Microstructure study of styrene/n-butyl acrylate emulsion copolymers by 13C nuclear magnetic resonance spectroscopy

A detailed study of the sequence distribution in styrene (S)/n-butyl acrylate (A) emulsion copolymers using ¹³C nuclear magnetic resonance spectroscopy is reported. From the interpretation of the spectra of the homopolymers and copolymers, assignment of the carbonyl (A) and quaternary (S) carbon atom resonances has been made. This provides a quantitative estimation of the compositional triad distributions in the copolymers. The results were found to be in relatively good agreement with calculated triad fractions deduced from a simulation program taking into account the actual reactivity ratios and type of emulsion process.     

Tailoring the swelling and glass‐transition temperature of acrylonitrile/hydroxyethyl acrylate copolymers

Novel polyacrylonitrile (PAN)‐co‐poly(hydroxyethyl acrylate) (PHEA) copolymers at three different compositions (8, 12, and 16 mol % PHEA) and their homopolymers were synthesized systematically by emulsion polymerization. Their chemical structures and compositions were elucidated by Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR spectroscopy. Intrinsic viscosity measurements revealed that the molecular weights of the copolymers were quite enough to form ductile films. The influence of the molar fraction of hydroxyethyl acrylate on the glass‐transition temperature (T_g) and mechanical properties was demonstrated by differential scanning calorimetry and tensile test results, respectively. Additionally, thermogravimetric analysis of copolymers was performed to investigate the degradation mechanism. The swelling behaviors and densities of the free‐standing copolymer films were also evaluated. This study showed that one can tailor the hydrogel properties, mechanical properties, and T_g's of copolymers by changing the monomer feed ratios. On the basis of our findings, PAN‐co‐PHEA copolymer films could be useful for various biomaterial applications requiring good mechanical properties, such as ophthalmic and tissue engineering and also drug and hormone delivery. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Pyrolysis of random and block copolymers of ethyl acrylate and methyl methacrylate

Pyrolysis gas chromatography can distinguish random from block copolymers of ethylacrylate and methyl methacrylate. The pyrograms depend on the pyrolytic temperature, the ratio of copolymerized monomers, the degree of conversion, and the method of polymerization. Larger amounts of ethyl methacrylate and methyl acrylate are formed on pyrolysis of random copolymers than of block copolymers. The presence of mixed dimers indicates random copolymerization. The sum of the percent recovery of ethyl alcohol and ethyl acrylate is fairly constant over a range of compositions and monomer sequence. Random copolymers produce less ethyl alcohol than ethyl acrylate on pyrolysis, while homopolymers and block copolymers produce more ethyl alcohol and less ethyl acrylate. In a set of random copolymers with different EA/MMA ratios, there is an increasing per cent recovery of EA monomer with decreasing EA in the copolymer, while ethyl alcohol shows the opposite behavior. The characteristic degradation patterns are thought to be governed by the availability of the tertiary hydrogen for abstraction by the alkoxy oxygen of a neighboring acrylate unit, the availability depending on the sequence distribution of acrylate/methacrylate molecules.     

Multivariate analysis of C NMR spectra of methacrylate copolymers and homopolymer blends

¹³C NMR spectra of copolymers of methyl methacrylate and tert-butyl methacrylate with various chemical compositions, the homopolymers of the two methacrylates, and blends of the homopolymers with various blend ratios were subjected to principal component analysis. The first and second principal components correlated chemical composition and the randomness of comonomer sequence, respectively. Chemical composition of the copolymers was determined with high accuracy and precision by the partial least-squares regression without assignment of individual resonance peaks.     

