Efficient synthesis of hydrolytically degradable block copolymer nanoparticles via reverse sequence polymerization‐induced self‐assembly in aqueous media

Hydrolytically degradable block copolymer nanoparticles are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous media. This efficient protocol involves the reversible addition-fragmentation chain transfer (RAFT) polymerization of N,N′-dimethylacrylamide (DMAC) using a monofunctional or bifunctional trithiocarbonate-capped poly(ϵ-caprolactone) (PCL) precursor. DMAC monomer is employed as a co-solvent to solubilize the hydrophobic PCL chains. At an intermediate DMAC conversion of 20–60 %, the reaction mixture is diluted with water to 10–25 % w/w solids. The growing amphiphilic block copolymer chains undergo nucleation to form sterically-stabilized PCL-core nanoparticles with PDMAC coronas. 1H NMR studies confirm more than 99 % DMAC conversion while gel permeation chromatography (GPC) studies indicate well-controlled RAFT polymerizations (Mw/Mn≤1.30). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) indicate spheres of 20–120 nm diameter. As expected, hydrolytic degradation occurs within days at 37 °C in either acidic or alkaline solution. Degradation is also observed in phosphate-buffered saline (PBS) (pH 7.4) at 37 °C. However, no degradation is detected over a three-month period when these nanoparticles are stored at 20 °C in deionized water (pH 6.7). Finally, PDMAC30-PCL16-PDMAC30 nanoparticles are briefly evaluated as a dispersant for an agrochemical formulation based on a broad-spectrum fungicide (azoxystrobin)

Synthesis and characterization of waterborne pyrrolidone-functional diblock copolymer nanoparticles prepared via surfactant-free RAFT emulsion polymerization

Polymerization-induced self-assembly enables the facile synthesis of a wide range of block copolymer nano-objects in the form of concentrated dispersions. In this context, many surfactant-free reversible addition–fragmentation chain transfer (RAFT) aqueous emulsion polymerization formulations have been reported using various nonionic and polyelectrolytic water-soluble precursors for the steric stabilizer block. In the present study, we examine poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP) as a new nonionic stabilizer block. A trithiocarbonate-based PNAEP precursor with a mean degree of polymerization of 67 was employed as the steric stabilizer for the RAFT emulsion polymerization of styrene, n-butyl acrylate (nBA), or statistical mixtures thereof. The RAFT emulsion polymerization of styrene using a VA-044 azo initiator at 80 °C and pH 7 led to essentially full conversion within 40 min, with induction times as short as 10 min, whereas gel permeation chromatography analysis confirmed efficient chain extension and relatively low dispersities (Mw/Mn < 1.30). Dynamic light scattering (DLS) studies indicated that systematically increasing the target degree of polymerization (DP) from 100 to 700 enabled the z-average diameter of the resulting kinetically trapped spherical nanoparticles to be varied from 55 to 156 nm. The same PNAEP67 precursor was then employed for the RAFT emulsion polymerization of nBA at 30 °C using a low-temperature redox initiator at pH 3. More than 99% conversion was achieved within 25 min, and efficient chain extension was observed up to a target DP of 700. However, relatively broad molecular weight distributions (Mw/Mn = 1.38–1.64) were obtained, presumably owing to side reactions such as chain transfer to polymer. DLS studies indicated that a series of kinetically-trapped PNAEP67–PnBAx spheres (where x = 100–700) exhibited z-average diameters ranging from 45 to 141 nm. Attempts to use this low-temperature initiator protocol for the homopolymerization of styrene led to essentially no conversion after 48 h at 30 °C. However, the statistical copolymerization of 45% styrene with 55% nBA could be achieved using this low-temperature redox initiator at 30 °C using the same PNAEP67 precursor. In this case, 1H nuclear magnetic resonance studies indicated a significantly longer induction period (95 min) compared to either homopolymerization. Nevertheless, once the statistical copolymerization commenced, essentially full conversion of both comonomers could be achieved within 45 min. Differential scanning calorimetry analysis indicated that these statistical copolymers exhibited intermediate glass transition temperatures compared to the two respective homopolymers. The film formation behavior of selected diblock copolymer nanoparticles was briefly explored

Synthesis of well-defined diblock copolymer nano-objects by RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in non-polar media

