Organometallic Polymers Charles E. Carraher, Jr. Wright State University, Dayton, OH 45435 lnterrelationshlp with Traditional Chemistry and Polymer Chemistry Just as the field of oreanometallic chemistrv emerged from both inorganic and organic chemistry, the area of organometallic . nolvmer chemistrv develoned through . - a range - of subdisciplines including organic, polymer, physical, inorganic chemistry and chemical engineering. I t is important to remember that the same factors that operate in regard to smaller molecules are in operation with macromolecules (including organometallic polymers) and polymerization reactions including electronic, steric, mechanistic, kinetic and thermodynamic factors. Further, since small differences are accentuated in nature because these parameters are often exponentially related, reactions resulting in the formation of polymers and polymeric interactions will enhance these small differences since theexponential difierenocs are now typic ally^ linerally enhanced as each step (or unit interaction) in the formation of macromolecules will be dependent on i i m i l ~ parameters. r Thus reactions leading to the synthesis of macromolecules and interactions involving the resulting macromolecule can be used in portraying to ytudents basic chemical ~ r i n c i ~ lto e sa hetter extent than illustrations now utilized to- illustrate these principles emnloving smaller molecules. one-frequent misconception concerns the type of honding that occurs between the metal and organic unit. With the exception of metals present in metallocene "sandwich" compounds, most of the metal-to-nonmetal honding is of the
-
-
same eeneral nature as that oresent in classical oreanic compounds. The percentage contribution of the metal-nonmetal hond due to covalent contrihutions is twicallv ?. - hieh " but within that found in some organic acid, alcohol, thio and nitro moieties (for instance usual limits are about 6% ionic honding character for the B-C hond to 55%for the S n - 0 hond). Thus the same general spatial, geometric laws which apply to honding in organic compounds apply to honding in organometallic monomers and polymers. Introduction The potential breadth of the field of organometallic polymers can he seen in relation to more traditional nolvmer chemistry by comparing the numher and variety of eiedents tvnicallv found in classic oolvmers (C.H.N.S.P.Cl.Br.0.F) . . . . . . G t h the numher and varie6 oireadily availahle metals (o;ei 44 metals). Further, many of the metals can he present in several oxidation states. The potential importance, academically and industrially, of organometallic polymers can he seen by considering the organopolysiloxanes.They are characterized by combinations of chemical, mechanical, and electrical properties not common to any other commercially availahle class of polymers. They have relatively high thermal and oxidative stability, low power loss, unique rheological properties, and high dielectric strength, and are relatively inert to most ionic reagents. A wide range of silicone polymers has been known for several decades. While research continues with these siloxanes, this paper will cover current, emerging frontiers, and as such
Volume 58
Number 11 November 1981
921
Table I. Vlnyllc Organometalllc Monomers H,C-CH
I
where X
-
X
With few exceptions, the same parameters which affect chain growth, branching, etc. for nonmetal containing polymerizations. affect chain erowth where metals are nresent. Table 1contains represen&ive structures for X and Y' already incor~oratedinto nolvmers. Manv of these have been svnthesized by the group working wit; Pittman, a leading figure in this area. The number of copolymers synthesized outweigh the number of homonolvmers svnthesized due to a hesitancv of many metal-coniain-ing monomers t o homopolymerize. The structures depicted in Table 1 are electron.rich svstems which undergo either cationic or radical polymerization;hut typically not anionic polymerization (1-3). Cationic polymerization may be initiated using Lewis acids such as BF30Et2, EtzAICl/M(acac)z (where M = Ni, Cu, VO, etc.) and HzS04. While a number of free radical initiators have been utilized, some problems which are initiator connected may be encountered. For instance, peroxide initiators can cause oxidation of the metal atom and extensive decomposition. Thus consideration must be given in the choice of initiator employed. Branching and/or crosslinking is more common with the VOP's than with classical polymers. Thus attack of the carbonium ion on a monomer such as vinyl ferrocene leads to branching and crosslinking (4). Internal hydride transfer would also lead to branching (5). R+
the topic of siloxane polymers remains outside the stated scope of the paper. Even so, siloxane polymers present a major area of industrial chemistry, an area which is ripe for presentation to the greater academic community, for the benefit of students. The use of siloxane polymers as adhesives, caulking compounds, hydrolyic oils, surgical materials, etc. gives students clear points to identify that the chemistry they are learning is "real." A number of nonmetal-containing polymers are often included as organometallic polymers since they exhibit metdlike behavior. narticularlv with reeard to electrical conductivity. 'l'hese polymers include the'sulfur nitrides, polyphos~hazenes,boron nitrides and ~olsphosnhinates. These . r~olv. .. . . k e r s will not be covered here. The topic of organometallic polymers can be divided by many means. Here the topic will be divided according to the type of reaction utilized to incorporate the metal-containing moiety into the polymer chain; i.e., addition, condensation and coordination. Emphasis is given to unifying factors, hoth interconnecting the given subject area and emphasizing that the fabric of chemistry which applies to smaller molecules also applies to this new, emerging area of organometallic polymer chemistry. Addition Polymers Vinyl-Organometallic Polymers Here we will consider vinyl-organometallic polymers, W O , as polymers resulting through addition of vinyl units where the metal-containing moiety is contained in either or hoth the X and Y. The resulting polymer is called a homogeneous polymer (or homopolymer) if X = Y. When X # Y the polymer is called a copolymer.
