PAA Segment Research Articles

Amphiphilic pH-responsive ABC triblock copolymers via RAFT-mediated aqueous PISA and comparison with their A-b-(B-co-C) diblock copolymer counterparts

The influence of the macroRAFT agent architecture on the morphology of the self-assemblies obtained by aqueous RAFT dispersion polymerization in PISA is studied by comparing amphiphilic AC, A(B-co-C) diblocks and ABC triblock copolymers, constituted of N,N-dimethylacrylamide (DMAm = A), acrylic acid (AA = B) and N-cyanomethylacrylamide (CMAm = C) monomer units. The aim of this study is to better understand the impact of the presence of pH-sensitive acrylic acid units and their spatial distribution in block copolymers. Generally, the presence of a fully protonated intermediate block of PAA between the two blocks (based on PDMAm and PCMAm) favors the formation of higher-order morphologies. These ABC triblock copolymers assemblies are pH-responsive and can undergo morphological transitions through the controlled deprotonation or protonation of the PAA segment, but do not completely dissociate at high pH (i.e. when AA units are fully ionized) unlike their A(B-co-C) diblock counterparts, where the pH-responsive monomer unit is homogeneously distributed within the solvophobic block.

Facile Synthesis of Fluorinated Polyacrylate Elastomer via Emulsion Polymerization Using Adjustable Amphiphilic Star Macro‐RAFT Agent as Surfactant

AbstractNovel thermoplastic fluorinated polyacrylate films possessing excellent mechanical performance are prepared by emulsion polymerization latex using adjustable amphiphilic star macro‐reversible addition‐fragmentation chain‐transfer (macro‐RAFT) agent as surfactants in this work. First, star macro‐RAFT agent equipped with six amphiphilic arms is synthesized via two‐step RAFT polymerization of acrylic acid (AA) and 2,2,2‐trifluoroethyl acrylate (TFEA) in the presence of hexa‐functional RAFT agents. The surface activities of the as‐synthesized amphiphilic star macro‐RAFT agents in aqueous solutions are studied. Subsequently, various fluorinated polyacrylate latexes are obtained by conducting emulsion polymerization of 2,2,3,4,4,4‐hexafluorobutyl acrylate (HFBA) and butyl acrylate (BA) using the amphiphilic star macro‐RAFT agents as both RAFT agents and surfactants. The latex particle morphologies are studied by transmission electron microscope (TEM) and particle size is measured by dynamic light scattering (DLS). The effects of PAA segment length, HFBA/BA mole ratio, and TFEA segment length on the surface morphologies of the fluorinated polyacrylate films are illustrated by investigating the surface properties using water contact angle test and atomic force microscopy (AFM). Finally, the elastomeric films obtained by directly casting the prepared fluorinated polyacrylate latexes show excellent comprehensive properties such as tensile strength over 4 MPa, elongation at break ≈700%, permanent deformation below 25%. Water absorption test is also provided as a reference.

A multifunctional antifog, antifrost, and self-cleaning zwitterionic polymer coating based on poly(SBMA-co-AA)

In this work, a multifunctional coating was developed by grafting a zwitterionic poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)-co-acrylic acid [poly(SBMA-co-AA)] polymer onto a glass slide, which possesses excellent antifog, antifrost, and self-cleaning properties. These properties are attributed to the strong hydration of the hydrophilic zwitterionic PSBMA segments. The durability of the coating can be improved because the carboxyl group (–COOH) of the PAA segment enables formation of a robust covalent bond with the amino group (–NH2) on the substrate. The coating presents long-term stability, as proved by water contact angles, which were stable at 12 ± 1° after exposing the coating in ambient environment for 60 days or immersing in deionized water for 24 h. In addition, the underwater oil contact angle measurement demonstrated that an oil stain on the zwitterionic poly(SBMA-co-AA) polymer coating can be easily removed upon contact with water, showing self-cleaning performance. These properties verified that the zwitterionic multifunctional coating exploited in this research has many potential application prospects, including construction, automotive, aerospace, shipbuilding, biomedical, and other optical fields.

