Laser light-scattering characterization of gelatin in formamide

Laser light scattering (LLS) including angular dependence of absolute integrated scattered intensity (static LLS) and of the spectral distribution (dynamic LLS) has been used successfully to characterize gelatin in formamide at room temperature. In static LLS, the use of formamide as a single solvent instead of an aqueous salt solution avoids the well-known problem of preferential sorption of salts in the domain of gelatin molecules. Therefore the true weight-average molecular weight M_w, the z-average radius of gyration, and the second virial coefficient have been determined. In dynamic LLS, precise measurements of the intensity-intensity time correlation function permit a Laplace inversion to obtain an estimate of the normalized characteristic linewidth distribution which could be reduced to a translational diffusion coefficient distribution, G(D). This report shows that the calibration between D and M can be established from M_w and G(D) by using only two broadly distributed gelatins instead of a set of narrowly distributed gelatin standards. After establishing a calibration between D and M, we were able to estimate the molecular weight distribution of gelatin from G(D). © 1994 John Wiley & Sons, Inc.     

Laser light scattering of the molecular weight distribution of unfractionated phenolphthalein poly(aryl ether sulfone)

Two unfractionated samples of phenolphthalein poly(aryl ether sulfone) (PES-C) were characterized in CHCl₃ at 25°C by applying a recently developed laser light-scattering (LLS) procedure. The Laplace inversion of precisely measured intensity–intensity time correlation function lead us first to an estimate of the characteristic line-width distribution G(Λ) and then to the translational diffusion coefficient distribution G(D). A combination of static and dynamic LLS results enabled us to determine D = (2.69 × 10⁻⁴)M^−0.553, which agrees with the calibration of D = (2.45 × 10⁻⁴)M^−0.55 previously established by a set of narrowly distributed PES-C samples. Using this newly obtained scaling between D and M, we were able to convert G(D) into a differential weight distribution f_w(M) for the two PES-C samples. The weight-average molecular weights calculated from f_w(M) are comparable to that obtained directly from static LLS. Our results showed that using two broadly distributed samples instead of a set of narrowly distributed samples have provided not only similar final results, but also a more practical method for the PES-C characterization. © 1997 John Wiley & Sons, Inc.     

RHEOLOGICAL BEHAVIOR OF ERWINIA GUM IN AQUEOUS SOLUTION*

Erwinia (E) gum, an extracellular polysaccharide, is composed of fucose, galatose, glucose andglucuronic acid. Its viscosity behavior was investigated by a low-shear-rate multiball viscometer and arotational viscometer. Its weight-average molecular weight M_w and intrinsic viscosity [η] in 0.2 mol/L NaClaqueous solution were measured by light scattering method at 35℃and viscometry at 25℃and found to be1.06×10~6 g/mol and 1050 mL/g, respectively, and its aggregates in aqueous solution were proved by gelpermeation chromatography (GPC). These results indicated that E gum in water has exceedingly highviscosity and exhibits Binham fluid behavior, owing to its aggregation. The viscosity of E gum decreasedwith increasing temperature, and the turning point appeared at 38℃for dilute solution and 80℃forconcentrated solution suggesting that the aggregates of E gum in water started to disaggregate under thesetemperatures. In addition, the aggregates can be disrupted by adding either acid or base. The experimentalresults indicated that the E gum is a good thickening agent, and its fluid behavior is similar to xanthan.     

Scalings of fluorine‐containing polyimides in cyclopentanone

Eight 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride‐4,4′‐diamino‐3,3′‐dimethylbiphenyl (6FDA‐OTOL) fractions and seven 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy) phenyl] propane dianhydride‐4,4′‐diamino‐3,3′‐dimethylbiphenyl (BISADA‐OTOL) fractions in cyclopentanone at 30 °C were characterized by a combination of viscometry and static and dynamic laser light scattering (LLS). In static LLS, the angular dependence of the absolute scattered intensity led to the weight‐average molar mass (M_w), the z‐average root mean square radius of gyration, and the second virial coefficient. In dynamic LLS, the Laplace inversion of each measured intensity–intensity time correlation function resulted in a corresponding translational diffusion coefficient distribution [G(D)]. The scalings of 〈D〉 (cm²/s) = 8.13 × 10⁻⁵ M_w^−0.47 and [η] (dL/g) = 2.36 × 10⁻³ M_w^0.54 for 6FDA‐OTOL and 〈D〉 (cm²/s) = 3.02 × 10⁻⁴ M_w^−0.60 and [η] (dL/g) = 2.32 × 10⁻³ M_w^0.53 for BISADA‐OTOL were established. With these scalings, we successfully converted each G(D) value into a corresponding molar mass distribution. At 30 °C, cyclopentanone is a good solvent for BISADA‐OTOL but a poor solvent for 6FDA‐OTOL; this can be attributed to an ether linkage in BISADA‐OTOL. Therefore, BISADA‐OTOL has a more extended chain conformation than 6FDA‐OTOL in cyclopentanone. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2077–2080, 2000     

