Elastomerization, impact resistance

The chapter discusses the development of new blends of PPS with polymers such as elastomeric impact resistant modifiers, polycarbonates, pol-yarylethersulfones, polyamide-imides, modified polyphenylene ethers,... 

Thermoplastic polymers, such as poly(styrene) may be filled with soft elastomeric particles in order to improve their impact resistance. The elastomer of choice is usually butadiene-styrene, and the presence of common chemical groups in the matrix and the filler leads to improved adhesion between them. In a typical filled system, the presence of elastomeric particles at a level of 50% by volume improves the impact strength of a brittle glassy polymer by a factor of between 5 and 10. 

By the process of vulcanization, rubber elasticity, impact resistance, flexibility, thermal stability and many other properties are either introduced or improved. In addition, the crosslinking of non-elastomeric polymers increases the toughness, abrasion resistance and, particularly, the maximum service temperatures of the material. 

Toughened polypropylene may be prepared by block copolymerization in which ethylene monomer is added during the final stages of the polymerization of propylene (4). Thus, some polypropylene chains would contain an end block of rubbery ethylene-propylene copolymer. Alternatively, a blend of an elastomeric copolymer of ethylene and propylene (EPR or EPDM) with isotactic polypropylene (PP) can produce an impact-resistant polymer (5). 

The excellent performance of metallocenes in copolymerizations also offer improvements in impact copolymers. In the wide variety of properties of impact copolymers, the stiffness of the material is determined by the matrix material, while the impact resistance largely depends on the elastomeric phase. While conventional catalysts show some inhomogeneities in the ethene/propene rubber phase due to crystalline ethene rich sequences, the more homogenous comonomer distribution obtained with metallocene catalysts results in a totally amorphous phase [153]. 

The addition of an elastomer (typically a high butadiene content SBS) to SBC will serve to enhance further the elastomeric properties of the SBC. One key feature mentioned previously was improvement in hinge life properties. SBS copolymers can also be added to thermoformed sheet in blends of SBC and crystal polystyrene. The SBS does cause some loss of clarity, but gives more impact resistance to the sheet. Selection of the proper SBS can result in minimal loss of clarity, typically at 3-10% loadings. Styrene-isoprene copolymers (SIS) have also been tested with SBC and can give similar results in impact property improvement. 

Glassy polymers, PMMA and PS, are suitable for many applications, but they are brittle when subjected to impact loads. The same things happens with thermoset polymers such as epoxy or phenolic resins. To solve this problem, impact-resistant polymers have been developed that basically consist of a matrix of the brittle polymer in which a second elastomeric... 

Howard E.G., Jr. Impact-Resistant Heat-Formable Filler-Containing Polymer/Elastomeric Fiber Composites U.S. Patent Applied 87-96098, Sept 11, 1987. 

For electrostatic and steric stabilization, the particles can be viewed effectively as colloids consisting of a soft and deformable corona surrounding a rigid core. Colloidal particles with bulk elastomeric properties are also available. These particles, which are generally of submicron size, are developed and used as reinforcement additives to improve the Impact resistance of various polymer matrices [28-30]. The rubber of choice is often a styrene/butadiene copolymer. The presence of chemical groups at the matrix-filler interface leads to improved adhesion between them. Typically, the addition of about 30% by volume of these elastomeric particles increases the impact strength of a brittle glassy polymer like polystyrene by up to a factor of 10. For some applications, particles with more complex architecture have been... 

The elastomeric materials most commonly used for this purpose are carboxyl-terminated acrylonitrile-butadiene copolymers. The carboxyl groups react with the epoxy group to produce an epoxy-terminated rubber that promotes interfacial bonding in two-phase systems (9). By controlling the concentrations of M, Xj, X2, Z, and U, a broad range of compatibilities can be achieved. Impact resistance and fracture toughness are Increased with minimal sacrifice in molulus and elevated-temperature performance. 

Miscellaneous applications of poly(phosphazenes) include ter-butoxycarbonyl protected materials for chemically amplified resists in microlithographythin film electroluminescent devices,optical wave guides, aryloxy derivatives as components of fire-, heat- and impact-resistant materials and components of a low-density, thermoplastic elastomeric, ablative insulation for rocket motors. ... 

Nature and Amount of the Dispersed Rubber Phase. The effect of the nature of the dispersed rubber phase became apparent during our work on selective plasticization of systems containing two resins A and B, a corresponding AB Cop, and a selective plasticizer of polymer A or B (13, 14) where A was polystyrene (PS) and B was poly (methyl methacrylate) (PMM) or poly (vinyl chloride) (PVC). Selective plasticization is a new method of obtaining resin elastomeric systems which have the advantage that the physical properties (e.g., mechanical properties and refractive index) of the rubbery phase can be varied by the nature and amount of the plasticizer. For such systems, impact resistance is maximum when the energy absorption capacity of the rubbery phase is maximum (e.g., for a given amount of plasticizer with respect to the dispersed phase). 

PC Blends PC with PDMS PC with siloxane elastomer PC with PArSi PC or PEC with PC-b-PDMS PC with elastomeric polysiloxane/ polyvinyl-based graft copolymer solution cast films impact resistance transparent, flame impact resistant low-flammability and good impact strength thermally stable, low-T ductility, impact- and heat- resistance Caird, 1961 De Boer Heuschen, 1988 Jordan Webb, 1992, 1994 Hoover, 1993 Derudder Wang, 1993... 

Saunders and Pelletier [1976] claim in a patent to have produced polymer blends having high impact resistance, by blending together a non-elastomeric monovinylidene aromatic polymer, such as polystyrene, with a radiation-crosslinked elastomeric copolymer, such as a block copolymer of styrene and butadiene. However, since in this work the blends were not irradiated, they will not be discussed here. 

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