Preparation and properties of hydrophobic filter paper and cotton fabric with reversible solvent response

The preparation of hydrophobic surfaces has been extensively studied, but the reversible responsive hydrophobic surface has received less attention. In this paper, poly(styrene-random-methyl methacrylate-random-acrylic acid) (P(St-r-MMA-r-AA)) was prepared by conventional free radical polymerization, and the filter paper and cotton fabric were immersed in P(St-r-MMA-r-AA) methanol solution to construct a hydrophobic surface. The hydrophobic property, chemical composition and surface morphology of the hydrophobic filter paper and cotton fabric surface were characterized by contact angle, Gibbs free energy, infrared spectroscopy and scanning electron microscopy. The optimum conditions for constructing hydrophobic filter paper and cotton fabric surface were investigated. When the surfaces of hydrophobic filter paper and cotton fabric were treated with methanol, tetrahydrofuran and deionized water respectively, the semihydrophobic-hydrophobic-hydrophilic reversible transformation could be achieved. After ten cycles of experiments, the contact angles under the three solvent stimulations had no significant change, and the hydrophobic properties of the hydrophobic cotton fabric were superior to that of hydrophobic filter paper. The Gibbs free energy calculation of the hydrophobic surface indicated that the change in surface hydrophobic property was due to the inversion between the hydrophobic PS segment, the PMMA segment, and the hydrophilic PAA segment.

Temperature-, pH- and CO₂-Sensitive Poly(N-isopropylacryl amide-co-acrylic acid) Copolymers with High Glass Transition Temperatures.

A series of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAAm-co-PAA) random copolymers were synthesized through free radical copolymerization in MeOH. The incorporation of the acrylic acid units into PNIPAAm tended to enhance the glass transition temperature (Tg), due to strong intermolecular hydrogen bonding between the amide groups of PNIPAAm and the carboxyl groups of PAA, as observed using 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopic analyses. The lower critical solution temperature (LCST) increased upon increasing the pH of the aqueous solution containing PNIPAAm-co-PAA because the COOH groups of the PAA segment dissociated into COO− groups, enhancing the solubility of the copolymer. In addition, high-pressure differential scanning calorimetry revealed that the LCSTs of all the aqueous solutions of the copolymers decreased upon increasing the pressure of CO2, suggesting that CO2 molecules had displaced H2O molecules around the polar CONH and COOH groups in PNIPAAm-co-PAA, thereby promoting the hydrophobicity of the copolymers in the aqueous solution. In addition, the values of Tg of a film sample increased upon treatment with supercritical CO2, implying that intermolecular interactions in the copolymer had been enhanced after such treatment.

Fabrication of V‐shaped brushes consisting of two highly incompatible arms of PEG and fluorinated PMMA and their protein‐resistance performance

ABSTRACTIn this article, the fluorinated amphiphilic V‐shaped brushes with two highly incompatible arms of mPEG42 and PMMA38‐b‐PFMAy were produced by reacting COOH in the PAA segment in methoxypoly(ethylene glycol)‐b‐poly(acrylic acid)‐b‐poly(methyl methacrylate)‐b‐poly(2‐perfluoro‐octylethyl methacrylate) (mPEG42‐b‐PAA11‐b‐PMMA38‐b‐PFMAy) with an epoxy group on the functionalized SiO2 substrate. It was found that the resulting phase separation structures of the V‐shaped brushes can be adjusted by altering the degree of polymerization (y) of PFMA. The brush surface with y = 8 showed an alternating phase separation structure, in which one domain was water‐soluble PEG and the other was ultralow surface energy domain with a crystalline fluorinated side group. Protein adsorption studies indicated that this surface structure exhibited desirable protein‐resistant performance. The reason was attributed to the stimuli‐responsive PEG domain, in which PEG chains stretch out at the interface in water, while the PFMA domain remains relatively stable. The synergistic effect of the hydrophilic PEG domain and the hydrophobic PFMA domain in water prevents protein adsorption. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2599–2610

