Reactive Oligomers - American Chemical Society

3 Arylether Sulfone Oligomers with Acetylene Termination from the Ullman Ether Reaction P.M.LINDLEY ,L.G.PICKLESIMER ,B.EVANS ,F.E.ARNOLD , and J. J. KANE 1

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Air Force Wright Aeronautical Laboratories, AFWAL/MLBP, Wright-Patterson Air Force Base, OH 45433 Department of Chemistry, Wright State University, Dayton, OH 45435

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Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: July 9, 1985 | doi: 10.1021/bk-1985-0282.ch003

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Acetylene terminated (AT) oligomeric arylether sulfones which upon curing possess higher molecular weight between crosslinks than earlier AT sulfones have been synthesized via a four step reaction sequence. The increase in chain length between reactive sites was obtained by synthesis of higher molecular weight diols using the nucleophilic aromatic substitution reaction of 4,4'-dichlorodiphenyl sulfone with various diols, including resorcinol, hydroquinone, bisphenol A, 4,4'-dihydroxybiphenyl and 4,4'-thiodiphenol. The higher molecular weight diols were reacted with excess dibromobenzene through the Ullmann ether reaction to produce bromo endcapped arylether sulfones. The final stages of the sequence involve replacement of bromine with acetylene groups to get AT oligomers which were evaluated to determine Tg's before and after cure. A substantial e f f o r t i n our laboratory has been directed toward the synthesis and characterization of acetylene-terminated (AT) matrix resins. The most s i g n i f i c a n t feature and d r i v i n g force f o r the e f f o r t i s that the thermal induced addition reaction provides a moisture i n s e n s i t i v e cured product. This technology o f f e r s a wide variety of thermoset resins f o r various high temperature applications. Backbone s t r u c t u r a l design f o r use temperature c a p a b i l i t i e s , processing c h a r a c t e r i s t i c s and mechanical performance has demonstrated the v e r s a t i l i t y of the AT type systems. A variety of aromatic and aromatic heterocyclic oligomers with terminal acetylene units have been synthesized and reported ( 1 - 3 ) i n recent years. Long term use temperatures f o r these materials are i n the range of 250-550°F with short term usage at 600-650°F depending on the s p e c i f i c molecular structure between acetylene cure s i t e s . These materials can be c l a s s i f i e d into r i g i d (high Tg) and f l e x i b l e (low Tg) systems. For higher use temperatures, the r i g i d aromatic heterocyclic backbones are employed to exhibit 0097-6156/85/0282-0031$06.00/0 © 1985 American Chemical Society

In Reactive Oligomers; Harris, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.


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REACTIVE OLIGOMERS

higher Tg's a f t e r cure. Materials which process s i m i l a r l y to the state-of-the-art epoxides require the more f l e x i b l e phenylene R type systems, where R refers to the functional group which imparts the f l e x i b i l i t y to the oligomeric backbone. The r i g i d high Tg systems are prepared by the formation of a heterocyclic low molecular weight oligomeric species followed by endcapping with an appropriate aromatic acetylene. These heterocyclic systems which have been prepared include the quinoxalines (4-6), imides (7) and N-phenylbenzimidazoles (8). The formation of the heterocycle i s generally a polymer forming polycondensation reaction i n which the molecular weight of the oligomer can be controlled by adjusting the stoichiometry of the reactants. The most convenient method of preparing the f l e x i b l e (low Tg) system i s to employ the Ullmann ether reaction of dibromobenzene and aromatic b i s - d i o l s followed by c a t a l y t i c replacement of the bromine atoms by terminal acetylene groups. A host of commercially available b i s - d i o l s have been used i n the synthesis with both meta and para dibromobenzene. Low Tg arylether oligomers have been prepared containing sulfone, s u l f i d e , carbonyl, isopropyl and perfluoroisopropyl groups i n the backbone (9). These f l e x i b l e systems do o f f e r the advantages of epoxy-type processing; however, the mechanical properties, i n p a r t i c u l a r the lack of toughness of the r e s u l t i n g resins, were drawbacks. Work with the quinoxaline series (10) had shown that the toughness of AT systems could be affected by decreasing the c r o s s l i n k density i n the polymer network. This was done by increasing the chain length of the units between terminal acetylenes. In an e f f o r t to determine whether t h i s finding with the r i g i d quinoxalines would also apply to the f l e x i b l e systems, work was undertaken to synthesize higher molecular weight monomer/oligomer systems of the Phenylene R type shown below. HC=C

