Synthesis of crystallizable poly(behenyl methacrylate)-based block and statistical copolymers and their performance as wax crystal modifiers

Two series of behenyl methacrylate-based diblock and statistical copolymers have been prepared by reversible addition–fragmentation chain transfer (RAFT) solution polymerization in n-dodecane and evaluated as additives for the crystal habit modification of a model wax (n-octacosane). DSC studies indicated that each statistical copolymer exhibited a significantly lower crystallization temperature (Tc) and melting temperature (Tm) for the semi-crystalline behenyl methacrylate component than the corresponding diblock copolymer of almost identical overall composition. Temperature-dependent turbidimetry studies were conducted for each copolymer using a series of solutions of 5.0% w/w n-octacosane dissolved in n-dodecane to determine Tcool, which is the temperature at which zero transmittance is first observed owing to wax crystallization. At a constant molar copolymer concentration of 0.26 mM, each of the eight copolymers produced a reduction in Tcool of approximately 3–5 °C. Scanning electron microscopy (SEM) studies confirmed that the presence of such copolymers led to a reduction in the overall size and/or a higher crystal aspect ratio. The diblock and statistical copolymers were similar in their performance as potential wax crystal modifiers. However, the statistical copolymers were easier to prepare and did not suffer from any homopolymer contamination. Moreover, optical microscopy and SEM studies revealed that needle-like crystals were formed instead of platelets when employing behenyl methacrylate-rich statistical copolymers.