Synthesis of PAA-g-PNIPAM well-defined graft polymer by sequential RAFT and SET-LRP and its application in preparing size-controlled super-paramagnetic Fe3O4 nanoparticles as a stabilizer

A series of well-defined double hydrophilic graft copolymers, poly(acrylic acid)-g-poly(N-isopropylacrylamide) (PAA-g-PNIPAM), was employed as a novel water-soluble coating for constructing superparamagnetic iron oxide nanoparticles. The copolymer was synthesized via a three-step procedure: firstly, a well-defined hydrophobic PtBA-based backbone, poly(tert-butyl 2-((2-chloropropanoyloxy)-methyl)acrylate)-co-poly(tert-butyl acrylate), (PtBCPMA₁₉-co-PtBA₁₈), was prepared through RAFT copolymerization of a new trifunctional acrylic monomer, tert-butyl 2-((2-chloropropanoyloxy)methyl)acrylate and tert-butyl acrylate; secondly, taking this backbone as a macroinitiator to initiate SET-LRP of N-isopropylacrylamide resulted in well-defined (poly(tert-butyl 2-((2-chloropropanoyloxy)methyl)-acrylate)-co-poly(tert-butyl acrylate))-g-poly(N-isopropylacrylamide) ((PtBCPMA-co-PtBA)-g-PNIPAM) amphiphilic graft copolymers with relatively narrow polydispersities (M_w/M_n ≤ 1.31); thirdly, handling (PtBCPMA-co-PtBA)-g-PNIPAM in acidic conditions afforded PAA-g-PNIPAM graft copolymers. The resulting PAA-g-PNIPAM copolymers were directly utilized as a polymeric stabilizer in the preparation of superparamagnetic Fe₃O₄ nanoparticles. The particle size can be readily tuned in the range of 12.1–23.2 nm by varying the amount of PAA-g-PNIPAM copolymer or the length of PNIPAM side chain. Besides, the structure and properties of prepared Fe₃O₄/polymer nanocomposites were characterized by XRD, FT-IR, TGA, TEM, and magnetic measurement in detail.     

Comparison of thermomechanical properties of statistical, gradient and block copolymers of isobornyl acrylate and n-butyl acrylate with various acrylate homopolymers

Well-defined statistical, gradient and block copolymers consisting of isobornyl acrylate (IBA) and n-butyl acrylate (nBA) were synthesized via atom transfer radical polymerization (ATRP). To investigate structure-property correlation, copolymers were prepared with systematically varied molecular weights and compositions. Thermomechanical properties of synthesized materials were analyzed via differential scanning calorimetry (DSC), dynamic mechanical analyses (DMA) and small-angle X-ray scattering (SAXS). Glass transition temperature (T_g) of the resulting statistical poly(isobornyl acrylate-co-n-butyl acrylate) (P(IBA-co-nBA)) copolymers was tuned by changing the monomer feed. This way, it was possible to generate materials which can mimic thermal behavior of several homopolymers, such as poly(t-butyl acrylate) (PtBA), poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA) and poly(n-propyl acrylate) (PPA). Although statistical copolymers had the same thermal properties as their homopolymer equivalents, DMA measurements revealed that they are much softer materials. While statistical copolymers showed a single T_g, block copolymers showed two T_gs and DSC thermogram for the gradient copolymer indicated a single, but very broad, glass transition. The mechanical properties of block and gradient copolymers were compared to the statistical copolymers with the same IBA/nBA composition.     

Preparation of poly(tert-butyl acrylate-g-styrene) as precursors of amphiphilic graft copolymers. 1. Kinetic study and thermal properties

Free radical copolymerizations of tert-butyl acrylate and a polystyrene macromonomer carrying a methacryloyloxy group at the chain end have been performed in benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator at 70 °C. The estimated values of the ‘lumped’ kinetic constant, k_p/k_t^1/2, have shown a clear dependency on the macromonomer concentration in the reaction medium. The obtained poly(tert-butyl acrylate-g-polystyrene) graft copolymers were characterized by size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). In addition, the thermal behavior of these copolymers was studied by thermogravimetric analysis (TGA). Subsequently, hydrolysis of precursor graft copolymer was performed to afford an amphiphilic graft copolymer. Characterization using FT-IR confirmed total hydrolysis of the ester group.     

