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Since temperature is one of the most significant physiological parameters that dictate the cellular status of living organisms, accurate intracellular temperature measurement is crucial and a valuable biomarker for the diagnosis and treatment of diseases. Herein, we introduce the foremost example of a non-conjugated polymer as a next generation fluorescent thermometer which is capable of addressing the key shortcomings including toxicity and thermal-induced fluorescence quenching associated with π–π conjugated system-based thermometers developed so far. We revealed, for the first time, the unique photophysical and aggregation-induced emission (AIE) characteristics of well-known thermoresponsive poly(N-vinylcaprolactam) (PNVCL) devoid of any classical fluorophore entity. PNVCL underwent a coil to globular conformational transition in an aqueous medium and appeared to be fluorescent above its lower critical solution temperature (LCST) near body temperature (38 °C). Eventually, this intriguing aspect enabled higher cellular uptake of PNVCL at the LCST boundary. By virtue of the AIE effect, the thermo-induced aggregation phenomenon has been ingeniously utilized to apply PNVCL as a novel fluorescent thermometer for intracellular temperature determination.

Traditional luminescent polymers typically contain extended π–π conjugated structures that suffer from associated aggregation-caused quenching (ACQ) and high cytotoxicity issues. Therefore, there is a huge demand for stand-alone luminescent polymers that can circumvent these drawbacks and can be employed in diverse applications. In view of that, nonconventional luminescent polymers (NLPs) are being developed and studied extensively for their distinctive characteristics and potential applications in wide-ranging areas, and for an in-depth understanding of photophysical processes in science. These polymers do not contain classical chromophores, but often involve isolated benzene rings or only electron-rich moieties (e.g. amine, CO, –OH, ether, imide, and heteroatoms N, O, P, S, etc.). This review article highlights the recent progress in the field of NLPs, including their synthesis, underlying emission mechanisms, and applications in materials and biological sciences. Besides, it is identified to be the foremost review that extensively emphasizes on both the fluorescence and phosphorescence features of NLPs. Finally, some prospects have been suggested for further exploration in this flourishing field of research.

Herein, a leucine-based perfectly alternating polyampholyte was synthesized by placing positively charged primary ammonium groups and negatively charged carboxylate groups alternatively onto the side chain of the poly(styrene-alt-maleimide) skeleton. The well-defined non-ionic macromolecular precursor was first prepared by sequence-controlled reversible addition–fragmentation chain transfer (RAFT) copolymerization of an N-maleoyl-L-leucine tert-butyl ester (M1) with a tert-butyl carbamate (Boc)-protected leucine appended styrenic monomer (M2), which could serve as an anionic and a cationic unit of the co-zwitterion monomers respectively, as a result of exclusion of the protecting groups. The aqueous solution behavior of the polyampholyte was studied by a combination of techniques, including pH, turbidity and zeta potential measurements, revealing net zero charge (isoelectric point (IEP)) with concomitant phase separation at pH = 7.0. The protected version of the as-synthesized copolymer displayed intense blue luminescence only in organic solvents, albeit it does not contain any conjugated fluorophore moiety. Interestingly, the alternating polyampholyte exhibited fluorescence activity in water and was used for the specific detection of carbon disulfide (CS2) among various volatile organic compounds (VOCs) in a 100% aqueous environment. Moreover, the polyampholyte could accomplish a colorimetric “naked-eye” sensing of CS2 vapour with high selectivity and sensitivity under ambient conditions.

Development of a speedy, selective, and sensitive detection method for picric acid (PA) in an aqueous medium using a simple, cost-effective, and portable sensory technique is in high demand not only because of PA's explosive nature but also because of its superior water solubility. This study reports a nonconjugated macromolecular luminogen for prompt sensing of PA in 100% aqueous environments. A novel water-soluble unconventional fluorescent alternating copolymer based on a poly(styrene-alt-maleimide) skeleton has been found to be selective for nanomolar detection of PA in pure water over other aromatic compounds, without any interference from other nitroaromatics and metal ions or common anions that may coexist. The polymeric sensor molecule also has the capability to detect PA in the solid state and vapor phase. The fluorimetric sensing mechanism of PA in the present fluorescent probe is attributed to combined ground-state electrostatic complex formation and ground-state electron transfer from picrate anion to the probe molecule, as evidenced by UV–vis and 1H NMR studies, time-resolved fluorescence measurement, cyclic voltammetry, and density functional theory (DFT) calculations.

