One of the challenges in the field of surface-initiated polymerization (SIP) is gaining access to conformational distributions allowing one to quantify the degree of brush/mushroom character during synthesis. Here, we put forward a novel kinetic Monte Carlo (kMC) tool to be successful in this respect, focusing on chain-to-chain deviations on and near the surface accounting for varying reaction probabilities and combining conventional kMC modeling with a modified version of the bond fluctuation model. The potential of the tool is illustrated for living SIP addressing the effect of shielding on the efficiency of surface initiation and propagation. It is shown that at higher reaction times shielding for propagation leads to the increased formation of hindered shorter chains, causing the formation of a bimodal number chain-length distribution (CLD) for tethered chains compared to the always unimodal number CLD for free larger chains near the surface. Moreover, it can be evaluated at any synthesis time if an individual chain possesses a mushroom, brushlike, or brush conformation. It is demonstrated that an optimal (average) initiator surface coverage exists, leading to a sufficiently high chain grafting density and a maximization of the brush character provided that an initiator with the correct (surface) initiation reactivity is selected. The developed tool is important for the multiangle design of future SIP processes focusing on optimization in reaction time, control over CLD, and conformational features in view of the desired application.

A systematic kinetic study of the isothermal cationic ring-opening polymerization of 2-ethyl-2-oxazoline (EtOx) in acetonitrile initiated by methyl tosylate under microwave irradiation (353−413 K) for a target degree of polymerization of 100 is reported as a basis for kinetic Monte Carlo simulations with parameters tuned based on monomer conversion and chain length data. It is highlighted that the size-exclusion chromatography (SEC) trace is needed to properly tune the less known macropropagation rate coefficient, which is related to the incorporation of enamine-terminated polymer chains resulting from chain transfer to monomer and which determines the contribution of linear and branched chains. A model-based design is applied to identify the reaction temperatures that lead to an optimum between the reaction time and control over molecular properties. A linear relationship is derived, which can be used to reliably assess the mass fraction of branched chains at sufficiently high monomer conversions based on the measurement of the location of the inflection point for the high molar mass part of the SEC trace.

One of the challenges for brush synthesis for advanced bioinspired applications using surface-initiated reversible deactivation radical polymerization (SI-RDRP) is the understanding of the relevance of confinement on the reaction probabilities and specifically the role of termination reactions. The present work puts forward a new matrix-based kinetic Monte Carlo platform with an implicit reaction scheme capable of evaluating the growth pattern of individual free and tethered chains in three-dimensional format during SI-RDRP. For illustration purposes, emphasis is on normal SI-atom transfer radical polymerization, introducing concepts such as the apparent livingness and the molecular height distribution (MHD). The former is determined based on the combination of the disturbing impact of termination (related to conventional livingness) and shielding of deactivated species (additional correction due to hindrance), and the latter allows structure-property relationships to be identified, starting at the molecular level in view of future brush characterization. It is shown that under well-defined SI-RDRP conditions the contribution of (shorter) hindered dormant chains is relevant and more pronounced for higher average initiator coverages, despite the fraction of dead chains being less. A dominance of surface-solution termination is also put forward, considering two extreme diffusion modes, i.e., translational and segmental. With the translational mode termination is largely suppressed and the living limit is mimicked, whereas with the segmental mode termination occurs more and the termination front moves upward alongside the polymer layer growth. In any case, bimodalities are established for the tethered chains both on the level of the chain length distribution and the MHD.

