Copolymerization of 1-vinylpyrrolidone with N-substituted methacrylamides: monomer reactivity ratios and copolymer sequence distribution

In order to enhance their resistance to polar solvents and their film forming ability compared to these of neat polyvinylpyrrolidone (PVP), water soluble copolymers which combined rather large PVP sequences with ammonium groups were obtained. Free radical copolymerization of 1-Vinyl-2-Pyrrolidone (NVP) with 3-(dimethylamino)propyl-methacrylamide (DMA) and 3-(methacrylamido)propyltrimethyl-ammonium, methylsulfate (TMA) was investigated in water at 68 °C using a water soluble initiator (4,4′-azobis(4-cyanovaleric acid ACVA)). The copolymer samples obtained at low conversion levels (<10%) could not be recovered quantitatively for these particular copolymers. Therefore, a numerical integration modeling, accounting for change in copolymer composition with conversion, was preferred to determine the optimal reactivity ratios from experimental data obtained at moderate conversions. The reactivity ratios (system TMA-NVP: r_TMA 4.47, r_NVP 0.038, system DMA-NVP: r_DMA 5.67, r_NVP 0.37) proved a strong preferential incorporation of the methacrylamide monomers. The reactivity ratios were then used to estimate the copolymer sequence distributions. It is shown that rather large NVP sequences can be obtained with low TMA or DMA initial contents at moderate conversion. Moreover, these copolymers easily formed films which withstood polar solvents and could be readily cross-linked by thermal curing, opening interesting prospects for membrane separation systems.     

Asymmetric morphology from an organic/organometallic block copolymer

Block copolymer self-assembly is a burgeoning subject in polymer and materials science driven by both fundamental and applied inspirations. Whereas the vast majority of block copolymer studies have focused on highly symmetric morphologies, here we report the first observation of an unusual asymmetric cylindrical phase in thick films of an organic/organometallic block copolymer, poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS). Microscopy and X-ray scattering data establish the lack of symmetry in this structure and reveal an unusual 3-D network organization. Following selective removal of the PS matrix, the remaining nanoporous film has characteristics of potential value in separation applications such as substantial interconnection (mechanical strength), uniform pore size, and chemical and physical stability.     

Formation and properties of multivariant assemblies of surface-tethered diblock and triblock copolymers

We present methodologies for fabricating block copolymer assemblies grafted onto flat solid substrates, where each block of the copolymer possesses a systematic and gradual variation of molecular weight as a function of the position on the substrate. We demonstrate the utility of this technique on two case studies. In the first project, we generate surface-tethered poly[(2-hydroxyethyl methacrylate)-b-(methyl methacrylate)] (PHEMA-b-PMMA) diblock copolymer brushes and study systematically morphological transitions associated with collapsing either the top PMMA or the bottom PHEMA block while keeping the other block solvated. Scanning force microscopy studies of systems having the top block collapsed reveal the presence of either flat (F), or micellar (M) or bicontinuous (BC) morphologies, whose locus in the phase diagram agrees with theoretical predictions and results of computer simulations. The second case study demonstrates the extension of the deposition method to the case of surface-anchored triblock copolymer brushes. Specifically, we present results pertaining to the formation of poly[(2-hydroxyethyl methacrylate)-b-(methyl methacrylate)-b-(dimethylaminoethyl methacrylate)] brushes with independent variation of all three block lengths.     

Anaerobic biodegradation of the microbial copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate): Effects of comonomer content, processing history, and semi-crystalline morphology

