An equation driven quality classification of (a)symmetric gradient, gradient-block, block-gradient-block and block copolymers. (17th February 2023)

• Record Type: Journal Article
• Authors: Conka, Robert; Marien, Yoshi W.; Van Steenberge, Paul H.M.; Hoogenboom, Richard; D'hooge, Dagmar R.
• Is Part Of: European polymer journal. Volume 185(2023)
• Publication Date: 2023-02-17
• Subjects: Copolymers -- Compositional distributions -- Gradient deviation -- Kinetic Monte Carlo; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2022.111769
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: Abstract: The control of the A/B comonomer distribution over individual chains targeting block and/or gradient monomer distributions is essential to control the macroscopic properties of the resulting copolymers. Matrix-based kinetic Monte Carlo simulations allow to compare each chain of a representative copolymer sample with the desired (mathematical) composition, as defined by monomer inclusion probabilities ( P A / B ) taking the B-functionalization degree (B-Func) as maximally 50%. A so-called average deviation ( SD ∗ value) results per chain, with a close to 0 average (normalized) structural deviation 〈 S D 〉 corresponding to an almost perfect structure and a 〈 S D 〉 close to 1 representing the worst case scenario of a B-homopolymer. The previously assigned 〈 S D 〉 transitions from excellent to good and from good to poor are, however, somewhat arbitrary, e.g. for both symmetric gradient and block copolymers a threshold 〈 SD Good / P o o r 〉 of 0.3 is currently utilized and only for specific asymmetric cases (30% B-Func block, block-gradient, and gradient) 〈 SD Exc / G o o d 〉 and 〈 SD Good / P o o r 〉 values have been reported. The present work puts forward an equation driven method to obtain 〈 S D 〉 threshold values, minimizing the arbitrary nature of the quality classification for a given copolymer type and more importantly aligning the quality assessment for any copolymer type containing block and/or gradient elements. Emphasis is on the complete SD distribution (instead of only its average) for (a)symmetric AB gradient, block A-gradient AB, block A-gradient AB-block B, and AB block copolymers by introducing the overall gradient and block fractions ( f Gr / B l ) as a novel parameter alongside the targeted degree of polymerization (target DP) and B-Func. Ideal theoretical structures with equal chain length and a perfect implementation of the desired P A / B profiles are dealt with, as they represent the best case an actual synthesis recipe could deliver in the limit. It is shown that the log-normal distribution can be reliably used to approximate the SD distribution, as coefficients of determination ( R 2 ) very close to one follow for (a)symmetric copolymers . It is further showcased that threshold values for gradient dominant structures must be higher than those for block-like structures and that well-defined symmetric structures are more difficult to achieve than asymmetric ones. It is also recommended to report 〈 S D 〉 together with its standard deviation σ SD .