Direct Polymerization Route

The direct polymerization method comprises the direct polymerization of aromatic diamine with the aromatic tricarboxylic acid anhydride in the presence of a dehydration catalyst. Dehydration catalysts include triphenyl phosphite, triphenyl phosphate, and tri-n-butyl phosphite. The reaction 

Alternarively, the azeohopic condensation technique is used to remove the water. In the modified direct polymerization route, diaminodi-phenyl ether, m-phenylenediamine (MPD) and trimellitic acid anhydride in a ratio of total 1 mol of diamino compound and 2 mol of anhydride compound are condensed in NMP using xylene to remove the water formed. The resulting diimidedicarboxylic acid is treated with thionyl chloride to form the acid chloride on the fly and the PAl is created by adding a mixture of diaminodiphenyl ether and MPD.  

PAI with a deflnite head-to-tail backbone can be prepared by condensation of trimelliric acid anhydride with 4-amino-4-nitrodiphenyl ether. Then the nitro group is reduced to give a monomer having amine and acid functional groups. This monomer is subjected to direct polymerization. The procedure is useful for the preparation of dissymmetric polymers. Further compounds with amino groups and nitro groups are 3-nitroaniline, 2-methyl-5-nitroaniline, and, 3-nitromesidine, i.e, 2,4,6-trimethyl-3-nitro-aniline. 

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Three approaches have been developed for the synthesis of polyphosphazenes. These are (1) The macromolecular substitution route (2) The cyclic trlmer or tetramer substitution/polymerization route, and (3) Direct synthesis from organosllylphosphazene monomers. This last method Is described In detail In another Chapter and will not be considered further In this review. 

Note 3 In most cases, the polymer can actually be made by direct polymerization of its parent monomer but in other cases, e.g., poly(vinyl alcohol), the description conceptual denotes that an indirect route is used because the nominal monomer does not exist. 

An additional elegant route to obtain disentangled UHMW-PE, and thus to control the interphase, is by direct polymerization in the reactor. In order to make UHMW-PE, a relatively low polymerization temperature is needed and a situation is easily encountered where the polymerization temperature is lower than the crystallization temperature of UHMW-PE in the surrounding medium in which the catalyst is suspended. In this situation, the growing chains on the catalyst surface tend to crystallize during the polymerization process. These UHMW-PE reactor powders, often referred to as nascent or virgin UHMW-PE, can be remarkably ductile. It was shown by Smith et al. [26] that reactor powders, in the same manner as solution-cast UHMW-PE, could be drawn easily into high-modulus structures. 

In order to introduce a functional group, a first route is based on the conversion of polyesters or polymers bearing pendant ester groups into the corresponding polyenolates, followed by reaction with a judiciously substituted electrophile. A second strategy is the direct polymerization of an acrylate or a methacrylate substituted by a functional group. 

In principle, conjugated materials may either be directly synthesized via metathesis polymerization of acetylene or 1-alkynes, via ROMP of various cyclooctatetraenes (COTs) or via ROMP of polyene precursors as realized in the Durham route [107-111]. The first direct polymerization of acetylene to yield black untreatable unsubstituted polyacetylene was achieved with W(N-2,6-i-Pr2-C6H3)(CH-t-Bu)(OC-t-Bu)2 [112]. In order to obtain soluble polymers, polyenes were prepared via the ROMP of a polyene-precursor, 7,8-bis(trifluoromethyl)tricyclo[4.2.2.02 5]deca-3,7,9-triene (TCDTF6), using initiators such as W(N-2,6-i-Pr2-C6H3)(CH-t-Bu)(OC-t-Bu)2) (Scheme 5.10) [113, 114]. 

The Durham route allows the preparation of polyacetylene in the form of continuous uniform and featureless films, as opposed to the entangled fibrillar morphology obtained by the direct polymerization of acetylene. 

Recently, researchers have foimd successful routes to the formation of highly monodisperse liquid crystalline polymers with well defined structures via direct polymerization of the mesogens -. In particular, anionic polymerization is very attractive and allows synthesis of liquid crystalline polymers with well-defined structures, high stereoregularity, and a uniform chain length. In addition, living anionic polymerization is... 

Azeotropic dehydration and condensation polymerization (route 2 in Figure 8.2) yields directly high molar mass polymers. The procedure, patented by Mitsui Toatsu Chemicals [13, 14], consists of the removal of condensation water via a reduced pressure distillation of lactic acid for 2-3h at 130°C. The catalyst (in high amounts) and diphenyl ester are added and the mixture is heated up to reflux for 30-40 h at 103°C. Polycondensated PLA is purified to reduce residual catalyst content to the ppm range [5,10,15]. 

The understanding of the mechanisms involved in the polymer synthesis with natural precursors is definitively a key factor for their appropriate exploitation. Taking into account this need, Ronda et al. explained recently different pathways to modify natural resources. These authors proposed three routes to modify vegetable oils to transform them into polymers (1) direct polymerization (cationic, radical, or thermal polymerization) (2) functionalization and polymerization and (3) monomer synthesized, chemical modification and polymerization [32]. 

Several process routes have been developed or are practised on industrial scale Ring Opening Polymerization (ROP), Direct Polycondensation in high boiling solvents (DP-S) and Direct Polymerization in bulk followed by chain extension with reactive additives. 

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