Polybutadiene green strength

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. 

With barium-containing anionic initiators [88] polybutadiene with a high trans content [89] and less then 5 % of vinyl double bonds can be synthesized. This rubber does not crystallize at room temperature but can undergo crystallization upon stretching. The properties of rubber, e. g., green strength, tackiness of the compound, as well as tensile strength of the vulcanizate, are much improved by strain-induced crystallization. 

A strain-crystallizing material like NR shows much better autohesion. It can be processed to a relatively low viscosity for easy wetting on contact, and still exhibit green strength due to strain-induced crystallization. Several other strain-crystallizable elastomers have been synthesized and shown to exhibit autohesion and green strength comparable or superior to that of NR. These include rran.s-polypen-tenamer, fran -butadiene-piperylene elastomers, and uranium-catalyzed polybutadiene. 

The added raw material and production costs relative to other elastomers (polybutadiene, styrene-butadiene copolymers, etc.) have kept polyoctenamer from entering the realm of a commodity mbber, but Vestenamer has achieved success as a minor component in numerous elastomer blends. Formulations containing 10-20% of Vestenamer have lower melt viscosity and better green strength than their parent... 

A small amount of another elastomer, such as EPDM or high cB-polybutadiene, blended with CSM increases compound green strength, especially in mineral-filled compounds, giving a stiffer, more easily handled compound. Better release of the stock is obtained with the polybutadiene. 

A high cw-polybutadiene or EPDM at levels of 3-5 phr are useful at improving release and increasing green strength. Their presence has little effect on cure rates... 

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