Journal of Intellectual Property Rights Vol 4 July 1999 pp 199-206

Value-Added Materials from Cashewnut Shell Liquid: A Study on Their Recent Patents

C K S Pillai

Regional Research Laboratory, Thiruvananthapuram 695019

Recent research has shown that cashewnut shell liquid (CNSL) has the potential of conversion into high value polymer. A number of patents have emerged highlighting the importance of this material. This paper reviews the recent patents and the inventions behind the patents, and describes value addition in R&D through an examination of technical information in patents.

Cashewnut shell liquid (CNSL) is a natural raw material available in India and in many parts of the world. Its potential applications have been described in a number of pat­ents,1.3 publications and reports4-13. The cashew industry, however, considers that it is still underutilized. Research carried out at the Regional Research Laboratory, Thiru­vananthapuram ~ TVM), with a view to transforming this material into a high value product showed that the vast scope and op­portunities for its utilization lie in its special . structural features which can be chemically transformed into speciality and high per­formance polymers. This involves a value addition of many orders of magnitude and the chemical transformation involves inter­mediates that are 100% chemically pure such that all the problems of CNSL utilization can at a stretch be overcome. It would be appro-

priate at this time to make an evaluation of prospects available for value-added materi­als for exports and internal markets. Both conventional applications and the futuristic potentials are described here.

The extraction and uses of CNSL have been described mainly through patents. These patents have been codified by the Cashew Export Promotion Council, Ernakulam, into three main documents1. ~ese patents mainly describe a number of applications such as automotive brake lining applications as binders/friction dust, surface coatings, foundry core oil, laminating resins, rubber compounding resins, adhesives, etc. A num­ber of reports and few reviews deal with the chemistry and utilization of CNSL 4.13.

The RRlr TVM has developed a number of speciality products from CNSL and cardanol

200 J INTELLEC PROP RIGHTS, JULY 1999

for applications as flame retardants (FRs), adhesives, matrix resins for brake linings and composites, transparent resin for sur­face coatings, liquid crystalline polymers, etc. These products have been protected through patents l 4-34. The characteristic fea­tures of the inventions protected through a total of 20 patents will be described in the following sections. The related publications will also be cited to in<Jicate the creation of basic support data.

Anorin Series Speciality CNSL Products /Polymers

The Anorin series polymers, Anori.n-35, 38, 44 and 53, are multi- purpose resins prepared by introducing phosphorus and/or bromine into CNSL. They can be used as wide spec­trum FRs, adhesives (except Anorin-53), ma­trix resins for composites, brake linings, etc. Anorin-35, 38 and 44 are prepared as a pre­polymers and their inventions are protected through patentsl 3-14. The prepolymer" tech­nology is advantageous in that it can be proc­essed into thermoset products. It also eliminates the problems such as blooming, migration, leachability, etc. associated with conventional FRs. Moreover, only a particu­lar FR is functionally found suitable for a specific application. TIley are also very ex­pensive. These problems are overcome by the use of wide spectrum FRs. The prepo­Iymers of compounds having hydrophobic and hydrophilic groups in the same mole­cule are expected to be compatible and mis­cible with a wide spectrum of polymers. If FRgroups can be introduced into their struc­tures they might act as non-blooming FRs fnsoluble in water without problems of mi­gration and of course cost-effective. As men­tioned earlier, the Anorin series FRs are wide spectrum FRs prepared by introducing phosphorus and/or bromine into CNSL.

Additionally, Anorin-35, 38 and 44 possess adhesive properties midway between those of phenol-formaldehyde resins and vinyl res­ins, but cost only one third to that of phenol­formaldehyde resins.

Invention-l: Prepolymer Technology

Anorin -35 and 38 are similar products pre­pared by the phosphorylation and simultane­ous polymerization of CNSL in a single-step reaction without the use of solvents and cata­lysts. A multi-purpose resin in the fonn of a prepolymer was obtained. The technology on Anorin - 38 was scaled-up at Vikram Sarabhai Space Centre at 50 Kg leveL The process for preparinj the resin has been filed for Indian patent 4.