Films of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB-co-3HHx) containing 3.8-10 mol% of 3-hydroxyhexanoate (3HHx) comonomer were subjected to anaerobic biodegradation to explore the effects of copolymer composition, crystallinity, and morphology on biodegradation. As biodegradation proceeded, samples with higher HHx fraction tended to have faster weight loss; on Day 7 of the degradation experiment, P3HB-co-10 mol%-3HHx lost 80% of its original weight, while P3HB-co-3.8 mol%-3HHx lost only 28%. Scanning electron microscopy (SEM) images revealed that the anaerobic biodegradation proceeded at the surface of the samples, with preferential erosion of the amorphous regions, exposing the crystalline spherulites formed inside the copolymer films. It was observed that copolymers with higher HHx fraction had smaller diameter spherulites, ranging from roughly 40 μm for P3HB-co-3.8 mol%-3HHx to 10 μm for P3HB-co-10 mol%-3HHx. A banded spherulite morphology was observed for P3HB-co-6.9 mol%-3HHx and P3HB-co-10 mol%-3HHx, with much wider band spacing (2 μm) for the former than the latter (0.3 μm). Different thermal history seemed to affect the morphological properties and, thus, the biodegradability of the P3HB-co-3HHx samples as well. When comparing copolymers with the same copolymer composition, P3HB-co-3HHx annealed at 70 °C had 5-30% more weight loss after the same duration of incubation in active sludge compared to the quenched samples. We suggest that annealing of P3HB-co-3HHx likely induces void formation in the semi-crystalline structure, facilitating the movement of water or perhaps enzymes to a higher degree of penetration into the sample and subsequently enhancing microbial degradation.     

Electropolymerization and electrochemical properties of (N-hydroxyalkyl)pyrrole/pyrrole copolymers

In this study, the N-hydroxyalkyl derivatives of pyrrole (Py), N-(2-hydroxyethyl)pyrrole (HE) and N-(3-hydroxypropyl)pyrrole (HP), were synthesized. The corresponding homopolymers, PHE and PHP, together with the copolymers of Py/HE and those of Py/HP were prepared by galvanostatic polymerization. These monomers and polymers were characterized by FTIR spectroscopy, elemental analysis, SEM and electrochemical techniques. The result of potential-time profiles showed that a higher potential was required for HE and HP than Py for the polymerization. This was ascribed to the steric hindrance of high concentration of the N-hydroxyalkyl groups. However, a similar potential was observed for the copolymerization of Py/HE and Py/HP systems as that of Py due to the reduction of the steric effect by lower content of the substituent. The SEM micrographs showed a rougher morphology for the films synthesized from the solutions with higher Py/derivatives ratio. The cyclic voltammograms indicated that all the copolymers were larger, while the homopolymers had smaller anodic/cathodic currents and specific charges than PPy. This implied that the existence of the proper amount of the N-hydroxyalkyl pendant groups enhanced the ionic mobility of the pyrrole polymers. The results of charge/discharge measurements showed that the copolymer PYHP82 has the highest discharge capacity among the pyrrole polymers prepared.     

Temperature- and pH-responsive photosensitization activity of polymeric sensitizers based on poly-N-isopropylacrylamide

We previously reported that a copolymer consisting of N-isopropylacrylamide (NIPAM) and benzophenone (BP) units, behaves as a photosensitizer showing temperature-controlled oxygenation activity in water (J. Am. Chem. Soc.2006, 128, 8751). This polymer shows a heat-induced oxygenation enhancement at low temperature region (5-20 °C), while showing a heat-induced oxygenation suppression at high temperature region (20-60 °C), resulting in an off-on-off activity profile against the temperature window. This is driven by a heat-induced phase transition of the polymer from coil to micelle and then to globule states. In the present work, effects of adding an amine component (N-[3-(dimethylamino)propyl]acrylamide: DMAPAM) to the polymer on the sensitization activity were studied, where the relationship between the phase transition behavior and the activity was clarified by several spectroscopic analyses. The polymers, poly(NIPAM_x-co-BP_y-co-DMAPAM_z), show activity controlled by temperature and pH. The off-on-off activity profile shifts to higher temperature with a pH decrease. This is because protonation of the DMAPAM units leads to an increase in the polymer polarity and, hence, the polymer aggregates at higher temperature. In addition, increase in the DMAPAM content of the polymer leads to further shift of the activity profile. In contrast, at pH < 8, no activity enhancement is observed because complete protonation of the DMAPAM units suppresses polymer aggregation.     

