CO AGENT

Whereas polyisobutylene and butyl mbber exhibit chain cleavage on free-radical attack, halobutyls, particulady bromobutyl and CDB, are capable of being cross-linked with organic peroxides. The best cure rate and optimal properties are achieved using a suitable co-agent, such as y -phenjiene bismaleimide. This cure is used where high temperature and steam resistance is required. 

Table 11.19 gives the cure characteristics of the blends for high and low peroxide, sulfur, and co-agent (peroxide + sulfur) combinations. They found that the maximum and minimum torques... 

Cure Characteristics of the Blends for High and Low Peroxide (P), Sulfur(S), and Co-Agent C (Peroxide -E Sulfur)... 

Mechanical and Physical Properties of EPDM and EPDM-SBR Blends Cured with Peroxide and Sulfur Co-Agent Cure System... 

Initially, the co-agents were mixed with PVDF and FMVQ separately and the mixtures were subjected to mild irradiation. Solubility tests indicated no cross-hnking during this operation. The polymeric components were then mixed in the presence of CaO/MgO in a Brabender plasticorder at a rotor speed of 60 rpm at 160°C. Subsequently, the temperature was lowered to 130°C and a 0.2% benzoyl peroxide paste was added. Mixing was continued for 10 more minutes. Cure characteristics... 

Peroxide Cross-Linking of EPM Using Polar Co-Agents.404... 

In order to test this concept a series of compounds was prepared in a 5 L Shaw Intermix (rubber internal mixer, Mark IV, Kl) with EPDM (Keltan 720 ex-DSM elastomers an amorphous EPDM containing 4.5 wt% of dicyclopentadiene and having a Mooney viscosity ML(1 +4) 125°C of 64 MU 100 phr), N550 carbon black (50 phr), diisododecyl phthalate (10 phr), stearic acid (2 phr), and l,3-bis(tert-butylperoxy-isopropyl)benzene (Perkadox 14/40 MB ex Akzo Nobel 40% active material 6 or 10 phr). A polar co-agent (15 phr) was admixed to the masterbatch on an open mill and compounds were cured for 20 min at 180°C in a rheometer (MDR2000, Alpha Technologies). The maximum torque difference obtained in the rheometer experiments was used as a measure of... 

FIGURE 13.8 Co-agents used. From left to right m-phenylenedimaleitnide (PDMI), m-phenylenedi(maleamic acid) (PDMA), l,6-hexamethylenedi(maleamic acid) (HMDMA), and trimethylolpropane trimethacrylate (TMPTMA). 

FIGURE 13.9 Effect of polar co-agents on oil swell properties of peroxide-cured ethylene-propylene-dicyclopentadiene terpolymer. 

Apart from peroxide types and amount of peroxide incorporated in compounds, the efficiency of cross-linking depends on co-agents. The commercially notably ones are... 

The crosslinking of ethylene-propylene copolymer rubber (EPR) in the presence of organic peroxides has been investigated by Natta and/or his coworkers (1-3) and others (4,5). Co-agents such as sulfur (3,4) and unsaturated monomers (6), including maleic anhydride (MAH)(3,7) have been utilized in an effort to increase the crosslinking efficiency in the EPR-peroxide system. 

To my friend and agent Mary Cunnane, I owe an enormous debt. She gave me the courage and inspiration to attempt the book, and she trained me patiently in how to overcome some academic bad habits. Thanks to my co-agent Peter McGuigan, whose zest, enthusiasm, and advice have proved indispensable at the U.S. end. Dan Conaway of HarperCollins was a wonderful editor his enthusiasm, patient hard work, and talent have greatly improved the book. 

Blends of poly (ethylene terephthalate) (PETP) and polypropylene (PP) with different rheological properties were dry blended or compounded, and extrusion foamed using both physical blowing and chemical agents, and the foam properties compared with those of foam produced from the individual components in the absence of compatibilisers and rheology modifiers. The foams were characterised by measurement of density, cell size and thermal properties. Low density foam with a fine cell size was obtained by addition of a compatibiliser and a co-agent, and foamed using carbon dioxide. The presence of PP or a polyolefin-based compatibiliser did not effect... 

Oxidizing agent Co-agent Solvent (%) trans .cis ee (%) R References... 

Co-agents are multi-unsaturated compounds, which are used in the peroxide-curing of elastomers. When classical co-agents, such as triallylcyanurate (TAC), trimethylolpropanetrimethacrylate (TRIM) or diallylterephthalate (DATP), are added, the crosslinking efficiency is enhanced [98-102]. Various mechanisms for the increase of the crosslinking efficiency have been proposed. In all cases a fast reaction between the... 

Apart from the effect on the crosslinking efficiency, the use of co-agents in peroxidecuring also imparts the molecular structure of crosslinks. It has been reported that coagents with two or more unsaturated moieties can be incorporated as individual molecules between two elastomer strands to form crosslinks [103-109]. In this way the crosslink structure of peroxide-cured elastomers can be altered. Thus, apart from the expected benefits, such as improved crosslinking efficiency, decreased compound viscosity and faster cure, the use of co-agents may also provide a tool for manipulating mechanical properties. 

If the effect of co-agents on crosslinking efficiency is just the suppression of macroradical side reactions, such as chain scission and disproportionation, one should expect monofunctional co-agents to be as effective as their multi-functional analogues (if compared at the same molar level of unsaturation). This is definitely not the case, as will be demonstrated. 

The results clearly demonstrate that a diallyl functional co-agent such as DAO, provides a marked improvement in the crosslinking efficiency, whereas its monoallyl functional... 

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