Electromagnetic (Microwave) Radiation Effects on Terminally Reactive

Chapter 22

Electromagnetic (Microwave) Radiation Effects on Terminally Reactive and Nonreactive Engineering Polymer Systems 1

S. C.Liptak,S. P. Wilkinson, J. C. Hedrick , T. C. Ward, and J. E. McGrath 2

Downloaded by CORNELL UNIV on May 18, 2017 | http://pubs.acs.org Publication Date: November 12, 1991 | doi: 10.1021/bk-1991-0475.ch022

Department of Chemistry and NSF Science and Technology Center: High Performance Polymeric Adhesives and Composites, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0212

Amorphous poly(arylene ether sulfones) of controlled Mn were synthesized by step polymerization of bisphenol-A phenolate with activated aromatic halides in the presence of m-aminophenol. Utilization of the amino terminated polysulfones (NHPSF) to co-cure with the diglycidyl ether of bisphenol A (DGEBA) and/or tetraglycidyl 4,4'diaminodiphenylmethane (TGDDM) via thermal or microwave (EM) processing was conducted at temperatures of ~190240ºC. 4,4-Diaminodiphenylsulfone (DDS) was employed as the curing agent. The bismaleimide systems (Matrimid 5292 A/B) were thermally or electromagnetically crosslinked through free radical reactions of the maleimide groups at temperatures of ~250ºC. The influence of oligomer molecular weight on the thermal, mechanical, and morphological properties of the thermoplastic toughened epoxy networks were investigated by DSC, fracture toughness (K ) and SEM. Microwave processing can dramatically enhance the rate of network formation in a variety of systems. Morphological structure in thermoplastic toughened thermosets can be controlled via the microwave power utilized. Non-reactive thermoplastics which contain even modestly polar groups (e.g., PEEK, polyimides, etc.) can also be rapidily melt processed. 2

,

IC

Radical ions which subsequently decay to free r a d i c a l s are usually considered to be responsible for the crosslinking and s c i s s i o n reactions observed i n polymers exposed to ionizing radiation. Nonionizing radiation, i n contrast, i s generated from that part of the electromagnetic spectrum for which the quantum energy i s too low to ionize an atom (1,). Microwave radiation i s not energetic enough to cause ionization or chain s c i s s i o n . Thus, any acceleration of reaction rates observed for systems exposed to microwave radiation 1

2

Current address: IBM Corporation, T. J. Watson Research Center, P.O. Box 218, Yorktown Heights, N Y 10598 Corresponding author 0097-6156/91/0475-0364S06.00/0 © 1991 American Chemical Society

Clough and Shalaby; Radiation Effects on Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


