Homogeneous branching

These comprise at least one homogeneously branched ethylene polymer and at least one blowing agent. They are particularly suitable for sealing food and liquid containers and do not contribute to taste and/or odour of the packaged product. 

Figure 18.8 Kratky s plot of the form factor of samples of branched polymers derived from potato starch by controlled acid degradation. The upper continuous line corresponds to a linear chain (C = 1) while the lower one to a homogenously branched polymer (C = 0). Source Reprinted with permission from Galinsky G, Burchard W. Macromolecules 1997 30 4445 [44]. Copyright 1997 American Chemical Society.

Deposition of paRmt on the constrained geometry catalyst technology (CGCT) based on the transition metals, M = Ti, Zr, Hf. The resulting PO is substantially linear. The preferred composition comprises 10-95 wt% of homogeneously branched linear a-olefin copolymta (p = 0.930-0.965 g mL ", MWD = 1.8-2.8, single r )... 

The SCBDI = wt% of macromolecules having a comonomer content within 50 % of the median total molar comonomer content, calculated from TREF (temperature rising elution fractionation) data. The elastic, substantially linear C2-Cg copolymer has 0.01 < LCB/IOOOC < 3, M /Mn = 1.5-2.5, 2 < SCB (CH3/IOOOC) < 30), and short-chain branch distribution index SCBDI > 50 %. The homogeneously branched copolymer may he produced as described in C. T. Elston (DuPont Canada Ltd.) patent. Films produced from the bimodal MWD new copolymers show good impact and tensile properties... 

To prepare degradable polymers, graft copolymers of PLA macromonomer and tert-huXy acrylate were prepared by free radical polymerization. An increase in lactic acid units resulted in an increase in degradation rate [84]. ATRP of MMA (96.5%) and (meth)acrylate-terminated PLA macromonomer (Mn 2800g/mol, 3.5%) yielded a homogeneously branched PMMA-g-PLA of low polydispersity index (PDI = 1.15) [85]. The reactivity ratio of MMA for conventional radical polymerization is 1.09 while with ATRP is 0.57. This accounts for the lower PDI of ATRP synthesized PMMA-g-PLA. 

In this experiment, the LLDPEs were simulated by hydrogenated (or deuterated) polybutadienes, because they can be prepared as monodisperse molecules (with a ratio of weight- and number-averaged molecular weights, Mw/M < 1.1) and a homogenous branch distribution within the chains. Such studies are therefore unaffected by polydispersity effects, either in the branch content or molecular... 

In an experiment to determine if this type of catalyst may have properties required for industrial applications, Jolly et cd. carried out a polymerization at 80°C with catalyst 3. The results showed that this particular catalyst exhibited an activity of 50,750 Kg PE/mol Cr/hr with a constant polymerization rate for an extended period, thus indicating very beneficial polymerization properties for commercial applications. In addition, catalyst 6 was evaluated in ethylene/1-hexene copolymerization experiments. In neat 1-hexene an elastomeric material was isolated with an activity of 40,000 Kg PE/mol Cr/ hr under polymerization conditions described in Table 3.12, while in toluene containing 20 vol% 1-hexene, an ethylene/1-hexene copolymer was isolated with a DSC melting point of 112°C, suggesting a LLDPE material (i.e., density of ca. 0.91-0.92 g/cc) was produced with a homogeneous branching distribution, which is expected based on the polydispersity value of 1.58 for the same catalyst in an ethylene homopolymerization experiment. This copolymerization data also shows that this particular catalyst has necessary copolymerization characteristics for industrial applications. 

High film clarity due to the homogeneous branching distribution in which the branch frequency (i.e., branches/1000 carbons) is independent of polymer molecular weight. 

The ability to introduce LLDPE products with lower densities (ca. 0.80-0.915 g/cc) due to the more homogeneous branching distribution and higher reactivity with higher 1-olefins such as 1-butene, 1-hexene and 1-octene. Titanium-based catalysts are usually limited to providing LLDPE materials with a density of about 0.915 g/cc. 

This patent disclosed a series of single-site, vanadium-based coordination catalysts for the preparation of ethylene/1-olefin copolymers with an intermolecular uniform branching distribution. The patent describes this preferred branching distribution as a homogeneous branching distribution in which the comonomer is randomly distributed within a given molecule, while the copolymer molecules contain the same ethylene/comonomer ratio. In addition, the copolymers produced with these coordination catalysts possess a narrow molecular weight distribution. 

Characterization Methods that Identify Polyethylene with a Homogeneous Branching Distribution Obtained with Single-Site Catalysts... 

Figure 4.11 Representation of the branching distribution along the polymer backbone with a heterogeneous (non-uniform) branching distribution shown as (A) and a homogeneous branching distribution (uniform) shown as (B).

Figure 4.23 Density of ethylene/1-octene copolymers with a homogeneous branching distribution at various 1-octene levels. Products below a density of about 0.91 g/cc represent new polyethylene compositions available for commercial applications [53].

DuPont s Sclair process was extremely important technology which was introduced in the 1960s, as it offered commercial ethylene copolymers at densities as low as 0.916 g/cc with improved physical properties over comparable polyethylene resins produced with the high-pressure process. In addition, DuPont scientists also developed improved catalysts for the Sclair process based on vanadium compounds that produced homogeneous branching distribution of the short-chain branches introduced along the polymer backbone by incorporation of a comonomer such as 1-butene into the polymer structure. 

The data show that polyethylene with a homogeneous branching distribution is provided by a vanadium catalyst based on VO(OBu) with... 

EtAlCl or EtAlcyEt AlCl as cocatalyst. The melting point data of the four examples shown above suggest that the polyethylene with a homogeneous branching distribution is consistent with a single-site polymerization catalyst similar to catalysts discovered by Kaminsky in the late 1970s based on a zirconocene compound and methylalumoxane as cocatalyst. 

The density (corrected to a 1.0 melt index value) vs comonomer content (mol%) relationship is dependent on variables such as branching distribution and branch length. For example, a single-site catalyst that provides a homogeneous branching distribution requires significantly less comonomer... 

Homogeneous branched structure, 36 Homogeneous crosslink stmcture, 40 HOPG, 240, 242 Hydrocolloids, 114 Hydrogels, 10, 336... 

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