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.     

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.     

Gas transport in poly(n-alkyl acrylate)/poly(m-alkyl acrylate) blends

Poly(n-alkyl acrylate)s can have side chains that crystallize independently of the main chain; side-chain length can thus be used as a tunable parameter to control the gas permeability of membranes. The gas permeation response of poly(n-alkyl acrylate) and poly(m-alkyl acrylate) blends as a function of temperature is reported for varying side-chain lengths, n and m, and blend composition in the semi-crystalline and molten states. Macroscopic homogeneity is observed for a small range of n and m where |n − m| ≤ 2-4 methylene units. Thermal analysis indicates that the blend components crystallize independently of one another; however, crystallization is hindered by the presence of the other component. Permeation responses of the blends investigated in some cases exhibited two distinct permeation jumps or increases at the melting temperature of each component. Blends with continuous permeation responses but higher effective activation energies of permeation (i.e., more thermally responsive) were observed for some blends over the temperature of interest for membranes to be used for modified atmosphere packaging.     

Grafting of end-functionalized poly(tert-butyl acrylate) to poly(ethylene-co-acrylic acid) film

Poly(tert-butyl acrylate) (PtBA) was grafted to the surface of poly(ethylene-co-acrylic acid) (EAA) film and the pendant groups of the tethered PtBA were modified to create chemically tailored surface modifying layers. The carboxylic acid groups in the copolymer film served as the grafting sites for the covalent tethering of end-functionalized PtBA. The progression of these reactions was monitored using attenuated total reflectance (ATR)-FTIR and X-ray photoelectron (XPS) spectroscopies along with static contact angle measurements. By controlling the reaction conditions, the chemical functionality of the grafted layer ranged from tert-butyl ester (EAA-g-PtBA) to carboxylic acid (EAA-g-PAA) and was demonstrated by corresponding changes in wettability. The choice of PtBA as the tethered polymer allows for the subsequent substitution of the tert-butyl ester groups. To demonstrate, a novel procedure was used to replace the tert-butyl ester with N,N-dimethylethylenediamine (DMEDA) to form EAA-g-PDMEDA. These reaction schemes can be used to create tunable surface-grafted layers with various pendant group chemistries.     

Structural studies of poly(butyl acrylate) - poly(ethylene oxide) miktoarm star polymers

Structural behavior of miktoarm star polymers comprising poly(butyl acrylate) (PBA) and poly(ethylene oxide) (PEO) arms was studied by means of Differential Scanning Calorimetry (DSC), Wide Angle X-Ray Scattering (WAXS), Polarized Optical Microscopy (POM) and Fourier Transform Infrared Spectroscopy (FTIR) methods. The aim of this study was to correlate changes in the composition of the arms of the PBA/PEO miktoarm star polymers with their structures. As a consequence of increasing PBA content, the decrease in crystallinity of the studied PBA/PEO heteroarm star copolymers was observed. Regardless of the copolymer composition, fraction of oxyethylene units in the crystalline PEO phase was similar in all investigated systems. The POM images showed spherulitic morphology of the materials having low PBA content, while an increase in PBA arms fraction leads to the formation of less ordered structures. The analysis of FTIR vibrational spectrum indicates helical conformation of PEO chains in the crystalline phase. Isothermal crystallization studies carried out using the FTIR technique suggest the existence of isolated domains in the nanoscopic scale of investigated materials.     

Synthesis and characterisation of hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) backbones via atom transfer radical polymerisation

Hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) (PMMA-b-PBA) backbones have been prepared via atom transfer radical polymerisation (ATRP) together with a nucleophilic substitution reaction. A hydroxyl-functionalised PMMA macroinitiator (HO-PMMA-Br) was prepared via ATRP at the optimised reaction temperature (60 °C) using 2-hydroxyethyl 2-bromoisobutyrate as the initiator. The high functionality of the bromo end group in the macroinitiator was confirmed by both ¹H NMR technique and a chain-extension reaction. Electrospray ionisation mass spectrometer proved to be a valuable tool for characterising PMMAs with a bromo end group (PMMA-Br), which provided signals corresponding to the intact polymers although multiply charged polymer chains were observed. The well-defined block copolymers HO-PMMA-b-PBA-Br were obtained by the ATRP of n-butyl acrylate using HO-PMMA-Br as a macroinitiator in a one-pot reaction at 100 °C. The kinetics as well as the dependence of the M_n,SEC and PDIs of the obtained block copolymers on the conversions of n-butyl acrylate in the chain-extension reaction suggested negligible radical termination during the reaction, demonstrating that the well-defined HO-PMMA-b-PBA-Br with a high functionality of bromo end group were obtained. The nucleophilic substitution reaction of a monohydroxyl-functionalised block copolymer HO-PMMA-b-PBA-Br with 5-amino-1-pentanol in dimethyl sulfoxide at room temperature was verified with ¹H and ¹³C NMR techniques, which resulted in a series of telechelic polymers HO-PMMA-b-PBA-OH with a functionality of hydroxyl groups up to 1.7 according to the gradient polymer elution chromatography.     

Synthesis and dipole-dipole interaction-induced mesomorphic behavior of poly(oxyethylene)s containing (n-octylsulfonyl)alkylthiomethyl or (n-octylsulfonyl)alkylsulfonylmethyl side groups

Two series of ((n-octylsulfonyl)alkylthio)methyl-substituted poly(oxyethylene)s ((-OCH₂CHR-)_n, where R=-CH₂S(CH₂)_MSO₂(CH₂)₈H) (OTP-M, M=3,4,5,6,7,9,12), and ((n-octylsulfonyl)alkylsulfonyl)methyl-substituted poly(oxyethylene) ((-OCH₂CHR-)_n, where R=-CH₂SO₂-(CH₂)_MSO₂(CH₂)₈H) (OSP-M, M=3,4,5,6,7,9,12), were synthesized using polymer analogous reactions from poly(epichlorohydrin) to study the effect of dipole-dipole interactions of the sulfone groups (SO₂) on the ordered structures of the poly(oxyethylene) derivatives. The ordered phases of these polymers were studied using polarizing optical microscopy, X-ray diffraction, differential scanning calorimetry and IR spectroscopy. OTP-Ms and OSP-3 showed ordered phases originated from side chain crystallization, while OSP-Ms except OSP-3 showed liquid crystalline behavior. The poly(oxyethylene) derivatives with M=5,6,7 had double-layer structures, while the polymers with M=3,4,9,12 had intercalating double-layer structures at room temperature. The layer structures of the poly(oxyethylene) derivatives were found to be affected by the positions of the side chain sulfone groups which can generate strong dipole-dipole interactions.     

Spontaneous polymerization and chain microstructure evolution in high-temperature solution polymerization of n-butyl acrylate

This study concerns understanding of the underlying mechanistic pathways in high temperature solution polymerization of n-butyl acrylate (nBA) in the absence of added thermal initiators. The particular system of interest is the batch polymerization of nBA in xylene at temperatures between 140 and 180 °C with initial monomer content between 20 and 40 wt%. A mechanistic process model is developed to capture the dynamics of the polymerization system. Postulated reaction mechanisms include chain-initiation by monomer (self-initiation), chain-initiation by unknown impurities, chain-propagation by secondary and tertiary radicals, intra-molecular chain-transfer to polymer (back-biting), chain-fragmentation (β-scission), chain-transfer to monomer and solvent, and chain termination by disproportionation and combination. The extent of the reactions is quantified by estimating the reaction rate constants of the initiation and the secondary reactions, based on a set of process measurements. The set of measurements considered in the parameter estimation includes monomer conversion, number- and weight-average molecular weights, and average number of chain-branches per chain (CBC). Effect of temperature on chain microstructures was observed to be most evident when microstructures are expressed in terms of their quantities per chain. The evolution of other microstructural quantities such as average number of terminal double bonds per chain (TDBC) and average number of terminal solvent groups per chain (TSGC) was then also investigated. Microstructural quantities per polymer chain (TDBC, TSGC, CBC) are defined based on combinations of ¹³C, ¹H NMR and chromatographic measurements. This study presents (i) a mechanistic explanation for the competing nature of short-chain-branch and terminal double bond formation (i.e. as temperature increases, number of chain branches per chain decreases and number of terminal double bonds per chain increases), (ii) quantitative insights into dominant modes of chain-initiation and chain-termination reactions, and (iii) mechanistic explanations for the observed spontaneous polymerization. The study also reports estimated Arrhenius parameters for second-order self initiation, tertiary radical propagation, secondary radical backbiting and tertiary radical β-scission reaction rate constants. Validation of the mechanistic process model with the estimated Arrhenius parameters and comparison of estimated parameter values to recently reported estimates are also presented.     

