Ethane polymerization

Parallel-plate electrodes Ethane polymerization Plug flow with axial dispersion Not applicable Assumed average electron density and energy 66... 

As an extension to their work, the same group have prepared polymer-supported Zr di-Ind complex 251 from polystyrene (Scheme 89). Lithiation of the polystyrene, treatment with 1,4-dibromobenzene, and further lithiation gave 249 which was treated with PhSi(Ind)2Cl to give the supported ligand 250. The metal complex 251 was formed by treatment of this with ZrCU. The use of 251 for ethane polymerization was assessed and subsequently the mechanism of polyethylene growth on the surface of the supported catalyst beads has been studied. 

A polymer containing an r -bridged zirconacene 262 was prepared by co-polymerization of monomer 263 with styrene. This was then used as a catalyst for ethane polymerization but found not to give good results due to the non-uniform distribution of the metal sites on the polymer backbone. Questions were also raised regarding the accessibility of the metal sites. 

Prepa.ra.tion, The preparation of amorphous high (99%) 1,2-polybutadiene was first reported iu 1981 (27). The use of a heterocycHc chelating diamine such as dipiperidine ethane iu the polymerization gave an amorphous elastomeric polymer of 99.9% 1,2 units and a glass-transition temperature of +5°C. In a previous description (53,54) of the use of a chelating diamine such as A/A/N(N -tetramethylethylene diamine, an 80% 1,2-polybutadiene with a glass-transition temperature of —30°C was produced. 

Moleeules that are normally unreactive can be readily polymerized in such a process. Examples include organie gases such as ethane and various organosilanes. Monomers such as hexamethyldisiloxane can be readily polymerized to fonn tightly adherent films having a silica-like structure ... 

Chemical Reactivity - Reactivity with Water Reacts violently to form flanunable ethane gas Reactivity with Common Materials Will react with surface moisture, generating flammable ethane gas Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

The dendritic growth of lithium was suppressed on a lithium electrode surface modified by an ultrathin solid polymer electrolyte prepared from 1,1—difluoro-ethane by plasma polymerization [114]. 

A third process involves use of the species (X-X) to generate (he stable radical in pairs and relies on the stable radical being able to react with monomer, albeit slowly, to generate P]X (Scheme 9.6). Polymerizations with dithiuram and other disulfides (Section 9.3.2.1) and hexasubstituted ethanes (Section 9.3.4) belong to this class. 

The first use of sterically hindered hexasubstituted ethanes [e.g. 33] as initiators of polymerization was reported by Bledzki et al.77,78 The use of related initiators based on silylatcd pinacols [e.g. 34, 35] has been reported by Crivcllo et a/.,7l>82 jjan( os et ai i anOther initiators of this class include 36 fi X/ and 37.The rates of decomposition of hexasubstituted ethanes and the derived macroinitiators are known to vary according to the degree of steric... 

The proposed polymerization mechanism is shown in Scheme 9.12. Thermal decomposition of the hexasubstituted ethane derivative yields hindered tertiary radicals that can initiate polymerization or combine with propagating species (primary radical termination) to form an oligomeric macroinitiator. The addition of the diphenylalkyl radicals to monomer is slow (e.g. k[ for 34 is reported as KT M"1 s l at 80 °C84) and the polymerization is characterized by an inhibition period during which the initiator is consumed and an oligomeric macroinitiator is formed. The bond to the Cl I formed by addition to monomer is comparatively thermally stable. 

The small molecules used as the basic building blocks for these large molecules are known as monomers. For example the commercially important material poly(vinyl chloride) is made from the monomer vinyl chloride. The repeat unit in the polymer usually corresponds to the monomer from which the polymer was made. There are exceptions to this, though. Poly(vinyl alcohol) is formally considered to be made up of vinyl alcohol (CH2CHOH) repeat units but there is, in fact, no such monomer as vinyl alcohol. The appropriate molecular unit exists in the alternative tautomeric form, ethanal CH3CHO. To make this polymer, it is necessary first to prepare poly(vinyl ethanoate) from the monomer vinyl ethanoate, and then to hydrolyse the product to yield the polymeric alcohol. 

Acetaldehyde (Acetic aldehyde, ethanal) CHjCHO -38 185 4.0-55.0 0.8 1.5 21 Colourless fuming liquid Pungent odour Irritant Water soluble Can polymerize exothermically, form explosive peroxides, or react violently with other chemicals... 

---