Gradient copolymers reactivity ratios

Gradient copolymers of St and AN were also prepared [115,116]. Since St and AN have reactivity ratios that are both significantly less than 1, the copolymerization has an alternating tendency along the backbone with an enrichment in AN at high conversions. Alternatively, a gradient along the backbone can be... 

Random and Gradient Type The spacing between the grafting sites in the polyinitiator backbone can be systematically varied by the incorporation of a noninitiating comonomer into a backbone. For example, TMS-HEMA as a precursor of an ATRP initiator has been copolymerized with MMA [94, 96, 114, 115). The reactivity ratios of MMA and TMS-HEMA are close to unity, which generally leads to random copolymers. However, when these random copolymers were applied as the main chains, CPBs with a random distribution of side chains along the... 

In ordinary batch copolymerization there is usually a considerable drift in monomer composition because of different reactivities of the two monomers (based on the values of the reactivity ratios). This leads to a copolymer with a broad chemical composition distribution (CCD). In many cases (depending on the specific final product application) a composition drift as low as 3-5% cannot be tolerated, for example, copolymers for optical applications on the other hand, during production of GRIN (gradient index) lenses, a controlled traj ectory of copolymer composition is required. This is partly circumvented in semibatch operation where the composition drift can be minimized (i.e., copolymer composition can be kept constant ) by feeding a mixture of the monomers to the reactor with the same rate by which each of them is consumed in the reactor. 

Via cationic living copolymerization, iPrOZO as hydrophobic monomer and EtOZO as hydrophilic monomer produced a copolymer P[iPrOZO-co-EtOZO]. Monomer reactivity ratios were determined as riProzo = d Z9 and rEtozo=l Z8, respectively. These values allowed the development of gradient copolymers 8000-10 000) with varying compositions... 

A forced gradient copolymer can also be prepared by controlled feeding of one or more monomers in a manner that compels the composition to be tapered through control over the ratio of available monomers. However, reactivity ratios still have to be considered. 

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