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.     

Morphology of poly[(t-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-b-(t-butyl acrylate)] pentablock terpolymers and their thermal conversion to the acrylic acid form

The morphology of a synthesized poly[(tert-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-(tert-butyl acrylate)] pentablock terpolymer was determined using transmission electron microscopy, atomic force microscopy and small angle X-ray scattering methods. The outer blocks of this material were converted to the acrylic acid form by a thermal process that caused a beta-scission reaction in a simple thermal process, as verified by FTIR and NMR spectroscopies as well as thermogravimetric analysis. An initial heat-vacuum treatment induced a morphology that was more disordered relative to the precursor material, but when these samples were recast in THF solvent and annealed again, a considerably more refined and ordered morphology consisting of hexagonally packed cylinders resulted. This simple heat treatment allows for the tert-butyl groups to be converted to acrylic acid groups without dissolving the polymer or further sample cleaning. A dynamic mechanical investigation of the PtBuA form revealed three or two relaxation features depending interpretations based on the presence of three-phase morphology or a two-phase morphology in which there are mixed hard block domains.     

Solution homopolymerizations of n-butyl acrylate and styrene mediated using 2,2,5-trimethyl-4-tert-butyl-3-azahexane-3-oxyl (TITNO)

Use of Styryl-TITNO (the styrene alkoxyamine of 2,2,5-trimethyl-4-tert-butyl-3-azahexane-3-oxyl) as mediator for nitroxide-mediated polymerization (NMP) of n-butyl acrylate (BA) and styrene has been investigated at temperatures ≤110 °C. Very good control of molecular weight and molecular weight dispersity with no measurable loss of active chains, and no evidence of tails in the molecular weight distribution as conversion increases, was observed at 90 °C for BA and at 70 °C for styrene. The alkoxyamine dissociation equilibrium constant values determined for polyBA-TITNO (8.5 × 10⁻¹¹ mol L⁻¹ at 90 °C) and polystyrene-TITNO (3.1 × 10⁻⁹ mol L⁻¹ at 70 °C) are consistent with those required for control when using more established nitroxides that require higher temperatures to achieve these values. The lower optimum polymerization temperatures with Styryl-TITNO as mediator provide new opportunities for NMP and are especially significant for styrene since this appears to eliminate completely the complications from thermal initiation.     

Microwave polymerization of poly(methyl acrylate): Conversion studies at variable power

Methyl acrylate (MA) was polymerized by microwave radiation at three different powers, namely, 200, 300, and 500 W. The percentage conversion of the reaction was followed by Fourier transform infrared (FTIR) spectroscopy. The specimen temperature during the polymerization process was measured to select a suitable temperature for comparison with the conventional method. The results indicate that a similar comparable temperature of about 52° was found for all the microwave power settings tested. The microwave polymerization process was compared with that of the thermal method at 52(±1)° under comparable reaction conditions. The reaction rate enhancement of the microwave polymerization compared to the thermal method was found to be as follows: 275% for the 500 W, 220% for the 300 W, and 138% for the 200 W, indicating a significant correlation between the reaction rate enhancement and the level of microwave power used.     

