Comparison of the unperturbed dimension of polystyrene for endothermal and exothermal heats of dilution within the same system

Light scattering measurements for two samples of polystyrene (I, M_w = 2.15 × 10⁵; II, M_w = 2.5 × 10⁶) were performed in the iso-refractive mixed solvent dimethoxymethane-diethyl ether. For sample I the temperature dependence of the second osmotic virial coefficient A₂ was determined for three constant compositions of the mixed solvent. In the range ?30° to +25°C the three curves run practically parallel and exhibit a maximum at approximately ?10°C. For the volume fraction of 0.7 diethyl ether in the mixed solvent, an endothermal theta-temperature θ₊ was found at ?27.0° ± 1.5°C and θ_?, the exothermal theta-temperature, at ?5.0 ± 1°C. The investigation of sample II in the abovementioned solvent confirmed the observed θ_?-temperature and displayed a higher exothermicity compared with I. Similarly to the temperature variation of A₂, the chain dimensions of II, determined from the angular dependence of the scattered light, run through a maximum. The unperturbed dimensions in the mixed solvent are found to be: $\text{r}{}_{\mathrm{w}}\text{= 448 ± 5}\text{A}\text{?}$ at θ₊ = ?27°C and $\text{r}{}_{\mathrm{w}}\text{= 443 ± 5}\text{A}\text{?}$ at θ_? = ?5°C, as compared with $\text{r}{}_{\mathrm{w}}\text{= 420 ± 10}\text{A}\text{?}$ at θ₊ = +33°C in cyclohexene. The inter-relation of the chain expansion coefficient and A₂ is quantitatively described by the Zimm-Stockmayer-Fixman equation over the entire range of heats of dilution.     

Lösungseigenschaften von statistischen Copolymeren aus Methylmethacrylat und n-Butylacrylat

Viscosity measurements and light-scattering measurements have been carried out on chemically homogeneous random copolymers of methyl methacrylate (MMA) and n-butyl acrylate (BA). In the good solvent chloroform, the copolymers in the composition range 79,5 ≥ [MMA] ≥ 20,5 wt.-% show a uniform relation between the viscosity [η] and the molecular weight (M), which lies between that of PMMA and that of PBA: [η] = 4,2 × 10^?3 M^0,8 (cm³ · g^?1), T = 20°C. In the fair solvent acetone the [η]-M function for MMA/BA = 56/44 wt.- % is above those of PMMA and PBA. The values of the second osmotic virial coefficient A2 behave in the same way. Using equations given by STOCKMAYER-FIXMAN , BURCHARD and KURATA et al., the effects of the short-range and the long-range interactions on the composition dependence of [η] and A₂ were estimated from the molecular weight dependence of A2 and [η]. It was found that the short-range interactions correspond to the mean of the values for the two comonomers, while the long-range interactions are considerably greater than those of the corresponding homopolymers. The increase in the viscosity and in A₂ in the random copolymers can be explained as a result of intramolecular incompatibility.     

Effects of drawing conditions on the properties of optical fibers made from polystyrene and poly(methyl methacrylate)

Monofilaments possessing various degrees of birefringence were obtained by changing the drawing rate, the molten polymer temperature, and the molecular weight of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The “brittle-toductile” transition point of optically pure PS was found in the range of birefringences of ?0.6 · 10^?3 to ?2.6 · 10^?3. Both the height and position of this point are influenced by M?_w, molecular weight distribution, and polymer melt temperature. The birefringence of PS is higher by two orders of magnitude than that of PMMA in which this transition point has not been observed. The mechanical and optical properties depend not only on the average amount of orientation characterized by the birefringence but on what portion of the relaxation spectrum of the polymer is preferentially oriented. During the drawing of PS and PMMA monofilaments crazes are formed in the centre of the fibers and do not reach the surface.     

Temperature and Time Dependence of Copolymer Mixtures on Interfacial Adhesion at PS/PMMA Interfaces

The effect of copolymer mixtures on the interfacial adhesion between slabs of PS and PMMA was investigated as a function of composition, time and temperature using the asymmetric double cantilever beam (ADCB) method. The nature of the interface was further probed using atomic force microscopy (AFM) and dynamic secondary ion mass spectroscopy (D-SIMS). The results show that mixtures of graft and block copolymers are much more effective than pure block copolymers in enhancing the interfacial adhesion. The most effective mixture consisted of a block copolymer of molecular weight 70K and a copolymer with two PS grafts of molecular weight 30K. This mixture yielded an interfacial fracture toughness of G_c = 127.5 J/m² as compared with G_c = 38.2 J/m² and G_c = 3.5 J/m² for the pure block and graft copolymer, respectively.

