The degradation of polymer molecules in solution under the influence of ultrasonic waves. Part I. Kinetic analysis

Abstract

Starting from the assumption that a polymer molecule in solution will only degrade under the influence of ultrasonic irradiation if both the resulting fragments are greater than Pe/2 in size, where Pe is the so‐called limiting degree of polymerization, rela tionships are derived giving the rate of degradation in terms of rate of breaking of bonds. If dBi/dt the rate of breakage of bonds in molecules of size Pi, the proposed rate equations are: dBi/dt = k(Pi – Pe)ni for Pi > Pe and dBi/dt = 0 for Pi ⪕ Pe, where k is a constant characteristic of the system and ni is the number of molecules of size Pi. Solutions of this equation are given for three sets of conditions.

Ultrasonic degradation for molecular weight reduction of pharmaceutical cellulose ethers

“…3) did not produce a linear relationship suggesting a deviation from this behaviour. Schittenhelm and Kulicke (2000) used a quasi-first order model with a term included for M lim (i.e., assuming first order degradation depending on the chain length in excess of M lim ) originally proposed by Ovenall, Hastings, and Allen (1958) (Eq. (3)).…”

Kinetics of Ultrasonic Polymer Degradation: Comparison of Theoretical Models with On‐Line Data

“…Models for describing the molecular weight evolution during sonication include those of Schmid, [21,22] Baramboim, [23] Ovenall et al, [24] Rodriguez and Winding, [25] El'tsefon and Berlin, [26] Harrington and Zimm, [27] Glynn and Van der Hoff, [13,14] Doulah, [15] Malhotra, [28] Madras and Chattopadhyay, [29] Giz et al, [30] Tang and Liu [31] in historical order. Some of these models start from a scission mechanism and derive the molecular weight evolution from the proposed mechanism, while phenomenological ones describe the evolution of the molecular weight without proposing a scission mechanism.…”

“…A simplified model proposed by Ovenall and co-workers as an approximate description of the degradation process gives the time dependence of the (number average) molecular weight during sonication by [24,26,36,37] …”

Producing homologous series of molar masses for establishing structure-property relationships with the aid of ultrasonic degradation

“…A simplified model proposed by Ovenall and co-workers [37] was exmployed as an approximate description of the degradation process. The degradation constant can be calculated by the following equation:…”