Glass transition temperature elastomeric networks

In any case, if this polymerized form of elemental sulfur is quenched (cooled rapidly), it becomes a solid. This solid is glassy at very low temperatures, but becomes highly elastomeric above its glass-transition temperature of approximately -30 °c.6 8 14 30 The situation is complicated by the presence of unpolymerized S8 molecules which would certainly act as plasticizers. So far, attempts to cross-link the elastomeric form into a network structure suitable for stress-strain measurements have not been successful. The polymer is unstable at room temperature, gradually crystallizing, and eventually reverting entirely to the S8 cyclics. 

For PDMS-modified Si02 glasses, structural analysis shows that this hybrid material has some degree of localized phase separation of the PDMS component, even though OH-terminated PDMS can be successfully incorporated into the Si02 network by chemical bonding. The PDMS component can behave as an elastomeric phase because the glass-transition temperature of PDMS is far below room temperature.52 54... 

In order to study elastomeric networks, simulating the type of polymers used for tires, we switched to polymers with low glass transition temperatures and oligoether bis-maleimides. A typical random copolymer structure, built from the radical copolymerization of n-hexyl acrylate and 2-furfuryl methacrylate, is shown below. These reactions were conducted in toluene at 80°C with AIBN as initiator. After 8 h, the copolymers were recovered by precipitation in 70 to 80% yields. The compositions varied fi om 2 to 30% of the furanic monomer (monomer feed and copolymer composition were always very similar, suggesting that ri and ti must have both been close to unity). The corresponding Tgs went from -70 to 30°C for molecular weights of about 20,000. Both homopolymers were also prepared as reference materials. 

In order to complete our model, we need to know the soft phase modulus, Egp. It depends on several factors, most notably polyol equivalent weight. Eg, polyol functionality, fp, and polyol glass transition temperature, Tgp. At temperatm-es substantially above (elastomeric region), the modulus of the soft phase can be described using network elasticity models [57-59] ... 

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