Sodium Dodecyl Sulfate (SDS)-Loaded Nanoporous Polymer as Anti-Biofilm Surface Coating Material

Biofilms cause extensive damage to industrial settings. Thus, it is important to improve the existing techniques and develop new strategies to prevent bacterial biofilm formation. In the present study, we have prepared nanoporous polymer films from a self-assembled 1,2-polybutadiene-b-polydimethylsiloxane (1,2-PB-b-PDMS) block copolymer via chemical cross-linking of the 1,2-PB block followed by quantitative removal of the PDMS block. Sodium dodecyl sulfate (SDS) was loaded into the nanoporous 1,2-PB from aqueous solution. The SDS-loaded nanoporous polymer films were shown to block bacterial attachment in short-term (3 h) and significantly reduce biofilm formation in long-term (1 week) by gram-negative bacterium Escherichia coli. Tuning the thickness or surface morphology of the nanoporous polymer films allowed to extent the anti-biofilm capability.     

Biodegradable vesicular nanocarriers based on poly(?-caprolactone)-block-poly(ethyl ethylene phosphate) for drug delivery

Biodegradable polymer vesicle for drug delivery is reported. Poly(?-caprolactone)-block-poly(ethyl ethylene phosphate) with well-defined structure (PCL₁₅₀-b-PEEP₃₀) has been prepared by ring-opening polymerization. It forms vesicles in aqueous solution using the thin-film hydration method and further exclusion of the as-formed vesicles results in vesicles at nano-size, demonstrated by confocal laser scanning microscope (CLSM) and transmission electron microscopy observations. Doxorubicin (DOX) has been loaded into the vesicles with a loading content of 4.38% using an acid gradient method. The release of DOX from the vesicles is accelerated in the presence of an enzyme phosphodiesterase I that is known to catalyze the degradation of polyphosphoester, achieving 83.8% release of total loaded DOX in 140 h. The DOX-loaded vesicles can be successfully internalized by A549 cells, and it results in enhanced inhibition to A549 cell proliferation, likely owning to the sustained intracellular release of DOX as observed by CLSM. With these properties, the vesicles based on the block copolymer of PCL and PEEP are attractive as drug carriers for pharmaceutical application.     

Photoinduced optical anisotropy and reorientation in copolymers containing 4-methoxyazobenzene side groups and methyl methacrylate units using linearly polarized 633 nm light

Liquid crystalline (LC) and non-LC copolymers that contain 4-methoxyazobenzene side groups and methyl methacrylate units were synthesized to compare the photoinduced reorientation behavior using the polarization absorption spectra of thin films. Irradiating with non-polarized 365 nm light saturated the Z-isomer in the copolymer films and subsequent exposure to a linearly polarized (LP) 633 nm light generated a photoinduced optical anisotropy (ΔA) for all Z-isomer films based on an axis-selective Z-to-E photoisomerization. When a copolymer did not exhibit a LC nature, ΔA gradually increased until 60-80 mol% of the Z-isomers isomerized to the E-isomers, but decreased upon further photoisomerization reaction. On the other hand, the magnitude of the photoinduced ΔA of a film continuously increased for LC copolymers until E-isomer formation was saturated. Thermal amplification of the photoinduced ΔA was observed for LC copolymers, but the thermal treatment resulted in the disappearance of the photoinduced ΔA for the non-LC copolymers. The axis-selective Z-to-E photoisomerization that preserves the direction of the transition moment of both isomers caused the photoinduced ΔA and increased the liquid crystalline nature of the film during the Z-to-E photoisomerization to induce the self-organization of the mesogenic groups.     

Poly(m-phenylendiamine-co-o-aminophenol) coatings on mild steel: Effect of comonomers feed ratio on surface and corrosion protection aspects

Copolymer of m-phenylendiamine (mPD) and o-aminophenol (oAP) has been electrochemically deposited on mild steel from an aqueous solution of oxalic acid using cyclic voltammetric technique. The copolymer structure was confirmed by Proton Nuclear Magnetic Resonance (¹H NMR) and Attenuated Total Reflection Infrared (ATR-IR) spectroscopic techniques. Surface characterisation results indicated that the formed copolymer coatings posses uniform, smooth surface and strong adherence towards the metal surface. Corrosion performance of copolymer coatings was investigated in 0.5 M HCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) methods. Results showed that corrosion performance of copolymer coatings depends on the feed ratio of both the monomer units in copolymer chain. It was found that the copolymer feed ratio of mPD:oAP = 70/30 in coatings exhibited the highest performance due to its superior surface nature than other copolymer coatings.     

