The copolymerization of α-methylstyrene
(MSt) and styrene
(St) to form random and blocky copolymers is well-known. Strongly
alternating copolymers of this type are rarely described, mainly because
of difficulties linked to their characterization. Indeed, the chemical
structures of St and MSt are sufficiently similar that quantitative
determination of the sequence distribution is rather difficult. Here,
we report a complementary pair of analytical methods based on nuclear
magnetic resonance (NMR) and high-resolution mass spectrometry, respectively,
to convincingly assess the structure of such copolymers. First, sequence-controlled
poly(α-methylstyrene-alt-styrene) copolymers
were obtained based on the single-unit addition principle, enabling
unit-by-unit addition of the two monomers. The alternating character
of these copolymers was then detected via carbon-13
(13C) NMR (13C NMR) and selective heteronuclear
multiple bond correlation 2-dimensional NMR (SHMBC NMR) on aromatic
quaternary carbons. Diad probabilities were quantified and used to
calculate statistically derived quantities, reflecting the nature
of the copolymer sequence distribution. In addition, HRMS and tandem
mass spectrometry were performed to further confirm the alternating
tendency of these copolymers, and they revealed a very narrow chemical
composition distribution and fragmentation patterns specific to a
primarily alternating structure.
The miscibility between two polymers such as rubbers and performance resins is crucial to achieve given targeted properties in terms of tire performances. To this aim, α-methylstyrene/styrene resin (poly(αMSt-co-St)) are used to modify the viscoelastic behavior of rubbers and to fulfill the requirements of the final applications. The initial aim of this work was to understand the influence of poly(αMSt-co-St) resins blended at different concentrations in a commercial styrene-butadiene rubber (SBR). Interestingly, while studying the viscoelastic properties of SBR blends with poly(αMSt-co-St), crosslinking of the rubber was observed under conditions where it was not expected to happen. Surprisingly, after the crosslinking reactions, the poly(αMSt-co-St) resin was irreversibly miscible with SBR at concentrations far above its immiscibility threshold. A detailed investigation involving characterization technics including solid state nuclear magnetic resonance led to the conclusion that poly(αMSt-co-St) is depolymerizing under heating and can graft onto the chains of SBR. It results in an irreversible compatibilization mechanism between the rubber and the resin.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.