Norbomene star polymers

The living ROMP reactions of norbomene and norbomene derivatives have been used to make a variety of polymers possessing unusual properties. Copolymerization of selected fimctionalized norbomenes with norbomene 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... 

The core-first approach was also adopted for the synthesis of star polymers. According to this procedure, the catalyst was reacted with the difunctional monomer to give the multifunctional initiator, followed by the addition of norbomene." Unfortunately, a multimodal product was obtained revealing the presence of linear chains, dimers, and star stmctures. 

Using the more successful arm-first approach, in-chain functionalized stars were prepared. 2,3-Dicarbomethoxynor-bomadiene was polymerized with the same catalytic systems followed by the addition of the difunctional monomer, leading to the desired functionalized star polymers. SEC revealed the presence of 10-20% unreacted homopolymers. Using the same procedure, star-block copolymers can also be prepared. 2,3-Dicarbomethoxynorbomadiene was initially polymerized followed by the addition of norbomene for the synthesis of the living diblock copolymers. Reaction of these living diblocks with the difiinctional monomer afforded the star-block copolymers with complete consumption of the living arms (Scheme 56). 

Another difiinctional monomer, endo-cis-endo-hexacydo-[10.2.l.l .l .0 .0 ]heptadeca-6,13-diene was also used for the synthesis of star polymers. Using the arm-first approach, star polymers of norbomene, 5,6-bis (methox3methyl)norbomene (DMNBE) and 5,6-bis(dicarbotri-methylsilyloxy) norbomene (TMSNBE) were obtained. Amphiphilic star-block copolymers were prepared by reacting... 

Figure 35).Another alternative to dendritic monomers involves the preparation of a dendritic core terminated in olefins which are available for metathesis with a catalyst s alkylidene such that the catalyst becomes incorporated at the ends of the dendrimer. From there, ROMP of monomers such as norbomene elongates the dendritic ends into linear arms to yield a star polymer with a dendritic core (Figure 36). Interestingly, prior to ROMP, the catalysts attached to the dendrimer reversibly dimerized at low temperatures and high concentrations. 

The introduction of monofunctional POSS macromers into an organic polymer by polymerization at the single reactive site leads to POSS-modified polymers. POSS macromers were incorporated in linear polymers, such as methacrylates, styrenics, norbomenes, ethylenes, propylenes, and urethanes in order to improve mechanical or thermal properties. If a multifunctional POSS with cross-linkable functions is used cross-linked materials are indeed formed. Star polymers are achieved if a multifunctional POSS unit contains initiator groups and a controlled polymerizatiOTi occurs, such as atom transfer radical polymerization. 

Amphiphilic star-block copolymers can be prepared by adding a polycyclic diene such as 238 to a living diblock copolymer made by sequential ROMP of (i) the monomer in Table 9 with R = COOSiMe3, and (ii) norbomene. The trimethylsilyl ester groups are then converted to carboxylic acids by soaking the cast film of the polymer in water for 2-3 days to give a product with a hydrophobic core of polynorbomene and a hydrophilic outer layer126,502. 

A real synthetic strength of the TEC reaction is its versatility with respect to ene substrates that can be used and include both activated and nonactivaed species such as norbomenes, (meth)acryl-ates, maleimides, and allyl ethers to name but a few (Yu et al., 2009). Recent examples describing the application of the thiol-ene reaction in the polymer/materials eld include the use in thioether dendrimer synthesis (Killops et al., 2008), convergent star synthesis (Chan et al., 2008), synthesis of multifunctional branched organosilanes (Rissing and Son, 2008), and modi -cation/functionalization of wide range of polymers (Justynska and Schlaad, 2004 Killops et al., 2008). 

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