Epoxy Resins

1 Novel Thermosetting Epoxy Resins Based on Pentaerythritol J. M. JORDAN, FRANCIS W. MICHELOTTI, E. M. PEARCE, and M. ZIEF

Downloaded by 149.202.44.177 on May 25, 2016 | http://pubs.acs.org Publication Date: June 17, 1970 | doi: 10.1021/ba-1970-0092.ch001

J. T. Baker Chemical Co., Phillipsburg, N. J. 08865

A novel polyglycidyl ether of pentaerythritol has been synthesized which exhibits a number of new and interesting features. It is water-soluble, low in chlorine content (< 0.5%) and viscosity (400-1500 c.p.s., depending on synthetic reaction conditions), and is completely aliphatic in nature. Under typical curing condition, it exhibits high reactivity, and yields castings with high heat distortion temperatures with most epoxy curing agents studied. Details of the physical properties of uncured epoxy resin as well as mechanical, electrical, and chemical resistance properties of the resultant thermosets cured with many typical anhydride and amine curing agents, respectively, are given.

'T'here is considerable patent literature which alleges the preparation of glycidyl ethers of pentaeiythritol. Zech (3, 4), for example, describes the preparation of a polyepoxide from the condensation of a mixture of pentaerythritol and trimethylolpropane with epichlorohydrin by BF catalysis followed by dehydrochlorination with sodium aluminate to give a product with 2.7 epoxide groups per molecule, a molecular weight of 427 and containing 7.6% chlorine. No data on resin performance are given. A comparable product is described by Price et al. (2)— i.e., a polyglycidyl ether of a mixture of pentaerythritol, glycerin, and trimethylolpropane with chlorine contents varying from 7.7-11.6%. Again, no data on the performance of the cured resins are given. Zuppinger et al. (5) described the synthesis of a polyepoxide from pentaerythritol in an aqueous/epichlorohydrin medium under basic conditions and obtained a product with approximately 8.65% oxirane oxygen (equiv. wt, ca. 185), 12.9% hydroxyl groups (hydroxyl equiv. wt., ca. 132) and 3.7% total chlorine. Again, no data on resin performance are cited. A

3

1 Lee; Epoxy Resins Advances in Chemistry; American Chemical Society: Washington, DC, 1970.

2

E P O X Y

RESINS

This paper describes the properties of a polyglycidyl ether of pentaerythritol (which shall henceforth be referred to as D P X100) which is low i n chlorine content, low i n viscosity and high i n oxirane oxygen functionality and presents extensive data of the cured resin with a variety of curing agents. The physical properties of the resin are listed i n Table I. Table I.

Physical Properties of D P X I 0 0


Epoxide equivalent wt. Hydroxyl equivalent wt. Viscosity, c.p.s., 25°C. Total chlorine content, % Solubility Color, Gardner scale Density Surface tension Shelf stability Flash Point (Cleveland Open Cup)

110-119 124-150 1000-1500 0.3-0.5 most solvents, including water; insoluble in saturated aliphatic hydrocarbons 9-11 1.20 grams/cc. 51 dynes/cm. well in excess of three months ca. 240°C.

Chemistry The details of the synthesis and structure of D P X100 resin w i l l be the subject of a separate paper i n the near future. However, the following simplified reaction scheme w i l l indicate the major constituents believed to be present in the resin. HOH C

CH.,OH

2

\ /

C

"

2

HOH C

CH —CH—CH C1

2

\ /

^ e x c e s s

2

\

C

2

'

CH OH

-

CH 0—CH —CH—CH 2

9

2

/\ HOH C

O / \

2

/

O

/\ HOHoC

CH 0—CH —CH—CH O 2

2

2

Experimental Preparation of Samples for Testing. One-eighth inch-thick sheets and 1/2 inch x 1/2 inch x 5 inches heat distortion temperature bars were cast from resin and various hardeners in the following manner. The desired amounts of resin and curing agent were weighed into a beaker. W i t h aliphatic amine curing agents, the resins and amines were precooled to 0 ° - 1 0 ° C . to prevent excessively short pot life—less than 10 minutes after mixing at room temperature. p,p'-Methylenedianiline ( M D A ) and hexahydrophthalic anhydride ( H H P A ) curing agents were premelted, maintained 0 ° - 1 0 ° C . above their melting points, and then mixed into resin preheated to about 60 °C. The components were mixed with a laboratory electric stirrer and subsequently degassed for several

Lee; Epoxy Resins Advances in Chemistry; American Chemical Society: Washington, DC, 1970.