Copolymers of Phenoxyethyl Methacrylate with Butyl Methacrylate: Synthesis,Characterization and Reactivity Ratios

Phenoxyethyl methacrylate (POEMA) and butyl methacrylate (BMA) were copolymerized by free-radical copolymerization using α,α′-azobisisobutyronitrile (AIBN) in 2-butanone solution at 333±1 K. Copolymers were characterized by FTIR, ¹H-NMR and ¹³C-NMR spectroscopic methods and by comparison of the spectra with the corresponding homopolymers. Thermogravimetric analysis of the copolymers was carried out in order to know their thermal stability. Copolymer composition was established by ¹H-NMR analysis. Monomer reactivity ratios (MRR) were computed using the classical Fineman – Ross (FR) and Kelen – Tüdos (KT) procedures. MRR were also estimated using a nonlinear computational fitting procedure, known as reactivity ratios error in variable model (RREVM). The mean sequence lengths of the copolymers were estimated and suggest that random copolymers were obtained.     

Synthesis of copolymers containing opposite charged comonomers and their interactions with metal ions

Radical polymerization was used to synthesize three copolymers of [3‐(methacryloylamino)propyl]trimethylammonium chloride and methacrylic acid [P(MPTA‐co‐MA)]; three copolymers of MPTA and 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid [P(MPTA‐co‐APSA)], which had different feed monomer mole ratios but a constant total number of moles (0.03 mol); and the homopolymers poly(MPTA), poly(MA), and poly(APSA). The yields for all homopolymers and copolymers were over 70 and 90%, respectively. All products were dissolved in water, purified, and fractioned by an ultrafiltration membrane with different exclusion limits of the molecular weight (3,000, 10,000, 30,000, and 100,000 g mol^?1). All fractions were lyophilized. The polymeric materials were characterized by FTIR and ¹H‐NMR spectroscopy. The metal ion interaction with the hydrophilic polymers was determined as a function of the pH and the filtration factor. It was dependent on the pH, type of ligand group, and charge of the metal ion. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1715–1721, 2003     

Design of novel poly(methyl vinyl ether) containing AB and ABC block copolymers by the dual initiator strategy

A new set of block copolymers containing poly(methyl vinyl ether) (PMVE) on one hand and poly(tert-butyl acrylate), poly(acrylic acid), poly(methyl acrylate) or polystyrene on the other hand, have been prepared by the use of a novel dual initiator 2-bromo-(3,3-diethoxy-propyl)-2-methylpropanoate. The dual initiator has been applied in a sequential process to prepare well-defined block copolymers of poly(methyl vinyl ether) (PMVE) and hydrolizable poly(tert-butyl acrylate) (PtBA), poly(methyl acrylate) (PMA) or polystyrene (PS) by living cationic polymerization and atom transfer radical polymerization (ATRP), respectively. In a first step, the Br and acetal end groups of the dual initiator have been used to generate well-defined homopolymers by ATRP (resulting in polymers with remaining acetal function) and living cationic polymerization (PMVE with pendant Br end group), respectively. In a second step, those acetal functionalized polymers and PMVE-Br homopolymers have been used as macroinitiators for the preparation of PMVE-containing block copolymers. After hydrolysis of the tert-butyl groups in the PMVE-b-ptBA block copolymer, PMVE-b-poly(acrylic acid) (PMVE-b-PAA) is obtained. Chain extension of the AB diblock copolymers by ATRP gives rise to ABC triblock copolymers. The polymers have been characterized by MALDI-TOF, GPC and ¹H NMR.     

Synthesis, Characterization and Reactivity Ratios of Phenylethyl Acrylate/Methacrylate Copolymers

2-Phenylethyl acrylate (PEA) and 2-Phenylethyl methacrylate (PEMA) were synthesized by reacting 2-Phenyl ethanol with acryloyl and methacryloyl chloride respectively. Homopolymers and copolymers were prepared by free radical polymerization technique using benzoylperoxide as initiator. Copolymers of PEA and PEMA with methyl acrylate (MA) and N-vinyl pyrollidone (NVP) of different compositions were prepared. The monomers and polymers were characterized by IR and NMR techniques. Thermal stability of the polymers were determined by TG analysis. The composition of the copolymer was determined using ¹H-NMR analysis. The reactivity ratios of the monomers were determined by the application of Finemann–Ross and Kelen–Tudos methods. The prepared copolymers were tested on leather for their pressure sensitive adhesive property.     

