CA1038994A - Epoxy novolac resins having a narrow molecular weight distribution and process therefor - Google Patents

Abstract

ABSTRACT

Epoxy novolac resins having a narrow molecular weight distribution are prepared by dissolving an epoxy novolac resin prepared by conventional means in a suitable solvent such as xylene, cooling below 50°C until separation into 2 phases occurs, separating the two phases and removing the solvent therefrom thereby producing a resin of relatively low molecular weight and a resin of relatively high molecular weight wherein each resin has a narrow molecular weight distribution.

Description

~038994 This invention relates to epoxy novolac resins and a process for preparing them. More particularly, the invention relates to an epoxy novolac resin having a narrow molecular weight distribution represented by the general formula ~O~CH l_CH2_CH_CH2 O-CH2-CH-CH2 ~ C~l ~ ,C~j~

wherein each R is independently hydrogen or an alkyl group having from 1 to 5 carbon atoms, each R' is independently hydrogen, chlorine, bromine, an alkyl group having from 1 to 6 carbon atoms or a glycidyloxy group and n has an average value greater than 0.1 and such that the viscosity in centistokes at 70C to average EgW ratio is less than 11:1 when the weight average molecular weight of the resin is below 2000 and a plot lS of Mw vs Mw:Mn falls on or within the area bounded by A, B, C, D in Figure 1 when the weight average molecular weight is above 2000.
The process of the present invention comprises q (A) dissolving an epoxy novolac resin having a wide . 20 molecular weight distribution in xylene, toluene, methyl isobutyl ketone, a solvent having a solubility parameter of 8.0-9.0 with low to mèdium hydrogen bonding, a solvent having a solubility parameter >11.5 and any hydrogen bonding value, or a mixture of such solvents, at a tem-perature between 50C and the boiling point of the , solvent, wherein the quantity of solvent is from 30% to ,:
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90~ by weight of the combined weight of solvent and resin, (B) cooling the resultant solution to a temperature below 50C and the freezing point of the solvent for a period of time sufficient to cause a separation into two distinct phases, (C) separating the two phases one from the other, and (D) removing the solvent from each of the phases;
thereby producing (1) an epoxy novolac resin wherein the weight average molecular weight is below 2000 and the viscosity in centistokes at 70C to average EEW ratio is -.
below 11:1 and (2) an epoxy novolac resin wherein the - -weight average molecular weight is above 2000 and wherein a plot of MW vs Mw:Mn falls on or within the boundary of ~-A, B, C, D in Figure 1.
The epoxy novolac resins which are suitably employed in the process of the present invention are . ~ -prepared by conventional means such as, for example, by ~ .
reacting in the presence of an acidic catalyst, e.g., oxali.c acid, an aldehyde such as formaldehyde and an aromatic hydroxyl-containing compound such as phenol in an aldehyde:phenol or like compound molar ratio suitable in preparing a novolac of intermediate molecular weight such as from 0.4:1 to 0.8:1 and preferably from 0.46:1 to 0.75:1. The excess phenol and water is then removed by .
any conventional means such as by flashing under vacuum.
Then the resultant novolac resin is reacted with an excess .
of an epihalohydrin such as epichlorohydrin or glycerine dichlorohydrin in the presence of a basic catalyst such as, for example, benzyl trimethyl ammonium chloride. t ' Then the resultant product is dehydrohalogenated with a base such as, for example, sodium hydroxide, sodium 17,296-F -2-~ , .