Herein, we report the synthesis of a new class of traditional fluorophore-free dual pH- and thermo-responsive fluorescent copolymer through sequence-controlled copolymerization of rationally designed monomers. The N-substituted maleimide monomer bearing a diethylene oxide side-chain, (N-(methoxy diethylene glycol) maleimide, M1), was copolymerized with a tert-butyl carbamate (Boc)-protected leucine appended styrenic monomer (M2) to obtain well-defined copolymers with perfectly alternating sequences of M1 and M2. The as-synthesized copolymers displayed bright-blue fluorescence in organic solvents. After Boc-group expulsion, the copolymers showed dual pH- and thermo-responsiveness, they retained their luminescence properties in organic solvents, and also showed pH/thermo-tunable fluorescence activity in water. The origin of the fluorescence in the copolymers was ascertained using density functional theory (DFT), where we observed that the “through-space” π–π interaction between the benzene ring and the neighbouring carbonyl group of the maleimide unit is responsible for the unexpected fluorescence in the alternating copolymer.

Main chain chiral poly(methacrylate)s have been synthesized by controlled reversible addition–fragmentation chain transfer (RAFT) copolymerization of chiral monomer Boc- l -alanine methacryloyloxyethyl ester (Boc- l -Ala-HEMA, A) with Boc- d -alanine methacryloyloxyethyl ester (Boc- d -Ala-HEMA, B) and achiral monomer Boc-2-methylalanine-methacryloyloxyethyl ester (Boc-Aib-HEMA, C), and B with C by changing comonomer feed compositions. We systematically examined the role of l -alanine, d -alanine and 2-aminoisobutyric acid (Aib) as folding nuclei in our designed hybrid polymer-amino acid conjugates. Specific optical rotation and circular dichroism (CD) spectroscopy studies reveal that poly(Boc- l -Ala-HEMA) and poly(Boc- d -Ala-HEMA) formed entirely opposite handed helical structure stabilized by intramolecular hydrogen bonding among the pendant chromophores of the chiral monomers. Poly(Boc-Aib-HEMA) formed random coil structures conformation (unstructured conformation), whereas the resultant copolymers of C with A and B showed an unusual linear relationship of optical activity against comonomer composition, in sharp contrast with Green’s “majority” and “sergeant-and-soldier” rule. After Boc-group expulsion in acidic environment from the polymer side-chains, backbone retained its helicity. Variable temperature chiroptical properties investigation was also performed to examine the thermal stability of the homo and copolymer’s helical conformations. Additionally, pH induced conformational transformation was observed for the homo and copolymers.

Summary By the combination of living carbocationic and reversible addition-fragmentation chain transfer (RAFT) polymerizations, a series of well-defined amphiphilic diblock copolymers composed of polyisobutylene (PIB) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) were successfully synthesized. First, cationic polymerization of isobutylene (IB) followed by chain end functionalization gave PIB-macro chain transfer agent, which was subsequently used for block copolymerization with oligo(ethylene glycol) methyl ether methacrylate (OEGMA). Gel permeation chromatography (GPC) confirmed successful and efficient block copolymerzation. The thermoresponsive behaviour of block copolymer aqueous solutions was determined by UV-vis spectroscopy. These block copolymers self-assembled into spherical core-shell nanostructures in an aqueous solution as evidenced by dynamic light scattering (DLS) and scanning electron microscope (SEM).

