1

CHAPTER-I

2

1.1 INTRODUCTION

Epoxy resin is thermosetting polymer which shows crosslinking of the epoxide or

oxirane group. There are many epoxy resins based on bisphenol –A/ novolac/

tetraphenylol ethane. Resin shows good moisture, solvent and chemical resistances, less

shrinkage, ease of curing and processing, adhesive strength, great mechanical and

electrical properties. It shows applications such as composites, laminates, Paints, glues

etc1,2. Recently resins have been used remarkably in printed circuit boards.

Diglycidyl ether of bisphenol-A (DGEBA) and N,N’-diglycidyl benzophenone

tetracarboxydiimide (DGBT) are quite importantly which reflects below peroperties:

• High dimensional stability

• Highers water absorption

• Lower Tg

1.2 OBJECTIVES OF THE PRESENT WORK

In present study hardening agents structural impact on DGEBA & DGBT was

investigated.The organotin dichlorides and aromatic imide-amines of the diffetrent

structures were being used as curing agents. Here biuret (quite cheaper) is being taken

alongwith DDS for this research work. The following studies were planned i.e.

1. CURING AND THERMAL BEHAVIOUR OF DGEBA IN THE PRESENCE OF

DIORGANOTIN DICHLORIDES

2. CURING AND THERMAL BEHAVIOUR OF DGEBA USING ADDUCT

(BIURET+DDS)

3. CURING AND THERMAL BEHAVIOUR OF DGBT IN THE PRESENCE OF

AROMATIC IMIDE-AMINES

3

1.3 VARIOUS KIND OF EPOXIES

1.3.1 Multifunctional Resins

Resins possessing more than two functional groups are called multifunctional epoxy

resins. The triglycidyl resins of p-aminophenol has good processability, nice heat

resistance and superb mechanical properties being used as adhesives, coatings, laminates

and composites. The triglycidylether of tris (4-hydroxyphenyl) methane6, tris (2-hydroxy-

hexafluoro-2-propyl) methane7 and 4-(4-amino-dimethylbenzyl) phenol8 have been

developed for performance enhancement The glycidylation of cyanuric acid with

epichlorohydrin provides triglycidyl isocyanurate, crystalline compound with m. pt. of

85-110ºC and an epoxy equivalent of 108. One liquid compound possessing better shelf

life, better heat and water resistance, being prepared from benzene triol and

epichlorohydrin/ substituted epichlorohydrin has been patented (I).9

(I)

Another multifunctional epoxy resin i.e.TGBAP) / or tetra glycidyl-4,4’-

diaminodiphenyl methane was prepared by the react. of bis (3-aminophenyl)methyl

phosphine oxide (BAP)/or diaminodiphenyl methane with epichlorohydrin (Scheme

1.1)10.

4

H2N NH2

ClCH2-CH-CH2

O

P

O

CH3

NN

O

CH2-CH-CH2

O

CH2-CH-CH2

O

CH2-CH-CH2

CH2-CH-CH2

O

X

X = P

O

CH3

or CH2

+

Scheme 1.1

Glycidylation of tetrakis (4-hydroxyphenyl) ethane yields the tetraglycidyl ether of the

polyphenol with a theoretical functionality of four, with softening point of 80ºC and

epoxy equivalent of 185-208ºC. These resins show coloured solids.

Novolac epoxy resins are glycidyl ethers of phenolic novolac resins. Novolac epoxy

resins are prepared as per below scheme:

(II)

Novolac epoxy resins commonly possess multiple epoxide groups.

5

1.3.2 Diglycidyl Resins

These are difunctional epoxies having two oxirane groups per molecule of the resin.

More commonly used commercial epoxide is based on bisphenol-A. The synthesis of

these resins happened by reacting bisphenol-A with excess of EPC in media of a base11-13

(Scheme 1.2).

(Scheme 1.2)

Tetrahalo bisphenol-A resins were found good in flame retardant applications. Among

chloro and bromo the later derivatives shows greater commercial importance.

Glycidyl ether of 1, 2-, 1, 3- and 1, 4- benzene diols and other mononuclear dihydric

phenols has also been reported.14 Dinuclear dihydric phenols with single atom in between

aromatic rings were used for preparation of epoxy resins.10 Such diols can be easily

synthesiszed by reacting --CHO and >C=O with substituted/ unsubstituted phenols.15

Very high molecular toughness can be provided to the cured network by diols with fused

ring structures for the preparation of epoxy resins. Lo16 and Pearce et al17 reported

phenolphthalein based epoxy resins. Korshak18 prepared diglycidyl ether of 9, 9-bis (4-

hydroxy phenyl) fluorene which upon curing with (trimellitic anhydride) produced heat

resistant substance. Diglycidyl ethers of 9, 9-bis (3-methyl-4-hydroxyphenyl) fluorene

and 9, 9-bis (3-chloro-4-hydroxyphenyl)-fluorene was too prepared19

Epoxy resins from 3, 6-dihydroxy spiro (fluorene-9, 9’-xanthane) and 10, 10-bis (4-

hydroxyphenyl) anthrone have been reported.20 Cured epoxy resins dependent on

glycidyloxy diketones (III) possess high thermal and mechanical properties.21

6

Where X is alkoxy, alkyl glycidyloxy

Y is H, alkyl

(III)

Diglycidyl ether derivatives of 1, 4-dimethylol cyclohexane (IV) has also been reported.22

(IV)

Epoxy resins related to ketone aryl diglycidyl ether composition for encapsulation of

semi-conductor devices were suggested by Akiba and coworkers.23

Glycidyl esters from acids as phthalic and hydrogenated phthalic acids were synthesized

by reaction of these acids and epichlorohydrin followed by dehydrohalogenation with

NaOH (Scheme 1.3).

