FULL PAPER Effect of polyhedral oligomeric silsesquioxane nanocage on the crystallization behavior of PEG 5k -b-P(MA-POSS) diblock copolymers achieved via atom transfer radical polymerization Asad Ullah 1† | Shakir Ullah 1† | Nasir Mahmood 2 | Syed M. Shah 1 | Zakir Hussain 3 | Hazrat Hussain 1 1 Department of Chemistry, Quaid-i-Azam University Islamabad, Islamabad, Pakistan 2 Institut für Chemie, FG Mikro- und Nanostrukturbasierte Polymerverbundwerkstoffe, Martin Luther University Halle-Wittenberg, Halle/Saale, Germany 3 School of Chemical and Materials Engineering (SCME), National University of Sciences and Technology (NUST), Islamabad, Pakistan Correspondence Hazrat Hussain, Department of Chemistry, Quaid-i-Azam University Islamabad, 45320 Islamabad, Pakistan. Email: hazrat.hussain@qau.edu.pk Funding information Higher Education Commision, Pakistan, Grant/ Award Number: project No. 20-3074/ NRPU/R&D/HEC/13 We report our findings on the effect of polyhedral oligomeric silsesquioxane (POSS) nanocages, incorporated into the block copolymer structure with poly(ethylene glycol) (PEG) via atom trans- fer radical polymerization, on the crystallization behavior of PEG-b-P(MA-POSS) diblock copoly- mers. The PEG, which is a highly crystalline polymer, could no longer retain its crystalline nature when connected with long bulky POSS segments as confirmed by various tools including differ- ential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide and small angle X-ray diffraction (WAXD and SAXD). The WAXS and SAXD investigations revealed that the PEG-b-P(MA-POSS) block copolymers with higher POSS content phase separate into a disor- dered state with amorphous PEG and POSS crystalline domains. The temperature dependent (20  C-90  C) WAXD or SAXD profiles of the block copolymers do not reveal any phase change. Thus, it could be argued that the POSS crystalline domains that retain their structural integrity during the heating and cooling cycles restrict the PEG chain mobility that hinders their crystalli- zation. Nevertheless, in DSC data, even with higher POSS content, still the PEG melting and crystallization peaks could be seen, suggesting that PEG chains can still organize to form smaller crystalline domains that could not be detected by the POM and WAXD instruments. KEYWORDS ATRP, block copolymers, crystallization, phase separation, POSS 1 | INTRODUCTION The incorporation of well-defined polyhedral oligomeric silsesquioxane (POSS) nanocage as nanofiller in polymer matrix, both physically and chemically, has been well-documented over the last many years, particu- larly, because of the commercially availability of various POSS derivatives from Hybrid Plastics. [1–3] Due to unique properties of the POSS, the nanomaterials based on POSS derivatives have been explored for a num- ber of potential applications, such as thermally and mechanically strong nanocomposites, [4–6] gas separation membrane, [7,8] photoresist mate- rials, [9] drug and gene delivery systems, [9,10] biomaterials, [11] water desali- nation membrane, [12] dental materilas, [13,14] optoelectronics, [15] to name a few. There is a growing interest in POSS cage integration into polymer architecture, as pendant group, [16–19] or as chain end (hemitelechelic/ telechelic), [20–23] or as core of hybrid star-like polymers [24–30] by the so- called “Controlled” radical polymerization (CRP) techniques or a com- bined approach of CRP and “click” reactions. The CRP techniques, namely, RAFT, [31] NMP, [32] and ATRP [33,34] offer a convenient and exper- imentally benign route as compared with the anionic polymerization to afford (co)polymers of various architectures with predefined molar mass, well-defined structure, and chain end functionality. ATRP is one of the most frequently used CRP techniques to afford well-defined (co)polymers from a wide array of vinyl type of monomers. It is based on a dynamic equilibrium between the halogen (Cl or Br) ter- minated dormant polymer chains and the active polymer chains bearing free radicals mediated by transition metal such as Cu, Ru, Fe, Ni, or Os in combination with different types of nitrogen-based ligands. Over the last several years, the ATRP has seen tremendous progress toward a “green” † Asad Ullah and Shakir Ullah contributed equally to this study. Received: 27 September 2018 Accepted: 2 January 2019 DOI: 10.1002/pcr2.10058 Polymer Crystallization. 2019;e10058. wileyonlinelibrary.com/journal/pcr2 © 2019 Wiley Periodicals, Inc. 1 of 9 https://doi.org/10.1002/pcr2.10058