Degradation on freezing dilute polystyrene solutions in p‐xylene

Abstract

Chain scission was observed during the crystallization of p‐xylene in dilute polystyrene solutions. Degradation yields were determined by gel permeation chromatography, as a function of the number of freeze‐and‐thaw cycles, polymer concentration, and initial polymer molecular weight (M). The rate constant for chain scission Kc increases with the polymer chain length, from 0.021%/cycle at M = 110·103 to 4.7%/cycle at M = 8.5·106. Over the two decades range of investigated molecular weights, Kc follows an empirical scaling law of the form Kc ∼ (M − Mlim)1.17578, where Mlim is a limiting molecular weight ≅ 29,000 g. mol−1 below which no degradation could be induced. Some propensity for midchain scission was detected, although this tendency was much weaker in comparison to flow‐induced degradation. A chain scission model based on crack propagation failed to reproduce the experimental results. To explain the observed dependence of Kc with the square of the radius of gyration, an interfacial stress transmission mechanism between the crystallization fronts and the polymer coil has been proposed. © 1994 John Wiley & Sons, Inc.

Mechanophores with a Reversible Radical System and Freezing‐Induced Mechanochemistry in Polymer Solutions and Gels

“…[27] The DH values for the linkages in the linear polymer solution and the gel were smaller than those for the monomers in 1,4-dioxane,a nd the values tended to decrease with the increasing number of polymer chains connected to the linkages.T he DS values also showed as imilar trend (Supporting Information, Table S3). This is probably because the structure was not designed to efficiently transmit such macroscopic forces to the linkages and because the dissociated radicals re-combined too quickly for acolor change to be observed due to the high chain motion even if the linkages were cleaved in response to the forces.O n the other hand, coagulation of the solution significantly decreased the chain motion, which prevented the re-combination, and therefore we could observe the color change of the gel.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] Force is also generated along polymer chains by sonicating polymer solutions [4,10,[14][15][16][17][18][19][20][21] and swelling cross-linked polymers. [23][24][25][26][27] This phenomenon was considered to result from polymer chain adhesion to solvent crystallites that formed upon freezing. [23][24][25][26][27] This phenomenon was considered to result from polymer chain adhesion to solvent crystallites that formed upon freezing.…”

Mechanophores with a Reversible Radical System and Freezing‐Induced Mechanochemistry in Polymer Solutions and Gels

“…[22] Heating commonly induces force or distortion in polymer chains because the molecular motion of the chains is activated with temperature.C onversely,cooling seems to stabilize bonds in polymers because of the decreased motion of the polymer chains.H owever, some researchers have reported that freezing polymer solutions can induce polymer chain scission. [23][24][25][26][27] This phenomenon was considered to result from polymer chain adhesion to solvent crystallites that formed upon freezing. Theo bservation of decreased solution viscosity and the increased retention volume of size-exclusion chromatography (SEC) were regarded to result from degradation of the polymer chains.O nt he other hand, Qian and co-workers suggested that freezing polymer solutions did not generate polymer chain degradation, but instead altered the singlechain polymer morphology to am ore compact coil owing to the formation of intra-chain cohesion entanglements.…”

Water Clusters in Liquid Fuels. Their Role and Surroundings

“…In conclusion, we consider the behavior of the unique cluster with the mass of 26 ± 3 kDa analyzed in both liquids and polymeric materials [25]. In the present study, this cluster is observed to be present in water, hydrocarbons and their mixtures thereof.…”

“…When water in the fuel or n-hexane is present, these hydrocarbon clusters seem to disappear and to be replaced by a water cluster (stability of f amounts to -8 %). It has to be mentioned that all cluster sequences in hy-drocarbons, water [8], polymers [25,26], solutions [27], pro-tein coils (lysozyme, L-arginine, Chymotrypsinogen-A [12]) and polysaccharides ( [28] amylopectin, etc.) are character-ized by similar masses.…”