Poly(ε-caprolactone)/polydopamine nanocomposites with near-infrared light-triggered shape memory effect

Abstract

Light activated shape memory polymers are relatively new kinds of smart materials having diverse technological applications. In this study, two different types of PCL/polydopamine hybrid nanocomposite with near-infrared light(NIR)-responsive shape memory effects were prepared. One is a chemically crosslinked PCL network containing PDA nanoparticle achieved by in-situ ring-opening polymerization of ε-caprolactone in the presence of PDA nanoparticles followed by a chemical crosslinking with hexamethylene diisocyanate(HDI). PDA nanoparticles were synthesized by self-polymerization of dopamine under weak alkaline solution. The other type is prepared by a simple blending of commercially available high molecular weight PCL with polydopamine coated halloysite nanotube (PDA-HNT). Coating of PDA onto HNT nanoparticles were also prepared by self-polymerization of dopamine in the presence of HNT dispersion under weak alkaline solution. Morphology, chemical structure, and thermo-mechanical properties of the two different type of nanocomposites were characterized by SEM, TEM, FT-IR, tensile testing, DMA and DSC, respectively. Results for chemically crosslinked PCL/PDA hybrids revealed that different length of PCL chains can be successfully grafted onto the PDA nanoparticles with average diameter of ~200 nm and crosslinked network can be formed via urethane bonds. With increasing PDA content in the hybrids, the melting temperature and degree of crystallinity of PCL decreased while moduli at the plateau region above its Tm increased in the hybrid networks. The chemically crosslinked PCL/PDA hybrids exhibited excellent thermally and infrared-triggered shape memory behavior. Similar shape memory behaviors were also observed for the PCL/PDA coated HNT hybrids prepared by a simple blending due to photothermal effects of PDA layer coated on the HNT surface as well as the formation of physically crosslinked structure via strong hydrogen bonding interactions between surface functional groups on the PDA coating layer and carbonyl group of matrix PCL. |광감응형 형상기억고분자는 다양한 분야에 응용될 수 있는 스마트고분자이다. 본 연구에서는 두 가지 서로 다른 타입의 근적외선 감응형 형상기억특성을 갖는 폴리카프로락톤(PCL)/폴리도파민(PDA) 하이브리드 나노복합체를 제조하였다. 이중 한 타입은 알카리 용액에서 도파민을 자가중합시켜 제조한 PDA 나노입자 존재 하에서 PCL을 실시간으로 개환중합시켜 PDA 입자표면에 PCL을 그라프트 시킨 후 이를 헥사메틸렌디이소시아네이트를 이용하여 화학적으로 가교시켜 제조하였다. 다른 한 가지 타입의 하이브리드는 표면에 PDA를 코팅시킨 halloysite 나노입자를 상업적으로 구할 수 있는 고분자량의 PCL과 용액 상에서 혼합하고 캐스팅함으로써 제조하였다. 제조된 두 가지 하이브리드들의 미세모폴로지, 화학구조, 열적, 기계적 특성을 각각 SEM, TEM, FT-IR, tensile testing, DMA, DSC 등을 이용하여 분석하였다. 화학적으로 가교시킨 PCL/PDA 하이브리드 분석 결과, 직경 약 200 nm 크기의 PDA 나노입자 표면에 서로 다른 사슬길이를 갖는 PCL를 성공적으로 그라프트 시킬 수 있었고, 또한, 우레탄 반응을 통하여 화학적으로 가교시킬 수 있음을 확인하였다. 일정한 PCL 단량체 대비 PDA 나노입자의 함량을 증가시킴으로써 제조된 네트워크의 가교밀도가 증가되어 용융온도와 결정화도가 감소되었으며, PCL의 용융온도 이상에서의 저장탄성율은 증가되었다. 이렇게 제조된 PCL/PDA 하이브리드 네트워크는 일정한 임시모양으로 잘 고정되었으며, 이러한 임시모양을 PCL의 용융온도 이상으로 가열하거나 또는 근적외선 조사 시 우수한 형상기억특성을 나타내었다. 이와 유사한 형상기억특성이 블렌딩에 의해 제조된 PCL/PDA-HNT 나노복합체에서도 잘 발현되었다. 이는 HNT 표면에 코팅된 박막의 PDA 층의 광열효과와 함께 코팅된 PDA 표면의 극성 관능기들과 매트릭스 PCL의 카보닐기간의 특정상호작용에 의한 물리적 가교구조의 형성에 기인한 것으로 판단되었다.; Light activated shape memory polymers are relatively new kinds of smart materials having diverse technological applications. In this study, two different types of PCL/polydopamine hybrid nanocomposite with near-infrared light(NIR)-responsive shape memory effects were prepared. One is a chemically crosslinked PCL network containing PDA nanoparticle achieved by in-situ ring-opening polymerization of ε-caprolactone in the presence of PDA nanoparticles followed by a chemical crosslinking with hexamethylene diisocyanate(HDI). PDA nanoparticles were synthesized by self-polymerization of dopamine under weak alkaline solution. The other type is prepared by a simple blending of commercially available high molecular weight PCL with polydopamine coated halloysite nanotube (PDA-HNT). Coating of PDA onto HNT nanoparticles were also prepared by self-polymerization of dopamine in the presence of HNT dispersion under weak alkaline solution. Morphology, chemical structure, and thermo-mechanical properties of the two different type of nanocomposites were characterized by SEM, TEM, FT-IR, tensile testing, DMA and DSC, respectively. Results for chemically crosslinked PCL/PDA hybrids revealed that different length of PCL chains can be successfully grafted onto the PDA nanoparticles with average diameter of ~200 nm and crosslinked network can be formed via urethane bonds. With increasing PDA content in the hybrids, the melting temperature and degree of crystallinity of PCL decreased while moduli at the plateau region above its Tm increased in the hybrid networks. The chemically crosslinked PCL/PDA hybrids exhibited excellent thermally and infrared-triggered shape memory behavior. Similar shape memory behaviors were also observed for the PCL/PDA coated HNT hybrids prepared by a simple blending due to photothermal effects of PDA layer coated on the HNT surface as well as the formation of physically crosslinked structure via strong hydrogen bonding interactions between surface functional groups on the PDA coating layer and carbonyl group of matrix PCL.