POLYMERIC TOUGHENING AGENT

Semicrystalline polyamide fine powders have been used as toughening agents for epoxy networks. The powders can be obtained by grinding granules, or directly by anionic polymerization of lactams, 6 or 12, in an organic solvent from which the formed semicrystalline polymer precipitates. Microporous powders with an average particle size in the range of 10 pm and a narrow particle-size distribution, are obtained. 

Two ASA polymers were studied Luran S 757R and Luran S 776S both were made by BASF. The polymers have similar SAN matrices but respectively contain ca. 30 and 40% of the acrylic rubber-toughening agent. The ABS polymer (ABS 500) was made by the Dow Chemical Co. It contained SAN-filled rubber particles ca. 1.0 /an in diameter, suggesting that it was manufactured by bulk or suspension polymerization. 

The impact modifiers or toughening agents described above are all hnear polymers or segments. More recently, there has been some interest in the use of Core-Shell tougheners. These materials consist of a glassy shell grafted by seeded emulsion polymerization onto an elastomeric core. 

Acrylic adhesives are applied to the substrates to be bonded as a liquid mixture of unreacted methacrylate (or acrylate) monomers, polymers to thicken or toughen, reactive resins for strength, adhesion promoters and polymerization agents. Polymerization or curing is... 

Reactive acrylic adhesives generally consist of a solution of a toughening rubber (chlorosulphonated polyethylene) in a partly polymerized mixture of monomers this is mainly methylmethacrylate but ethane diol dimethacrylate is added as a cross-linking agent. The remaining monomer is polymerized in a free radical chain polymerization redox initiation involves an organic peroxide and a tertiary amine. Acrylic cements consist of a partly polymerized acrylic monomer containing an initiator. Cure is established by the thermal or UV decomposition of the initiator (see Radiation-cured adhesives). 

Emulsion graft polymerization processes can be used to obtain coreshell modifiers, in which the core consists of crosslinked poly B (Tg = -6 to -85) or NBR (Tg -45). The latex particle size is very crucial for effective toughening of the diverse matrices styrenic polymers require larger particles (d > 0.2 pm) than engineering polymers id < 0.2 pm), due to their different toughening mechanisms. The ABS composition and properties are affected by the following polymerization variables (1) monomer amount (2) initiator type and amount (3) emulsifier concentration (4) reaction temperature and time (5) chain transfer agents. 

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