Ordered comonomer sequences

Thermotropic Aromatic Copolyesters Having Ordered Comonomer Sequences Syntheses and Properties... 

In this article, in connection with our previous endeavor, we would like to report synthesis and properties of new copolyesters having ordered comonomer sequences consisting of mesogenic units and polymethylene spacers, i.e., thermotropic aromatic-aliphatic copolyesters having sequentially ordered structures ... 

In order to test higher-order or multi-site models, it is preferable to study HMR data of polymer fractions. In this work, we shall use the pairwise HMR/fractions data to fit to multi-site models. This Is carried out in the same way as in the pairwise fraction on the tactlcity data. We can either use the two-state B/B model, or even three-state B/B/B model If applicable. The comonomer sequence intensity data for the two fractions are entered Into the computer. A total of 12 entries are Involved (6 for each fraction). The equations for the three-state copolymer... 

When a unsymmetrical dyad type monomer is polymerized with another reactant, the comonomer sequence is not perfectly ordered (14) ... 

Mesophase-forming ability of a copolyester strongly depends on its comonomer sequence. For example, the ordered sequence copolyester shown below is not liquid crystalline, whereas its random counterpart is nematic(4,15) ... 

FAB-MS has been applied also to the characterization of the oligomers present in copolymers, in order to obtain detailed information on the comonomer sequence. For instance, an exactly alternating copolyester (PET/ PETx) containing ethylene terephthalate (PET) and ethylene truxillate (PETx) units... 

While some s)uithetic copolymers - alternating, di-, tri-, and mirltiblock copolymers - possess an ordered-sequence distribution of monomeric units along the chain backbone, random copolymers (RCPs) represent a special class of macromolecules, which possess a disordered monomer sequence distribution. A series of papers have been published which established that tuning the copolymer chemical composition and comonomer sequence distribution profoundly afferts the characteristics of RCPs. " Of those characteristics intrinsic to the polymeric materials, most work performed to date addressed the role of the chemical composition. By judiciously... 

In order to rank performance of catalysts in copol)unerization with respect to comonomer incorporation and comonomer sequence distribution, copolymerization parameters have proven to be very useful. They are determined by means of nuclear magnetic resonance spectroscopy (NMR copolymer sequence analysis) taking into account the Markovian statistics of chain growth, as reviewed by Randall [4], Galimberti and coworkers [5] described the analysis of EPM prepared by means of... 

Even more sophisticated data analyses have been applied to comonomer sequences in order to extract even more specific information from the data [136-142]. These detailed reaction models allow derivation of mechanistic and kinetic parameters from sequence-distribution data. While most of these... 

Besides its effects on morphology, comonomer sequence distribution also affects copolymer crystallization kinetics. In statistical copolymers, due to the broad distribution of crystaUizable sequence lengths, bimodal melting endotherms are typically observed. In block copolymers, the dynamics of crystallization have features characteristic of both homopolymer crystallization and microphase separation in amorphous block copolymers. In addition, the presence of order in the melt, even if the segregation strength is weak, hinders the development of the equihbrium spacing in the block copolymer solid-state structure. 

In the region of the methyl carbon in the propylene unit (from 21.4 to 22.0 ppm), the side-chain methylene carbon in the 1-butene unit (from 27.5 to 28.5 ppm), and the central methylene carbon of the PP diad (from 46.5 to 47.5 ppm), the peaks arising from different comonomer sequences longer than pentad are observed. In order to provide assignments of these peaks, the chemical shift differences among pentad and hexad comonomer seqnences were calcnlated by the y-effect method. Table 7.4 shows the calculated chemical shift differences in the resonance regions of methyl and methylene carbons in 1-butene-propylene copolymer are shown below ... 

When discussing various methods for the synthesis of protein-like HP-copolymers from the monomeric precursors (Sect. 2.1), we pointed to the possibility of implementation of both polymerization and polycondensation processes. The studies of the potentials of the latter approach in the creation of protein-like macromolecular systems have already been started. The first published results show that using true selected reactions of the polycondensation type and appropriate synthetic conditions (structure and reactivity of comonomers, solvent, temperature, reagent concentration and comonomer ratio, the order of the reagents introduction into the feed, etc.) one has a chance to produce the polymer chains with a desirable set of monomer sequences. 

The statistical anionic copolymerization of acrylates and methacrylates is also controlled in the presence of LiOEEM (30), as testified by the copolymerization of MMA and tBuA in THF at —78°C. Block copolymers were also prepared by the sequential polymerization of at least two methacrylates and acrylates. For instance, PMMA- >/c cA -PbBuA and PMMA-fcZocA -PnNonA were synthesized . The addition order of the comonomers is important. Indeed, when living PnBuA is the macroinitiator of the MMA polymerization, the expected block copolymer is contaminated by homo-PnBuA, which is not the case when the polymerization sequence is reversed. A fuUy acrylic-based thermoplastic elastomer, PMMA-fcZocA -P(2EtHA)-fcZocA -PMMA, was prepared by the sequential LiOEEM-ligated polymerization of MMA, 2-EtHA and MMA. ... 

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