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~38994 carbonate, or mixtures thereof. After washing with water until neutral and filtering, excess epihalohydrin is removed by flashing under vacuum thereby producing an epoxy novolac resin.
In this process, the top layer or phase con-tains the epoxy novolac resin having a relatively low average molecular weight, whereas the bottom layer or phase contains the epoxy resin having a relatively high average molecular weight.
Aldehydes which may be suitably employed to prepare the epoxy novolac resins employed in the present invention include those aliphatic aldehydes having from 1 to 6 carbon atoms such as, for example, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and mixtures thereof.
Aromatic hydroxyl-containing compounds which may be suitably employed to prepare the epoxy novolac resins employed in the present invention include those represented by the formula ~R

wherein R is hydrogen, a halogen such as bromine or chlorine, a hydroxyl group or an alkyl group having from 1 to 6 carbon atoms. Suitable such compounds `;
include, for example, phenol, methyl phenol, ethyl phenol, propyl phenol, hydroquinone, resorcinol, catechol, and mixtures thereof.
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~038994 :
Suitable solvents which may be employed in -the process of the present invention include, for example, xylene, toluene, methyl isobutyl ketone, solvents having solubility parameters of 8.0-9.0 ~-with low to medium hydrogen bonding and those with solubility parameters >11.5 and any hydrogen bonding value as described in an article entitled "Quanti-fication of the Hydrogen Bonding Parameter" by E. P.
Lieberman, Official Digest, published by the Federation of Societies for Paint Technology, Easton, Pa., Jan. -1962, pp. 30-50, and mixtures thereof.
The accompanying Figure 1 is a graph or a -plot for determining those epoxy novolac resins having -weight average molecular weights above 2000 which are encompassed by the present invention. The area bounded by the points A, B, C, D is that which is encompassed by the present invention. The labeled points are those resins which illustrate the present invention and com-parative experiments with respect to those resins having weight average m~lecular weights above 2000.
The weight average molecular weight (Mw) is plotted as the ordinate and the weight average molecular weight:number average molecular weight (Mw:Mn) is plotted as the abscissa. The coordinates for point A
are Mw = 2000; Mw:Mn = 2. The coordinates for point B
are Mw = 6500; Mw:Mn = 5. The coordinates for point C
are Mw = 11000; Mw:Mn = 5. The coordinates for point D
are Mw = 11000; Mw:Mn = 2.
.

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For resins having a weight average molecular weight below 2000 that are encompassed by the present invention the ratio of the viscosity in centistokes at 70C to average epoxy equivalent weight (EEW) is below 11:1.
Throughout this specification the molecular weights are as determined by gel permeation chromato-graphy.
The epoxy novolac resins of the present invention which are of relatively low molecular weight may be suitably employed as adhesives, laminates, coat-ings and castings. They have a weight average molecular weight below 2000 and viscosity in centistokes at 70C:
average EEW of <11:1. When compared to a conventionally prepared epoxy novolac resin having an average molecular weight of below 2000 they possess an improvement in one or more of the properties such as a reduction in viscosity, reduction in average EEW, .
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17,296-F 5 -~0~8994 increased heat distortion temperature, or increased flexural properties.
The epoxy novolac resins of the present invention which are of relatively high lecular weight may be suitably employed as electrical var-nishes, encapsulants, and molding powders. They have a weight average molecular weight above 2000 and a plot of Mw vs Mw:Mn falling on or within the area bounded by A, B, C, D in Figure 1. When compared to a conventionally prepared epoxy novolac resin having an average molecular weight above 2000 and a plot of Nw vs Mw:Mn falling outside the area bounded by A, B, C, D they possess an improvement in one or more of the properties such as a reduction in solu-tion viscosity, increased heat distortion temperature, increased flexural properties, a sharper melting point and improved flow properties, or a higher melt-ing point (i.e. a grindable solid such that the resin can be ground without the particles sticking together).
The epoxy novolac resins of the present in-vention can be employed alone or they may be employed in admixture with other epoxy resin compositions. The resins of this invention can be cured by any of the conventional epoxy curing mechanisms, e.g. by employ-ing such curing catalysts as teritary amines, Lewis acids and the like or ~uch coreactive crosslinking agents as primary and secondary amine-containing compounds, polycarboxylic acids and anhydrides, ~ -mercaptans, dicyandiamide, and the like.

