Copolymer star branched

The TMS protective group was quantitatively deprotected by treatment with (C4H9)4NF in THF at room temperature (Scheme 7). SEC profiles of the resulting poly(12) and poly (13) exhibited narrow monomodal distributions similar to those of the original poly(12a) and poly(13a), respectively. Thus, TMS group is capable of protecting the active ethynyl hydrogen of 12 in addition to hydroxyl and amine functions. Since ethynyl and the related C=C bonds have been recently used in click reaction with azides to prepare block copolymers, star-branched polymers, and even hyperbranched... 

Spot tests, 245 Spray elastomers, 204 Star-branched polymers, 187 Star copolymers, 7... 

Puskas, J.E., Pattern, W.E., Wetmore, P.M., and Krukonis, A. Multiarm-star polyisobutylene-polystyrene thermoplastic elastomers from a novel multifunctional initiator, Polym. Mater. Set Eng., 82,42 3, 1999. Brister, L.B., Puskas, J.E., and Tzaras, E. Star-branched PIB/poly(p-t-bu-Styrene) block copolymers from a novel epoxide initiator, Polym. Prepr., 40, 141-142, 1999. 

Isobutylene-based elastomers include HR, the copolymer of isobutylene and isoprene, halogenated HR, star-branched versions of these polymers, and the terpolymer isobutylene-p-methylene styrene-bromo-p-methyl styrene (BIMS). A number of recent reviews on isobutylene-based elastomers are available [33-35]. 

Star-branched butyl rubber, 4 437-438 copolymers, 4 445-446 Starch(es), 4 703-704, 20 452-453 as blood substitute, 4 111-112 cationic, 18 114-115 in cereal grains, 26 271-274 in cocoa shell from roasted beans, 6 357t compression effects in centrifuges, 5 513 depolymerization, 4 712 in ethanol fermentation, 10 534—535 etherified, 20 563 as a flocculant, 11 627 high-amylose, 26 288 Mark-Houwink parameters for, 20 558t modified and unmodified, 12 52-53 in paper manufacture, 18 122-123 performance criteria in cosmetic use, 7 860t... 

Similar to the branches in copolymer stars and miktoarms, the grafted chains in brushes can be of different chemical compositions. Brown et al. [223] studied the microphase separation of grafted mixtures of homopolymer chains composed of immiscible A and B units and also [224] of diblock AB copolymers. In the former case, the brushes expand laterally and then experience lateral microphase separation. In the latter case, however, monomers segregate vertically to the surface forming a three layer structure. 

Consider a star branched polymer with Nb branches (Fig. 2). Each branch is composed of two monomeric blocks A and B (copolymer) of nA and nB monomers respectively (the A block is assumed to be at the outside of the branch). The single-branch correlations Ssb(Q) involve the scattering functions SSA(Q), SBB(Q), and SAB(Q) that were derived [24] for diblock copolymers ... 

Fig. 2. Four-arm star branched copolymer with three outer A blocks and two inner B blocks...

For every sample, an aliquot of the reaction medium was drawn before the coupling reaction to obtain the linear copolymer corresponding to the arm of the star-branched copolymer. The use of both compounds facilitates the interpretation of the GPC experiments. 

As the coupling reaction is not fully efficient, the star-branched copolymers contain a nonnegligible amount of uncoupled linear copolymer. To get the star-branched copolymers as pure as possible, a purification step where linear chains were extracted by fractional precipitation using different solvent or nonsolvent methods was necessary (J). 

Table II contains the results of the analysis of star-branched copolymers (Mw, Mn, and polydispersity d) by both the viscometric coupling (V) and the light-scattering coupling (L). The numerical values are in agreement, especially for the values. These results confirm that the universal calibration is perfectly valid for branched molecules, even for a high degree of long-chain branching.

Considering the results from Tables II and III, it is difficult to determine which parameter, Br-Lin(V) or Br-Lin(L), seems the most appropriate to characterize the average number of branches of our star-branched copolymers, which roughly varies from 3 to 12. 

The intrinsic viscosity [ry] of both linear and branched macromolecules and the branching parameter values of the star-branched copolymers were also calculated by the GPC software and are reported in Table IV. The ratio [vlhAvlim, between the intrinsic viscosity of the... 

Figure 11. Variations of the branching parameter as a function of the number of branches in the star-branched copolymer PMl.

ABA tribiock, or all three can be different, as in an ABC triblock copolymer. Obviously, the number of possible block sequences increases rapidly with the number of blocks and the number of different types of block in the chain. One can also synthesize block copolymers with branched architecture, such as star-branched block copolymers, in which each of the arms of the star contains either the same or different block sequences (see Fig. 13-1). One or more of the blocks could also be stiff or liquid crystalline (Chiellini et al. 1994 Chen et al. 1996 Radzilowski et al. 1997 Jenekhe and Chen 1998). For a given type of block copolymer, the degree of polymerization N of the whole molecule, or the degree of polymerization Ni of one or more of the blocks, can be varied. Thus, the number of different types of block copolymers is practically endless. 

Anionic polymerization of functionalized cyclotrisiloxanes is a good method for the synthesis of well-defined functionalized polysiloxane with control of molecular mass, polydispersion, and density and arrangement of functional groups. These polymers may serve as reactive blocks for the building of macromolecular architectures, such as all-siloxane and organic-siloxane block and graft copolymers, star-, comb- and dendritic-branched copolymers and various polysiloxane-inorganic solid hybrids. 

---