Waterborne polyurethane/poly(n-butyl acrylate-styrene) hybrid emulsions: Particle formation,film properties,and application

In this work, a hybrid synthesis technology has been used to fabricate waterborne polyurethane (WPU)/poly(n-butyl acrylate-styrene) (PBS) emulsions with dimethylol-propionic acid (DMPA) as chain extender. The influences of the PBS, styrene, and DMPA contents on the physical properties of the resultant emulsions and cast films have been investigated in detail using various characterization methods. The experimental results show that with an increase in the PBS or styrene content, the particle size in emulsions increases but the viscosity of the emulsions decreases and that the opposite applies for the DMPA content. For cast films, with an increase in the styrene or DMPA content, the tensile strength increases whereas the elongation decreases. The water absorption capacity of the film decreases with an increase in the styrene content or a decrease in the DMPA content. Furthermore, the emulsions synthesized have been used for paper sizing applications. The treated papers exhibit greatly improved water resistance, and the Cobb values at 30 and 60 s are only 10.23 and 11.89%, respectively, of those of unsized papers. The other paper properties, such as gloss, smoothness, folding resistance, and burst strength, are also considerably improved.     

Surface segregation and miscibility in blends of poly(ethyl acrylate) with poly(vinylidene fluoride-co-hexafluoroacetone)

In blends of poly(ethyl acrylate) (PEA) and poly(vinylidene fluoride-co-hexafluoroacetone) [P(VDF-HFA)], surface segregation of the P(VDF-HFA) component was confirmed by X-ray photoelectron spectroscopy. The PEA/P(VDF-HFA) blends exhibited lower critical solution temperature phase behaviour, with a critical temperature of 150°C. Since the surface tension value of P(VDF-HFA) is lower than that of PEA, this may influence surface segregation behaviour in PEA/P(VDF-HFA) blends. Surface segregation results of the PEA/P(VDF-HFA) blends are compared with those from a previous study on immiscible acrylate copolymer/fluoro copolymer blends.     

Synthesis and phase separation during film formation of novel methyl methacrylate/n-butyl acrylate/methacrylic acid (MMA/BA/MAA) hybrid urethane/acrylate colloidal dispersions

Hybrid acrylic/urethane colloidal dispersions were prepared by incorporation of a novel multifunctional urethane castor vinyl ether (UCVE) macromonomer derived from castor oil in acrylic latexes. Single-stage and two-stage semi-continuous emulsion polymerization processes were utilized to control placement of UCVE in colloidal dispersions with core/shell and spherical particle morphologies. While the single-stage process resulted in optically clear and chemically homogeneous films, the two-stage process led to heterogeneous film formation. Internal reflection infrared imaging (IRIRI) spectroscopic analysis of the film-air (F-A) interfaces revealed phase-separated urethane- and urea-rich domains ranging in size from approximately 4-40 μm. Based on these measurements, a model of film formation is proposed which incorporates the effect of exceedingly high shear conditions to achieve fine dispersions of UCVE. These experiments indicate that features of the single-stage process facilitate uniform dispersion of UCVE and efficient grafting between UCVE and the acrylic polymer matrix resulting in intimately mixed networks and homogeneous films.     

Synthesis and characterization of copolymers of 5,6-benzo-2-methylene-1,3-dioxepane and n-butyl acrylate

The ATRP copolymerization of 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) with n-butyl acrylate (nBA) was studied by using ethyl 2-bromoisobutyrate (EBriBu) and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA)/Cu(I)Br as the initiator and catalyst, respectively. The reactivity ratios of the monomers in the copolymerization were determined using the Kelen-Tüdõs method and were found to be r_BMDO=0.08 and r_nBA=3.7. The copolymer yield decreased with higher amounts of BMDO in the initial feed. The structure of these copolymers was thoroughly characterized by 1D and 2D NMR techniques and quantitative ring opening of BMDO in its copolymerization was demonstrated. The hydrolytic degradation behavior of the BMDO/nBA copolymers was also studied.     

Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) synthesis and properties

Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) or P(EXA-r-tBA)-PCEA was synthesized by atom transfer radical polymerization. Reactivity ratios of EXA and tBA for copolymerization were determined. The specific refractive index increments of six diblocks were measured as a function of their composition. The diblocks were thermally stable and formed micelles in an automobile engine oil. Such micelles may be useful as an anti-friction additive in lubricating oils.     

Nanopatterns of poly(styrene-block-butyl acrylate) block copolymer brushes on the surfaces of exfoliated and intercalated clay layers

We report a study of poly(styrene-block-butyl acrylate) (PSBA) block copolymer brushes on the surfaces of intercalated and exfoliated silicate (clay) layers. The PSBA/clay nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. Transmission electron microscopy (TEM) analysis showed the existence of both intercalated and exfoliated structures in the nanocomposite. Block copolymer brushes on the surface of exfoliated or intercalated clay layers were found to create nanopatterns after treatment in different solvents. For the block copolymer brushes after treatment in THF, uniform collapsed brush layers are observed. After treatment in acetone, a selective solvent for PBA, wormlike surface aggregates are observed. After treatment in methanol, a precipitant for both of the blocks, micelles as well as wormlike aggregates can be observed. Furthermore, the polymer brushes tend to aggregate together and change their nanopatterns at an elevated temperature.     

Fabrication and apparent kinetic study of poly(methyl methacrylate)/poly(octyl acrylate) and poly(octyl acrylate)/poly(methyl methacrylate) latex interpenetrating polymer networks

Two latex interpenetrating polymer networks (LIPNs) were synthesized with methyl methacrylate (MMA) and octyl acrylate (OA) as monomers, respectively. The apparent kinetics of polymerization for the LIPNs was studied. This demonstrates that network II does not have a nucleus formation stage. The monomers of network II were diffused into the latex particles of network I and then formed network II by in situ polymerization. It indicates that the polymerization of network I obeys the classical kinetic rules of emulsion polymerization. But the polymerization of network II only appears a constant‐rate stage and a decreasing‐rate stage. The apparent activation energies (E_a) of network I and network II of PMMA/POA were calculated according to the Arrhenius equation. The E_a values of POA as network I (62 kJ/mol) is similar to that of POA as network II PMMA/POA (60 kJ/mol). However, the E_a value of PMMA as network II POA/PMMA (105kJ/mol) is higher than that of PMMA as network I (61 kJ/mol). Results show that the E_a value of the network II polymerization is related to the properties of its seed latex. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Glass transition behaviour of poly(ether ether ketone)/poly(aryl ether sulphone) blends: dynamic mechanical and dielectric relaxation studies

Blends of poly(ether ether ketone) (PEEK) and poly(aryl ether sulphone) (PES) have been prepared in the whole composition range. The molecular dynamics and α-relaxation behaviour of these materials have been studied using dynamic mechanical and dielectric relaxation spectroscopy. From dynamic mechanical relaxation studies, two α-relaxation peaks corresponding to the segmental relaxation process of pure components in the blend was observed. Also, it was found that the temperature at which α-process of the homopolymers occurs, shows a slight change with blend composition, corresponding to a PEEK-rich and PES-rich phase. The relaxation intensities of the homopolymers in the blend compared to that in pure state were approximately proportional to their respective content in the blend. From the phase composition of the respective phases obtained using Fox equation, it has been inferred that PEEK dissolves more in PES than vice-versa. The α-relaxation of PES could not be detected from dielectric relaxation spectroscopy because of the possible influence of dc conduction and electrode polarization losses. Otherwise, the α-relaxation behaviour of PEEK-rich phase observed from dielectric relaxation studies agree with those inferred from dynamic mechanical relaxation studies. Furthermore, activation energies for molecular motions (E_a) at the α-relaxation have also been determined using an Arrhenius form of equation and it has been found that E_a for both PEEK-rich and PES-rich phase show variation with composition. Similarly, the relaxation times associated with the mobility of relaxing species in both PEEK and PES are influenced in the blends. It is likely that these observations are related to some interactions and a partial segmental mixing between the blend components, which result in changes in the local molecular environment on blending.