Comonomer sequence

In the most common production method, the semibatch process, about 10% of the preemulsified monomer is added to the deionised water in the reactor. A shot of initiator is added to the reactor to create the seed. Some manufacturers use master batches of seed to avoid variation in this step. Having set the number of particles in the pot, the remaining monomer and, in some cases, additional initiator are added over time. Typical feed times ate 1—4 h. Lengthening the feeds tempers heat generation and provides for uniform comonomer sequence distributions (67). Sometimes skewed monomer feeds are used to offset differences in monomer reactivity ratios. In some cases a second monomer charge is made to produce core—shell latices. At the end of the process pH adjustments are often made. The product is then pumped to a prefilter tank, filtered, and pumped to a post-filter tank where additional processing can occur. When the feed rate of monomer during semibatch production is very low, the reactor is said to be monomer starved. Under these... 

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... 

For example, the amount and stability of the crystals formed in E-V copolymers depend on the number and length of uninterrupted, all E unit runs. Our ability to computer-simulate the (n-Bu)3SnH reduction of PVC permits us to obtain this information concerning the longer comonomer sequences in the resultant E-V copolymers. 

The final class of polymers are copolymers containing one or more of the repeat units of classes 2 and 3 (15-18). Copolymer effectiveness would presumably be a function of the chemical structures of each comonomer, comonomer sequence distribution, and polymer molecular weight. The comonomer could be a relatively... 

Monomer reactivity ratios and thus comonomer sequence distributions in copolymers can vary with copolymerization reaction conditions. The comonomer distribution could affect the geometry of the adsorbed polymer - mineral complex and the fines stabilization properties. 

In what follows, we use simple mean-field theories to predict polymer phase diagrams and then use numerical simulations to study the kinetics of polymer crystallization behaviors and the morphologies of the resulting polymer crystals. More specifically, in the molecular driving forces for the crystallization of statistical copolymers, the distinction of comonomer sequences from monomer sequences can be represented by the absence (presence) of parallel attractions. We also devote considerable attention to the study of the free-energy landscape of single-chain homopolymer crystallites. For readers interested in the computational techniques that we used, we provide a detailed description in the Appendix. ... 

All the described properties of such a s-fraction of poly(NVCl-co-NVIAz) synthesized at the temperature above the PST of the reacting system allowed us to draw the conclusion that the chains of this type had the comonomer sequence, which at the temperatures above the conformation transition facilitated the formation of polymer particles, where H-blocks are in the interior shielded by the P-blocks against additional intermolecular association. Such a behaviour of this copolymer in aqueous media is close to that of oligomeric proteins similar to casein [46] possessing a rather hydrophobic core surrounded by the polar segments. 

Conformational energies are calculated for chain segments in poly(vlnyl bromide) (PVB) homopolymer and the copolymers of vinyl bromide (VBS and ethylene (E), PEVB. Semlempirical potential functions are used to account for the nonbonded van der Waals and electrostatic Interactions. RIS models are developed for PVB and PEVB from the calculated conformational energies. Dimensions and dipole moments are calculated for PVB and PEVB using their RIS models, where the effects of stereosequence and comonomer sequence are explicitly considered. It is concluded from the calculated dimensions and dipole moments that the dipole moments are most sensitive to the microstructure of PVB homopolymers and PEVB copolymers and may provide an experimental means for their structural characterization. 

Wu, Ovenall and Hoehn have published a detailed study of the H- ajid 13C-NMR spectra of the QH —CO copolymers with varied QH /CO ratios, comparing them with appropriate model compounds 48). Based on their work, it is possible to determine copolymer compositions, comonomer sequence distributions, end groups, branching and conformational transitions in these copolymers. 

Perhaps the widest application is that of conventional high-resolution spectroscopy in solution for the purpose of learning in detail about polymer chain structure. In this field, proton NMR, formerly dominant, has given way to carbon-13 NMR with the development of pulse Fourier transform spectrometers with spectrum accumulation. Carbon spectroscopy is capable of giving very detailed and often quite sophisticated information. For example, a very complete accounting can be provided of comonomer sequences in vinyl copolymers and branches can be identified and counted, even at very low levels, in polyethylenes. 

The configuration of the polysilylene chain can range from the simple structure of the symmetrically substituted homopolymer (in which R = R ), to the more complicated structure of the asymmetrically substituted homopolymer (in which R R ), and finally, to the very complex structure of the asymmetrically substituted copolymers, in which both stereochemical and comonomer sequences need to be considered. 

Consequently, there can be a co-elution of species possessing different chain length and chemical composition. The influence of different comonomers copolymerized into the macromolecule on the chain size can be measured by the GPC elution of homopolymer standards of this comonomer. Unfortunately, the influence of the comonomer sequence distribution on the hydrodynamic radius cannot be described explicitly by any theory at present. However, there are limiting cases which can be discussed to evaluate the influence of the comonomer placement in a macro-molecular chain. 

In cases where the number of heterocontacts can no longer be neglected, this simplifled reasoning breaks down and copolymer molar masses cannot be measured accurately by GPC alone. This is the case with statistical copolymers, polymers with only short comonomer sequences and high side-chain densities [2]. In such cases, more powerful and universal methods have to be employed (e.g., 2D separations) (see below). 

In the case of a low content of a comonomer in a copolymer, the peak characteristics for fragment molecules generated from the comonomer or comonomer sequences can be very small. Since most pyrograms are very complex, with hundreds of small components, it is in many instances difficult to assign a particular compound to a low level comonomer. This is, for example, the case of the pyrolysis of the terpolymer poly acrylonitrile-co-butadiene-co-acrylic acid) dicarboxy terminated 18 wt % acrylonitrile, 2.4 carboxyl/molecule, CAS 68891-50-9. No peaks characteristic for the acrylic acid are seen in the pyrogram. 

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

Depending on the sequential structure of the monomer(s) used in the polymerization reactions the resulting copolyesters can have several variations in comonomer sequence ... 

The polymer of Equation 6(15) has a peculiar comonomer sequence compared with polymers in Equations 2 and 3. In the latter the two repeating units, A-B and A-C, are of the same type esters, whereas in... 

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) ... 

However, interchange reactions appear to be rather slow at temperatures below Tm(15). We(50) observed that thermal treatment of some of liquid crystalline, aromatic copolyesters at the temperatures substantially lower than Tm did not lead to any changes in the comonomer sequence even after a prolonged period of time. A copolyester especially of 4-hydroxybenzoic acid, however, can undergo a special type of sequence changes below Tm, which is called the crystallization induced reaction(51). 

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