Rheological properties and interfacial tension of polypropylene-poly(styrene-co-acrylonitrile) blend containing compatibilizer

Rheological and morphological properties of the polypropylene (PP) and poly(styrene-co-acrylonitrile) (SAN) blend containing polypropylene-g-poly(styrene-co-acrylonitrile) (PP-g-SAN) was studied by advanced rheometric expansion system (ARES) and scanning electron microscopy (SEM). Blends of the PP-SAN (20/80) with compatibilizer of the PP-g-SAN, ranging from 0 to 20 wt% (phr) were prepared using a twin screw extruder. In the study of the complex viscosity of the PP-SAN (20/80) blend, the complex viscosity of the blend showed maximum value in the 1.0 phr PP-g-SAN copolymer content, which suggested that the compatibilizing effect of the PP-g-SAN copolymer was achieved. From the morphological studies, the PP-SAN (20/80) blend showed droplet dispersion type morphology, and the PP droplet size showed minimum value (0.44 μm) in the 1.0 phr PP-g-SAN copolymer content. The interfacial tension of the PP-SAN (20/80) blend was determined from the morphological studies and form relaxation time using the Palierne and the Choi and Schowalter models and showed minimum value in the 1.0 phr PP-g-SAN copolymer content in each models. The results of the interfacial tension was consistent with the results obtained from the rheological and morphological studies of the PP-SAN (20/80) blend. From the results of the morphological, rheological studies and the values of the interfacial tension, it was suggested that the compatibility of the PP-SAN (20/80) blend increased more in the 1.0 phr PP-g-SAN copolymer content.     

Morphology of PEO/PDMS blends during shear: Coexistence of two droplet/matrix structures and additive effects

The morphologies of blends of polyethyleneoxide (PEO 37) and poly(dimethylsiloxane)s (PDSM), with viscosity ratios, λ, of approximately one (PDMS 230) or 2.8 (PDMS 314, being the component of higher viscosity) and interfacial tensions on the order of 10 mN/m, were investigated at 70 °C as a function of shear rate (up to 10 s⁻¹) and of time. For the system PEO 37/PDMS 230 we have also studied the influence of the compatibilizer dimethyl-ethyleneoxide-copolymer (PDMS-co-PEO), which is only reasonably soluble in PEO. To investigate the morphologies we have used an optical shear cell in combination with a light microscope. The most important observation consists in the formation of two coexisting droplet/matrix structures for volume fractions of PDMS ranging from 0.4 to 0.6 for both λ values; the presence of the copolymer extends this region to 0.7. In the case of λ≈1 the average droplet radii are within experimental error independent of composition and morphology; for λ=2.8 they depend on the matrix phase in which they are contained and do again not vary with composition. The reduction in drop size caused by the copolymer is markedly larger if PEO forms the matrix. The present morphological observations suggest that the two coexisting droplet/matrix phases develop out of a single droplet/matrix structure via coalescence processes.     

Dispersion of polymer-grafted magnetic nanoparticles in homopolymers and block copolymers

The dispersion of magnetic nanoparticles (NPs) in homopolymer poly(methyl methacrylate) (PMMA) and block copolymer poly(styrene-b-methyl methacrylate) (PS-b-PMMA) films is investigated by TEM and AFM. The magnetite (Fe₃O₄) NPs are grafted with PMMA brushes with molecular weights from M = 2.7 to 35.7 kg/mol. Whereas a uniform dispersion of NPs with the longest brush is obtained in a PMMA matrix (P = 37 and 77 kg/mol), NPs with shorter brushes are found to aggregate. This behavior is attributed to wet and dry brush theory, respectively. Upon mixing NPs with the shortest brush in PS-b-PMMA, as-cast and annealed films show a uniform dispersion at 1 wt%. However, at 10 wt%, PS-b-PMMA remains disordered upon annealing and the NPs aggregate into 22 nm domains, which is greater than the domain size of the PMMA lamellae, 18 nm. For the longest brush length, the NPs aggregate into domains that are much larger than the lamellae and are encapsulated by PS-b-PMMA which form an onion-ring morphology. Using a multi-component Flory-Huggins theory, the concentrations at which the NPs are expected to phase separate in solution are calculated and found to be in good agreement with experimental observations of aggregation.     

