Chain structure block copolymer main chains

BD. They reported an improvement in shape memory properties as a result of introduction aromatic structure into the main chain. Yang and co-workers [122] compared the mechanical, dynamic mechanical and shape memory properties of PU block coPolymers with planar shape hard segment (1,6-diphenyl diisocyanate (PDI)) and bent shape hard segment (MDI). The PDl-based PU showed superior properties compared with MDI-based PU (Table 2.11) as a result of better interaction among hard segments due to the planar shape of PDI. 

In detail, the structure of a macroinitiator with active sites in the main chain is classified into two types that derive different types of block copolymers, as shown in Fig. 1. 

As stated above, we postulated that fast, reversible chain transfer between two different catalysts would be an excellent way to make block copolymers catalytically. While CCTP is well established, the use of main-group metals to exchange polymer chains between two different catalysts has much less precedent. Chien and coworkers reported propylene polymerizations with a dual catalyst system comprising either of two isospecific metallocenes 5 and 6 with an aspecific metallocene 7 [20], They reported that the combinations gave polypropylene (PP) alloys composed of isotactic polypropylene (iPP), atactic polypropylene (aPP), and a small fraction (7-10%) claimed by 13C NMR to have a stereoblock structure. Chien later reported a product made from mixtures of isospecific and syndiospecific polypropylene precatalysts 5 and 8 [21] (detailed analysis using WAXS, NMR, SEC/FT-IR, and AFM were said to be done and details to be published in Makromolecular Chemistry... 

Thermoresponsive polymeric micelles with PIPAAm block copolymers can be expected to combine passive spatial targeting specificity with a stimuli-responsive targeting mechanism. We have developed LCSTs of PIPAAm chains with preservation of the thermoresponsive properties such as a phase transition rate by copolymerization with hydrophobic or hydrophilic comonomers into PIPAAm main chains. Micellar outer shell chains with the LCSTs adjusted between body temperature and hyperthermic temperature can play a dual role in micelle stabilization at a body temperature due to their hydrophilicity and initiation of drug release by hyperthermia resulting from outer shell structural deformation. Simultaneously, micelle interactions with cells could be enhanced at heated sites due... 

Block copolymers are named by using dashes (double-length hyphens) for the bonding of bloeks with each other and with junction units. With graft and star polymers, the grafts or the arms, respectively, are eonsidered to be substituents to the main chain, and the structure is named in the same way as a regular or irregular polymer. Table 8 lists some examples. 

Block copolymer phase separation has first and foremost been studied in bulk. The mesoscale structure is determined by molecular parameters such as chain length (N), volume fractions of the components, interaction between the blocks (x) and temperature (Figure 2.6). In this Chapter, we will be concerned mainly with diblock copolymers,... 

The variety of branched architectures that can be constructed by the macromonomer technique is even larger. Copolymerization involving different kinds of macromonomers may afford a branched copolymer with multiple kinds of branches. Macromonomer main chain itself can be a block or a random copolymer. Furthermore, a macromonomer with an already branched or dendritic structure may polymerize or copolymerize to a hyper-branched structure. A block copolymer with a polymerizable function just on the block junction may homopolymerize to a double comb or double-haired star polymer. 

We have a specific interest in the self-assembled structures formed by poly(ferrocenylsilane) block copolymers, such as poly(ferrocenyldimethylsilane-Z -dimethyl-siloxane) (PFS-PDMS) and (ferrocenyldimethylsilane-Z>-isoprene) (PFS-PI). The PFS block contains an iron atom in the main chain repeat unit. These polymers are particularly promising for novel applications, since they can be used as charge-transport materials and, by pyrolysis, as precursors to ferromagnetic ceramics [4-6], Moreover, they can by synthesized with a very narrow molar mass distribution, with excellent control over chain length and composition [7], An important feature of PFS is that the polymers bearing two methyl groups on the silane unit are crystalline, whereas polymers with two different substituents on each silane (methyl, ethyl methyl, phenyl) are atactic and remain amorphous. This feature of the polymer composition has a strong influence on the type of self assembled structures that these poly-... 

Among the structural factors that should be controlled in polymer syntheses (Fig. 1, Section I), perhaps the least exploited is the sequence of constitutional repeat units along a polymer main chain. We have already discussed the syntheses of block copolymers, where two or more homopolymer segments are connected, such as AAAAA-BBBBB- -, which is among the most primitive examples of sequence control in synthetic polymers. 

Liquid crystallinity can be attained in polymers of various polymer architectures, allowing the chemist to combine properties of macromolecules with the anisotropic properties of LC-phases. Mesogenic imits can be introduced into a polymer chain in different ways, as outhned in Fig. 1. For thermotropic LC systems, the LC-active units can be connected directly to each other in a condensation-type polymer to form the main chain ( main chain liquid crystalline polymers , MCLCPs) or they can be attached to the main chain as side chains ( side chain liquid crystalline polymers , SCLCPs). Calamitic (rod-Uke) as well as discotic mesogens have successfully been incorporated into polymers. Lyotropic LC-systems can also be formed by macromolecides. Amphiphihc block copolymers show this behavior when they have well-defined block structures with narrow molecular weight distributions. 

In their structure the copolymers may contain the monomeric units randomly, and their overall composition is determined by the composition of the initial feed mixture of monomers (see Section 2.3). Alternating copolymers (a//-copolymers) also are known, where the monomers alternate regularly along the chain. Other types include block polymers where a linear arrangement of groups of one type of monomers is present, graft polymers that have side chain blocks connected to a polymer main chain, per-copolymers where ordered sequences of more than two units are present, etc. 

Microstructure of copolymers typically refers to the proportion and the arrangement of the monomer units in the polymeric backbone. In their structure the copolymers may contain the monomeric units arranged randomly, they may alternate regularly, may form large blocks of one type of monomer, or may appear as side chain blocks connected to a polymer main chain (see Section 1.1). This distribution also depends on the relative amounts of each monomer present in the copolymer [7]. Analytical pyrolysis, particularly Py-GC-MS, has been used successfully for the analysis of microstructure of copolymers (see e.g. [8]). Pyrolysis generates small fragments that represent sections of the polymer and can make distinctions between random and block copolymers fairly straightfonward. 

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