcellulose (hypromellose) 1-contain methoxy (27-30% ) and propoxy ether linkage (4-7.5%) 2- hyprocellulose has 2 grades 1st: HM20 is 2% soln (viscousity bet 15-25 cp at 20c ) HM15000 in 2% soln (vis. bet 12000-18000cp )at 20c 3-used in medicated eye drops and artificial tear fluid and in soln of contact lens. and it is better than ethyl me.ce. |
| natural gums and mucilage | |
| gum arabic (acacia gum) | 1-used as emulsifier(emulsifing agent) 2-it is polyelectrolyte and its soln is highly viscous due to branched structure 3-it has high Mwt bet 200,000 & 250,000 (250,000 when measuered by os.pr) and bet 300,000 (by sedimentation and diffusion) and 1 million by( light scattering and could determine shape). 4-its shape is short stiff spirals with numerous side chains 5-gum arabic is incompatible with several phenolic comp (phenol,thymol,eugemol,cresols) ,,, ARABIC ACID is prep from gum arabic by pptn ,, a-very strong acid (2.2-2.7) b-higher viscousity than gum arabic c-so it is used as emulsifier not gum acaciabut emulstions prepared by arabic cream are unstable (separation of emulsion). |
| gum tragacanth | partially dissolves in water and the sol part called tragacanthin 1-purified by pptn from water by acetone or alc 2-highly viscous polyelectrolyte (max viscousity at (PH=8)initially but due to aging effects it is found that max stable at (PH=5) 3-it is one of the most widely natural emulsifier and thickener 4-used as combination with gum acacia as emulsifing agent but g.tragacanth only used as thickening and suspending agent and can be used in spermicidal jellies (act as viscous barrier in which sperm is retained against its transfere) في تحديد النسل |