G_c at the PS/PMMA interface reinforced only with block copolymer was maximal after an annealing temperature of 150°C for 1 hr. It decreased by an order of magnitude when the temperature was increased to 180°C or the joining time was increased from 1 to 10 hours. G_c at the interface reinforced with a graft/diblock copolymer mixture was also maximum at an annealing temperature of 150°C but it decreased only by a factor of 2 with increasing joining time or temperature. Dynamic Secondary Ion Mass Spectroscopy (DSIMS) data show that this effect may be due to decrease in the diffusion of the copolymer from the interface when the mixture is present, i.e, the diblock copolymer is trapped within the graft copolymer.     

Solubility of polystyrene in liquid sulfur dioxide

The two-phase equilibrium in the system polystyrene (PS)-liquid sulfur dioxide [SO₂(l)] was investigated, mainly at room temperature. The system consisted of an upper PS-rich phase, concentration (30–50)% depending on the way of preparation, and a lower phase containing less than 1% PS. The range of molecular weights of the PS samples used was 22,000–350,000 (M?_w). PS with an M?_w value of 22,000 dissolved homogeneously in SO₂(l). In systems forming two phases a fractionation of PS with respect to molecular weight was observed. The M?_w value of the PS fraction dissolved in the lower PS lean phase was always substantially lower than that of the upper phase. When increasing the temperature to 90–95°C, the two phases disappeared and the PS component formed a jellylike mass with a very low solubility in SO₂(l). Also in the supercritical dense SO₂ gas, the solubility of PS was a few tenths of a percent only. Experiments with Soxhlet extraction indicated an extractability of a few percent.     

Theta point of polyacrylamide in aqueous solution and temperature dependence of the molecular dimensions

The molecular weight (M_w) and temperature (T) dependence of the expansion factor and the second virial coefficient of polyacrylamide (PAAm) in dilute solution are investigated. The theoretical predictions of the blob and of the modified Flory's theory are compared with experimental results on polystyrene. We note similar behaviour for these two polymers which cannot certify in the intermediate region if the volume exponent v is higher than the theoretical asymptotic value or not. In addition we give an experimental determination of the theta temperature for PAAm in water θ = ?8°C.     

Programmed polymer light-scattering data

An ALGOL computer program has been devised to manipulate light-scattering data from the Brice-Phoenix photometer. The input consist of experimental values of the galvanometer deflections and filter factors used for each concentration c and angle of measurement θ. These are transformed to the appropriate variables in the fundamental equation including the particle scattering factor, viz: c/Qθ = (W/K^*)M?_w^?1[1 + (16/3) × π²n₁²λ〈S²〉 sin² (θ/2)] + (W/K^*)2A₂c + (W/K^*)3A₃c² in which Qθ is a corrected from of the Rayleigh ratio and (W/K^*) is a composite constant term for the instrument and polymer–solvent system. By writing X?_ij for the variable c/Q_θ at θ_i and c_j, a function X is found by least squares to fit X?_ij, thus X = l + m sin (θ/2) + nc_j + bc_j². The equations arising from minimizing Σ_i^K=1 Σ_j^L=1 (X_ij ? X?_ij)² are solved by the computer to yield the best-fitting coefficients l, m, n, and b. These can then be related simply to the molecular weight, root-mean-square radius of gyration, second and third virial coefficients, respectively. The final portion of the program is designed to check the fit of these coefficients. It yields a table of the differences between all experimental c/Qθ values and the coressponding ones obtained by inserting the derived l, m, n, and b into the fundamental equation. The procedure has been tested satisfactorily by using a well-standardized sample of polystyrene in toluene at 30°C. and a wavelength of 436 mμ.     

Preparation and characterization of a foam regulator with ultra‐high molecular weight

Multistage emulsion polymerization was used to prepare ultra‐high molecular weight foam regulator of low cost, with methyl methacrylate (MMA), butyl acrylate (BA), styrene (St) as main raw materials. Ubbelohde viscometer, dynamic light scattering, infrared and raman spectra, TEM, DSC, TGA, and GPC were all used to characterize constituent and structure, morphology, and molecular weight. As a result, when the ratio of soft monomer (BA) and hard monomer (St + MMA) is 1:3, MMA:St = 4:1, potassium persulfate (KPS): 0.15%, sodium hydrogen sulfite (SHS): 0.05%, azodiisobutyronitrile (AIBN): 0.15%, divinyl benzene (DVB): 0.3%, the final product terpolymer has obvious core‐shell structure and ultra‐high molecular weight (M_w = 1,400,000). This kind of foam regulator showed improvements in the melt strength, prevention of bubble coalescence and reduction on cost when compared with the traditional. Finally, the coefficients of poly (methyl methacrylate‐butyl acrylate‐styrene) terpolymer's Mark‐Houwink equation were calculated with tetrahydrofuran (THF) solvent at 25 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44479.     