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~0~8994 The epoxy novolac resins of the present invention may be admixed with inert materials such as, for example, pigments, fillers, extenders, flexi-bilizers, mold release agents, solvents and flow con-trol agents as well as witl~ reactive diluents, accel-erators, and fire retardand agents.
The following examples further illustrate the present invention.
In the following examples, the molecular weight data was obtain by gel permeation chromato-graphy.
EXAMPLE I
A novolac resin having a 96C Durran's soften-ing point was prepared using a 0.75:1 mole ratio of formaldehyde to phenol.
Formaldehyde was fed into phenol (contain-ing 0.6 wt. % oxalic acid) at 100C over approx. 1 ;~- -.,;
hour period. This was reacted 1 hour and then the - -excess phenol and water were removed under vacuum to 180C. The resulting novolac was dissolved in 5 moles epichlorohydrin per equivalent of novolac or about 4.5:1 wt. ratio. 60~ aqueous benzyltrimethyl am-monium chloride (about 3% of novolac wt.) was added ;~
and reacted at 60C for 4 days. The resulting novo-lac polychlorohydrin ether was dehydrochlorinated ~ - ;
at about 20-25C using 50% excess aqueous solution containing 15% NaOH and 10% Na2CO3 for 90 and 60 minutes respectively. This was washed with water until neutral and the excess epichlorohydrin and water were removed under vacuum to 160C to yield ., :, .

17,296-F -7-. .
, 1;~38994 an epoxy novolac having a 170 epoxide equivalent weight, 5.4 average functionality, a 52C Durran's softening point, a weight average molecular weight of 2850, and a weight to number average molecular weight ratio (Mw:Mn) of 3.098 (this resin is de-signated as I in Figure 1). This epoxy novolac was mixed at 20 weight percent solids in xylene and heated to 80C to effect solution. This was then cooled to 40C until separation into two phases oc-curred. The phases were separated and the solvent re ved from each phase. The low molecular weight or soluble phase (45% of original resin weight) had a 166.7 epoxide equivalent weight, 3.67 functionality, a neat viscosity of 1177 cs at 70C, a weight average molecular weight of 1112, and a viscosity in centi-stokes at 70C : average EBW ratio of 7.06:1. The higher molecular weight or insoluble phase (48.8~ of -original resin weight) had an epoxide equivalent weight of 181.4, 9.5 functionality, an 85C Durran's softening point, a weight average molecular weight ~
of 4978, a weight average molecular weight to num- -ber average molecular weight ratio of 2.891:1, and a 50 weight percent acetone solution viscosity at 25C of 11.95 c8.
Samples of the low molecular weight fraction were cured with stoichiometric quantities of methylene dianiline for 16 hours at 125C plus 2 hours at 175C.
These samples are designated as I-l-A.
Additional samples were cured as above plus -an additional 2 hours at 225C. These samples are designated as I-l-B.

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~he physical properties of samples I-l-A and I-l-B as well as the properties of the uncured resin designated as I-l are given in Table I.
Samples of the high molecular weight frac-tion were cured with stoichiometric quantities of 4,4'-methylene bis(o-chloroaniline) for 16 hours at 140C plus 2 hours at 175C plus 2 hours at 250C.
These samples are designated as I-2. The physical properties of these cured samples, as well as the prop-erties of the uncured resin, also designated as I-2, are given in Table II.
EXAMPLE II
An epoxy novolac was prepared as in Example I ~ -from a novolac with a 101C Durran's softening point. The epoxy novolac had a 176.2 epoxide equivalent weight, 5.45 functionality, a 57C Durran's softening point, a weight average molecular weight of 2869, and a weight to number average molecular weight ratio of 2.990 (this resin is designated as II-A in Figure 1). This resin was frac- ~
tionated at 20 weight percent solids in xylene. The ~-low molecular weight fraction (46.3% of original resin weight) had a 166.7 epoxide equivalent weight, 3.53 functionality, a neat viscosity of 1683 cs at 70C, a weignt average molecular weight of 869, and a viscosity in centistokes at 70C : average EEW ratio of 10.1:1.
The higher molecular weight fraction (52.9% of original resin weight) had a 180.2 epoxide equivalent weight, 9.5 funtionality, an 87C Durran's softening point, a weight average molecular weight of 4463, a weight average mole-cular weight to number average molecular weight ratio of 17,296-F -9-~)38994

