Norbornene monomers, ring-opening metathesis

Wolfe and Wagener have developed main-chain boronate polymers (59) (Fig. 38) by the acyclic diene metathesis (ADMET) polymerization of symmetrical ,oj-dienes, containing both methyl- and phenyl-substituted boronate functionalities using Mo and Ru catalysts.84 The ring-opening metathesis polymerization (ROMP) of several norbornene monomers containing methyl- and phenyl-substituted boronates into... 

The living character of the ring opening metathesis polymerization described earlier in this review enables a simple preparation of functionalized norbornene-based monoliths. Adding one more in situ derivatization step that involves functional norborn-2-ene and 7-oxanorborn-2-ene monomers that react with the surface-bound initiator, the pores were provided with a number of typical functional groups such as carboxylic acid, tertiary amine, and cyclodextrin [58,59]. 

With the discovery of ruthenium carbene complexes as highly effective catalysts for olefin metathesis under mild reaction conditions [233,234], the scope of ring-opening metathesis polymerization could be extended to include functionalized and sensitive monomers. The resulting (soluble) polymers have been used as supports for simple synthetic transformations [235-237]. Insoluble polymers have been prepared by ringopening metathesis copolymerization of norbornene with l,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene. These polymers have been used as supports for ruthenium carbene complexes [238]. 

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). 

Scheme 7.36 Synthetic scheme for the polymerization of norbornene and its derivatives via free radical polymerization (FRP), ring-opening metathesis polymerization (ROMP), and vinyl addition polymerization (VAP) techniques. Polymers I, II, and III are isomers that differ in their enchainment and physical properties. Co- and terpolymerization of norbornene and derivatives of norbornene with other alicyclic monomers such as maleic anhydride, methyltetracyclododecene carboxylic acid, etc. are also successfully synthesized with this scheme. (Note that 2, 3- and 2,7-enchainments of repeating units are reported in type I polymers. °°)...

For the ring-opening metathesis polymerization (ROMP) in heterophase [81], a water-soluble ruthenium alkylidene was employed for the emulsion polymerization of norbornene, and an oil-soluble catalyst for the miniemulsion polymerization of norbornene and 1,5-cyclooctadiene. Similar to the polymerization of ethylene in heterophase, an organic solution of the catalyst was first miniemulsified in water, after which the monomer was added to the miniemulsion. This resulted in a high monomer conversion for norbornene ( up to 97%), and a particle size of 250nm. 

This is the case of the first study reporting on the ROMP of fatty-acid derivatives [57], a subject that has been studied by the research team of Larock for almost a decade. In this first publication, castor oil was functionalised with 5-norbornene-2,3-dicarboxylic anhydride. Resulting monomer structure was submitted to ring-opening metathesis copolymerisation with cyclooctene (Scheme 5.15) to produce thermoset polyesters with good thermo-mechanical properties. 

In the search of novel materials with low dielectric constants (e) and low water absorption for the electronics industry as well as transparent, high oxygen permeable and crosslinkable materials for the fast production of contact lenses, the Ring-Opening Metathesis Polymerization (ROMP) became an interesting opportunity for our company [1]. In 1988, it was shown, that strained (heterocyclic) monomers with or without pendant functionalities, especially 7-oxa-norbornene (7-oxabicyclo[2.2.1]hept-5-ene) type monomers, can be efficiently polymerized in aqueous solutions at moderate temperatures (Scheme 1) [2]. 

Metallocene/methylaluminoxane (MAO) and other single site catalysts for olefin polymerization have opened a new field of synlhesis in polymer chemistry. Strained cyclic olefins such as cyclobutene, cyclopentene, norbornene (NB), and their substituted compounds can be used as monomers and comonomers in a wide variety of polymers." Much interest is focused on norbornene homo- and copolymers because of the easy availability of norbornene and the special properties of their polymers. Norbornene can be polymerized by ring opening metathesis polymerization (ROMP), giving elastomeric materials, or by double bond opening (addition polymerization). Homopolymerization of norbornene by double bond opening can be achieved by early and late transition metal catalysts, namely Ti, Zr, Hf, Ni, - ° and Pd (Scheme 16.1). 

The ring-opening metathesis polymerization of side chain functionalized norbornene monomers was applied to obtain electroluminescent polymers (Scheme 38) [100,101]. Homo- and copolymers with 25 or 50 repeat units were prepared with ranging from 19,400-53,000Da and M jM = 1.02-1.04. The color of emission could be fine tuned by... 

We have reported that norbornene monomers functionalized with arene complexes also undergo ring-opening metathesis polymerization to produce the corresponding cyclopentadienyliron-coordinated polynorbomenes. Scheme 13 shows the synthesis of polymers containing aromatic ether sidechains functionalized with organoiron moieties. ... 

Scheme 3 Ring-opening metathesis polymerization of the bicyclic monomers (norbornene and its derivatives).

Ring-opening metathesis polymerization (ROMP) of norbornene monomers (91) (Scheme 11) fimctionalized with cyclopentadienyliron cations has been accomplished using transition metal catalysts to yield the corresponding organoiron polymer (92). The resulting polynorbomene has the metallic moieties present in the... 

Schrock, Gibson et al. [52d] found that styrene and 1,3-pentadiene could be used as chain transfer reagents for the living ring-opening olefin metathesis polymerization of norbornene with molybdenum based catalyst 35a. Renewed norbornene addition to a polymerization mixture containing initiator 35a and 30 equivalents of styrene resulted in the formation of polynorbomene with a low polydispersity and a molecular weight controlled by the number of norbornene equivalents in each of the individual monomer solutions, Eq. (38). This method allows a more efficient use of the catalyst. 

The ring-opening polymerization of a simple cyclic olefin such as cyclooctene yields two structures of maximum order, which are distinguished by the configuration (cis or irans) of their main-chain olefins. In contrast, polymers made from bicyclic olefins such as norbornene are inherently more complicated and have four structures of maximum order (Scheme 24). In addition to cis- and trans-olefins, the polymers can also be isotactic or syndiotactic. The stereochemistry of these polymers becomes even more complicated when the monomer is asymmetric, since head—head, head—tail, and tail—tail regioisomers are possible. Nevertheless, single-site metathesis catalysts have been developed that can control polymer stereochemistry to an impressive degree by both chain-end and site-control mechanisms. ° ° ... 

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