the hydrophobically modified polymer of the invention shows improved solution properties such as enhanced viscosification , shear and temperature stability . although , there are a few reports on modified paa , this is the first report on the modification of paa with hydrophobic compounds of formula ( 2 ) and ( 3 ) above obtained from the renewable resources , cnsl ( cashew nut shell liquid ). the present invention provides for the synthesis of hydrophobically modified poly ( acrylic acid ) with 3 - pentadeyl phenol derived from the cashew nut shell liquid ( cnsl ), a renewable resource material , available in abundance in india . these modified polymers show excellent solution properties compared to the unmodified precursor . because of their enhanced properties , they have potential application in eor , cosmetic lotions and creams . the present invention is the first attempt to modify paa with the hydrophobic compounds , which are obtained from renewable resource materials . the present invention relates to the hydrophobically modified poly ( acrylic acid ) and preparation thereof . the hydrophobic compounds used in this study were derived from a renewable resource material viz cnsl . the approach described herein consists of post - polymerization coupling of hydrophobic groups onto poly ( acrylic acid ). therefore , the hydrophobic groups are randomly dispersed along the polymer backbone chain . the present invention involves a coupling reaction of alkyl phenol with a carboxylic groups of paa in an aprotic solvent such as nmp , 1 - 4 dioxane etc . in the presence of dicyclohexyl dicarbodiimide ( dcci ). poly acrylic acid was chosen as the backbone chain in the present invention due to several reasons . the chemistry of paa is more versatile and the coupling reactions can be carried out in both aqueous and organic media . furthermore , under the ionized form , paa is highly soluble in water even with hydrophobic content of as high as 20 mol %. incorporation of hydrophobic groups onto polymers containing carboxylic groups can in principle be done by acid chloride reactions . however , the handling of acid chloride of polymers is very difficult and moreover these reactions are very sensitive to the moisture . alternatively , dcci coupling reactions are well established for amines , alcohols and acids . therefore , in the present investigations , dcci coupling reaction was used for the modification of paa . dcci is found to be an efficient reagent for such coupling reactions . a base such as dimethyl amino pyridine ( dmap ) is used as a catalyst / accelerator in these reactions . additionally , the side product is dicyclohexyl urea in these reactions , which can be easily removed from the product since it is insoluble in most aprotic solvents that are used for such coupling reactions . we have found that coupling reaction beween 3 - pdp and paa is more efficient in aprotic solvent , 1 , 4 dioxane . many of the water - soluble polymers such as polyethylene glycol , polyvinyl alcohol , poly ( acrylic acid ), polyamide , poly ( aspartic acid ), polysaccharides ( epec , hpc ) etc . can be hydrophobically modified by incorporating hydrophobic groups . the hydrophobic content in these polymers is less than 3 - 4 mol % and above this , the polymer becomes insoluble in water due to the dominance of hydrophobicity of the polymer the term hydrophobic modification means the incorporation of hydrophobic groups such as long chain alkyl [ c 8 - c 18 ] groups ( octyl , dodecyl , hexadecyl , octadecyl amines etc ), nonyl phenols , long chain terminal epoxides . various molecular architectures such as random , block , graft copolymers , end - capped polymers and interpolymer complexations have been envisaged for designing hydrophobically modified polymers . wherein , r 1 is c 6 h 5 - c 15 ( alkyl phenyl ) the ‘ m ’ and ‘ n ’ vary depending on the molecular weights . the molecular weight of the backbone poly ( acrylic acid ) ranged from 100 , 000 to 250 , 000 daltons and the hydrophobic content varies from 0 . 1 - 4 . 0 mol % ( w / w ). the process for preparation of the hmp of formula ( 1 ) essentially comprised coupling of hydrophobic compounds ( formula 2 and 3 ) using dcci reagent in an aprotic solvent , allowing the reaction for a period of 12 - 24 hrs . at 60 ° c ., isolating the product by precipitating in a non - solvent , vacuum drying the product at 40 ° c . to obtain the pure hmp . the water - soluble polymer used for the preparation of hmps can be poly ( acrylic acid ), poly ( methacrylic acid ), poly ( aspartic acid ), copolymer of poly ( acrylic acid ) and the poly ( 2 - acrylamido 2 - methyl propane sulfonic acid ). the hydrophobic compounds can be 3 - penta decyl phenol [ 3 - pdp ], alkyl amines . the aprotic solvents used for hydrophobic modifications are preferably n - methyl pyrrolidone , dimethyl formamide or 1 - 4 dioxane . the coupling agent is selected from compounds such as dcci , 1 - cyclohexyl 3 - 2 - morpholino ethyl carbodiimide metho - p - toluene sulfonate ( cmc ), 1 - ethyl - 3 -( 3 - dimethylamino propyl ) carbodiimide ( edc ). a catalyst / accelerator , dmap can be used to enhance the reaction rate . the hydrophobic content in these polymers ranges from 0 . 