Καλά καθορισμένα κτενοειδή πολυμερή

Abstract

Two methodologies, based on living star polymers and anionic polymerizations high vacuum techniques, were used for the synthesis of exact comb polybutadienes (PBds) with two (C-2 or H-type) and three identical branches (symmetric, sC-3, H-type with an extra identical branch at the middle of the connector and asymmetric, aC-3, H-type with the extra identical branch at any other position along the connector). The first methodology involves (a) the selective replacement of the two chlorines of 4-(dichloromethylsilyl)diphenylethylene (DCMSDPE, key molecule) with 3-arm star PBds, by titration with identical (C-2, sC-3) or different (aC-3) living 3-arm star PBds, (b) the addition of s-BuLi to the double bond of DPE, and (c) the polymerization of butadiene from the newly created anionic site (sC-3, aC-3).The second methodology involves the reaction of living stars with dichlorodimethylsilane (C-2) or the selective replacement of the three chlorines of trichloromethylsilane with star and linear chains (sC-3, aC-3). Intermediate and final products were characterized via size exclusion chromatography, low angle laser light scattering and 1H NMR. The first methodology does not require fractionation, but in contrast to the second methodology, cannot afford polymers with branches of identical molecular weight. Both methods are general and can be extended to combs with 2 or 3 different branches at controllable positions along the backbone. The rheological as well as the glass transition temperature of the PBds synthesized were examined. The rheological data clearly show that exact PBd combs, follow the concept of hierarchy of motions, i.e. the outer branches relax first and the connectors later. The influence of the number and molecular weight of branches, as well as of the total molecular weight on the relaxation was also studied. This investigation helps to better understand the behavior of LDPE, which is a complicated mixture of complex branched structure.