C=CH

The approach used involved a four step sequence to obtain the desired product. A number of low cost d i o l s and b i s - d i o l s were studied, including bisphenol A, r e s o r c i n o l and hydroquinone. An Ullmann ether condensation was used i n the reaction sequence i n an e f f o r t to obtain very f l e x i b l e systems which would have low i n i t i a l Tg's f o r ease of processing. The objectives of t h i s work were to synthesize a series of arylether sulfone oligomers with an increased chain length between reactive s i t e s by the proposed synthetic route. In addition, i t was to be determined i f the products obtained by t h i s route would have i n i t i a l glass t r a n s i t i o n temperatures near or below room temperature while having cured Tg's i n the 300-350°F range of epoxides·


3.

L I N D L E Y ET A L .

Arylether Sulfone Oligomers

Results and Discussion The reaction sequence used to synthesize these f l e x i b l e systems involved four steps which are outlined i n Figure 1. The f i r s t of these was an aromatic n u c l e o p h i l i c substitution, a polymer forming reaction i n which 4,4 -dichlorodiphenyl sulfone reacts with various d i o l s . The second step, an Ullmann ether reaction, gives bromine terminated products i n which the bromines can be replaced by ethynyl end groups i n the f i n a l stages. Both the s u b s t i t u t i o n and Ullmann reactions provide sources of oligomers, making the f i n a l product a mixture of monomeric and oligomeric species. While t h i s was desirable f o r the o v e r a l l objective of the work, increasing chain length between c r o s s l i n k s i t e s , the presence of oligomers did complicate characterization of the products obtained from the various reactions. For t h i s reason, a reaction scheme which would give a pure monomeric product was formulated and used for a l l of the d i o l systems to do preliminary evaluations.


,

Monomer Systems. The f i r s t step i n the synthesis of the model monomeric systems required formation of a mono(bromophenoxy)phenol (I) system by the Ullmann reaction outlined i n Figure 2. Here, meta or para dibromobenzene was reacted with the appropriate d i o l under either of two sets of Ullmann conditions. The f i r s t method involved using pyridine, potassium carbonate and cuprous iodide, while the second entailed using 2,4,6-collidine and cuprous oxide. Both of these syntheses w i l l give a small amount of dibrominated material as well as the desired product since two hydroxy linkages are present i n the d i o l , but by c o n t r o l l i n g the stoichiometry of the reaction the predominant product can be directed toward the mono-bromo material. This Ullmann reaction was done without regard to y i e l d or to optimize conditions, but rather to get enough of the mono(bromophenoxy)phenol product to continue on i n the sequence. Through the use of one of the methods outlined above, a l l f i v e of the d i o l s shown i n Figure 2 were reacted with an isomer of dibromobenzene. The products obtained from t h i s reaction were carried through the sequence shown i n Figure 3. The mono(bromophenoxy)phenol was reacted with 4,4'-dichlorodiphenyl sulfone i n a n u c l e o p h i l i c aromatic substitution using l-methyl-2-pyrrolidinone (NMP) as a solvent and potassium carbonate as base. The reaction was run using a 2:1 r a t i o of bromo compound to sulfone, and since the substitution i s a polymer forming reaction under normal circumstances, good conversion to the dibromo product was observed with no oligomer formation. The second and t h i r d steps i n the monomer synthesis involve the replacement of bromine with an acetylene protected by an acetone adduct, followed by cleavage of the adduct. These steps w i l l be discussed i n more depth l a t e r as they are the same f o r systems containing only monomer or a monomer/oligomer mixture. Evaluation of Monomers. Following the completion of t h i s sequence of reactions, the monomeric models (III) f o r a l l of the d i o l systems were formed. The products were then evaluated f o r i n i t i a l and f i n a l Tg's and the results compiled i n Figure 4.


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REACTIVE OLIGOMERS

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Synthesis of mono(bromophenoxy)phenols.



LINDLEY ET AL.


CM, Hfl-C-C =CH ι CH, CH. MO- C- C : C

CH, I

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Figure 3 .

Synthesis of model monomer systems.


REACTIVE OLIGOMERS

36

AR

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Figure 4.

(KPC/MIN)

Evaluation of monomeric AT arylether sulfones.