Preparation of nanoporous films from self-assembled poly(vinyl chloride-g-methyl methacrylate) graft copolymer

We report on the preparation of nanoporous films based on an amphiphilic graft copolymer of poly(vinyl chloride-graft-methyl methacrylate), i.e., PVC-g-PMMA. The PVC-g-PMMA graft copolymer was synthesized via atom transfer radical polymerization (ATRP), as confirmed by nuclear magnetic resonance spectroscopy (¹H NMR), Fourier transform-infrared (FT-IR) spectroscopy, and gel permeation chromatography (GPC) analysis. The PVC-g-PMMA graft copolymer molecularly self-assembled into nanophase domains of PVC main chains and PMMA side chains, as revealed by wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). The graft copolymer film prepared from tetrahydrofuran (THF), a good solvent for both chains, had a random microphase-separated morphology. However, when prepared from dimethyl sulfoxide (DMSO), a solvent selectively good for PVC, the film exhibited a micellar morphology consisting of a PMMA core and a PVC corona. Nanoporous films with different pore sizes and shapes were prepared through the selective etching of PMMA chains using a combined process of UV irradiation and acetic acid treatment.     

Phase separation of polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) deposited on polystyrene thin films

Phase separation of a triblock copolymer, polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) on the thin films of a homopolymer, polystyrene (PS), was studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The final morphology after phase separation was found to be greatly dependent on the relation between the molecular weight of the PS block and homo-PS. Dispersed spherical and worm-like micelles of SEBS were observed when the molecular weight of homo-PS is smaller than the PS block in SEBS, while large structures with inner micro-phase separation of SEBS was found when the molecular weight of homo-PS was much higher than that of the PS block. The origin of such a change in morphology is attributed to the difference of structure and interfacial tension at the interface between the matrix homo-PS and the PS block in SEBS triblock copolymer assembly.     

Imprinting of nanopores in organosilicate dielectric thin films with hyperbranched ketalized polyglycidol

Hyperbranched polyglycidol (PG) was synthesized via a new polymerization pathway of glycidol using zinc glutarate (ZnGA) as a catalyst. ZnGA was found to be a highly active catalyst for the ring-opening polymerization of glycidol. The complex chemical structures of hyperbranched PG and its ketalized derivative (K-PG) were determined by specialized ¹³C nuclear magnetic resonance spectroscopic techniques. In addition, a new soluble silsesquioxane copolymer, poly(methylsilsequioxane-co-1,4-bis(ethylsilsesquioxane)benzene), i.e. a PMSSQ-BESSQB precursor, was synthesized via the sol-gel reaction of its monomers. The precursor solution was found to produce good quality thin films. K-PG was found to have good solubility in common solvents and good miscibility with the PMSSQ-BESSQB precursor. Moreover, K-PG was found to exhibit a sacrificial thermal decomposition characteristic that makes it suitable for use as a porogen in the fabrication of porous PMSSQ-BESSQB dielectric films. K-PG can be loaded into the PMSSQ-BESSQB precursor at concentrations up to 40 wt%. Synchrotron grazing incident small-angle X-ray scattering studies of the porous thin films prepared from PMSSQ-BESSQB/K-PG composite films with various compositions found that the average size of pores in the porous dielectric films varies from 6.7 to 18.5 nm as the initial loading of the K-PG porogen is increased from 10 to 40 wt%. These pores are spherical and have a sharp interface with the dielectric matrix. The porosities P of the porous PMSSQ-BESSQB films were found to increase almost linearly from 0 to 37 vol% as the initial loading of the K-PG porogen was increased up to 40 wt%. The presence of the imprinted pores reduced the refractive index n and dielectric constant kvalues of the PMSSQ-BESSQB films almost linearly as the initial loading of the K-PG porogen was increased. These results lead to the conclusions that the sacrificial thermal decomposition of the K-PG porogen molecules successfully imprints nanopores into the PMSSQ-BESSQB dielectric films and that the population of the imprinted pores increases proportionally with increases in the initial loading of the porogen, up to concentrations of 40 wt%. The pore structures and properties of the nanoporous PMSSQ-BESSQB films imprinted by the K-PG porogen indicate that they are good candidates for use as interdielectric materials in the fabrication of advanced microelectronic devices.     