Polymerization-induced self-assembly (PISA) is widely recognized to be a powerful technique for the preparation of diblock copolymer nano-objects in various solvents. Herein a highly unusual non-aqueous emulsion polymerization formulation is reported. More specifically, the reversible addition–fragmentation chain transfer (RAFT) polymerization of N-(2-acryloyloxy)ethyl pyrrolidone (NAEP) is conducted in n-dodecane using a poly(stearyl methacrylate) (PSMA) precursor to produce sterically-stabilized spherical nanoparticles at 90 °C. This relatively high polymerization temperature was required to ensure sufficient background solubility for the highly polar NAEP monomer, which is immiscible with the non-polar continuous phase. A relatively long PSMA precursor (mean degree of polymerization, DP = 36) was required to ensure colloidal stability, which meant that only kinetically-trapped spheres could be obtained. Dynamic light scattering (DLS) studies indicated that the resulting PSMA36–PNAEPx (x = 60 to 500) spheres were relatively well-defined (DLS polydispersity <0.10) and the z-average diameter increased linearly with PNAEP DP up to 261 nm. Differential scanning calorimetry studies confirmed a relatively low glass transition temperature (Tg) for the core-forming PNAEP block, which hindered accurate sizing of the nanoparticles by TEM. However, introducing ethylene glycol diacrylate (EGDA) as a third block to covalently crosslink the nanoparticle cores enabled a spherical morphology to be identified by transmission electron microscopy studies. This assignment was confirmed by small angle X-ray scattering studies of the linear diblock copolymer nanoparticles. Finally, hydrophobic linear PSMA36–PNAEP70 spheres were evaluated as a putative Pickering emulsifier for n-dodecane–water mixtures. Unexpectedly, addition of an equal volume of water followed by high-shear homogenization always produced oil-in-water (o/w) emulsions, rather than water-in-oil (w/o) emulsions. Moreover, core-crosslinked PSMA36–PNAEP60–PEGDA10 spheres also produced o/w Pickering emulsions, suggesting that such Pickering emulsions must be formed by nanoparticle adsorption at the inner surface of the oil droplets. DLS studies of the continuous phase obtained after either creaming (o/w emulsion) or sedimentation (w/o emulsion) of the droplet phase were consistent with this interpretation. Furthermore, certain experimental conditions (e.g. ≥0.5% w/w copolymer concentration for linear PSMA36–PNAEPx nanoparticles, ≥0.1% w/w for core-crosslinked nanoparticles, or n-dodecane volume fractions ≤0.60) produced w/o/w double emulsions in a single step, as confirmed by fluorescence microscopy studies

RAFT dispersion polymerization of N,N-dimethylacrylamide in a series of n-alkanes using a thermoresponsive poly(tert-octyl acrylamide) steric stabilizer

Herein we report the reversible addition–fragmentation chain transfer (RAFT) solution polymerization of tert-octyl acrylamide (OAA) in 1,4-dioxane using a trithiocarbonate-based RAFT agent. POAA homopolymers were synthesized with good control (Mw/Mn < 1.22) within 1 h at 70 °C when targeting mean degrees of polymerization (DP) of up to 100. Differential scanning calorimetry studies conducted on a series of five POAA homopolymers indicated a weak molecular weight dependence for the glass transition temperature (Tg), which varied from 67 to 83 °C for POAA DPs ranging from 22 to 99. High blocking efficiencies were observed when chain-extending such homopolymers with OAA, suggesting that most of the RAFT end-groups remain intact. Subsequently, we employed POAA as a steric stabilizer block for the PISA syntheses of spherical nanoparticles in n-heptane via RAFT dispersion polymerization of N,N-dimethylacrylamide (DMAC) at 70 °C. Targeting PDMAC DPs between 50 and 250 resulted in reasonably good control (Mw/Mn ≤ 1.42) and produced well-defined spherical diblock copolymer nanoparticles (z-average diameters ranging from 23 nm to 91 nm, with DLS polydispersities remaining below 0.10) within 5 h. A facile one-pot synthesis route to near-monodisperse 36 nm diameter POAA82-PDMAC100 nanoparticles was developed in n-heptane that provided similar control over the molecular weight distribution (Mw/Mn = 1.19). Unfortunately, POAA85-PDMACx diblock copolymer nanoparticles tended to deform and undergo film formation prior to transmission electron microscopy (TEM) studies. To overcome this problem, ethylene glycol diacrylate (EGDA) was introduced towards the end of the DMAC polymerization. The resulting core-crosslinked POAA85-PDMAC195-PEGDA20 triblock copolymer nano-objects exhibited a relatively well-defined spherical morphology. Interestingly, the colloidal stability of POAA85-PDMACx diblock copolymer dispersions depends on the type of n-alkane. Spherical nanoparticles produced in n-heptane or n-octane remained colloidally stable on cooling to 20 °C. However, the colloidally stable POAA-PDMAC nanoparticles prepared at 70 °C in higher n-alkanes became flocculated on cooling. This is because the POAA steric stabilizer chains exhibit upper critical solution temperature (UCST)-type behavior in such solvents. Nanoparticle aggregation was characterized by variable temperature turbidimetry and dynamic light scattering experiments

Synthesis of poly(propylene oxide)–poly(N,N′-dimethylacrylamide) diblock copolymer nanoparticles via reverse sequence polymerization-induced self-assembly in aqueous solution