The i n i t i a l Tg's found i n column three of the table were determined by d i f f e r e n t i a l scanning calorimetry at a scan rate of 10°C/min. F i n a l Tg's were determined by TMA on samples which had been cured i n a i r at 550°F f o r 8 h. No r e s i d u a l exotherm was found i n any of the samples when scanned by DSC following t h i s cure cycle. The second column i n the table indicates whether the dibromobenzene used was the meta or the para isomer. In order to provide more f l e x i b i l i t y f o r the r i g i d d i o l s , 4,4 -dihydroxybiphenyl and hydroquinone, the meta isomer of dibromobenzene was used i n preference to para. I t was postulated that the meta isomer would increase the free volume of the chain 1


3.

LINDLEY ET AL.


thus lowering the i n i t i a l Tg. The hydroquinone system was synthesized with both para and meta dibromobenzene isomers to provide a comparison between the e f f e c t s of the v a r i a t i o n i n structure. The v a r i a t i o n i n the i n i t i a l Tg s show the e f f e c t on processability of the structures of the d i o l and the dibromobenzene. Two of the systems, those based on thiodiphenol and dihydroxybiphenyl, gave c r y s t a l l i n e products which could not be made amorphous upon heat treatment. The e f f e c t on chain f l e x i b i l i t y of dibromobenzene structure could be seen with the two hydroquinone systems. In t h i s case, the meta isomer gave an i n i t i a l Tg of 12°C while the more r i g i d para system had a Tg of 59°C. Variation of d i o l structure shows a p a r a l l e l effect as shown with the resorcinol/j)-dibromobenzene system. This material has a softening temperature of 20°C. A similar trend was postulated f o r f i n a l Tg's of the cured materials. This result was observed i n some cases, as with the hydroquinone systems where the more f l e x i b l e meta product gave a s i g n i f i c a n t l y lower f i n a l Tg. The highest cured Tg's were seen i n the bisphenol A, dihydroxybiphenyl and r e s o r c i n o l systems. The lowest f i n a l Tg was observed with the thiodiphenol product, at 174°C, less than 350°F. The fact that the incorporation of thiodiphenol into the backbone produced both undesired c r y s t a l l i n i t y and a low f i n a l Tg led to a decision not to synthesize the monomer/oligomer mixture for t h i s system.


f

Monomer/Oligomer Synthesis. The f i r s t two steps i n the four step reaction sequence of Figure 1 are capable of producing both monomer and oligomer. The f i r s t step, aromatic nucleophilic substitution, i s a polymer forming reaction under the correct stoichiometric conditions. In order to favor the formation of monomer with a small amount of oligomer, the substitution was carried out at a 4:1 r a t i o of d i o l to dichlorodiphenyl sulfone. This l e d to a predominantly monomeric product (IV) with only the requirement that the excess d i o l be removed from the product to eliminate the potential presence of low molecular weight species i n l a t e r reactions. It should be noted that one of these d i o l s , the hydroquinone, did not provide any oligomer i n the f i r s t step. This was due to the formation of the quinone structure which made i t impossible to use hydroquinone d i r e c t l y i n the substitution reaction. An alternate method was used to overcome t h i s problem which involved the use of 4-methoxyphenol to obtain the sulfone product, followed by cleavage of the methyl ether to the d i o l (VIII) with boron tribromide. This set of reactions i s outlined i n Figure 5. A l l of the sulfone d i o l s were able to form oligomers i n the second step of the reaction sequence, the Ullmann ether synthesis. As with the synthesis of the mono(bromophenoxy)phenol products, two methods were used to form the dibromo materials. Method A used pyridine, potassium carbonate and cuprous iodide, while Method Β employed c o l l i d i n e and cuprous oxide with the dibromobenzene and higher molecular weight d i o l (IV). The major difference between the syntheses of the mono(bromophenoxy)phenols described e a r l i e r and these l i e s i n the stoichiometry of the reactions. In order to


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REACTIVE OLIGOMERS


obtain bromo endcapped product and to allow formation of predominantly monomeric species, the reactions were run at a 10:1 r a t i o of dibromobenzene to d i o l . This r a t i o has been found (11) to form monomer as the major product, while also affording a reasonable amount of higher molecular weight products (V). The monomer/oligomer mixtures were used i n the t h i r d step of the reaction sequence, the replacement of bromine with 2-methyl-3-butyn-2-ol by use of the bis(triphenylphosphine) palladium chloride catalyst system. This reaction used a triethylamine/pyridine solvent system to replace the bromines on the ether sulfone with ethynyl groups protected by acetone adducts. The acetone protecting groups were then removed i n a toluene/methanol/potassium hydroxide solvent system.

