Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Abstract

We report a numerical study of crystallization and melting in bulk statistical homogeneous (random), homogeneous (slightly alternating), and heterogeneous (produced in a batch reaction) copolymers formed by crystallizable monomers and noncrystallizable comonomers. In our dynamic Monte Carlo simulations of lattice chains, the current model further assumes that the comonomers cannot move into crystalline regions by sliding diffusion of the chains. We find that both the overall composition and the statistical distribution of the monomers affect the phase-transition temperature, the resulting relative crystallinity, and the crystal morphology. However, the final absolute crystallinity of homogeneous copolymers seems insensitive to these parameters. Intramolecular segregation between monomers and comonomers is accompanied by crystallization, demonstrating the concept of sequence segregation or nanophase separation of statistical copolymers with assembling structures like in thermoplastic elastomers. Moreover, if crystallization of homogeneous copolymers has started but not yet completed on cooling, subsequent heating will show cold crystallization before melting, which can be attributed to insertion-mode lamellar growth. For heterogeneous copolymers, intermolecular segregation occurs on cooling before crystallization. On the basis of our observations, a pair of master melting and crystallization curves for the crystallinity of a statistical copolymer as a function of temperature are suggested to reflect the characteristic of the monomer-sequence-length distribution. This suggestion facilitates the clarification to the kinetic disturbance in local temperature regions and to the principle of some fractionation methods, such as temperature rising elution fractionation (TREF).

Effect of block asymmetry on the crystallization of double crystalline diblock copolymers

“…To locate the transition point from melt to crystal, we calculate specific heat ( v C ) as equilibrium specific heat from the total energy fluctuations in the simulation box. 42,52,53 To locate the …”

Polymer crystallization in the presence of “sticky” additives

“…23 In contrast, Hu et al 29 used MC simulations to examine copolymer crystallization and were able to successfully reproduce experimentally observed, nontrivial trends such as the influence of comonomer content on the development of crystallinity on cooling, etc. Therefore, we use a dynamic MC ͑DMC͒ methodology similar to that of Hu et al [27][28][29] to address the crystallization of homopolymer melts containing additives. We now describe our simulation technique in detail.…”

“…We arbitrarily define a bond as crystalline if it is surrounded by more than five nearest nonbonded parallel bonds in a manner similar to that of Hu et al 29 Crystallinity is defined as the ratio of the number of crystalline bonds to the total number of bonds in the system. A crystallite is a contiguous aggregate of crystalline bonds with the same orientation.…”

“…32 Polymer crystallization is a nonequilibrium phenomenon and results in a coexistence of amorphous and crystalline phases over a range of temperatures. The work of Hu et al 29 demonstrated that several experimental details of copolymer crystallization can be accurately reproduced by DMC simulations with a similar methodology. Specifically, previous work demonstrated that DMC simulations faithfully capture the dynamical evolution of semicrystalline microstructure during chain folding, 40 sectorization of solution crystals, 41 and melting of lamellar polymer crystals.…”

Thermal Degradation of Statistical Copolymers of 2-Vinyl Pyridine with Functional Methacrylates

“…solubility [1], crystallinity [2] and glass transition temperature (Tg) [3] in order to create new materials of scientific interest as well as diverse applications, such as drug transfer systems [4], photoresists for lithography [5] and smart materials [6]. Its utility is stressed by the large number of commercial applications and investigations that have been conducted to correlate the structure with the properties of the materials [3], [7].…”