Syntheses of diblock copolymers of isobutylene (IB) with amino acid-based monomers were carried out by a combination of living carbocationic and reversible addition–fragmentation chain transfer (RAFT) polymerizations. Cationic polymerization of IB followed by hydroboration oxidation produced hydroxyl end-capped polyisobutylene, which was subsequently converted into macro-chain-transfer agent (macro-CTA) for the RAFT polymerization of tert-butyloxycarbonyl (Boc)-protected amino acid-based monomers such as Boc-l-alanine methacryloyloxyethyl ester (Boc-l-Ala-HEMA) and Boc-l-leucine methacryloyloxyethyl ester (Boc-l-Leu-HEMA). The block length and molecular weight could be controlled while maintaining a narrow molecular weight distribution. These block copolymers form core–shell type micellar structure in methanol—a good solvent for side-chain amino acid block but bad solvent for polyisobutylene segment. Specific rotation and circular dichroism (CD) studies indicated the chiral nature of the block copolymers ...

Poly{(N,N-(dimethylamino)ethyl methacrylate]-co-(methyl methacrylate)} copolymers of various compositions were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization at 70 degrees C in N,N-dimethylformamide. The polymer molecular weights and molecular weight distributions were obtained from size exclusion chromatography, and they indicated the controlled nature of the RAFT polymerizations; the polydispersity indices are in the range 1.11.3. The reactivity ratios of N,N-(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA) (rDMAEMA = 0.925 and rMMA = 0.854) were computed by the extended KelenTudos method at high conversions, using compositions obtained from 1H NMR. The pH- and temperature-sensitive behaviour were studied in aqueous solution to confirm dual responsiveness of these copolymers. The thermal properties of the copolymers with various compositions were investigated by differential scanning calorimetry and thermogravimetric analysis. The kinetics of thermal degradation were determined by Friedmann and Chang techniques to evaluate various parameters such as the activation energy, the order and the frequency factor. (c) 2012 Society of Chemical Industry

This work demonstrates the successful application of dynamic covalent chemistry for the construction of self-healing gels from side-chain primary amine leucine pendant diblock copolymers of polyisobutylene (PIB) ((P(H2N-Leu-HEMA)-b-PIB)) in the presence of PIB based dialdehyde functionalized cross-linker (HOC-PIB-CHO) through imine (-HC═N-) bond formation without aiding any external stimuli. Gels were synthesized in 1,4-dioxane at room temperature at varied wt % of gelator concentration, [H2N]/[CHO] ratios and molecular weight of the block segments. The mechanical property of gels was examined by rheological measurements. We observed higher value of storage modulus (G') than the loss modulus (G″) within the linearity limits of deformation, indicating the rheological behavior in the gel is dominated by an elastic property rather than a viscous property. The G' values significantly depend upon the extent of cross-linking in the gel network. To establish self-healing property of the gels, rheology analysis through step-strain measurements (strain = 0.1 to 200%) at 25 °C was performed. The polymeric gel network shows reversible sol-gel transition for several cycles by adjusting the pH of the medium with the help of hydrochloric acid (HCl) and triethylamine (Et3N) triggers. FT-IR spectroscopy established formation of imine bonds in the gel network and these gels showed poor swelling behavior in various organic solvents because of the small interstitial porosity, confirmed by field emission-scanning electron microscopy (FE-SEM).

Effects of counterions of side chain amino acid based polyelectrolytes (PEs) on the solubility in aqueous medium, pH responsiveness, thermal properties, and ionic conductivities have been appraised. Deprotection of the tert-butyl carbamate (Boc) group from poly(Boc-l-leucine methacryloyloxyethyl ester) [P(Boc-l-Leu-HEMA)] was carried out to produce PE with trifluoroacetate as an associative counteranion (1a). PEs with bis(trifluoromethylsulfonyl)imide and hexafluorophosphate counteranion were prepared through anion exchange reactions of 1a. Protonation of the neutralized polymer (2) obtained from 1a, followed by anion exchange, leads to the production of miscellaneous PEs bearing different counteranions, such as tetrafluoroborate, trifluoromethanesulfonate, chloride, and nitrate. Differential scanning calorimetry traces of the PEs reveal that the comparatively larger and weakly coordinated counteranions require less thermal energy to dissociate, and thus, the glass transition temperature (Tg) of the PEs fall off with an increase in the size of the counteranion. A remarkable conductivity of 2.1 mS/cm was obtained in deionized water when Cl(-) acted as the counteranion. Steric and electronic factors of the counteranion induce a change of transition pH in different PEs, although the chiroptical nature was retained, as confirmed by circular dichroism spectroscopy.

