Ezat Khosravi

Tailored copolymers via coupled anionic and ring opening metathesis polymerization. Synthesis and polymerization of bicyclo[2.2.1]hept-5-ene-2,3-trans-bis(polystyrylcarboxylate)s

Abstract The preparation of polystyrene macromonomers containing a norbornene unit and their living ring opening metathesis polymerization (ROMP) to produce comb graft copolymers is described. The ROMP was initiated by the well defined Schrock initiators, Mo(CHR)(NAr)(OR′)2, where R is (CH3)3C or C6H5C(CH3)2, Ar is 2,6-diisopropylphenyl and R′ is (CH3)3C. Well characterized macromonomers and comb graft copolymers with polystyryl grafts with average degrees of polymerization (DPs) of 4, 7, and 9 were successfully produced. The graft copolymers exhibit single mode molecular weight distributions and narrow polydispersities. Attempts to prepare copolymers with longer polystyryl grafts gave products which exhibited bimodal molecular weight distributions in which one component of the distribution had the same retention time as that of the macromonomer, this observation is rationalized in terms of steric inhibition of the ROMP of such macromonomers.

Synthesis of well-defined graft copolymers via coupled living anionic polymerization and living ROMP

Abstract Well-characterized polystyrene macromonomers containing a norbornene unit at the chain end were prepared by capping living polystyrene with exo-5-norbornene-2-carbonyl chloride. The macromonomers were then ring opened polymerized using well-defined Schrock molybdenum initiators, Mo(N-2,6-i-Pr2C6H3)(OCMe3)2(CHR) where R is CMe3 or CMe2Ph, to produce well-defined graft copolymers. Well-characterized graft copolymers with polystyryl grafts of average degrees of polymerization 15, 22, 35, 50, 100 and 130 were successfully prepared. Ring opening metathesis polymerization (ROMP) of macromonomers with a molecular weight of 1550 ( DP =13 ) goes to completion at a macromonomer:initiator molar ratio of 200:1. Ring opening metathesis polymerization of macromonomers with molecular weights of 3500 and 4900 ( DP s of 32 and 46, respectively) also goes to completion even at comparatively high macromonomer:initiator molar ratios of 100:1. This produces relatively long polynorbornene backbone chains with relatively short polystyrene grafts. On the other hand, macromonomers with number average molecular weights of 10 200 and 13 200 ( DP s of 96 and 127) are completely polymerized only up to macromonomer:initiator molar ratios of 20 and 10:1, respectively. Beyond this stage polymerization stops without destruction of the living chain ends before complete consumption of macromonomers, giving short polynorbornene backbone chains with relatively long polystyrene grafts.

Dielectric and pyroelectric properties of poly[2,3-bis(trifluoromethyl)norbornadiene]

The fluoropolymer poly[2,3-bis(trifluoromethyl)norbornadiene] (poly(BTFMND)) has been synthesized via ring-opening metathesis polymerization, using initiators based on W, Mo or Ru compounds or via variations of the Schrock-type initiator Mo(CHR)(N-2,6-C 6 H 3 -i-Pr 2 )(OR′) 2 (R = CMe 3 , CMe 2 Ph; R′ = CMe 3 , CMe(CF 3 ) 2 ), giving poly(BTFMND) with controllable proportions of trans -vinylene units. Analysis of the 13 C nuclear magnetic resonance fine structure establishes that the high- trans (> 98%) polymer is 92% tactic and the high- cis (> 98%) polymer is 75% tactic, but these methods cannot determine whether the material is predominantly isotactic or syndiotactic. Dielectric and thermally stimulated current measurements have been performed and give relaxed permittivities % strongly dependent on trans content, ranging from above 40 for the 98% trans material through 15 for the 54% trans polymer to 6 for 98% cis polymer. The significantly higher permittivity above T g for the high- trans material than for the 54% trans polymer and the significantly reduced value for the 98% cis polymer suggest that both the high- cis and high- trans materials have syndiotactic structures. The total polarization for free films of 98% trans poly(BTFMND) saturates at about 20 mC m −2 , with a pyroelectric coefficient approaching 6 μ C m −2 K −1 above poling fields of 200 MV m −1 . These usefully high values combined with low dielectric loss in its glassy state at ambient temperatures indicate an excellent material for potential use as a pyroelectric transducer, with a figure of merit comparable with or better than that of poly(vinylidene fluoride).