22. LIPTAK ET AL

Radiation Effects on Engineering Polymer Systems 365

compared with thermal curing i s probably due to more e f f i c i e n t energy transfer. Polarization phenomena i n homogeneous d i e l e c t r i c materials may be c l a s s i f i e d into three categories based on the nature of the atomic or molecular o r i g i n s ^ ) * (1) E l e c t r o n i c polarization that results from a s h i f t of electron o r b i t s with respect to the center of the atom. (2) Atomic polarization that results from a s h i f t i n r e l a t i v e positions, e.g., between the carbon and hydrogen atoms by stretching i n response to an e l e c t r i c f i e l d . (3) Dipole polarization that results from orientation of permanent dipoles under the influence of the electron field. The mechanism of energy transfer in microwave heating i s thought to occur by e l e c t r i c dipolar coupling of the radiation to permanent dipole moments in the polymer (Category 3), rather than by thermal conductivity as i n conventional processing. Indeed, most molecules by their very nature are polarizable i n an e l e c t r i c f i e l d . The degree of p o l a r i z a t i o n and the energy required to achieve i t control the loss factor or d i s s i p a t i o n factor of a material. A material that i s readily polarized by a small e l e c t r i c f i e l d has a high loss factor and i s observed to be easy to heat. Reactive systems inherently contain a large concentration of very mobile dipolar groups, and thus, are easy to heat v i a electromagnetic radiation. As the reaction proceeds though, the loss c h a r a c t e r i s t i c of the material decreases with the consumption of polar functional groups and the decreasing mobility of polarizable moieties, thereby necessitating a greater input of energy to maintain the "global temperature" of the reacting system. By the same reasoning, nonreactive systems with their associated n e g l i g i b l e concentration of highly polar reactive endgroups and hindered dipolar rotation require higher input energies to attain e f f i c i e n t heat generation by dipolar relaxation mechanisms. In our laboratories(3,6), and elsewhere, microwave radiation has been u t i l i z e d to process both reactive thermosetting polymers and nonreactive thermoplastic(7-11) polymers. More s p e c i f i c a l l y , Gourdenne et.al.(12-15) and colleagues at Michigan State University(16-17) have examined continuous and pulsed microwave processing of epoxy/amine systems. In these studies both groups have independently v e r i f i e d that energy transferred by a pulsed electromagnetic source i s more e f f i c i e n t than by an energy equivalent generated continuous wave. During these investigations Hawley et a l . made an important contribution to the f i e l d of microwave processing with their implementation of computer controlled pulsed microwave processing of epoxies(18). Supplementing the work conducted i n the area of the epoxy/amine systems, Gourdenne(19) and Jullien(20) have investigated other step growth thermosetting type systems, such as the polyurethanes, processed v i a electromagnetic radiation at a frequency of 2.45 GHz. Additionally, T e f f a l and Gourdenne(21), i n some of his e a r l i e r work, investigated microwave radiation activated r a d i c a l polymerization of hydroxyethyl methacrylate. Employment of the microwave processing technique possesses a number of potential advantages when compared to more t r a d i t i o n a l thermal methods. There i s the potential for fast volumetric heating of thermoplastics, s i g n i f i c a n t l y reduced cure times in thermosetting



366

RADIATION EFFECTS ON POLYMERS

systems, the a b i l i t y to produce materials that may display lower residual stresses (,22). Other reported advantages of EM processing include maintenance of mechanical properties (5,17,23-24), an increase i n thermal properties and an improvement i n adhesion at the interface of carbon fiber/epoxy composites(25) when compared to thermally processed samples. An additional reported benefit i s that a reduction i n chemical p o l l u t i o n occurs with some microwave processing applications (1) · In t h i s investigation, the f e a s i b i l i t y of processing high performance polymeric matrix resins for composite structures u t i l i z i n g microwave radiation has been analyzed. The systems which were investigated include thermoplastic toughened epoxy resin networks, thermosetting bismaleimides, and nonreactive thermoplastics such as PEEK and Ultem. The relationships between processing conditions on the thermal, mechanical and morphological properties i n these material systems were investigated. EXPERIMENTAL The thermoplastic modified epoxy resins were prepared by reacting DGEBA ( d i g l y c i d y l ether of bisphenol A) epoxy resin (DER 332) with an amino functional poly(arylene ether sulfone) oligomer with a number average molecular weight of 16,000 gm/mole. The crosslinked network was prepared by reacting DGEBA i n a 2:1 molar r a t i o with respect to the NH PSF oligomer and the curing agent, DDS (4,4*-diaminodiphenylsulfone) (Aldrich Chemical). The synthesis of the NH PSP thermoplastic modifier and i t s reaction into the epoxy resin network have been previously described (26,27). Additionally, thermoplastic modified epoxy resins were prepared by reacting TGDDM ( t e t r a g l y c i d y l 4,4'-diaminodiphenylmethane) epoxy resin (Ciba-Geigy MY-721) with an amino functional PSF oligomer with a number average molecular weight of 14,700 gm/mole. In contrast with the other epoxy systems investigated, t h i s crosslinked network was prepared by reacting TGDDM i n a 1:1 molar r a t i o with respect to the NH^PSF oligomer and the curing agent, DDS. Bismalêimide resins based on 4,4·-bismaleimidodiphenylmethane (57% w/w) (Ciba-Geigy Matrimid 5292 A/B) were cured u t i l i z i n g either microwave or thermal processes. The Matrimid 5292 resin was degassed with continuous s t i r r i n g under vacuum at 130°C for 30 minutes prior to processing. Various testing specimens could be prepared by pouring the homogeneous solution of either epoxy/modifier/curing agent or maleimide/hardener into preheated RTV s i l i c o n e rubber molds. These samples were then cured v i a microwave or conventional thermal processing techniques into specimens of suitable dimensions for fracture toughness, dynamic mechanical thermal analysis, and stresss t r a i n measurements. The instrumentation u t i l i z e d for the electromagnetic processing experiments i s shown schematically i n Figure 1. I t consists of a Raytheon magnetron that generates continuous microwave energy at a frequency of 2.45 GHz. The power i s transmitted through coaxial transmission l i n e s to a c i r c u l a t o r which protects the magnetron from reflected power by terminating i t at a dummy load. A d i r e c t i o n a l coupler i s u t i l i z e d to divert power so the incident and reflected radiation can be monitored v i a power meters. An 18 cm diameter, 2

