Monomer unit, defined

The synthesis of biopolymers in vivo leads to macromolecules with a defined sequence of units. This effect is very important for living organisms and is different in comparison with random copolymerization in which sequences of units are distributed according to stochastic rules. On the other hand, the predicted sequence of units can be achieved by a set of successive reactions of respective monomer molecule addition. In template copolymerization, the interaction between comonomers and the template could pre-arrange monomer units defining sequence distribution in the macromolecular product. 

It is not possible to apply (C2.1.1) down to the level of monomers and replace by the degree of polymerization N and f by the sum of the squares of the bond lengths in the monomer because the chemical constitution imposes some stiffness to the chain on the length scale of a few monomer units. This effect is accounted for by introducing the characteristic ratio defined as C- — The characteristic ratio can be detennined... 

Poly(methyl vinyl ether) [34465-52-6] because of its water solubility, continues to generate commercial interest. It is soluble in all proportions and exhibits a well-defined cloud point of 33°C. Like other polybases, ie, polymers capable of accepting acidic protons, such as poly(ethylene oxide) and poly(vinyl pyrroHdone), each monomer unit can accept a proton in the presence of large anions, such as anionic surfactants, Hl, or polyacids, to form a wide variety of complexes. 

Distribution of the monomer units in the polymer is dictated by the reactivity ratios of the two monomers. In emulsion polymerization, which is the only commercially significant process, reactivity ratios have been reported (4). IfMj = butadiene andM2 = acrylonitrile, then = 0.28, and r2 =0.02 at 5°C. At 50°C, Tj = 0.42 and = 0.04. As would be expected for a combination where = near zero, this monomer pair has a strong tendency toward alternation. The degree of alternation of the two monomers increases as the composition of the polymer approaches the 50/50 molar ratio that alternation dictates (5,6). Another complicating factor in defining chemical stmcture is the fact that butadiene can enter the polymer chains in the cis (1), trans (2), or vinyl(l,2) (3) configuration ... 

The average kinetic chain length r is defined as the number of monomer units consumed per active centre formed and is given by R fV (or R tV ). 

The number average degree of polymerisation x is defined as the average number of monomer units per polymer chain. Therefore if termination is by disproportionation r = jc, but if by combination r = x. 

For the purpose of our discussion, a polycrown is here defined as a polymer system arising by polymerization of a crown monomer unit. Extensive work has been done in this field by Kopolow, Hogen Esch and Smid and the examples presented here are taken from a paper by all three of these workers. A typical preparation of vinylbenzo-15-crown-5 is accomplished according to the scheme shown as Eq. (6.25). One might also have utilized a formylation/Wittig sequence on benzo-15-crown-5 to accomplish the same end. 

Several different types of copolymers can be defined, depending on the distribution of monomer units in the chain. If monomer A is copolymerized with monomer B, for instance, the resultant product might have a random... 

Hyperbranched polymers are characterized by their degree of branching (DB). Hie DB of polymers obtained by the step-growth polymerization of AB2-type monomers is defined by Eq. (2.1) in which dendritic units have two reacted B-groups, linear units have one reacted B-group, and terminal units have two unreacted B-groups191 ... 

This physically unrealistic assumption may be abolished by dividing by x, the number of permutations of the monomer units for a given configuration as originally defined. Hence... 

Clearly there are two sets of absorptions, as shown in Table 3.7, which were attributed to polarons and bipolarons by the authors. All the IRAV bands are relatively narrow and so suggest that the carriers occupy a well-defined number of monomer units. The highest frequency IRAV has been attributed to a combination of the intra-ring OC vibration and the inter-ring C-C stretch which increases in frequency as the conjugation length decreases, consistent with the bipolaron being somewhat shorter than the polaron. 

The conversion of pendant vinyl groups, x3, may be defined as the fraction of divinyl monomer units with both vinyl groups reacted... 

