Molecular Weight Distribution Generated on Initiation of Free RadicalPolymerization by Sequence of Laser Pulses

A new approach for the simulation of PLP (pulsed laser polymerization) is presented. This approach allows one to obtain new analytical solutions for different polymerization schemes, including either chain transfer to the monomer or intramolecular chain transfer to the polymer. The first results of the simulation of PLP experiments on n‐butyl acrylate at 20 °C and ambient pressure are presented.MWDs simulated for PLP of n‐butyl acrylate, in bulk at 20 °C and ambient pressure using three models: the model with intramolecular chain transfer to the polymer (solid line), the model with chain transfer to monomer (dashed line), and the classical model (dotted line).imageMWDs simulated for PLP of n‐butyl acrylate, in bulk at 20 °C and ambient pressure using three models: the model with intramolecular chain transfer to the polymer (solid line), the model with chain transfer to monomer (dashed line), and the classical model (dotted line).

Section: Theorymentioning

confidence: 99%

Section: Consideration Of Ideal Polymerization Kineticsmentioning

confidence: 99%

Simulation of Molecular Weight Distributions Obtained by Pulsed Laser Polymerization (PLP): New Analytical Expressions Including Intramolecular Chain Transfer to the Polymer

Nikitin

Castignolles

Charleux

et al. 2003

“…This must be true, of course, since transfer events conserve the total number of living chains and k is independent of chain length in the present approximation. The crucial point is that C(t) and H(t) ¼ ÀkC(t) appearing in Equation (22) are the same periodic functions of time as without chain transfer, Equation (10).…”

Section: Living Mwdmentioning

confidence: 99%

Pulsed Laser Polymerization at Low Conversions: Broadening and Chain Transfer Effects

O’Shaughnessy

Vavylonis

2003

Pulsed laser polymerization (PLP) is widely employed to measure propagation rate coefficients k p in free radical polymerization. Various properties of PLP have been established in previous works, mainly using numerical methods. The objective of this paper is to obtain analytical results. We obtain the most general analytical solution for the dead chain molecular weight distribution (MWD) under low conversion conditions which has been hitherto obtained. Simultaneous disproportionation and combination termination processes are treated. The hallmarks of PLP are the dead MWD discontinuities located at integer multiples of n 0 = k p t 0 C M , where t 0 is the laser period and C M is the monomer concentration. We show that chain transfer reduces their amplitude by factors e −ctrLn0 , consistent with numerical results obtained by other workers. Here c tr is the chain transfer coefficient and Ln 0 (L =integer) are the discontinuity locations. Additionally, transfer generates a small amplitude continuous contribution to the MWD. These results generalize earlier analytical results which were obtained for the case of disproportionation only. We also considered 2 classes of broadening: (i) Poisson broadening of growing living chains and (ii) intrinsic broadening by the MWD measuring equipment (typically gel permeation chromatography, GPC). Broadening smoothes the MWD discontinuities. Under typical PLP experimental conditions, the associated inflection points are very close to the discontinuities of the unbroadened MWD. Previous numerical works have indicated that the optimal procedure is to use the inflection point to infer k p . We prove that this is a correct procedure provided the GPC resolution σ is better than n 1/2 0 . Otherwise this underestimates Ln 0 by an amount of order σ 2 /n 0 .

“…In ref. 5' the analytical solution of a system of equations is proposed for a polymeriza-tion scheme that contains the reactions of chain initiation, propagation and termination by recombination or disproportionation, under polymerization initiation by an arbitrary sequence of radiation pulses. By using this solution it is possible to investigate the effect of any nonstationary initiation of polymerization on MWDs.…”

Section: Introductionmentioning

confidence: 99%

Postpolymerization effect on molecular weight distribution generated by pulsed laser radical polymerization

Nikitin

1996

SUMMARYThe postpolymerization effect on molecular weight distributions (MWDs) and on the Pulsed Laser Polymerization (PLP) technique for evaluation of kinetic constants is investigated. General expressions for moments are derived for a polymerization scheme that contains the reactions of chain initiation, propagation, and termination by recombination or disproportionation, under polymerization initiation by an arbitrary sequence of radiation pulses. The results of calculation of MWDs and of the weight-average degree of polymerization (pw) for methyl methacrylate are presented. It is shown that the pw value strongly depends on postpolymerization. A new method for determining the rate constants of chain propagation and chain termination from a single experiment by polymerization with packets of laser pulses is presented.