Effect of chain rigidity on block copolymer micelle formation and dissolution as observed by 1H-NMR spectroscopy

Amphiphilic copolymers poly(methyl methacrylate-b-acrylic acid), poly(methyl methacrylate-b-methacrylic acid), poly(methyl acrylate-b-acrylic acid) and poly(methyl acrylate-b-methacrylic acid) were prepared by reversible addition fragmentation chain-transfer (RAFT) polymerization. The hydrophilic polyacid blocks were either synthesized directly or formed by the hydrolysis of poly(tert-butyl acrylate) or poly(tert-butyl methacrylate) blocks. The hydrophobic blocks consisted of either the more rigid, high glass transition temperature (T _g ) poly(methyl methacrylate) or more flexible, low T _g poly(methyl acrylate) material. The hydrophilic blocks were either poly(methacrylic acid) (rigid, high T _g ) or poly(acrylic acid) (flexible, low T _g ). The micellization behavior of the polymers was studied by proton nuclear magnetic resonance (¹H-NMR) spectroscopy in mixtures of 1,4-dioxane-d₈ and D₂O. All four polymers were soluble in neat dioxane. In solutions of higher water content, the polymers with the more rigid hydrophobic blocks formed into micelles as was evidenced by broadening of the resonances resulting from the protons in those blocks. At moderate water concentration (25–50%), dissolution of the micelles was observed upon heating the solution. No micellization was observed in polymers containing the less rigid poly(methyl acrylate) hydrophobic block regardless of the identity of the hydrophilic block. As further evidence of micellization formation and dissolution, the spin-lattice (T ₁) and spin-spin (T ₂) relaxation times of protons in the hydrophobic and hydrophilic blocks were measured. Significant differences in the relaxation times as functions of temperature and solvent concentration were observed between the hydrophilic and hydrophobic blocks of the micelle-forming polymers.     

Ultrasonically initiated emulsifier-free emulsion copolymerization of n-butyl acrylate and acrylamide. Part I: Polymerization mechanism

The polymerization mechanism of ultrasonically initiated emulsifier-free emulsion copolymerization of n-butyl acrylate (BA) and acrylamide (AM) was investigated. A four-step polymerization mechanism of the ultrasonically initiated emulsifier-free emulsion was put forward based on the monomer conversion and the main reaction locus. Improving the power output would increase the monomer conversion and the rate of polymerization. However, when the reaction temperature was 30 °C and the concentration of Na₂SO₄ was 0.1%, the monomer conversion and the rate of polymerization achieved maximum. The FTIR spectra showed that the sample obtained by this way was the copolymer of BA and AM, but not the blend of poly(butyl acrylate) and polyacrylamide.     

Compatibilizing effects of poly(styrene-graft-ethylene oxide) in blends of polystyrene and butyl acrylate polymers

The compatibilizing effect of poly(styrene-graft-ethylene oxide) in polystyrene (PS) blends with poly(n-butyl acrylate) (PBA) and poly(n-butyl acrylate-co-acrylic acid) (PBAAA) was investigated. No significant effects of the graft copolymer on the domain size were found in the PBA blends. By functionalizing PBA with acrylic acid, the average size of the polyacrylate domains was reduced considerably by the graft copolymer. Thermal and dynamic mechanical analysis of the PS/PBAAA blends revealed that the PBAAA glass transition temperature (T_g) decreased with increasing graft copolymer content. The effect of the graft copolymer in the PS/PBAAA blends can be explained by interactions across the interface due to the formation of hydrogen bonds between the poly(ethylene oxide) (PEO) side chains in the graft copolymer and the acrylic acid segments in the PBAAA phase. Hydrogen bonding was confirmed by IR analysis of binary blends of PEO and PBAAA. Partial miscibility in the PEO/PBAAA blends was indicated by a PEO melting point depression and by a T_g reduction of the PBAAA phase. The thermal properties of the PEO/PBA blends indicated only very limited miscibility. © 1996 John Wiley & Sons, Inc.     

Calorimetric study of block-copolymers of poly(n-butyl acrylate) and gradient poly(n-butyl acrylate-co-methyl methacrylate)

The nanophase separation in diblock and triblock copolymers consisting of immiscible poly(n-butyl acrylate) (block A) and gradient copolymers of methyl methacrylate (MMA) and n-butyl acrylate (nBA) (block M/A) were investigated by means of their heat capacity, C_p, as a function of the composition of the blocks M/A and temperature. In all copolymers studied, both blocks are represented by their C_p and glass transition temperature, T_g, as well as the broadening of the transition-temperature range. The low-temperature transition of the blocks A is always close to that of the pure poly(n-butyl acrylate) and is independent of the analyzed compositions of the block copolymer, but broadened asymmetrically relative to the homopolymer due to the small phase size. The higher transition is related to the glass transition of the copolymer block of composition M/A. Besides the asymmetric broadening of the transition due to the phase separation, it decreases in T_g and broadens, in addition, symmetrically with increasing acrylate content. The concentration gradient is not able to introduce a further phase separation with a third glass transition inside the M/A block.     

