Block copolymer metallocene polymerization

The first reactor-type thermoplastic polyolefin (R-TPO) was LLDPE/PP [Yamazaki and Eujimaki, 1970, 1972]. The three-component R-TPO s (PE with PP and EPR) soon followed [Strametz et al, 1975]. PE was also polymerized in the presence of active catalyst and an olefinic copolymer [Morita and Kashiwa, 1981]. Blending amorphous co-polyolefins with crystalline PO s (HDPE, LLDPE, PP), and a filler resulted in moldable blends, characterized by excellent sets of properties [Davis and Valaitis, 1993, 1994]. Blends of polycycloolefin (PCO) with a block copolymer (both polymerized in metallocene catalyzed process) and PE, were reported to show outstanding properties, viz. strength, modulus, heat resistance and toughness [Epple and Brekner, 1994]. 

A half-metallocene iron iodide carbonyl complex Fe(Cp)I(CO)2 was found to induce the living radical polymerization of methyl acrylate and f-bulyl acrylate with an iodide initiator (CH3)2C(C02Et)I and Al(Oi- Pr)3 to provide controlled molecular weights and rather low molecular weight distributions (Mw/Mn < 1.2) [79]. The living character of the polymerization was further tested with the synthesis of the PMA-fc-PS and PtBuA-fi-PS block copolymers. The procedure efficiently provided the desired block copolymers, albeit with low molecular weights. 

Metallocene catalysis has been combined with ATRP for the synthesis of PE-fr-PMMA block copolymers [123]. PE end-functionalized with a primary hydroxyl group was prepared through the polymerization of ethylene in the presence of allyl alcohol and triethylaluminum using a zirconocene/MAO catalytic system. It has been proven that with this procedure the hydroxyl group can be selectively introduced into the PE chain end, due to the chain transfer by AlEt3, which occurs predominantly at the dormant end-... 

As stated above, we postulated that fast, reversible chain transfer between two different catalysts would be an excellent way to make block copolymers catalytically. While CCTP is well established, the use of main-group metals to exchange polymer chains between two different catalysts has much less precedent. Chien and coworkers reported propylene polymerizations with a dual catalyst system comprising either of two isospecific metallocenes 5 and 6 with an aspecific metallocene 7 [20], They reported that the combinations gave polypropylene (PP) alloys composed of isotactic polypropylene (iPP), atactic polypropylene (aPP), and a small fraction (7-10%) claimed by 13C NMR to have a stereoblock structure. Chien later reported a product made from mixtures of isospecific and syndiospecific polypropylene precatalysts 5 and 8 [21] (detailed analysis using WAXS, NMR, SEC/FT-IR, and AFM were said to be done and details to be published in Makromolecular Chemistry... 

Block copolymers have been successfully synthesized because many metallocene polymerizations of MMA proceed as living polymerizations, and it is possible to have a single one-way crossover from carbanion (alkene) polymerization to MMA (enolate) polymerization with metallocene and related initiators, especially when group 3 transition metal initiators are used [Boffa and Novak, 2000 Desurmont et al., 2000a,b Jin and Chen, 2002 Yasuda et al., 1992],... 

It was also reported that terminally borane-containing POs is available as another macroinitiator to prepare block copolymers (Fig. 4). These polymers were prepared by (1) the metallocene-catalyzed (co)polymerization of olefin(s) with organoborane compounds, for example, 9-borabicyclononane (9-BBN), as chain transfer agents [32], or by (2) the hydroboration of terminally unsaturated polyolefins with BBN [33-36]. 

The synthetic procedure of PE-fo-PCL using hydroxyl terminated polyethylene was reported [39]. Terminally hydroxylated polyethylene was prepared during a metallocene-catalyzed polymerization using controlled chain transfer reaction with alkylaluminum compounds. PE-fo-PCL block copolymer was synthesized from terminally hydroxylated PE and e-caprolactone (e-CL) using Sn(Oct)2 as a catalyst for ring opening polymerization. 

Block copolymers can be produced from terminally borane-containing polyolefins. These borane-containing POs can be synthesized by the metallocene-catalyzed (co)polymerization of olefin(s) monomer with 9-BBN as a chain transfer agent or by the metallocene catalyzed copolymerization of olefins with allyl-9-BBN [55,56], as referred to above. Alternatively, borane-containing POs were prepared by hydroboration of terminally unsaturated PO, for instance, terminally vinyl PE and terminally vinylidene PP [33-35,57]. Such method could produce diblock copolymers, such as polyethylene-block-poly(methyl methacrylate) (PE-fo-PMMA), polypropylene-foZock-poly(methyl methacrylate) (PP-fc-PMMA), polypropylene-foZock-poly(butyl methacrylate) (PP-fc-PBMA), and PP-fc-PS. 

It has also been demonstrated that a PP-fc-EPR block copolymer was prepared with a living polymerization catalyst composed of V(acac)3/AlEt2Cl at -78 °C [ 145]. Also, PP-fo-EPR was produced with metallocene catalyst systems at -78 °C [146],... 

