Copolymer Sequence Distribution Research Articles

Characterization of poly(styrene‐co‐methacrylonitrile)s obtained by low‐temperature radiation polymerization and thermal degradation behavior measured by Py‐GC and CRTG

Poly(styrene-co-methacrylonitrile)s were polymerized in solutions with different polarities (n-hexane and THF) by low-temperature γ-ray irradiation polymerization in a temperature range of −83.6–30 °C. It was found by IR measurement that the composition of the copolymers changed remarkably due to the effects of the polarity of solvents and the polymerization temperature. The thermal degradation behavior in the flash pyrolysis and in the continuous heating pyrolysis of these copolymers was measured by Py-GC and controlled rate thermogravimetry (CRTG). The effects of the copolymer composition and sequence distribution on the thermal degradation behavior were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3569–3577, 2000

Reactivity ratios and sequence distribution of styrene–acrylonitrile copolymers synthesized in microemulsion medium

The reactivity ratios of styrene and acrylonitrile in ternary oil-in-water anionic microemulsions were observed to be very much different than those in bulk, solution, emulsion and cationic microemulsion media. The results are discussed in terms of partitioning of partially water soluble monomers in the aqueous phase and monomer droplets. The behavior of polymerization was observed to follow a terminal model rather than the penultimate model in a microemulsion medium. Sequence distribution in copolymers was calculated from reactivity ratios using the Alfrey–Mayo model and was observed to be in good agreement with that calculated from 13C-NMR studies. A good agreement was observed in glass transition temperatures of copolymers and those calculated from 13C-NMR.

Characterization of poly(styrene-co-methacrylonitrile)s obtained by low-temperature radiation polymerization and thermal degradation behavior measured by Py-GC and CRTG

Poly(styrene-co-methacrylonitrile)s were polymerized in solutions with different polarities (n-hexane and THF) by low-temperature γ-ray irradiation polymerization in a temperature range of −83.6–30 °C. It was found by IR measurement that the composition of the copolymers changed remarkably due to the effects of the polarity of solvents and the polymerization temperature. The thermal degradation behavior in the flash pyrolysis and in the continuous heating pyrolysis of these copolymers was measured by Py-GC and controlled rate thermogravimetry (CRTG). The effects of the copolymer composition and sequence distribution on the thermal degradation behavior were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3569–3577, 2000

Radical copolymerization of fumaric acid with styrene in DMF solution

The radical copolymerization of fumaric acid (FA) with styrene (St) was carried out in DMF solution at 70°C. The UV spectroscopy excludes the presence of a charge-transfer complex between FA and St in the copolymerization system. The copolymerization of FA with St was described by using the terminal and penultimate models. The Joshi–Joshi, Fineman–Ross, Kelen–Tüdo ̋ s and Ezrielev–Brokhina–Roskin methods were used to determine the reactivity ratios in terminal model. The reactivity ratios in penultimate model were found by iterative procedure without constraint and with constraint r 1≥ r′ 1 and r 2≥ r′ 2. Both the classic model as well as the penultimate model were a relatively adequate description of the copolymerization mechanism. From the calculated reactivity ratios, Q and e values were calculated, as well as the sequence distribution in copolymers. The copolymers were analysed by FTIR, 1H NMR and TG methods.

Radical copolymerization of citraconic anhydride with styrene in benzene solution

The radical copolymerization of citraconic anhydride (CAn) with styrene (St) was carried out in benzene solution at 70 °C. UV spectroscopy confirmed the presence of a 1:1 charge-transfer complex between CAn and St in the copolymerization system. The copolymerization of CAn with St was described by using the terminal model, penultimate model and complex participation model. The Joshi–Joshi, Fineman–Ross, Kelen–Tüdo ̋ s and Ezrielev–Brokhina–Roskin methods were used to determine the reactivity ratios in terminal model. It has been found that the terminal model is the adequate description of copolymerization mechanism, although the complex participation model predictions can also explain copolymer compositions at equimolar feed composition. From the calculated reactivity ratios, the Q and e values for citraconic anhydride were calculated, as well as the sequence distribution in copolymers. The sequence distribution was studied by 1H NMR.