Toward efficient water/oil separation material: Effect of copolymer composition on pH‐responsive wettability and separation performance

Interest in functional soft matter with stimuli‐responsive wettability has increasingly intensified in recent years. From the chemical product engineering viewpoint, this study aims to fabricate reversible pH‐responsive polymeric surfaces with controllable wettability using [poly(2,2,3,4,4,4‐hexafluorobutyl methacrylate)‐block‐ poly(acrylic acid) (PHFBMA‐b‐PAA)] block copolymers. To attain this aim, three block copolymers with different PAA segment lengths were synthesized for the first time through Cu(0)‐mediated reversible‐deactivation radical polymerization and hydrolysis reaction. pH‐induced controllable wettability was achieved by spin‐coating the resulting block copolymers onto silicon wafers. Results showed that the pH‐responsive wetting behavior was introduced by incorporating the PAA block, and that the responsiveness of as‐fabricated surfaces was greatly influenced by PAA content. All three evolutions of water contact angle with pH shared a similar inflection point at pH 5.25. Furthermore, on the basis of the wetting properties and mechanism understanding, the application of copolymer coated meshes in layered water/oil separation was exploited. Given their superhydrophilicity and underwater superoleophobicity, PHFBMA70‐b‐PAA148 and PHFBMA70‐b‐PAA211 coated stainless steel meshes (SSMs) can efficiently separate water from different mixtures of organic solvent and water with high flux. However, considering long‐term use, the PHFBMA70‐b‐PAA148 coated SSM with good stability may be the best copolymer for water/oil separation. Therefore, a coordination of structure, composition, and functionality was necessary to enable practical applications of the functional materials. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1758–1771, 2016

Preparation of hierarchical porous carbons from amphiphilic poly(vinylidene chloride-co-methyl acrylate)-b-poly(acrylic acid) copolymers by self-templating and one-step carbonization method

Based on our previous proposed method to fabricate the hierarchical porous carbons (HPCs), a series of amphiphilic poly(vinylidene chloride-co-methyl acryalte)-b-poly(acrylic acid) (PVDC-b-PAA) copolymers were prepared via RAFT polymerization and used to prepare the HPCs by self-templating and one-step carbonization method. The phase structure and thermal degradation behavior of PVDC-b-PAA copolymers, as well as the morphology and pore structure of corresponding carbons were investigated. It was found that all block copolymers exhibited micro-phase separation feature and showed the PAA-dispersed, bi-continuous, and PAA-dominated phase structures as the PVDC/PAA molar ratio varied from 3:1 to 0.77:1. Although the PVDC-b-PAA copolymers exhibited the individual glass transitions of each block, the thermal degradations of PVDC and PAA blocks were interacted and overlapped. The carbons prepared from PVDC-b-PAA contained the micro- and meso-pores, which were mainly originated from the thermal degradation of PVDC segment and the pyrolysis of PAA segment, respectively. The carbons prepared from PVDC66-b-PAA22 copolymer exhibited a maximum Brunauer–Emmett–Teller surface area of 1093m2g−1 and a maximum total pore volume of 0.51cm3g−1. Due to the incomplete pyrolysis of PAA segment and the jamming effect to pores caused by the PAA-based carbon, the total pore volume of HPCs prepared from PVDC-b-PAA copolymers were lower than that of HPCs prepared from the PVDC-b-polystyrene copolymers (J. Mater. Sci. 49 (2014) 1090–1098).

