Polyethylene backbone

Figure 1.8 Hindered rotation around a carbon-carbon bond, (a) The definition of (p (from 0 = 0) in terms of the ethane molecule, (b) The potential energy as a function of (p. (c) Here (p is shown (from (p = 0) for a carbon-carbon bond along a polyethylene backbone, (d) The potential energy for case (c) shown as a function of (p. [Panels (b) and (d) reprinted with permission from W. J. Taylor, J.Chem.Phys. 16 257 (1948).]...

The first patent on the chlorination of polyethylene was taken out by ICI in 1938. In the 1940s scientists of that company carried out extensive studies on the chlorination process. The introduction of chlorine atoms onto the polyethylene backbone reduces the ability of the polymer to crystallise and the material becomes rubbery at a chlorine level of about 20%, providing the distribution of the chlorine is random. An increase in the chlorine level beyond this point, and indeed from zero chlorination, causes an increase in the Tg so that at a chlorine level of about 45% the polymer becomes stiff at room temperature. With a further increase still, the polymer becomes brittle. 

Macromonomers always lead to the formation of graft copolymers. For example, the vinyl-terminated polystyrene can be copolymerized with ethylene to produce a graft copolymer of polyethylene, whereby the vinyl moiety of polystyrene is integrally polymerized into the linear polyethylene backbone ... 

Random methyl branch placement on the polyethylene backbone... 

Reduction of the unperturbed dimensions of the main chain is calculated when ethyl groups are attached to a polyethylene backbone. Values of most of the paramters are taken from the well-known RIS model for unperturbed polyethylene (Abe, A. Jernlgan, R. L. Flory, P, J, J, Am. Chem. Soc. 1966, 88, 631) the bond angle is 112°, gauche states are located at 60° trans 180°l. First- and second-order interactions are weighted by using o 0.43 and m 0.034 (for 300 K). An additional statistical weight, denoted by t, is required at each bond to an atom that constitutes a trifunctional branch point (Flory, P, J, Sundararajan, P. R. DeBolt, L. C. J. Am. Chem. Soc. 1974, 96, 50151. Calculations are performed with t = 0 and t = [Pg.410]

Each set of experiments was carried out under the same reaction condition except using different comonomers, i.e. p-methylstyrene, o-methylstyrene, m-methylstyrene and styrene, respectively. The compositions of copolymers were determined by H NMR spectra, and the thermal properties (melting point and crystallinity) were obtained by DSC measurements. Overall, all comonomers show no retardation to the catalyst activity. In fact, the significantly higher catalyst activities were observed in all copolymerization reactions (runs 2-5), comparing with that of ethylene homopolymerization (run 1). Within each set (runs 2-5 and 6-9) of comparative experiments, p-methylstyrene consistently shows better incorporation than the rest of comonomers, i.e. o-methylstyrene, m-methylstyrene and styrene. Both catalysts with constrained mono- and di-cyclopentadienyl ligands are very effective to incorporate p-methylstyrene into polyethylene backbone. In runs 2 and 6, more than 80 % of p-methylstyrene were converted to copolymer within one hour under constant (- 45 psi) ethylene pressure. On the other hand, only less than half of styrenes (runs 5 and 9) were incorporated into ethylene copolymers under the same reaction conditions. The significantly... 

The poly(ethylene-co-p-methylstyrene) with 10.9 mole % of p-methylstyrene shows a low melting point (76 °C) and very small crystallinity (5.4%), which implies the random distribution of p-methylstyrene along the polyethylene backbone [17]. The detailed sequence distribution can be quantitatively determined by 13C NMR measurements. 

With a polyethylene backbone, this grafting technique will not yield pure poly (ethylene-g-vinyl chloride)—"pure graft copolymer —but a mixture of this compound with PVC homopolymer and unmodified polyethylene. We call this raw graft polymerization product "VC/PE graft copolymer. Sometimes, we add its gross composition between parentheses—for example, VC/PE (50-50) graft copolymer. The same statement applies to the other backbone polymers. 

Examples of kinetic inhibitor chemicals are shown in Figure 8.10. In the figure, each inhibitor is shown with a polyethylene backbone, from which a pendant group (typically a ring compound with an amide [—N—C=0] linkage) is suspended. There are several types of kinetic inhibitors, and due to proprietary... 

Polyethylene Backbone and Side-Chain C-13 Chemical Shifts in ppm from TMS (+0.1) as a Function of Branch Length (y Carbon Chemical Shifts, which occur near 30.4 ppm, are not given because they are often obscured by the major 30 ppm resonance for the "n" equivalent, recurring methylene carbons). Sol vent 1,2,4-trichlorobenzene. Temperature 125°C. 