922
Journal of Chemical Education
+ H,C=CH
-
Fa
I R-cH-cH+FE%R-cH,-c~+
+
R-CH,-C-CHI-CH,
1
Fe
1
Fe
5
where Fe =
Branching andlor CroJslinlring 4
@ @ J ,
Typically, the vinyl-metal monomers are considered as "chain stiffening" units. Flexibility for copolymen is increased through the use of "flexible" comonomers and/or limiting the amount of metal-containing moiety present in a copolymer. More flexible polymers may also be obtained if the organometallic group is moved away from the vinyl moiety. The flexibility can also be enhanced through the addition of plasticizers. Typically there is a direct relationship between polymer flexibility and such thermal properties as the onset of whole chain mobility (melting point, T,) and segmental chain mobility (glass transition, Tg) and softening range, and material these in turn are important in determing.. if a given . may be used for certain applications. Studiesof the free radical copolymerization of a numher of metal-containing vinyl monomers with organic monomers such as methyl methacrylate, acrylonitrile and styrene have been conducted. Reactivity ratios r , and r z have been calculated and Q and e values obtained for the monomers (see reference ( I ) for a further discussion of this general approach). Q is a measure of the resonance stabilization of the free radical formed from the monomer and e is a measure of the electron density in the vinyl group. A negative e value indicates the vinyl group is electron rich relative to ethylene, and a positive e value indicates the vinyl group is electron poor. Typically metal-containing monomers show a lower reactivitv com~ared to more cornmu& uaed organic monomers because of g k t e r steric hindrance and resonance sulhilization of the free radical derived from the metal-containing monomer. Reactivity ratios for homopolymerizations, r, utilizin~oreanometallic vinyl monomers are particularly low. Some of th;?metal-containing monomers exhibit the highest e values ever studied. The type of copolymers formed can be readily determined
from the values of the reactivity ratios. For instance, the typically low r values found for styrene, compared to high r values for metal-containing monomers, indicate the OM monomer will enter the growing polymer chain as single units followed by short blocks of styrene units. Somewhat alternatine-cooolvmers are formed onlv at hiah . . involvine stvrene concentrations of the metal-containing monomer. Low values for both r , and rv are twicallv ". " found for the cooolvmerization . . of metal-containing monomers with acrylonitrile indicating a tendency toward alternation. Classical polymers have been extensively emplnyed in the electrical industry as coatings of wires due to their low electrical conductivity, high insulator properties (polyethylene has a hulk resistivity, p, of about 10"' ohm cm). Organometallic polymers provide alternate electrical uses where the polymeric nature of the metal-containing polymer may be envisioned to increase the electrical conductivity of the polymer. Results involving organometallic vinyl polymers have been mixed with reeard to achievine electrical condurting materials. l'ulyvin;.~ferrocene (6) i; an insulator ( p = 10'' ohm cm, which can he oxidized usine mild oxidirinnagents such na beneuquinone, dirhlondicyanohenzoquinone and A "r - to -vield a oolvmer (7, whwh includes ferrocene and ferricinium units where, it is postulated, electrons can "hop" from one ferrocenyl group to the next. The resistivity decreases to 10Sohm cm for products containing 20 to 70%oxidation ( 4 ) . Ferrocene appears to be unique among the meti~lloreoesin that it is r&&sit,ly and readily oxidiled ( 5 ) . The eifect of achieving a completely conjugated backbone to perm11 rlectrical ronducti\.ity had been a major reason for making polyethynylferrorene. Present results show it to be an insularur in = I0I4 ohm cm). with essentiallv the same bulk conductivityas polyvinyl feiiocene (8, I). ~ h u extended s conjugation was not effective in enhancing the conductivity of this polymer. ~
~~~~
~
~~
~~
~
tCH,-CH-CH,-CHf Fr
% tCH!-CH-ClL-CHI Fe
Fe
Fe
+
Another approach related to improving the electrical, and other selected properties is the reduction of metal-containing polymers permitting a chemical method of forming metals, plastics, composites, etc. with selected metal oxides present in a homogenous fashion in very small particle size. Thus homopolymers of n6-(2-phenylethyl acrylate) tricarbonylchromium (9) were cast as yellow films on glass. Thermal decomposition of the films at 150% in the dark resulted in mixed chromium oxides imbedded in the crosslinked film (6).
A numher of vinyl polymers containing tin have been synthesized by Subramanian, Yeager, Castelli and others (such as 7-9). Many of these polymers contain trialkyltin esters. Polvmers containine the trialkvltin moieties are formed bv radical initiated copolymerizations with a variety of comonomers including methyl acrylate and methyl methacrylate. Through varying the comonomer feed ratios and nature of the comonomers i t is possible to generate a wide variety of polymers including polymers containing (a) blocks of tin units separated by random copolymers, ( b ) blocks of nontin-containing comonomers separated by random copolymers, and (c) purely random copolymers. The copolymers generally contain crosslinking agents introduced during andlor subsequent to the initial copolymerization reaction. Crosslinking agents employed include triamines and epoxide-containing vinyl monomers. These tin-containine-. oolvmers have been extensivelv tested and are now used in antifouling paints to prevent thegrowth of fungi and barnacles on ship bottoms and shore installations. The antifouling nature results from the hydrolysis and subsequent leaching out of minute amounts of the trialkylstannanols, which are toxic to marine organisms, a t a controlled rate so that "kill" occurs a t the boat hull surface. Further away, the stannane is diluted so that other marine life is unaffected. The rate of stannane hydrolysis can be effectively controlled through varying the nature and amount of either comonomer. amount of crosslinkinn, and application of the paint. s o m i paints which contain these stknane-polymers are markedly superior to paints containing trialkyltin oxides, used almost exclu&ely, hoth with rewhich were gard to longevity of antifouling activity, less harm to other marine life, and better adhesive properties of the paint. Widespread commercial application of these materials is likely within the next five vears. The synthesis of the organnrnetallic monomers, polymers and copolymers is typically not straightforward and often demands elegant synthetic steps which vary from compound to comoound. These svntheses reouire hoth classical and novel approaches befitting a challenge to any good synthetic chemist. Thus, vinylcyclopentadienyltricarbonylmanganese (12) is prepared from cyclopentadienylmanganesetricarbonyl (11) by acylation, hydride reduction of the carbonyl function and dehydration (10.11). ?
0
I
ca
O/H
I
Stvrenetricarbonvlchromium (14) . . is orepared . . from henzaldeiyde diethylacetal (13) which is complexed and then hvdrolvzed to its aldehvde. The aldehvde is convened to the t c - C f
I
tc-Cf
I
I
/C=O 0
\
H-C-H
I H-C-H
I 0
a
\
+ C T ~ O ,+ 03
H-C-H H-C-H
I
Volume 58 Number 11
November 1981
923
Metallocenemethyleneand MetallocenylenePolymers
Metallocenemethylene polymers have been prepared by a number of investigators (2). Synthesis typically proceeds in two steps; generation of an alpha-metallocenyl carhonium ion and subsequent polymerization in the presence of an acidic catalyst. Common precursors include the metallocene and an aldehyde, alcohol, ketone or tertiary amine. Acid catalysts such as BF3,ZnCln and Hi304 have been employed. The high molecular weight soluble polymers have been formed when the salt of the carhonium ion is isolated in pure form and allowed to polymerize at elevated temperatures (13). Linkage in the polymer is a mixture of 1 2 , 1,3 and 1,1'. The most commonly employed metallocenes are those where M = Fe, Ru and Ni. R
7
M
+ R-C-H
-
d - o \ H M
H
d
o r
Mixed valence polymers have been divided into three categories with Class I polymers having essentially no interR action between valence centers heing typically nonconductors or low semiconductors; Class 11, weak interaction between valence centers as indicated bv valencv transfer bands in the + visiblc-near infrared spertral region wlrh Class I1 compounds Hl heing semicondurturs and Class I11 compounds where srrone interactions (more correctly classified-as average valenci materials) exist between themetal sites making such materials srmi~nducturstu condurtors. For M = Fe, roipoundi23 and 21 are insulators ip = 1O1*ohmcm). When oxidized with iodine to the extent of 30 to 7OVo23 forms a mixed valence.SMIP .- . product of Class II,25, which is a semiconductor @ = 107 ohm cm, 15). Polymers of form 28, possibly Class 111polymers, have not been prepared.