2


Radiation Effects on Engineering Polymer Systems


22. LIPTAK ET AL.


367

368



T E

c y l i n d r i c a l brass cavity resonating i n the ^ j i mode was used for the electromagnetic processing. This single mode applicator has the d i s t i n c t advantage over multimode c a v i t i e s i n that the impedance mismatch between the external c i r c u i t and the cavity due to changes of d i e l e c t r i c properties of the loaded material during processing can be avoided by tuning the cavity (16,7). Greater d e t a i l s of t h i s instrumentation have been provided elsewhere (3,5)· Thermoplastic toughened epoxy systems consisting only of DGEBA were cured by a two stage process i n the microwave cavity. The power introduced to the applicator was i n i t i a l l y set at 20 watts to quickly attain the cure temperature. Gradually the power was reduced to 14 watts so as to maintain a constant cure temperature of "240°C. Once the cure temperature had been attained, a processing time of 10 minutes was u t i l i z e d to y i e l d networks with 2 99% conversion (via DSC). The sample temperature was continually monitored during the course of the crosslinking reaction v i a a Luxtron (Model 750) f i b e r optic temperature probe. Systems containing the more highly reactive TGDDM r e s i n were reacted f o r longer times at lower microwave powers. For instance, epoxy networks incorporating 100 mole% TGDDM were f i r s t heated at 6 watts for ~10 minutes, then 8 watts for "25 minutes, and f i n a l l y 10 watts for "20 minutes to e f f e c t a cure temperature of 195 - 200°C As the TGDDM was "diluted" by the incorporation of DGEBA, higher processing powers could be r e a l i z e d . A 50/50 mole % DGEBA/TGDDM thermoplastic modified epoxy resin was cured by increasing the applied power to the cavity i n a stepwise fashion. Overall, the power had been increased from 6 watts to 14 watts, by 1 watt intervals, every 4-8 minutes, u t i l i z i n g this cure schedule a higher cure temperature ("225 - 230°C) was achieved. The lowering of the d i e l e c t r i c loss of the materials, as the cure progressed, necessitated the increase i n microwave power to maintain the cure temperature at optimal l e v e l s . The Matrimid 5292 A/B resin was EM processed i n a manner similar to that of the epoxy resin systems. To raise the temperature of the BMI/Diallyl resin to 200 C, 25 watts of power was employed. This temperature was maintained by continually tuning and detuning the microwave cavity. The samples were maintained at 200°C f o r 5 minutes and then raised to 250°C where again the temperature was held isothermally by tuning and detuning the cavity. For fracture toughness specimens the samples were held at 250°C for 40 minutes. Samples u t i l i z e d i n the extraction experiments were held at 200°C and 250°C for various lengths of time, again by tuning and detuning the cavity. Extraction experiments were performed using chloroform solvent for 4 days. The samples were weighed before and a f t e r extraction when constant weights had been attained. The r a t i o of the weights after and before extraction gave the percent gel f r a c t i o n remaining for the given length of time at a certain temperature. Samples for extraction that followed a thermal cure were performed i n a forced a i r convention oven held isothermally at either 177 C or 200°C for p a r t i c u l a r time i n t e r v a l s . e