Aliphatic Polycarbonates with Controlled Quantities of d-Xylofuranose in the Main Chain

Polycarbonates were synthesized by ring-opening copolymerizations of trimethylene carbonate (TMC) with 1,2-O-isopropylidene-d-xylofuranose-3,5-cyclic carbonate (IPXTC). Subsequent deprotection of the ketal protecting groups gave controlled quantities of vicinal diol pendant groups. Studies of TMC/IPXTC copolymerization showed that MAO and ZnEt2−0.5H2O were the preferred catalysts. The reactivity ratios measured by the Fineman−Ross method and using ZnEt2−0.5H2O as the catalyst were 0.31 and 0.20 for IPXTC and TMC, respectively. Hence, even though IPXTC has bulky substituents, IPXTC was more reactive than TMC early in the copolymerization. Consistent with the above, the average IPXTC chain segment length was longer early in the copolymerization but decreased with increased conversion. 1H and 13C NMR were used to analyze the repeat unit sequence distribution of copolymers. For copolymers with high IPXTC contents, three types of IPXTC linkages were found: head−head, tail−tail, and head−tail. The protecting ketal groups were removed by CF3COOH/H2O to give a novel polycarbonate with hydroxyl pendant groups. Longer deprotection times led to higher extents of deprotection but lower molecular weight. Studies by differential scanning calorimeter (DSC) showed that copolymers having from 8 to 83% IPXTC were all amorphous. In addition, a physical aging transition was apparent. The Tg of the copolymer increased with increasing IPXTC copolymer content. Furthermore, the experimental Tg values were in good agreement with that calculated by the Fox equation. After deprotection, the copolymer Tg decreased, which is consistent with the loss of the bulky ketal side group.

A Monte Carlo study of the effect of polymer rigidity on adsorption behaviour

The effect of copolymer sequence distribution and stiffness on the adsorption–desorption transition and configuration of an adsorbed polymer chain is examined by Monte Carlo methods. Trends in the adsorption–desorption transition temperatures show that the transition temperature of the block and alternating copolymers are determined by entropic factors while the copolymers with a random sequence distribution (block-ran, random, or alt-ran, defined below) are controlled by enthalpic considerations. Analysis of the conformation of adsorbed chains and monomer density profiles suggests that utilizing an adsorbed rigid copolymer may be useful at tuning the properties of an interface in a multiphase material. A block copolymer can be utilized to affect substantial surface coverage and extensive expansion away from the surface. Additionally, an increase in the rigidity of the diblock chain will improve the expansion of the chain in all three dimensions. Alternatively, random copolymer structures offer a chain that will adopt a flatter adsorbed configuration that offers more efficient surface coverage. In this case, the expansion of the copolymer along the surface can be enhanced by increasing the stiffness of the chain with little or no change in the expansion away from the interface.

Determination of triad sequence distribution of copolymers of maleic anhydride and its derivates with donor monomers by 13C n.m.r. spectroscopy

Several alternating and semi-alternating copolymers were analysed by quaternary 13C n.m.r. spectroscopy. The aromatic `next to polymer chain' carbon (C7) of donor monomer (1) units is sensitive to the unit 1-centred triad sequence distribution. The acceptor monomer is referred to as 0. The chemical shifts of the non-alternating (111), semi-alternating (011+110) and alternating (010) triad sub-peaks were assigned in ppm in Table 1Table 1Copolymer of monomer with monomer 1111011(+)110010 triad sequenceMaleic anhydride with styrene147.5145146141.5140.5136.5Maleic anhydride with trans-stilbene138132Maleic anhydride with α-methylstyrene152148148 (145.5)142.5139Maleic anhydride with allylbenzeneNot sensitive to triad sequence distribution and appears at 142–139ppmCitraconic anhydride with styrene147.5145147143.5137.5Bromomaleic anhydride with styrene147.5145141.5140136.5Dichloromaleic anhydride with styrene147.5145141.5138133Maleimide with styrene147.5145140.5136.5.