d ?f
Low molecular weight polymers (2000 to 20,000 amu for soluble fractions) have been mixed with crosslinking agents such as 1,l'-bishydroxymethylferroceneand an acid catalyst, laminated with fiberglass or carbon fibers and cured a t 400 psi and 200 to 300°C (14). The resulting laminates have a moduli of 2 to 5 X lo6 psi, tensile strengths to 3 X lo4psi, and they char rather than melt or soften when exposed to high temperatures. Rosenherg and coworkers synthesized a number of these metallocene polymers for use as ablative materials for heat shields of space capsules. Ruthenocene derivatives were studied as radiation shields for communications satellites. Before these materials were perfected, less expensive ceramic materials were found which performed satisfactorily. Metallocenylene polymers can he synthesized through several routes including demercurating, 18, in the presence of silver; coupling, 19 or 20, in the presence of CoC12; using the Ullman reaction with 21 or 22; coupling of 19 with slight excess
Ferrocenyl-Silyl and Ferrocenyl-Siloxanyl Polymers and Other Polymers A wide variety of ferrocenyl-silyl (29) and ferrocenyl-siloxany1 (30) polymers have been prepared. Such polymers have been shown to offer reasonable thermal stabilities, good resistance to UV and gamma radiation, and flexibility over a wide temperature range (often -50 to 150°C). Low molecular products are typically oils with possible application as high temperature lubricating oils or hydraulic fluids (16). High molecular products can be cast to give tough flexible films which can be drawn from melts to form fibers (17). (Weight average molecular weights range from about lo4 to 106.) The ferrocenyl-silyl and ferrocenyl-siloxanyl polymers have been p r e m e d through several routes. One route is as follows. ~ r e c & r silylamin& are made by attaching the silanyl or siloxanvl mour, to cvclo~entadiene.followed bv reaction with ferrous-chlorideto formatheferrocenyl group. ~e silylamines are then condensed with sisilanols. lv +R+ + , , ~ - i sF~ - ~ -@
29
of 21 and the direct polymerization of the metallocene in the presence of a stoichiometric amount of di-t-butyl peroxide. Metallocenylene polymers, the metallocene analogs of polyphenylene, can exist as 1,l' (23); 1,2 (24); 1,3 (25) isomers and as 1,l'and 3,3' (26) bridged products. Considerable interest has been expressed in these products because of their high rigidity and thermal stability and because partial oxidation could produce conjugated mixed-valence materials which may act as semiconductors or conductors. 924
Journal of Chemical Education
I I R'
Ferrocene-siloxanyls are also prepared from ferrocene itself with subsequent reaction with silicon containing reactants. Such ferrocene-siloxanyl hydrides have been used as precursors in the synthesis of a number of vinyl monomers which can then he copolymerized or alternatively used in the synthesis of a number of diols, diamines, diesters and diepoxides which can also be used to form polymers (18).
b) coordination of a metal ion by a polymer containing chelating groups; and Group IVA containing polymers have been synthesized were usine" hvdride addition reactions (19-21 ).The oolvmers . . , liquids to elastomers and resins with molecular weigh& to 10:'. The heat stabilitv was eenerallv of the order of Si > Ce > Sn ~
~
~~~
~~
R.MH,
+
36
CM-CH=CH,-R'-CH=CH+
I
C)polymer formation through reaction of metal donor atom coordination.
R 37
Coordination Polymers
Coordlnatlon Polymers Coordination polymers have been utilized since before recorded history, though not recognized as such until recently. For instance, the tanning of leather depends on the coordination of metal ions with the proteins which make up the hide. These protein-metal ion complexes resist bacterial attack, wear and weathering which befall nontanned animal skins. Metals hound to other natural polymers, including proteins, affect numerous enzymatic and membrane interactions (22). Metals can be coordinated with oreanic lieands to form a polymer or to form a coordination complex within an already formed polymer. The reactions forming coordination polymers can he like those which form polymers through condensation routes. Here we will consider ~olvmersformed through chelation of metal and nonorga&c metal-containing ions and polymer complexation of metal ions. For ready correlation of product structure with property it is best that the coordination polymer contains a repeat unit with one metal ion per unit. Even so there exists a larger number of synthesized coordination polymers where the exact structure is both unknown and probably varies within a single polymer chain. Coordination polymers can be prepared by a number of routes, the three most common being a ) preformed metal complexes polymerized through functional groups, where the actual polymer forming step may he a condensation or addition reaction; ~~~~
~
~~
-
A listing of polymers utilized to form coordination polymers through route b appean as Tahle 2. Tahle 3 contains a listing of families of chelating compounds utilized to form coordination polymers through route c. (These tables are only illustrative of reagents utilized in forming coordination polymers.) Polymers formed through routes a and c typically contain definable, "exact" repeat units while structures of polymers formed through route b vary depending on the reaction conditions including solvent, temperature, nature of reactants and concentration ratio of the two reactants; and the structure will vary within a given chain for such polymers. The synthesis and characterization of coordination polymers was supported by the USA Air Force in a search for materials which exhihit hieh thermal stabilities. However. attempts to prepare stable, tractable cuordination polymers which would simulate the excer)tional thermal nndlor chemical stability of model monomkric coordination compounds such as comer ethvlenediaminohisacetvlacetonate(II) or copper phtklocyaninetll) have been dicnppointing. l'ypicallv. " . onlv. short chains are formed. and the thermally stable "monomers" lost most of their stability when linked by the metals into polymeric units. Bailar listed a number of principles in designing coordination polymers (23).Briefly, 1)little flexibility is imparted by the metal ion in its immediate environment, thus, flexibility ~~~~
~~~~~
~
-
Volume 58 Number 11 November 1981
925
Table 2. *H,-CHt
I NH"
Polymer Chelates Utilized in the Synthesis of Coordination Polymers
fCH,-CHt
I
OH
+cH*--CH!-
I /"=" -0
*&*Ht
I
+H8-CHt
I
S--H
O "/ H0
Table 3. Chelates Utilized in the Synthesis of Coordlnatlon Polymers Through Chelatlon with Metal Ions Chelate Group
Repre~entativeStrucNre
Chelate Group
Bis-1.2-amino acids
BiSOaminO phenols
Bis-0-hydrow Schiff bases
BisdiamineS
Bis-Bdiketones (Bist,Miketones)
Bis-dithiacarbamates
as-u-hydroxy acids
Phosphinous anions
Bi-nihites and 1.2dinihiies
926
Journal o f Chemical Education
Repre~enlativeSmcture
must arise from the organic moiety; 2) metal ions only stabilize ligands in their immediate vicinity, thus the chelates should be strong and close to the metal atom; 3) thermal, oxidative and hydrolytic stability are not directly related, thus, polymers must be designed specifically for the properties desired; 4) metal-ligand bonds have enough ionic-character to permit them to rearrange more readily than typical "organic bonds", 5) flexibility increases as the covalent nature of the metalligand bond increases; 6) coordination number and stereochemistw of the metal ion determines . wlvmer - structure (such as square planar; linear; planar or three-dimensional); 7) complex formation is favored through use of pure reactants in stoichiometric amounts; and 8) if a solvent is used for the polymerization, i t must not form a strong complex with either the metal ion or chelating agent. Many of these points should be self-evident to upper level undergraduate students since they are simple extensions of material typically presented in intermediate level inorganic courses. Following are brief discussions of several families of coordination polymers. Polymeric metal phosphinates have been extensively studied by Block and coworkers (24). Single-, double- and triple-bridge phosphinate polymers have been produced, containing metals as Al, Be, Co, Cr, Ni, Ti and Zn. Some of the nroducts eive films with tensile streneths of several thousand psi, and tkermal stabilities to 45006. Thermal degradation commences with loss of the awl or alkvl eroum . which in turn attacks other phosphinate g r ~ u p s~iim-forming . characteristics are enhanced by use of plasticizers.