e


22. LIPTAK ET AL.


RESULTS AND DISCUSSION Thermoplastic Modified Epoxy Resin Networks of DGEBA: The polysulfone toughened epoxy resin networks of DGEBA cured with microwave radiation (MR) demonstrated e s s e n t i a l l y complete cure ("99% conversion by DSC) a f t e r the 10 minute processing period. Fracture toughness results and glass t r a n s i t i o n temperatures for the microwave and thermally processed epoxy resin networks as a function of increasing PSF incorporation are shown i n Table I .


Table I· Fracture Toughness Properties and Glass Transition Temperatures of Polysulfone Modified Epoxy Resin Networks of DGEBA wt.% NH PSF* 2

Thermal cures:

xlO (N/M ' )

Tg(°C)

0 10 20 25 30 40

0.5 0.5 0.9 1.2 1.6 1.8

238 185, 186, 185, 186, 186,

230 230 229 227 229

0 10 20 25 30

0.6 0.7 0.8 1.2 1.4

221 **, **, 179, 182,

221 214 210 217

Microwave cures:

* **

Κ

* 16,000 gm/mole Not Detected V i a DSC

These results demonstrate that fracture toughness increases continually with increasing weight percent of the PSF modifier for both thermal and MR processed materials. Furthermore, the values for the MR and thermally processed systems were e s s e n t i a l l y i d e n t i c a l , possibly indicating that fracture toughness was independent of processing conditions. DSC results demonstrated that two d i s t i n c t Tg's occur i n this phase separated system. The glass t r a n s i t i o n temperatures i n the thermally cured networks appeared at ~185 C and ~230°C., f o r the PSF and epoxy r e s i n phases, respectively, thus indicating complete phase separation. In contrast, the MR processed system exhibited depressed Tg's at ~180°C and "*220°C suggesting some degree of phase mixing. e

Thermoplastic Modified Epoxy Resin Networks of DGEBA/TGDDM: The PSF toughened epoxy resin networks of 50/50 mole % DGEBA/TGDDM, as i n the case of the 100 mole % DGEBA series, cured v i a MR also demonstrated e s s e n t i a l l y complete cure ("99% conversion by DSC) a f t e r the 50-55 minute processing cycle. In contrast, however, networks incorporating 100 mole % TGDDM cured by MR were found to contain unreacted species, as evidenced by a minor exotherm appearing i n the DSC trace. Fracture toughness values and glass t r a n s i t i o n


369


370

temperatures for the microwave and thermally processed epoxy resin networks as a function of 0,15 and 30 weight percent incorporation of the PSF modifier are shown i n Table I I . As expected, these results demonstrate that fracture toughness increases for microwave and thermal processed samples as the thermoplastic modifier was increased from 0 to 30 weight percent, unexpectedly though, the fracture toughness results were comparable to the DGEBA systems of lower crosslink d e n s i t i e s . I t i s also of interest to note that the presence of unreacted endgroups i n the 100 mole % TGDDM systems did not compromise the fracture toughness data obtained. As i n the previous series, e s s e n t i a l l y i d e n t i c a l K values for the MR and thermally processed system seems to indicate that fracture toughness was independent of the processing technique u t i l i z e d . Downloaded by CORNELL UNIV on May 18, 2017 | http://pubs.acs.org Publication Date: November 12, 1991 | doi: 10.1021/bk-1991-0475.ch022