The characteristic features of Anorin-35 in­clude: processability into highly insoluble and infusible thermoset products having properties for tensile strength of 17-25 MN/m2, impactstren~ of 1.63-2.04 J (com­pared to 24-48 MN/m and 0.8 -1.5J respec­tively for phenol-formaldehyde resin (novolac) prepared under similar condi­tions), lap shear strength Oss) of anorin-35 bonded wood pieces-400±10 N/cm2, poten­tial use as multi-functional additive (a single additive to replace many of the conventional additives) for natural rubber, matrix resin for composites with superior (to phenolics) impact properties, bonding and resistance to hydrolysis but was inferior in tensile proper­ties.

AnOlin-35 has a number of potential applica­tions such as matrix resin for brake linings - longer life and lower fade values are ob­tained and as adhesive for wood, plywood and similar materials. Anorin - 35 gives bet­ter bonding than phenolic resin and can also replace synthetic adhesives of the water­based vinyl resins. Aqueous emulsion based on Anorin -35 enhances its applica-

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PIUA!: VALUE-ADDED MATERIALS FROM CNSL ...... 201

tion as adhesive and this has been recently protected through another patent15. Anorin-35 can be processed into thermally stable non-flammble friction dust for brake linings and this also has been protected through another patent16.

Anorin-35 can be used as matrix resin for composites to replace costly phenolic resin, as raw material for the preparation of Anorin - 44 and as leak proofs in concrete buildings.

Invention-2: Ablative Material

Anorin - 44 is prepared by the bromination of Anorin-35 prepolymer such that only 3 bromine atoms are introduced. Anorin-44 prepolymer itself can be processed into a solid in the powder form by heating it in an oven at 11 OCC for two hours. The prepolymer has vacant sites for poly-condensation reac­tions of the type of phenol-formaldehyde re­actions and gives further opportunities for processing into thermoset products. The process of .preparation of the resin has been patended1 ,

Introduction of bromine has raised the lim­iting Oxygen Index (LO!) value of Anorin -35 to 44 for the cured product giving it excel­lent flame retardant efficiency in terms of self- extinguishing characteristics equiva­lent to that passing UL 94 of V-O grade.

. Another significant property is its ablative cnaracteristics. It can protect materials from deterioration when exposed to hyper-ther­mal conditions such as what a space vehicle experiences when entering the earth.

Application of Anorin -44 includes as FR ad­ditive for plastics, elastomers and compos­ites (its potential use as FR additive for natural rubber has been filed for patent17

) as a matrix resin for composite materials, as surface coating for thermal insulation. As the material is black in colour and has a very

low thermal conductivity, it will tum out as a suitable coating for the interior of cars and refrigerators for controlling heat.

Invention-3: Anorin -53

Anorin -53 {3-(tetrabromo pentadecyl) 2,4,6-tribromophenol ([BPTP») is an FR obtained by the direct bromination of CNSL so that a total of seven bromine atoms are introduced such that they are distributed between the aliphatic (four) and aromatic (three) moie­ties. It was found that it is an efficient FRLS Oow smoke flame retardant) for ethylene vinyl acetate-based cable material. The processes of the preparation of the resin and related resins have been filed for patent1S-20.

The even distribution of bromine atoms be­tween the aliphatic and aromatic moieties of the same molecule gives a structural advan­tage for Anorin - 53 over fully aromatic FRs such as decabromodiphenyloxide (DBDPO). This permits the molecule to liberate hydrogen bromide or bromine dur­ing thermal decomposition over a wide­range of temperatures so that effective flame retardation is possible where as fully aro­matic FRs such as DBDPO liberates bro­mine at a much higher temperatures by which time decomposition of the polymer might have already started. As TBPTP pos­sesses both hydrophilic and hydrophobic groups in its structure, it will have good miscibility and compatibility with a wide va­riety of polymers.

It can substitute any halogenated flame re­tardant in the market especially those that are used in the cable industry. It scores over other halogenated flame retardants used by the cable industries particularly for use in polyolefins such as dichlorane plus, de­cabromodiphenyl oxide (DBDPO- Sytex 102) and 1,2- bis(tetrabromo phthalimide)­Sytex BT-93 in many respects. Dichlorane

202 J INTELLEC PROP RIGHTS, JULY 1999

plus exhibits the problem of blooming whereas DBDPO does not disperse uni­formly and reduces the mechanical proper­ties. TBPTP, on the other hand, does not bloom, and the reduction in mechanical properties is within the specified limits. In­dustrial testing and evaluation carried out at M/s NICCO Corporation, Calcutta, showed that TBPTP gives a FRLS composition with ethylene vinyl acetate (EVA) with a Limiting Oxygen Index of 30, UL 94 grade ofV-O, acid emission of less than 20%, and percentage smoke density rating of 7 - all within speci­fication for cable jacketing materials. The price of DBDPO is Rs 280/Kg compared to the cost of production ofTBPTP which is Rs 120/Kg.

