Polyolefin diblock copolymers

Chung, T. C. Xu, G Process for preparing polyolefin diblock copolymers involving borane chain transfer reaction in transition metal-mediated olefin polymerization. U.S. Patent 6,248,837 B1 (Perm State Research Foundation), June 19, 2001. 

Rangarajan P., Register R. A., Fetters L. J., Bras W., Naylor S., and Ryan A. J. (1995) Crystallization of a weakly segregated polyolefin diblock copolymer. Macromolecules 28 4932-4938. 

Diblock copolymers, especially those containing a block chemically identical to one of the blend components, are more effective than triblocks or graft copolymers. Thermodynamic calculations indicate that efficient compat-ibilisation can be achieved with multiblock copolymers [47], potentially for heterogeneous mixed blends. Miscibility of particular segments of the copolymer in one of the phases of the bend is required. Compatibilisers for blends consisting of mixtures of polyolefins are of major interest for recyclates. Random poly(ethylene-co-propylene) is an effective compatibiliser for LDPE-PP, HDPE-PP or LLDPE-PP blends. The impact performance of PE-PP was improved by the addition of very low density PE or elastomeric poly(styrene-block-(ethylene-co-butylene-l)-block styrene) triblock copolymers (SEBS) [52]. 

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. 

Lohse, D.J., Fetters, L.J., Doyle, M.J., Wang, H.-C. and Kow, C. (1993) Miscibility in blends of model polyolefins and corresponding diblock copolymers Thermal analysis studies. Macromolecules, 26, 3444-3447. 

Thus Xu and Lin (154) successfully compatibilized a high molecular weight blend of iPS and iPP with a iPS-iPP diblock copolymer, where the molecular weight of both blocks amoimted to 150,000. Feng (165) has shown that for PS/polyolefin blends, even PE-g-PS graft copolymers can be suitable compatibihzers. 

Chung, T. C. Xu, G Lu, Y. Hu, Y. Metallocene-mediated olefin polymerization with B-H chain transfer agents synthesis of chain-end functionalized polyolefins and diblock copolymers. Macromolecules 2001,34, 8040-8050. 

Scheme 2 The reaction route for preparation of chain-end-functionalized polyolefin and diblock copolymers using the reactive chain transfer approach...

On the other hand, the incorporated p-MS group in the polyolefin (the synthesis discussed in Sect. 2.2), provides the active site to transform metallocene polymerization to living anionic polymerization [56]. Scheme 11 illustrates the anionic reaction process fi om the PP-t-p-MS to the PP-f>-PS diblock copolymer involving only one p-MS group per polymer chain. The entire reaction process provides an ultimate test for examining the efficiency of the chain transfer reaction to p-MS and the subsequent chain extension process. 

Freed and Dudowicz have studied several experimental systems using the LCT. The most extensive comparisons have been for polystyrene (PS) polyvinylmethylether (PVME) blends where the LCT successfully describes the phase behavior and also the variation of the chi parameter with temperature and pressure. In addition they show that adding a PS-PVME diblock copolymer to the blend can either stabilize or destabilize the blend depending on the composition of the diblock. Similarly good agreement is also found for PS-PMMA blends. For polyolefin blends Freed and Dudowicz do not attempt to fit the experimental data, but find that they can reproduce many of the trends observed in experiment. In addition, they show that both entropic and enthalpic contributions to the chi parameter are equally important. 

A first systematic study of such systems with SANS was performed on the relatively large molar mass symmetric polyolefins PE and PEP and the corresponding diblock copolymer PE-PEP, PE being polyethylene and PEP being poly(ethylene propylene) [46]. A mean field lifshitz-hke behavior was... 

A first systematic study of such system was performed on the relatively large-molar-mass symmetric polyolefins PE and PEP and the corresponding diblock copolymer PE-PEP PE being polyethylene and PEP being poly(ethylene propylene). A mean-field Lifshitz like behavior was observed near the predicted isotropic Lifshitz critical point with the critical exponents y=l and v=0.25 of the susceptibility and correlation length, and the stmcture factor following the characteristic mean-field Lifshitz behavior according to S(Q)ocQ". Thermal composition fluctuations were apparently not so relevant as indicated by the observation of mean-field critical exponents. On the other hand, no Lifshitz critical point was observed and instead a one-phase channel of a polymeric bicontinuous miaoemulsion phase appeared. Equivalent one-phase channels were also observed in other systems. 

The theoretical lower limit of the molecular weight distribution for the diblock OBC is 1.58. The observed MJMn of 1.67 indicates that the sample contains a very large fraction of polymer chains with the anticipated diblock architecture. The estimated number of chains per zinc and hafnium are also indicative of a high level of CCTP. The Mn of the diblock product corresponds to just over two chains per zinc but 380 chains per hafnium. This copolymer also provides a highly unusual example of a polyolefin produced in a continuous process with a molecular weight distribution less than that expected for a polymer prepared with a single-site catalyst (in absence of chain shuttling). 

Recent advances in the development of well-defined homogeneous metallocene-type catalysts have facilitated mechanistic studies of the processes involved in initiation, propagation, and chain transfer reactions occurring in olefins coordi-native polyaddition. As a result, end-functional polyolefin chains have been made available [103].For instance, Waymouth et al.have reported about the formation of hydroxy-terminated poly(methylene-l,3-cyclopentane) (PMCP-OH) via selective chain transfer to the aluminum atoms of methylaluminoxane (MAO) in the cyclopolymerization of 1,5-hexadiene catalyzed by di(pentameth-ylcyclopentadienyl) zirconium dichloride (Scheme 37). Subsequent equimolar reaction of the hydroxyl extremity with AlEt3 afforded an aluminum alkoxide macroinitiator for the coordinative ROP of sCL and consecutively a novel po-ly(MCP-b-CL) block copolymer [104]. The diblock structure of the copolymer... 

---