Thermoplastic elastomers (TPEs) exhibit the functional properties of conventional thermoset rubber, yet can be processed on thermoplastic fabrication equipment. The great majority of TPEs have hetero-phase morphology, whether the TPE is derived from block copolymers, rubber-plastic compositions or ionomers. Generally speaking, the hard domains (or the ionic clusters) undergo dissociation at elevated temperatures, thus allowing the material to flow. When cooled, the hard domains again solidify and provide tensile strength at normal use temperatures. The soft domains give the material its elastomeric characteristics. In this review article, the focus is on rubber-plastic polymer compositions as a group of TPEs which have achieved significant growth in the marketplace in the last two decades. The growth has been primarily in the nonpolar (olefinic) elastomer/polyolefin thermoplastic materials because of the wide range of products generated, their performance and their significant acceptance by the automotive sector in applications requiring elastic recovery. The field of TPEs based on polyolefin rubber-plastic compositions has grown along two distinctly different product lines or classes: one class consists of a simple blend and classically meets the definition of a thermoplastic elastomeric olefin (TEO), commonly called a thermoplastic polyolefin (TPO) in earlier literature. In the other class, the rubber phase is dynamically vulcanized, giving rise to thermoplastic vulcanizates (TPVs), named elastomeric alloys (EAs) in some previous literature. Both the simple blends and the dynamically vulcanized TPEs have found wide industrial application. It is the dynamically vulcanized TPE that has the performance characteristics required for true thermoset rubber replacement applications. The first TPE introduced to the market based on a crosslinked rubber-plastic composition (1972) was derived from W. K. Fisher's discovery of partially crosslinking the EPDM phase of EPDM/polypropylene (PP). Fisher controlled the degree of vulcanization by limiting the amount of peroxide, to maintain the thermoplastic processability of the blend. Crosslinking was performed while mixing, a process known as dynamic vulcanization. It is worth noting, however, that the dynamic vulcanization process and the first crosslinked EPDM/PP composition were discovered independently by Gessler and Haslett and by Holzer, Taurus and Mehnert in 1958 and 1961, respectively. Significant improvement in the properties of these blends was achieved in 1975 by Coran, Das and Patel by fully vulcanizing the rubber phase under dynamic shear while maintaining the thermoplasticity of the blend. These blends were further improved by Abdou-Sabet and Fath in 1977 by the use of phenolic curatives to improve the rubber-like properties and the flow (processing) characteristics.

The field of thermoplastic elastomers has shown an explosive growth with the successful commercialization of elastomeric alloys (EAs) in 1981, based on the original work of Coran, Das, and Patel on dynamic vulcanization and the discovery of preferred cure system by Abdou-Sabet and Fath. These discoveries have led to the development of commercial products having true elastomeric properties while maintaining excellent thermoplastic processing. The success of EAs in the marketplace has led to the introduction of new products by Monsanto and others at a rate of 60 products per year in the last half of the eighties. Elastomeric alloys have been characterized as compositions containing rubber particulate domains approximately 1–2 µm in diameter in a matrix of thermoplastic resin. Such dispersed phase morphology has not been widely accepted, especially when it came to explaining the true elastomeric properties of the soft elastomeric products, i.e. 64 and 55 Shore A hardness products. Interaction among the rubber particles leading to a network of vulcanized elastomer phase that gave the appearance of two continuous networks has been proposed. In this paper, the morphology of EPDM/polypropylene elastomeric alloys is examined with some detail, and evidence leading to dispersed phase morphology is provided. There are several variables to such an investigation which can be grouped under the following headings: 1. Molecular weight of EPDM and polypropylene (PP). 2. Ratio of EPDM to PP. 3. Crosslinked or uncrosslinked blend. 4. Degree of crosslinking. 5. Type of crosslinks. 6. Typical and commercial products. It is not the subject of this paper to review the morphology of different binary polymer blends, which have been extensively covered in the literature. It can be concluded that a variety of morphologies can be obtained, however, depending on the mixing conditions, polymer ratios, relative surface energies of the polymer pair, and viscosities and molecular weights of the two polymers. In this study, the mixing conditions were kept similar as much as possible to eliminate the possibility of morphological changes as a function of the applied mixing intensity as influenced by shear rate, mixing time, and temperature.

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The article contains sections titled: 1. Thermoplastic Polyolefin Elastomers 1.1. Introduction and Definition 1.2. Thermoplastic Polyolefin Blends 1.2.1. Morphology 1.2.2. Elastomer Component, Soft Domain 1.2.3. Plastic Component, Hard Domain 1.2.4. Compounds, Trade Names 1.2.5. Processing 1.3. Thermoplastic Vulcanizates 1.3.1. Dynamic Vulcanization 1.3.2. Production and Morphology 1.3.3. Types 1.3.4. Processing 1.3.5. Performance and Product Positioning 1.3.6. Uses 1.3.7. Commercial Products and Trade Names 2. Thermoplastic Polyurethane Elastomers 2.1. Introduction 2.2. Raw Materials 2.3. Production 2.4. Properties 2.5. Processing and Use 2.6. Economic Aspects 2.7. Toxicology and Occupational Health 3. Thermoplastic Copolyester Elastomers 3.1. Introduction 3.2. Raw Materials 3.3. Production 3.4. Microstructure and Composition of Segments 3.4.1. Short‐Chain Ester Units (Hard Segments) 3.4.2. Long‐Chain Polyether Soft Segments 3.4.3. Hydrocarbon Soft Segments 3.4.4. Polyester Soft Segments 3.5. Properties 3.6. Blends 3.7. Uses 3.8. Producers, Trade Names 4. Thermoplastic Polyamide Elastomers 4.1. Introduction 4.2. Raw Materials 4.2.1. Oligoamide Unit 4.2.2. Polyether Units 4.3. Manufacture of Block Polyetheramides 4.3.1. Polyetherester Amides 4.3.2. Synthesis of Polyetheramides 4.4. Physical and Chemical Properties 4.4.1. Block Variations 4.4.2. Morphology 4.4.3. Outstanding Properties 4.4.4. Chemical Resistance 4.4.5. Processing 4.5. Uses 4.6. Trade Names 5. Styrenic Block Copolymers 5.1. Introduction 5.2. Synthesis 5.3. Properties 5.4. Uses 5.4.1. Adhesives, Sealants, and Coatings 5.4.2. Modification of Bitumen 5.4.3. Compounded Products 5.4.4. Modification of Plastics

Distillation yielded 7.6 g (84%) of dimethyl-p-nitrobenzylamine, bp 96-98°( 1.5 mm), to20d 1.5421.