Abstract
ABSTRACTThe sizes and structures of isolated functionalised polymers in a hydrocarbon solvent are studied using atomistic molecular dynamics simulations and Monte Carlo simulations of coarse-grained chains. A specific functionalised polyethylene-polypropylene random copolymer in n-heptane is studied using atomistic simulations. The functional groups contain aromatic and polar groups, and eight of them are distributed on an polymer backbone in several different ways. It is shown that the radius of gyration and the end-to-end distance depend sensitively on the functional-group distribution. A random distribution of functional groups gives the most compact polymer structure, but other distributions give values up to larger; the largest values are when the functional groups are split evenly between both ends of the polymer. This is shown to be due to the association of the polar, and hence solvophobic, functional groups. A coarse-grained bead-spring model is then studied that includes solvophilic beads (representing unfunctionalised units) and solvophobic beads (representing functionalised units). Monte Carlo simulations are used to survey functional-group concentration and distribution. The results show that the collapse of a polymer with increasing solvophobicity depends sensitively on the distribution of different beads. Form factors are presented for both the atomistic and coarse-grained models and are analysed as if they were experimental scattering measurements. The apparent radii of gyration are in good agreement with those determined directly from the simulation.
Highlights
Recent advances in synthetic strategies mean that functionalised polymers (FPs) can be produced with a variety of compositions, structures, and architectures [1,2,3]
If an FP possesses a solvophilic backbone and solvophobic functional groups, one can anticipate repulsive interactions between backbone groups because they are in good-solvent conditions, and attractive effective interactions between the functional groups because they are in bad-solvent conditions
Both radius of gyration (Rg) and Ree decrease with increasing x2 because the polymer collapses as it moves from good-solvent conditions to bad-solvent conditions
Summary
Recent advances in synthetic strategies mean that functionalised polymers (FPs) can be produced with a variety of compositions, structures, and architectures [1,2,3]. If the FPs are only sparsely functionalised, though, their behaviour can be quite different from that of block copolymers, because the functional groups do not have to be concentrated in large domains Taking this to an extreme, the structures, properties, and functions of biological polymers such as proteins are dictated by the numbers and precise locations of residues on a polypeptide backbone of, on average, 150 amino acids [19]. Biological polymers obviously present a much more complicated and subtle problem than FPs, given the complexity and specificity of the interactions between residues (electrostatic interactions, hydrogen bonding, hydrophobic interactions, disulfide bridges, etc.) and the variety of secondary structures Even for this complicated problem, modelling proteins as amphiphilic polymers can uncover some important features, for example, how the distribution of hydrophilic and hydrophobic residues controls the aggregation of proteins [20].
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