Determination of chain transfer constant to dodecanethiol in styrene/methyl methacrylate and butyl acrylate/methyl methacrylate copolymerization and effect of chain length on composition and stereochemical configuration of copolymers

Free radical copolymerization of styrene/methyl methacrylate (S/MMA) and butyl acrylate/methyl methacrylate (BA/MMA) in the presence of n-dodecanthiol (DDT) has been studied at 60°C in a 3 mol/L benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator. Overall chain transfer constant to DDT has been determined for both copolymerization systems, as a function of monomer feed composition using complete molecular weight distribution and the Mayo method. Overall transfer coefficients have values which are dependent on both monomer feed composition and individual comonomer transfer values. Composition, sequence distribution, and stereoregularity of copolymers obtained are, in our experimental conditions, independent of copolymer molecular weight. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2913–2925, 1998

Binding of Polycarboxylic Acids to Cationic Mixed Micelles: Effects of Polymer Counterion Binding and Polyion Charge Distribution

Mixed micelles of cetyltrimethylammonium chloride (CTAC) and n-dodecyl hexaoxyethylene glycol monoether (C12E8) bind to polyanions when the mole fraction of the cationic surfactant exceeds a critical value (Yc).Yccorresponds to a critical micelle surface charge density at which polyelectrolyte will bind to this colloidal particle. Turbidimetric titrations were used to determineYcfor such cationic-nonionic micelles in the presence of acrylic acid and acrylamido-2-methylpropane sulfonate homopolymers (PAA and PAMPS, respectively) and their copolymers with acrylamide, as function of pH, ionic strength, and polyelectrolyte counterion. In 0.20 M NaCl,Ycfor PAA is found to be remarkably insensitive to pH, i.e., virtually independent of the apparent polymer charge density ξapp. On the other hand, the expected inverse relationship betweenYcand ξappis observed either for PAA when NaCl is replaced by TMACl (tetramethylammonium chloride), or when ξappis manipulated using acrylic acid/acrylamide copolymers at high pH. The effective charge density of PAA is thus seen to be suppressed by specific sodium ion binding, indicating that the influence of salts on the interaction of polycarboxylic acids with colloidal particles may differ qualitatively from their effect on the analogous behavior of strong polyanions. Comparisons between homo- and copolymers of acrylic acid were carried out also to test the hypothesis that the “mobility” of charges on PAA at moderate pH (degree of ionization less than unity) could make this “annealed” polymer exhibit the behavior of a more highly charged one. The results, while consistent with this expectation, were obscured by the likely effect of copolymer sequence distributions.

Microstructure and pressure—volume—temperature properties of ethene/1-octene random copolymers

Copolymers of ethene and 1-octene were synthesized covering the entire composition range by means of the methylalumoxane activated rac-Me 2 Si(2-MeBenz[e]Ind) 2 ZrCl 2 catalyst. 13 C-NMR spcctroscopy revealed first-order Markov statistics to be reasonably suited for the description of the copolymer sequence distribution. Characteristic parameters of ethene/1-octene copolymers were obtained by evaluation of pressure-volume-temperature data using the Flory-Orwoll-Vrij equation-of-state theory. The characteristic pressure could not be correlated with 1-octene comonomer incorporation when assuming validity of the mixing rules known for homopolymer blends, whereas the characteristic specific volume and characteristic temperature are independent of copolymer composition within experimental errors. A possible explanation is presented for why the attempts to predict the characteristic pressure of ethene/1-octene copolymers from the corresponding homopolymer parameters fail using Flory's mixing rules.

Synthesis, Modification, and Characterization of l-Lactide/2,2-[2-Pentene-1,5-diyl]trimethylene Carbonate Copolymers

This paper explores the copolymerization of l-lactide (l-LA) with 2,2-[2-pentene-1,5-diyl]trimethylene carbonate (cHTC). Since cHTC has a cyclohexene group, this provided a route for preparing poly(lactic acid), (PLA), based chains decorated with controlled quantities of CC substituents. Ring-opening copolymerizations of l-LA with cHTC were successfully conducted in bulk by using AlR3−H2O (R = ethyl, isobutyl), Al(OiPr)3, ZnEt2−H2O and Sn(Oct)2 as catalysts. Comparison of these copolymerizations showed that the Sn(Oct)2 catalyst system gave copolymers of relatively higher molecular weight. Increasing the reaction time of Sn(Oct)2 catalyzed copolymerizations from 6 to 24 h resulted in higher copolymer cHTC content and yield but lower copolymer molecular weight. Variation of the comonomer feed ratio was useful in regulating the content of cyclohexene pendant groups in the copolymer. However, regardless of the catalyst used, the mole percent of cHTC incorporated into the copolymer was lower than that used in the monomer feed. Determination of the comonomer reactivity ratios for Sn(Oct)2 catalyzed copolymerizations gave values of 8.8 and 0.52 for l-LA and cHTC, respectively. All gel permeation chromatography (GPC) traces showed unimodal molecular weight distributions. Determination by 13C-NMR of the copolymer sequence fractions HLL, LLL, LLH, HLH, HL, and LH (H = cHTC units, L = l-lactyl units) showed that they were close to those calculated by assuming a Bernoulli statistical propagation. On the basis of these results and the effects of reaction conditions on the copolymer sequence distribution, a mechanism which involves insertion of cHTC into the polymer chain was proposed. Studies by differential scanning calorimetry (DSC) showed that cHTC units in the copolymers disrupted ordering of the l-PLA crystalline phase. Furthermore, the glass transition temperatures (Tg) ranged from 60 (l-PLA) to 33 °C (P(cHTC)). Conversion of CC to epoxy side groups was successfully carried out by using 3-(chloroperoxy)benzoic acid at room temperature with only small decreases in copolymer molecular weight.