Double Bridged 4s
overcome if the platinum is present in a polymer which can both act as a long-acting controlled-release agent and be prevented from entering catastrophically into the human circulatory and excretion system.
C-DDP 45
Allcock and coworkers attached C-DDP to a preformed, water-soluble polymer, poly[bis(methlamine)phosphazene], 46, that bears coordination sites on both the side group and chain nitrogen atoms (2628). The compound reacts with KzPtC4 and 18-crown-6-ether in organic media yielding a coordination complex, 47, containing C-DDP (20). This complex shows tumor inhibitory activity against mouse P388 lymphocytic leukemia and in the Ehrlich Ascites tumor regression test (28). CH, CH,
K,PtX, f H,NRNH,
44
The metal nhosnhinates are DreDared from metal salts and dialkyl or di~rylp~osphonic acids-utilizing melt or solution svstems. The metal wlv~hosnhinatesare utilized as additives. lg., chromium(111j p&phbsphinates thicken silicones td greases and improve their high pressure physical properties. Chromium and titanium polyphosphinates impart antistatic properties to a wide range of plastics. Allcock and Carraher and coworkers have synthesized what mav be considered as platinum coordination polymers as antkumoral agents. aligna ant neoplasms ar& thk second leading cause of death. In 1964 Rosenberg and coworkers discov&ed that bacteria failed to divide, but ebntinued to grow giving filamentous cells in the presence of platinum electrodes. A major cause of this inhibition to cell growth division is cisdichlorodiamine platinum 11, C-DDP, which was recently licensed as an antineoplast drug. It is currently successfully used in conjunction with other drugs in the treatment of a wide varietv of tumors. The use of C-DDP is comnlicated due to a wide ;umber of negative side effects. ~ l l c i c kand Carraher recognized that a number of these side effects may be
CH,
Carraher and coworkers included the cis-dihaloplatinum diamine into polymers using diamine-containing reactants including aromatic, aliphatic, pyrimides, pyridines, purines (29, 30). These polymers show a wide variety of biological activities. At concentrations of 10 to 20 Ng/ml they can suppress, enhance or have no effect on the replication of viruses such as poliovirus type I, a L RNA virus, hut none of the polymers show activity towards any of the tested cell lines, including L929 (mouse), HeLa and WISH a t these concentrations. At concentrations of 30 ~ g l mand l above most of the platinum polyamines inhibit tumoral cell growth. Further, mice can tolerate dosages in excess of 20 pglgram weight with no apparent ill effect.
X
Triple Bridged
CH.
-. 48
\ /" Pt
I ( \
NHzRNHif where X = CI,Br, I
Carraher and coworkers have also utilized formation of coordination polymers as a model for uranyl ion retrieval for both environmental and industrial . DurDoses. Select salts of . diacids, dioximes, etc. are capable of removing the uranyl ion to 10-Qo 10-8 M (31,32). (The uranyl ion is the most common natural-occurring water soluble form of uranium.) This has been extended to removal utilizing salts of polyacrylic acids, polyacrylic acid itself, and a wide variety of carboxylic acid sulfonate and sulfate containing resins (33). Almost all of these compounds containing the complexed uranyl moiety have greatly reduced toxicities to a wide range of bacteria and fungi compared to UNHH itself (33). Thus the toxicity has been significantly reduced through chelation of the uranyl ion.
Volume 58 Number 11 November 1981
927
Usine resins to remove and detect metal ions. includine the uranyl yon, has been practiced for some time (34). ~ e a c & n s , in which metal-containing coordination polymers are formed, are critical analytical and chromatographic reactions, hut are often not recognized as involving coordination polymer . . chemistry in itsbroadest sense. Further, there are a number of plants which are known to chelate various ions (35.37). Currently stud& are underway concerninr the cornplrxation uf the uranyl ion by such plants, specifical& sphagnum fimhriatum and spagnum reiurrum mosses (38).Thus future efforts at identification, separation and isolation of metal containing moieties might include use of natural occurring reagents. The most widely studied coordination polymer family is that derived from his-6-diketones. The diketones utilized are usuallv of two structural tvoes with the alkvlene bridge oc,. curring either hetwren thr rwosets ofcarh&ls (form%) or to one side of the rarhnyls rforrn 51). R R W I I I
-en-N-N+
W-N-N-R R I 1M-C-R-M I R
P
HC-R-OH
*
H N-R-NH
Such polymers are formed through the hulk polymerization of the bis-B- diketone withmetal acetates or metal acetvlacetonates (23,39,40). Thermal decomposition of polymks of form 52 occurs in the range of 225 to 350°C.
Of the many coordination polymers studied by Bailar and Marvel and coworkers, those derived from bisthiopicolinamides showed the best thermal stahilities. The zinc I1 derivatives showed the hest thermal stability and could he heated at 300°C for 6 hours without aonreciahle loss in wei~ht or change in the infrared spectra (41;.;l'he zinc 11 derivatiies of hid-salicaldiminesalso show the hest thermal stability (42). A reason (41) cited for the often found superior thermal stahility of zinc I1 derivatives is that zinc possesses only one (common) oxidation state. Transition metals, etc. can be oxidized to higher states, catalyzing the decomposition of the polymer chains.
I 1 I 4M-N-R-NI I R
2
Table 5. Organometalllc Compounus Employed In the Synthesis of Condensatlon Oraanometallb Polymers and the Modllcatlon of
GC
Table 6. R H H O 1 1 1 1
OHH
1 1 1 1
CM-N-N-C-R-c-N-N+
I R Figure 1. Representative shuctures of condensailon polymers.
Table 4. Lewis Eases Employed in the Synthesis of Condensation Organometalllc Polymers /NOH
HON
HON
\c-R-c R
NOH
'c-R-c
/
"R
HN
oximes
HO-R-OH
HS-R-ISH
/
amidmimes
thlol~
X
X
II
II
HINNH-C-R-C-NHNH,
HzN-NH
I
R dlols
hydrmines
HN-R-NH
H-N
hydrazides and thiohydraddes
fR\
N-H
e~l~-~-~~3e
R '.' l~rlmaw$mines
928
(sec0nda~)amines
Journal of Chemical Education
acid salts
Polymers Modlilcatlon Through Condensatlon wHh Organometalllc Compounds
Condensation Organometalllc Polymers Here we consider polymers synthesized utilizing condensation reactions where the reaction site can he a t the metal atom, adjacent to the metal or somewhat removed from the metal. Here reactions directly involving the metal already chemically bonded to an organic moiety (for instance 53) will be considered under the current topic, while reactions involving nonorganic containing metals (for instance 54), such as metal ions and metal oxide ions, will be considered under the topic of coordination metal polymers.
