Because every part of the ethylene monomer is included in the finished polymer, the free radical polymerization of polyethylene is referred to as an addition polymerization; the ethylene molecules are simply added together. Polymerizations that use only portions of a monomer, however, are known as condensation polymerizations. The monomers that condense with each other must contain at least two reactive groups in order to form a chain. Condensation reactions result in "condensed" polymers that have less total mass than the monomers used to create them and the by-products, or "condensates," combined.
Algae can be used to produce ' green diesel ' (also known as renewable diesel, hydrotreating vegetable oil  or hydrogen-derived renewable diesel)  through a hydrotreating refinery process that breaks molecules down into shorter hydrocarbon chains used in diesel engines.   It has the same chemical properties as petroleum-based diesel  meaning that it does not require new engines, pipelines or infrastructure to distribute and use. It has yet to be produced at a cost that is competitive with petroleum .  While hydrotreating is currently the most common pathway to produce fuel-like hydrocarbons via decarboxylation/decarbonylation, there is an alternative process offering a number of important advantages over hydrotreating. In this regard, the work of Crocker et al.  and Lercher et al.  is particularly noteworthy. For oil refining, research is underway for catalytic conversion of renewable fuels by decarboxylation .  As the oxygen is present in crude oil at rather low levels, of the order of %, deoxygenation in petroleum refining is not of much concern, and no catalysts are specifically formulated for oxygenates hydrotreating. Hence, one of the critical technical challenges to make the hydrodeoxygenation of algae oil process economically feasible is related to the research and development of effective catalysts.  
Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.