Sequence distribution affect the phase behavior and hydrogen bonding strength in blends of poly(vinylphenol-co-methyl methacrylate) with poly(ethylene oxide)

Experimental results indicate that the PEO was miscible with PVPh-r-PMMA copolymers as shown by the existence of single composition-dependent glass transition temperature over the entire compositions. However, the PVPh-b-PMMA copolymer with PEO shows a like closed loop phase-separated region in this copolymer/homopolymer blend system. Furthermore, FTIR reveals that at least three competing equilibrium are present in these blends; self-association (hydroxyl-hydroxyl), interassociation (hydroxyl-carbonyl) of PVPh-co-PMMA, and hydroxyl-ether interassociation between PVPh and PEO. Based on the Painter-Coleman Association Model (PCAM), a value for inter-association, K_C=300 is obtained in PVPh-b-PMMA/PEO blend system at room temperature. Although the relative ratio of interassociation equilibrium constant of PEO to PMMA is larger in PVPh-b-PMMA/PEO blend system, the PVPh-r-PMMA/PEO blend system has greater Δν and greater homogeneity at the molecular scale than the PVPh-b-PMMA/PEO blend system because of the ΔK effect.     

Fabrication of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/chitosan blend material: synergistic effects on physical, chemical, thermal and biological properties

A new blend material was fabricated from poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] and chitosan through simple solvent casting method. In this investigation, the impact of different contents of chitosan and molar fractions of 4HB monomer towards the hybrid films was determined. The hydrophobic nature of the P(3HB-co-4HB) copolymer was modified by blending with a hydrophilic polymer—chitosan. Thus, the water-absorption capacity and solubility of the blend films were increased proportionally with the increasing content of chitosan. Miscibility of the blend films between the pure components was detected through Fourier transform infrared analysis. The thermal property was altered in terms of melting temperature, whereas the thermal stability of the blend films was greatly increased. Moreover, the scanning electron microscope images indicated that the surface of the blend films was homogenous and porous. Impregnation of chitosan enabled the blend films to exhibit antimicrobial activity against both Gram-negative and Gram-positive bacteria. The blend films with 20 wt% of chitosan were more hydrophilic, porous, biocidal and they have a wider opportunity in various applications such as wound dressing and tissue engineering than the native P(3HB-co-4HB) copolymer.     

Protective properties of polyaniline and poly(aniline-co-o-anisidine) films electrosynthesized on brass

Polyaniline and poly(aniline-co-o-anisidine) films were deposited on brass (Cu40Zn). The synthesis processes of homo and copolymer film were carried out under cyclic voltammetric condition from 0.12 M aniline and 0.06 M aniline + 0.06 M o-anisidine containing 0.2 M sodium oxalate solutions. Homo and copolymer films were characterized by scanning electron microscopy (SEM). SEM images clearly show that one of the brass electrodes was covered with a black copolymer film of strongly adherent homogeneous characteristic while the other one with a porous dark green homo polymer one. The corrosion performances of coated and uncoated electrodes in 3.5% NaCl were evaluated with the help of AC impedance spectroscopy, anodic polarization plots and open circuit potential–time curves. The protective effect of homo and copolymer films formed on brass grew in parallel with extended exposure time. It was only observed with copolymer-coated electrode that changes in the charge transfer resistance of copolymer-coated electrode were related to strong adsorption of copolymer film on the brass surface which led to the formation of a protective oxide layer due to its catalytic behaviour.