C OH

C OH+ 2 CH2-CH-CH2-Cl

O C-O-CH2-CH-CH2-Cl

C-O-CH2-CH-CH2-Cl

NaOH

C-O-CH2-CH-CH2

C-O-CH2-CH-CH2

O

O

diglycidyl ester of phthalic acid

O

O

O

O

OH

OH

O

O

OCH2CHCH2

O

X Y

O

R

OO CH2

CH CH2

O

YX

O

OHO

OOO

O

7

Scheme 1.3

Epoxy resins with both glycidyl ether and ester groups were also given (V).24

(V)

Glycidyl ester derived were prepared from benzophenone tetracarboxylic acid

dianhydride (BTDA) .

Where R'= alkyl or aryl

(VI)

Aromatic imide epoxy esters (VII) made by Saito et al26,27

(VII)

Epoxy ending imide resins were synthesized by treatment of methyl trimellitimide with

aliphatic amines that when further react to epichlorohydrin give N, N’- diglycidyl imide

derivatives (VIII).

Br

C

BrOBr CH2 CH CH2

O

OCH2CHCH2-O

O

R'

O

OCH2CHCH2

O

N R'

O

O CH2CH CH2

O

O

OO

N

O

O

O

N

O

O

O CH2CH CH2

O

O

N

OO

OCH2CHCH2

O

S

O

O

8

(VIII)

N, N’- diglycidyl benzophenone tetracarboxydiimide (IX) was also prepared initiated by

BTDA & allyl amine. Epoxy end capping.28 is obtained when diallyl interme. is Per-

oxidated.

(IX)

Cyclic monoterpene bisphenols used as initiators for preparation of epoxy resins in the

presence of phase transfer catalyst, tetrabutylammonium bromide, at 80ºC in the absence

of alkali followed by epoxidation with aq.sodium hydroxide soln. at a low temperature. It

include a terpene bisphenol, mixture of 1,3-menthane bisphenol and 2,8-menthane

bisphenol (60:40 wt ratio), when using 3,3'-dimethyl-5,5'-diethyl-4,4'-diaminodiphenyl

methane as a curing agent. Tg's of the cured DGETB resins were higher than that of the

cured DGEBA resin.29

C H 2C HCH 2

O

C H 2 C H C H 2

O

N

O

OO

N

O

O

O

N

O

O

O CH2CH CH2

O

O

N

OO

OCH2CHCH2

OR'

9

1.3.3 Epoxies as Flame Retardant

Lots of modification hve been done to imptove subject property of epoxy.Reconstitution

to epox. chain using monomer with flame retard substances such as halogen, nitrogen,

phosphorous, boron, antimony etc is could be possible approach, which is quite

expensive, needs new monomers and affects the normal properties of the materials to

great extent.

Novel emphasis on new flame retardant polymers concentrate on different

methods:Flame suppressents30 have been achieved by decomposition of high temp.

stable substances non-flammable polymers, mixture of plastics with surface active flame

retardants31 or substances which possess radiation heat of polymer by producing

electrically neutral char with pores. Other than halogen , silicon is also used as a flame

retardant element32-37 because of its reliebility at very high temperatures.

Epoxy resins prepared by reacting DGEBA with dialkyl (or aryl) phosphate possess good

flame retardency. Curing of these resins was made with 4, 4’-diaminodiphenyl sulfone

(DDS).

Flammability and thermal behavior of improved DGEBA/DDS resin depend upon the

nature of phosphate groups and their conc. in the material.40

The oxaphosphorin-6-[2,5-bis-oxi-ranylmethoxy)phenyl]-6-oxide (DOPO epoxy resin)41

(X), possess flame retardant, few fumes and more stable in terms of heat capacity than

the halogen containing conformist flame-retard epoxies.

(X)

OCH2 CH CH2

O

OCH2CHH2C

P=O O

10

Phosphorous possess advanced epoxies are generated by Scheme 1.4 & 1.5. DOPO &

DGEBA reaction will have cyclic P (Scheme 1.7).

Glass fibre reinforced laminates were synthesized using DICY as hardener.These will

have

• Better fire resistance

• Better heat resistance

C

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2

O

P

O

HO OH

C

CH3

CH3

O CH2-CH-CH2OCH2-CH-CH2

O OH

P

O

O O CH2-CH-CH2

OH

O

C

CH3

CH3

OCH2-CH-CH2

O

n

Scheme 1.4

11

O

O P

O

OOHHO

C

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2

O

C

CH3

CH3

O CH2-CH-CH2

OH

O O CH2-CH-CH2

OH

O

O

O P

O

O

C

CH3

CH3

OCH2-CH-CH2

O

OCH2-CH-CH2

O

n

Scheme 1.5

C

C H 3

C H 3O

O C H 2-C H -C H 2OC H 2-C H -C H 2

O

P OO

H

C

C H 3

C H 3

O XXO

C H 2-C H -C H 2 P

O

OO HO

C H 2-C H -C H 2

X = A or B

A = B =

Scheme 1.6

12

H 3 C

O

O

C H 2 - C H - C H 2

C H 2

H 3 C

O

O

C H 2 - C H - C H 2

C H 2

H 3 C

O

O

C H 2 - C H - C H 2

P OO

H

H 3 C

O X

C H 2

H 3 C

O X

C H 2

H 3 C

O X

C H 2 - C H - C H 2

O H

P

O

OO

C H 2 - C H - C H 2

1 0+

1 0

B =

X = A o r B

A =

Scheme 1.7

Other examples of advanced epoxies are below:

C

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2

O

C

CH3

CH3

O CH2-CH-CH2OCH2-CH-CH2

O OH

O

P OO

O CH2-CH-CH2

OH

O

C

CH3

CH3

OCH2-CH-CH2

O

P OO

OHHO

n

13

Scheme 1.8

In the same way phosphorus having diacids were synthesized {Scheme 1.9} or maleic

acid (Scheme 1.10) and then treated with DGEBA to produce more refined epoxies47

CHH2C

CH2 COOH

COOHP OOC

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2

O

CHH2C

CH2

P OO C

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2O

C

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2

O

OH

OH

CO

CO

+

Scheme 1.9

CH

CH2

P OO

CH

CH2 COOH

COOHP OOC

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2

O

CO

CO

C

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2O

C

CH3

CH3O

O CH2-CH-CH2OCH2-CH-CH2

O

OH

OH

+

Scheme 1.10

14

Epoxies which contains cyclic phosphine oxide and four oxirane rings, posssess on cure

much heat property and increased C.R.48

Scheme 1.11

P having oxirane, bis (3-glycidyloxy) phenyl phosphine oxide (BGPPO) (P=11.5%) is

synthesized by rxn. of phenyl phosphonic dichloride with glycidol (Scheme 1.12).49,50

P

O

ClCl

CH2-CH-CH2

O

OHTHF

CaCl2

P

O

CH2-CH-CH2

O

O O CH2-CH-CH2

O

+

BGPPO

Scheme 1.12

Epoxies which are retarded to flame (4-diethoxyphosphoryloxyphenoxy)(4-

glycidoxyphenoxy) cyclotriphosphazene (PPCTP) synthesized by rxn. of

epichlorohydrin with (4-diethoxyphosphoryloxyphenoxy) (4-hydroxyphenoxy)

cyclotriphosphazene (Scheme 1.13), possess low mass loss temperatures.

PhO

HOOC

HOOC

COOH

COOHP

O

ClCH2-CH-CH2

O

PhOP

O

OO

OC CH2-CH-CH2

O O

O CCH2-CH-CH2

O

COCH2-CH-CH2

O

O

C

O

O CH2-CH-CH2

+

15

N3P3Cl6 HOC6H4OCH3N3P3(OC6H4OCH3)6

CH2Cl2

BBr3

N3P3(OC6H4OH)6

THF TEA

OC2H5

N3P3(OC6H4OPOC2H5)2.37(OC6H4OH)3.63

KOH/EtOHN3P3(OC6H4OPOC2H5)2.37(OC6H4OH2CHC-CH2)3.63

H5C2OPCl

O

OC2H5

OO

OC2H5

O

O

ClH2CHC-CH2

+ 6

,

Scheme 1.13

Polyphosphonates epoxy resins were prepared by reaction of BPA & phenylphosphonic

dichloride (DCPPO) and epichlorohydrin.

16

1.3.4 Cycloaliphatic Epoxy Resins

The epoxidation of unsaturated compounds with peracids is included in preperation of

cycloaliphatic epoxy resins (XI-IV).55 Cycloaliphatic epoxy resins are more stable to

ultra-violet exposure than bisphenol-A derived epoxy resins.

[4', 4’-epoxycyclohexylmethyl-3, 4 - epoxycyclohexane carboxylate] (XI)

[1', 2'-epoxyethyl-3, 4 – epoxycyclohexane] (XII)

[ 2-(3, 4-epoxycyclohexyl-5, 5-spiro-3, 4 - epoxy)-cyclohexane metadioxane] (XIII)

(Dicyclopentadiene-containing epoxy) (XIV)

O O

O

O

CH2 - O - C

O

OO

O

OCH CH2

O

CH2 CH CH2

O

CH3 n

17

1.4 HARDENERS

In curing process epoxide group in epoxy resin reacts with a hardener to give highly

cross-linked three-dimensional network. Because of formation of cross linkes between

various chains the mobalility of the system get reduced.

Hardners are very important to get final desired prpoerites for example penetarin,

dimension stability drying beaviour etc.

The choice of hardening agent depends on Physical and chemical cost. Initiation is done

by catalytic hardener whereas co reactive hardner works as co- monomer.

[Scheme 1.14].

Catalytic:

Coreactive:

Scheme 1.14

(n+1) -CH CH 2

O

R 3 N

R3N CH2 CH

( OCH2 CH ) n O

C H C H 2O

+ N H 2 R N H 2 C H C H 2 N H R N H C H 2 C H O HO H

C H C H 2 N R N C H 2 C H

C H 2C H O H

C H 2

C H O H

O H

O C H 2C H

18

Various curing agents as aliphatic or aromatic amines, mercaptans, melamine-

formaldehyde, urea-formaldehyde etc. have been explained in the literature.56 .Amines

and anhydrides will be reviewed here.

1.4.1 Acids and Their Anhydride

Acid and their anhydrides are the second most used reactants in curing epoxy resins and

best suited for electrical applications. Anhydrides are not skin- sensitizing agents but

their vapors can be irritating. Solid anhydrides require heat and considerable mixing to

incorporate well into liquid epoxies; however, no danger of runway reaction is present.

Liquid anhydrides are easy to handle as the aliphatic amines.

As explained in the introduction, cured epoxy- acid structure contains ester-type bonds.

This chemical linkage causes anhydride cured epoxy resins to be more caustic sensitive

than amine cured systems. Acid anhydride cured systems are generally more stable

thermally and chemically; however, their low exotherms require that systems employing

them, be cured for relatively long periods at elevated temperature. This involves some

risk of vaporization with volatile anhydrides such as phthalic anhydride. The introduction

of tertiary amine accelerators and the use of liquid anhydrides offsets many of the earlier

difficulties encountered in the use of anhydride hardeners.