2.605:1, and a 50 weight percent acetone solution viscosity at 25C of 11.84 cs (this resin is designated as II-B in Figure 1).
EXAMPLE III (COMPARATIVE) Preparation of Low Molecular Weight Conventional Epoxy Novolac A novolac resin was prepared using 0.46:1 formalin to phenol mole ratio. Each equivalent of novolac was dissolved in 5 moles epichlorohydrin. This was heated to 100C and 10% excess aqueous 50% NaOH was added slowly over approximately 2 hours. The excess epichlorohydrin was removed under vacuum to 150C.
This was then diluted with toluene to 15~ solids and water washed to remove NaCl. The toluene was flashed under vacuum to 150C to yield an epoxy novolac having the following properties:
weight average molecular weight 1081 number average molecular weight 609 EEW, average 179.2 Functionality 3.4 Viscosity at 70C, cs (centistokes) 2542 Viscosity in centistokes at 70C
to EEW ratio 14.19:1 Cured samples were prepared employing stoichio-metric quantities of methylene dianiline and curing at - -125C for 16 hours plus 2 hours at 175C. The samples were designated as III-A.
Cured samples were also prepared as above excep~ that they were cured an additional 2 hours at 225C. These samples are designated as III-B.
The properties of these samples as well as the properties of the uncured resin designated as III
are given in Table I.

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1~38994 EXAMPLE IV (COMPARP.TIVE) Preparation of High Molecular Weight Conventional Epoxy Novolac A novolac resin was prepared using a 0.72:l mole ratio of formaldehyde to phenol.
Formaldehyde was fed into phenol (contain-ing 0.6 wt. % oxalic acid) at 100C over approx. 1 hour period. This was reacted 1 hour and then the ex- -cess phenol and water were removed under vacuum to ---180C. The resulting novolac was dissolved in 5 moles epichlorohydrin per equivalent of novolac or about a -~ -- 4.5:1 wt. ratio. 60~ aqueous benzyl trimethyl am-monium chloride (about 3~ of novolac wt.) was added and reacted at 60C for 4 days. The resulting novo-lac polychlorhydrin ether was dehydrochlorinated at about 20-25C using a 50~ excess aqueous solution containing 15~ NaOH and 10 Na2CO3 for 90 and 60 min- ~ ~
utes respectively. This was washed with water until ~ ;
neutral and the excess epichlorohydrin and water were removed under vacuum to 160C to yield an epoxy novolac having a 173.3 epoxide equivalent weight, a `
; 6.14 average functionality, a 62.5C Durran's soften-ing point, a weight average molecular weight of 4386 and a weight average molecular weight to number ave-rage molecular weight ratio of 4.124:1 (this resin -i8 designated as IV in Figure 1). `
Cured samples were prepared using a stoici-ometric quantity of 4,4'-methylenebis~o-chloroaniline) and curing for 16 hours at 140C plus 2 hours at ~75C plus 2 hours at 250~C.
'; `' ' '.'~-'.., 17,296-F -11-These samples are designated as IV and - these properties as well as the properties of the uncured resin are reported in Table II. .-,296-F -12-.i,,. -- , :

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1~)38994 - TABLE II
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SAMPLE NUM~ER
Present Invention Comparative PROPERTY (UNCURED) I-2 IV
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Wt. avg. mol. wt. 4978 4386 No. avg. mol. wt. 1722 1064 MW:Mn 2.891 4.124 EEW 181.4 173.3 Functionality (avg.) 9.5 6.14 Durran's softening point, C 85 62.5 PROPERTY (CURED) I-2 IV

Heat distortion temp. >250 >250 Flexural Strength, psi 12,250 10,200 -(kg./sq. cm) (858) (714) Flexural modulus, psi 485,000 460,000 (kg./sq. cm) (33,950) (32,200) .'- ' `~ .