Sterically-stabilized diblock copolymer nanoparticles comprising poly(propylene oxide) (PPO) cores are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous solution. N,N′-Dimethylacrylamide (DMAC) acts as a cosolvent for the weakly hydrophobic trithiocarbonate-capped PPO precursor. Reversible addition-fragmentation chain transfer (RAFT) polymerization of DMAC is initially conducted at 80% w/w solids with deoxygenated water. At 30-60% DMAC conversion, the reaction mixture is diluted to 5-25% w/w solids. The PPO chains become less solvated as the DMAC monomer is consumed, which drives in situ self-assembly to form aqueous dispersions of PPO-core nanoparticles of 120-190 nm diameter at 20 °C. Such RAFT polymerizations are well-controlled (Mw/Mn ≤ 1.31), and more than 99% DMAC conversion is achieved. The resulting nanoparticles exhibit thermoresponsive character: dynamic light scattering and transmission electron microscopy studies indicate the formation of more compact spherical nanoparticles of approximately 33 nm diameter on heating to 70 °C. Furthermore, 15-25% w/w aqueous dispersions of such nanoparticles formed micellar gels that undergo thermoreversible (de)gelation on cooling to 5 °C

Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)ethylpyrrolidone

© 2018 American Chemical Society. Poly(N-vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-soluble polymer. However, N-vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymerized with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymerization conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(N-methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymerization formulations. However, PNMEP homopolymers are significantly less hydrophilic than PNVP and exhibit inverse temperature solubility in aqueous solution. In the present work, we studied the RAFT aqueous solution polymerization of 2-(N-acryloyloxy)ethylpyrrolidone (NAEP) using either AIBN at 70 °C or a low-temperature redox initiator at 30 °C. PNAEP homopolymers are obtained in high yield (>99%) with good control (Mw/Mn99%) and good control (Mw/Mn< 1.31). In addition, a PNAEP95macro-CTA was chain-extended via RAFT aqueous solution polymerization of N-isopropylacrylamide (NIPAM) at 22 °C. Dynamic light scattering (DLS) analysis indicated that heating above the lower critical solution temperature of PNIPAM led to so-called "anomalous micellization" at 35 °C and the formation of near-monodisperse spherical micelles at 40 °C. Finally, 2-(diethylamino)ethyl methacrylate (DEA) was polymerized using an N-morpholine-functionalized trithiocarbonate-based RAFT chain transfer agent and subsequently chain-extended using NAEP to form a novel pH-responsive diblock copolymer. Above the pKaof PDEA (∼7.3), DLS and1H NMR studies indicated the formation of well-defined PDEA-core spherical micelles

RAFT dispersion polymerisation of lauryl methacrylate in ethanol–water binary mixtures: synthesis of diblock copolymer vesicles with deformable membranes

Polymerisation-induced self-assembly (PISA) is widely recognised to be a powerful platform technology for the rational synthesis of diblock copolymer nano-objects. RAFT alcoholic dispersion polymerisation is an important PISA formulation that has been used to prepare block copolymer spheres, worms and vesicles. In this study, we have utilised the RAFT dispersion polymerisation of lauryl methacrylate (LMA) using a poly(N-(2-methacryloyloxy)ethyl pyrrolidone) (PNMEP) stabiliser in order to prepare vesicles with highly deformable membranes. More specifically, a PNMEP28 precursor was chain-extended with LMA in an 80 : 20 w/w ethanol–water mixture to produce a series of PNMEP28-PLMAx diblock copolymer nano-objects (Mw/Mn ≤ 1.40; LMA conversions ≥98% in all cases, as indicated by 1H NMR spectroscopy). Differential scanning calorimetry studies confirmed that the membrane-forming PLMA block had a relatively low glass transition temperature. Transmission electron microscopy and small angle X-ray scattering were used to identify copolymer morphologies for these highly asymmetric diblock copolymers. A mixed sphere and vesicle morphology was observed when targeting x = 43, while polydisperse vesicles were obtained for x = 65–151. Slightly smaller vesicles with lower mean aggregation numbers and thicker membranes were obtained when targeting higher PLMA DPs. A minor population of sheet-like lamellae was observed for each target copolymer composition, with lamellar stacking leading to a structure peak in the scattering patterns recorded for PNMEP28-PLMA129 and PNMEP28-PLMA151. Bearing in mind potential industrial applications, RAFT chain-end removal strategies were briefly explored for such PNMEP28-PLMAx vesicles. Thus, 96% of dithiobenzoate chain-ends could be removed within 3 h at 50 °C via LED irradiation of a 7.5% aqueous dispersion of PNMEP28-PLMA87 vesicles at a wavelength of 405 nm. This appears to be an attractive method for RAFT chain-end removal from diblock copolymer nano-objects, particularly those comprising highly hydrophobic cores