CRITICAL CONCENTRATIONS OF α(1→3)-D-GLUCAN FROM LENTINUS EDODES IN NaOH AQUEOUS SOLUTION

Critical concentrations of α-(1→3)-D-glucan L-FV-Ⅱ from Lentinus edodes were studied by viscometry andfluorescence probe techniques. The dependence of the reduced viscosity on concentration of the glucan in 0.5 mol/L NaOHaqueous solutions with or without urea showed two turning points corresponding to the dynamic contact concentration c_s andthe overlap concentration c~* of the polymer. The values of c_s and c~* were found to be 1×10~(-3) g cm~(-3) and 1.1×10~(-2) g cm~(-3),respectively, for L-FV-Ⅱ in 0.5 mol/L NaOH aqueous solutions. The two critical concentrations of L-FV-Ⅱ in 0.5 mol/LNaOH aqueous solutions were also found to be 1.2×10~(-3) g cm~(-3) fbr c_s and 9.2×10~(-3) g cm~(-3) for c~* from the concentrationdependence of phenanthrene fluorescence intensities. The overlap concentration c~* of L-FV-Ⅱ in 0.5 mol/L NaOH aqueoussolutions was lower than that of polystyrene with same molecular weight in benzene, owing to the fact that polysaccharidetends to undergo aggregation caused by intermolecular hydrogen bonding. A normal viscosity behavior of L-FV-Ⅱ in 0.5 mol/L urea/0.5 mol/L NaOH aqueous solutions can still be observed in an extremely low concentration range at 25℃.     

Can the Theoretical Fitting of the Proton‐Nuclear‐Magnetic‐Relaxation‐Dispersion (Proton NMRD) Curves of Paramagnetic Complexes Be Improved by Independent Measurement of Their Self‐Diffusion Coefficients?

The self‐diffusion (D_c) coefficients of various lanthanum(III) diamagnetic analogues of open‐chain and macrocyclic complexes of gadolinium used as MRI contrast agents were determined in dilute aqueous solutions (3–31 mM ) by pulsed‐field‐gradient (PFG) high‐resolution ¹H‐NMR spectroscopy. The self‐diffusion coefficient of H₂O (D_w) was obtained for the same samples to derive the relative diffusion constant, a parameter involved in the outersphere paramagnetic‐relaxation mechanism. The results agree with an averaged relative diffusion constant of 2.5 (±0.1)×10^?9 and of 3.3 (±0.1)×10^?9 m² s^?1 at 25 and 37°, respectively, for 'small' contrast agents (M_r 500–750 g/mol), and with the value of bulk H₂O (2.2×10^?9 and 2.9×10^?9 m² s^?1 at 25° and at 37°, respectively) for larger complexes. The use of the measured values of D_c for the theoretical fitting of proton NMRD curves of gadolinium complexes shows that the rotational correlation times (τ_R) are very close to those already reported. However, differences in the electronic relaxation time (τ_SO) at very low field and in the correlation time (τ_V) related to electronic relaxation were found.     

LIGHT SCATTERING OF POLYSACCHARIDE FROM LACQUER IN AQUEOUS SOLUTION

The polysaccharide having weight-average molecular weight M_w=1. 09×10~5, isolated from the sap of lac trees (Vietnam), was separated into 12 fractions by aqueous-phase preparative gel permeation chromatography. The molecular weights and molecular weight distributions of the fractions were measured in aqueous 0.08M KCl/0.01 M NaAc and 0.4M KCl/0.05M NaAc at pH =7. 6 by light scattering, viscometry and gel permeation chromatography. The Mark-Houwink equation in aqueous 0.08M KCl/0.01M NaAc at 30℃was found to be [η]= 2.28×10~(-2) M_w~(0.52) (cm~3/g), which indicated the polysaccharide chain in the aqueous solution to be a spherical random coil.     

Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry

Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a ¹³C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10^?2 weight‐average molecular weight (M_w)^0.815 (mL g^?1) in the M_w region from 3.2 × 10⁴ to 12.9 × 10⁴. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were 6.0 nm, 350 nm^?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004     

Characterization of novel optically active conjugated polyarylenes and poly(aryleneethnylene)s by a combination of off-line static and dynamic light scattering with gel permeation chromatography

By combining the offline static and dynamic laser light scattering (LLS) and gel permeation chromatography (GPC) results of a broadly distributed polymer sample, we were able to characterize a series of chiral binaphthyl-based polyarylenes and poly(aryleneethnylene)s in THF at 25°C. For each of the samples, we obtained not only the weight-average molar mass M_w, the second virial coefficient A₂ and the z-average translational diffusion coefficient 〈D〉, but also two calibrations: V = A + Blog(M) and D = k_D M^−αD, where V, D, and M are the elution volume, the translational diffusion coefficient and the molar mass for monodisperse polymer chains, respectively, and A, B, k_D, and α_D are four calibration constants. Using these calibrations, we estimated the molar mass distributions of these novel polymers. We showed that using polystyrene to calibrate the GPC columns could lead to a smaller M_w. Our results indicate that all the polymers studied have a rigid chain conformation in THF at 25°C and the introduction of the —NO₂ groups into the monomer can greatly promote the polymer solubility in THF.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2615–2622, 1998     

PREPARATION AND STRUCTURE OFFIVE DERIVATIVES OFβ-(1→3)-D-GLUCAN ISOLATED FROM PORIA COCOS SCLEROTIUM*

A new solvent of cellulose (1.5 mol/L NaOH/0.5 mol/L urea aqueous solution) was used as one of the homogeneous reaction media of polysaccharides for methylation, hydroxyethylation and hydroxypropylation. A water insoluble β-(1→3)-D-glucan, sample PCS3-Ⅱ, isolated from fresh sclerotium of Poria cocos was sulfated in dimethyl sulfoxide (Me2SO), carboxymethylated in NaOH, isopropanol solution, as well as methylated, hydroxyethylated and hydroxypropylated in the new solvent system, respectively, to obtain five water-soluble derivatives coded as S-PCS3-Ⅱ, C-PCS3-Ⅱ, M-PCS3-Ⅱ, HE-PCS3-Ⅱand HP-PCS3-Ⅱ. Their chemical structure and distribution of substitution were characterized by infrared spectroscopy (IR), elementary analysis (EA), ^1H-NMR, ^13C-NMR, 2D-COSY, 2D-TOCSY and 2D-^1H-detected ^1H ^13C HMQC spectra. The results reveal that the relative reactivity of hydroxyl groups of the β(1→3)-D-glucan is in the order C-6 ＞ C-4 ＞ C-2 on the whole. The substitution of the samples S-PCS3-Ⅱ, C-PCS3-Ⅱ and M-PCS3-Ⅱ occurred mainly at C-6 position and secondly at C-4 and C-2 positions, and that of HE-PCS3-Ⅱ occurred at C-6 and C-4 positions and of HP-PCS3-Ⅱ almost completely occurred at C-6 position. The degrees of substitution (DS) obtained from ^13C-NMR range from 0.23 to 1.27. The water solubility of the derivatives is in the order S-PCS3-Ⅱ ＞ C-PCS3-Ⅱ ＞ M-PCS3-Ⅱ ＞ HE-PCS3-Ⅱ ＞ HP-PCS3-Ⅱ. This work provides a novel and nonpolluting process for the methylation, hydroxyethylation and hydroxypropylation of β-(1→3)-D-glucan.     