Determination of Monomer Unit Sequence Distribution and Linkage Configuration of Copolymers of Styrene and Citraconic Anhydride, and Possibility of a Participation of Electron Donor-Acceptor Complex in the Copolymerization

The copolymerization system of styrene (ST) and citraconic (α-methymaleic) anhydride (CA) was found to form semi-alternating copolymers when polymerized with a total monomer concentration of 4 mol/L in CCl4 at 50°C, with alternating copolymers being formed only when the CA mole fraction in feed was greater than 0.9. More than 50% of the linkage configurations at the cyclic CA units in the copolymers were found to be in cis configuration. This, together with the following observations, is consistent with a participation of the electron donor-acceptor (EDA) complex formed between ST and CA: (a) the complex participation model fits best, although only marginally, to the experimental triad mole fraction of alternating sequences; (b) the alternating monomer unit sequences and the cis linkage configuration at the cyclic CA units are more efficiently formed in non polar CCl4 solutions than in polar methy ethyl ketone. The equilibrium constant for the EDA complexation of ST and CA in CCl4 at 23°C is determined to be 0.142 ± 0.015 L/mol.

Copolymer Sequence Distribution in Which Monomer Unit Sequence and Its Cotacticity Both Obey Correlatively the First Order Markov Process. Applications to Poly(acrylonitrile-co-methyl methacrylate) and Poly(acrylonitrile-co-ethyl methacrylate)

Copolymer Sequence Distribution in Which Monomer Unit Sequence and Its Cotacticity Both Obey Correlatively the First Order Markov Process. Applications to Poly(acrylonitrile- co -methyl methacrylate) and Poly(acrylonitrile- co -ethyl methacrylate)

Copolymer Sequence Distribution with Chiral Stereoregularity and Its Application to Poly(acrylonitrile-co-methacrylonitrile)

An attempt was made to elucidate the general mathematical expression of the polymer sequence distribution for copolymers with two stereoregular monomer units by considering their chirality (D or L form) distribution based on Markov statistics. The equations derived (DL equations) were compared with those based on conventional meso and racemo conformation (mr equations) [K. Kamide and K. Hisatani, Polym. J., 24, 1377 (1992)]. For this purpose the literature data of NMR on sequence distribution of three kinds of poly(acrylonitrile-co-methacrylonitrile) i.e., poly(AN-co-MAN), prepared by radical polymerization using redox catalysis and anionic method using dialkylmagnesium as initiator at high and low temperature, were analyzed. DL equations were found to explain well the monomer unit sequence distribution with cotacticity of two poly(AN-co-MAN), polymerized by radical method and by anionic methods at temperatures, rather than mr equations. The reaction probability of these copolymers estimated by [Bernoulli]−[1st Markov]cor statistics where monomer unit sequence and its cotacticity obey Bernoulli and 1st order Markov processes, respectively, has revealed that racemo addition of MAN monomer does not occur in the above anionic polymerization essentially. For all of three samples, the stereoregular sequences obey 1st order Markov statistics, but monomer unit ones obey 2nd order Markov statistics for low temperature anionic method and Bernoulli for the other two method.

Effects of Copolymer Sequence Distribution on the Miscibility of Poly(ethylene oxide)/Poly(styrene-co-acrylic acid) Blends: A Molecular Simulation Approach

The effect of the copolymer sequence distribution on the miscibility of a poly(ethylene oxide) (PEO)/poly(styrene-co-acrylic acid) (SAA) blend has been investigated by molecular simulations. The molecular simulation provides a method to calculate the interaction energy parameter and hydrogen-bond energy. It is observed that both the sequence distribution and the composition of the SAA copolymer significantly affect the degree of miscibility. For a fixed composition, there exists an optimal range of sequence distributions for which the blend system is miscible.

