Polymerization instantaneous degree

Figures 1-4 show that when polymerizations were carried out at low concentrations of initiator and/or at low temperatures, the agreement between the model predictions and the experimental data is not so good. This is due to the fact that under those reaction conditions where R is low a large kinetic chain length is expected. When this is so, chain transfer to monomer becomes a reaction to be taken into account, since it markedly influences the chain length of the polymer being formed. A decrease in the instantaneous degree of polymerization, due to chain transfer to monomer, will reduce the concentration of the entangled radicals and, consequently, a decrease in the rate of polymerization is expected.

Once again, elimination of [M ] using Eq. (3.74) gives a general expression for the instantaneous degree of polymerization as a function of rate constants and concentrations ... 

Here r is the rate of polymerization, a is the probability of propagation, DP)nst is the instantaneous degree of polymerization, i.e., the number of monomer units on the dead polymer, and/is the initiation efficiency. Compare r in Eq. (7-144) with the simpler Eq. (7-68). When chain transfer is the primary termination mechanism, such as in anionic polymerization, then the polydispersity is 2. 

Chains depolymerize up to the end and the instantaneous degree of polymerization is equal to the initial degree of polymerization x0. Also it can be shown [2] that... 

Under these (generally valid) assumptions, the classic expressions for rate of polymerization Rpoi), kinetic chain length (o, the average number of monomer units on a living chain), and instantaneous degree of polymerization (DP, the average number of monomer units on a dead polymer chain formed at any instant) are given in Eqs. (10)-(12), respectively. 

The instantaneous degree of polymerization, in the absence of termination, can be derived as ... 

The instantaneous degree of polymerization gives a measure of the instantaneous kinetic chain length. It may be written as the ratio of the rate of propagation to the rate of production of dead chains by various mechanisms ... 

The instantaneous number and weight average degrees of polymerization are given by... 

A way to narrow the MWD and to approach the structure of dendrimers is the addition of a small fraction of a/-functional initiator, to inimers [40,71]. In this process the obtainable degree of polymerization is limited by the ratio of inimer to initiator. It can be conducted in two ways (i) inimer molecules can be added so slowly to the initiator solution that they can only react with the initiator molecules or with the already formed macromolecules, but not with each other (semi-batch process). Thus, each macromolecule generated in such a process will contain one initiator core but no vinyl group. Then, the polydispersity index is quite low and decreases with / M /Mn l-i-l//. (ii) Alternatively, initiator and monomer molecules can be mixed instantaneously (batch process). Here, the normal SCVP process and the process shown above compete and both kinds of macromolecules will be formed. For this process the polydispersity index also decreases with/,but is higher than for the semi-batch process, M /Mn=Pn//. ... 

Assume that 1.0 x 10-3 mol of sodium naphthalene is dissolved in tetrahydrofuran and then 2.0 mol of styrene is introduced into the system by a rapid injection technique. The final total volume of the solution is 1 liter. Assume that the injection of styrene results in instantaneous homogeneous mixing. It is found that half of the monomer is polymerized in 2000 s. Calculate the propagation rate constant. Calculate the degree of polymerization at 2000 and at 4000 s of reaction time. 

Even when all prerequisites are fulfilled, solution of eqn. (68) only yields the degree of polymerization of the instantaneously produced polymer. In the stationary state, of course, the ratio of the growth and termination rates does not change. If the ratio [XT]/[M] also remains essentially unchanged, a polymer with equal mean chain length is formed in the course of the whole stationary period. When [XT]/ [M] increases, the degree of polymerization... 

It is then easy to figure out that the instantaneous number average degree of polymerization is given by Equation 4-39-... 

The "ideal" concept of emulsion polymerization was built on the assumption that the monomer was water insoluble and that in the absence of chain transfer, the number average degree of polymerization, Xj can be related to the rate processes of initiation and propagation by the steady-state relationship Xjj = 2 Rp/Rj. Since Ri and Rp are both constant and termination is assumed to be Instantaneous during the constant rate period described by Smith-Ewart kinetics, the above equation predicts the generation of constant molecular weight polymer. Data has been obtained which agrees with Smith-Ewart but there is... 

P7-16b The instantaneous number-average degree of polymerization, Xfj, can be expressed as... 

P7-16ii The instantaneous number-average degree rf polymerization, can be... 

For non-equilibrium polymerizations, the average degree of polymerization of linear molecules is related to the instantaneous monomer concentration [L] through equation... 

The polymerization degree of native cellulose ranges from 400 to 500 glucose units and the hbers are shorter (2-20 /tm) than those in paper chromatography, preventing the instantaneous spreading of solutes. The specific surface area is about 2 m /g. 

Consequently, to create PA/PO blends with a high melt viscosity it is advisable to use fully functionalized polyolefins. It can be expected that proper dispersion in melt of PA blended with high viscosity g-PO can yield composites with satisfactory structural homogeneity and high melt viscosity. This possibihty is based on the above data showing that contact between the phases in a PA/g-PO blend is created instantaneously, and the development of contact zones between the polymeric phases depends much on the degree of mechanical dispersion of the components and not on the diffusion processes taking place in the mesophase. 

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