Block, blocky gradient and random copolymers of 2-ethylhexyl acrylate and acrylic acid by atom transfer radical polymerization

The controlled synthesis of low-T_g poly(2-ethylhexyl acrylate) (P2EHA) and derived random, block and blocky gradient copolymers via atom transfer radical polymerization (ATRP) is described. After optimizing the reaction conditions for the homopolymerization of 2EHA via ATRP, the synthesis of a variety of copolymers with poly(t-butyl acrylate) (PtBuA) was investigated. First, AB-block copolymers were targeted, starting from P2EHA and PtBuA as macroinitiators. Second, random copolymers of tBuA and 2EHA with different monomer ratios were synthesized. Finally, the synthesis of “blocky” gradient copolymers via a one-pot procedure was investigated, starting with the homopolymerization of tBuA, followed by the addition of 2EHA. The hydrolysis of the PtBuA-segments to poly(acrylic acid) (PAA), which was carried out with methanesulfonic acid, resulted in block, blocky gradient and random copolymers consisting of PAA and P2EHA. Solubility testing of the copolymers in slightly basic water (pH ∼ 9) demonstrated that the gradient structure significantly enhances solubility compared to the block copolymer structures with equal composition. The polymers have been characterized by MALDI-TOF MS, GPC and ¹H NMR.     

A comparative study on water-based coatings prepared in the presence of oligomeric and conventional protective colloids

Poly(vinyl acetate-co-butyl acrylate) latexes were prepared by using semi-continuous emulsion polymerization method in presence of two different protective colloids which were oligomeric N-methylol acrylamide and conventional poly(vinyl alcohol). The effects of these protective colloids on colloidal, surface and film properties of latexes were examined. Poly(vinyl acetate-co-butyl acrylate) synthesized with oligomeric N-methylol acrylamide, which was characterized by FT-IR, NMR and MALDI-TOF MS, was found to have lower viscosity, finer particle size, better latex stability, lower polydispersity, higher T_g and better film forming behavior compared to those synthesized from the poly(vinyl alcohol).     

Amphiphilic cylindrical brushes with poly(acrylic acid) core and poly(n-butyl acrylate) shell and narrow length distribution

Core-shell cylindrical polymer brushes with poly(t-butyl acrylate)-b-poly(n-butyl acrylate) (PtBA-b-PnBA) diblock copolymer side chains were synthesized via ‘grafting from’ technique using atom transfer radical polymerization (ATRP). The formation of well-defined brushes was confirmed by GPC and ¹H NMR. Multi-angle light scattering (MALS) measurements on brushes with 240 arms show that the radius of gyration scales with the degree of polymerization of the side chains with an exponent of 0.57±0.05. The hydrolysis of the PtBA block of the side chains resulted amphiphilic cylindrical core-shell nanoparticles. In order to obtain a narrow length distribution of the brushes, the backbone, poly(2-hydroxyethyl methacrylate), was synthesized by anionic polymerization in addition to ATRP. The characteristic core-shell cylindrical structure of the brush was directly visualized on mica by scanning force microscopy (SFM). Brushes with 1500 block copolymer side chains and a length distribution of l_w/l_n=1.04 at a total length l_n=179 nm were obtained. By choosing the proper solvent in the dip-coating process on mica, the core and the shell can be visualized independently by SFM.     

ABA triblock copolymers containing polyhedral oligomeric silsesquioxane pendant groups: synthesis and unique properties