Highly ordered microporous polystyrene-b-poly(acrylic acid) films: Study on the influencing factors in their fabrication via a static breath-figure method

A series of well-defined amphiphilic polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymers with different molar ratios of PS and PAA segment were were synthesized via subsequential atomic radical polymerizations of styrene and tert-butyl acrylate (tBuA) followed by hydrolyzation of tert-butyl groups. Highly ordered microporous films of such copolymers were fabricated by a static breath-figure (BF) method using carbon dioxide (CS2) or chloroform (CHCl3) as solvent under a saturated relative humidity of water. The porous films of PS-b-PAA copolymers with average pore size of 0.64–1.79μm and good regularity were fabricated. Some critical influencing factors, such as concentration of the diblock polymer solution, solvent, temperature, particularly molar ratio of PAA and PS segment were investigated to control the morphology of PS-b-PAA microporous films.

Self‐assembling Linear and Star Shaped Poly(ϵ‐caprolactone)/poly[(meth)acrylic acid] Block Copolymers as Carriers of Indomethacin and Quercetin

A amphiphilic linear AB, BAB, and star shaped (AB)3 block copolymers of poly(ϵ-caprolactone) (PCL)/poly(meth)acrylic acid (P(M)AA) are used for the preparation of nanoparticles and drug entrapment, where indomethacin and quercetin are employed as model drugs. Drug loading experiments with the nanoparticles based on PAA block copolymers demonstrate a higher efficiency for the star structure, whereas the PMAA star copolymer presents the lowest entrapment ability. The release properties are studied at room temperature and 37 °C in phosphate buffer solutions with pH equal to 5 and 7.4. The kinetic profiles show a strong relation to the copolymer's topology, indicating the lowest release rates from the star based superstructures, while the PMAA particles are less stable than those containing PAA segment(s).

Synthesis of amphiphilic heteroarm star‐shaped polymer via free radical polymerization using polyfunctional chain transfer agent and its self‐assembly behavior

AbstractAmphiphilic heteroarm star‐shaped polymers have important theoretical and practical significance. In this work, amphiphilic heteroarm star‐shaped polymer was synthesized by the use of polyfunctional chain transfer agent via sequential free radical polymerization in two steps. First, conventional free radical polymerization of methyl methacrylate (MMA) initiated by 2,2′‐azobis (isobutyronitrile) (AIBN) was carried out in the presence of polyfunctional chain transfer agent, pentaerythritol‐tertrakis (3‐mercaptopropinate) (PETMP). At appropriate monomer conversion, about two‐arm s‐PMMA having two residual thiol groups at the chain center was obtained. Second, the s‐PMMA obtained above was used as macro‐chain‐transfer agent for free radical polymerization of acrylic acid (AA). The heteroarm star‐shaped polymer with the hydrophobic PMMA segment and the hydrophilic PAA segment was obtained. The successful synthesis of heteroarm star‐shaped polymers, (PMMA)2(AA)2, was confirmed by 1H‐NMR and its self‐assembly behavior in different solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Reduction and temperature dual-responsive crosslinked polymersomes for targeted intracellular protein delivery

