Microstructure metathesis-polymer

To conclude this section, an example is given of the application of statistical models to examine double bond sequences in polymers with unsaturated backbones. The presence of backbone unsaturation leads to the occurrence of cisitrans isomerism and this can be treated entirely analogously to comonomer sequence. Ivin [42] and others have used NMR spectroscopy extensively to study the microstructure of polymers prepared by transition metal catalysed ring-opening metathesis polymerisation (ROMP) such as polynorbornene (PNB). 

Abstract For the first time, cyclopentene (CPE) has been copolymerized with the strained cycloolefin norbomene (NBE) using catalytic amounts of the electrochemi-cally prepared metathesis catalyst. The microstructure of polymers was determined by H NMR and NMR spectroscopy. The polymers were also characterized by differential scanning calorimehy and gel permeation chromatography (GPC) techniques. 

We have reported the first example of a ring-opening metathesis polymerization in C02 [144,145]. In this work, bicyclo[2.2.1]hept-2-ene (norbornene) was polymerized in C02 and C02/methanol mixtures using a Ru(H20)6(tos)2 initiator (see Scheme 6). These reactions were carried out at 65 °C and pressure was varied from 60 to 345 bar they resulted in poly(norbornene) with similar conversions and molecular weights as those obtained in other solvent systems. JH NMR spectroscopy of the poly(norbornene) showed that the product from a polymerization in pure methanol had the same structure as the product from the polymerization in pure C02. More interestingly, it was shown that the cis/trans ratio of the polymer microstructure can be controlled by the addition of a methanol cosolvent to the polymerization medium (see Fig. 12). The poly(norbornene) prepared in pure methanol or in methanol/C02 mixtures had a very high trans-vinylene content, while the polymer prepared in pure C02 had very high ds-vinylene content. These results can be explained by the solvent effects on relative populations of the two different possible metal... 

Since its discovery more than 50 years ago, olefin metathesis has evolved from its origins in binary and ternary mixtures of the Ziegler-Natta type into a research area dominated by well-defined molecular catalysts. Surveys of developments up to 1993 were presented in COMC (1982) and COMC (1995). Major advances in ROMP over the last 10 years include the development of modular, stereoselective group 6 initiators, and easily handled, functional-group tolerant ruthenium initiators. The capacity to tailor polymer functionality, chain length, and microstructure has expanded applications in materials science, to the point where ROMP now constitutes one of the most powerful methods available for the molecular-level design of macromolecular materials. In addition to an excellent and comprehensive text on olefin metathesis, a three-volume handbook s has recently appeared, of which the third volume focuses specifically on applications of metathesis in polymer synthesis. 

The above examples show that the ring-opening metathesis polymerisation of cycloolefins, even simple substituted bicyclic olefins, gives rise, in principle, to polymers with a very wide range of microstructures defined by the frequency and distribution of cis and trans vinylene units, m and r diads and h-h, t-t or h-t arrangements of cycloaliphatic units. 

Polymers with carbon-carbon double bonds in their backbone can undergo two types of metathesis, both leading to degradation. In an intramolecular reaction cyclic oligomers are formed, while many unsaturated polymers can be degraded by intermolecular cross-metathesis with low-molecular-weight olefins. Identification of the degradation products provides valuable information on the microstructure of the polymer [7] (cf Section 3.3.10.1). 

Analytical Degradation of Polyalkenylenes. - Microstructure characterization of polyalkenylenes via metathetical degradation with a low-molecular-weight olefin continues to be investigated.High yields of degradation products of unmodified polymers and copolymers are usually obtained in contrast, the metathesis degradation products of modified polyalkenylenes is much less reproducible, and low yields are obtained. ... 

ButG5H3, G9H6) have been synthesized either by the standard salt metathesis or the amine elimination procedure. These compounds are used as pre-catalysts for norbornene homopolymerization and ethylene-norbornene co-poly-merization. The influence of the catalyst symmetry and structure on the activity, norbornene incorporation, and polymer and co-polymer microstructure has been studied.706... 

These secondary metathesis reactions of course may also affect the microstructure of the polymers, e.g., the fraction of cis double bonds [275,283]. The extend of these reactions depends in particular on steric factors and the activity of the applied catalyst. The sterical shielding of polynorbomenes backbone by the 5-membered rings is probably responsible for the low reactivity in degradation reactions via cross methathesis with acyclic olefins, too [276]. 

On the other hand, a hi -trans polymer is formed with TiCU/AlEts [370,380] or WCle in presence of suitable cocatalysts (e.g., AlEts) [380,381], Not only the catalyst and cocatalyst choosen are crucially for the microstructure of the resulting polypentenamers, but also the particular reaction conditions, especially the temperature or concentration [379], Selected examples for the ring-opening metathesis polymerization of cyclopentene are listed in Table 10. 

Polymers formed by the ring-opening metathesis polymerisation (ROMP) reaction [54] exhibit a wide variety of microstructures which may be evaluated by specctroscopic techniques. The first ROMP polymers were analysed by IR spectroscopy [55], but that can only determine the absolute stereochemistry of... 

A new synthetic method to prepare soluble phenyleneviny-lene polymers by the ring-opening metathesis polymerization (ROMP) of 4,7,12,15-tetraoctyloxy-[2.2]paracyclophane-1,9-diene was also presented under microwave irradiation (Figure 23). The polymerization showed a living character and gave polymers of controlled molecular weight, with a narrow polydispersity, fewer chain defects, and an alternating cis, trans-microstructure. 

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