Influence of intramolecular crosslinking on gelation in living copolymerization of monomer and divinyl cross-linker. Monte Carlo simulation studies Piotr Polanowski a , Jeremiasz K. Jeszka b , Kamil Krysiak a , Krzysztof Matyjaszewski a, c, * a Department of Molecular Physics, Technical University of Lodz, 90-924, Lodz, Poland b Department of Man-Made Fibres, Technical University of Lodz, 90-924, Lodz, Poland c Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA,15213, USA article info Article history: Received 22 August 2015 Received in revised form 3 October 2015 Accepted 7 October 2015 Available online 22 October 2015 Keywords: ATRP copolymerization MC simulations Gelation Intramolecular crosslinking Cyclization abstract The effect of intramolecular crosslinking (IC) (cyclization) on gelation was studied using Monte Carlo simulations. The consumption of crosslinker in the IC process is proposed as one of the main reasons of significant overestimation of the gel point by Flory-Stockmayer theory. The system under study is atom transfer radical polymerization (ATRP) of a monomer and bifunctional (e.g. divinyl) crosslinker. The simulation method is based on dynamic lattice liquid algorithm (DLL) and reproduces changes of the system dynamics during polymerization. The effect of cyclization on gel point for various reagents ratios and dilutions was investigated. It is shown that intramolecular crosslinking does not change significantly the gel point in condensed systems (no solvent or below 10%). By contrast, it significantly increases gel points in diluted systems (40e90% of the solvent). © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Polymer gels are a class of branched and cross-linked materials with a numerous applications involving cosmetics (e.g. ointments and beauty products), medical systems (e.g. drug delivery and cell culture growing) and surface coatings (e.g. lubricants and sealing pasts) [1e3]. They are obtained mainly by (i) crosslinking of linear polymers by multifunctional vinyl compounds or (ii) copolymer- izing mixture of mono-functional and multi-functional monomers (in situ gelation). The latter may be done by applying radical-based processes such as free radical polymerization (FRP), reversible deactivation radical polymerization (RDRP) or even poly- condensation [4]. Among these, the RDRP, and especially the Atom Transfer Radical Polymerization (ATRP) [5,6], are the only processes that allow to control the distribution of crosslinks and homogeneity of the structure of gel due to suitable relation of fast initiation to much slower propagation during polymerization [7]. The development of RDRP methods is undeniably one of the most intensely explored areas of research in polymer science. Due to fast initiation and relatively slow chain propagation, the growth of polymer chain follows the first-order kinetics and leads to pre- cise control over molecular weights and their distribution and the structure of obtained chains [8]. During the last two decades, the RDRP methods were success- fully applied in syntheses of many interesting materials, previously impossible to obtain by classical FRP. Among these novel polymeric materials one can distinguish: (i) ideally alternating copolymers [9], (ii) block copolymers [10], (iii) tapered and gradient materials [11], (iv) polymers grafted from the surface of inorganic materials [12], (v) cyclic polymers [13], (vi) star-shaped polymers [14] and many others. During the copolymerization of a mixture of mono-functional and multi-functional monomers gelation should occur at specific conversion of monomers, independently on the temperature of reaction, amount of the catalyst used or relations between addition rates of the components of mixture [15]. The probability of creation of continuous, covalently bounded network with sufficient number of chain branches that ensures the “infiniteness” of the network emerges clearly from: (i) the functionality of monomers [16], (ii) the amount of solvent in the system during gelation [17] and (iii) exact moment of addition of cross-linking agent [14]. These * Corresponding author. Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA, 15213, USA. E-mail address: km3b@andrew.cmu.edu (K. Matyjaszewski). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2015.10.018 0032-3861/© 2015 Elsevier Ltd. All rights reserved. Polymer 79 (2015) 171e178