Polyethylene random copolymers

Dielectric relaxation measurements of polyethylene grafted with acrylic acid(AA), 2-hydroxyethyl methacrylate (HEMA) and their binary mixture were carried out in a trial to explore the molecular dynamics of the grafted samples [125]. Such measurements provide information about their molecular packing and interaction. It was possible to predict that the binary mixture used yields a random copolymer PE—g—P(AA/HEMA), which is greatly enriched with HEMA. This method of characterization is very interesting and is going to be developed in different polymer/monomer systems. 

Figure 4. The linear dependence of density on butadiene content in various block copolymers. Density of amorphous HB (polyethylene) is estimated from the extrapolation of the density of HI through that of the random copolymer HBI-50 to axis where butadiene content is 100%.

Despite this tremendous versatility, there is still a fundamental limitation for these random copolymers melting point and modulus (stiffness) are inextricably coupled to the density (or percentage short-chain branching from LAO comonomer) as shown in Fig. 1. The same method employed to lower modulus (incorporation of comonomer) results in a thinning of the polyethylene crystals, concomitant with a lowering of the melting point, according to a relationship established by Flory [8],... 

Fig. 20 Analytical TREF profiles of a random copolymer, an OBC, and a blend of HDPE with ultra-low density polyethylene (ULDPE) of similar overall densities [46]...

This patent is a reissue (RE 34607). The composition described, capable of forming foams with excellent mechanical properties and heat resistance, is made of (a) 14-80 wt.% of a propylene-ethylene random copolymer having an ethylene content of 1.5-6 wt.%, (b) 10-60 wt.% of a propylene-ethylene random copolymer having an ethylene content of 0.2-1.0 wt.%, (c) 10-60 wt.% of a linear low-density polyethylene, and (d) 1-30 pbw, per 100 pbw of the above resin composition, of a foaming agent. JAPAN... 

Single crystals with a Tm of 423 K have been produced from low-density polyethylene (ldpe). Isotactic PP crystals have a Tm of 444 K and syndiotactic PP has a Tm of 411 K, whereas atactic PP is amorphous and has a Ts of 255 K. Isotactic polyolefins with pendant groups, such as polyhexene, have high Tm values. Random copolymers of ethylene and propylene are amorphous, but block copolymers of these monomers are crystalline. 

Example 11.2 Investigation of the Effects of Interfacial Cross-linking, Diffusion, and Area Generation Rates on Multilayer Miscible (PE-8% GMA)/PE-4% MAH) Films on the Extensional Rheometry of Such Films. Saito and Macosko (54) prepared multilayer films of two low density polyethylene (LDPE) miscible copolymers a random copolymer of... 

Blending of polymers is an attractive method of producing new materials with better properties. Blends of aliphatic polyesters, especially of poly(e-CL), have been investigated extensively and have been the subject of a recent review paper [170]. Poly(e-CL) has been reported to be miscible with several polymers such as PVC, chlorinated polyethylene, SAN, bisphenol A polycarbonate, random copolymers of Vdc and VC, Vdc and AN, and Vdc/VAc, etc. A single composition-dependent Tg was obtained in the blends of each of these polymers with poly(e-CL). This is of interest as a polymeric plasticizer in these polymers. Blends of PVC and poly(e-CL) with less than 50 wt % of poly(e-CL) were homogeneous and exhibited a single Tg. These blends were soft and pliable because the inherent crystallinity of poly(e-CL) was destroyed and PVC was plasticized... 

So far in our discussion of micros tincture, we have considered homopolymers. To some degree, however, there is an element of semantics involved in our definition. Is a branched polyethylene a true homopolymer or should it be considered a copolymer of ethylene and whatever units comprise the branches Here our concern is real copolymers, those synthesized from two (or more) distinct monomers. The simplest possible arrangements are shown in Figure 2-22 and are self-explanatory. But, as we will see, real life is more complex. True random copolymers are rare and in most cases there are tendencies to blockiness or alternating arrangements. There are also graft copolymers, but we will discuss all this in more detail when we consider copolymerization. 

Strength of the specific interaction. An example of this is shown in Fig. 9 for blends of poly(butyl acrylate) with chlorinated polyethylene. In this case the blend requires a higher activation energy than its additivity value in the form of heat to allow chain movements. A review of this subject and of the relations between and chemical structure of blends has been given by Cowie For miscible blends many attempts have been made to correlate the with the blend composition as is frequently done with random copolymers. Several miscible blends studied by Hammer and Hichman and Ikeda exhibit a composition dependence of which can be described by the simple Fox relationship. 

Ethylene-styrene pseudo-random copolymers (known as ethylene-styrene interpolymers) [14] have also been used to improve the compatibility between sPS and polyolefins, mainly polyethylene (entry 12). 

Ethylene-propylene rubbers (EPR) are basically random copolymers of ethylene and propylene, with 60-70% (w/w) ethylene. Polyethylene and polypropylene are homopolymers that display too high a degree of crystallinity to be used as elastomers. Nevertheless, random copolymerization produces linear chains with sufficient structural irregularity to prevent crystallization. The copdlymerization process leads to amorphous, fully saturated chains. 

Fig. 18. Two isomers of the random copolymer (E XEEX)N a stiff molecule of linear polyethylene En=(C4H8)n (x=0) with a larger statistical segment length a and a flexible chain of branched poly(ethyl ethylene) EEN=(C2H3(C2H5))N (x=l) with a smaller statistical segment length a...

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