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The development of simulation methods to study the structure and dynamics of a macroscopically sized piece of polymer material is important as such methods can elucidate structure-property relationships. Several methods have been reported to construct initial structures for homo- and co-polymers; however, most of them are only useful for short linear polymers since one needs to pack and equilibrate the far-from-equilibrium initial structures, which is a tedious task for long or hyperbranched polymers and unfeasible for polymer networks. In this method article, we present PolySMart, i.e., an open-source python package, which can effectively produce fully equilibrated homo- and hetero-polymer melts and solutions with no limitation on the polymer topology and size, at a coarse-grained resolution and through a bottom-up approach. This python package is also capable of exploring the polymerization kinetics through its reactive scheme in realistic conditions so that it can model the multiple co-occurring polymerization reactions (with different reaction rates) as well as consecutive polymerizations under stoichiometric and non-stoichiometric conditions. Thus, the equilibrated polymer models are generated through correct polymerization kinetics. A benchmark and verification of the performance of the program for several realistic cases, i.e., for homo-polymers, co-polymers, and crosslinked networks, is given. We further discuss the capability of the program to contribute to the discovery and design of new polymer materials.

Simulation studies of step-growth polymerization, e.g., polymerization of polyurethane systems, hold great promise due to having complete control over the reaction conditions and being able to perform an in-depth analysis of network structures. In this work, we developed a (completely automated) simulation method based on a coarse-grained (CG) methodology, i.e., the MARTINI model, to study the cross-linking reaction of a diol, a tri-isocyanate molecule and one-hydroxyl functional molecule to form a polyurethane network without and with dangling chains. This method is capable of simulating the cross-linking reactions not only up to very high conversions, but also under rather complicated reaction conditions, i.e., a non-stoichiometric ratio of the reactants, solvent evaporation and multi-step addition of the reactants. We introduced a novel network analysis, similar to size-exclusion chromatography based on graph theory, to study the growth of the network during the polymerization process. By combining the reaction simulations with these analysis methods, a set of correlations between the reaction conditions, reaction mechanisms and final network structure and properties is revealed. For instance, a two-step addition of materials for the reaction, i.e., first the dangling chain to the tri-isocyanate and then the diol, leads to the highest integrated network structure. We observed that different reaction conditions lead to different glass transition temperatures (Tg) of the network due to the distinct differences in the final network structures obtained. For example, by addition of dangling chains to the network, the Tg decreases as compared to the network without dangling chains, as also is commonly observed experimentally.

Polymer networks with hydrophilic dangling chains are ideal candidates for many submerged applications, e.g., protein non-adhesive coatings with non-fouling behavior. The dangling chains segregate from the polymer network towards the water and form a brush-like structure at the interface. Several factors such as the polymer network structure, dangling chain length, and water/dangling chain interaction may all affect the interfacial performance of the polymer. Therefore, we employed a Martini based coarse-grained (CG) molecular dynamics (MD) simulation to elucidate the influences of the abovementioned parameters on dangling chain interfacial segregation. We built up several polyurethane (PU) networks based on poly(tetra methylene glycol) (PTMG), as a macrodiol, and methoxy poly(ethylene glycol) (mPEG), as a dangling chain, with varying molecular weights. We found out that the macrodiol/dangling chain length ratio considerably smaller than one impedes the migration of dangling chains towards the water interface, while the dangling chain hydrophilicity and length determine the polymer interfacial layer density/thickness. Then, we artificially changed the dangling chain affinity to water from an intermediate to a very attractive water/dangling chain interaction. We justified that a brush-like structure forms in two consecutive steps: first, a longitudinal, and then a lateral migration of dangling chains in water. The latter step results in a uniform interfacial layer over the polymer interface that mainly occurs in the case of the attractive water/dangling chain interaction.

PEG-modification is a proven method to enhance the hydrophilicity, protein resistance, and anti-biofouling properties of polymer coatings. It is considered as the gold standard interfacial modification technique such that the higher PEG content, the higher hydrophilicity, and lower protein adsorption, i.e., the initial stage of the biofouling process. Nevertheless, increasing the PEG content causes a higher water uptake, which declines the polymer mechanical strength and increases its hydrolytic degradation rate. Thus, an effective strategy to produce a limited-water-absorbing PEG-modified polymer is to force the majority of PEG molecules to migrate towards the interfacial region while the modification takes place. In the current paper, we report the synthesis and characterization of crosslinked polycarbonate-based polyurethanes (PU) containing methoxy polyethylene glycol (mPEG) dangling chains. We show that the simultaneous incorporation of a limited amount of a low-surface-energy dangling chain, i.e., 1-octadecanol (oDEC), along with mPEG, results in a considerably higher mPEG surface concentration, according to X-ray photoelectron spectroscopy (XPS), and a significantly lower water contact angle (WCA), up to 45° lower. We also put forward a reasonable mechanism for our outstanding observation and verified it through extensive experiments, e.g., dynamic WCA, Atomic force microscopy (AFM), and XPS. Moreover, we outline a delicate dynamic WCA experimental protocol, by which the smart and responsive behavior of our coatings is illustrated. Eventually, we examined the mixed hydrophobic/hydrophilic dangling chains strategy for low-protein adsorption applications, in which a great potential has been discovered.

Organic–inorganic polyurethane coatings were prepared using two polyester resins and two polyhedral Oligomeric Silsesquixane (POSS) compounds. The effect of hydroxyl content and POSS functionality was studied on hardness and scratch resistance. FTIR spectroscopy was used to reveal bond formation between isocyanate and hydroxyl groups. Vickers hardness, nanoindentaion and nanoscratch experiments were performed to study the mechanical properties of the hybrids. The results showed that intrinsic hardness of POSS affected the crosslink density, the result of which was increased free volume and improved scratch resistance of POSS/PU hybrid coatings. This behavior was dependent on the hydroxyl percent of the polyol.