Monomer reactivity ratios in UV-initiated free-radical copolymerization reactions

The homopolymers of styrene (S) and vinyl acetate (VA) and their copolymers were prepared in bulk by ultraviolet (UV)-radiation-initiated free-radical polymerization with azobisisobutyronitrile (AIBN) as an initiator. The reacitivity ratios for these copolymerizations were determined by analyzing the monomer content in the copolymers by UV spectroscopy. The same method was extended to other copolymers of styrene such as styrene–methyl methacrylate and styrene–ethyl acrylate. A new analysis method was developed to measure reactivity ratios. For this purpose, UV light was used as a photochemical initiator and UV absorption spectroscopy was used for the determination of the instantaneous composition of copolymers. Nuclear magnetic resonance (NMR) was used to calculate percent conversion. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of styrene–acrylic ester copolymers

Homopolymers and copolymers of styrene and different acrylic esters (i.e., acrylates) were synthesized by the free‐radical solution polymerization technique. Feed ratios of the monomers styrene and cyclohexyl acrylate/benzyl acrylate were 90 : 10, 75 : 25, 60 : 40, 50 : 50, 40 : 60 and 20 : 80 (v/v) in the synthesis of copolymers. All 6 homopolymerizations of acrylic ester synthesis were carried out in N,N(dimethyl formamide) except for the synthesis of poly(cyclohexyl acrylate) (PCA), where the medium was 1,4‐dioxane. Benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN) were used as initiators. The polymers synthesized were characterized by FTIR, ¹H‐NMR, ¹³C‐NMR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and viscosity measurements. The reactivity ratios were determined by the Fineman–Ross method using ¹H‐NMR spectroscopic data. The reactivity ratios (r) for the copolymerization of styrene (r_S) with cyclohexyl acrylate (r_CA) were found to be r_S = 0.930 and r_CA = 0.771, while for the copolymerization of styrene with benzyl acrylate, the ratios were found to be r_S = 0.755 and r_BA = 0.104, respectively. The activation energies of decomposition (E_a) and glass‐transition temperature (T_g) for various homo‐ and copolymers were evaluated using TGA and DSC analysis. The activation parameters of the viscous flow, voluminosity (V_E) and shape factor (ν) were also computed for all systems using viscosity data. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1513–1524, 2001     

Toughening effect of comonomer on acrylic denture base resin prepared via suspension copolymerization

In this article, three copolymers used as denture base resins were prepared via suspension copolymerization using butyl acrylate (BA), butyl methacrylate (BMA), or methyl acrylate (MA) with methyl methacrylate (MMA), respectively. The homopolymers and copolymers were characterized by ¹³C nuclear magnetic resonance (¹³C NMR). The influence of the three comonomers on the mechanical property was investigated in details and the fracture surfaces of copolymer specimens were examined using scanning electron microscopy (SEM). Meanwhile, the T_g values of three copolymers were examined by differential scanning calorimetry (DSC). The results indicate that, poly(methyl methacrylate) (PMMA) copolymers with BA, BMA, or MA have been successfully prepared via suspension copolymerization. The presence of BA, BMA, or MA could improve the mechanical property especially the impact strength, the toughness of the materials was remarkably improved. The toughening effect of BMA monomer is most significant. When the content of BA is 2 wt %, the flexural strength improves by 51% and the impact strength improves by 81.3%. The T_g values of three copolymers all decrease. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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.     

Synthesis of third-order nonlinear optical polyacrylates containing an azobenzene side chain via atom transfer radical polymerization

A series of polyacrylates containing different substituted-azobenzene chromophores were synthesized and polymerized via atom transfer radical polymerization. Nonlinear optical homopolymers containing an azobenzene side chain, of controllable molecular mass and low polydispersity (1.1–1.4) were obtained. In addition, side-chain copolymers were prepared in which the composition of the copolymers was controlled by using different feed ratios of the azobenzene monomer and methyl methacrylate. The third-order nonlinear optical properties of azobenzene monomers and their polymers were measured using the degenerated four-wave mixing technique. Each of the polymers displayed a high χ⁽³⁾ of about 10^?11 esu and rapid response time in femto-second magnitude. The effect of substituents on the azobenzene group and the composition of the polymer chain on the third-order nonlinear optical properties of the polymers were investigated.     