Study on conformational transition phenomena of poly(methyl methacrylate) in acetonitrile near theta conditions

The coil–globule transition for poly(methyl methacrylate) (PMMA) has been studied in a theta solvent, acetonitrile (Θ = 45 °C). The viscosity of PMMA was measured as a function of temperature in the range 26–55 °C. The contraction and expansion of the molecular chains are determined using the measured viscosity values. The temperature dependence of the intrinsic viscosity can be represented by a master curve in a versus |τ|M _w^1/2 (g^1/2 mol^−1/2) plot, where τ = |T − Θ|/T is the reduced temperature and M_w‐is the weight‐average molecular weight. A universal plot of reduced viscosity versus reduced blob parameter (N/N_c) shows the attainment of the collapsed state below the theta temperature. The dimensions of PMMA in acetonitrile (M_w = 3.15 × 10⁶ g mol⁻¹) decrease to 63 % at 26 °C of those in the unperturbed state. The results in this work are compared with those previously published. © 2000 Society of Chemical Industry     

Photo‐Induced atom transfer radical polymerization with nanosized α‐Fe2O3 as photoinitiator

Photo‐induced atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was achieved in poly(ethylene glycol)‐400 with nanosized α‐Fe₂O₃ as photoinitiator. Well‐defined poly(methyl methacrylate) (PMMA) was synthesized in conjunction with ethyl 2‐bromoisobutyrate (EBiB) as ATRP initiator and FeCl₃·6H₂O/Triphenylphosphine (PPh₃) as complex catalyst. The photo‐induced polymerization of MMA proceeded in a controlled/living fashion. The polymerization followed first‐order kinetics. The obtained PMMA had moderately controlled number‐average molecular weights in accordance with the theoretical number‐average molecular weights, as well as narrow molecular weight distributions (M_w/M_n). In addition, the polymerization could be well controlled by periodic light‐on–off processes. The resulting PMMA was characterized by ¹H nuclear magnetic resonance and gel permeation chromatography. The brominated PMMA was used further as macroinitiator in the chain‐extension with MMA to verify the living nature of photo‐induced ATRP of MMA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42389.     

Photo-induced controlled radical polymerization with new Photocatalyst

Photo-induced electron transfer reversible addition-fragmentation chain transfer (PET RAFT) of methyl methacrylate (MMA) was investigated at 25 °C with rose bengal (4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein) (RB) as photoredox catalyst under visible light irradiation. The traditional chain transfer agent 4-cyanopentanoic acid dithiobenzoate (CPADB) was employed in this study. The kinetic curve of the photo-induced PET RAFT polymerization exhibited a good linear behavior. The number average molecular weights (M_n,GPC) of the poly(methyl methacrylate) (PMMA) increased linearly with respect to monomer consumption and they were in good agreement with the calculated values (M_n,th). At the same time the molecular weight distribution (M_w/M_n) was narrow. Temporal control of PET RAFT polymerization of MMA was demonstrated by “ON/OFF” experiments. The resulting PMMA was characterized by ¹H–NMR, and GPC. The resultant PMMA could be used as macro-chain transfer agents for the PET RAFT radical polymerization. The chain experiments were successfully carried out and the living characteristics were demonstrated. The probable mechanism was discussed.     

Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. II. Structural changes occuring in low-density polyethylene at an oxygen content less than 0.0005%

Samples of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen. Changes in molecular weight distribution (MWD), molecular weight averages, and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). At 284° and 315°C, the MWD's were shifted toward higher molecular weights and the M?_w values increased. At 333° and 355°C, the MWD's shift toward lower molecular weight, but the high molecular weight, tail is largely retained. M?_w decreases slowly at 333°C. At 355°C, M?_w undergoes a rapid initial drop which levels off. M?_w/M?_n and the degree of LCB increase with heating time and temperature. Olefinic unsaturation increases. The vinyl groups show a larger relative increase than do the trans-vinylene and vinylidene groups. At 355°C, the peak of the unimodal DSC thermogram is shifted to ～3°C higher temperature. A lower melting peak then develops, and after 72 and 90 min the two peaks are about equal in size. The density increases from 0.922 g/cm³ to 0.930 g/cm³ for samples heated at 355°C, and the weight loss was 1.5% after 90 min. A reaction scheme for the thermal degradation of polyethylene is discussed. Initiation is suggested to be accomplished by scission of allylic C? C bonds. Propagation proceeds by both intra- and intermolecular hydrogen abstraction, followed by β-scission. Termination can occur by both combination and disproportionation. Combination reactions are suggested to account for the observed formation of LCB and high molecular weight material. Due to changes in the degree of LCB during the degradation, viscometry alone will not give a proper measure of the changes in molecular weight.     

