Ethylene Styrene Interpolymers

Blends of LDPE with ethylene styrene interpolymers (ESI, see Section 3.2) also have a complex microstructure. The semi-crystalline LDPE is immiscible with the amorphous ESI, which has a glass transition temperature (Tg) just above room temperature. Consequently there are rigid crystalline regions and rubbery amorphous LDPE, mixed on a 0.1 pm scale, together with regions of leathery ESI on a 5 to 10 pm scale (71). 

Ethylene styrene interpolymers (ESI) were produced by Dow with the use of single site metallocene 

The ESI domains in ESI/LDPE blends are 0.1 to 2.8 pm in length (71). As the ESI (S series with 70% styrene) used was amorphous, the use of ESI reduced the overall crystallinity of the blend. However, with 25% ESI, the compressive stress at 25% compression of the foam is unchanged. Eor ESI, the processing window is wider, and the cell structure is slightly finer than for the equivalent LDPE foam. 

The styrene content affects the crystallinity of ESI (131) for 50% styrene the copolymers are amorphous. As the styrene content is increased from 50 to 70% styrene the Tg increases from -15 °C to 20 °C. Low density foams were made (8) from a blend of 50% of various ESI polymers, 33% of EVA and 17% of azodicarbonamide blowing agent. Thermal analysis showed that the blends, with an ESI having approximately 70% styrene, had a Tg in the range 22 to 30 °C. Dynamic mechanical thermal analysis (DMTA) traces (see Section 5.1) show that these blends 

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Copolymerization of ethylene and styrene by the INSITE technology from Dow generates a new family of ethylene-styrene interpolymers. Polymers with up to 50-wt% styrene are semicrystalline. The stress-strain behavior of the low-crystallinity polymers at ambient temperature exhibits elastomeric characteristics with low initial modulus, a gradual increase in the slope of the stress-strain curve at the higher strain and the fast instantaneous recovery [67], Similarly, ethylene-butylene copolymers may also be prepared. 

Chen H., Guest M.I., Chum S., Hiltner A., and BaerE. Classification of ethylene-styrene interpolymers based on comonomer content, J. Appl. Polym. Sci., 70, 109, 1998. 

There have been more efforts to use blends such as Nova Chemicals Arcel (an ethylene styrene interpolymer in bead form) to create a more durable foam than EPS. EPP can be moulded into complex shapes, with the steam bonding of the beads (291). These packaging foams compete with polyolefin film products such as Jiffy foam (bubblewrap) and macrobubbles made by heat sealing 150 mm lengths of tubular LDPE film. As it is difficult or costly to recycle such foam products, in some countries there is a move towards biodegradable starch foams and moulded paperboard. 

Foams were prepared from blends of EVA and ethylene-styrene interpolymers having styrene contents ranging from 30 to 73 wt.% and Tgs ranging from -2 to 33C, in the presence of various amounts of dicumyl peroxide and their viscoelastic and mechanical properties investigated. The effects of styrene content and peroxide concentration on the morphology, degree of crosslinking and expansion ratio of the foams were assessed as was the influence of the type of ethylene-styrene interpolymer on the Tg of the foams. It was found that the Tg of the blends could be tailored by selection of the appropriate interpolymer. 19 refs. 

ETHYLENE-STYRENE INTERPOLYMER FOAM BLENDS MECHANICAL PROPERTIES AND SPORT APPLICATIONS... 

Foamed blends of ethylene-styrene interpolymer and LDPE were subjected to a range of mechanical tests, including compressive impact testing, Instron compression and Poisson s ratio measurements, compressive creep measurements and compression set and recovery measurements. The data obtained were compared with those for EVA and the suitability of these foamed blends as replacements for EVA in the manufacture of soccer shin guards and midsoles for sports shoes was evaluated. 20 refs. 

Foams 2000 Second International Conference on Thermoplastic Foam. Conference proceedings. Parsippany, N.J., 24th-25th October 2000, p. 102-7 NEW PRODUCTS MADE FROM ETHYLENE-STYRENE INTERPOLYMER/LDPE BLEND FOAMS FOR VARIOUS APPLICATIONS Ramesh N S Sealed Air Corp. 

Dallas, Texas, 6th-10th May, 2001, paper 443 USE OF ETHYLENE/STYRENE INTERPOLYMERS IN CROSSLINKED FOAMS FOR THE FOOTWEAR INDUSTRY Dubois R Karande S Wright D P Martinez E Dow Chemical Co. 

Patent Number US 6111020 A1 20000829 CROSSLINKED FOAMS FROM BLENDS OF ETHYLENE VINYL ACETATE AND ETHYLENE-STYRENE INTERPOLYMERS... 

Disclosed are ethylene-vinyl acetate/ethylene-styrene interpolymer blends, which are useful in preparing foams exhibiting improved compression set resistance, dimensional stability and rebound resilience at similar foam densities than known foam systems, e.g. EVA. The crosslinked foams are particularly useful in fabricating footwear and gaskets. 