Reversible addition-fragmentation chain transfer polymerization at 70 °C in N,N-dimethylformamide was used to prepare poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers in various compositions to afford well-defined polymers with pre-determined molecular weight, narrow molecular weight distribution, and precise chain end structure. The copolymer compositions were determined by 1H NMR spectroscopy. The reactivity ratios of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA) were calculated as r NIPAM = 0.838 and r DMA = 1.105, respectively, by the extended Kelen–Tudos method at high conversions. The lower critical solution temperature of PNIPAM can be altered by changing the DMA content in the copolymer chain. Differential scanning calorimetry and thermogravimetric analysis at different heating rates were carried out on these copolymers to understand the nature of thermal degradation and to determine its kinetics. Different kinetic models were applied to estimate various parameters like the activation energy, the order, and the frequency factor. These studies are important to understand the solid state polymer degradation of N-alkyl substituted polymers, which show great potential in the preparation of miscible polymer blends due to their ability to interact through hydrogen bonding.

pH-reversible covalently cross-linked polymeric gels from a side-chain polymer with multi-amino groups and a difunctional aldehyde cross-linker have been prepared by employing dynamic covalent chemistry in the form of reversible imine (CN) bond formation. Two different series of dual pH- and thermo-responsive amino acid based copolymers with primary amine groups located at different positions and various chemical compositions are synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization of tert-butyl carbamate (Boc)-tryptophan methacryloyloxyethyl ester (Boc-Trp-HEMA) with 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and N,N-(dimethylamino)ethyl methacrylate (DMAEMA) respectively, followed by Boc-group expulsion. The pH-induced thermoresponsive properties of the copolymers have been observed with the high content of thermoresponsive MEO2MA/DMAEMA segments (∼80%) in the copolymer. The tryptophanyl moiety present in the copolymer chain provided florescence characteristics, which were studied by florescence spectroscopy. Copolymers with free amino groups were employed for cross-linking with a difunctionalized aldehyde cross-linker, 4-formylphenyl 4′-formylbenzoate (FPFB), to form dynamic covalent gels through the formation of CN bonds in the network. Rheological measurements have been conducted with various ratios of CHO/NH2 from 1 to 0.33 for homopolymer gels and copolymer gels with different amino acid contents (20–80%), which showed a plateau of storage modulus (G′) over a wide range of angular frequencies indicating the independent nature of G′ with respect to angular frequency, and the mechanical properties of dynamic gels are a function of cross-linking density. The pH-dependent reversible sol–gel transition has also been investigated.

Reversible addition-fragmentation chain transfer (RAFT) polymerization was employed to afford two different chiral copolymer series having opposite chiroptical properties based on 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and Boc-L/D-leucine methacryloyloxyethyl ester (Boc-L/D-Leu-HEMA) with varying co-monomer proportions. The random nature of the copolymers was indicated by the reactivity ratios of the two monomers for the two systems (MEO2MA with Boc-L-Leu-HEMA and Boc-D-Leu-HEMA), and further supported by smooth variation of the single glass transition temperature (Tg) determined from differential scanning calorimetry (DSC). With an increasing amino acid content in the copolymer, the specific rotation and molar ellipticity values increased, as examined by polarimeter and circular dichroism (CD) spectroscopy, respectively. After Boc-group cleavage under acidic conditions, all the copolymers exhibited cationic nature, as confirmed by dynamic light scattering (DLS), as well as the dual thermo and pH-dependent solubility behaviour in aqueous solution. The temperature induced phase transition of these copolymers was investigated as a function of the copolymer compositions over the pH range from 5.5 to 6.5 using a UV-Vis spectrophotometer. Furthermore, the chiral recognition ability of the synthesized monomers and homopolymers towards 1,1′-bi-2-naphthol (rac-BINOL) was studied by 1H NMR spectroscopy.