-
R'
+ X-M-XI I II"
HA-R-AH
I I R"
53
0
/I + M+'
HA-R-AH
I/
-
0 CA-R-A-Mj
1I II
Research in this area was catalyzed by the observation that organometallic halide moieties possess a high degree of covalent character and can chemically behave like an urganic Thus manv ot'the ureanometallic conacid chloride 132.43). . , " densations are extensions of classical organic and inorganic condensations. Condensation polymers are prepared by condensing an organometallic halide (or other organometallic moiety possessing a suitably high degree of polarity) with difunctional (or higher) Lewis bases. Typically employed reactants appear in Tables 4-6 and corresponding structures are given in Figure 1. 0
1I
+ H.a
R-C-CL
-
=.-A+
R
R
I M *=N-O-MCI-
I I R 61
where M = Fe. Ru. ~ h ' .Co'
R'
CA-+A-M+
R
Some of the polycondensations were hased on reactions known to occur but producing only small molecules. For instance. the svnthesis of the M-S bond (where M is a Groun IVB metal) is well known (44,45). ~ h u s ~ p s ~reacts r ~ lwith z benzene thiol and 1.2-dithiolhenzene in benzene in the Dresence of EtaN giving metal thiols of forms 62 and 63 (44).A seemingly straiahtfonvard extension of this is to emolov . . dithiols where the twu thid units are sufficiently separated so as to encourage reaction with different metal halides. Pdymcr was not formed employing a similar reaction system hut polymer was formed usingan interfacial reaction system (46). The prior literature existence of reactions forming the Zr-S bond provided evidence that polymers of form 64 could he formed. Further. the chemical and ~hvsical in. . .oronerties. . cluding spectral assignments, derived from studying 62'and 53 aided in rhe chamcterization of 6 3 .
0
I
+ HCI
R-C-OH
55
0
0
I
R-CCI
+ R-NHl
H
I I
+
RC-
N-R
58
Condensation Polymer
-
R
I CI-M-CI
I
+
H2N-R-NH,
R
H
I I IM-N-R-N+
N
I
I
R 59 Condensation Organometallic Polymer
The organometallic moiety can also be introduced through condensations occurring away from the actual metal site as in the case with employing Lewis hase-containing metallocenes.
Emphasis has included construction of new condensation reaction systems and modifications of existine systems. Since many of ;he reactants and products are ther&lly unstable, low temperature condensation systems (solution and interfacial condensation systems) have typically been utilized (32, 48,49). There are a numher of nossible solution condensation svstems, all of which appea;to be homogeneous but which &ssess subtle differences which actuallv effect marked differences in reaction conditions. Used variations include addition of bases, phase transfer agents, surface active agents, nonsolvents, salts and multiliquid systems. The most useful solution condensation systems contain water. For organometallic monomers such as CpzTiC1z effective condensation systems have been developed consisting of the Lewis base and added base (such as NaOH, triethylamine) and CpzTiClz all in aqueous solution. Here the titanium compound hydrolyzes to form moieties which condense as C .D.I T-~units ~ 132). . . For water ina~lublemonomers other systems have heen designed. Thus H?l'hX,n,mwunds are insoluble in m s t owanic liauids and wakr. F'&est&s were formed through iniriailv dir&ing the salt ofrhe diacid in a minimum of water and then addition of one to ten fold (by volume) of DMSO. The lead reactants were dissolved in DMSO. The two solutions. when brought together, result in the formation of lead pol;esters 65, G2, 50). ~~
R H o d *
R
M *=NOH
I
0
+
I
c~-c-R-C--cI
0
II
-
Volume 58
~~
Number 11 November 1981
~
929
imethamine (69.60); or neutral as is the case with titanium, zirconium and hafnium containing polymers. N
/Ot
65
At least two general aqueous interfacial systems have been utilized, each differing only in the location of the reactants. The normal interfacial systems employ the Lewis acid in the organic liquid and the Lewis hase in the aqueous phase. Reversing this (i.e., the Lewis hase in the organic soivent, etc.) leads to what is called the inverse or reverse interfacial svstems. The normal interfacial system has proven to he the most versatile of all systems thus far employed for synthesis of condensation polymers and polymer modification through condensation routes (32). A numher of nonaqueous systems have been reported which involve usage of glycols, etc. These systems are not satisfactory for the types of condensations considered here because of the real chemical activity of the metal-containing Lewis acids with alcohols generally forming ether and oxide linkages. (In fact the actual usage of such systems with organic acid chlorides should be further investigated before active usage of the systems.) Thus nonaqueous systems generated fromnonreact&e liquids were devised since a numher of aqueous systems yielded the oligomeric polyoxides rather than the desired condensation products. A numher of Group IV A polyethers, polyamines and polyhydrazines were synthesized using the usual organic phase containing the organometallic compound in contact with a liquid diol, diamiue, etc. containing suitable added hase (for instance 51,52). Since many liquid diols, diamines and hydrazines are immiscible with organic solvents as hexane, octane and carbon tetrachloride the Lewis hase acts hoth as a reactant and forms an interface with the metalcontainine ~ h a s e Products . are formed ranidlv- (less . than 3 mind in KGh yield (usually 70%). The products are low to intermediate in molecular weight (DPN = 10 to 150). A second, more general system was devised which was compatible with both liquid and solid Lewis bases. Solvents such as pentane, hexane, carbon tetrachloride and cyclohexane are immiscible with nitrohenzeue, acetonitrile.. 2.5-hex. anedione and tetrahydrothiophene-1,l-dioxide.Thus successful condensations were carried out with the Lewis hase contained in the nitrobenzene, etc. and the Lewis acid contained in the hydrocarbon liquid (for instance 53-56). These systems have subsequently found industrial use for the condensation of a numher of other reactants. Each new set of reactants renresents ootential new oonortunities for innovation, development of new condensation systems or modification of existing systems. The general construction of polymerization systems remains a major problem in the further synthesis of potentiallv useful metal and nonmetal-containing polymers,~includin~many natural polymers. Many of the organometallic monomers exhibit catalytic properties. Polymers containing moieties derived from such monomers may offer not only catalytic activity, hut also certain stereoregulating properties as a consequence of the inherent steric requirements present about the metal-containing moiety contained as part of the polymer. The organometallic polymers offer a ready avenue as delivery agents for biologically active agents. The desired targeting agent may he contained in either or hoth comonomer unitk). Thus titanium derivatives of vitamin K may be used to deliver, over extended periods, the vitamin K moiety (66, 57); stannane polyethers were synthesized as delivery agents for tin (67,58); and tin derivatives of select steroids were synthesized as delivery agents for both We tin and steroid (68, 59). The desired effect of the delivered moieties mav he intended to be harmful, as in the case of the stannanebortion of the stannane polyethers; beneficial as in the case of the manganese polyamines derived from condensation with pyr-
.
..