From an industrial point of view, it has often been claimed that MMDs need to possess a sufficiently large mass average molar mass M m (e.g., 10 6 g mol −1 ) to ensure sufficient entanglements and must be broad, requiring dispersity (Ð) values well above 1.5. [5,8] For specific applications, such as coatings, MMD bimodality has even been put forward as the primary target, leading to dispersity values higher than 4. [15][16][17] For the determination of the radical propagation, [18][19][20][21][22][23] backbiting, [24][25][26][27] and β-scission [24,28] rate coefficients or the quantification of photo dissociation quantum yields, [29] a modulated MMD trace is beneficial. In contrast to modulated and broad MMDs, the more recent chemical development of living and reversible deactivation radical poly merization (L/RDRP) mechanisms has made clear that more niche applications (e.g., drug delivery or high-end cosmetics) can benefit from lower M m values (e.g., 10 4 g mol −1 ) and narrow monomodal MMDs with Ð values below 1.5. [30][31][32][33][34][35][36] This dedicated molecular tailoring is also related to control over end-group functionality to enable the synthesis of more special polymers such as block, gradient, and star (co)polymers. [37][38][39][40][41] Therefore, a dedicated knowledge of the relationship between reaction conditions and MMD is indispensable for any polymerization mechanism.The key analytical tool for MMD characterization is size exclusion chromatography (SEC) or equivalently gel permeation chromatography (GPC) in which longer chains-so species with higher molar masses-elute first, as they have fewer interactions with the smaller pores in the packed columns. The chains with the highest molar masses are thus located at the lowest retention times (RTs) in the chromatogram so that the recorded chromatogram corresponds to a "reverse" MMD. This is illustrated in Figure 1a employing a refractive index (RI) detector, which is also known as single GPC detection. Ideally, calibration takes place with standards of the same polymer type that are characterized by very narrow MMDs (Ð values close to 1), as demonstrated in Figure 1b. In many research groups, one finally aims at a log-MMD representation, requiring a normalization on logarithmic scale. This is illustrated by the arrow between Figure 1c,d and leadsThe molar mass distribution (MMD), which is also known as the molecular weight distribution (MWD), is a key molecular property for a polymerization process, as it determines polymer strength and polymeric material deformation. Several MMD and related chain length distribution (CLD) representations are however used interchangeably, often leading to biased conclusions. Herein it is highlighted how the most interesting simulated CLD/MMD representations, i.e., the number, mass, z-based, and logarithmic CLD/MMD, can be translated into each other and how they need to be corrected to facilitate comparison with experimental size exclusion chromatography traces. Their relevance is highlighted by including case st...

The oxodegradation of an injection molding grade polypropylene (PP), formulated with 0%, 1.5%, and 3% w/w of a prooxidant additive, was studied. The degradation was conducted in a weathering tester at 60 8C for 40 h. The process was monitored by Fourier transform infrared spectroscopy, standard differential scanning calorimetry, and successive self-nucleation and annealing. Neat PP samples did not exhibit significant changes during the exposure time employed. PP samples with oxo-additive presented similar changes independently of the amount of oxo-degradative additive employed; however, the changes manifested more rapidly in the formulation with higher pro-oxidant content. Fourier transform infrared spectroscopy studies revealed the presence of hydroxyl and carbonyl functional groups whereas differential scanning calorimetry tests showed the decrease in the melting and crystallization temperatures as a consequence of the chain scission and oxidation reactions taking place during exposure. In addition, the induction time (t id ) of the oxo-degradative process was determined for each technique employed and successive self-nucleation and annealing was found to be the most sensitive characterization technique to reveal structural modifications in PP samples. V C 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46088.

Front Cover: Guidelines to translate simulated chain length and molar mass distributions are presented, facilitating the comparison with experimental size exclusion chromatography data and the retrieval of mechanistic information. These guidelines are illustrated considering linear, branched and crosslinked chain‐growth products. This is reported by Yoshi W. Marien, Mariya Edeleva, Freddy L. Figueira, Francisco J. Arraez, Paul H. M. Van Steenberge, Dagmar R. D'hooge in article number 2000008.

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Cationic ring-opening polymerization (CROP) is an interesting synthesis technique to obtain well-defined polymers with narrow molar mass distribution (MMD). Upon using a multifunctional initiator, well-defined multi-arm or star polymers can...