Norbornene block copolymers

The extension of fhis novel chain transfer event to higher molecular weight a-olefins has enabled us, and ofhers, to make unique poly(norbornene) block copolymers [44]. Examples of fhe diversity of this chain transfer chemistry are given in Fig. 4.15 where chain transfer to efhylene, allylglycidyl ether, isobutylene, cyclo-... 

Gibbs et al [63] reported the formation of dendrimers from norbornene block copolymers with detection probe DNA and... 

Cyclopentene-norbornene block copolymers have been prepared with the living tungsten-carbene system (W(CHt-Bu)(NAr)(Ot-Bu)2, but the structure of this product has not been studied in detail [54]. Because there is a marked difference in the reactivity of the two monomers, rigorous reaction conditions must be applied to obtain the virtual block copolymer (76). 

Scheme 10 Sythesis of ethylene/norbornene block copolymers using 66b/MA0.

Adapting this method, block copolymers composed of PPV and norbornene blocks can also be made available. These copolymers are promising, highly efficient emitters for potential application in organic materials-based LEDs. 

Synthesis of block copolymers of norbornene derivatives, with different side groups, has been reported via ROMP [101]. Initially, exo-N-bulyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide was polymerized in acetone at room temperature with a ruthenium initiator (Scheme 40). The conversion of the reaction was quantitative. Subsequent addition of norbornene derivative carrying a ruthenium complex led to the formation of block copolymers in 85% yield. Due to the presence of ruthenium SEC experiments could not be performed. Therefore, it was not possible to determine the molecular weight... 

The first documented example of the living ROMP of a cycloolefin was the polymerization of norbornene using titanacyclobutane complexes such as (207) 510-512 Subsequent studies described the synthesis of di- and tri-block copolymers of norbornenes and dicyclopentadiene.513 However, functionalized monomers are generally incompatible with the highly electrophilic d° metal center. 

Well-defined nanoclusters (w 10-100 A diameter) of several metals have been prepared via the polymerization of metal-containing monomers. The synthetic approach involves the block copolymerization of a metallated norbornene with a hydrocarbon co-monomer which is used to form an inert matrix. Subsequent decomposition of the confined metal complex affords small clusters of metal atoms. For example, palladium and platinum nanoclusters may be generated from the block copolymerization of methyl tetracyclododecane (223) with monomers (224) and (225) respectively. 10,611 Clusters of PbS have also been prepared by treating the block copolymer of (223) and (226) with H2S.612 A similar approach was adopted to synthesize embedded clusters of Zn and ZnS 613,614... 

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. 

They obtained moderately monodispersed (1.2 + 0.1) polymacromonomers with 30% initiator efficiency when short macromonomers (DP = 21 to 75) are polymerized. Higher MW macromonomers polymerized only partially. Evidence for interaction of the PEO ether groups with the catalytic center is given and assumed to be responsible for the shortcomings of the living system. Random and block copolymers of PS and PEO macromonomers, as well as of P(EO-b-S) and P(S-b-EO) macromonomers have also been made [112], The same group successfully prepared PS macromonomers with a norbornene group in the a position [113]. 

The preparation of copolymers and block copolymers does not make problems. For example, cyclopentadiene can be copolymerized with norbornene using the following procedure. Cyclopentadiene and the norbornene are mixed with benzene and added to the reactor... 

Copolymerizations of benzvalene with norbornene have been used to prepare block copolymers that are more stable and more soluble than the polybenzvalene (32). Upon conversion to (CH), some phase separation of nonconverted polynorbomene occurs. Other copolymerizations of acetylene with a variety of monomers and carrier polymers have been employed in the preparation of soluble polyacetylenes. Direct copolymerization of acetylene with other monomers (33—39), and various techniques for grafting p oly acetylene side chains onto solubilized carrier polymers (40—43), have been studied. In most cases, the resulting copolymers exhibit poorer electrical properties as solubility increases. 

In a living system, if Mi is much more reactive than M2 and polymerization is allowed to proceed to completion, the end-product is a tapered block copolymer, in which only the middle section contains units of both monomers, e.g. with anti-1-methylnorbomene (Mi)/syw-7-methylnorbomene (M2), see Section VIII.C.4 also with norbornene (Mi)/cyclooctatetraene (M2), catalysed by 8W (R = Me)360. In the extreme case the cross-propagation reactions may be so slight that the product is indistinguishable from a perfect block copolymer, e.g. with bicyclo[3.2.0]hept-2-ene (Mi)/norbornene (M2) catalysed by 18109,597, or with awft -7-methylnorbornene (Mi) syn-1 -methylnorbomene (M2), catalysed by 7 (R = Me)128. The successive polymerization of the two monomers can be readily followed by NMR. 

Polyethylene-Wock-poly(clhylcnc-co-norbornene) (PE-fo-P(E-co-NBl ) block copolymer was successfully synthesized by a titanium complex with two non-symmetric bidentate /J-cnaminokclonalo ligands [136,137]. Bis(pyrrolide-imine)titanium complex also has the ability to produce the PE-fo-P(E-co-NBE) block copolymer. PE-fo-PS was synthesized via sequential monomer addition during homogeneous polymerization with bis(phenoxy-imine)metal catalysts [138]. 

