End group control

Yoon TH, Arnold CA, McGrath JE (1990) Effect of molecular weight and end-group control on the adhesion behavior of thermoplastic polyimides and poly(imide siloxane) segmented copolymers. 35th International SAMPE Symposium 1892... 

Combination of the head and end group control provides a novel synthetic route for the synthesis of a-hydroxyl-co-methoxycarbonyl asymmetric telechelic PIB H0PIBC(R)(R )C00CH3 (a condensation macromonomer). Hydrolysis of the methoxycarbonyl end group results in the formation of a-hydroxyl-co-carboxyl asymmetric telechelic PIB HOPIBC(R)(R )COOH, while ester dcoholysis provides a method for polycondensation reactions of PIB. In the present publication we report the synthesis of these materials. 

The most widely used rubbers in epoxy technology are butadiene-acrylonitrile copolymers end-capped with carboxyl, vinyl or amine groups. The end-groups control the rubber s particle size and they can also be chosen to ensure that precipitation occurs regardless of the nature and polarity of the curing agent. The polarity of the copolymer determines the compatibility of the modifier with the polymer. 

An example of the importance of end-group control is in acetal resin or polyoxymethylene (POM). As normally prepared from cationic polymerization of sym-trioxane, this polymer has —OH end groups, which readily initiate depropagation to formaldehyde (2) by a molecular mechanism (9) ... 

Spunbonded fabrics have been made from both nylon-6 and nylon-6,6 polymers. Because nylon is more costly and highly energy-intensive, it is less economical than either polyethylene or polypropylene. Although a considerable body of knowledge exists in the preparation of nylon polymers, such as end group control, it has been of little advantage in spunbonded fabric production. Historically, nylon-6,6 spunbonded fabrics have been commercially produced at weights as low... 

Controlled free radical polymerization of acrylonitrile has been achieved by ATRP (atom transfer radical polymerization) [741-747]. Control of molar mass was shown to be possible up to values of = 30,000 g/mol with polydispersities as low as 1.06. However, end group control was limited. This was attributed to oxidation of the free radical to an anion by reaction with Cu [741-743]. 

Furthermore, despite still being the route able to prepare the highest Mjy, ROP inherently produces polymers with broad polydispersities (Mjy/M >2) due to its initiation mechanism, in which the formation of new chains can occur throughout. Although such polydispersity is perfectly tolerable for many medical applications, for example, as inert biomaterials, the method is less suitable for some biomedical applications, in which precise molecular size is often an essential property. Furthermore, advanced polymer architectures and macromolecular constructs cannot be readily attained via this method, due to the absence of end-group control, and hence the development of poly(dichloro)phosphazene with controlled... 

In most reports, the peptide-polymer-conjugates are prepared by using a polymeric macroinitiator for the polymerization of the polypeptide however, the sequence can also be reversed. Polypeptides can be prepared and used as macroinitiators for a polymerization. Particularly suited for this approach are controlled polymerization techniques because they usually allow good end-group control and adjustment of the molecular weight and the molecular weight distribution of the polymer block. There are different mechanisms for a controlled radical polymerization that can be used for this purpose stable free-radical polymerization (SFRP), ATRP, and reversible addition fragmentation chain transfer (RAFT) polymerization. 

For an ideal living polymerization, fe, = 0 and fe = 0 (however, a transfer could occur though reversible ). ROP of cyclic esters, the subject of this chapter, could also proceed as living processes. However, the molar mass and end group control of the resultant polymer are possible only when fej > fep and fe,r = 0. 

The new generation of the single-site catalysts explored until now in CL polymerization do not show any particular advantage over the multiple-site ones, like Al(0 Pr)3, with respect to the molar mass control as well as molar mass distribution (MMD) or the end group control in the resulting Results reported for polymerization... 

In general reviews on telechelics, carbocationic polymerization of vinyl monomers has received little attention due to the high reactivity and low selectivity of the growing species. Therefore, until recently it was widely accepted that the molar mass and end group control necessary for the synthesis of usehil telechelics would not be accessible by carbocationic polymerization. This situation has changed in recent years. 

For an ideaUzed, Uving polymerization k, = 0 and kp = 0. A discovery of the anionic living polymerization of vinyl and diene monomers by Szwarc and coworkers opened a new chapter in macromolecular science [18-20]. ROP, being the subject of the present chapter, may also proceed as a living process. However, molar mass and end group control of the resultant polymer is only possible when kj > kp (Equations 1.3a and 1.3b). 

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