J C

Table I I . Fracture Toughness Properties and Glass Transition Températures of Polysulfone Modified Epoxy Resin Networks of DGEBA/TGDDM wt.% NH PSF* 2

DGEBA/TGDDM(mole%)

6

3

2

K ^ x l O (N/M ^ ) Tg(°C)

Thermal

*

0 15 15 15 15 15 15 30 30 30 30 30 30

0/100 100/0 80/20 60/40 40/60 20/80 0/100 100/0 80/20 60/40 40/60 20/80 0/100

0.3 0.7 0.6 0.5 0.6 0.7 0.6 1.6 1.3 1.5 1.6 1.7 1.6

** 184, 233 **, 223 **, 225 **, 234 186, 252 185, ** 186, 227 186, 221 187, 223 187, 233 190, 250 188, **

0 15 15 30 30

0/100 50/50 0/100 50/50 0/100

0.3 0.5 1.0 1.7 1.5

179 185, 188, 187, 187,

• 14,700 gm/mole?

235 ** 232 **

** Not Detected Via DSC

DSC results again demonstrate that two d i s t i n c t Tg's occur i n this phase separated system. The glass t r a n s i t i o n temperatures i n the thermally cured networks appeared at ~187 C and, depending on the molar r a t i o of DGEBA to TGDDM, from ~221°C to 252°C f o r the PSF and epoxy resin phases, respectively. In the MR processed specimens, the glass t r a n s i t i o n temperatures of the cured networks appeared at ~187°C and ~233°C., respectively, f o r the PSF and epoxy resin phases. The MR cured materials of this series show undepressed Tg's, thereby e



22. LIPTAK ET AL.

Radiation Effects on Engineering Polymer Systems 371

indicating i n both microwave and thermal processed materials, that a well defined phase separated morphology had been developed. Fracture surface electron micrographs (SEM) of the thermoplastic toughened epoxy r e s i n networks are shown i n Figures 2-4 f o r the thermally processed systems, respectively. The thermally cured networks exhibited a s i g n i f i c a n t change i n morphology as the weight percent incorporation of PSF was varied from 10 to 40 i n the DGEBA systems and from 15 to 30 i n the DGEBA/TGDDM systems. A continuous epoxy matrix with phase separated spheres of PSF was observed at low weight percent incorporations of the thermoplastic modifier. As the incorporation of PSF increased, however, phase inversion resulted, producing a continuous matrix of PSF surrounding discrete spheres of epoxy resin. Morphological differences were observed f o r the DGEBA and DGEBA/TGDDM incorporated systems (thermally cured) at low and high compositions of the thermoplastic modifier. Whereas the phase separated PSF spheres, at low weight percent incorporation of PSF, were of uniform size (~0.6 ym) and d i s t r i b u t i o n i n the systems composed of DGEBA (Figure 2 ) , those materials that employed TGDDM as the epoxy resin consisted of PSF spheres which varied i n size ( " 0 . 5 1.9pm) and d i s t r i b u t i o n (Figure 3 ) . A d d i t i o n a l l y , the phase inverted morphology, exhibited at the higher loadings of thermoplastic modifiers, evolved into an occluded-type phase inversion (Figure 4) as the levels of TGDDM were increased. Also i t was observed that small pockets of phase inverted material developed at 15 weight percent incorporation of the thermoplastic modifier when 100 mole percent TGDDM was u t i l i z e d . The morphology of the microwave processed systems of DGEBA was less defined. No d i s t i n c t point of phase inversion was observed from the SEM micrographs as shown i n Figure 5 . Furthermore, the phase separated spheres of PSF at low incorporation were much smaller ("0.1 ym) than those observed f o r the thermally cured systems ( 0 . 6 ym) at the same l e v e l of incorporation. These observations suggested that the microwave cured systems of DGEBA were incompletely phase separated and possibly possessed some degree of phase mixing. At the higher weight percent loadings of thermoplastic modifier, microwave cures of systems incorporating TGDDM, rather than DGEBA, had better defined morphologies as shown i n Figure 6 . This possibly indicates the increase i n cure time allowed phase separation to occur more f u l l y . As i n the case of the thermally cured material, pockets of phase inverted material were present i n the 100 mole percent TGDDM system with 15 weight percent of the polysulfone modifier. These pockets appeared to be larger and more numerous i n the MR cured specimens and possibly lend an explanation to the high K values obtained f o r t h i s set of samples. J C