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, 1~38994 EXAMPLE V
A. An epoxy novolac was prepared as in Example I from a novolac with a 104C Durran's softening point.
The resulting epoxy novolac had a 170.6 epoxide equiva-lent weight 5.44 functionality, a 56C Durran's sof-tening point, a weight average molecular weight of 2688, and a weight to number average molecular weight ratio of 2.897 (this resin is designated as V-A in ~-Figure 1).
B. After fractionation according to the pro-cedure of Example I, the higher molecular weight fraction (45.8~ of original weight) had a 175.5 epox- -ide equivalent weight, 9.9 functionality, an 88C
Durran's softening point, a weight average molecular weight of 4580, a weight average molecular weight to `
number average molecular weight ratio of 2.633:1, and a 50% acetone solution viscosity at 25C of 12.56 cs (this resin is designated as V-B in Figure :
1). ' .
EXAMPLE VI
: A. An epoxy novolac was prepared as in Exam-ple I from a 90C Durran's softening point novolac, .
had a 172 epoxide equivalent weight, 4.88 function- :
ality, a 51C Durran's softening point, a weight - .~ .
average molecular weight of 2101, and a weight to number average molecular weight ratio of 2.504 (this . resin is designated as VI-A in Figure 1). .:
; a. The higher molecular weight portion from fractionation (43.4% of original weight) as in Ex-ample I had a 182.2 epoxide equivalent weight, 8.2 17,296-F -15-1~38994 : functionality, an 82C Durran's softening point, a weight average molecular weight of 3671, a weight average lecular weight to number average molecu-lar weight ratio of 2.453, and a 50% acetone solu-tion viscosity at 25C of 10.50 cs (this resin is designated as VI-B in Figure 1).
EXAMPLE VII
An epoxy novolac resin similar to that of Example II-A was fractionated on a larger scale and resulted in a higher molecular weight portion with a 183.8 epoxide equivalent weight, 9.22 functiona-lity, an 84C Durran's softening point, a weight average molecular weight of 4752, and a weight ave-: rage molecular weight to number average molecular weight ratio of 2.804. 52% of the original resin : weight was recovered as the higher lecular weight product (this resin is designated as VII in Figure 1) .
- EXAMPLE VIII
An epoxy novolac resin having a 179.2 epox-ide equivalent weight, 3.40 functionality, a Durran's softening point of less than 50C, a weight average molecular weight of 1081, and a weight to number ave-rage molecular weight ratio of 1.774 was fraction-ated as in Example I. The unfractionated resin is designated as VIII-A in Figure 1. The resulting resin had a 207.7 epoxide equivalent weight, 5.18 functionality, a 67.5C Durran's softening point, a weight average molecular weight of 2154, and a weight average molecu~ar weight to number average molecular 17,296-F -16-~/~38994 weight ratio of 2.002. The 504 acetone solution vis-cosity at 25C was 7.9 cs (this resin is designsted - as resin VIII-B in Figure l). -EXAMPLE IX ( COMPARATIVE ) :
213.6 grams of 88~ phenolic solution and 162.4 grams of water were charged into a reactor.
5.8 grams of concentrated sulfuric acid (95.0-98.0%) was added. The acidified solution was heated to 80C, then 80.6 grams of 37.2% formaldehyde was added to the stirred acidified solution o~er a - -period of 4 hours while the temperature was main-tained at 80C.
Upon the completion of the addition of - the formaldehyde solution, the temperature was main-tained at 80C for an additional period of a half hour, after which 8.0 grams of sodium carbonate was added to neutralize the acid. ~
The system was then placed under vacuum --at a pressure of 35 mm mercury and water distilled by heating until the temperature reached 80C. Then, ; additional water was slowly added to the system at a rate such that the distillation temperature was held - -approximately constant at 80C. The addition of water was continued until the total distillate col-: ~ .
lected amounted to 630 grams.
The still residue was then used, it being the no~olac resin. 50 grams of the resin was then dissol~ed in 75.0 grams of methyl ethyl ketone and 81.0 grams of epichlorohydrin. The resulting solu~
tion was then heated; 40.0 grams of 50% sodium :,, ,, , . - - .

