A new room temperature photoresponsive side chain liquid crystalline polymer has been synthesized and tested. It combines a side-on azobenzene LC with a low glass transition temperature polysiloxane backbone to obtain a nematic LCP at room temperature. The LCP also exhibits a crystalline phase that is kinetically trapped by the nematic phase at room temperature. Thermal transitions were observed at −7, 42, and 73 °C for the T g, T m, and T iso, respectively, and polarizing optical microscopy with in situ UV irradiation was used to characterize the room temperature photoresponsive behavior of its metastable nematic phase. Upon irradiation, the nematic phase almost completely disappeared in about 35 s. The isotropization was linear with a rate of 1.9 × 10–11 mol/s at short times, but the final clearing process was exponential with a time constant of 4.6 s. These relatively short response times can be achieved at room temperature and are fast enough to be relevant for actuator and responsive elastomer applications.

A new, low-T g siloxane thermoplastic elastomer with a functionalizable backbone was synthesized via sequential anionic polymerization and coupling, and its utility as a platform to produce functional elastomers was demonstrated by the attachment of a photoresponsive liquid crystal to produce a rapid, room temperature photoactuator. Polystyrene was used as a hard glassy end block, and poly(vinylmethylsiloxane) served as the soft middle segment in a polystyrene-b-poly(vinylmethylsiloxane)-b-polystyrene ABA triblock copolymer. The vinyl side chain was used to attach a side-on oriented mesogen to the siloxane backbone, and the resulting liquid crystal triblock copolymer was characterized with reversible photocontraction tests, where it was shown to be both elastomeric and rapidly photoresponsive at room temperature. Rather than simply undergoing a bending mechanism, an oriented thin cast film of the elastomer was observed to contract reversibly at a tensile strain of 3.3% against 25.7 kPa of applied stress in ∼5.9 s. This strategy to produce functional liquid crystal elastomers is based on the formation of spherical block copolymers with a low temperature T g for the soft domain, in contrast to cross-linked elastomers. Because the approach is simple, robust, and applicable to a wide variety of functional moieties, the resulting materials are thermoplastics that can be processed to achieve preferential orientation using standard methods, thus enhancing the capability to produce and utilize functional actuators.

Emulsion polymerization remains a challenging system for in situ Raman spectroscopic analysis, despite extensive research in the necessary instrumentation and chemometric data analysis methods. In this study we demonstrate a new and facile data analysis method, making in situ Raman spectroscopy a more versatile research tool for monitoring the concentrations of monomers in reactions spanning a wide range of compositions. The method improvement stems from the use of the homopolymer as an internal standard for the corresponding monomer. Classical least squares or indirect hard modeling is used for the spectral analysis to determine the spectral responses of major monomers and polymers within the system. Once the relative response factor ratios for a number of monomerhomopolymer pairs are determined in the calibration, they can be used to calculate the concentration ratio for such pairs based on reaction spectra. This approach offers two important advantages in determining the conversion of monomer to polymer. First, because the polymer internal standard will always be present for the corresponding monomer, it is straightforward to compensate for variable signal intensity due to changes in light scattering or instrumental fluctuations. Second, it is possible to calibrate based on a small set of monomer and homopolymer standards. The appropriate pairs can then be selected to establish a calibration method for any polymer product involving a combination of monomers from this set without the need for re-calibration. To demonstrate this technique, examples of in situ Raman monitoring for both batch and semi-batch emulsion polymerizations are provided.

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Mass spectrometry (MS) is a uniquely informative technique in the characterization of copolymers, where spectra prominently feature peak clustering. The spacing of these clusters, in general, is dominated by the spacing of one repeat unit, and contained herein is the theory to explain this observation. Extension of this theory also explains the more subtle observation that, even though the spacing is generally that of one unit, occasionally, the spacing between the maxima of adjacent clusters shifts by that of the other unit. Furthermore, the theory predicts that, in the low molecular weight region of the spectrum, there is a total switch to the spacing of the other unit along with asymmetric peak clusters that have a “sawtooth” shape. The analysis uses the Gaussian, log–normal, and Schulz–Zimm models as well as the random coupling hypothesis to explicitly demonstrate that (1) the major peak cluster spacing naturally arises from the unit in the copolymer with the widest distribution, as measured by the scaled standard deviation, (2) the spacing shift naturally occurs due to the marginal probabilities away from the spectrum maximum, and (3) the low molecular weight switch is a natural consequence of the tail of the distribution of the unit with the widest distribution. Results are provided to predict which unit in the copolymer will govern the major peak cluster spacing, how often the spacing will shift to that of another unit in the middle and high molecular weight regions of the spectrum, the molecular weight and composition of the maximum peak in every cluster, and the molecular weight below which the spacing will be that of the another unit. We believe that our results are the first to provide tangible theory to explain the previously unknown origins of these empirically observed phenomena.