Anhydride cures produce two competing reactions of the epoxy resins. They may form

ethers under acid catalysis or they may react with acid to form ester bonds. A variety of

many anhydride/ dianhydride have been employed for curing epoxy resins. Eutectic

anhydride has been used to enhance the mixing of solid anhydride to liquid epoxy resin.

In the reaction between a carboxylic acid and an epoxy (Scheme 1.15

RCOOH + CH2 CH

O

CH2 RCOO CH2 CH

OH

CH2

RCO O-CH 2 CH

O H

CH 2 + CH 2 CH

O

CH 2 R COO -CH 2 -C H

OCH 2 CH

O H

CH 2

CH 2

RCOOH + RCOO-CH2CHCH2

OH

RCOO CH2CH

OOCR

CH2

19

Scheme 1.15

Citric acid piperazine salt was prepared with acid-base molar ratio of 2.9 for the cure to

epoxies. The piperazine content in the salt was 52%.57

There will be esterification and etherification due to the reaction of epoxies with acid

anhydrides (Scheme 1.16).A chemical reaction of epoxy with anhydride result in

formation of half esterification that further make a rxn with epoxy grp. to form diester

On other hand 2o alcohol formed during the esterification, resulting in the formation of

β-hydroxy ether.

Scheme 1.16

CH2CH OH + O

O

O

R

R

R

R

C-O-CH

O

C

O

-OH

CH2

CH2

CH2CHO-

O

C

O

C-O-CH

R

R

CH2

HO-

O

C

O

C-O-CH

R

R

+

+ CH2 CH

O

OH

CH OH

CH2+

O

CHCH2

CH2

O-CH2CH-CH

OH

20

1.4.2 Imidazoles

Epoxies which were cure with imodazoles show good resistant to chemicals, oxid. Rxns.

resistant to change in shaped, excellent parameters to dielectric properties better heat

resistance, higher modulus, wider range of cure temperatures and great physical

properties when made a comparision with amine cured systems.58,59

Mechanism of the rxn. of diepoxide/imidazole system consist of adduct and etherification

reaction as shown below (Scheme 1.17).

A2

Scheme 1.17

Collectively Imidazoles perform two parallel functions, firstly starts esterification rxn

when it is combined with epoxy anhydride and secondly it brings catalytic selectivety

when introduced to phenol-epoxy method. Not only phenol-epoxy rxn is initiated but

also there will be homo-polymz. of epox grp. Work performed in history59-65 on

O O

CH R

OH

CH CH 2 +

N N CH 2

- O

CH R CH H 2 C A1 + E CH 2

21

epoxy/imidazole methods (using N-substituted imidazole (XV) has throw a beam of light

on rxn. betw. phenyl glycidyl ether (PGE) & different imidazoles giving adducts.

Applications of imidazoles lie with in electronic industry as casting and seal composite.

(XV)

Barton etal65-67 determined the following:

• If we open the pydine type N than it is verymuch possible to attain 1:1 & 2:1

compositions.

• Result in lastingly assimilation of epoxy linkages with imidazole by onset of

procedure of polymeriz.

In the procedure of cure & production of polyethers we can observe presence of

imidazoles in whole process, and the cure rate differ with the structure design of

imidazole. Farkas and Strohm68 establish and witnessed curing to be a difficult procedure

in context with epoxies and imidazoles. In this process there will be linkage of C of epox.

to the N of imidaz. We can observe a inmitable cure process in cure of epoxies with

imidazole and it is quite easy to restore initial imidazole in rxn. Many literatures shows

the proof of restoration of Imidazole69, 70 Bresser & Goumans worked together on

imidazole and found that lone pair of e- at 1- substituted N possibly brought an spell to

the epox. funct. grp. Cook et al72 studied in detail about the cure mechanisms and

movement of rxn of DGEBA by making use of 2-methyl/ 1,2-dimethyl/ 2-phenyl

imidazoles (XVI-XVIII) as curing agents.

(XVI) (XVII) (XVIII)

Adduct of an imidazole with an unsaturated compound such as (poly) acrylates has been

N

N

CH3

N

N

N

N

N

N

CH3

CH3

N

CH3N

H

N

N

H

22

reported as catalyst for curing of epoxy resins used in powder or solvent borne coatings

or laminates.73 1-Imidazolylmethyl-2-naphthols are effective catalysts and accelerators

for curing epoxy resins. These compounds are providing epoxy resin systems with

prolonged room-temperature stability and fast curing at temperatures of 110ºC-150°C

gave a cured product with low water absorption and good mechanical properties.74

1.4.3 Amines

Commonly used curing agents for epoxies are primary & secondary amines. Rate of

reaction is hampered by:

• Steric hinderence

• E taking or giving gp on amine

>> E’n withdrawing gp will reduce the rate of reaction by slowing down the

nucleophilicity.

>> These reactions are exo-thermic in nature.

Follwong steps observed;

1. Produciton of Sec. Alcohol & Sec. Amines

2. Sec. Amine will produce Ter. Amine & two Sec –OH groups.

Sec amines reacts 50 % slower as compare to pri amines80 (Scheme 1.18).

Scheme 1.18

23

Unsubstituted monofunctional aliphatic alcohols are poor accelerators (Scheme 1.19).

Scheme 1.19

Highly effective amines which have been bought into usage to cure epoxies are Ethylene

diamines. They outcome in the formation of cross link netwk. And in nature they possess

good reactivity and less mol. wt. Numerous modifications have been done to increase the

molecular weight, reduce the hygroscopic nature and increase compatibility of these

curing agents with epoxy resins (XIX).