The study of biological functions of proteins in cells as well as therapeutic exploration of many protein drugs demands efficient and nontoxic intracellular protein delivery systems. Herein, reduction and temperature dual-responsive crosslinked polymersomes were developed for the facile encapsulation of various proteins under mild conditions as well as rapid release of proteins in cancer cells. Two thermo-sensitive triblock copolymers, PEG5k-PAA1.7k-PNIPAM22k and PEG5k-PAA0.7k-PNIPAM12k (denoted as polymer 1 and 2, respectively), were prepared by controlled reversible addition–fragmentation chain-transfer (RAFT) polymerization. Interestingly, polymers 1 and 2 exhibited lower critical solution temperatures (LCST) of 39 and 38 °C in PBS (pH 7.4, 20 mM, 150 mM NaCl) and 34 and 32 °C in MES (pH 5.5, 20 mM), respectively. Increasing the temperature of polymer solutions in MES to 40 °C yielded robust polymersomes with average diameters of ca. 150∼170 nm following crosslinking the PAA segment with cystamine (Cys) viacarbodiimide chemistry. These crosslinked polymersomes kept their structures in PBS at 37 °C but rapidly dissociated into unimers in response to 10 mM dithiothreitol (DTT). Remarkably, various proteins including bovine serum albumin (BSA), lysozyme (Lys), cytochrome C (CC), and ovalbumin (Ova) could be conveniently loaded into the polymersomes with markedly high protein loading efficiencies of 60∼100% at theoretical protein loading contents of 10∼50 wt%. The in vitro release studies using Cys-crosslinked polymersome 1 showed that release of BSA, Lys, and CC was minimal (ca. 20%) in 11 h in PBS at 37 °C, while fast protein release of over 70% was observed under an intracellular mimicking reductive environment. MTT assays revealed that these polymersomes were practically non-toxic to HeLa and MCF-7 cells up to a tested concentration of 200 μg mL−1. Confocal laser scanning microscope (CLSM) observations showed that FITC-CC loaded Cys-crosslinked polymersomes efficiently delivered and released FITC-CC into the cytosol of MCF-7 cells after 12 h incubation. In contrast, little FITC-CC fluorescence was observed in MCF-7 cells treated with free FITC-CC as well as FITC-CC loaded 1,4-butadiamine crosslinked polymersomes (reduction-insensitive control). Flow cytometry studies showed that CC loaded Cys-crosslinked polymersomes induced markedly enhanced apoptosis of MCF-7 cells as compared to free CC and the reduction-insensitive controls. These novel reduction and temperature dual-responsive crosslinked polymersomes have opened a new avenue to targeted intracellular protein delivery.

Synthesis and characterization of fluorine‐containing PAA‐b‐PTPFCBPMA amphiphilic block copolymer

AbstractA series of perfluorocyclobutyl (PFCB) aryl ether‐based amphiphilic diblock copolymers containing hydrophilic poly(acrylic acid) (PAA) and fluorophilic poly(p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate) segments were synthesized via successive atom transfer radical polymerization (ATRP). 2‐MBP‐initiated and CuBr/N,N,N′,N′,N″‐pentamethyldiethylenetriamine‐catalyzed ATRP homopolymerization of the PFCB‐containing methacrylate monomer, p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate, can be performed in a controlled mode as confirmed by the fact that the number‐average molecular weights (Mn) increased linearly with the conversions of the monomer while the polydispersity indices kept below 1.38. The block copolymers with narrow molecular weight distributions (Mw/Mn ≤ 1.36) were synthesized by ATRP using Br‐end‐functionalized poly(tert‐butyl acrylate) (PtBA) as macroinitiator followed by the acidolysis of hydrophobic PtBA block into hydrophilic PAA segment. The critical micelle concentrations of the amphiphilic diblock copolymers in different surroundings were determined by fluorescence spectroscopy using N‐phenyl‐1‐naphthylamine as probe. The morphology and size of the micelles were investigated by transmission electron microscopy and dynamic laser light scattering, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Interchain Hydrogen-Bonding-Induced Association of Poly(acrylic acid)-graft-poly(ethylene oxide) in Water

Poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) in aqueous solutions shows one fast and one slow relaxation mode in dynamic light scattering (DLS), but the mixture of PAA and PEO (PAA/PEO) in aqueous solution only has a single fast mode. The effects of pH, polymer concentration, and salt concentration on these two modes have been investigated using laser light scattering (LLS), viscometry, and rheological measurements. Our results showed that the hydrogen bonding between carboxylic group and ether oxygen led to the formation of large complexes among PAA-g-PEO chains, which were absent between PAA and PEO chains in PAA/PEO aqueous solutions. The addition of formamide can break these interchain complexes because the hydrogen bonding between formamide and PAA segment is stronger than that between PEO and PAA segment. Thermodynamically speaking, the formation of hydrogen bonds among PAA-g-PEO chains leads to a less entropy loss than that between PAA and PEO chains in PAA/PEO aqueous solution, becaus...