Thermosetting Bismaleimides (Matramid 5292 A/B)s A comparison of the dynamic mechanical spectra of both the thermal and microwave cured BMI resins (Figure 7) i l l u s t r a t e s an increase i n storage modulus a f t e r the i n i t i a l drop f o r the microwave cured specimen. The absence of t h i s peak i n the spectra f o r the thermally cured resin suggests that the microwave cured material had not reached the same l e v e l of c r o s s l i n k density as the thermally cured material. Any differences i n crosslink density would be d i f f i c u l t to measure using swelling experiments on such highly crosslinked material, however the



Figure 2 .

Fracture Surfaces of Thermally Cured Epoxy Resin (DGEBA)Networks.


Clough and Shalaby; Radiation Effects on Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1991. Fracture Surfaces of Thermally Cured Epoxy Resin (DGEBA/TGDDM) Networks with 15 Weight Percent Incorporation of Thermoplastic Modifier.



Figure 4.

Fracture Surfaces of Thermally Cured Epoxy Resin (DGEBA/TGDDM) Networks with 30 Weight Percent Incorporation of Thermoplastic Modifier.


ι ^ Ρ g

ο 52

3

W

Ο

Ο

5

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Figure 5 .

Fracture Surfaces of Microwave Cured Epoxy Resin (DGEBA) Networks.


in

I

I

s.

i

3

Î§ I

a*

r


Figure 6.

Fracture Surfaces of Microwave Cured Epoxy Resin (DGEBA/TGDDM) Networks with 15 and 30 Weight Percent Incorporation of Thermoplastic M o d i f i e r .


Ο

Ο

w

as

Ο

1

0\

22.

LIPTAK ET AL.

377 Radiation Effects on Engineering Polymer Systems

e f f e c t of the apparent difference i n crosslink density on fracture toughness was studied. Table III indicates that within experimental error the fracture toughness was not affected.

Table I I I . Fracture Toughness Properties of Thermal and Microwave Processed Matramid 5292 A/B Systems

6

K „xl0 (N/M


T

Thermal Cure

0.5

Microwave Cure

0.5

3/2

)

The interaction of microwaves with dipoles i n crosslinking polymeric materials changes as their mobility i s hindered by the growing network. Once the network has reached the point of gelation, chemical conversion proceeds through d i f f u s i o n controlled reactions. The e f f e c t on the percent gelation due to isothermal cures by both microwave and thermal processes was studied using Soxhlet extraction techniques. Figure 8 i l l u s t r a t e s the differences i n the time taken to reach a p a r t i c u l a r l e v e l of gelation f o r the thermal and microwave processes. Such rapid improvements i n reaching higher levels of gelation i n shorter cure times was f i r s t reported by Hedrick et al.(28) where epoxy resins were used to form the thermosetting network. Nonreactive Thermoplastics: Nonreactive poly(arylene ether ketone) or polyimide thermoplastics such as PEEK and Ultem were processed very e f f e c t i v e l y using microwave radiation as shown i n Figures 9 and 10, respectively. Rapid temperature equilibrium was reached i n short processing times due to the coupling of the electromagnetic radiation with the permanent dipole moments within the backbone of these systems. Rapid volumetric heating of t h i s type can be very advantageous i n future investigations on MR processing of thermoplastic composites. CONCLUSIONS Microwave radiation can be u t i l i z e d to process both reactive (thermosetting) and nonreactive (thermoplastic) polymeric materials very e f f e c t i v e l y . Accelerated MR processing of thermoplastic modified epoxy resin networks was achieved with the retention of good mechanical properties. A greater reduction i n processing time could be realized f o r the less reactive DGEBA containing systems than f o r the highly MR absorbing samples incorporating TGDDM. In contrast to those samples cured v i a conventional thermal processing, networks that underwent electromagnetic processing were shown to contain novel morphologies. Systems which consisted solely of DGEBA as the epoxy resin were found to have a poorly defined phase inverted morphology, perhaps due to incomplete phase separation. In



