ABA triblock copolymers containing polyhedral oligomeric silsesquioxane pendant groups: synthesis and unique properties

• Published in: Polymer (Guilford) 2003-04, Vol.44 (9), p.2739-2750
• Main Authors: Pyun, Jeffrey, Matyjaszewski, Krzysztof, Wu, Jian, Kim, Gyeong-Man, Chun, Seung B, Mather, Patrick T
• Format: Article
• Language: English
• Subjects: Applied sciences; block copolymers; Exact sciences and technology; Inorganic and organomineral polymers; Physicochemistry of polymers; polyhedral oligomeric silsesquioxane; POSS; Preparation
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(03)00027-2

The synthesis and characterization of POSS containing ABA triblock copolymers is reported. The use of atom transfer radical polymerization (ATRP) enabled the preparation of well-defined model copolymers possessing a rubbery poly( n-butyl acrylate)(pBA) middle segment and glassy poly(3-(3,5,7,9,11,13,15-heptaisobutyl-pentacyclo[9.5.1.1 3,9.1 5,15.1 7,13]-octasiloxane-1-yl)propyl methacrylate(p(MA-POSS)) outer segments. By tuning the relative composition and degree of polymerization (DP) of the two segments, phase separated microstructures were formed in thin films of the copolymer. Specifically, dynamic mechanical analysis and transmission electron microscopy (TEM) observations reveal that for a small molar ratio of p(MA-POSS)/pBA (DP=6/481/6) no evidence of microphase separation is evident while a large ratio (10/201/10) reveals strong microphase separation. Surprisingly, the microphase-separated material exhibits a tensile modulus larger than expected (ca. 2×10 8 Pa) for a continuous rubber phase for temperatures between a pBA-related T g and a softening point for the p(MA-POSS)-rich phase. Transmission electron microscopy (TEM) images with selective staining for POSS revealed the formation of a morphology consisting of pBA cylinders in a continuous p(MA-POSS) phase. Thermal studies have revealed the existence of two clear glass transitions in the microphase-separated system with strong physical aging evident for annealing temperatures near the T g of the higher T g phase (p(MA-POSS). The observed aging is reflected in wide-angle X-ray scattering as the strengthening of a low-angle POSS-dominated scattering peak, suggesting some level of ordering during physical aging. The T g of the POSS-rich phase observed in the microphase separated triblock copolymer was nearly 25 °C higher than that of a POSS-homopolymer of the same molecular weight, suggesting a strong confinement-based enhancement of T g in this system.