Polynorbornene block copolymers

Table 17. Phase behavior of polynorbornene block copolymers (Schemes 34 and 35) [343].

The first report of ROMP activity by a well-characterized Mo or W species was polymerization of norbornene initiated by W(CH-t-Bu)(NAr)(0-f-Bu)2 [122]. In the studies that followed, functionality tolerance, the synthesis of block copolymers, and ring-opening of other monomers were explored [30, 123]. Two important issues in ROMP concern the cis or trans nature of the double bond formed in the polymer and the polymer s tacticity. Tacticity is a consequence of the presence of two asymmetric carbons with opposite configuration in each monomer unit. The four ROMP polymers (using polynorbornene as an example) that have a regular structure are shown in Scheme 3. 

Sequential addition methods were utilized to synthesize block copolymers of polybenzvalene with polynorbornene to yield block copolymers of PA and pol-ynorbornene after isomerization [43]. (It should be noted that both benzvalene and polybenzvalenes are sensitive to shock and mechanical stress causing ring strain-promoted explosions in the precursor materials.)... 

One example of a 1 1 AB block copolymer with poly-(IX-8) and poly-(X-S) blocks showed a smectic A phase the mesophase of the homopolymer of X-8. The more ordered smectic A phase dominated the nematic phase of the polynorbornene block. 

Polynorbornene Styrene/isoprene/styrene block copolymer co-Yulcanizing agent p,p -Dichlorobenzoyl peroxide CR cements, self-curing Butyraldehyde-monobutylamine condensation, prod. 

Acrylic elastomer Acrylonitrile-butadiene rubber, hydrogenated Polyethylene, ultrahigh m.w. high-density Polynorbornene Polyurethane elastomer, thermoplastic Styrenated diphenylamine , Styrene-ethylene/butylene-styrene block copolymer seals, chemical-resistant Chlorotrifluoroethylene polymer seals, dynamic aerospace Polyfluoroalkoxyphosphazene seals, dynamic industrial Polyfluoroalkoxyphosphazene seals, dynamic military Polyfluoroalkoxyphosphazene seals, high performance Tetrafluoroethylene/perfluoromethylvinyl ether copolymer seals, oil... 

Treatment of this block copolymer with hydrogen sulfide resulted in the presence of small partieles of lead sulfide in an essentially polynorbornene matrix. Semiconductors based on metal sulfides (PbS, CdS) have been generated by this method. Similar block copolymers have been prepared from norbornenes that contain tin, zinc, cadmium, palladium, and gold. 

The topology of this product with a bulk hydrophobic structure inside and a hydrophilic part outside makes it particularly attractive for applications such as unimo-lecular micelles. On using the same procedure, norbor-nyl-poly(ethylene oxide)-polystyrene macromonomer was polymerized to polynorbornene-poly(ethylene oxide)-polystyrene block copolymer (121) [Eq. (53)]. 

Figure 11.13 Microdomain spacings (d) for hydrogenated poly(norbornene-Z -(ethylidene norbornene)) diblock copolymers, plotted in a format consistent with the scaling law docNfNa. Dashed horizontal lines represent hydrogenated polynorbornene block with indicated number of folds per block. Reprinted with permission from Reference [104]. Copyright 2004 American Chemical Society.

Ring-opening metathesis polymerization has also been exploited to build blocks from cyclic olefins, especially polynorbornene [5]. The development of ROMP for block copolymer synthesis has recently been facilitated by the introduction of functional-group-tolerant metathesis catalysts by Grubbs [21]. 

In contrast, the data in Table 17 demonstrates that the nematic-isotropic temperature of polynorbornene copolymers with either 20 or 50 repeat units in the liquid crystalline block are more similar to the higher molecular weight homopolymer than to that with 20 repeat units. This trend is demonstrated more conclusively by the diblock (PS-PChEMA) [208,209] and triblock (PChEMA-PS-PChEMA [208] and PS-PChEMA-PS [209]) copolymers of 2-(cholesteryloxycarbonyloxy)ethyl meth-... 

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