The synthesis and characterization of POSS containing ABA triblock copolymers is reported. The use of atom transfer radical polymerization (ATRP) enabled the preparation of well-defined model copolymers possessing a rubbery poly(n-butyl acrylate)(pBA) middle segment and glassy poly(3-(3,5,7,9,11,13,15-heptaisobutyl-pentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]-octasiloxane-1-yl)propyl methacrylate(p(MA-POSS)) outer segments. By tuning the relative composition and degree of polymerization (DP) of the two segments, phase separated microstructures were formed in thin films of the copolymer. Specifically, dynamic mechanical analysis and transmission electron microscopy (TEM) observations reveal that for a small molar ratio of p(MA-POSS)/pBA (DP=6/481/6) no evidence of microphase separation is evident while a large ratio (10/201/10) reveals strong microphase separation. Surprisingly, the microphase-separated material exhibits a tensile modulus larger than expected (ca. 2×10⁸ Pa) for a continuous rubber phase for temperatures between a pBA-related T_g and a softening point for the p(MA-POSS)-rich phase. Transmission electron microscopy (TEM) images with selective staining for POSS revealed the formation of a morphology consisting of pBA cylinders in a continuous p(MA-POSS) phase. Thermal studies have revealed the existence of two clear glass transitions in the microphase-separated system with strong physical aging evident for annealing temperatures near the T_g of the higher T_g phase (p(MA-POSS). The observed aging is reflected in wide-angle X-ray scattering as the strengthening of a low-angle POSS-dominated scattering peak, suggesting some level of ordering during physical aging. The T_g of the POSS-rich phase observed in the microphase separated triblock copolymer was nearly 25 °C higher than that of a POSS-homopolymer of the same molecular weight, suggesting a strong confinement-based enhancement of T_g in this system.     

Synthesis of amphiphilic triblock copolymers and application for morphology control of calcium carbonate crystals

A series of amphiphilic triblock copolymers poly(ethylene glycol)-block-poly(acrylic acid)-block-poly(n-butyl acrylate) (PEG-b-PAA-b-PnBA) differing only in the relative block lengths were synthesized by the acid-catalyzed elimination of the tert-butyl groups from poly(ethylene glycol)-block-poly(tert-butyl acrylate)-block-poly(n-butyl acrylate) (PEG-b-PtBA-b-PnBA), which was synthesized by atom-transfer radical polymerization (ATRP). The degree of polymerization, molecular weight and percentage of hydrolysis of the product PEG-b-PAA-b-PnBA were studied by gel permeation chromatography (GPC), NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS). Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to study the aggregation states of copolymers in water solution. The radii of the copolymer micelles shrink as Ca²⁺ is introduced into the solutions. The crystallization behaviors of calcium carbonate controlled by copolymer 1 (PEG₁₁₂-b-PAA₈₆-b-PnBA₆₀) and copolymer 2 (PEG₁₁₂-b-PAA₄₀-b-PnBA₇₂) differing mainly in the length of PAA block were systematically studied. It was found that the crystallization products are composed of calcite and vaterite, and the ratio of vaterite to calcite increases with increasing the concentration of copolymer 1. For copolymer 2, however, only calcite is obtained at all the concentration range investigated in this work.     

Polyisobutylene-based miktoarm star polymers via a combination of carbocationic and atom transfer radical polymerizations

Poly(isobutylene-b-styrene) (PIB-PS) copolymers and polyisobutylene (PIB) homopolymers were synthesized via quasiliving carbocationic polymerization from the initiator 3,3,5-trimethyl-5-chlorohexyl acetate, which contains a protected hydroxyl group. The PIB block was created at −70 °C in a methylcyclohexane/methyl chloride (60:40) cosolvent system, using TiCl₄ as co-initiator, followed optionally by sequential addition of styrene. Using a strong base, the acetate head group of the resulting block copolymer was cleaved to yield a hydroxyl group, which was subsequently esterified with the branching agent 2,2-bis((2-bromo-2-methyl)propionatomethyl)propionyl chloride (BPPC) to create dual initiating sites for atom transfer radical polymerization (ATRP). ATRP of tert-butyl acrylate was carried out using a Cu(I)Br/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) catalyst system. In some cases, the ester side chains of the poly(tert-butyl acrylate) (PtBA) blocks were cleaved to create poly(acrylic acid) (PAA) blocks. The final miktoarm star polymers had compositions that were very close to theoretical.     

Functional biohybrid materials synthesized via surface-initiated MADIX/RAFT polymerization from renewable natural wood fiber: Grafting of polymer as non leaching preservative

Crude wood fibers represent a wide class of renewable resources. The surface modification of such materials via covalent grafting of polymer offers new surface properties with non-leaching coating. The grafting of the polymer chains was achieved by surface-initiated controlled radical polymerization through a grafted xanthate chain transfer agent. Macromolecular design via interchange of xanthate (MADIX) technique was chosen to graft poly(vinyl acetate), polystyrene, poly(n-butyl acrylate) and poly(4-vinylbenzyl chloride)-polystyrene amphiphilic cationic copolymers. Water contact angle measurements highlighted the hydrophobization of the wood fiber surface with a nanoscaled polymer monolayer indicating the appropriate coverage of the fiber. X-ray photoelectron spectroscopy showed the successful grafting of the polymer after drastic washing procedure. The quaternization of the grafted polystyrene-co-poly(4-vinyl benzyl chloride) copolymers with tertiary amine allows the introduction of biocide quaternary ammonium functions while preserving the hydrophobic character of the modified wood fiber when introducing a long alkyl chain in the statistical copolymer. Finally, the cationic copolymer was subjected to Coniophora Puteana to evaluate its propensity to limit the fungi expansion.     

