Reaction, chain, copolymer without termination

In THF, however, no difference in the monomer reactivity ratios was observed between the (S)-MBMA-TrMA and (RS)-MBMA-TrMA systems, and the ratios (r =0.39 and 2- . ) showed similar reactivity of MBMA (Mi) and TrMA ( 2). The copolymerization seemed to proceed without termination and chain transfer reactions. An abnormal optical property was observed in some of the copolymers of (S)-MBMA and TrMA. Table shows the tacticity and optical data of the copolymers which were obtained in various polymer yields from the monomer mixtures of a constant molar ratio, [Mllo/[M2]o = The (S)-MBMA content in the copolymers decreased... 

To further demonstrate the livingness of the process a chain extension of PNIPAAm was carried out. The initial block was obtained by using a ratio [M]o/[BIBA]o/[CuCl]o/[CuCl2]o/[Me6TREN]o of 120/1/1.6/0.4/2 with a NIPAAm concentration of 0.5 M. Then the block copolymer was synthesized by sequential addition after 38 min of a degassed aqueous solution of monomer (0.5 M) without purification of the macro-initiator. A CuCl-based catalyst was chosen to perform the reaction to avoid any termination. Indeed, in water, bromide-terminated polymers can be sensitive to halogen abstraction by nucleophilic substitution. Then with CuCl the resulting polymer-halide bound C-... 

The polymerization methods leading to linear diblock, triblock or segmented block copolymers are based on two general reaction schemes. In a first one, a or a, oj active sites are generated on a polymer chain poly A which then initiate the polymerization of a second monomer B. Such a polymerization can be of free radical, anionic or cationic type and preferably of living type which proceed without termination and transfer reactions. The concept of this synthesis is given in Figure 7.2. 

The analysis of the reaction serum (the continuous phase without polymer particles) at the end of polymerization led to the conclusion that the molecular weight of the soluble oligomers of styrene and PEO macromonomer varied from 200 to 1100 g mol-1. This indicates that the critical degree of polymerization for precipitation of oligomers in this medium is more than ten styrene units and only one macromonomer unit per copolymer chain. Several reasons for the low molecular weight of the soluble copolymers were proposed, such as the thermodynamic repulsion (or compatibility) between the PEO chain of the macromonomer and the polystyrene macroradical, the occurrence of enhanced termination caused by high radical concentration, and, to a lower extent, a transfer reaction to ethanol [75]. 

In the past two years, a number of new approaches have been reported for obtaining controlled NCA polymerizations. These approaches share a common theme in that they are all improvements on the use of classical primary amine polymerization initiators. This approach is attractive since primary amines are readily available and since the initiator does not need to be removed from the reaction after polymerization. In fact, if the polymerization proceeds without any chain breaking reactions, the amine initiator becomes the C-terminal polypeptide end-group. In this manner, there is potential to form chain-end-functionahzed polypeptides or even hybrid block copolymers if the amine is a macroinitiator. The challenge in this approach is to overcome the numerous side-reactions of these systems without the luxury of a large number of experimental parameters to adjust. 

Polyimide containing poly(ethylene oxide) is a simple and convenient way to improve the gas separation properties. The copolymers are synthesized by the reaction of dianhydride and diamines with/without amine-terminated poly(ethylene oxide). Maya el al. and Munoz et al. reported thermal treatment effect of PEO-Z)-PI copolymer on the gas permeation properties. Phase segregation of the polymer chain at higher treatment temperature to 300 °C contributed to improvement of gas permeability of the membrane. Molecular weight of poly(ethylene oxide) of 6000 was appropriate to induce microphase separation. CO2 permeability was reached from 2.3 to 24 Barrer according to the PEO composition before thermal treatment, while it was enhanced by three to ten times higher permeability after thermal treatment at 300 °C without serious reduction in permselectivity. 

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