Structure property relationships in linear and cross-linked poly(imidonorbornenes) prepared using ring opening metathesis polymerisation (ROMP)

Abstract The production and properties of a new family of materials synthesised via ring opening metathesis polymerisation (ROMP) is described. The monomers offer potential alternatives to dicyclopentadiene (DCPD) for either reaction injection moulding (RIM) or resin transfer moulding (RTM) use and provide new materials with an extended range of properties vis-a-vis poly(DCPD). Improvements include lower monomer odour together with control of both the reaction rate and the crosslinking reaction. A series of monofunctional imidonorbornene monomers, with different N-alkyl side chains, were polymerised to give a range of linear polymers, and, by copolymerisation with difunctional monomers with different N,N′-alkylene spacer lengths, a range of crosslinked materials. Processing conditions were established which gave over 95% conversion of the monomer for the linear materials, and over 95% gel fraction for the crosslinked materials. For the crosslinked materials, a value of the monomer:initiator ratio was established which gave homogeneously cured materials. The glass transition temperature (Tg) of the linear polymers was found to depend on the length of the alkyl side chain, while a sub Tg, β relaxation was observed, the position of which was independent of the side chain length. For the crosslinked polymers, the molecular weight between crosslinks was found to be lower than expected at low percentage loading of the crosslinking unit, and this was attributed to the contribution of physical crosslinks. At higher percentage loading of the crosslinking unit, the molecular weight between crosslinks was higher than expected, suggesting that under these conditions not all the crosslinking units were fully bound into the network, i.e. bound at both ends. Mechanical properties of the various materials were measured using the three-point bend geometry. Of particular interest were the high values of yield strength and toughness of the crosslinked polymers, which are comparable to known ‘high toughness’ materials, such as polycarbonate.

Synthesis of fluorinated polymers via ROMP: a review

Abstract This review is concerned with the work conducted in the Durham group during the last twenty years. It is specifically concerned with ROMP of fluorinated monomers with classical and well-defined initiators, with the synthesis of stereoregular polymers, block and stereoblock copolymers.

Bimolecular termination in living ring opening metathesis polymerization

Abstract Previously observed high molecular weight impurities in the products of living ring opening metathesis polymerizations are identified as arising from a post-polymerization bimolecular dimerization initiated by dioxygen.

Approaches to highly polar polymers with low glass transition temperatures. 1. Fluorinated polymers via a combination of ring-opening metathesis polymerisation and hydrogenation

Abstract The synthesis and hydrogenation of two fluorinated polymers is described. The products were characterised through a detailed study of their 1 H-, 13 C- and 19 F-NMR spectra, together with thermal and GPC analysis. Hydrogenation resulted in a significant lowering of the glass transition temperatures of the polymers.

ROMP of n-alkyl norbornene dicarboxyimides: from classical to well-defined initiators, an overview

Abstract The ring opening metathesis polymerisation (ROMP) of n -alkyl norbornene dicarboxyimides using a wide range of initiators has been extensively studied. ROMP of exo - n -alkyl norbornene dicarboxyimides with classical initiators WCl 6 /Me 4 Sn ( I ) and MoCl 5 /Me 4 Sn ( II ) gave polymers with 63% and 85% trans vinylene content, respectively. In contrast, the endo -isomer could not be polymerised in any of several attempts. Both exo -and endo - n -alkyl norbornene dicarboxyimides were polymerised using well-defined initiators Mo(CH- t -Bu)( N -2,6- i -Pr 2 C 6 H 3 )(OCMe 3 ) 2 ( III ) and Mo(CHCPhMe 2 )( N -2,6- i -Pr 2 C 6 H 3 )(OCMe(CF 3 ) 2 ) 2 ( IV ). In the case of exo isomers, III gave polymers with 97% trans vinylene content and IV gave polymers with about 30% trans vinylene content. In the case of endo isomer, III gave polymer with 93% trans vinylene content and IV gave polymer with 57% trans vinylene content. The living nature of these polymerisations was confirmed by synthesising AB diblock copolymers by sequential addition of monomers. Both exo - and endo - n -alkyl norbornene dicarboxyimides were also polymerised using well-defined initiator RuCl 2 (CHPh)(PCy 3 ) 2 ( V ). The polymers obtained from exo and endo monomers contain 82% and 100% trans vinylene content respectively. The course of the polymerisation reactions using well-defined initiators III – V were followed by 1 H NMR and both the initiator and propagating alkylidenes signals were observable. The multiplicity and broadening of the backbone resonances in 13 C NMR, in all cases, is consistent with a multiplicity of overlapping environments associated with atactic microstructures.