(XIX)

Poly (oxypropylene) diamines, Poly (oxypropylene) triamines etc. have also been

developed as curing agents. DGEBA with phosphine oxide grp. report curing properties

with usage of amide amines82. There we are having some mediators which are cross

linked and generally synthesized by condens. rxn. of polyamines along with CHO & C=O

and further with phosphite which is o-substited as presented in diagram 1.20 produces

light wt. but stable metal resin83 which got self terminate in 8 sec.

NH

R'

R

+ CH2 CH

O

+ HOR'' NR'

RH

CH2 CHO

HOR"

NR'

RCH2 CH

OH

+ R"OH

24

H2NCH2CH2NHCH2CH2NH2 HCHO

P

H2NCH2CH2NHCH2CH2NH

CH2

O

H2NCH2CH2NHCH2CH2N

HO (OMe)2

P (OMe)2CH2

+

Scheme 1.20

Curing agents such as polyamides, poly (amido-amines) and imidazolines, adducts with

epoxy functional materials, Mannich bases, associated salts, ketimines and acrylonitrile

adducts and polyether amines84 have been used to increase the molecular weight, to

reduce the hygroscopic nature and increase compatibility with epoxy resins. Aromatic

diamines containing imide group were also investigated as curators for epoxy resin by

Varma etal.85,86 Better thermal stability in air and N2 atmosphere was observed in epoxy

cured with such amines in comparison to commercially available curing agents i.e. 4,4’-

diaminodiphenyl methane (DDM) and 4,4’-diaminodipheny sulphone (DDS). Laminates

fabricated with imide- amines as curators have shown good toughness, excellent thermal

stability and improved mechanical properties. Generally amines aromatic in nature were

found compact at room temp. and they have been used for thermal curing applicat.

While mixing with cyclo polyamines and their liquification is made for blending

themwith epoxies.Major commercially available amines are DDM, DDS and m-

phenylene diamine (m-PDA). Cure epox. web become more temp. resistant while we

use DDS. In order to carry operation at military level greately it is important to curing of

epoxies like tetra-glycidyl of DDM with grouping of BF3 & M.E.A . A comparative

study of use of 4,4’-diaminodipheny sulphone and 3,3’-diaminodiphenyl sulphone as

curative for epoxy resin was reported by Satyabhama.87 3, 3’-DDS imparts reduced heat

resistance as compared to DDS. It has been adopted for its enhanced honey comb peel

strength in aerospace laminating applications. Urech et al88 reported a low viscosity

liquid mixture of 2,4-diamino- 3,5-diethyl toluene (XX)/ 2,6- diamino-3,5 diethyl toluene

(XXI). The amino groups are sterically hindered due to the presence of bulky alkyl

groups in this curing agent. As a result, it is much less reactive than DDM.

25

(XX) (XXI)

Gardener et al used extended chain aromatic diamines (XXII) for curing of epoxy

resins.89

(XXII)

Furfuryl amine (FA), tetrahydrofurfuryl amine (THFA) and 5, 5’- methylene- bis-2- furan

methaneamine (DFA) were considered to cure agent of epoxies (XXIII).90 The

effectiveness of FA and THFA have been restricted becoz oftheir high volatile nature &

considered to be useful in cure of DGEBA based epoxy resins. One of the best cure

agentis supposeto be DFA and is capable of curing DGEBA at a very high rate and even

exceeds to ritual agent as DETA.

(XXIII)

Novel aromatic diamines prepared by nucleophillic addition of diamines with maleimides

(2:1 molar ratio) have also been used as curing agents for DGEBA.91

CH3

NH2

C2H5

NH2

C2H5

CH3

NH2NH2

C2H5C2H5

OO CH2 CH2 NH2CH2NH2

zNH2z z z NH2

26

4, 4’- diamino- 3, 3’- 5, 5’- tetraethyldiphenyl methane and the tetra- alkylated- di (4-

aminophenyl)-di- isopropyl benzenes such as the tetramethyl derivatives92 (XXIV) were

considered harmless as compared to DDM if we keep in mind the toxic factor. They are

used in variety of laminated applications for their long working life and ready

compatibility with liquid epoxy resins.

(XXIV)

For high- and low-temperature curing of epoxy resins oxazolidone-containing polyamine

curing agents without separation of N-methylol-2-oxazolidone using 2-oxazolidone,

formaldehyde, and polyamines (hexamethylene diamine, diethylene triamine, ethylene

diamine) were used.93

The amides based on 4-hydroxyphenylacetic or benzoic acids and alicyclic or aromatic

di- and triamines were useful for curing of epoxy resins. The resins provide chemical

resistant coatings. Alicyclic triamine condensed with Megallate to give a mixture of

monoamides used to cure a bisphenol-A diglycidyl ether. A coating obtained there from

was resistant to dilute acetic acid and curable at room temperature at 100% humidity.94

If a comparision is made for keeping in consideration heat of polym. than DSC is lower

than curing of system with help of amines aromatic 95 in nature.

Epoxy resins cured with crosslinking agents containing alicyclic diamines I (R1 = lower

alkyl) to give products with low discoloration and good heat and chemical resistance96

(XXV).

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

NH2NH2

27

R1 R1

NH2NH2I

(XXV)

A stable polyamine-functional silane resin prepared by reaction of an aminoalkoxysilane

and a hydroxy and amine-functional compound used in low-temperature curable

coatings.97

Wang and coworkers investigated phosphorylated triamine i.e. tris (m-aminophenyl)

phosphine oxide (TAPO) (XXVI) as curing agent for epoxy terminated imide resin.98

(XXVI)

These phosphorylated curing agents improve the fire resistance of the cured epoxy

network. Ratna etal.99 sugested that formation of amine terminated polyamide sulfone is

centered on DDS . We can acknowledge the impact of ATPS with techniques as DMTA

& DSC where the former got merged like a transformer in epoxies. When studies were

carried out it was observed that ATPS is capable of making a harmonious combination

with epoxies & provides elasticity for epox. medium. As it has been observed that there is

presence of sulfonic grp. in polymeric substances and due to the impact of this they

possess few of the properties as great oxidizing, excellent motoriozed property.100,101 It is

very much clear from the above discussion that if we are using sulfonic grp. in assistance

of a modified polymer than not only it will produce an good impact on its properties but

also it would bring flexibility in the product.