Invention 4: FRLS EVA Cable Material

FRLS EVA cable material refers to a low smoke flame retardant cable material based on ethylene vinyl acetate co-polymer con­taining Anorin-53 [3-(tetrabromo pen­tadecyl) 2,4,6- tribromophenol (fBPTP) 1 as flame retardant formulated and com­pounded to get low smoke and self-extin­guishing flame retardant characteristics maintaining all the other properties such as mechanical, electrical, ageing, acid emis­sion, etc. within specifications. The compo­sition for this material forms content of the patent filed recently21 and two related pat­ents describe compositions in the case of flame retardant polyethylene and 50/50 blend of polyethylene and ethylene vinyl acetate co- polyme~2.23.

The test results carried out at M/s NICCO Corporation, Calcutta, for three composi­tions of An orin -53 with EVA were compared to those of DBDPO-EVA blends prepared under similar conditions. Thus, with EVA copolymer, Anorin-53 gave low smoke FRLS grades with self-extinguishing behaviour

(passes vertical burning tests equivalent to UL 94 V-O test) without adversely affecting other cable properties. The control sample has totally burnt off where as the test sample did not bum at all. There was no propaga­tion of flame and no after glow. The test was self-extinguishing. The evolution of smoke (smoke density rating 7) and acid emissions «2%) were within specifications. All other properties are within the specification for cable materials.

Invention 5: Poly (Cardanyl Acrylate)

One of the serious problems in the utilization of CNSL is its colour because of which only brown or dark/light brown products could be made from CNSL and this impedes its competitiveness with synthetic resins. So, there exists possibilities for developing transparent/ clear resin from CNSL which, if achieved, will totally solve many of the prob­lems in the utilization of CNSL. RRL-TVM has been successful in converting cardanol into a transparent resin by the method of acrylation/methacrylation and polymeriza­tion . Poly (cardanyl acrylate) (PCA) thus synthesized by various routes and optimiza­tion of the parameters to make the process cost-effective followed by studies on the properties of the resins for use as a base for surface coating. It is expected that the paint systems developed from CNSLI cardanol will have advantages in terms of cost and performance, particularly resistance to ac­ids, alkalis, etc. (because of the presence of the aliphatic segments in the PCA) over the conventional paints based on acrylates. The chemistry of the process24 essentially in­volves a chemical conversion of the hy­droxyl group of cardanol into acrylic group to get cardanyl acrylate (CA) and its polym­erization to get PCA. The process can be effected directly with CNSL, but further

PILlAl : VALUE-ADDED MATERIALS FROM CNSL ..... . 203

work has to be carried out to ensure the number of purifiers to be used.

There are many advantages for PCA: (i) This fully transparent and water clear resin was found to· be suitable for use as vehicle for pigment of any colour for paint formula­tions, (ii) As PCA is a thermoset acrylic resin, it will have a number of applications including automobile body surface coatings, (iii) PCA can also be be prepared as emul­sion acrylics, (iv) As PCAand poly (cardanyl methacrylate) (PCMA) are curable under controlled conditions to give thermoset films, they have potential for use in elec­tronic application. This aspect needs a spe­cial study to assess the potential which at the outset appears vast, and (v) PCA and PCMA can be converted into polymer supports and hence can find applications in polymer sup­port materials.

Invention 6: Liquid Crystalline Polymers

Liquid crystalline polymers (LCPs) possess a unique molecular morphology which in tum controls the rnicro- and macro-morphol­ogy giving rise to a property profile much superior to the conventional polymers. The molecular morphology is directly related to the polymer architecture which can be tai­lor-made to suit a particular property profile using both molecular design and process design aspects of control of polymer devel­opment. The exceptional balance of proper­ties with the ability to tailor the properties of the LCPs for a particular end use is creating new opportunities for materials scientists and technologists. The present industrial scene is dominated by Amoco and Hoescht­Celanese, USA

The industries still face a number of proL­lems such as: (i) the intractability and insolu­bility of the aromatic homopolyesters and homopolyamides, and (ii) the high cost of

the monomers. Use of naturally available comonomers with or without modification is expected to address this issue in a positive way. A new monomer 8-3-(hydroxyphenyl)oc­tanoic acid (HPOA) prepared 'by phase transfer catalyzed permanganate oxidation of cardanol derived from CNSL was found to be effective in reducing the transition tem­perature of polyparahydroxy benzoate. The process of synthesis of this monomer, its homopolyester and liquid crystalline co polyester have been filed for patents25-27.