Random ethylene copolymers with small amounts (4-10 wt-%) of 7-olefins, e.g. 1-butene, 1-hexene, 1-octene and 4-methyl- 1-pentene, are referred to as linear low-density polyethylene, which is a commercially relevant class of polyolefins. Such copolymers are prepared by essentially the same catalysts used for the synthesis of high-density polyethylene [241]. Small amounts of a-olefin units incorporated in an ethylene copolymer have the effect of producing side chains at points where the 7-olefin is inserted into the linear polyethylene backbone. Thus, the copolymerisation produces short alkyl branches, which disrupt the crystallinity of high-density polyethylene and lower the density of the polymer so that it simulates many of the properties of low-density polyethylene manufactured by high-pressure radical polymerisation of ethylene [448] (Figure 2.3). 

Figure 3.3.5 (A) Chemical structure of sulfonated perfluorinated polyethylene (Nafion ). (B) Schematic illustration of the microscopic structure of hydrated Nafion membrane perfluorinated polyethylene backbone chains form spherical hydrophobic clusters. Sulfonic end groups interface with water-filled channels and mediate the migration and diffusion of protons. The channels are filled with water and hydronium ions. Figure adapted from [4].

ADMET polymerization is performed on a,co-dienes to produce strictly linear polymers with unsaturated polyethylene backbones, as shown in Scheme 2. This step-growth polymerization is a thermally neutral process driven by the release of a small molecule condensate, ethylene [16-20]. Ring-opening metathesis polymerization (ROMP) is widely used to polymerize cyclic olefins and is performed with the same catalysts as in ADMET polymerizations. 

The influence of the cyclohexane ring on the glass transition temperature and sub-Tg transitions has been studied by dynamic mechanical methods [10,16,42]. These comparative studies have focused on the influence of the cyclohexyl substituent on observed thermal transitions. A systematic study of cycloalkyl substituents on alternating carbons of a polyethylene backbone was performed to study the influence of these substituents on the dynamic mechanical spectra of the polymers [42], These workers also prepared materials in which the cycloalkyl substituents were spaced away from the polymer backbone by successively longer methylene chains, testing the influence of ring proximity... 

Recently, much attention has been devoted to modeling polyolefins and copolymers of ethylene and polar monomers. Eor example, polymers with regularly spaced methyl groups on a polyethylene backbone have been synthesized and display very interesting and surprising thermal properties and microstructure [12]. This represents a rational synthesis of branched polyethylene that cannot be achieved by any other means at this time (Scheme 6.12). 

In early work. Hartley and Guillet (25) associated the reduction in < >n in PE-CO at about —40 C with restrictions in conformational mobility associated with the glass transition, Tg. However, measurable values of n were observed down to about — 100°C due to the occurrence of a crankshaft motion of the polyethylene backbone chains which permitted the formation of the cyclic intermediate (Eq. 25) required for reaction within the lifetime of the n-ir excited state of the carbonyl (= 20 ns). The activation energy for )n below —40 C was = 2 kcal moF, which is similar to that of the crankshaft motion. Below — 100°C this motion is frozen out and no further photochemistry is observed. On the other hand, in the absence of quencher the photophysical processes of fluorescence and phosphorescence may be quite efficient. 

Three-dimensional networks of polyethylene are manufactured through peroxide-initiated covalent bonding between preformed linear molecules. These peroxide-thermal-decomposition reactions lead to free radical Intermediates which abstract hydrogen atoms from the polyethylene backbone to produce long chain polymer radicals. Combinations of these chain polymer radicals lead to a crossllnked network. ( ) (Figure 1)... 

We have first seen that polyethylene exists in the planar zigzag conformation. Polypropylene can be considered as having a linear polyethylene backbone, but with the H atom on every other carbon atom... 

Irradiation of polyethylenes (PEs) could lead to graft some oxidized species on the polyethylene backbone. This treatment was performed in order to improve the compatibility of polyethylenes toward polar polymers as poly(ethylene terephthalate) or polyamide Irradiation in air of... 

Markova et al. have prepared phosphonated polyalkenes where the acid groups were precisely sequenced along an unsaturated polyethylene backbone.The authors reported proton conductivities of 10 mS cm under anhydrous as well as humidified conditions. 

These gels are derived from the polymerization of the monomer N-acryloyl-2-amino-2-hydroxymethyl-l,3-propane diol. The trisacryl monomer creates a microenvironment that favors the approach of hydrophilic solutes (proteins) to the gel polymer surface, since the polyethylene backbone is buried underneath a layer... 

We have used the tandem ADMET/hydrogenation method to produce a series of model EVA copolymers with pendant acetate functionality on every 19, 2V 23, and 2T carbon atom along the polyethylene backbone Figure 2, polymer 3, n = 18, 20, 22, and 26) [23]. Molecular weight analysis by GPC indicates that all of these polymers are in the range of 30,000 to 70,000 g/mol and have typical ADMET molecular weight distributions (PDI 2). Due to its low (23 °C), the copolymer with n = 18 lacks form stability at room temperature. However, the copolymers with n = 20, 22, and 26 all yield tough films and fibers from solution or the melt, and transparent or- translucent materials can be obtained from the melt. 

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