Evaluation of Oligomeric Systems. Completion of the cleavage reactions gave the f i v e acetylene terminated systems (VII) evaluated i n Figure 6. The t h i r d column of the table contains monomer/oligomer r a t i o s f o r the various systems. These r a t i o s were determined by a column chromatography separation of products, and were based on a weight percent r a t i o of the amount of monomer to oligomer. The v a r i a t i o n i n these r a t i o s i n the f i v e systems i s extreme, ranging from 60% monomer with dihydroxybiphenyl to 95% monomer with hydroquinone/p-dibromobenzene. Some of the v a r i a t i o n i s attributable to the use of 4-methoxyphenol i n the aromatic nucleophilic substitution reaction of the hydroquinone products which precludes the formation of oligomers i n t h i s step. The remaining d i o l s are capable of forming oligomers i n both the f i r s t and second steps of the synthesis. Though the r a t i o s of reactants used i n these steps are the same f o r each system, a v a r i a t i o n of 60-85% monomer can s t i l l be observed from dihydroxybiphenyl to r e s o r c i u o l . The structure of the d i o l used obviously influences the formation of monomer and oligomer i n the f i r s t steps of the reaction sequence. The e f f e c t of either meta or para dibromobenzene isomers i s seen with the two hydroquinone products, where the meta isomer forms more oligomer than the para. The difference between the two dibromobenzene isomers which was noted i n the monomeric systems with regards to i n i t i a l Tg also holds true f o r the oligomers. The meta system s t i l l has a lower i n i t i a l Tg with the r e s o r c i n o l system as an intermediate between the two hydroquinone products. The other i n i t i a l glass transitions are higher than the hydroquinone systems. The dihydroxybiphenyl material exhibits a melting point at 135°C, and though lower than the pure monomer i t i s s t i l l high f o r the desired room temperature processability. Cured Tg's of a l l of the systems studied were above 350°F. Isothermal aging of the samples at was done at 600°F i n a i r . A weight loss of 20-30% was observed f o r a l l of the systems over 200 h. There i s l i t t l e difference between the various products since the c o n t r o l l i n g factor of the thermoxidative s t a b i l i t y , the sulfone linkage, i s common to each of them.


LINDLEY ET AL.

Arylether Suif one Oligomers

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Figure 6 .

Evaluation of oligomeric AT arylether suifones.


REACTIVE

40

OLIGOMERS


Conclusions The synthesis of phenylene R type systems v i a the proposed route afforded two materials which had both f i n a l Tg's above the 350°F l i m i t and i n i t i a l Tg's which were at or below room temperature. The two systems which offered the most desirable properties were those based on resorcinol/£-dibromobenzene and hydroquinone/m-dibromobenzene. Of the two, the hydroquinone system offered a lower i n i t i a l softening temperature while also providing a cured Tg above 200°C. For this reason the product from hydroquinone and m-dibromobenzene was chosen as the candidate system f o r future work. A scale-up of the reaction sequence to obtain enough of the material f o r mechanical testing i s i n progress. Following completion of the synthetic work, evaluation of the mechanical properties of the chosen system w i l l be carried out to determine whether increasing chain length between reactive s i t e s w i l l indeed bring an improvement i n toughness of acetylene terminated Phenylene R systems. Experimental Mono(bromophenoxy)phenol ( I ) . The mono(bromophenoxy)phenols required f o r the monomeric models were synthesized by two methods. Method A: A mixture of pyridine (90mL), d i o l (60 mmol), dibromobenzene (56.4g, 240 mmol), anhydrous potassium carbonate (33.3g, 250 mmol) and cuprous iodide (1.62g, 9 mmol) was heated at reflux under nitrogen f o r 20h. After cooling to room temperature, the reaction mixture was a c i d i f i e d with IN HC1 and the product extracted with chloroform. The chloroform was evaporated and the residue extracted with 10% aq. NaOH. The aqueous phase was a c i d i f i e d , extracted with chloroform, and reduced i n volume to an o i l that was s t i r r e d with 20% aq NaOH to afford the sodium s a l t of the product. The s a l t was i s o l a t e d and dried to give a white s o l i d . The s o l i d was a c i d i f i e d to pH 1 i n water, and the freed mono(bromophenoxy)phenol was washed with water and dried. C-H analysis f o r products was s a t i s f a c t o r y . Method B: A mixture of d i o l (50 mmol), dibromobenzene (47.Og, 200 mmol), cuprous oxide (1.97g, 15 mmol) and 2,4,6-collidine (lOOmL) was heated to reflux under nitrogen f o r 20h. The product was i s o l a t e d as i n Method A. 1