Tailor‐Made Poly(amidoamine)s for Controlled Complexation and Condensation of DNA

A set of polymer carriers for DNA delivery was synthesized by combining monodisperse, sequence-defined poly(amidoamine) (PAA) segments with poly(ethylene oxide) (PEO) blocks. The precise definition of the PAA segments provides the possibility of correlating the chemical structure (monomer sequence) with the resulting biological properties. Three different PAA-PEO conjugates were synthesized by solid-phase supported synthesis, and the cationic nature of the PAA segments was systematically varied. This allows for the tailoring of interactions with double-stranded plasmid DNA (dsDNA). The potential of the PAA-PEO conjugates as non-viral vectors for gene delivery is demonstrated by investigating the dsDNA complexation and condensation properties. Depending on the applied carrier, a transition in polyplex (polymer-DNA ion complex) structures is observed. This reaches from extended ring-like structures to highly compact toroidal structures, where supercoiling of the DNA is induced. An aggregation model is proposed that is based on structural investigations of the polyplexes with atomic force microscopy (AFM) and dynamic light scattering (DLS). While the cationic PAA segment mediates primarily the contact of the carrier to the dsDNA, the PEO block stabilizes the polyplex and generates a "stealth" aggregate, as was suggested by Zeta potentials that were close to zero. The controlled aggregation leads to stable, single-plasmid complexes, and stabilizes the DNA structure itself. This is shown by ethidium bromide intercalation assays and DNase digestion assays. The presented PAA-PEO systems allow for the formation of well-defined single-plasmid polyplexes, preventing hard DNA compression and strongly polydisperse polyplexes. Moreover carrier polymers and the resulting polyplexes exhibit no cytotoxicity, as was shown by viability tests; this makes the carriers potentially suitable for in vivo delivery applications.

Hydrogen Bonded Assembly of Poly(acrylic acid)-block-poly(l-valine) in Dilute Solutions

The self-assembly of four hybrid poly(acrylic acid)-block-poly(l-valine) (PAA-b-PLVAL) block copolymers (i.e., PAA40−PLVAL100, PAA80−PLVAL100, PAA80−PLVAL80, and PAA80−PLVAL60) was investigated. Formation of core−shell spherical micelles was observed, and it correlated with the extent of β-sheet ordering in PLVAL hydrophobic domains. PAA80−PLVAL60, having the lowest β-sheet content (12%), existed only as random aggregates at pH < 5 and in an unaggregated state at high pH. The β-sheet formation also produced an unusual pH dependence of the micelles, where the swelling of micelles occurred only within a narrow degree of deprotonation (α) range of between 0.15 to 0.2 and 0.4 to 0.5 for PAA80−PLVAL80 and PAA80−PLVAL100, respectively. An additional role of the length of the PAA segment was identified as providing sufficient shielding to the hydrophobic core, which prevents further association into large compound micelles, as was observed for PAA40−PLVAL100.

Poly(acrylic acid)-block-poly(l-valine): Evaluation of β-Sheet Formation and Its Stability Using Circular Dichroism Technique

Secondary structure formation in four novel hybrid poly(acrylic acid)-b-poly(L-valine) (PAA-b-PLVAL) block copolymers, that is, PAA(40)-PLVAL(100), PAA(80)-PLVAL(100), PAA(80)-PLVAL(80), and PAA(80)-PLVAL(60), was investigated by circular dichroism. The formation of stable and well-defined beta-sheet structure in the PLVAL hydrophobic domains was observed for all the copolymers. At pH 5, PAA(80)-PLVAL(60) with the lowest PLVAL/PAA molar ratio possessed the lowest beta-sheet content of 12%, and it increased to 62% for PAA(40)-PLVAL(100) system. The beta-sheet formation in the block copolymers was controlled by both random PAA-PLVAL hydrogen bonds at low pH and electrostatic repulsive forces on the PAA segment at high pH; hence, the beta-sheet structure was most stable at intermediate pH. The length of PAA segments was critical in the beta-sheet solubilization and in providing sufficient shielding of the hydrophobic core from denaturing agents such as urea.