The significance of this monomer is its ori­gin from natural material and hence its ex­tremely low cost and also its possessing both a molecular 'kink' and a flexible segment in its structure. Its co polyester with p-HBA [poly (p-hydroxybenzoate-co-hydroxyphen yl octanoate) 1 was liquid crystalline with ne­matic texture and gave a transition tempera­ture of 256°C. However, its thermal properties were not encouraging. Another polymer [poly(2-bromo-4-hydroxybenzoate­co-3-hydroxyphenyl octanoate) 1 containing a -Br group was synthesized. This polymer also gave LC behaviour. Composition vari­ation study carried out on these polymer indicated that the bromo derivative has a good range of nematic phase for processabil­ity studies. This polymer shows com para-

. tively good thermal stability and it is propused to study this bromo derivative fur­ther. Copolymers of HPOA with 4- hy­droxyphenyl acetic ac id (HPAA) and 4-hydroxyphenyl acetic acid (HPPA) were also prepared. As the LC phases of these polymers were of smetic focal conic and fan shaped textures, these polymers were not turther investigated. Ternary co polyesters based on naphthalene dicarboxylic acid (NDA), hydro quinone (HQ), and 8-(3- Hy­droxy phenyl octanoic acid) (HPOA) were synthesized. Ternary copolyesters contain-

204 J INTELLEC PROP RIGHTS, JULY 1999

ing various moles ratios of NDA, I-iQiHPOA were prepared by bulk condessationin 'pres­ence of magnesium acetate as catalyst. The process for the preparation of. the poly'ester is descriJ:>ed in the patent filea29

: DSCand PLM studies reveal that the ternary polyes­ter containing 10 to 20 mole % ef HPOA showed nematic LC transitions around 350°C. These copolyesters exhibited t9Pical nematic threaded textures when sheared on a glass plate at about 300°C and these tex­tures persisted up to 400°C. Another patent provides processes for the preparation of poly(4-phenylene terephthalate -co­oxyphenyl acetate/ propionate)s, poly(4,4'­biphenylene terephthalate -co-oxyphenyl acetate/ propionate)s, poly (2,6-naphthylene terephtl1alate -co-oxyphenyl acetat~6 propionate)s and related terpolyesters . They are liquid crystalline polymers which can be used in electronics (e.g. surface mount units, connectors, printing wiring boards, etc. where low coefficient of thermal expansion and low dielectric properties are required), in computer fields, in industry for making chemically resistant parts (e.g. tower packing saddles to replace ceramics) or as process aids 'in. thermoplastic process­ing or in bionle4ical area because they are biodegradable also. DSC and PLM studies reveal that the ternary polyester showed ne­matic LC transitions around 260°C with a thermal stability (5% weight loss) of 395°C.

Invention 7: Liquid Crystalline Phase under Cross-linked Network Structure

Azobenzene mesogen containing LC poly­mers are well-known to give non-linear opti­cal behaviour and for such applications the polymers should not absorb in the UV range of 100-200 nm. An LC polymer based on the biomaterial cardanol showed remarkable LC behaviour and forms the contents of two patents31,32. Another patent deals with the

formation of cross-linked network struc­tures in which the azobenzene mesogen is freezed33

. This is expected to give rise new opportunities for utilization of the LC phase in electro-optical devices.

References

1 Cashewnut Shell Liquid Patents: U.S. (Cashew Export Promotion Council, Ernakulam) Voll, 1964.

2 Cashewnut Shell Liquid Patents: UK, India andJapan (Cashew Export Pro­motion Council) Ernakulam 1964.

3 Cashewnut Shell Liquid: Extraci£on and Uses - A Survey of World Patents up to 1976 (Cashew Export Promotion Council, Ernakulam) 1978.