A copolymer of butadiene and styrene is known as poly (butadiene-costyrene). A copolymer obtained from two monomers is a bipolymer, a copolymer from three monomers is a terpolymer and so on. Run numbers R is defined as average number of monomer sequences in 100 monomer units. In a bipolymer from monomers M and M2, fraction [M1]/[M2] in the copolymer formed is denoted by f and fraction... 

Recent developments in the design of dendritic molecules has provided both new methodology and molecular architecture which are structure controlled macromolecules, globular-shaped, dendritic-branched tree-like structures with nanoscscale dimensions [1], Dendrimers generally consist of a focal core, many building blocks (monomer units) and a mathematically defined number of ex-... 

The butadiene polymers represent another cornerstone of macromolecular stereochemistry. Butadiene gives rise to four different types of stereoregular polymers two with 1,2 linkage and two with 1,4. The first two, isotactic (62) and syndiotactic (25), conform to the definitions given for vinyl polymers, while the latter have, for eveiy monomer unit, a disubstituted double bond that can exist in the two different, cis and trans, configurations (these terms are defined with reference to the polymer chain). If the monomer units all have the same cis or trans configuration the polymers are called cis- or trans-tactic (30 and 31). The first examples of these stereoisomers were cited in the patent literature as early as 1955-1956 (63). Structural and mechanistic studies in the field have been made by Natta, Porri, Corradini, and associates (65-68). 

Until now the discussion has centered on the addition polymers obtained fiom unsaturated monomers by reaction of the C=C or C=0 double bond. However, polymers obtained by other methods (ring-opening polymerization, polycondensation, etc.) offer interesting stereochemical phenomena also. As a rule, in these classes of macromolecular compounds the monomer units are clearly defined, the direction of the chain is often distinguishable and the stereo-isomeric elements present in the chain already preexist in the monomer. There are, however, numerous exceptions and further clarification is called for. 

It is however possible to find conditions, called unperturbed or theta conditions (because for each polymer-solvent pair they correspond to a well-defined temperature called d temperature) in which a tends to 1 and the mean-square distance reduces to Q. In 6 conditions well-separated chain segments experience neither attraction nor repulsion. In other words, there are no long-range interactions and the conformational statistics of the macromolecule may be derived from the energy of interaction between neighboring monomer units. For a high molecular weight chain in unperturbed conditions there is a simple relationship between the mean-square end-to-end distance < > and the mean-... 

The residue from each diol and each diacid (separately, not together) in the polymer chain is termed a structural unit (or a monomer unit). The repeating unit of the chain consists of two structural units, one each of the diol and diacid. The total number of structural units in any particular system equals the total number of bifunctional monomers initially present. The number-average degree of polymerization X is defined as the average number of structural units per polymer chain. (The symbols P and DP are also employed to signify... 

Equation 6-12 is known as the copolymerization equation or the copolymer composition equation. The copolymer composition, d M /d Mi, is the molar ratio of the two monomer units in the copolymer. monomer reactivity ratios. Each r as defined above in Eq. 6-11 is the ratio of the rate constant for a reactive propagating species adding tis own type of monomer to the rate constant for its additon of the other monomer. The tendency of two monomers to copolymerize is noted by r values between zero and unity. An r value greater than unity means that Mf preferentially adds M2 instead of M2, while an r value less than unity means that Mf preferentially adds M2. An r value of zero would mean that M2 is incapable of undergoing homopolymerization. 

Figures 22,23 and 24, respectively, depict the apparent hydrodynamic radius distributions f(Rh) for STVPh-3, STVPh-9, and STVPh-15, as well as their blends with PEMA in toluene. Here, the STVPh unit fraction Fr is defined as the total moles of styrene and vinylphenol monomer units of STVPh relative to those of PEMA plus STVPh. In LLS experiments done, PMMA cannot be seen , because its dn/dc in toluene is close to zero. As seen in Fig. 22, the f(Rh) of the STVPh-3/PEMA (50 50, w/w) blend is similar to that of pure STVPh-3, indicating that...

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