Precise synthesis of poly(macromonomer)s containing sugars by repetitive ROMP and their attachments to poly(ethylene glycol): synthesis, TEM analysis and their properties as amphiphilic block fragments

Star-Shaped ROMP Polymers Coated with Oligothiophenes That Exhibit Unique Emission

A series of oligo(thiophene)-modified "soluble" star-shaped ring-opening metathesis polymerization (ROMP) polymers were prepared by sequential living ROMP of norbornene and a cross-linking agent using a molybdenum-alkylidene catalyst, followed by Wittig-type coupling for termination with oligo(thiophene) carboxaldehydes. The resultant star-shaped ROMP polymers displayed unique emission properties affected by the core size and arm repeat units as well as the kind of oligothiophene coated. The effects of the thiophene groups on photophysical properties of star-shaped/linear polymers were studied via time-resolved fluorescence spectroscopy. Fluorescence lifetimes were determined in THF as 400, 640, 730, and 820 ps for Star 3TPh, Linear 3TPh, Star 4T, and Linear 4T, respectively. A significant enhancement of the nonradiative rate constants k _nr in the star-shaped polymers results in relatively lower fluorescence quantum yields and shorter fluorescence lifetimes compared to the corresponding linear polymers.

Synthesis of Soluble Star-Shaped Polymers via In and Out Approach by Ring-Opening Metathesis Polymerization (ROMP) of Norbornene: Factors Affecting the Synthesis

The methods for one-pot synthesis of ‘soluble’ star-shaped polymers by sequential living ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and cross-linking (CL) reagent using Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 have been explored. The method (called the “in and out” or core-first approach) basically consists of (i) the living ROMP of NBE (formation of arm), (ii) reaction with CL (formation of core), (iii) additional living ROMP of NBE (propagating arms from the core, formation of star), (iv) end-modification via Wittig-type cleavage of metal–carbon double bonds containing polymer chain with aldehyde. Two different approaches in the core formation step (reaction with CL mixed with/without NBE) for synthesis of the high molecular weight star-shaped ROMP polymers with more branching, unimodal molecular weight distributions have been explored in detail. The method (reacting CL with NBE in the core formation step) under highly diluted conditions afforded the high molecular weight polymers with unimodal molecular weight distributions.

One-pot synthesis of end-functionalised soluble star-shaped polymers by living ring-opening metathesis polymerisation using a molybdenum-alkylidene catalyst

Precise synthesis of soluble star-shaped polymers has been achieved by adopting living ring-opening metathesis polymerisation (ROMP) using a molybdenum-alkylidene catalyst with sequential addition of norbornene and cross-linking agent; the method provides efficient one-pot synthesis of high molecular weight end-functionalised star-shaped polymers (M_n = >1.37 × 10⁵) with more arms (branching) with rather low PDI values (M_w/M_n = 1.17–1.37) under the optimised conditions.

Precise synthesis of star-shaped polymers has been achieved by living ROMP using a molybdenum catalyst with sequential addition of norbornene and cross-linker.

Designing polymers with sugar-based advantages for bioactive delivery applications

Sugar-based polymers have been extensively explored as a means to increase drug delivery systems' biocompatibility and biodegradation. Here,we review he use of sugar-based polymers for drug delivery applications, with a particular focus on the utility of the sugar component(s) to provide benefits for drug targeting and stimuli responsive systems. Specifically, numerous synthetic methods have been developed to reliably modify naturally-occurring polysaccharides, conjugate sugar moieties to synthetic polymer scaffolds to generate glycopolymers, and utilize sugars as a multifunctional building block to develop sugar-linked polymers. The design of sugar-based polymer systems has tremendous implications on both the physiological and biological properties imparted by the saccharide units and are unique from synthetic polymers. These features include the ability of glycopolymers to preferentially target various cell types and tissues through receptor interactions, exhibit bioadhesion for prolonged residence time, and be rapidly recognized and internalized by cancer cells. Also discussed are the distinct stimuli-sensitive properties of saccharide-modified polymers to mediate drug release under desired conditions. Saccharide-based systems with inherent pH- and temperature-sensitive properties, as well as enzyme-cleavable polysaccharides for targeted bioactive delivery, are covered. Overall, this work emphasizes inherent benefits of sugar-containing polymer systems for bioactive delivery.