Principal component and stepwise discriminant analysis of the morphometric traits of three dual-purpose breeds of chicken

Using the principal component procedure of SAS, 10 variables; body weight (BW), body length (BL), breast girth (BG), shank length (SL), thigh length (TL), comb length (CL), comb height (CH), wing length (WL), wattle length (WAL) and wattle thickness (WT) obtained from three dual-purpose chicken breeds (Shika, Kuroiler, and Sasso), variables were separated. Similarly, stepwise discriminant analsis procedure of the SAS software was employed to evaluate variables that contribute to the overall differences in breeds. Results showed three principal components (PC1, PC2 and PC3) were extracted for all the breeds and pooled data. 45.60% of total variance was accounted for by PC1, 28.17% by PC2 and 16.22% by PC3. The principal components partitioning of total variance were 50.80, 15.10 and 9.70%, 50.82, 19.90 and 14.90%, and 48.63, 14.00 and 12.67% for Shika, Kuroiler, and Sasso breeds respectively, with different factor loadings. Communalities ranged from 0.43-0.97, 0.45-0.83, 0.45-0.88 and 0.45-0.90, indicating that a good amount of variance was accounted for. Stepwise discriminant analysis indicated that seven morphometric traits, TL, SL, WAL, WL, CL, CH and BL, contributed significantly (P&lt;0.001) to the separation of the birds into breeds. TL and SL, however, indicated higher discriminating power compared to others. The principal component analysis allowed for better understanding of the complex correlations among traits and reduced the number of traits along with high communalities, using only PC1, PC2 and PC3the first three PCs, without loss of information. Summary of stepwise discriminant analysis shows that lengthwise measures of long bones of the body of chickens, such as thigh and shank, are viable metrics for phenotypic differentiation of birds in the studied population.Keywords: Principal Component, Stepwise discriminant Analysis, Morphometric traits, chicken

Synthesis and characterization of charge-stabilized poly(4-hydroxybutyl acrylate) latex by RAFT aqueous dispersion polymerization: a new precursor for reverse sequence polymerization-induced self-assembly

The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 4-hydroxybutyl acrylate (HBA) is conducted using a water-soluble RAFT agent bearing a carboxylic acid group. This confers charge stabilization when such syntheses are conducted at pH 8, which leads to the formation of polydisperse anionic PHBA latex particles of approximately 200 nm diameter. The weakly hydrophobic nature of the PHBA chains confers stimulus-responsive behavior on such latexes, which are characterized by transmission electron microscopy, dynamic light scattering, aqueous electrophoresis, and 1H NMR spectroscopy. Addition of a suitable water-miscible hydrophilic monomer such as 2-(N-(acryloyloxy)ethyl pyrrolidone) (NAEP) leads to in situ molecular dissolution of the PHBA latex, with subsequent RAFT polymerization leading to the formation of sterically stabilized PHBA-PNAEP diblock copolymer nanoparticles of approximately 57 nm diameter. Such formulations constitute a new approach to reverse sequence polymerization-induced self-assembly, whereby the hydrophobic block is prepared first in aqueous media

Synthesis and aqueous solution properties of shape-shifting stimulus-responsive diblock copolymer nano-objects

We report the synthesis of poly(N-(2-acryloyloxyethyl)pyrrolidone)-poly(4-hydroxybutyl acrylate) (PNAEP85-PHBAx) diblock copolymer nano-objects via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 4-hydroxybutyl acrylate (HBA) at 30 °C using an efficient two-step one-pot protocol. Given the relatively low glass transition temperature of the PHBA block, these nano-objects required covalent stabilization prior to transmission electron microscopy (TEM) studies. This was achieved by core crosslinking using glutaraldehyde. TEM analysis of the glutaraldehyde-fixed nano-objects combined with small-angle X-ray scattering (SAXS) studies of linear nano-objects confirmed that pure spheres, worms or vesicles could be obtained at 20 °C in an acidic aqueous solution by simply varying the mean degree of polymerization (x) of the PHBA block. Aqueous electrophoresis, dynamic light scattering and TEM studies indicated that raising the dispersion pH above the pKa of the terminal carboxylic acid group located on each PNAEP chain induced a vesicle-to-sphere transition. 1H NMR studies of linear PNAEP85-PHBAx nano-objects indicated a concomitant increase in the degree of partial hydration of PHBA chains on switching from pH 2-3 to pH 7-8, which is interpreted in terms of a surface plasticization mechanism. Rheological and SAXS studies confirmed that the critical temperature corresponding to the maximum worm gel viscosity could be tuned from 2 to 50 °C by adjusting the PHBA DP. Such tunability is expected to be useful for potential biomedical applications of these worm gels