930
Journal of Chemical Education
69
All of the tin- and arsenic-containing condensation polymers have shown some antibacterial and/or antifungal activity. The stannane-modified polyethyleneimines are among the most potent mildew and rot resistant compounds thus far tested showing inhibition to a wide range of species including Aspergillus furnagatus, Aspergillus flauus and a combination of Penicillin species (70;62). Polysaccharides derived from a number of sources including cotton and dextran, modified through condensation with organostannane halides, also exhibit mildew and rot resistance (71; 63). Suggested uses for the stannane and arsenic containing polymers include as additives for paints, commercial insulation, within specialty bandages and topical medical applications. The polymer can also be designed to "induce, encourage" host acceptance and suhsequent demise or help. Thus arsenic (V) polyprymidines were synthesized to deliver the arsine portion utilizing the pyrimidine moiety as a metabolizable segment, which when metabolized will result in the release of the arsenic moiety, supposedly toxic to the host. Thus 72 was specifically active towards Psedomonas fluorescens at polymer concentrations in excess of 55 pg/ml(64). Further activity was markedly greater in nutrient broth solutions compared to saline solutions consistent with inhibition being related to active metabolism. Also inhibition of &AsC12 itself was about 50%less than that for 72 and was essentially the same for the broth and saline solutions.
71
All of the tested condensation polymers are semiconductors with bulk resistivities typically ranging from 102 to 10'2
Table 7. Metal-Contalnlng Anchored Catalysts Structure of Metal Containing Catalyst Portion
Figure 2. Orientation of polymer with flow plane for (lelt) organometallic condensation polymers and (right) classical organic polymers.
ohm-cm for both AC and DC measurements. They exhibit some of the highest dielectric constants and dissipation factors yet measured. Thus a numher of electrical applications can he envisoned. Many of the linear polymers are fairly rigid and crystalline and exhibit low solution viscosities/chain length ratios attributed to a combination of factors including chain stiffness and poor solubility and the presence of the metal atom. The first two factors encouraee the . nolvmer . chains to reside hetween flow planes rather than through flow planes minimizing viscous drar! (see Fig. 2). The latter factor concerns the relatively high weight of the metal atoms per occupied volume. Thus the (atomic) volume occupied by antimony is about five times that of carbon, yet the mass is about ten times as great (65). A number of polymers (mostly those derived from Cp,Ti) exhibit a characteristic known as "anomolous fiber formation" reminiscence of "metal whiskers" (66). . . Some of the fibers are formed on mechan~cnl"strukiny" of the material in the solid slate. Cermin of the fiher~are2 cm in 1enuth.offerrood weight retention (80% weight retention to 1 2 0 0 0 ~with ) some bimensional stability at that temperature (66). A numher of metal-containing polydyes have been synthesized. Thus a numher of dyes, such as phenolphthalien and mercurochrome (73),possess two basic functional groups which can be condensed with organometdic halides (67,68). Those containing tin show a wide range of biological activity, not unexpected since a numher of the dyes are employed in hioloev .,. and medicine as cell stains. The metal .nolvdves . . are fluorescent and readilv impregnante painls, paper, cloth and la stirs vieldinpl fluorescent materials ( 6 8 1 . Suaeested uses h u d e as tracer additives for identification, iiraser applications, as permanent coloring ayents in paints, paper, cluth and plastics, and in hiomedicnl applications as sperialized stains and toxins. HnOH
Other potential uses for organometallic condensation polymers include photosensitive media in photocopying devices, adhesives and as flame retarders. Anchored Metal Catalysts One of the most active research areas in chemistry involves the use of chemical reagents and catalysts supported on polymers. A majority of these can he considered organometallic polymers. A numher of "anchored metal catalysis" offer advantages over "nonanchored" catalysis in terms of efficienry, selectivity, and separation. Following are brief descriptions of several of these catalysis svstPms. Tahlr 7 contains additional examples. Homogeneous metal complex catalysts selectively promote a large numher of useful reactions under mild conditions. Such reactions in-
Activity
Ref.
Stereospecific t.4-hydrogbnation of dimes to cis olefins
(74)
Hydrogenation of olefins
(75)
Asymmebic hydrogenation of a-acstamidoacrylic acid derivatives
(77)
Asymmatnc hydraformylationof styrene
(77)
Oxidation of alcohols to corresponding carboxyl compounds
(7 4
Selective hydrogenation of (79) conjugated dienes to monaenes
Dimerimtion-alk~xylation Of butadiene to the isomeric methaxyactadienes
(84
Oiefin metathesis
(811
Synthesis of 24hylhsxanol using ( 8 a a multifunctional bound catalyst Generation of ketones hom acid chlorides
(83)
Alkane isomeriration and cracking ( 8 4
Oxidation of alcohols to carbonyl compounds
(85)
Hydrogenation of dienes to mmoenes
(8s)
Coupling and conjugate addition reactions
(87)
FisChBr-Tropsch catalysis
(84
Baeyer-Viiliger oxidations
(8s)
Volume 58 Number 11 November 1981
931
clude hydrocarboxylation, linear oligomerization, cyclooligomerization, hydroformylation, decarhoxylation and bydrogenation. Through attachment of a homogeneous catalyst to a crosslinked uolvmer. the catalyst is "heterogenized with . . respect to the specific reaction envinrnment. Xlany transition metal com~lexeshave heen attached ro swellable styrenedivinylheniene resins. The rhodium-phosphorus compound (PPh3)sRhHCO is an excellent hydroformylation catalyst. Pittman and Hanes (69) introduced a similar moiety into a styrene-divinylbenzene resin. This catalyst promotes selective hydroformylation of terminal olefins without isomerization of the double bond. Both linear and branched aldehyde products are obtained. The normal to branched product selectivity is much higher using the polymer bound catalyst compared to the nonbound catalyst as long as the phosphorus loading within the polymer is high.
normpil
branched
Selectivitv loading, ,denends . on crosslink densitv.. .~hosuhine .
CO pressure, solvent and temperature.
The nickel-catalvzed linear oliromerization of butadiene to (E,E)-1,3,6-octatriene (70) is achieved in better than 95% vield with a ereater than 99% selectivity when NiBrz is complexed with a phosphinated styrene-divnylhenzene resin followed by reaction of the complexed nickel chloride with sodium borohydride. When (PPh3)zNiBrz-NaBH4 is used alone, a complex mixture of proaucts is obtained.
Through attachment of two different catalysts to the same nolvmer. . . . or bv mixina hatches of polymers each binding a separate catal&, the two catalysts &a; he employed to carry out "one-pot", multistep, sequential organic syntheses. Thus (PPh3)3Ni(CO)z,which catalyzes the cyclooligomerizationof hutadiene was anchored to resins which contained anchored (PPh3)2Ru(C0)2CIz, a catalyst for the reduction of dienes or trienenes to monoenes. Thus sequential cyclooligomerization followed by selective hydrogenation was effected (71).
