Copolymers metallocene polyethylene

Xu, G. Chung, T.C. Borane chain transfer agent in metallocene-mediated olefin polymerization synthesis of borane-terminated polyethylene and diblock copolymers containing polyethylene and polar polymer. J. Am. Chem. Soc. 1999,121, 6763. 

The highest global consumption of any plastic coupled with the many distinct types of commercially available polyethylenes are testament to the rich history of major innovations in products, processes and breadth of applications of polyethylene. This chapter will give a historical perspective of these innovations in polyethylene including a breadth of product applications of polyethylene and the impact of metallocene polyethylenes commercialized in last 15 years. A very recent innovation of olefin block copolymers by The Dow Chemical Company will be described and some remarks will be made on future product innovations and trends. 

Polymers prepared by metallocene catalysts have special properties. Metallocene-polyethylene is an excellent film wrap and has excellent barrier properties to oxygen and moisture. Special polymers such as linear low-density polyethylene (LLDPE) which is a copolymer of ethylene and 1-butene (or 4-methyl-l-pentene) can be manufactured readily by the use of metallocene catalysts. LLDPE is a high strength film-forming polymer. 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

Several copolymers of or-olelins are used as drag reducers. Suggested recipes are summarized in Table 12-1. Linear low-density polyethylene is a copolymer of ethylene and a-olefins. It is obtained by copolymerization utilizing Ziegler-Natta catalysts or metallocene catalysts. Concentrates may be prepared by... 

With the details associated with ADMET chemistry reasonably well understood, we have embarked on a study of the synthesis of well-controlled polymer structures via metathesis polycondensation chemistry [37]. A series of well-defined polyolefins have been designed to model the crystallization behavior of polyethylene and its related copolymers, including new materials synthesized by metallocene-based catalysts. This synthesis concept has been reduced to practice, and polymers that will aid in the understanding of branching within polyethylene itself have been produced. 

Metallocenes give polyethylene producers a long list of opportunities to work on. They have already created polyethylene copolymers that compete well in applications that have been formerly the exclusive domain of the more costly, so-called high value plastics. Further, they are augmenting the chromium oxide and Ziegler-Natta catalysts systems that have been used for HDPE and LLDPE with metallocene catalysts. That creates even further... 

Eaves (92) distinguished between polyolefin plastomers (POP) with density >910 kg m and polyolefin (POE) elastomers with densities <910 kg m-3. The density of a polyethylene at 20 °C is a linear function of the crystallinity, with limiting values of 854 kg m 2 for zero crystallinity and 1000 kg m for 100% crystallinity. The polyolefin elastomer foams compete with EVA copolymer foams. Metallocene chemistry also allows the production of copolymers with a larger comonomer content in the high molecular weight part than in the low molecular weight part this... 

Harden s (27) market survey of the growth of polyolefin foams production and sales shows that 114 x 10 kg of PE was used to make PE foam in 2001. The growth rate for the next 6 years was predicted as 5-6% per year, due to recovery in the US economy and to penetration of the automotive sector. In North America, 50% of the demand was for uncrosslinked foam, 24% for crosslinked PE foams, 15% for EPP, 6% for PP foams, 3% for EVA foams and 2% for polyethylene bead (EPE) foam. As protective packaging is the largest PE foam use sector, PE foam competes with a number of other packaging materials. Substitution of bead foam products (EPP, EPE, ARCEL copolymer) by extruded non-crosslinked PE foams, produced by the metallocene process was expected on the grounds of reduced costs. Compared with EPS foams the polyolefin foams have a lower yield stress for a given density. Compared with PU foams, the upper use temperature of polyolefin foams tends to be lower. Eor both these reasons, these foams are likely to coexist. 

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 should be mentioned that many of the requirements necessary for the economic production of polyethylene and polypropylene have been achieved. However, catalysts of greater activity and of greater selectivity in the production of polymers and copolymers can be anticipated. This is of prime concern to alkene polymerisation processes in the presence of single-site metallocene catalysts. Such catalysts, undoubtedly of great scientific and commercial importance, have been developed on a large scale within recent years [29,30],... 

These monocyclopentadienyl amidotitanium complexes, which are classified as constrained-geometry catalysts, are capable of producing low-density polyethylene (ethylene copolymers with C4, C(, or Cg 1-alkenes) that also contain long-chain branches, in contrast to strictly linear low-density polyethylene (ethylene copolymers with C4, C(, or Cg 1-alkenes) produced by bent metallocene-based catalysts [30,105,148,149]. 

Group 4 metallocene catalysts are, in addition to polyethylene and polypropylene, able to generate syndiotactic polystyrene, to polymerize cycloolefins (cyclopentene, nor-bomene, and their substituted compounds), and to give access to various copolymers. During the polymerization of cycloolefins, only the double bond is opened and not the ring. 

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