Synthesis and characterization of hafnium and molybdenum bifunctional initiators for the preparation of triblock copolymers

Abstract

Chapter 1. Three monofunctional mixed alkyl hafnium complexes containing the (MesNpy)2 ligand ([(MesitylNCH2)2CMe(2-CsH4N)]2) were synthesized. (MesNpy)Hf(Neo)R ((2b), R = Me; Neo = CH2CMe2Ph) and (MesNpy)Hf(CH2TMS)(R), ((3b), R = Me and (4b), R = i-Bu)) were activated with {Ph3C} {B(C6F5)4} and one alkyl group was selectively removed in all cases. The kinetics of activated 4b were studied and the resulting complex was an initiator for the living polymerization of 1-hexene, with the exception of a slight initiation effect. Five linker molecules were investigated for the preparation of bifunctional hafnium mixed alkyl complexes. One complex synthesized, disilyl[(MesNpy)HfMe]2 (disilyl(X)2 = X-CH2SiMe2(CH2)5SiMe2CH2-X) was activated with {Ph3C} {B(C6F5)4} and the methyl groups were successfully removed to form {disilyl[(MesNpy)Hf]2} {B(C6F5)4}2. This complex was also a living catalyst for the polymerization of a-olefins.

Chapter 2. Addition of p-divinylferrocene to Mo(CHCMe2Ph)(NAr)(ORF6)2 (ORF6 = OCMe(CF3)2; Ar = 2,6-diisopropylphenyl) produced the bimetallic species [Mo(NAr)(ORF6)2(=CHC5H4)]2Fe (6), which upon treatment with lithium tert-butoxide produced the related tert-butoxide complex (7). X-ray crystallography studies of 6 and 7 showed them to be "syn/syn " bimetallic species. In solution, two resonances can be observed in 'H NMR spectra in the alkylidene region for the "syn/anti" isomer of 6 and 7; the total amounts were 4 and 8%, respectively. Bimetallic species 6 and 7 have been shown to initiate competitively at both ends and to produce homopolymers of 2,3-dicarbomethoxynorbornadiene (DCMNBD) and methyltetracyclododecene (MTD) in a living fashion. MALDI-TOF mass spectra of ferrocene-containing species were obtained and are consistent with the polymerization process being living. Triblock copolymers (poly[(MTD)x/2(DCMNBD)y(MTD)y(MTD)x/2]) were prepared by adding y equivalents of DCMNBD to the bimetallic initiators followed (after consumption of DCMNBD) by x equivalents of MTD. These triblocks were shown to be of high purity (free of homopolymer and diblock copolymers) and to have relatively low PDIs (< 1.2).

Chapter 3. A series of monomers suitable for ring opening metathesis polymerization (ROMP) containing a side chain liquid crystal mesogen were synthesized, where the mesogen was biphenyl-4-carboxylic acid 4-(1-butoxycarbonyl-ethoxy)-phenyl ester (abbreviated as BPP4). Two of the monomers have BPP4 attached to norbornene with a six or ten carbon spacer ((R)-4'- (5-bicyclo[2.2.1 ]hept-5-en-2-yl-pentyloxy)-BPP4, NB6wBPP4, and (R)-4'-(10- bicyclo[2.2.1]hept-5-en-2-yl-decyloxy)-BPP4, NB10OwBPP4, respectively), and the third monomer has BPP4 attached to norbornadiene via a ten carbon spacer ((R)-4'-(10- bicyclo[2.2.1]hepta-2,5-dien-2-yl-decyloxy)-BPP4, NBD10wBPP4). The monomers were polymerized by ROMP using the bimetallic initiator, [Mo(NAr)(ORF6)2(=CHCsH4)]2Fe (Ar = 2,6-diisopropylphenyl; ORF6 = OCMe(CF3)2). ABA triblock copolymers were also synthesized where the B block is NBD10OwBPP4 or NBnwBPP4 (n = 6, 10) and the A block is methyltetracyclododecene (MTD). All polymerizations are living with isolated yields greater than 90% and PDI values ranging from less than 1.05 to 1.31. The triblock copolymers were found to have glass transition temperatures of the inner block at approximately 20 'C and smectic to isotropic transitions around 150 'C. Small angle X-ray scattering (SAXS) indicated that the triblock copolymers exhibit phase segregation. SAXS data demonstrated that the triblock copolymer containing NB6wBPP4 forms smectic C* monolayers while the triblock copolymers that contain NB10OwBPP4 and NBD10wBPP4 form smectic C* bilayers at room temperature. Dynamic mechanical analysis of the triblock copolymers reveals an elastic plateau above the glass transition temperature of the center block, suggesting these systems may be interesting materials for shape-memory elastomers.