NH2

P

O NH2

NH2

28

(XXVII)

There will be formation of an adduct which contains amine grp. when we brought up a

rxn between DGEEG & MXDA and it has been used to cure epoxies along with VA to

introduce flexibility & hard layering.102 As far as cure resin is concerned its cure is reliant

on cure temp. and also influenced by amt. of cure substance. It is evident that gelation is

directly proportional to growing temp. Both, compound103 assets as well as struct. of cure

resin is influenced by cure temp. A study has been made to observe synergistic impact of

Dicy. & resorcinol substance. A considerable lower down of cure temp. has been

observed. Dicy simplified the formation of phenol anions by providing a ground to

reaction between epoxide & Phenolic OH grp. which is further simplified by resorcinol

which add NH2 grp. to the epoxide. It becomes more convenient to add OH grp. to cyano

because of the existence of resorcinol. Arylhydrazino-bismaleimide (AHBM) prepared by

Michael addition reaction of various phenyl hydrazine derivatives with N, N'-(4,4'-1,1'-

sulfonyl biphenylene) bis-maleimide (SBM) using 2-methyl imidazole as catalyst were

employed for curing epoxy resins. The cured materials had good chemical resistance and

good mechanical strength. The bisphenol A epoxy resins cured with (alkoxysilyl)

alkylamines, i.e., N-(2-aminoethyl)-3-aminopropyl trimethoxysilane and 3-aminopropyl

trimethoxysilane were also reported.106

Silicone containing organic amine curing agent has recently been reported to cure various

epoxies such as cycloaliphatic epoxy, glycidyl ether & glycidyl ester in presence of co-

curing agents and has good defoaming performance. The cured epoxy resin is totally

uniform and transparent and has glossy surface and no bubbles or pinholes and the cured

NH2SO2 NH

O

R

O

NH SO2 n NH2

(CH2)4

O

O CH2 CH2 O

O

(CH2)4 n

n

WhereR =

YX

29

resin also has good mechanical and electric insulation properties, low dielectric constant

and dielectric loss, low water absorption rate etc.

1.5 CURING STUDIES

Many processes are available to show tviscosity, ultrasonic he conversion process from

soln. to gel form and than to glass form includes processes as viscosity105, calorimetry,

dielectric106,107 and mechanical relaxations 108,109 dilatometry109 and ultrasonic

measurements110. Several spectroscopic methods including infrared111,112 and Raman

spectroscopy113, Nuclear magnetic resonance114, Electron paramagnetic resonance115

flourescenceFluresence116 Brillouin scattering117 and photon correlation spectroscopy115.

The process which is cut above among all others for cure of epoxies kinetics is DSC.

Prime 130 has introduced a very interesting method for applying DSC technique in order

to check curing of resins which cannot be remoulded again. Other techniques used were

differential thermal analysis (DTA)131(b) Fourier transform infrared spectroscopy (FT-

IR)132 and (c) high pressure liquid chromatography (HPLC)133,134

Curing kinetics of epoxies was investigated by using isothermal and dynamic DSC

methods to establish guidelines for usage of either method. Dynamic methods are fast

and provide approx. data but are limited to one type of reaction, the n-order reaction.

Isothermal DSC generates data that are easy to analyze and can describe two types of

reaction, n-order and autocatalytic reactions. The isothermal DSC method produces

precise kinetic data th at require longer data acquisition times than the dynamic method,

i.e., at least three DSC scans are required vs. one. The method developed by H. Borchard

and F. Daniels (1956) requires only one dynamic scan to describe n-order curing kinetics.

Using this method, it was determined that Ea and the pre-exponential factor increase

with heating rate, however, the two parameters were over-established as compared with

values obtained using the isothermal method. The method developed by T. Ozawa (1965,

1970) is recommended when the DSC baseline is irregular, when there are multiple

exotherms, or when it is necessary to account for solvent effects on curin.135

30

1.6 THERMAL STABILITY OF CURED RESINS

Thermogravimetry (TG) has been used to determine the thermal stability of cured

network, which is varied by varying resins/hardener; ratio of resin: hardener; temperature

of curing and time.

Table 1.1 and 1.2 show the effect of phosphorus addition on C.Y. and Limiting oxygen

index of different epoxies / curin agent formulations.

Table 1.1. Arrangement of Hardening influence on Thermal Behaviour of

Epoxies

Epoxies/Curing Agent C.R. (%) Phosphorus content (%)

LOI

N2* Air

D.G.E.B.A. /4-D.A.P.P.O.

D.G.E.B.A. /3-B.A.P.P.O.

D.G.E.B.A. /B.A.O.D.O.P.P.

D.G.E.B.A. /D.D.M.

D.G.E.B.A. /4-D.A.P.P.O.

D.G.E.B.A. /3-B.A.P.P.O.

D.G.E.B.A. /P.C.A.O.

D.G.E.B.A. /B.A.P.

D.G.E.B.A. /D.D.S.

D.G.E.B.A. /D.D.E.

D.G.E.B.A. /T.A.P.

