Remarkable glass transition breadths up to 120 K exhibited by block-gradient copolymers and by gradient copolymers plasticized by oligomer

The glass transition temperature (T_g) breadth of gradient copolymers can be dramatically increased by covalent attachment of homopolymer (or random copolymer heavy in one comonomer) leading to block-gradient copolymers or by blending with oligomer. Styrene/n-butyl acrylate (S/nBA) and styrene/4-vinyl pyridine (S/4VP) gradient and block-gradient copolymers were synthesized by one-pot, semi-batch nitroxide-mediated polymerization. The glass transition responses were characterized using derivative heat flow curves from differential scanning calorimetry. For moderately segregating S/nBA gradient copolymer, covalently attaching a homopolymer or quasi-homopolymer block leads to nanophase separation with extreme local compositions closer to those of neat S or neat nBA repeat units. The achievement of such extreme local compositions results in significant T_g breadth increases (from 87 K for gradient copolymer up to 120 K in the block-gradient copolymer) and the onset or endpoint of the block-gradient copolymer T_g breadth being close or equal to the T_g of high molecular weight (MW) polystyrene (PS) or poly(n-butyl acrylate). Equally notable, with 20 wt% PS oligomer blended as selective plasticizer, the T_g breadth of a strongly segregating S/4VP gradient copolymer nearly triples relative to that of neat gradient copolymer (109 K vs. 38 K) and exhibits an onset ∼80 K below the onset of neat gradient copolymer and the T_g of high MW PS. Besides its scientific significance in tuning local compositions accessible in nanophase-separated gradient copolymers, this study provides powerful tools for the design of gradient copolymer systems for potential applications as damping materials that are effective over extraordinarily broad temperature ranges.