1.

JORDAN

E T A L .

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Novel Thermosetting Resins

minutes i n a vacuum desiccator (until no more bubbles occurred at 1-5 mm. H g ) . A l l amines were used at 100%, and a l l anhydrides were used at 90% of theoretical stoichiometry based on epoxide functionality. W i t h D P X100, anhydride cures were accomplished either with or without benzyldimethylamine accelerator. W i t h t i e diglycidyl ether of bisphenol A , benzyldimethylamine was used with all anhydride cures. The resinhardener solutions were poured into Teflon sprayed or coated aluminum molds to produce 8 inches X 8 inches X 1/8 inch sheets or 5 inches X 1/2 inch X 1/2 inch bars. Initial cure was accomplished at room temperature or lower with the aliphatic amine hardeners, and at 80°C. for M D A , N M A ( N a d i c M e t h y l Anhydride), and H H P A . Post-cures at higher temperatures (such as 150 °C.) were generally used to improve the properties of the castings prior to testing. Test Methods Test Ult. Tensile Strength & Ult. Elongation Dielectric Constant & Dissipation Factor Volume Resistivity Gel Time Coefficient of Linear Thermal Expansion Heat Deflection Temperature ( H D T ) Compressive Strength

ASTM No. D-638-61T D150-59T D257-61 Tecam Gelation Timer D696-44 D648-56 D695-61T

Discussion and Results. Results obtained i n curing D P X100 with amine curing agents are summarized i n Table II, while those obtained with some typical anhydrides are shown i n Table III. For comparative purposes, data obtained under comparable conditions with a diglycidyl ether of bisphenol A ( D G E B A , epoxide equivalent weight of 190) is shown i n parenthesis. The unexpectedly high H D T s obtained with D P Table II. Curing Agent TETA

MDA

a

DP XI00 Cured with Amines

Cure Schedule

HDT, °C.

Tensile, p.s.i.g.

Elongation, %

7 days RT Above + 4 hrs. 100°C.

57 (54) 148 (119)

10,450 (8,890)

3.9 (5.0)

2 hr. 80°C. + 4 hr. 150°C. Above + 16 hr. 175°C.

206 (150)

10,250 (8,900)

3.4 (5.2)

234

• Triethylenetetramine.

Lee; Epoxy Resins Advances in Chemistry; American Chemical Society: Washington, DC, 1970.

4

E P O X Y

RESINS

X100 as compared with conventional epoxy resins may arise from the relative compactness and spiro-like character of the molecule. As is typical with most anhydride-cured epoxy systems, maxima i n H D T s were obtained at approximately 90% of theoretical stoichiometry. Table III. Curing Agent


NMA

HHPA

DP XI00 Cured with Anhydrides

Cure Schedule

HDT, °C.

Tensile, p.s.i.g.

Elongation

4 hrs. 80°C. + 22 hrs. 150°C. Above + 16 hrs. at 200°C. 2 hrs. 80°C. + 4 hrs. 150°C.

187 (147)

6,200 (11,125)

1.4

233 (173)

7,620

2.6

144 (125)

8,000

3.0

It should be noted that reactions of D P X100 epoxy resin are extremely rapid with all types of aliphatic amines or polyamides at room temperature. This marked reactivity may be caused by the accelerating characteristic of hydroxyl functionality (1). W i t h anhydride cures there is no need for tertiary amine catalysis as is customary with conventional epoxy resins although the use of such catalysis i n D P X100 systems markedly enhances reactivity (Table I V ) . Depending on curing agent, D P X100 is approximately from two to eight times as reactive as D G E B A (data in parenthesis). Table IV.

Exotherm and Gel Time Data for DP XI00 Cured with Two Hardeners

Curing Agent

NMA

B D M A accelerator, phr. Mass of sample, grams Bath temp., °C. Time to initial exotherm, min. Time to peak exotherm, min. Tecam gel time, min. Temp, at peak exotherm, °C. Table V .

Acetone Toluene Water b c

1.0 (1.0) 250 (250) 80 (80) 40-50 (110) 57 (137) 46 (122) 132 (120)

--(-) 250 (500) 80 (70) —5 (40)

Epoxy Resins

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