PN/ODOPB-A

PN/ODOPB-B

PN/ODOPB-C

PN/ODOPB-D

DGEBA /DOPO-PN

DGEBA /DOPO-PN

DGEBA /DOPO-PN

DGEBA /DOPO-PN

DGEBA /DOPO-PN

CNE/DOPO-PN

35

35

32

13,18

37

37

52.0

22.0

19.9

18.7

26.4

40

41

44

49

19.5 a

31.4 a

33.7 a

37.9 a

40.2 a

34.4 a

26

28

18

1,7

32

29

40.7

15.0

0

0

9.8

32

32

34

38

2.5 a

7.5 a

12.2 a

16.2 a

14.9 a

7.0 a

4.03

4.25

2.5

0

4.16

5.10

5.40

4.93

0

0

3.46

1.1

2.0

3.1

4.4

0

1.50

3.22

4.11

5.20

0

33

33

30

21,24

34

35

-

-

-

-

-

-

-

-

-

21.0

24.5

29.0

32.0

34.0

21.0

31

CNE/DOPO-PN

CNE/DOPO-PN

CNE/DOPO-PN

CNE/DOPO-PN

DGEBA/PA

DGEBA/HA

DGEBA/DMSA

Epoxy Novolac/PA

Epoxy Novolac/HA

Epoxy Novolac/DMSA

DGEBA/PCAO

DGEBA/BAP (30% resin)

36.7 a

37.8 a

41.1 a

45.3 a

8.5 b

10.0 b

28.9 b

35.9 b

35.1 b

52.3 b

52.0

-

16.7 a

19.9 a

23.1 a

28.5 a

-

-

-

-

-

-

40.7

-

1.45

3.11

3.99

5.05

0

0

4.4

0

0

4.5

5.40

-

25.0

29.5

32.5

35.5

19.3

19.0

37.0

22.5

22.0

28.1

-

57

* = C.Y. at 700oC

a = C.Y. at 800oC

b = C.Y. at 550oC

Table 1.2. Showing influence of arrangement of epoxies on Thermal

Behaviour

Epoxy Resin/Curing Agent Char yield (%) Phosphorus

content (%)

LOI

N2* Air

DOPO-epoxy/DICY x

DOPO-epoxy /DDM x

DOPO-epoxy /DDS x

DOPO-epoxy /PN

DOPO-epoxy /DDS

DOPO-epoxy/DICY

DOPO-A /PN

DOPO-B /PN

DOPO-C /PN

DGEBA/DICY

BGPPO/DDM

54.0 a

49.1 a

44.8 a

48

40

32

31

34

36

8.0

40

31.8 a

25.6 a

20.1 a

37

32

28

7

11

21

0

25

6.4

5.8

5.6

4.8

4.5

7.2

0.58

1.03

1.45

0.0

6.8

54.3

46.5

45.0

34

32

36

28

30

34

21

35

32

BGPPO/DICY

BGPPO/DDS

BGPPO/4-DAPPO

BGPPO/DICY

BGPPO/DDM

BGPPO/DDS

PPCTP/DICY

PPCTP/DDM

PPCTP/DDS

DGEBA/DDS

DOPO-DGEBA1/DDS

DOPO-DGEBA2/DDS

DOPO-DGEBA3/DDS

DGEBA/PN

DOPO-DGEBA1/PN

DOPO-DGEBA2/PN

DOPO-DGEBA3/PN

44

43

52

50.0

40.0

28.0

50.0

41.2

53.1

15.1

15.93

17.64

20.0

19.1

22.5

25.0

26.9

30

27

32

33.0

33.0

20.0

-

-

-

0.0

4.0

11.3

18.7

0

15.9

19.5

20.7

8.5

5.8

10.6

8.1

6.8

5.8

11.68

10.45

10.85

0.0

0.78

1.60

2.49

0.0

0.67

1.41

2.23

45

35

49

43

34

33

36

32

34

22

25

28

30

21

23

25

27

* = C.R. at 700oC if definite

a = C.R. at 800oC

x = Composite Data

where

BAODOPP = 1,4-bis(3-aminobenzoyloxy)-2-(6-oxido-6H-dibenz[c,e]

[1,2]oxaphosphorin-6-yl) pheneylene

3-BAPPO = Bis (3-aminophenyl)-phenyl phosphine oxide

4-DAPPO = Bis (4-aminophenoxy)-phenyl phosphine oxide

DICY = dicyandiamide

B = Bis (3-aminophenyl) methyl phosphine oxide

DEA = 3,3’5, 5’-tetraethyl-4, 4’-diamino diphenyl methane

33

TGDDM = tetraglycidyl derivative of diamino diphenyl methane

DDM = 4,4’ diamino diphenyl sulphone

TGCAO = Cyclic phosphine oxide epoxy resin

PPCTP = 4-diethoxyphosphosporyloxyphenoxy)(4-glycidoxyphenoxy)

cyclotriphazene

PA = Phthalic anhydride

HA = Hexahydrophthalic anhydride

CNE = o-cresol formaldehyde novolac epoxy resin

DOPO-PN = 9,10dihydro-9-oxo-10-phosphophenanthren phenol novalac

DMSA = 9,10dihydro-9-oxo-10-phosphaphenanthrene-10-oxide)methyl

succinic anhydride

T = Tris (3-aminophenyl) phosphine oxide

3-DAPPO = Bis (3-aminophenoxy)-phenyl phosphine oxide

BHPP = Bis (3-hydroxyphenyl) phenyl phosphonate

The 9,10 dihydro-9-oxo-10-phosphophenanthren phenol novalac (DOPO-PN) cure

epoxies are less stable to temperature whereas resins which are P free are highly stable to

temp. It happened so because of the breakdown of DOPO even at very less temp. which

is exactly reverse at high temp. i.e.above 440oC. At such high temp. P possessing resins

are more stable than other one.P possessing resins are having more C.R. than Pfree cure

resin. Increase in P content result in increase in C.R.

o-cresol formaldehyde novolac epoxy resin (CNE) possss more C.R.than the DGEBA.

