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We report preliminary results for the synthesis of polyethylene-graft-poly(dimethylsiloxane) copolymers obtained by catalytic hydrogenation of polybutadiene-graft-poly(dimethylsiloxane) copolymers (PB-g-PDMS). These last copolymers were synthesized by hydrosilylation reactions between commercial polybutadiene and ω-silane poly(dimethylsiloxane). The reaction was carried in solution catalyzed by cis-dichloro bis(diethylsufide) platinum(II) salt. The PB-g-PDMS copolymers were analyzed by ¹H and ¹³C NMR spectroscopies, and the relative weight percentages of the grafted poly(dimethylsiloxane) macromonomer were determined from the integrated peak areas of the spectra. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2920–2930, 2004

Polypeptides containing azobenzene or spiropyran units attached to the macromolecules respond to light or dark conditions giving reversible variations of their structure. In this Account we provide a short overview of current research in the field and describe the most significant experimental examples of photoresponse effects. They include photoinduced random coil/α-helix transitions, helix-sense reversal, photostimulated aggregation/disaggregation processes, and photomechanical effects. These fascinating properties suggest that photoresponsive polypeptides may become suitable materials for designing sensors and devices that can be photomodulated. Findings also demonstrate that it is possible to synthesize model systems which respond to light similarly to naturally occurring photoreceptors.

High molecular weight poly(l-glutamic acid) was chemically modified with a spiropyran reagent to give polypeptides containing 35 and 85 mol % spiropyran units in the side chains. To investigate the photochromic and conformational behavior in acid conditions, the polypeptides were dissolved in hexafluoro-2-propanol (HFP) and a small amount of trifluoroacetic acid was added (TFA, c = 5 × 10^-4 g/mL). In the absence of acid, the same polypeptides were found to respond to light, giving reversible coil/α-helix transitions. In the presence of TFA, by contrast, photoisomerization of the chromophores in the side chains did not result in any conformational variation of the macromolecular main chains, and CD spectra showed that the macromolecules adopted a random coil structure, both in the dark and after light exposure. However, when appropriate amounts of cosolvents such as methanol (MeOH) or trifluoroethanol (TFE) were added to the HFP/TFA solutions, the system again responded to light, giving reversible coil/α-helix transitions of the macromolecular structure. The extent of the photoinduced conformational changes depended on solvent composition and the photoresponse could be modulated by the combined action of light and chemical environment. For HFP/MeOH solvent mixture, it is possible to trigger the photostimulated coil/α-helix transition in a narrow window of solvent composition, so that the system is characterized by a gated photoresponse. The molecular processes responsible for the observed photoinduced conformational changes are discussed on the basis of absorption and fluorescence results. These results also allow us to set up a detailed picture of the molecular mechanisms responsible for the described chemo-modulated photosensory system.

Poly(l-lysine) was reacted with p-phenylazobenzenesulfonyl chloride to give polypeptides containing azobenzene units linked to the Lys chains by means of sulfonamide functions. The azo-modified polymers were soluble in hexafluoro-2-propanol (HFP), in which they exhibited photochromism due to the trans/cis photoisomerization of the azobenzene units. The sulfonate azobenzene moieties were found to be thermally stable at room temperature, so that interconversions between the two isomers were achieved only photochemically, by irradiating at 340 and 417 nm, respectively. Previously reported poly(N^ε-(phenylazobenzoyl)-l-lysine) was found to adopt the α-helix structure in HFP and did not give photoinduced conformational changes. For poly(N^ε-((phenylazophenyl)sulfonyl)-l-lysine), by contrast, CD spectra showed that the macromolecules adopted a disordered structure in HFP, when azo units were either in trans or in cis configuration. However, when appropriate amounts of methanol or 1,2-dichloroethane were added to the HFP solutions, irradiation at 340 and 417 nm, alternately, produced reversible formation of a helical and random coil structure of the macromolecules. The photostimulated structural changes have been discussed on the basis of the interactions between HFP and azobenzenesulfonyl groups, which seem to be different depending on whether the azo units are in trans or in cis configuration.