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) pentablock copolymers from a combination of quasiliving carbocationic and atom transfer radical polymerization

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) (PAA-PS-PIB-PS-PAA) block copolymers were prepared using a combination of quasiliving carbocationic and atom transfer radical polymerization (ATRP) techniques. Poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymer macroinitiators with targeted molecular weights and high degrees of chain end functionality (F_n>1.7) were prepared by quasiliving carbocationic polymerization of isobutylene followed by sequential addition of styrene. Poly(tert-butyl acrylate-b-styrene-b-isobutylene-b-styrene-b-tert-butyl acrylate) (PtBA-PS-PIB-PS-PtBA) pentablock terpolymers with targeted molecular weights and low polydispersities (PDIs) were synthesized from the PS-PIB-PS macroinitiators via ATRP of tBA using either a Cu(I)Cl/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2-(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. Deprotection of the tert-butyl groups using trifluoroacetic acid at 25 °C resulted in the formation of PAA-PS-PIB-PS-PAA pentablock terpolymers. Comonomer composition of the final terpolymers, determined by ¹H-NMR spectroscopy, was very close to theoretical.     

A study of thermoassociative gelation of aqueous cationic poly(N-isopropyl acrylamide) graft copolymer solutions

In this work thermoassociative gel formation of a new family of aqueous temperature-responsive copolymer solutions has been investigated. This was achieved using a cationic poly(N-isopropyl acrylamide) (PNIPAm) graft copolymer recently prepared [Liu R, De Leonardis P, Cellesi F, Tirelli N, Saunders BR. Langmuir 2008;24:7099]. The PDMA⁺_x-g-(PNIPAm_n)_y copolymers have x and y values that originate from the macroinitiator; the value for n corresponds to the PNIPAm arm length. DMA⁺ is quarternarized N,N-dimethylaminoethyl methacrylate. The copolymer solutions exhibited cloud point temperatures (T_clpt) of about 33 °C, which were not significantly affected by x/y ratio or the value for n. Thermoassociative gel formation occurred above T_clpt at copolymer concentrations (C_copol) greater than or equal to 4 wt.%. This is a reasonably low C_copol value and is a consequence of the graft copolymer architecture employed. We investigated the effect of temperature, C_copol and copolymer structure on gelation and gel elasticity using variable - temperature dynamic rheology. For PDMA⁺₃₀-g-(PNIPAm₂₁₀)₁₄ solutions at 39 °C it was found that G′ (elastic modulus) scales with C_copol according to G′ ∼ C_copol^3.85. The data suggested that a significant proportion of PNIPAm units is not directly involved in network formation. Thermoassociative gel formation and the gel properties for these systems appear to be governed by a balance between electrostatic repulsion involving the DMA⁺ units (favouring spatial extension of the copolymer backbones) and attractive hydrophobic interactions between PNIPAm side chains (favouring associative crosslink formation).     

Mechanistic investigation of 9-bromoanthracene photodimers as initiators in atom transfer radical polymerization

Mechanistic pathways accounting for the lack of control in polymerizations employing photodimers of 9-bromoanthracene as alkyl halide initiators in atom transfer radical polymerization (ATRP) reactions are presented. Converting the aryl bromide on the anthracene moiety into an alkyl bromide via a [4+4] cycloaddition reaction effectively generated the photodimer with two alkyl halide sites, which were investigated as potential initiating sites for the ATRP of styrene and n-butyl acrylate. Polymers synthesized using these photodimers as initiators possessed relatively broad polydispersity index (PDI) values and displayed a non-linear relationship between their number average molecular weights (M_n) and monomer consumption, consistent with slow initiation from the bridgehead alkyl halide. Reactions performed at 80 °C in bulk or THF generated polystyrene with M_n values 3-5 times higher than calculated based on monomer-to-initiator ratios. UV-vis spectrometry of the products demonstrated absorbance bands indicative of polymer-bound anthracene, caused by thermal degradation of the photodimer during the polymerization. When the initiator was introduced last into the reaction mixture in an attempt to suppress photodimer cleavage prior to initiation, PDI values and M_n values were generally lowered with the resulting polymers showing similarly high anthracene content. Composition of polystyrene and poly(n-butyl acrylate) products was also studied as a function of reaction temperature, with decreased anthracene labeling observed at lower temperatures (40 and 60 °C), further validating a model of heat-induced cleavage of the photodimer.     