Ring opening metathesis polymerisation of n-alkyl norbornene dicarboxyimides using well-defined initiators

Abstract Exo - n -alkyl norbornene dicarboxyimides and endo - n -octyl norbornene dicarboxyimide were polymerised by ring opening metathesis polymerisation using well-defined initiators Mo(CH- t -Bu)(NAr)(OCMe 3 ) 2 and Mo(CHCPhMe 2 )(NAr)(OCMe(CF 3 ) 2 ) 2 . Using Mo(CH- t -Bu)(NAr)(OCMe 3 ) 2 and Mo(CHCPhMe 2 )(NAr)(OCMe(CF 3 ) 2 ) 2 as initiators with the exo -monomers gave polymers with 97% trans and 70% cis vinylene content, respectively, and with the endo -monomer gave polymers with 93% trans and 57% trans vinylene content. In both cases the 13 C n.m.r. spectra were complex indicating that these polymers are essentially atactic. 1 H n.m.r. Spectroscopy and GPC analyses of polymeric materials prepared from exo - and endo -monomers demonstrated that the initiator carrying t-butoxy ligands gives fairly well-defined living polymerisation; whereas with the initiator bearing fluorinated ligands propagation is significantly faster than initiation which leads to much higher molecular weights than expected on the basis of monomer to initiator ratio and a broadening of the molecular weight distribution. The living character of these systems was confirmed by the synthesis of AB diblock copolymers via sequential addition of monomers. A series of block copolymers were prepared using exo - n -alkyl norbornene dicarboxyimides as monomer and 2,3-bis(trifluoromethyl)norbornadiene as comonomer. The glass transition temperatures of the polymers obtained from endo -monomers are significantly higher than those of the poly( exo - n -alkyl norbornene dicarboxyimide)s, probably as a consequence of a stiffer less mobile backbone resulting from the endo repeat units.

Ring-opening metathesis polymerization of 7-methylbicyclo[2.2.1]hepta-2,5-diene initiated by well-defined molybdenum and ruthenium carbene complexes

Abstract Polymers of 7-methylnorbornadiene (7-MNBD) have been prepared by ring-opening metathesis polymerization (ROMP) using Mo(CHCMe 2 Ph)(NC 6 H 3 -2,6- i- Pr 2 )(OR) 2 [ 1 , OR=OCMe(CF 3 ) 2 ; 2 , OR=OCMe 3 ], Mo(CHCMe 3 )(NC 6 H 3 -2,6- i- Pr 2 )(OR) 2 ( 2′ ) and Ru(CHPh)Cl 2 (PCy 3 ) 2 ( 3 ) as initiators in CD 2 Cl 2 . The structures of the polymers were investigated by 1 H- and 13 C-NMR spectroscopy. In all cases the ROMP was very fast and the initial product was essentially a polymer of anti units, linked by 88% cis double bonds for initiation by 1 , 68% for 2 or 2′ , and 17% for 3 . The tacticities of the polymers varied from atactic using 1 as initiator to fully tactic ( t/m and c/r ) using 2 or 2′ as initiator. Values of k p /k i were derived from the proportion of initiator consumed and the initial ratio of monomer to initiator: k p /k i =550 for 1 , 1100 for 2 , 64 for 2′ , and 61 for 3 . Two kinds of secondary reaction were observed: the first gave rise to a second set of 13 C-NMR peaks (10–20% of the intensity of the main peaks), and the second, observed only with 1 , was characterised by sudden gelation of the reaction mixture some time after the monomer had been consumed, and was followed by a marked fall in the intensity of the main 13 C-NMR peaks. These effects are attributed to secondary intra- and inter-molecular metathesis reactions, respectively. The high- trans polymer could be fully hydrogenated, but the high- cis polymer could only be partially hydrogenated.