4 Indian Cashewnut Shell Liquid -A Ver­satile Industrial Raw Material of Great Promise (Regional Research Labora­tory, Trivandrum, and Cashew Export Promotion Council, Ernakulam) 1983.

5 Wilson R ], The Market for Cashew Kernels and Cashew Shell Liquid (fropical Products Institute, London) Repqrt No. G91, 1975.

6 Nair K M :& Bhaskara Rao E V V, Nambiar'K K Nand Nambiar M C (Eds). Cashew Anacardium Occiden­talle L .; Monograph on Plantation Crops-1 (Central Plantation Crops Re­search Institute, Kasargod, Kerala) 1979.

7 Thyman] H P, Chem Soc Rev, 8, 1979, 499.

8 Murthy B G K, Menon M C, Aggarwal ] Hand Zaheer S H,Paint manu/, 31, 1961,47.

9 Gedam P Hand Sampathkumaran P S, Prog Org Coatings, 14, 1986, 115.

10 Aggarwal] S, J Clour Sci, 15, 1976,14.

PILLAI: VALUE-ADDED MATERIALS FROM CNSL ...... 205

11 Murthy B G K and Sivasamban M A, CNSL/cardanol based resins (patent Cashew Causerie, 1, 1979,8. filed).

12 Pillai C K S, in Handbook 0/ Advanced 19 Pillai C K S, J ayakumari V G, Pavithran Polymeric Engineering Materials (Ed. C, Menon A R R, Prasad V S, Sudha J N. P. Cheremisinoft) (Marcel Dekker D, Brahmakumar M, Damodaran AD, Inc. New York) 1997. A proc¢ss for the preparation of 3-

13 Pillai C K S, Thirty Years of Research (tetrabromo pentadecyl) 2,4,6 -tribro-

in Cashewnut Shell Liquid and Its Eco- mophenol, Indian Pat 897 DEL 93,

nomic Exploitation: Problems and 1993 (provisional) .

Prospects Thereof, in Souvenir of Na- 20 J ayakumari V G, Pillai C K S, Pavithran tional Seminar on Development 0/ C, Menon A R R, Prasad V S, Sudha J Cashew Industry in India (Organized D, Brahmakumar M and Damodaran by the Directorate of Cashew Develop- AD, A process for the preparation of ment, Cochin) 14-15 December 1996, 3- (tetra bromopen tadecyl)2 ,4,5,6-Bhubaneswar,98. tetrabromophenol, Indian Pat 898,

14 Pillai C K S, Sudha J D, Prasad V S, DEL 93, 1993 (provisional).

Bera S C, Menon A R R, Damodaran A 21 J ayakumari V G, Pillai C K S, Pavithran

D, Alwan S, Lakshmidasn S K and C, Menon A R R, Prasad V.S, Sudha J

Govindaraman K N, A process for th~ D, Brahmakumar M and Damodaran

preparation of Phosphorylated prepo- AD, A process for the preparation of

lymer from alkyl/alkenyl phenols, In- 3-(tetrabromopentadecyl) 2,4,4,6-

dianPat1157DeI88, 1988 (provisional). tetrabromo 2,5-cyclohexadienone,

15 Pillai C K S, Sudha J D, Prasad V S, Indian Pat 102 DEL, 94, 1994 (provi-

Bera S C, Mathew A G and Damodaran sional).

A D, A process for the development of 22 Pillai C K S, J ayakumari V G, Pavithran

ablative resins/polymers/Composites C, Menon A R R, Prasad V S, Sudha J

from cashew nut shellliquidicardanol D, Brahmakumar M and Damodaran

or their derivatives, Indian Pat 171782 AD, Three novel compositions for

(to CSIR), 13 July 1988. flame retardant low smoke ethylene

16 Menon A R R, Pillai C K S and Damo-vinyl acetate copolymer based cable

daran A D, A new synergistic flame jacketing material containing 3-

retardant composition for natural rub-(tetrabromopentadecyl) 2,4,6-tribro-

ber and its products, Indian Pat 950 mophenol as flame retardant, Indian

DEL 89, 1989 (provisional) Pat 1403 DEL 95, 1995 (provisional) .