-150

LogE' (Pa)

-50

Temp deg C

THERMALLY CURED O N E H O U R 200C T W O H O U R S 250C


Tan δ

20 Hz 10 Hz 3 Hz 1 Hz .3 Hz

0.3 to 20 ! STRAIN =x8 1 degC/min - L O G k = 3.967 i SINGLE CRNT ! 1.69 χ 12.92 x8mm CLAMPS M/B FILE SWDMTR01 BY SPW ON 24-02-90

Ο Δ χ • +

DMTfl


Figure 7.

Dynamic Mechanical Thermal Analysis Spectra of Thermal and Microwave Cured Matramid 5292 A/B Thermosetting System,


380



ζ Ο Η Ο < CE

LU ϋ

°

r—

THERMAL CURE 200C

•

MICROWAVE CURE 200C

ο

THERMAL CURE 177C

•

MICROWAVE CURE 250C

,

—— ,

40

80

60

TIME/MIN F i g u r e 8.

Time R e q u i r e d t o Reach the G e l P o i n t f o r Thermal and Microwave Cured Matramid 5292 A / B S y s t e m s .

400

320

Ο ο

LU OC ID h< DC LU CL

Έ

240H

160

PEEK (380G) T = 143°C Tm =343°C

LU

g

CYLINDRICAL CAVITY 80 WATTS

20

10

30

TIME (min.) Figure 9.

Microwave

P r o c e s s i n g o f PEEK.


40


22.

LIPTAK ET AU


400

CYLINDRICAL CAVITY 80 WATTS

°0

10

20

30

TIME (min.) Figure 10.

Microwave Processing of Ultem.


40

381

382



c o n t r a s t , t h e systems i n c o r p o r a t i n g TGDDM were shown t o have a w e l l d e v e l o p e d phase i n v e r t e d morphology, i n t h i s c a s e , p o s s i b l y due t o the h i g h e r f u n c t i o n a l i t y o f t h e epoxy r e s i n , which would r e s u l t i n g e l p o i n t s a t lower e x t e n t s o f r e a c t i o n . A t 15 weight p e r c e n t l o a d i n g o f t h e t h e r m o p l a s t i c m o d i f i e r an u n e x p e c t e d l y h i g h v a l u e o f f r a c t u r e toughness was o b t a i n e d , a g a i n perhaps r e l a t i n g t o t h e h i g h e r f u n c t i o n a l i t y o f the TGDDM r e s i n and t h e r e s u l t a n t l a r g e r p o c k e t s o f phase i n v e r t e d m a t e r i a l b e i n g p r e s e n t i n t h e s e specimens. The e x a c t nature of t h i s o b s e r v a t i o n i s the s u b j e c t of a c o n t i n u i n g study i n our l a b o r a t o r i e s . I n i t i a l r e s u l t s on the MR c u r i n g o f t h e r m o s e t t i n g b i s m a l e i m i d e s s u g g e s t f u r t h e r o p t i m i z a t i o n o f t h e p r o c e s s i n g parameters i s needed to a c h i e v e f u l l c u r e . The Matramid 5292 A/B system i s a l s o a prime c a n d i d a t e f o r t h e r m o p l a s t i c t o u g h e n i n g v i a amino o r maleimide terminated p o l y ( a r y l e n e ether sulfones) o r p o l y ( a r y l e n e ether k e t o n e s ) and t h e i r subsequent c u r e by t h e r m a l o r e l e c t r o m a g n e t i c means.