Insite Not a process, but a range of constrained-geometry metallocene catalysts for polymerizing olefins. Olefin block copolymers made using these catalysts have the trade name Infuse. Developed by J.C. Stevens at the Dow Chemical Company, for which he received several medals. 

Neutral lanthanide-series metallocenes exhibit the remarkable ability to polymerize polar monomers such as methyl methacrylate to highly stereoregular polymers of extremely narrow molecular weight distribution (Mw/Mn 1) (equation 14). It is possible to prepare block copolymers of ethylene and poly(methyl methacrylate) by first adding MMA to Cp 2SmMe to produce a PMMA segment followed by addition of ethylene the reverse order of addition fails to give block materials because the ethylene monomer cannot insert into the enolate. 

The dual function of the precatalysts 4 opened the way to well-controlled block polymerization of ethylene and MMA (eq. (5)) [89, 90]. Homopolymerization of ethylene (Mn = 10000) and subsequent copolymerization with MAA (Mn 20000) yielded the desired linear AB block copolymers. Mono and bis(alkyl/silyl)-substituted flyover metallocene hydride complexes of type 8 gave the first well-controlled block copoymerization of higher a-olefins with polar monomers such as MMA or CL [91]. In contast to the rapid formation of polyethylene [92], the polymerization of 1-pentene and 1-hexene proceeded rather slowly. For example, AB block copolymers featuring poly( 1-pentene) blocks (M 14000, PDI = 1.41) and polar PMMA blocks (M 34000, PDI = 1.77) were obtained. Due to the bis-initiating action of samarocene(II) complexes (Scheme 4), type 13-15 precatalysts are capable of producing ABA block copolymers of type poly(MMA-co-ethylene-co-MMA), poly(CL-co-ethylene-co-CL), and poly(DTC-co-ethylene-co-DTC DTC = 2,2-dimethyltrimethylene carbonate) [90]. 

The period following the Second World War saw the emergenee, with an accelerated speed, of new polymerization methods in 1953-1954, polymerization catalysis by coordination was developed by K. Ziegler and G. Natta (Nobel Prize, 1963), which led to for high-density polyethylene (PEHD) and polypropylene (PP). Anionic polymerization and the concept of living polymerization proposed by M. Szwarc in 1956 led to the design of blocks copolymers and the first macromolecular architectures. We then saw the emergence of catalysis by metallocene in 1980 by W. Kaminski. Radical polymerization controlled by M. Sawamoto and K. Matyjaszewski in 1994 combined the benefits of radical and ionic polymerization without the drawbacks of the former. 

Block-Type Brushes by Sequential Polymerization The sequential hving polymerization of two macromonomers or a macromonomer with a conventional comonomer forms either block-block- or block-coil-type brush structures. For example, giant rod-coil amphiphilic block copolymer bmshes were prepared via a stepwise metallocene-catalyzed polymerization [58]. In the first step, a concentrated solution of methacryloyl end-functionalized PS macromonomer (DP = 18.3, MWD = 1.05) was polymerized by the organosamarium(iii) catalyst in THF. After PS macromonomer was completely consumed, the active center remained living, and tert-butyl methacrylate tert-butyl methacrylate (tBMA) as a comonomer was added to grow the second block. After termination by ethanol, the poly(tert-butyl methacrylate) (PtBMA) coil block was hydrolyzed into a hydrophihc block, poly(methacrylic acid) (PMAA). The final product consisted of a hydrophobic PS brush block and a hydrophihc PMAA coil. The hydrophilic PMAA coil collapsed in nonpolar solvents, which forced the block-coil CPBs to self-assembled into giant micelles with PMAA as the core component and the stiff PS brush block as the shell to stabihze the micelles. 

Mulhaupt and coworkers have reported the details of several studies related to the preparation of block copolymers from thiol, maleic acid and hydroxy-functional polypropylene prepared by a metallocene catalyst [157, 158]. The same group also reported the transformation of metallocene-mediated olefin polymerization to anionic polymerization by a novel consecutive chain-transfer reaction for the preparation of polypropylene-based block copolymers [159]. The latter were also... 

Scheme 11.40 Synthesis of block copolymers by combination of metallocene polymerization and ATRP methods.

In a recent study, Yu et al. combined the palladium-diimine-catalyzed metallocene polymerization and ATRP to synthesize polyethylene-h-polystyrene and polyethylene-h-poly(butyl acrylate) [165]. A relatively new coordination olefin polymerization method - degenerative transfer coordination polymerization - was recently combined with ATRP to prepare block and graft copolymers with linear polyethylene segments [166-169]. 

Matyjaszewski, K. Saget, J. Pyun, J. Schlogl, M. Rieger, B. Synthesis of polypropylene-poly(meth)acrylate block copolymers using metallocene catalyzed processes and snbseqnent atom transfer radical polymerization. J. Macromol. ScL, PureAppl. Chem. 2002, A39, 901-913. 

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