1,1 -Sulfonylbis[4-[mono(bromophenoxy)phenoxy]benzene] Monomer (11). A mixture of dry l-methyl-2-pyrrolidinone (45mL), benzene (25mL), I (52.8 mmol), 4,4 -dichlorodiphenyl sulfone (7.58g, 26.4 mmol) and anhydrous potassium carbonate (3.83g, 27.7 mmol) was purged with nitrogen f o r 15 minutes. The mixture was heated to reflux and the benzene azeotrope collected between 80°C and 150°C. When most of the benzene had been removed, the reaction was heated at 165°C f o r 7h. After cooling to room temperature, the mixture was poured into 350mL 10% s u l f u r i c acid and was extracted with chloroform. The organic phase was washed f i r s t with 25% s u l f u r i c acid, then with d i s t i l l e d water. A f t e r drying over MgSO^, the chloroform solution was evaporated to dryness affording a 75-85% y i e l d of the monomeric sulfone. f



3. L I N D L E Y E T A L .


1,1*-Suifonylbis[4-(phenolphenoxy)benzene] Monomer and oligomer (IV). A mixture of dry l-methyl-2-pyrrolidinone (40mL), benzene (20mL), d i o l (95 mmol), 4,4»-dichlorodiphenyl sulfone (6.79g, 23.7 mmol) and anhydrous potassium carbonate (3.43 g, 24.8 mmol) was purged with nitrogen f o r 15 minutes. The mixture was heated to reflux and the benzene azeotrope collected u n t i l the reaction temperature reached 190°C. When most of the benzene was removed, the reaction was heated at 190°C f o r 7h. After cooling to room temperature, the reaction was poured into 400mL 10% HC1. A dark, gummy s o l i d separated and the aqueous solution was decanted from the gum. This s o l i d was dissolved i n lOOmL g l a c i a l acetic acid, and the acid solution was precipitated into 1200mL i c e water to give a l i g h t s o l i d . The precipitate was dissolved i n d i e t h y l ether and f i l t e r e d over a bed of s i l i c a gel to remove a dark impurity. The ether solution was dried giving a l i g h t amorphous s o l i d i n 75-85% y i e l d . Brominated Monomer/Oligomer Mixtures from IV (V). The brominated sulfone monomer/oligomer mixtures were prepared by two d i f f e r e n t methods. Method A: A mixture of pyridine (70mL), IV (11.5 mmol), dibromobenzene (26.96g, 115 mmol), anhydrous potassium carbonate (7.94g, 57.5 mmol) and cuprous iodide (0.13g, 0.7 mmol) was heated at reflux under nitrogen f o r 24h. After cooling to room temperature, the reaction mixture was a c i d i f i e d with IN HC1 and the aqueous solution extracted with ether. The organic phase was reduced i n volume to a brown gum which was washed several times with hexane and then dried to give a 75-95% y i e l d of the dibromo product. Method B: After combining 2,4,6-collidine (9mL), IV (10.25 mmol), dibromobenzene (24.2g, 102.5 mmol) and cuprous oxide (2.95g, 20.51 mmol), the reaction mixture was heated at r e f l u x under nitrogen f o r 24h. When the reaction had cooled to approx. 80°C, the mixture was f i l t e r e d , then diluted with chloroform. The organic phase was warmed to 60°C with lOOmL cone. HC1, washed with water and then was f i l t e r e d through a short bed of s i l i c a g e l . The product, a l i g h t amorphous s o l i d , was obtained i n 75-90% y i e l d . Acetone Protected Acetylene Monomer/Oligomer From V (VI). A solution of V (5.5 mmol), 2-methyl-3-butyn-2-ol (2.76g, 32.9mmol), pyridine (15mL), triethylamine (30mL), bis(triphenylphosphine) palladium chloride (0.10g), cuprous iodide (0.10g) and triphenylphosphine (0.20g) was degassed with nitrogen f o r 15 minutes. The reaction was heated at reflux f o r 24h, cooled and f i l t e r e d , then a c i d i f i e d with IN HC1. The product was extracted with toluene. The organic phase was washed with IN HC1 and then was heated f o r i h at 60°C with ethylene diamine. After washing well with water, the toluene solution was dried over MgSO^ and chromatographed on s i l i c a g e l using chloroform as eluent. The chloroform was removed to give a l i g h t , amorphous s o l i d i n 70-85% yield. Ethynyl Terminated Monomer/Oligomer Mixtures from VI (VII). A mixture of the bis-butynol adduct, VI (3.9 mmol), toluene (40mL) and 10% methanolic KOH (40mL) was heated to reflux under nitrogen. The methanol and toluene were removed by d i s t i l l a t i o n , adding more toluene as needed to maintain the reaction volume at 40mL. After


