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What happens in the dark? Assessing the temporal control of photo-mediated controlled radical polymerizations.

ABSTRACT: A signature of photo-mediated controlled polymerizations is the ability to modulate the rate of polymerization by turning the light source 'on' and 'off.' However, in many reported systems, growth can be reproducibly observed during dark periods. In this study, emerging photo-mediated controlled radical polymerizations are evaluated with in situ 1H NMR monitoring to assess their behavior in the dark. Interestingly, it is observed that Cu-mediated systems undergo long-lived, linear growth during dark periods in organic media.

SUBMITTER: Dolinski ND

PROVIDER: S-EPMC6474683 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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What happens in the dark? Assessing the temporal control of photo-mediated controlled radical polymerizations.

Dolinski Neil D ND Page Zachariah A ZA Discekici Emre H EH Meis David D Lee In-Hwan IH Jones Glen R GR Whitfield Richard R Pan Xiangcheng X McCarthy Blaine G BG Shanmugam Sivaprakash S Kottisch Veronika V Fors Brett P BP Boyer Cyrille C Miyake Garret M GM Matyjaszewski Krzysztof K Haddleton David M DM de Alaniz Javier Read JR Anastasaki Athina A Hawker Craig J CJ

Journal of polymer science. Part A, Polymer chemistry 20181108 3

A signature of photo-mediated controlled polymerizations is the ability to modulate the rate of polymerization by turning the light source 'on' and 'off.' However, in many reported systems, growth can be reproducibly observed during dark periods. In this study, emerging photo-mediated controlled radical polymerizations are evaluated with <i>in situ</i> <sup>1</sup>H NMR monitoring to assess their behavior in the dark. Interestingly, it is observed that Cu-mediated systems undergo long-lived, lin ...[more]

PMID: 31011240

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Project description:ObjectivesPolymerization shrinkage stress and factors involved in the stress development such as volumetric shrinkage and modulus were investigated in photo-CuAAC (photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition) polymerization and compared with conventional BisGMA-based methacrylate polymerization for their use as alternative dental resins.MethodsTri-functional alkyne and di-functional azide monomers were synthesized for photo-CuAAC polymerization. Conversion kinetics, stress development and polymerization shrinkage were determined with FTIR spectroscopy, tensometery, and with a linometer, respectively, for CuAAC and BisGMA-based monomer mixtures using a camphorquinone/amine visible light photoinitiator system. Thermo-mechanical properties for the cured polymer matrices were characterized by dynamic mechanical analysis and in three-point bending on a universal testing machine. Polymerization kinetics, polymerization shrinkage stress, dynamic volumetric shrinkage, glass transition temperature (Tg), flexural modulus, flexural strength, and flexural toughness were compared between the two different resin systems.ResultsA glassy CuAAC polymer (Tg=62°C) exhibited 15-25% lower flexural modulus of 2.5±0.2GPa and flexural strength of 117±8MPa compared to BisGMA-based polymer (Tg=160°C) but showed considerably higher energy absorption around 7.1MJ×m-3 without fracture when strained to 11% via three-point bend compared to the flexural toughness of 2.7MJ×m-3 obtained from BisGMA-based polymer. In contrast to BisGMA-based polymers at 75% functional group conversion, the CuAAC polymerization developed approximately three times lower shrinkage stress with the potential to achieve quantitative conversion under ambient temperature photocuring conditions. Moreover, relatively equivalent dynamic volumetric shrinkage of around 6-7% was observed via both CuAAC and dimethacrylate polymerization, suggesting that the low shrinkage stress of CuAAC polymerization was due to delayed gelation along with slower rate of polymerization and the formation of a more compliant network structure.SignificanceCuAAC crosslinked networks possessed high toughness and low polymerization shrinkage stress with quantitative conversion, which eliminated obstacles associated with BisGMA-based dental resins including limited conversion, unreacted extractable moieties, brittle failure, and high shrinkage stress.

Dataset Information

What happens in the dark? Assessing the temporal control of photo-mediated controlled radical polymerizations.

Publications

What happens in the dark? Assessing the temporal control of photo-mediated controlled radical polymerizations.

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