17 Prasad V S, Sudha J D, Pillai C K S, 23 Pillai C KS,]ayakumariVG, Pavithran

C, Menon A R R, Prasad V S, Sudha J Menon A R Rand Damodaran A D, A D, Brahmakumar M and Damodaran process for the preparation of friction AD, A novel composition for preparing dust useful as a friction modifier in flame retardant cable material based brake/ clutch facings (patent filed) . on 50-50 blends of ethylene vinyl ace-

18 Pillai C KS, SudhaJ D, Prasad VS and tate copolymer and polyethylene con-Anandan P. A process for the prepara- taining a new flame retardant tion of aqueous emulsion from 3-(rabromopentadecyl) 2,4,6 -tribro-

206 J INTELLEC PROP RIGHTS, JULY 1999

mophenol, Indian Pat 1404 DEL 95, 1995 (provisional).

24 PiIlai C K S, J ayakumari V G, Pavithran C, Menon A R R, Prasad V S, Sudha J D, Brahmakumar M and Damodaran AD, A novel composition for preparing flame retardant polyethylene contain­ing a new flame retardant 3-(tetrabro­mopentadecyl) 2,4,6 -tribromophenol, Indian Pat 1405 DEL 95, 1995 (provi­sional).

25 PiIlai C K S, John George, Mol Biji, Damodaran A D, Suresh M and Sunu G L, A process for the preparation of transparent or clear resin film from cashewnut shell liquid or cardanol or anaca,dic acid or cardol by the method of acryloylation, methacryloylation and polymerization, Indian Pat 674, DEL 96,1996 (provisional).

26 PiIlai C K S, Sherrington D C and Sned­don A, A process for the preparation, 8-(3-hydroxy phenyl) octanoic acid - a bifunctional monomer Indian Pat 677 DEL 92 (to CSIR) 29 July 1992.

27 PiIlai C K S, Sheerington D C and Sned­don A, A process for the preparation of poly(1,3 - phenyl octanoate) - ho­mopolyester, Indian pat 678 DEL 92 (to CSIR) 29 July 1992.

28 PiIlai C KS, Sherrington D C, Sneddon A, A process for the preparation of poly(1,3-phenyl octanoate)-a liquid crystalline copolyester, Indian Pat 679 DEL 92, 1992(to CSIR) 29 July 1992

29 Vijayanathan Veena, Prasad V S, and PiIlai C K S, A process for the prepara­tion of melt processable liquid crystal­line poly(4-phenylene naphthalene -2, 6-carboxylate - co- 8 (3- oxyphenyl)oc­tanoate) s poly(4-phenylene, 2-methoxynaphthalene-2,6-carboxylate

-co-8 (3- oxyphenyl) octanoate) s, poly(4-phenylene 2-phenyl naphtha­lene-2, 6-carboxylate -co- 8(3-oxyphenyl) octanoate)s and related terp~lyesters (patent filed).

30 Prasad V S, Ravindranathan M and PiI­lai C K S, A process for the preparation of poly(4-phenylene terephthalate -co­oxyphenl1 acetate/ propionate) s, poly(4,41 -biphenylene terephthalate­co-oxyphenyl acetate/ propionate)s, poly(2,6-naphthalene terephthalat-e -co-oxyphenyl acetate/ · propionate)s and related terpolyester (patent filed).

31 Saminathan M, PiIIai C K S and Pavithran C, A process for the prepara­tion of 4-[ (4-hydroxy-2-pentadecyl phenyl)azo]benzoic acid, a bifunc­tional monomer, Indian Pat 12791 DEL 9231, December 1992.

32 Saminathan M, PiIIai C K Sand Pavithran C, A process for the prepa­ration of poly4-[ (4-hydroxy-2-pe n­tadecyl phenyl) azo]benzoic acid, a bifunctional monomer, a processable liquid crystalline homopolyester, In­dian Pat 12972 DEL 92 (to CSIR) 31 December 1992.

33 Saminathan M and PiIlai C K S, Novel monomers and their polymers: proc­esses for the preparation of 4-[ (4- Car­danyl) azo] benzoicacid and 4-[ (4-Acryloylcardanyl) azo ]benzoic acid and their polymers Poly4-[ (4-car­danyl) azo] benzoic acid and their polyrspoly4-[ (4-acryloylcardanyl) azo ]benzoic acid including a process for the cationic polymerization of 260, 2 Times New Roman, 0, 0, 04][4-(car­danyl)azo]benzoic acid and their co­polymers (patent filed).