Synthesis and characterization of some water soluble polymers

Homopolymers and copolymers of acrylamide (AA) and acrylic acid (AAc) were synthesized by the free radical solution polymerization technique. Feed ratios of the monomers were 85 : 15 (w/w), 65 : 35 (w/w), and 50 : 50 (w/w) of acrylamide and acrylic acid, respectively, for synthesis of copolymers. All reactions were carried out in aqueous media, except for the synthesis of polyacrylic acid, where the medium was n-butanol. Hydrogen peroxide, potassium persulfate, and benzoyl peroxide were used as initiators. The copolymers were purified by removing homopolymers. The homopolymers and copolymers were characterized by infrared (IR), ¹³C-nuclear magnetic resonance (NMR), ¹H-NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and viscosity measurements. The fusion temperature and the energy change for various phase transitions were obtained from DSC measurements. The activation energy values for various stages of decomposition were calculated from TGA. The activation parameters for the viscous flow (i.e., free energy, enthalpy, and entropy of activation) were evaluated from the viscosity measurements. Voluminosity and Simha shape factor were also calculated for different systems. Effects of various concentrations of electrolytes, NaNO₃, and Al(NO₃)₃ on viscosity behavior were studied. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 45–56, 1997     

Stereocomplex crystallization and spherulite growth behavior of poly(l-lactide)-b-poly(d-lactide) stereodiblock copolymers

The non-isothermally and isothermally crystallized stereodiblock copolymers of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) with equimolar l-lactyl and d-lactyl units and different number-average molecular weights (M_n) of 3.9 × 10³, 9.3 × 10³, and 1.1 × 10⁴ g mol⁻¹, which are abbreviated as PLLA-b-PDLA copolymers, contained only stereocomplex crystallites as crystalline species, causing higher melting temperatures of the PLLA-b-PDLA copolymers compared to those of PLLA homopolymers. In the case of non-isothermal crystallization, the cold crystallization temperatures of the PLLA-b-PDLA copolymers during heating and cooling were respectively lower and higher than those of PLLA homopolymers, indicating accelerated crystallization of PLLA-b-PDLA copolymers. In the case of isothermal crystallization, in the crystallizable temperature range, the crystallinity (X_c) values of the PLLA-b-PDLA copolymers were lower than those of the PLLA homopolymers, and were susceptible to the effect of crystallization temperature in contrast to that of homopolymers. The radial growth rate of the spherulites (G) of the PLLA-b-PDLA copolymers was the highest at the middle M_n of 9.3 × 10³ g mol⁻¹. This trend is different from that of the PLLA homopolymers where the G values increased monotonically with a decrease in M_n, but seems to be caused by the upper critical M_n values of PLLA and PDLA chains as in the case of PLLA/PDLA blends (in other papers), above which homo-crystallites are formed in addition to stereocomplex crystallites. The disturbed crystallization of PLLA-b-PDLA copolymers compared to that of the PLLA/PDLA blend is attributable to the segmental connection between the PLLA and PDLA chains, which interrupted the free movement of those chains of the PLLA-b-PDLA copolymers during crystallization. The crystallite growth mechanism of the PLLA-b-PDLA copolymers was different from that of the PLLA/PDLA blend.     

Orientation in acrylonitrile copolymers

Rubber modified and unmodified poly(acrylonitrile/methyl acrylate) (75/25) copolymers [(Barex^® resins) (Barex^® is a registered trademark of Vistron Corporation, a subsidiary of The Standard Oil Company, Ohio)] were stretched at varying strain rates at different temperatures. Molecular orientation of the stretched samples at different extension ratios was determined using birefringence, the X-ray orientation factor, and infrared dichroism. The birefringence of rubber modified copolymers, which were prepared by graft copolymerization of the poly(acrylonitrile/methyl acrylate) copolymer with 10 parts (by weight) of a poly(butadiene/acrylonitrile) rubber, is found to be appreciably different as compared with the birefringence of unmodified poly(acrylonitrile/methyl acrylate) copolymer. The possible reasons for this difference are discussed. The orientation measured from the three techniques is compared, and the effects of temperature of stretching and of strain to are discussed. The maximum values of the birefringence of these two copolymers and that of the polyacrylonitrile have been estimated. Transition moment angles for CH₂ and C?N stretching bonds are obtained. From the birefringence data at various temperatures and strain rates, the activation energies of these two copolymers have been obtained.     

