Chain extension experiments

Figure 3 shows the molecular weight versus conversion plot for the polymerization of VAc mediated by Co(acac)2. The plot was hnear and passed the origin, and the polydispersity of the prepared PVAc was lower than 1.3, indicative of living features of the polymerization. The hving features were further confirmed by a chain extension experiment. " ... 

Figure 11. GPC curves of the PVAc macroinitiator (a) and the resulting PVAc polymer (b) in chain extension experiment. Experimental conditions 70°C, [VAc] = 10.8 M, [CuBr] = [tPyJ = [PVAc acroini] = 0.11 M. (Reproduced with...

To avoid autoinitiation, the bulk polymerization was carried out at 65 °C. When DBU was used as a catalyst in the presence of benzyl alcohol, TMC was polymerized within minutes, yielding polymers with controlled molecular weight and small dyspersity index (1.09-1.15). To demonstrate the living nature of the polymerization carried out under bulk conditions, the chain extension experiment was conducted. Resultant polymer growth proceeded in a linear fashion. It was demonstrated that the intermediate chains can be employed for further growth, by the addition of more... 

Several examples of chain-extension experiments and block copolymer syntheses carried out in the absence of donor ligands have been reported for PVAc-Co(acac)2 maaoinitia-... 

Also present in the first test tube is a synthetic analog of ATP in which both the 2 and 3 hydroxyl groups have been replaced by hydrogens This compound is called 2 3 dideoxyadenosme triphosphate (ddATP) Similarly ddTTP is added to the second tube ddGTP to the third and ddCTP to the fourth Each tube also contains a primer The primer is a short section of the complementary DNA strand which has been labeled with a radioactive isotope of phosphorus ( P) When the electrophoresis gel is examined at the end of the experiment the positions of the DNAs formed by chain extension of the primer are located by a technique called autoradiography which detects the particles emitted by the P isotope... 

The parameters of neutron scattering theory of polymer networks are A, the macroscopic stretching of the sample, or linear degree of swelling, f, the network functionality, K. which accounts for restricted junction fluctuations and a, a measure of the degree to which chain extension parallels the macroscopic sample deformation. The functionality is known from knowledge of the chemistry of network formation, and A is measured. Both K and a must be extracted from experiments. 

In this review, we have given our attention to Gaussian network theories by which chain deformation and elastic forces can be related to macroscopic deformation directly. The results depend on crosslink junction fluctuations. In these models, chain deformation is greatest when crosslinks do not move and least in the phantom network model where junction fluctuations are largest. Much of the experimental data is consistent with these theories, but in some cases, (19,20) chain deformation is less than any of the above predictions. The recognition that a rearrangement of network junctions can take place in which chain extension is less than calculated from an affine model provides an explanation for some of these experiments, but leaves many questions unanswered. 

Bunz et al. explored the possibility of doping PPE chains covalently with small amounts of fluorescence-quenching cyclobutadiene complexes, in order to endow their optical properties to the base polymer, PPE [80]. Due to their extensive experience of cyclobutadiene complexes in polymer synthesis [81], the authors prepared several polymers PAE-CoCpl-5 (Table 4) containing different contents of CoCp complexes. The quantum yields were determined by simple comparison of the intensities of the emitted light to that of a standard... 

In one experiment (Hindley, J., unpublished data) a set of dideoxy-nucleotide chain extension reactions, using an identical primed-template, was carried out at 14, 20 and 29°C respectively and the reaction products analysed on a standard thin sequencing... 

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