A fluorescence study on dissolution of polymeric glasses prepared in various molecular weights

Poly(methyl methacrylate) (PMMA) discs in various molecular weights, M_w, were prepared by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the gelation and dissolution processes in chloroform vapor and solvent, respectively. In-situ steady state fluorescence (SSF) experiments were performed to monitor vapor uptake and chain desorption processes. Direct illumination of PMMA discs were performed to excite the P molecules embedded inside the PMMA glass. Variation in P intensity, I, was monitored during the swelling of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked polymeric gel at early times by obeying the Li-Tanaka equation. Swelling time constants, τ_c, of PMMA discs were measured and found to have a strong correlation with the molecular weight, of PMMA. In a separate experiment, when the PMMA discs were in chloroform, desorption of PMMA chains from glass discs was monitored by observing the change of pyrene fluorescence intensity. A diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It was observed that desorption coefficient, D, decreased by increasing M_w by obeying the D≈M_w ⁻¹ law. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, New Orleans, LA. Department of Physics, 80626 Maslak, Istanbul. Turkey.     

Relations of weight-average molecular weights and the thermal properties of N-cyclohexyl maleimide–methyl methacrylate

N-cyclohexyl maleimide (CHMI) was used to copolymerize with methyl methacrylate (MMA) by a suspension copolymerization method to produce heat-resistant poly(MMA) (PMMA) in this article. The copolymers were synthesized by changing the weight fractions of azobisisobutyronitrile (AIBN) and dodecanethiol (DDM), while the weight ratio of CHMI to MMA was defined. The effects of the weight fractions of AIBN and DDM on weight-average molecular weight (M_w) were studied. Meanwhile, relations between M_w and the glass transition temperature (T_g) and decomposition temperature (T_d) and M_w and the melt flow index (MFI) were described. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2001–2005, 1998     

Kinetic study on the poly(methyl methacrylate) seeded soapless emulsion polymerization of styrene. I. Experimental investigation

In this work, methyl methacrylate (MMA) and styrene (ST) were used as monomers in the first stage and second stage of polymerization, respectively, and potassium persulfate (K₂S₂O₈) was used as the initiator to synthesize the poly(methyl methacrylate)-polystyrene (PMMA/PS) composite latex by the method of two-stage soapless emulsion polymerization, i.e., PMMA seeded soapless emulsion polymerization of styrene. The morphology of the latex particles was observed by transmission electron microscopy (TEM). It showed that the composite latex particles had a core–shell structure. The particlesize distribution of the composite latex was very uniform. The kinetic data of seeded soapless emulsion polymerization showed that the square root of polymer yield (Wp)^1/2 was proportional to the reaction time in the earlier period of the reaction. The slope of the line of (Wp)^1/2 vs. reaction time was independent of the content of the seed, but proportional to 0.5 power of the initiator concentration. The gel effect was apparent after monomer droplets disappeared. A glassy effect was found in the latter period of the reaction. The number-average molecular weight of the polymers increased but the weight-average molecular weight of the polymers decreased with decrease of the MMA/ST weight ratio. The number- and weight-average molecular weight increased with decreasing the temperature significantly. © 1995 John Wiley & Sons, Inc.     

Solution blending of polystyrene and poly(methyl methacrylate)

Blends of poly(methyl methacrylate) (PMMA) and polystyrene (PS) have been investigated by differential scanning calorimetry and scanning electron microscopy. Blends were made of a low molecular weight PS with three PMMAs having number-average molecular weights of (1) 18,300, (2) 37,000, and (3) 211,000, The blend was found to be partially miscible. The composition-dependent values of the polymer-polymer interaction parameter (g₁₂) were determined and found to be from 0.015 to 0.029 for solution casting at 25°C. The interaction parameter (g₁₂) increases with increasing PMMA molecular weights in the PMMA/PS blend systems. This result is consistent with the behavior of the glass transition temperatures and with the microscopy study which indicate that compatibility is greater in the PMMA-1/PS blends having the low molecular weight of PMMA than in the PMMA-3/PS blends having the higher molecular weights of PMMA.     

