Photoreactivity of polymers with dimerizable side-groups: Kinetic analysis for probing morphology and molecular organization

Abstract

SUMMARY:The solid state photoreactivity of polymers with pendant chromophores of the cinnamic type has been examined by monitoring the reaction by UV spectroscopy. Two series of photosensitive polymers with polysiloxane or polyvinylamine main chains were selected to exemplify specific behaviors contrasting on various aspects with that of poly(vinyl cinnamate) as the reference photocross-linkable polymer. Valuable kinetic information was obtained from simple photoirradiation experiments for probing the physical structure of the condensed polymeric material and for studying the influence of chromophore content. Photoisomerization of the chromophore competes efficiently with dimerization for both the liquid polysiloxanes with cinnamic esters connected by long spacers and for the glassy cinnamoylated polyvinylamines, the density of sites paired for dimerization being expectedly low in these amorphous matrices. The variations of the quantum yield for dimerization in the neat polymers as a function of their composition are discussed and correlated to the changes of practical sensitivity for photocuring. For polysiloxanes with pendant cyanostyrylacrylic groups, the leveled reactivity observed with quantum yields at zero conversion independent on the macroscopic chromophore content in the samples is explained by phase separation leading to dispersed domains rich in photoreactive side-groups. The layered order evidenced by wide angle X-ray scattering is consistent with the clean and reversible photoreaction. In spite of the discussed structural differences, the variation of the normalized quantum yield for dimerization U Dim /U 0 as a function of conversion p is described by the same scaling law U Dim /U 0 = (1-p) 3 as was established for the amorphous and homogeneous samples of cinnamoylated polysiloxanes or polyvinylamines.

Labelling cell structures and tracking cell lineage in zebrafish using SNAP-tag

“…One of the most prominent reactions applied for the crosslinking of polymers is the UV‐induced [2 + 2] cycloaddition reaction of cinnamic acid derivatives. Because the pioneering work of Schmidt and coworkers17–19 as well as many others,20–26 the topochemical dimerization reaction of cinnamic acid and its derivatives has become a useful tool in polymer chemistry27–31 and material science 8, 11, 32–36. Herein, we report the synthesis and characterization of statistical and amphiphilic block‐random copolymers prepared by ring opening metathesis polymerization (ROMP).…”

Reversible Cross-Linking of Aliphatic Polyamides Bearing Thermo- and Photoresponsive Cinnamoyl Moieties

“…16 The so-obtained cyclobutane dimer combines thermal stability 17,18 and photosensitivity. 19 The photochemical reversibility of the cross-linking was, for instance, nicely exploited for the synthesis of self-healing polymers 20,21 and tunable shape-memory 22 materials. Recently, Oriol, Barner-Kowollik, and co-workers studied on miktoarm star polymer bearing azobenzene photoresponsive units and reported the self-assembly properties of this novel polymer in water.…”

Photochemical modification of the lower critical solution temperature of cinnamoylated poly(N-2-hydroxypropylmethacrylamide) in water

“…[7] Noteworthy, one of the possible photoreactions, the E-Z (or trans-cis) photoisomerization, renders the cinnamate residues much more polar [7] and, thus, increases its hydrophilicity. Under appropriate conditions, the photoisomerization can be selective, avoiding e. g. competing crosslinking by [2 + 2] photocycloaddition.…”