Acknowledgments The a u t h o r s wish t o acknowledge t h e s u p p o r t of t h i s r e s e a r c h by DARPA and a d m i n i s t e r e d through t h e AFML under c o n t r a c t #F33615-85-C-5153. The r e s e a r c h samples of DER 332 from Dow Chemical Company and Matramid 5292 A/B r e s i n o b t a i n e d from C i b a - G e i g y a r e a l s o g r a t e f u l l y acknowledged. U t i l i z a t i o n o f the NSF S & TC f a c i l i t i e s a r e a l s o appreciated.

LITERATURE CITED

1.

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22.LIPTAKETAL.RadiationEffectsonEngineeringPolymerSystems 383 10. Manring, Ε. B. M.Sc. Thesis, Michigan State University, East Lansing, MI, 1988. 11. Chen, M. Ph.D. Thesis, Viginia Polytechnic Institute and State university, Blacksburg, VA, 1989. 12. LeVan, Q.; Gourdenne, A. Eur. Polym. J. 1987, 23(10), 777. 13. Beldjoudi, N.; Bouazizi, Α.; Douibi, D.; Gourdenne, A. Eur. Polym. J . 1988, 24(1), 49. 14. Beldjoudi, N.; Gourdenne, A. Eur. Polym. J. 1988, 24(1), 53. 15. Beldjoudi, N.; Gourdenne, A. Eur. Polym. J. 1988, 24(3), 265. 16. Jow, J . ; Hawley, M. C.; Finzel, M.; Asmussen, J . ; Lin, Η. H.; Manring, B. IEEE Trans. Microwave Theory Tech. 1987, MTT-35(12), 1435. 17. Singer, S. M.; Jow, J.; DeLong, J. D.; Hawley, M. C. SAMPE Quarterly 1989, 20(2), 14. 18. Jow, J . ; DeLong, J. D.; Hawley, M. C. SAMPE Quarterly 1989, 20(2), 46. 19. Silinski, B.; Kuzraycz, C.; Gourdenne, A. Eur. Polym. J . 1987, 23(4), 273. 20. Jullien, H.; Valot, H. Polymer 1985, 26, 506. 21. Teffal, M.; Gourdenne, A. Eur. Polym. J. 1983, 19(6), 543. 22. Metaxas, A. C.; Meridith, R. J. Industrial Microwave Heating; Peter Peregrinus Ltd.: London, 1983. 23. Hedrick, J. C.; Lewis, D. Α.; Ward, T.C.;McGrath, J. E. Polymer Preprints 1988, 29(1), 363. 24. Liptak, S. C.; Wilkinson, S. P.; Hedrick, J. C.; Joseph, W. D.; Ward, T. C.; McGrath, J. E. Polymer Preprints 1990, 31(2), 320. 25. Jow, J.; Hawley, M. C.; DeLong, J. D. Proceedings of the American Society for Composites; Technomic: Lancaster, PA, 1988; 4th Technical Conference, pp. 305-312. 26. Hedrick, J. L.; Yilgor, I.; Wilkes, G. L.; McGrath, J. E. Polymer Bulletin 1985, 13, 201. 27. Jurek, M. J.; McGrath, J. E. Polymer 1989, 30, 1552. 28. Hedrick, J. C.; Lewis, D. Α., Lyle, G. D.; Wu, S. D.; Ward, T. C.; McGrath, J. E. Polym. Mater.; Sci. and Eng. Preprints 1989, 60, 438. RECEIVED June

7, 1991


Electromagnetic (Microwave) Radiation Effects on Terminally Reactive

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