Long-chain branching in low-density polyethylene

A sample of a commercial low-density polyethylene was fractionated and values of number ? M_n and weight-average M_w, molecular weights obtained together with intrinsic viscosities [η], measured in decalin at 135° and in a theta-solvent, diphenyl at 118°. Results are compared with those obtained using samples of high-density polyethylene, of narrow molecular weight distribution, in decalin at 135° and in diphenyl at 125°. Values of the z-average mean square radius of gyration (S^?2)_z, are converted to the weight-average unperturbed state. The branching parameters g and g¹ thus obtained, indicate that long-chain branching increases with increasing molecular weight. Intrinsic ivscosities under theta-conditions for the low-density polyethylene fractions lead to a relationship [η]_θ = K _w^0·20, agreeing with the treatment of Zimm and Kilb. Some of the approximations involved in the estimation of long-chain branching are discussed.     

Synthesis of stereoblock poly(methyl methacrylate) via transformation of isotactic-specific living polymer anion to syndiotactic-specific anion

Polymerization of methyl methacrylate (MMA) by isotactic poly(methyl methacrylate) (PMMA) living anion, prepared with t-C₄H₉MgBr in toluene at ?60°C, was carried out at ?78°C in the presence of trialkylaluminiums (R₃Al; R = CH₃, C₂H₅, and n-C₄H₉) to obtain a stereoblock PMMA, isotactic PMMA-block-syndiotactic PMMA. Among the R₃Als, (CH₃)₃Al gave most effectively the steroblock PMMA with narrow molecular weight distribution. The fraction of rr triad in the syndiotactic PMMA block increased with increase in the ratio of Al/Mg and reached about 76% at a ratio of Al/Mg ≥ 6. The method was also used to prepare stereoblock copolymer comprising isotactic PMMA block and syndiotactic block of butyl methacrylate. Stereocomplex formation and solution viscosity of the stereoblock PMMA were also studied.     

Studies on bulk diffusion and local diffusion of polystyrene in melt

Results of bulk viscosity (η) and local viscosity (ξ) of various molecular weights of polystyrene (PS) have been reported. In this paper the relationship between η and bulk diffusion coefficient (D_B), and that between ξ and local diffusion coeffizient (D_L) are presented. Data obtained lead to several conclusions. From the results of unperturbed dimensions and a universal constant (Φ), it was found that F. Bueche's equation D_B · η = const. is valid for polystyrenes with molecular weights over 600. Temperature and component concentration dependence of bulk diffusion coefficient for the two-component blend system may be interpreted in terms of the free volume theory. At an iso-free volume state, molecular weight dependences of bulk diffusion coefficients for both PS of narrow distribution of molecular weight and blend PS can be composed to a single curve, which is composed of two straight lines in a double logarithmic presentation with intersection at M_w = 1.78 × 10⁴ g/mol. The slopes of these two lines were ? 1.0 and ? 3.3, respectively. The product D_L · ξ was determined to be 1.10 × 10^?7 (c.g.s) for n-paraffines from the data of self-diffusion coefficient and ξ. This made it possible to determine D_L from ξ. For higher molecular weights of PS, log D_B is a linear function of log M_w while log D_L stays almost constant.     

Light-scattering studies on solutions of high and low molecular weight polystyrene mixtures used as models of microgel-containing solutions

Diluted solutions of linear polystyrene (PS) in toluene and dioxane were studied by the light-scattering method. The solutes were mixtures of high-M?_w and low M?_w PS. The dissolved PS mixtures were regarded as polymer solutions containing microgels, the high-M?_w PS being looked upon as the microgel counterpart. The calculation method as proposed by Strazielle¹ and Burchard² was used to evaluate the microgel percentage and particle size, whereby the method could be verified against mixtures with well-known weight composition and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document}. The \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values evaluated for the mixtures from the experimental data were compared with those estimated from the molecular weights of the components, their weight concentrations, and their \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values. The method^1,2 was found to be useful for evaluating the microgel content in a sample, but not for \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values as calculated by Guinier's procedure nor those calculated by Zimm's procedure; the former were low and the latter were even incongruous. A comparative analysis of the theoretical function P^?1(θ)-versus-sin² (θ/2) and experimental (Kc/R(θ))_c=0-versus-sin² (θ/2) curves allowed to discuss the effect of the course of these curves at samll angles from 0° to 30° on M?_w and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} as determined for the high and low molecular weight polystyrene mixtures in toluene as solvent.