Effect of ‘‘blockiness’’ on the thermal transition of the terephthalate–adipate copolymers

Now, it is well established that sequence distributions in copolymers greatly affect their thermal transitions. Random and block terephthalate–adipate copolymers, for instance, are known to have different thermal transitions while maintaining the same chemical structures. While no theory was able to fully predict the characteristics of the thermal transition of copolymers, modeling techniques have shown good reliance in simulating the copolymeric chains and related physical properties. This is done by generating representative sequences and studying the packing of such sequences into crystalline regions in multichain systems. The quantities of particular interest were the nature of the sequence distribution in random and block copolyesters, the degree of crystallinity, melting points, the standard free energy of fusion, interfacial free energies, and the moduli (calculated on the basis of the crystallites acting as cross-links in an elastomeric structure). The work is also capable of predicting the size and the distribution of the crystals and the minimum sequence length required for crystallization.

The Role of Copolymer Architecture on the Interfacial Structure of a Ternary Polymer Blend

ABSTRACTThe role of copolymer sequence distribution on the interfacial characteristics of a ternary polymer blend containing 2 homopoiymers and a copolymer in the phase separated state are examined using Monte Carlo Simulation. The copolymer does migrate to the biphasic interface in the phase separated regime while the configuration and expansion of the copolymer at the interface is a function of sequence distribution within the copolymer. This effect is interpreted in terms of the efficiency of the copolymer to strengthen the biphasic interface. These results suggest that block, alternating, and block-ran structures show promise as interfacial modifiers, while the purely random and alt-ran copolymers will be less efficient as an interfacial strengthener. It is also found that a variation of the sequence distribution away from a purely random structure can dramatically effect the ability of the copolymer to modify the interface. As most polymers which are not block nor alternating are termed ‘random’, this differentiation may have an effect on experimental studies of ‘random’ copolymers as compatibilizers in polymer blends.

Influence of the physical characteristics of the polymer on the glass transition of various chemically modified PVCs

AbstractVinylchloride–vinylthiocresol and vinylchloride–vinylthionaphthol copolymers of various compositions were prepared by the substitution reaction of PVC with sodium thiocresol and sodium thionaphthol, respectively, in different solvents and at different temperatures. The variation of the glass transition temperature of these copolymers with chemical com‐position does not follow the Flory–Fox equation, but is found to depend on the solvent and the temperature at which the copolymer is obtained. The comonomer sequence distribution and stereosequence content of the above copolymers, and those of vinylchloride–vinyl‐thiobenzene copolymer, were determined by 1H‐ and 13C‐NMR spectroscopy. The depen‐dence of comonomer distribution and stereoregularity content with chemical composition for the three series of copolymers, prepared in different solvents and temperatures, are similar. The Tg deviations for the three series of copolymers were attributed to the con‐tribution of physical characteristics of the PVC structure, originating from polymer–solvent interactions. © 1995 John Wiley & Sons, Inc.

Using Monte Carlo simulations and self‐consistent field theory to design interfacially active copolymers

AbstractWe use both Monte Carlo computer simulations and numerical self‐consistent field lattice calculations to determine the behavior of copolymers at penetrable and impenetrable interfaces. These computational techniques are useful as “design tools”: they allow us to systemically vary the copolymer architecture, determine optimal structures for specific applications, and establish guidelines for fabricating copolymers that yield the desired interfacial properties. We illustrate this principle with three different examples. In the first study, we combine the techniques to design copolymer compatibilizers that enhance the strength of immiscible polymer blends. These copolymers contain teeth that associate across the penetrable interface between the phase‐separated regions and form a “molecular velcro” that effectively binds the regions together. In the case of impenetrable interfaces, we determine how the copolymer sequence distribution affects the structure of a layer of copolymers grafted onto a solid surface. The results indicate how to control the morphology of the layer and the surface properties of the substrate, by varying the microstructure of the grafted copolymers. Finally, we design a polymer channel that “opens” and “closes” in response to changes in the pH and quality of the surrounding solvent. The channel is formed from polyacid chains that are anchored onto a solid surface. Due to these properties, the system can be used for controlled release or sensor devices.