Now we can say thatresin with P is more stable andalso it will possess high no. of phenyl

grp. If a comparision is made than wecan say C.R. value and confrontation to flame

ismuch higher in DGEBA or epoxy novolac/DMSA provided the atmosphere of N and

34

air than the epoxies which don’t contain P such as DGEBA/DDM137-140 Epoxies which

have been cure with cyclic phosphine oxide diacid curing agent (PCAO) remarkably

result in having more C.R. and temp. retardation as compare to BAP, DDE resins.

Considering case of cycl. Phos. epoxies they are found possessing less temp. retard. And

more C.R. ascompareto DGEBA141, 142 Epoxies that have been produced by P possessing

di alcohol ODOPB and ether glycidyl of cresol-HCHO shows increased aromatic

properties & cyclic O=P-O units. As we can see the presence of = bond it is responsible

for deleivering more temp. stab. than those which are – bonded. Epoxiesbecome more

heat resistant when we introduce amount of 1.3% P but it goes upto the remarkable

height if we are usin 2.2% P143-149 composites of DOPO possess high C.R. & LOI values

if it is compared with DGEBA & epox. noval. compos.146, 147 dGEBA which don’t

contain P possess 14 times less LOI value than PPCTP epoxies polym. because of the

presence of high N and P content. Also in addition the PPCTP/dicyanide polym.

possess more LOI than PPCTP due to the presence of more N in dicyanide.149

35

1.7 LIMITING OXYGEN INDEX & RESIDUAL CHAR

For halogen free polymers Van Krevelen performed study & made linkage b/w limiting

oxxigen index and residual chars. If p content raises residual char also increases also we

found liner hike in limiting oxygen index also.This particular plot will have lots of

scattered points.The amount of residual char will dependent upon :

• Cured matrix structure

• P content

Exapmle : Epoxies which are DGEBA based having low residual char when they

compared with P containing curing agent.

Fig. 1.1 show the plot of Limiting Oxygen Index vs. Residual Char of epoxy binder

(D.G.E.B.A.) cured with P-containing hardener i.e. D.O.P.O.-P.N..

Relationship as below:

Limiting Oxygen Index = 1.0118 Char Yield - 6.3467 (for DGEBA)[a]

= 1.0917 CY- 13.288 (for novolac) [b]

20

25

30

35

40

25 30 35 40 45 50

Char Yield (%)

LO

I (%

)

ab

36

Figure 1.1 char yield Effec on Limiting Oxygen Index of D.G.E.B.A. epoxies cured

using D.O.P.O.-P.N.

20

25

30

35

40

45

50

55

60

20 25 30 35 40 45 50 55

Char Yield (%)

LO

I (%

)

Figure 1. 2 Eeffect of CY on Limiting Oxygen Index of BGPPO -epoxies

Plot for P possessing epoxies (BGPPO) cure with various cure agents shown in Fig. 1.2.

Relationship is :

LOI = 0.6499 CY + 11.569

37

1.8 THERMAL DECOMPOSITION

The structural matrix of epoxies are basis of thermal decomposition. Any kind of epoxy

when thermally decomposed first step is of elimination of water which happens

approximately 300 degree.

• FT-IR Technique detects the reduction in the –OH functionality.

• Unsaturation groups presence is verified by I.R. at 1650 cm-1 band

Carbon – oxygen or carbon – nitrogen bonds are weaken by the presence of unsaturation.

Also consiquences of weak carbon – oxygen bond Phenolic chain ends generated while

because of week carbon – nitrogen bonds sec. amine terminal functions results.

Complex process being suggested for DGEBA units.

N C H 2C H C H 2

O H

O

N C H C H 2OC H

N C H C H 3H OC H

N C HC H 2OC H

N H O

C HC H 3OC HN H

N C H 3O N C H 2 C C H 2

O H

H O

N C H 2 C C H 3

O

-H 2 O

-H 2 O-H 2 O

+

+

+

+ +

Ac e to ne

Scheme 1.21

38

1.9 VARIOUS APPLICATIONS OF EPOXY RESINS

1.9.1 Multi substrate Bonding & use as Adhesives

The adhesives which are based on epoxies & thrie adducts are used in metal to metal

bonding & sealing. A number of examples are available in automotive & aerospace

industry. For specific to such application high functionality epoxies are used.

1.9.2 Epoxy Laminates & Epoxy Composites

Below parameters make the choice material to use in subject application:

• Excellent adhesion

• Low shrinkage

• Dimensional stability

• Good electrical & chemical perforamce

• Low moisture absorption

1.9.3 Use of epoxies in Coating Industry

Mulisubstrate adhesion & corrosion resistance parameters are making epoxies as a choice

material to use them in paint industry.Some common example:

• Marine coating

• Transpotation coating in primer

Major advantage is in terms of application i.e. these can be used by brush application,

spray application or roller application.

Latest development in coating area is that these are utilized in ED i.e. electro deposition.

39

1.9.4 Application of epoxies in Electronic Applications

Below properties make them ideal for electronics application:

• High mechanical strength

• Good process ability

• Nice Moldability

• Heat resistance

•

For such kind of applicaitn high molecular weight epoxies are utilized.

1.9.5 Application in Tooling, Molding and Casting

1. Because of poor conductivity & higher dimensional stability epoxies are used to

make A.C. Transformers , Accessories for cables accessories and other same kind

of equipments.

2. Master mould & other tools are being made by these polymers.

40

1.9.6 Epoxy application in Constructions

The commonly used epoxies improve the durability of flooring & other repair area where

high strength is required. Here thick matrix adducts are used.