Telechelic starts

Synthesis of Well Defined Copolymer Structures Starting from Ozonized Polymers Block Copolymers, Graft Copolymers, Telechelic Oligomers... 

The synthesis of telechelic oligomers by oxidative cleavage has been extensively studied by numerous authors and Cheradame [117] reviewed the main reactions leading to telechelic polymers starting from high molecular polymers. As he showed, ozonolysis remains one of the preferred method in addition to Ruthenium tetroxide oxidation to obtain a-co functional oligomers. 

Amphiphilic triblock copolymers were prepared from polyethylene glycol) (PEG) [35], Starting from PEG segments of different lengths (Mw = 200,400, MO, 1000 and 1500) and with different end-groups (e,g, hydroxy, acetoxy, benzoyl, oleoyl, phenylurethane), telechelic macroazoinitiators are first prepared. By polymerization of styrene, a wide range of original copolymers are produced ... 

Investigations were mainly devoted to the synthesis of telechelic polymers and copolymers rather than to living radical polymerization. In particular, from 1960, Imoto et al. [234] started surveys on the synthesis of block copolymers from this method. Thus, polystyrene-i>-poly(vinyl alcohol) diblock copolymer... 

The synthesis, starting from a bifunctional initiator followed by quenching the double-headed living ends, gives homotelechelic polymers (method B). Carboxylate-capped telechelic poly(isobutyl vinyl ether) has been obtained in this way [82], where the adduct of a bifunctional vinyl ether with trifluoroacetic acid is the initiator, and the quencher is the malonate anion. For method C, a bifunctional trimethylsilyl enol ether, CH2=C[OSi(CH3)3]C6H4OCH2CH20C6H4[(CH3)3SiO]C=CH2, is a useful terminator (chain coupler) for vinyl ethers [142,147] and a-methyl-styrene [159] (see also Section VI.B.4). 

Let us start with a simple estimation of the hydrogen bonding strength required to avoid macrophase separation under strong segregation conditions, assuming that both telechelic polymers are present in the same number. Sup-... 

Fully swollen modulus of end-linked PDMS networks swollen to equilibrium in toluene at 25 °C. The starting telechelic chains had = 4400 gmol and they were crosslinked at various preparation concentrations in the range 0.3 < < 1. The line is the... 

Such a reaction has been performed successfully, starting from anionically prepared telechelic polymers PX, and neutralizing them quantitatively with very reactive... 

In regard to Step 2, it has been shown that I can be quantitatively converted to the telechelic diolefin II by regioselective dehydrochlorination with a strong hindered base e.g., t-BuOK,in refluxing THF [3]. This diolefin is a valuable starting material for the synthesis of a large variety of other products e.g., telechelic diols [4], diepoxides [11], dialdehydes [12], diacids [13], etc., whose exploration is actively pursued in our laboratories. 

In regard to Step 3, the telechelic diolefin II can be quantitatively converted to the diol V by hy-droboration/alkaline oxidation. Specifically, hydro-boration of II by BH 3 THF (or 9-BBN) yields an intermediate III which without isolation can be converted in situ by alkaline oxidation (NaOH/H2C>2) to the diol IV, the starting material for polyurethane synthesis. The number average functionality of IV was found to be 2.0 within experimental error. The analytical methods used were 1H NMR and UV spectroscopy [4]. The latter method involved the reacting of the diol with phenyl isocyanate, PhNCO, removing the excess PhNCO, filtration, Mn determination and differential UV spectroscopy. Table I shows representative data. 

Figure 1. Gel Permeation Chromatography (GPC) traces of mono-aldehyde functional starting polymer and a,co-telechelic polymer obtained by ATRC.

In some aqueous polymer solutions, hydration is noncompetitive with association. For instance, in solutions of telechelic polymers, main chain hydration only indirectly affects the end-chain association. There is interference only in the region very close to the chain end. Dehydration and chain collapse start near the core of the flower micelles in the form of heterogeneous nucleation. The solutions with such coexisting hydration and association turn into gels on cooling (low-temperature gelation), while they phase separate at high temperatures. 

Notably, the number of functionality of the telechelics thus formed is related to the number of chloro groups present in the inifer. Preparation of telechelics by this method requires low temperatures and highly pure starting materials. 

The hydroxy-terminated telechelics were used as starting material for numerous derivatives (252,253) ... 

Oxidation. Treatment of PVC with ozone (416-418) gives telechelics the attack probably starts at the vinyl double bonds. 

Because of its relative ease of synthesis from inexpensive starting materials, the ureido pyrimidinone (UPy) supramolecular motif has been widely exploited in recent years (Figure la). Appending UPy residues at the terminal positions of telechelic polymers such as end-functional polysiloxanes and polyethylene-co-butylene (pE-co-B), transforms previously free flowing, liquid starting materials into tough, elastomeric solids (Scheme 1). 

While end-functional polymers are clearly important industrial products for materials synthesis, they are also interesting from an academic point of view. Many complex macromolecular architectures can be realized from end-functional polymeric starting materials. Two mono-telechelic polymers can, for example, be joined to form a diblock copolymer, or several such polymers can be joined to form star-like polymers. Mono-telechelic polymers can also be attached to a linear, multifunctional polymer to yield graft copolymers. Depending on the functional end group, such polymers can attach to macroscopic or nanoparticle surfaces or form conjugates with bio-oligomers [5] or biomacromolecules [6]. 

Figure 3.1 gives a generalized graphical overview of all reported syntheses of telechelic polymers via ROMP. Any polymerization within this scheme will start at the far left with either a commercially available ruthenium initiator or precatalyst (initiation box), which is either used as is or needs to be functionally derivatized (initiation box, middle). Alternatively, Mo, W, Ta, or Ti carbene initiators are used (initiation box, top). Subsequently, a monomer... 

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