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1~38994 hydroxide solution were added gradually with Rtirring over a 4-hour period to the warmed solution at about 80C. After the NaOH solution had been added the tem-perature was maintained at 80C for an additional 1/2 hour.
The aqueous layer containing salt was then withdrawn from the reactor. The organic layer con-taining the resin was washed twice with 100 ml of H20 to complete the removal of salt. The washed organic layer was then distilled to remove most of the methyl ethyl ketone. The remaining solution was then stripped under vacuum to remove the remaining solvent.
- The resultant resin was a very viscous liquid at room temperature and was a clear amber color. The resin had the following properties:
~ epoxide = 19.98 average EEW = 215 viscosity ~ 1360 centistokes at 70C
MW = 240 Mn = 616 Mw:Mn - 3.905 The plot of MW vs Mw:Mn is designated as IX i~ Figure 1.

17,296-F -18--

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An epoxy novolac resin having a narrow molecular weight distribution represented by the general formula wherein each R is independently hydrogen or an alkyl group having from 1 to 5 carbon atoms, each R' is independently hydrogen, chlorine, bromine, an alkyl group having from 1 to 6 carbon atoms or a glycidyl-oxy group and n has an average value greater than 0.1 and such that the viscosity in centistokes at 70°C
to average EEW ratio is less than 11:1 when the weight average molecular weight of the resin is below 2000 and a plot of Mw vs Mw:Mn falls on or within the area bounded by A, B, C, D in Figure 1 when the weight ave-rate molecular weight is above 2000.

2. The epoxy novolac resin of Claim 1 wherein each R and R' is hydrogen.

3. A process for preparing an epoxy novo-lac resin having a narrow molecular weight distribu-tion which comprises (A) dissolving an epoxy novolac resin having a wide molecular weight distribution in xylene, toluene, methyl isobutyl ketone, a solvent having a solubility parameter of 8.0-9.0 with low to medium hydrogen bonding, a solvent having a solubility parameter >11.5 and any hydrogen bonding value, or a mixture of such solvents, at a temperature between 50°C and the boiling point of the solvent, wherein the quantity of solvent is from 30% to 90% by weight of the combined weight of solvent and resin, (B) cooling the resultant solution to a tempera-ture below 50°C and the freezing point of the solvent for a period of time sufficient to cause a separation into two distinct phases, (C) separating the two phases one from the other, and (D) removing the solvent from each of the phases;
thereby producing (1) an epoxy novolac resin wherein the weight average molecular weight is below 2000 and the viscosity in centistokes at 70°C to average EEW ratio is below 11:1 and (2) an epoxy novolac resin wherein the weight average molecular weight is above 2000 and wherein a plot of MW vs Mw:Mn falls on or within the boundary of A, B, C, D in Figure 1.

4. The process of Claim 8 wherein the step (A) is performed at from 70° to 80°C, step (B) is performed at from 45° to 50°C, and wherein the quantities of solvent is from 50% to 80% by weight of the combined weight of solvent and resin.

5. The process of Claim 4 wherein the solvent is xylene.

6. A curable composition comprising an epoxy novolac resin of Claim 1 or Claim 2 and a catalytic quantity of a catalyst or a curing amount of a curing agent therefor.

7. Composition of Claim 6 wherein the curing agent is methylene dianiline, or 4,4'-methylene bis (o-chloroaniline).