Insite technology from Dow Chemical has enabled the production of ethyl ethylene-styrene interpolymers (ESI) by copolymerisation of ethylene and styrene monomers. The properties of interpolymers vary significantly with copolymer styrene content. Interpolymers with up to about 45 wt.% copolymer styrene are semi-crystalline and exhibit good low temperature toughness. Interpolymers with greater than about 45 wt.% copolymer styrene are... 

Several other produces have been developed based on the relatively new soluble stereoregulating catalysis systems. Index, an ethylene-styrene interpolymer, was introduced in 1998... 

Figure 1.12 shows the timeline of discovery of various styrenic polymers and copolymers. It would be naive to suggest that the rate of invention and innovation will level off in this century. Rather, the pace of discovery of new styrenic polymers will probably increase. Advances in new catalyst technology and controlled radical polymerisation technology will undoubtedly yield new styrenic polymers with well-defined architecture, as we have recently seen with the introduction of syndiotactic PS and ethylene-styrene interpolymers. 

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). 

An overview of the synthesis of ethylene-styrene copolymers has been compiled by Pellecchia and Olivia [12]. A short overview of ethylene-styrene interpolymer technology, including an identification of the most widely investigated catalysts cited in basic patents, has been presented [27]. Whilst the knowledge base continues to grow, the interrelationships of catalyst structure, polymerization conditions such as temperature and the chain microstructures of the resulting polymers will still be subjects of interest. 

STRUCTURE-PROPERTY RELATIONSHIPS FOR ETHYLENE-STYRENE INTERPOLYMERS... 

As a result of the catalyst and process conditions used in their manufacture, the particular copolymers of current major interest are atactic, and contain typically up to about 50 mol% ( 80 wt%) styrene. These materials have been described as pseudo-random , since successive head-to-tail styrene chain insertions have been shown to be absent, even at high levels of styrene incorporation [1,2]. The term ethylene-styrene interpolymer (ESI) is used here to describe the specific ethylene-styrene copolymers produced via INSITE Technology. For convenience, all subsequent comonomer contents are expressed in weight percentages, unless otherwise stated. For example, the code ES70 refers to an interpolymer having 70 wt.% comonomer styrene incorporation. 

Figure 26.1 Thermal transitions of ethylene-styrene interpolymers (ESI). 7m, Tc and 7g denote the melting, crystallization and glass transition temperatures, respectively...

Although most polymers are in fact modified to a greater or lesser degree to optimize their utility in end-use applications, certain basic characteristics of these ethylene-styrene interpolymers make them particularly likely to be modified, or to be used as modifiers. These characteristics are as follows ... 

BLENDS OF ETHYLENE-STYRENE INTERPOLYMERS MISCIBILITY CONSIDERATIONS... 

Ethylene-styrene interpolymers exhibit a novel balance of properties that are uniquely different from polyethylenes and polystyrenes. In contrast to other ethylene-a-olefin copolymers, ESI display a broad range of material response ranging from semicrystalline, through elastomeric to amorphous. The styrenic functionality and unique molecular architecture of ESI are postulated to be the basis of the versatile material attributes such as processability (shear thinning, melt strength and thermal stability), viscoelastic properties, low-temperature toughness and broad compatibility with other polymers, fillers and low molecular weight materials. 

Ethylene-styrene interpolymers are a novel class of polymers exhibiting a unique combination of material attributes that are not found in polyethylenes,... 

Guest, M.J., Cheung, Y.W., Diehl. C.F. and Hoenig, S.M. Structure, properties and applications of ethylene/styrene interpolymers , in Metallocene-based Polyolefins Preparation, Properties and Technology, Vol. 2, ed. J. Scheirs and W. Kaminski, Wiley, Chichestes, Chapt. 12, pp. 271-292, (1999). 

Special Feature I. Ethylene-Styrene Interpolymers Technologies, Products and Markets . The Metallocene and Single Site Catalyst Monitor, The Catalyst Group, Spring House, PA (December 2000). 

Guest, M. J. Cheung, Y. W. Diehl, C. F. Hoenig, S. M. Structure, Properties and Applications of Ethylene-Styrene Interpolymers. In... 

It follows directly from this that the theoretical maximum amount of styrene units in the polymer is 50 mole%, i.e. 77% by weight and Dow claim that it can produce copolymers (which it tends to refer to as interpolymers, or more specifically as ethylene-styrene interpolymers, ESIs) from this figure down to 17 wt%. As experienced with ethylene-propylene copolymers the copolymers with high ethylene contents show a measure of crystallinity and indeed crystallinity can be traced in polymers up to 50 wt% styrene (Figure 11.18). Data on glass transition temperatures indicate that the polymers are rubbery below normal indoor ambient temperatures with up to about 70 wt% of styrene. (It is of interest here that the data here is in line with the author s suggestion for the Tg of polyethylene given in Section 10.4.)... 

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