The use of fluorescent Nile red and BODIPY for lipid measurement in microalgae

Microalgae are currently emerging as one of the most promising alternative sources for the next generation of food, feed, cosmetics and renewable energy in the form of biofuel. Microalgae constitute a diverse group of microorganisms with advantages like fast and efficient growth. In addition, they do not compete for arable land and offer very high lipid yield potential. Major challenges for the development of this resource are to select lipid-rich strains using high-throughput staining for neutral lipid content in microalgae species. For this purpose, the fluorescent dyes most commonly used to quantify lipids are Nile red and BODIPY 505/515. Their fluorescent staining for lipids offers a rapid and inexpensive analysis tool to measure neutral lipid content, avoiding time-consuming and costly gravimetric analysis. This review collates and presents recent advances in algal lipid staining and focuses on Nile red and BODIPY 505/515 staining characteristics. The available literature addresses the limitations of fluorescent dyes under certain conditions, such as spectral properties, dye concentrations, cell concentrations, temperature and incubation duration. Moreover, the overall conclusion of the present review study gives limitations on the use of fluorochrome for screening of lipid-rich microalgae species and suggests improved protocols for staining recalcitrant microalgae and recommendations for the staining quantification.

Precise one-pot synthesis of fully conjugated end-functionalized star polymers containing poly(fluorene-2,7-vinylene) (PFV) arms

A facile one-pot synthesis of end-functionalized star polymers consisting of PFVs has been achieved by olefin metathesis and Wittig-type coupling.

Precise Synthesis of Poly(fluorene vinylene)s Capped with Chromophores: Efficient Fluorescent Polymers Modified by Conjugation Length and End-Groups

Poly(9,9-di-n-octylfluorene-2,7-vinylene)s containing F-BODIPY [PFV-(F-BODIPY)₂] and Zn(II)-porphyrin have been prepared by olefin metathesis of the vinyl group in the PFV chain ends followed by subsequent Wittig-type coupling. An introduction of tris(2,5-dialkoxy-1,4-phenylene vinylene) into PFV-(F-BODIPY)₂ has also been achieved. The emission properties can be modified by the PFV chain length, chromophore, and the middle segment: PFV-(F-BODIPY)₂ exhibits white-light emission with high quantum efficiency.

Precise Synthesis of Amphiphilic Multiblock Copolymers by Combination of Acyclic Diene Metathesis (ADMET) Polymerization with Atom Transfer Radical Polymerization (ATRP) and Click Chemistry

Various block (graft) copolymers have been prepared by combination of acyclic diene metathesis (ADMET) polymerization of 9,9-dialkyl-2,7-divinyl-fluorene with Cu-catalyzed atom transfer radical polymerization (ATRP) of styrene using macroinitiators prepared by introduction of initiating functionalities into poly(9,9-dialkylfluorene-2,7-vinylene)s (PFVs) chain ends: a precise synthesis of the amphiphilic ABCBA-type block copolymers has also been attained by subsequent combination with click reaction after modification of the chain end with NaN₃.

Metal-catalyzed synthesis of alternating copolymers

The creation of polymers with a high degree of sequence and/or stereocontrol represents an exciting frontier in materials science. In order to obtain alternating polymers, coordination polymerization using well-defined metal complexes has played a leading role in the last two decades. In the following paper, we will describe selected published efforts to achieve these research goals using discrete, structurally well-characterized metal complexes.

Synthesis of copolymers by alternating ROMP (AROMP)

The alternating polymerization of cyclobutene 1-carboxylic esters and cyclohexene derivatives with the precatalyst [(H(2)IMes)(3-Br-pyr)(2)Cl(2)Ru=CHPh] is described. This reaction is synthetically accessible and provides (AB)(n) heteropolymers with an alternating backbone and alternating functionality. The regiocontrol of heteropolymer formation derives from the inability of the cyclobutene ester and cyclohexene monomers to undergo homopolymerization in combination with the favorable kinetics of cross polymerization.