The use of anchored reagents has permitted the development of a three ~ h a s test e for certain reactive intermediates. For instance, consider a general process
where a precursor A generates reactive intermediate B which in turn reacts with D forming C. A test which can prove if intermediate B has a discrete and inde~endentexistence can be carried out through attachment of;eagent A to one solid polymer phase and reagent D to another solid polymer phase. If compound C is formed on the @-D solid phase, after interaction with +A solid phase then B must have a distinct, independent lifetime to allow diffusion from the &A solid phase, through the solution, to the @-D solid phase. 932
Journal of Chemical Education
This technique was used to prove the postulate that cyclohutadiene exists free of iron when generated by the oxidation of cyclobutadienyliron tricarbonyl with ceric ion (72). Cyclohutadiene, prepared from the ceric ion oxidation of cyclobutadienyliron tricarbonyl, forms a Diels-Alder adduct with maleanil. Thus, two anchored reagent solid phases were synthesized, one containing cyclobutadienyliro~tricarhonyl and the second containing malenil. The oxidation of cyclohutadienvliron tricarbonvl was carried out hv addition of the ceric ion in the presence of the two resins (physicallyseparated from one another). The cvclobutadienvl-maleaniladduct was formed proving that cyciobutadiene tknsversed the solution phase as a separate, discrete species (72).
Another interesting situation concerns the use of natural occurrine materials as catalvsts to assist in the svnthesis of difficultto obtain compounds. This can be envisioned as occurring either through direct modification of a chemically active site followed by subsequent removal of the activating reagent or through chemical attachment of a chemically active catalyst with the steric and electronic constraints, environment of the natural material acting to assist the catalytic function(s). For instance. enzvmes tvnicallv Dossess chemically act&; asymmetric sites. 1f an achiial me"G catalyst could he anchored (immobilized) inside an enzvme. . . near the enzyme's active site, the enzyme's chirality might become manifest in both "natural" and synthetic reactions. Whitesides and Wilson (73) have utilized the above concept in designing a reagent which can selectively catalyze the hydrogenation of alpha-acetamidoacrylic acid. The enzyme avidin is known to irreversibly hind ( k d = 1014)biotin. Thus, a biotin was converted to a chelatine dinhosnhine comnound and then complexed with a rhodium?~)concining compound. The resulting complex selectively catalyzed the hydrogenation of alpha-acetarnidoacrylicacid at 0°C and 1.5 atm of hydrogen gas with molar yields in excess of 500 and enantiomeric retention of about 40%. Thus anchoring of the rhodium catalyst into avidin allowed the enzvme to act as a stereo-selecting agent.
seen as net endothermic or exothermic. Melting may or may not occur prior to initial degradation for metal containing polymers. 6rganometallic polymer^ are typirally hydn,phohir and resistant to hvdrulysis until "wetted" by addition id a suitahle wetting agent, such as a solvent or near solvent for the polymer. Many of the polymers are semiconductors to near semiconductors exhibiting bulk resistivities withm the range of lo3 to 1013ohm-cm and thus can be considered for certain semiconductor applications. Potential Reasons for desiring inclusion of metal atoms and metalcontaining moieties into oolvmers are manv and varied. For . instance, compounds containing the Cm41 moiety (\I = Fe. Ti, Zr. 110 are r e ~ o n e dto be stahiliziers to U V radiation: thus addition of pol;mers containing such moieties into paint mixtures, etc., might impart to the outdoor paint better weambility regardjng [:\'photo stability. h s ; rompounds conraining tin cxhihit antifungal and antibacterial properties potentially imparting to rugs, paint, rlothing. err. containing the tin polymer sum? mildew and rut resistance. Manv metal rumpounds exhibit catnlytic properties with regard tocertnin reactions, thus specific metal-containing ~ x d p e r might s offer huth specific catalytic acti\,iry and select rtereoregularing properties related tu the constraints imposed by the polymer chain. Applicat;ons i n the electnmir and photo industries are apparent. In iact, potential applications may t)pically be only limited by the vantare vcrint d t h e srientists since the rarictv of potential^^ avai~ab~d metal-containing polymers is almost limitless. While the above is true, there currently exists several practical limitations. First, synthesis of many desired monomers is difficult or not vet accomolished. For instance a good synthesis of tungstanyi c h l o r i d e , ' ~ ~ p ~isl pyet , to he foind. Svnthesis of a number of desirable "sandwich" nickel.. iron.. cobalt compounds has yet to he achieved. Synthesis of certain arsenic and antimony compounds has proven dangerous, with explosions occurring. Second, the physical and chemical properties, including actual structure, of many potentially useful monomers are unknown, little known, or conflicting. Third, selection of reaction conditions is critical and often quite limited. For instance, synthesis of antimony. .polyoximes . a t concentrations normally &nployed in interfacial systems takes -9 hours a t a stirring rate -10,000 rpm; whereas product is rapidly formed (-within 30 secs) employing much greater concentrations of reactants. Formation of zirconocene poly(cohalticinium dicarhoxvlate) decreases with stirrine time after 30 sec with no product obtained if stirring is allowed to proceed past several minutes. Synthesis of Group IV B polyethers has thus far been accomplished only with aromatic diols with aqueous systems. Use of excess Group IV B Cp2MX2 monomers results in the formation of crosslinked polyamidoximes rather than the (generally desired) linear products. Synthesis of antimony polyesters has occurred only with certain antimony compounds, being dependent on such factors as inherent reactivity, aqueous solubility and hydrolysis rate. Fourth, the inherent reactivity and solubility and thermal stabilities of many metal-containing reactants may not permit the construction of adequate polymerizing systems. Last, applications will he limited with regard to the cost and availability of hoth the metal and metal-containing reactant. Polymers containing relatively abundant metals such as tin, lead, silicon, iron, and copper may be used in large scale applications but polymers containing scarce metals such as platinum, rhodium and hafnium will he delegated to small scale. hut ~otentiallv The de"auite . imoortant..anolications. .. mand for specialty materials'is expanding a t a rate corresponding to the growth in the complexity of our technology.
-
0
/I
C-OH
I
H.C-C-H
I
N-C-CH H'
The wider topic of polymer supports in organic synthesis is covered hy a continuing column (since vol. 4, 1977) by Charles Pittman in Polymer News. General Properties Relative to classical oreanic oolvmers. oreanometallic polymers are soluble in fewer s&&ts a i d lesser extents within these solvents. (The t o ~ i cof polvmer soluhilitv has already been reviewed in T H I JOURNAL). ~ While a few are soluble in typical organic solvents such as toluene and chloroform, most are either insoluble or only soluble in a few select solvents which include dipolar aprotic solvents and salt-dipolar solvent combinations. Even where solubility appears to have been achieved, it is best to retrieve the polymer from the supposed solvent and to reexamine it spectrophotometrically, etc. The poor solubilities are probably due to a comhination of related factors including (a) high cohesive (secondary honding) forces between chains, (b) highly crystalline microstructure of a number of products, and (c) a peculiar comhination of bonding offered by the organometallic polymers-a comhination of both nonpolar (organic) and low to high polar contributions. Attempts to achieve better solubility include (a) use of flexible and/or dissymmetric reagents, (h) copolymerization either or hoth using two metal with one nonmetal containing reactant(s) or one metal with two nonmetal containing reactants, (c) use of model compounds (monomers) as a predictor of polymer solubility, and (d) addition of a chain terminator to shorten the chain length. Many of the organometallic polymers are powders which can he cast to give films or fibers only with great difficulty. Some of this can he overcome by addition of suitable plasticizers, often as the polymer is actually being formed, as one of the materials pressent in the reaction vessel. Thermal degradation typically occurs through a series of kinetically dependent and/or kinetically independent stability olateaus characteristic of the differences in the thermal stabilities of the bonds present in the organometallic. In comoarison. classical oolvmers tvnicallv undereo thermallv inhuced &eight loss~sthrough i s o m e i b a t smoothly contdured manner since the bond energies present are of about the same hond energy with similar oxidative characteristics. Thermal degradation in air often occurs through highly energetic exothermic oxidative routes whereas degradation in inert atmospheres occur through less energetic routes, either being
Volume 58 Number 11 November 1981
~
~~~
~
933
Thus thewis a large, real and potential market for metalcontaining polymers.
