Chapter 9
Dicyclopentadiene Polymerization Using WellCharacterized Tungsten Phenoxide Complexes
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Andrew Bell Research Center, Hercules Advanced Materials and Systems Company, Hercules Incorporated, 1313 North Market Street, Wilmington, DE 19894-0001
Pure WOCl - (OAr) complexes (x = 1, 2, 3 and 4; and OAr = phenoxide) were prepared in essentially quantitative yield by reacting tungsten oxytetrachloride (WOCl4) with the requisite amount of phenol or metal phenoxide. The ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) by WOCl (OAr), WOCl (OAr) , and WOCl(OAr) , in combination with trialkyltin hydride (R SnH) was assessed. The tungsten catalysts produced are capable of bulk-polymerizing DCPD to very high polymer yields. The polymerization ability of a particular procatalyst was correlated with the reduction potential (W(VI)-->W(V)) of the complex and the charge on the oxygen of the di- or tri-substituted phenoxide ion. The effects of changing DCPD:W, Sn:W, and rate moderator:W ratios on residual monomer levels were studied. 4 x
3
x
2
2
3
3
Transition metal-catalyzed ring-opening metathesis polymerization (ROMP) of cyclic olefins is an important application of the olefin metathesis reaction (Scheme 1) [7]. Polynorbornene, polyoctenamer, and polydicyclopentadiene are currently produced on an industrial scale using this process [2].
Scheme 1. Mechanism for ROMP of Cycloolefins
0097-6156/92/0496-0121$06.00/0 © 1992 American Chemical Society
In Catalysis in Polymer Synthesis; Vandenberg, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
Downloaded by NORTH CAROLINA STATE UNIV on October 11, 2012 | http://pubs.acs.org Publication Date: June 22, 1992 | doi: 10.1021/bk-1992-0496.ch009
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CATALYSIS IN POLYMER SYNTHESIS
Dicyclopentadiene (DCPD) polymerizes quite readily using metathesis catalysts, but the nature of the product is highly dependent on specific details of catalyst structure and polymerization conditions. Known products range from soluble or only partially soluble thermoplastics [3] to an insoluble, brittle polymer [4], Ring-opening metathesis of the very strained norbornene ring with concomitant co-metathesis of a limited number of less-strained cyclopentene rings results in the highly cross-linked thermoset network depicted in Scheme 2. Recently, it has been found that such a highly crosslinked thermoset resin has properties which make it useful as an engineering plastic [5, 6]. METTON® liquid molding resin is a Hercules Incorporated trademark for a proprietary blend of polydicyclopentadiene formed by thering-openingmetathesis polymerization of DCPD.
Scheme 2. Formation of PolyDCPD Utilizing a Tungsten Catalyst (Depicted in a Stepwise Fashion for Clarity) The DCPD polymerization reaction has characteristics which make it readily adaptable to reaction injection molding (RIM) [71, resin transfer molding (RTM), pour molding, and other liquid-molding processes. The active metathesis catalyst is formed when two separate reagents, a procatalyst component and an activator component, are combined. The procatalyst is defined as a metal complex which, when combined with a suitable activator, generates thering-openingmetathesis polymerization catalyst. This makes it possible to use separate solutions of the individual components in DCPD monomer to generate an active catalyst when the components are combined in the mixhead prior to injection into a mold. (See Scheme 3.)
In Catalysis in Polymer Synthesis; Vandenberg, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
9. BELL
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Tungsten Phenoxide Complexes
DCPD Elastomer Procatalyst Additives
DCPD Elastomer Activator Additives
I
Downloaded by NORTH CAROLINA STATE UNIV on October 11, 2012 | http://pubs.acs.org Publication Date: June 22, 1992 | doi: 10.1021/bk-1992-0496.ch009
Mixhead
Mold
Scheme 3. Schematic for METTON
polyDCPD RIM System
In our continuing efforts to develop new catalyst systems, we have focused our attention on tungsten chemistry supported by bulky phenoxide ligation. Of particular interest are a number of tungsten complexes with phenoxide ligands which have been utilized as olefin metathesis catalyst precursors, e.g., tungsten hexaphenoxide (W(OC