Chapter 4. The reaction of [Mo(NAr)(ORF6)2]2DVF (ORF6 = OCMe(CF3)2; Ar = 2,6- diisopropylphenyl; DVF = divinylferrocene) with lithium pyrrolide (LiPyr) or lithium 2,5- dimethylpyrrolide (LiMe2Pyr) formed the complexes [Mo(NAr)(Pyr)2(=CHCsH4) 2Fee2Li(Pyr) (8) and Mo(NAr)(Me2Pyr)2(=CHCsH4)]2Fe (9), respectively. X-ray crystallography studies of 8 reveal it to be a dimer of imetallic complexes while 9 is a monomer in the solid state. The reaction of [(DME)Mo(NAr)(ORF6)2]2DVB (DVB = ivinylbenzene; DME = dimethoxyethane) with LiMe2Pyr formed [Mo(NAr)(Me2Pyr)2(=CH)]2(1,4-C6H-4) (10). The reactivities of 8, 9, and 10 with various diols were studied. Three compounds, namely, [Mo(NAr)(Biphen)(Biphen)(=CHC5H4)2Fe (11, H2[Biphen] = 3,3'-di-tert-butyl-5,5',6,6'- tetramethylbiphenyl-2,2'-diol), [Mo(NAr)(Benz2Bitet)(=CH)]2(1,4-C6H4) (12, (R)- H2[Benz2Bitet] = (R)-3,3'-dibenzhydryl-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2,2'-diol) and [Mo(NAr)(MesBitet)(=CH)]2(1,4-C6H4) (13, (R)-H2[MesBitet] = (R)-3,3'-dimesityl- 5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2,2'-diol) were found to be isolable compounds and could be generated cleanly in situ. 2,3-Dicarbomethoxynorbomadiene (DCMNBD) and 2,3- bis(trifluoromethyl)norbornadiene (NBDF6) were polymerized using initiators 11, 12, and 13, both isolated and in situ generated. Poly(DCMNBD) and poly(NBDF6) prepared with 12 and 13 were found to be highly cis and highly tactic. Triblock copolymers were also prepared, and the tacticity of the polymer was maintained.

Appendix A. Various monomers suitable for ROMP were synthesized for optimized application in thermoplastic liquid crystal elastomers. Two new inner block monomers, CBEwBPP4 [4-(1- butoxy-l-oxopropan-2-yloxy)phenyl 4'-(2-(2-(cyclobut-2-enylmethoxy)ethoxy)ethoxy)biphenyl- 4-carboxylate] and ONBwMPOB [4-methoxyphenyl 4-(4-(7-oxabicyclo[2.2.1]hept-5-en-2- ylmethoxy)butoxy)benzoate] were polymerized and the thermal properties of the polymers were studied. Poly(CBEwBPP4) exhibited a glass transition temperature (Tg) of -10 oC but no liquid crystal (LC) transition was observed. Poly(ONBwMPOB) exhibited a Tg of 15 oC and a broad LC transition was observed around 40 TC. Three new outer block monomers, exo-4-cyclohexyl- 4-aza-tricyclo[5.2.1.02,6]dec-8-ene-3,5-dione (NBwNCy), [3-(4-fluoro-benzoyl)- bicyclo[2.2.1 ]hept-5-en-2-yl]-(4-fluoro-phenyl)-methanone, (NBwCOPhF), and bicyclo[2.2.1]hept-5-en-2-yl-phenyl-methanone (NBwCOPh) were also polymerized and their thermal properties were studied.