Copolymerizations involving N-vinyl-2-pyrrolidone

Low conversion copolymerizations have been conducted with N-vinyl-pyrrolidone (VP) as monomer-1 and the following reagents were used as monomer-2: acryloxymethylpentamethyldisiloxane (AMS), methacryloxymethylpentamethyl disiloxane (MMS), n-butyl acrylate (BA) and 2-hydroxyethylmethacrylate (HEMA). In the same order the derived monomer reactivity ratios (r₁, r₂) were (0.34, 1.57); (0.04, 4.92); (0.02, 0.80) and (0.05, 3.12). For a range of different feed compositions within each system integral curves were thereby computed for the instantaneous copolymer composition throughout all stages of conversion. These gave predictions on compositional heterogeneity which compared satisfactorily with the clear, translucent or opaque appearance of copolymers prepared to very high conversion via γ-irradiation. However, the VP-HEMA system, for which there is no azeotropic composition, yielded optically clear copolymers at all feed compositions. This finding is explained on the basis of the almost iso-refractive nature of the two homopolymers and/or strong thermodynamic compatibility among copolymers and homopolymers as evidenced by a single T_g observed on cast films.     

Investigations on the morphology and melt crystallization of poly(L‐lactide)‐poly(ethylene glycol) diblock copolymers

Ring opening polymerization of L ‐lactide was realized in the presence of monomethoxy poly(ethylene glycol), using zinc lactate as catalyst. The resulting PLLA‐PEG diblock copolymers were characterized by using ¹H‐NMR, SEC, WAXD, and DSC. All the copolymers were semicrystalline, one or two melting peaks being detected depending on the composition. Equilibrium melting temperature (T_m⁰) of PLLA blocks was determined for three copolymers with different EO/LA molar ratios. T_m⁰ decreased with decreasing PLLA block length. A copolymer with equivalent PLLA and PEG block lengths was selected for melt crystallization studies and the resulting data were analyzed with Avrami equation. The obtained Avrami exponent is equal to 2.6 ± 0.2 in the crystallization temperature range from 80 to 100°C. In addition, the spherulite growth rate of PLLA‐PEG was analyzed by using Lauritzen‐Hoffmann theory in comparison with PLLA homopolymers. The nucleation constant was found to be 2.39 × 10⁵ K² and the free energy of folding equal to 53.8 erg/cm² in the range of 70–94°C, both higher than those of PLLA homopolymers, while the spherulite growth rate of the diblock copolymer was lower. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

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.     

Physical properties of poly(n-alkyl acrylate) copolymers. Part 1. Crystalline/crystalline combinations

The physical properties of n-alkyl acrylate copolymers containing two crystallizeable monomers, including thermal characteristics, structure as determined by small angle X-ray scattering, and gas permeability as a function of temperature, were examined in detail and compared to the corresponding homopolymers. The copolymers exhibit co-crystallization and, thus, for a given average side-chain length have comparable melting temperatures as the corresponding homopolymers. For a given side-chain length, the copolymers have somewhat lower heats of fusion than the corresponding homopolymers because of a reduction in crystallite size as revealed by SAXS. This depression in crystallinity is reflected in the permeability data for the copolymers. Poly(n-alkyl acrylates) exhibit a ‘jump’ in their gas permeability at the T_m of the side-chain lengths that is mainly caused by a switch in the side-chain morphology from crystalline to amorphous upon melting. The depression in crystallinity for the copolymers results in a smaller permeation jump. The jump breadth correlates with the melting endotherms for these polymers as determined by DSC. Ultimately, the melting endotherms for these copolymer systems provide an excellent tool for predicting permeability changes across the melting region.