Charlos, R.. J Polymer S e i , A-I, 267 I19631 and J Phys. Chom. 64.1747 119601. Kornhak. V.. and Vinozradma. S..Dokl. Akod. Nauk SSSR. 138.1353 119611.
Literature Cited 11) Pittman,C.."O'gan'ganmefal8e Resnim"(Edirora: kker.E.andTsutmi. M.l,Planum Preu, NY, 1977, uol. 6. (21 Neuse, E., and Rosenherg. H.. "Metallacene Polymers". Msreel Dekker NY,1970. (31 Carraher, C., Sheace, J., and Pittman. C., (Ediforsl."OrganometslliePolymcrs~Aeademiepress. NY. 1978.
M o w . P. w., 'Yimdensstion ~iymeymBy toterfacial and Solution MethaQ'. Wiley. NY, 1965. Carrsher. C., and Preston, J., (Editors) '"Interfacial Synthesis I11 h n t Advances: Marcel Dekker. NevYork. 1981. Carraher C., and Deremo-Reerr. C.. Angew. Mokmmokhdore Chemie. 65, 95
Carrah~rC..Sheate..l.. and Pitunan.C.1. AcedemicPress. NY. I978
Rauseh. M.. lnors. Chem.. 14.506 119751. ll~meyorinarganie~o~ymen."NWCR-ISSSU 1161 G ~ . ~ ~ ~ , A .A' H d .M~I~&.E:F., . HRI-395 Contract NAS 3-21369,1979. (17) Pittman, C.. Pattersob, W.. and McManus, 8.. J Polym. Sci. Polym. Chrm. Ed., 12. 837 (1974) and 14,1715l19761. (181 Greher. G..andHdlensleben. M.. Mohromal Chem.. 83.148 (1965),92.137 (1966) and
."*,*" , , ,70!2", \."",,. I*"
(19) Noltoa, J.. and Van der Kerk, G., Rse. T m r Cham., 80,623 (1961) and 81.41 (1952). (20) Luneua. L.. Sladkau, A., and Korshsk. V.. Vysokomoldulo Sopdin.. 7 131, 427 IAGSI. 1211 Rahor,E..sndStem.R.,U.SSP~t.3.291,783I1998l. (22) Vallee. B. L.. and Riordan. J. F., "Praeeding. of Be IntrmatiomJ Symposium on Proteini'(Ediror: C. H. LO, AcedemicPrm, NY, 1978. (23) Bailar, J. C., "Preparstive InorganicReactions'' (Editor: JoUy, W.) lnfendenrr Pubs., NY. (24) B l a k (251 Rosenbem, 8..VsnCsmp, L., and Krim
Carraher,C..andScheruhel, G., Makromol. Chemie, 152.61 (1972). Carraher, C.. Trornbley, M.,andTorre. L.. unpublished resulfa. Canaher. C.. Fmler. V.. Mallov. H.. Tavlor. M.. Ticman.. T... and SEhroeder. J.. J. ~ ~ ~ ~ ~ci-Chs;, ~ h . 1 A-I, : in p r w . Carreher, C., Schrader, J., Venable. W., McNeely, C., Giron, D., W a l k W., and Feddersen, M.. "Additives for Plaatien", Vol. 2 (Editor: Seymour. R., chpt. 8, AcaA"-:-cL"""
h,"
...". s0.a
Csrraher. C., Schrader. J.. McNeely, C., Workman, J., and Gimn, D.."Mcdiflmtion of Polymers" (Editor: Carrahcr. C.. and Tsuda, M.1, ACS, Wsshingfon, D.C., 1980. Csnsher, C.,Moon, W., and Langmrthy, T., Polymer P., 17.1I1976l. Carraher.C.,and Hedlund. L., J . Macmmol. S&Chem.,A14 (51,713 (19801. Carreher. C.. Cham. Tech., 741 11972). Carraher, C.. and Venkatschalam, R. S.. unreporkd results. Carreher. C.. Schvluz..R...Schraoder. J.. and Sehaan..M...J. Morromol. Sci-Chsm.. -I. in press. c . . d H ~ ~ . . R . . J . A ~ ~ ~ . ~ (19761. ~~~.s~..~~,~~o~
. .
,...
~~~~.~
Rphrk..l..and Cavina. F..,J. Amsr. Chsm Sor..PL71121LE1741. Wil8o~,M.E.,andWhitoaide8.G. M..J.~mer.'Chem. Soc., 100,306 (19781. Pittman. C.. J. Or*. Chom. 40.690 11979). Jarrall, M. s., G&, B. C..sod Nicholson, E. 0.. J. Amor Cham. Soc.. 100. 5727 ~~
C l , ~ h k26:kcademie . P&,NY, 1978. 1291 Csrrshor. C.. Giron. D..Scott. W., endSchmder, J., J Mocromol. Sci-Cham.,A15
. . . , ....
"
I.li, tinmgnt. A f.'ru,k W .rind Inkrnn, R . .Sorure, 1%. 111 IMI,. OCI r l ) m l 11 . A M nri L o w . \ .27.309t16? I Crow e. I .and hIaab.h . l o n o L . ~ / B u i u n ) . N S.M. 15311966, 38, ~'",r,ner.~',H!lnt*mm.11.9.1 l,..I..T.rrnmmdTwlor.\I . l l n n p ~ n e d u l r k
934
Journal of Chemical Education
Taranishi, J Catalpla, 51,406 (1978). pitunan, c., and ~ gQ.,, J o~gonomernl.c h m , 158.65 11978). Warmel, S., and Buachmeya, P., Angew Chem. Intermot. Ed., I?. 131 (19781. Bsvheldcr. R. F., Gates. B. C., Kuijpers, F. P., Preprinls 6th intermof. Congress on Coialysis. London. July 1976, A40. pp 1-8. Pittman, C., and H s n a , R., J. Org. Ch~m.,42,1194 118771. Magnotla, V., and Gstos, B.. J. PolymerSei. Chem. Ed., 15.1341 (19771. Rechet, J. M., Warnock, J., and Farrdl, M. J.. J. O~gonicChom, 43,2618 (1978). Neckers,D.C.,lsrnel J. Chem.. 17,268 119781. khwart., R. H., and Filippa, J . 8.. J. Org. Chem., 44,2705 (19791. Perkina, P., and Vollherd. K. P. C.. J. Amer Chem Soc, 101.3985 (19791. Jacobson, 8.. Meres,F., and 2ambrig.P. M., J Amsr, Chem. Sac, 101.693Sand6946 (19791.
