Polybutadiene crystallinity level

The minimum service temperature is determined primarily by the Tg of the soft phase component. Thus the SBS materials ctm be used down towards the Tg of the polybutadiene phase, approaching -100°C. Where polyethers have been used as the soft phase in polyurethane, polyamide or polyester, the soft phase Tg is about -60°C, whilst the polyester polyurethanes will typically be limited to a minimum temperature of about 0°C. The thermoplastic polyolefin rubbers, using ethylene-propylene materials for the soft phase, have similar minimum temperatures to the polyether-based polymers. Such minimum temperatures can also be affected by the presence of plasticisers, including mineral oils, and by resins if these become incorporated into the soft phase. It should, perhaps, be added that if the polymer component of the soft phase was crystallisable, then the higher would also affect the minimum service temperature, this depending on the level of crystallinity. 

Polyester diols are often combined with polyether diols to provide green strength through crystallization or elevated r . Most prevalent and least expensive is hexamethylene diol adipate (HDA) with a Tm of about 60°C. A variety of polyesters are available with various levels of crystallinity — from wax-like to amorphous — and crystallization rate, and with values ranging well below 0°C to above room temperature. Polybutadiene diols are the most expensive and most hydrophobic. They provide low surface tension and thus good wet out of non-polar surfaces. 

Hydrogenation of 1,4 polymerized polyisoprene leads to a perfectly alternating ethylene-propylene rubber. Such a polymer is non-crystalline, has a Tg of about -60 C, and makes a good rubber. On the other hand, hydrogenation of 1,4 polymerized polybutadiene leads to a polyethylene (polymethylene) chain which is crystalline and not a good rubber at all. Butadiene also readily polymerizes through the 1,2 carbons which are converted to a butylene structure on hydrogenation. The crystallinity introduced by the methylene enchainment of a 1,4 polymerized butadiene monomer can be broken up by the butylene structure. About 40% 1,2 addition is needed to ensure a low level of crystallinity and preserve a low Tg. ... 

Graessley and co-workers " were able to crystallize a polybutadiene sample which only contained 56 mol % of the 1,4-trans units. Depending on molecular weight, the level of crystallinities that developed ranged from 2 to 5%. Thus, copolymers which contain a very high non-crystallizing content can be crystallized not only in principle but also in practice. At low temperatures, where these small amounts of crystallinity develop, anomalies were observed in the viscoelastic behavior of these polybutadienes. " Presumably, other physical properties will also be affected. 

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