Polymerized ionic liquid diblock copolymers with long alkyl side-chain length

A polymerized ionic liquid (PIL) diblock copolymer with a long alkyl side-chain, poly(MMA-b-MUBIm-Br), was synthesized at various compositions from an ionic liquid monomer, (1-[(2-methacryloyloxy)undecyl]-3-butylimidazolium bromide) (MUBIm-Br), and a non-ionic monomer, methyl methacrylate (MMA). The PIL diblock copolymer was synthesized via post-functionalization from its non-ionic precursor PIL diblock copolymer, poly(MMA-b-BrUMA) (BrUMA = 11-bromoundecyl methacrylate), which was synthesized via the reverse addition fragmentation chain transfer (RAFT) polymerization technique. Differential scanning calorimetry reveals two distinct constant glass transition temperatures (T_gs) with a low PIL segment T_g. These PIL block copolymers result in easily processable, flexible, transparent films with high mechanical strength. A high bromide ion conductivity of 64.85 mS cm⁻¹ at 80 °C and 90% RH was measured for the PIL diblock copolymer with an ion exchange capacity (IEC) of 1.44 meq/g (23.3 mol% MUBIm-Br). Interestingly, this result was three times higher than its analogous PIL homopolymer (2.75 meq/g; 100 mol% MUBIm-Br) and an order of magnitude higher than a PIL block copolymer from a previous study with similar chemistry, similar IEC, higher water content, but shorter alkyl side-chain length. Ion conductivity did not scale as expected with water content, which is unusual for water-assisted ion transport (e.g., protons, hydroxide, chloride) in ion-containing polymers, and therefore suggests other mechanisms that impact ion transport in PIL block copolymers.     

Synthesis and self-assembly behavior of POSS tethered amphiphilic polymer based on poly(caprolactone) (PCL) grafted with poly(acrylic acid) (PAA) via ROP,ATRP, and CuAAC reaction

This investigation reports the preparation and self-assembly behavior of polyhedral oligomeric silsesquioxane (POSS) containing poly(caprolactone)-graft-poly(acrylic acid) (POSS-PCL-graft-PAA) polymer. This article focuses on the self-assembly behavior of POSS tethered amphiphilic graft copolymer. In this investigation, POSS tethered alkyne functionalized polycaprolactone (PCL) was prepared by strategic ring opening polymerization (ROP) of ε-caprolactone and α-propargyl-ε-caprolactone using hydroxyl-terminated POSS as an initiator. Azide-terminated poly(tert-butyl acrylate) (P ^t BA) was grafted onto functional PCL via Cu-catalyzed azide-alkyne “click” (CuAAC) reaction. Finally, hydrolysis of the tert-butyl ester group into acid furnished the POSS tethered PCL-graft-PAA polymer. This amphiphilic graft copolymer was characterized by GPC, NMR, and FT-IR analyses and the morphology of the graft copolymer analyzed by HRTEM and FESEM analyses. On changing the graft copolymer concentration (low to high) in water, the morphology of the final graft copolymer changed from micelles to worm-like and core-shell. The structural motif of POSS plays an important role in this morphological transformation. The pH sensitivity was studied using DLS analysis as well as via release profile of rhodamine B as a model compound.     

Preparation of poly(tert-butyl acrylate-g-styrene) as precursors of amphiphilic graft copolymers: 2. Relaxation processes and mechanical behavior

Viscoelastic relaxations of four poly(tert-butyl acrylate-g-styrene) copolymers are studied over a wide range of temperatures. The temperature location and apparent activation energy of the distinct relaxations observed under tension mode are discussed. As grafted polystyrene content increases in the copolymer, microdomains of both components occur and, consequently, two relaxations associated with cooperative motions of either the acrylate backbone or the graft are observed. A bending deformation mode is also analyzed in the region of the glass transition of the two components to study the phase separation. Moreover, the glass transition temperature of the acrylic backbone is estimated by microhardness measurements. The relationship between microhardness and storage modulus is established either below or above the glass transition of the tert-butyl acrylate backbone.