Crystallization Behavior and Melt Memory Effects in PEO-B-PCL Copolymer for Tailoring Drug Delivery

Poly(ethylene-oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) is a copolymer that has been researched for a variety of medical applications including drug delivery. Having an understanding of the crystallization behavior of PEO-b-PCL is paramount to optimizing its performance and tailoring it to specific needs. In the case of drug delivery, this can manifest when different drugs need to be released at different rates. One drug may need a constant release over a long period of time, or another may need to be released in bursts. This study focuses on understanding which part of the copolymer will crystallize first during a cooling process while casted in toluene, and the effects that melt memory has on the crystallization process. The experimental approach used a hot stage to melt and subsequently cool samples of PEO-b-PCL casted in toluene. Samples varied in molecular weight with both 5k10k and 5k5k polymer being used. Fourier-transform infrared spectroscopy was utilized to monitor peaks that correspond to PEO and PCL. Additionally, varying the melting temperature allowed changes due to melt memory effects to be measured. The results show a distinct difference between the crystallization behavior of the two molecular weight variants. In the 5k10k samples, PCL crystallization occurred first and also occurred sooner in trials with a lower melting temperature. The 5k5k samples showed no distinct difference in the temperature in which PEO or PCL crystallization, which suggests coincident crystallization behavior. The differences between the behavior of samples with different molecular weights indicate that PEO-b-PCL can be fine-tuned to the needs of specific applications. Being able to control the crystallization behavior, influenced by both melt memory effects and molecular weight, is promising for the future of optimizing the usage of PEO-b-PCL in drug delivery.