1 to 4 . 0 mol %. the non - solvent used to precipitate the hmp may be methanol , ethanol , isopropanol . the hydrophobic modification is preferably carried out in the temperature range of 50 - 80 ° c . the hydrophobically modified polymers are useful for applications in health care products such as lotions and creams , etc . the hmps exhibit enhanced / improved solution properties and are more stable towards temperature , salts and shear as compared to their unmodified precursors . it is believed that the present invention is the first report on the hydrophobic modification of paa by using hydrophobic compound , which is derived from the renewable resources . the observed enhanced solution properties of hmps are attributed to association of hydrophobic groups dispersed along the backbone chain . the synthesis of hmps of the invention is described below with reference to illustrative examples , which should not be constructed to limit the scope of the present invention in any manner . this example describes the process for the preparation of hydrophobically modified paa using 3 - penta decyl phenol ( 3 - pdp ), which is derived from cnsl . hydrophobically modified paa was synthesized by the coupling reaction of alkyl phenol ( 3 - pdp ) on carboxyl groups of paa ( paa - 250 aldrich , mw - 250 , 000 ) in an aprotic solvent , 1 , 4 dioxane , in the presence of dcci . paa - 250 ( 0 . 695 mol ) was dissolved over 12 h in 1 , 4 dioxane ( 175 ml ) at 60 ° c . 3 - pdp ( 0 . 0138 mols ) and dcci ( 0 . 00694 mols ) were separately dissolved in 1 , 4 dioxane ( 25 ml ) each and added drop wise ( over 15 min ) to paa - 250 solution . the reaction was carried out at 60 ° c . for 24 h . the product was dissolved in water and neutralized with sodium bicarbonate ( 10 wt %). the neutralized polymer was precipitated in methanol . washing with hot dioxane and methanol , purified the polymer . finally the product was dried under vacuum at room temperature . hydrophobically modified paas with different contents of hydrophobic compounds were prepared using the above - mentioned procedure . the stoichiometry of the reaction is given in table 1 this example describes the theological characterizations of the hydrophobically modified paa ( 2 . 0 mol % modification ). in order to evaluate the solution properties of the modified paa , the steady shear experiments were performed on 2 . 0 wt % solution of the unmodified and the hydrophobically modified paa using a strain controlled rheometer ( ares , rheometric scientific ). cup and bob , parallel plate , cone and plate geometries were used depending on the consistency of the solutions . steady shear stress and corresponding viscosities were measured at 30 , 40 , and 60 ° c . the comparative study between the steady shear rheology of the unmodified and the hydrophobically modified poly ( acrylic acid ) solutions at 30 ° c . and 40 ° c . shows that the poly ( acrylic acid ) solutions exhibit a newtonian behaviour , i . e ., the shear stress increases linearly with shear rate and the shear viscosity (˜ 7 cp ) is constant over the range of shear rates probed . the low viscosity and the newtonian behaviour are indicative of the fact that the solution is probably dilute ( i . e ., there are no entanglement effects ). the viscosity decreases with increasing temperature as expected . in contrast , the hydrophobically modified poly ( acrylic acid ) shows very high low - shear viscosity (˜ 50 , 000 times higher than that of the unmodified poly ( acrylic acid ) solution under the similar conditions ).
the present invention relates to the development of hydrophobically modified polymers , which have emerged as promising materials in diverse fields such as paints , cosmetics , oils , food and textiles . they are used as thickeners in these applications . in our study , the hydrophobic modification on paa was performed using hydrophobic compounds obtained from naturally occurring materials such as cashew nut shell liquid , . the dcci coupling method was chosen for the hydrophobic modification of paa . a series of hydrophobically modified paas were synthesized with different degrees of hydrophobic contents and were characterized by solution rheology .