Ahn Suk-Kyun, Carrillo Jan-Michael Y, Han Youngkyu, Kim Tae-Hwan, Uhrig David, Pickel Deanna L, Hong Kunlun, Kilbey S Michael, Sumpter Bobby G, Smith Gregory S, Do Changwoo
Neutron Science Division, Department of Reactor Utilization and Development, Korea Atomic Energy Research Institute, 1045 Daedeok-daero, Yuseong-gu, Daejeon, Republic of Korea.
Departments of Chemistry and Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States.
ACS Macro Lett. 2014 Sep 16;3(9):862-866. doi: 10.1021/mz5003454. Epub 2014 Aug 18.
Structural evolution from poly(lactide) (PLA) macromonomer to resultant PLA molecular bottlebrush during ring opening metathesis polymerization (ROMP) was investigated for the first time by combining size exclusion chromatography (SEC), small-angle neutron scattering (SANS), and coarse-grained molecular dynamics (CG-MD) simulations. Multiple aliquots were collected at various reaction times during ROMP and subsequently analyzed by SEC and SANS. These complementary techniques enable the understanding of systematic changes in conversion, molecular weight and dispersity as well as structural details of PLA molecular bottlebrushes. CG-MD simulation not only predicts the experimental observations, but it also provides further insight into the analysis and interpretation of data obtained in SEC and SANS experiments. We find that PLA molecular bottlebrushes undergo three conformational transitions with increasing conversion (i.e., increasing the backbone length): (1) from an elongated to a globular shape due to longer side chain at low conversion, (2) from a globular to an elongated shape at intermediate conversion caused by excluded volume of PLA side chain, and (3) the saturation of contour length at high conversion due to chain transfer reactions.
首次通过结合尺寸排阻色谱法（SEC）、小角中子散射（SANS）和粗粒度分子动力学（CG-MD）模拟，研究了在开环易位聚合（ROMP）过程中从聚乳酸（PLA）大分子单体到所得PLA分子刷的结构演变。在ROMP过程中的不同反应时间收集多个等分试样，随后通过SEC和SANS进行分析。这些互补技术有助于理解转化率、分子量和分散度的系统变化以及PLA分子刷的结构细节。CG-MD模拟不仅预测了实验观察结果，还为SEC和SANS实验中获得的数据的分析和解释提供了进一步的见解。我们发现，随着转化率的增加（即主链长度增加），PLA分子刷经历了三种构象转变：（1）在低转化率下，由于侧链较长，从伸长形状转变为球形；（2）在中等转化率下，由于PLA侧链的排除体积，从球形转变为伸长形状；（3）在高转化率下，由于链转移反应，轮廓长度达到饱和。