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REACTIVE OLIGOMERS


4h, the reaction was cooled to room temperature and filtered over a bed of packed Celite. The toluene solution was washed with water, dried over MgSO,, and reduced in volume to give the ethynyl product (VII) a light colored solid, in 80-95% yield. Monomer/oligomer ratios were determined by column chromatography as weight % monomer: weight % oligomer. 4,4'-[Sulfonylbis(4,1-phenyleneoxy)]bis[phenol] (VIII). A dry flask containing 1,1*-Sulfonylbis[4-(4-methoxyphenoxy)benzene] (10.Og, 22 mmol) was cooled in a dry ice - acetone bath for 15 minutes. After cooling, a 1.0M solution of Boron tribromide in methylene chloride (16.5g, 66 mmol) was added and the reaction was allowed to reach room temperature. After stirring for 18h, the solution was slowly added to 300mL water and stirred for several hours until a light solid could be filtered. The solid was washed with water and dried to give the product in 95% yield. Characterization. Differential scanning calorimetry and thermal mechanical analysis data were obtained on a DuFont 990 thermal analyzer coupled with a DuPont DSC or TMA c e l l . Isothermal aging studies were carried out with an automatic multisample apparatus. Literature Cited 1.

Hedberg, F. L.; Kovar, R. F . ; Arnold, F. E. In "Contemporary Topics in Polymer Science"; Pearce, Ε. M., Ed.; Plenum Publishing: New York, 1977; Vol. 2, p. 235. 2. Hergenrother, P. M. Macromol. Sci. Rev. Macromol. Chem. 1980, C19, 1. 3. Bilow, N. In "Resins for Aerospace"; ACS SYMPOSIUM SERIES No. 132, American Chemical Society: Washington, D.C., 1982; p.139. 4. Kovar, R. F . ; Ehlers, G. F . ; Arnold, F. E. J. Polym. Sci. Polymer Chem. Ed. 1977; 15, 1081. 5. Hedberg, F. L.; Arnold, F. E. J. Appld. Polym. Sci. 1979; 24, 763. 6. Hergenrother, P. M. In "Chemistry and Properties of Crosslinked Polymers"; Zabana, S. S., Ed.; Academic: New York, 1977; p. 139. 7. Landis, A. L.; Bilow, N.; Boschan, R. H . ; Lawrence, R. E.; Aponyi, T. J. Polym Prep. 1974, 15, 533. 8. Lau, K.S.Y.; Kellaghan, W. J.; Boschan, R. H . ; Bilow, N. J. Polym. Sci. Polym. Chem. Ed. 1983, 21, 3009. 9. Reinhardt, Β. Α.; Loughran, G. Α.; Soloski, E. J.; Arnold, F. E. In "New Monomers and Polymers"; Culbertson, Β. M., Ed.; Plenum Publishing: New York, 1983; p.29. 10. Helminiak, T. E.; Jones, W. D. Org. Coat. and Plast. Prepr. 1983, 48, 221. 11. Harrison, J. T . ; Sabourin, E. T . ; Selwitz, C. M.; Feld, W. Α.; Unroe, M. R.; Hedberg, F. L. Polym. Prepr. 1982, 23, 189. RECEIVED January 17, 1985


Reactive Oligomers - American Chemical Society

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