Symmetrical telechelic

A more general strategy to approach symmetrical telechelic polyesters consists of the control of both initiation and termination steps. Indeed, combination of a functional initiator for the (di)lactones ROP with an effective coupling... 

Telechelic or a, )-bifunctional and multifunctional polymers carry functional groups at each terminal. Symmetric telechelic or multifunctional polymers can be readily prepared by employing bi- or multifunctional initiators followed by functionalization of the living end as described above [132]. 

Another problem associated with the batch technique is poor reaction control (unsatisfactory stirring, temperature control, etc). To overcome the problems outlined above a semi-continuous polymerization technique has been introduced [27]. In this technique a mixed monomer/inifer feed is added at a sufficiently low constant rate to a well stirred, dilute BC13 charge. Due to stationary conditions maintained during the whole polymerization, well-defined telechelic products with symmetrical end groups and theoretical polydispersities could be obtained. The kinetics of the polymerization has been discussed and the DPn equation has been derived. In contrast to the batch technique, the DPn for the semi-continuous technique is simply given by the [monomer]/[inifer] ratio. Thus, very reactive or unreactive inifers, unsuitable for batch polymerization, can also be used in the semi-continuous process. 

The selectivity and efficiency of RUO4 was verified not only with butyl rubber, which yields asymmetric a-carboxy-cu-ketone telechelics, but also with poly(isobutylene-co-2,3-dimethylbuta-diene), which yields symmetric a,oj-diketone and a,co-dicarboxy telechelics. If incorporation of the diene is sterically specific, these methods can be used to obtain ideal functionalization (/=2), provided that high molar mass starting materials are employed. The scope of RUO4 cleavage is not restricted to copolymers of isobutylene and dienes. It was also applied to partially hydrogenated polybutadiene to yield an a,co-dicarboxy-(PE). ... 

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