Interesting evidence supporting the mechanism of polymerisation of acetylenes via carbene species is provided by the block and random copolymerisation of acetylenic monomers with cycloolefins. For instance, block copolymers of acetylene and cyclopentene with the WC —AlEtCT catalyst [41] and block copolymers of acetylene and norbornene with the (MeA. Oj2W(=NAr)= CHMe3 catalyst [42] have been obtained moreover, random copolymers of phenylacetylene and norbornene with the WC16 catalyst have also been obtained [149, 150],... 

The polymerization of norbornene, Eq. (19), is stopped by cooling the reaction mixture to room temperature. The active polymer 11 can be stored for long periods of time. Heating 11 to temperatures above 65 °C in the presence of monomer causes renewed chain propagation. The subsequent addition of different cyclic olefins, such as endo- and exo-dicyclopentadiene, benzonorbomadiene and 6-methylbenzonorbornadiene resulted in the formation of well-defined AB- and ABA-type block copolymers, Eq. (21) [38]. Triblock copolymers 13 with narrow molecular weight distributions (polydispersity = 1.14) were prepared. Thus, the living character enables the preparation of new uniform block copolymers of predictable composition, microstructure and molecular weight. 

Komiya et al. described the living ROMP synthesis of AB-type block copolymers that contain side chain liquid crystalline polymer blocks and amorphous blocks [62]. Norbornene (NBE), 5-cyano-2-norbornene (NBCN) and methyl-tetracyclododecene (MTD) were used for the amorphous polymer blocks, while I-n (n=3,6) were used for the SCLCP block (see Fig. 9). Initiator 1 was used for the ROMP. Block copolymers with monomer ratios from 75/25 to 20/80 (amor-... 

Table 7 Properties of block copolymers containing I-n and norbornene(NBE), methylcy-clododecene (MTD) or cyanonorbornene (NBECN)...

The introduction of perfluorinated groups generally favors microphase separation due to the immiscibility of fluorocarbons with hydrocarbons [66]. Norbornene derivatives with perfluorinated endgroups in the side chain were prepared by Wewerka et al. [67]. Monomer XII contained a relatively long (CF2)8-chain, separated via a long spacer (11 methylene-groups) from the norbornene, whereas monomer XIII has two relatively short (CH2)2(CF2)4-side chains (Fig. 11). Homopolymers and block copolymers were synthesized with one fluorinated monomer (XII or XIII) and one non-fluorinated non-liquid crystalline monomer (NBDE or COEN) with the Schrock-type initiators 4 and 5, respectively, leading to microphase-separated block copolymers. Table 9 and Table 10 summarize the physico-chemical properties of the homopolymers and block copolymers. 

Koltzenburg et al. report the synthesis of AB block copolymers of acetylene and norbornene derivatives bearing mesogenic moieties [68]. A norbornene... 

As a consequence of the living nature of the copolymerization wifh fhis catalyst, palladium-capped block copolymers of norbornene and ethene as well as of norbornene, ethene, and styrene were synthesized [61]. Higher activities (up to ten times higher) were observed for a series of oxazohne-phosphine complexes (e.g., 31). Several complexes, modified with bisphosphine monooxide and monosulfide ligands (Scheme 8.8, 32 and 33), were also used as catalysts precursors. The best reported turnover frequency is 0.6x10 mol (molh) at 80°C [62, 63]. A slightly lower activity was observed for fhe ketophosphine containing catalyst precursor 34 [64]. The activity of catalyst precursors 35, 36, and 37 is even lower [65]. 

Matyjaszewski et al. demonstrated that living ring opening metathesis polymerization (ROMP) could also be combined with ATRP to produce novel block copolymers [292]. ROMP of norbornene (NB) and dicyclopentadiene (CPD) were performed using an Mo-alkylidene complex, followed by reaction with p-(bro-momethyl) benzaldehyde to generate a benzyl bromide terminated polymer capable of being used as a macroinitiator for ATRP (Scheme 41). 

Ring-opening metathesis polymerization was also used recently for the preparation of amphiphilic star-block copolymers [25]. Mo (CH-f-Bu) (NAr) (0-f-Bu)2 was used as the initiator for sequential polymerization of norbornene-type, unfunctionalized and functionalized, monomers. The living diblocks were reacted with endo-ris-endo-hexacyclo- [ 10.2.1.1.3/115>8.02>l 1. O 1-9] heptadeca-6,13-diene, a difunctional monomer in a scheme analogous to the use of DVB in anionic polymerization, to form the central core of the star (Scheme 10). 

The living ROMP reactions of norbornene and norbornene derivatives have been used to make a variety of polymers possessing unusual properties. Copolymerization of selected functionalized norbornenes with norbornene has been used to synthesize star polymers and side-chain liquid crystal polymers. " This chemistry has also resulted in the preparation of phase separated block copolymers that contain uniform sized metal or semiconductor nanoparticles. The... 

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