Kinetic Monte Carlo Studies on the Importance of the Reaction Scheme in Segmental Exchange of Copolymer Chains

Abstract

Kinetic Monte Carlo studies (confirmed by integration of the corresponding differential equations) are used to demonstrate the fundamental differences between the two most often accepted schemes of segmental exchange. Modeling of reshuffling systems, originally composed of homopolymers of various $\overline {DP} _{{\rm n}} $, various mass distributions, and different compositions, is carried out until the equilibrium copolymers are obtained. It is shown that one of the schemes leads always to a random microstructure (Bernoulli statistics) whereas modeling of the other one indicates possibility of formation of all achievable distributions of comonomer units (from multiblock to nearly alternate). The concepts of the degrees of randomness and reshuffling are discussed and new definitions are proposed.

Evolution of Chain Length Distribution and Microstructure of Macromolecules in Irreversible Copolymerization Proceeding with Segmental Exchange Investigated with a New Monte Carlo Algorithm

“…Our previous studies have shown that equilibration time of copolymer microstructure corresponds to a certain number of attacks on an average copolymer unit (about 7, depending on the reshuffling rate constants), independently of copolymer DP n . [9] Taking this into account our results are understandable: the same time is needed to get the same average number of reshuffling attacks on a copolymer unit independently of copolymer DP n because reshuffling rate is proportional to DP n for the same concentration of active Table 1. species. This time corresponds to equilibration time unless reshuffling is not too fast.…”

Importance of Statistical Factors in the Description of Kinetics of a Segmental Exchange in Polyester Systems. Re‐Analysis of Reshuffling in PET/PEN Blends

“…By the way, the name of this parameter seems to be incorrect and therefore the quotation marks are used in this paper–see the discussion on this subject in our previous paper . The value of RD being smaller than unity is in contradiction with understanding of thermodynamics of segmental exchange because it indicates (contrary to expectation based on the assumed rate constants) deviation from randomness towards the increased contribution of homo‐dyads.…”

“…The importance of the principle of microscopic reversibility (microreversibility) in copolymerization systems with reshuffling of copolymer units was already discussed . One of consequences of this principle is a necessary agreement between the microstructure of copolymer stemming from thermodynamics and that stemming from segmental exchange processes.…”

“…One can expect random microstructure also when some rate constants of reshuffling differ but ones corresponding to interconversions of homo‐ and hetero‐dyads are equal. In this paper we consider only reshuffling involving merely internal ester groups, contrary to the previous paper, where segmental exchange with participation of terminal groups was analyzed . For reshuffling through internal ester groups only reactions between homo‐dyads giving hetero‐dyads and the reverse reaction change proportion of copolymer dyads (c.f.…”

Synthesis of norbornene–cyclooctene copolymers by the cross-metathesis of polynorbornene with polyoctenamer

“…However, this does not necessarily mean the absence of Ru-carbene complex selectivity with respect to NB or COE units. According to the theory of interchange reactions involving chain ends [14], the fully random chain structure is attained when k NB-NB k COE-COE = k NB-COE k COE-NB , where k α-β is the elementary rate constant describing the attack of an α terminal unit on a β internal unit. As is seen from Fig.…”