Guild Jonathan D, Knox Stephen T, Burholt Sam B, Hilton Eleanor M, Terrill Nicholas J, Schroeder Sven L M, Warren Nicholas J
School of Chemical and Processing Engineering, University of Leeds, Woodhouse, Leeds LS2 9JT, U.K.
Diamond House, Harwell Science and Innovation Campus, Diamond Light Source, Didcot OX11 0DE, U.K.
Macromolecules. 2023 Aug 4;56(16):6426-6435. doi: 10.1021/acs.macromol.3c00585. eCollection 2023 Aug 22.
In situ small-angle X-ray scattering (SAXS) is a powerful technique for characterizing block-copolymer nano-object formation during polymerization-induced self-assembly. To work effectively in situ, it requires high intensity X-rays which enable the short acquisition times required for real-time measurements. However, routine access to synchrotron X-ray sources is expensive and highly competitive. Flow reactors provide an opportunity to obtain temporal resolution by operating at a consistent flow rate. Here, we equip a flow-reactor with an X-ray transparent flow-cell at the outlet which facilitates the use of a low-flux laboratory SAXS instrument for in situ monitoring. The formation and morphological evolution of spherical block copolymer nano-objects was characterized during reversible addition fragmentation chain transfer polymerization of diacetone acrylamide in the presence of a series of poly(dimethylacrylamide) (PDMAm) macromolecular chain transfer agents with varying degrees of polymerization. SAXS analysis indicated that during the polymerization, highly solvated, loosely defined aggregates form after approximately 100 s, followed by expulsion of solvent to form well-defined spherical particles with PDAAm cores and PDMAm stabilizer chains, which then grow as the polymerization proceeds. Analysis also indicates that the aggregation number () increases during the reaction, likely due to collisions between swollen, growing nanoparticles. In situ SAXS conducted on PISA syntheses using different PDMAm DPs indicated a varying conformation of the chains in the particle cores, from collapsed chains for PDMAm to extended chains for PDMAm. At high conversion, the final decreased as a function of increasing PDMAm DP, indicating increased steric stabilization afforded by the longer chains which is reflected by a decrease in both core diameter (from SAXS) and hydrodynamic diameter (from DLS) for a constant core DP of 400.
原位小角X射线散射（SAXS）是一种用于表征聚合诱导自组装过程中嵌段共聚物纳米物体形成的强大技术。为了在原位有效工作，它需要高强度X射线，以实现实时测量所需的短采集时间。然而，常规使用同步加速器X射线源成本高昂且竞争激烈。流动反应器提供了通过以恒定流速运行来获得时间分辨率的机会。在这里，我们在流动反应器的出口配备了一个X射线透明流动池，这便于使用低通量实验室SAXS仪器进行原位监测。在一系列具有不同聚合度的聚（二甲基丙烯酰胺）（PDMAm）大分子链转移剂存在下，对双丙酮丙烯酰胺的可逆加成断裂链转移聚合过程中球形嵌段共聚物纳米物体的形成和形态演变进行了表征。SAXS分析表明，在聚合过程中，大约100秒后形成高度溶剂化、定义松散的聚集体，随后溶剂被排出，形成具有PDAAm核和PDMAm稳定剂链的定义明确的球形颗粒，然后随着聚合的进行而生长。分析还表明，反应过程中聚集数（）增加，这可能是由于肿胀的生长纳米颗粒之间的碰撞。对使用不同PDMAm聚合度的PISA合成进行的原位SAXS表明，颗粒核中链的构象不同，从PDMAm的塌陷链到PDMAm的伸展链。在高转化率下，最终值随着PDMAm聚合度的增加而降低，这表明较长的链提供了增加的空间稳定性，对于恒定的400核聚合度，这反映在核心直径（来自SAXS）和流体动力学直径（来自DLS）的减小上。