Complexation and release of doxorubicin from its complexes with pluronic P85- b-poly(acrylic acid) block copolymers

Poly(acrylic acid) (PAA) was attached on both termini of Pluronic P85 copolymer (EO 27PO 39EO 27) via atom transfer radical polymerization (ATRP) to produce a novel block copolymer, PAA- b-P85- b-PAA (P85PAA). The P85PAA–DOX complex formation and drug loading were strongly dependent on the PAA segment length and pH, where the protonation of carboxyl groups in the PAA segment at pH < 7.2 reduced the binding sites of DOX onto P85PAA chains, resulting in a diminished DOX uptake at low pH. The composition of copolymer–DOX complexes at pH 7.2 was close to the stoichiometric 1:1 DOX:carboxyl molar ratio, confirming the dominance of electrostatic interactions between cationic DOX molecules and carboxyl groups. The stability study of the copolymer–DOX complex suggested that non-polyelectrolyte interactions may also participate in the complexation of drug and P85PAA block copolymer. DOX loading at pH 5.0 decreased to 60% of the total binding capacity, indicating that protonation of carboxyl groups reduced the DOX binding to P85PAA block copolymer. DOX release from the complex is a pH-responsive process, where the protonation of carboxyl groups at mildly acidic condition resulted in a faster dissociation of copolymer-DOX complex, leading to an accelerated release of DOX at pH 5.0. Thus, complexation of DOX with P85PAA yielded a drug delivery system affording a pH-triggered release of DOX in an acidic environment of pH 5.0.

Solid-Phase Supported Polymer Synthesis of Sequence-Defined, Multifunctional Poly(amidoamines)

A novel synthesis route toward multifunctional, sequence-defined polyamides is described. A fully automated, solid-phase supported polymer synthesis was developed and utilized to obtain linear poly(amidoamine) segments (PAAs) that exhibit the absence of molecular weight and chemical distribution. This was achieved by an alternating assembly of diacids and diamines, using a forced step-growth mechanism, and driving each coupling step to completion. Within the monodisperse PAA segment, functionalities can be precisely positioned along the polymer chain allowing local control of the chain properties. The versatility of the approach was demonstrated by the conjugation of the monodisperse PAA segment toward an oligopeptide, leading to a single component block copolymer as verified by mass spectrometry. Moreover, two different poly(ethylene oxide)-PAA conjugates were synthesized utilizing the direct, solid-phase supported route. By varying the PAA repeat unit, the cationic nature of the PAA segment was adjusted, demonstrating the potential of the approach. The products were characterized by means of 1H NMR and matrix-assisted laser desorption mass spectrometry (MALDI-TOF-MS) methods, which confirmed the chemical structures conclusively.

Self-Assembly of Mixtures of Block Copolymers of Poly(styrene-b-acrylic acid) with Random Copolymers of Poly(styrene-co-methacrylic acid)

The effects of the addition of random copolymers of poly(styrene-co-methacrylic acid) [P(S-co-MAA)] on the self-assembly of block copolymers of poly(styrene-b-acrylic acid) (PS-b-PAA) are described. The effects of variation of five factors, including the MAA content, the weight fraction and molar mass of the P(S-co-MAA), the initial concentration of the mixture, and the length of the PAA segment in the block copolymer, were investigated. With increasing MAA content, the localization of the random copolymer in the aggregate changed from the core to the interface, which led to a morphological transition from spheres to vesicles. Vesicles, mixtures of vesicles and large spheres, and large spheres alone were formed with increasing weight fraction of the random copolymer. When the molar mass of the random copolymer was high, both rods and vesicles were observed at low water contents; otherwise, only vesicles were observed. The vesicle size increased (from 100 to 140 nm) with increasing initial polymer concentration, whereas the vesicle membrane thickness remained constant. The size of the vesicles prepared from the mixtures increased with water content but decreased with the length of PAA in the diblock.