Molecular weight and aggregation of Aeromonas gum treated with dimethyl sulfoxide in aqueous solution

Aeromonas (A) gum, an acidic hetero polysaccharide, in 0.2 M LiCl/dimethyl sulfoxide (DMSO) was fractionated satisfactorily according to the nonsolvent addition method. Eight fractions were chosen to examine their aggregation behavior in aqueous solution. The weight‐average molecular weight (M_w), radius of gyration 〈S²〉^1/2, and intrinsic viscosities [η] of the fractions in 0.2 M LiCl/DMSO and 0.5 M NaCl aqueous solution at 25 °C were measured by static light scattering and viscometry. The results indicated that the A gum was aggregated in 0.5 M NaCl aqueous solution at 25 °C, and the aggregates were broken in 0.2 M LiCl/DMSO. The apparent weight‐average aggregation number (N_ap) of the fractions increased with the process of fractionation, that is, N_ap increased from 1.1 to 15 with decreasing M_w of the single chain. The fractions obtained by treating with DMSO were more easily dissociated in the aqueous solution, and its N_ap was lower than that of the A gum fractions that were not treated with DMSO. Moreover, the A gum molecules with relatively low M_w aggregated easily to form a compact spherelike structure in the aqueous solution. Elemental analysis and ¹³C NMR spectroscopy indicated that DMSO was adsorbed on the A gum molecules caused by the fractionation program; DMSO not only prevented the polysaccharide aggregation but also increased the solubility. A model has been proposed to describe the aggregation behavior of the A gum chains with DMSO overcoat in the aqueous solution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2269–2276, 2002     

Intramolecular stacking interaction in mixed-ligand complexes containing ATP4- and aromatic N-heterocyclic ligands

The stability constants of the binary ML2+ and ternary M(ATP)L2- complexes,where L=Iq (isoquinoline) or BIm (benzimidazole) and M=Zn2+ or Cd2+,have been determined by poten-tiometric pH titration in aqueous solution at I=0.1 mol/L (NaClO4),T=25℃.The stability of the ternary complexes characterized by corresponding to the equilibrium M(ATP)2-+ML2+=M(ATP)L2-+M2+ is higher than what would be expected on statistical grounds.The increase may be related to the stacking interaction between the aromatic ring of the ligands L and the purine moiety of ATP4- 1H NMR studies of Zn2+/ATP4-/L confirm the presence of stacking in the ternary complexes.It is concluded that the strength of the intramolecular stacking interaction is dependent on the structure of the aromatic ring of the ligand L and the formation of a metal ion bridge.Possible implications are discussed briefly.     

CHEMOENZYMATIC SYNTHESIS OF BIODEGRADABLE POLY(1’-O-VINYLADIPOYL-SUCROSE)

t A novel polymer containing the sucrose group was synthesized by radical polymerization from an enzymaticallyprepared monomer, l'-O-vinyledipoyl-sucrose (VAS). Transesterification reaction of sucrose with divinyl adipate inanhydrous pyridine catalyzed by an alkaline protease from Bacillus subtilis at 60℃ for 7 days gave VAS (yield 55%) withoutany blocking/deblocking steps. The vinyl sucrose ester could be polymerized with potassium persulfate and H_2O_2 as initiatorto give poly(l'-O-vinyladipoyl-sucrose) with M_n = 33,000 and M_w = 53,200, M_w/M_n = 1.61. The polymer was biodegradable.After 6 days in aqueous buffer (pH 7), this alkaline protease could degrade poly(l'-O-vinyladipoyl-sucrose) to M_n of ca.1080, M_w/M_n = 3.30 (37℃), and M_n of ca. 5200, M_w/M_n = 2.44 (4℃). The polymer containing the sucrose branch would be afunctional material in various application fields.     

Stoichiometrical coordination behaviour of hexaza tripodal ligands towards zinc(II), copper(II), nickel(II) and cobalt(II)

The stability constants of Zn^II, Cu^II, Ni^II and Co^II with different tripodal ligands, 1,3,5-tris(2,5-diazaoctxyl)benzene (L1), 1,3,5-tris(2,5-diazanonxyl)benzene (L2) and 1,3,5-tris[3-(2-pyridyl)-2-azapropyl]benzene (L3) have been studied at 25 °C in 0.1 mol dm^–3 KNO₃ aqueous solution using potentiometric titrations. During the titrations, the ligand concentrations were kept constant at 1 × 10^–3 mol dm^–3, while 1:1 and 1:3 metal:ligand ratios were used for each system. The results indicated that, in the 1:1 metal:ligand ratio, the binding of M^II to the ligand gives rise to several 1:1 complexes differing in their degree of protonation whereas in the 3:1 ratio, polynuclear complexes are formed. Additionally, the ternary complexes of the tripod ligands, with Cu^II-5-substituted-1, 10-phenanthroline have been investigated and the results show that linear free energy relationship exists in such ternary systems.     

Measuring Positive Cooperativity Using the Direct ESI-MS Assay. Cholera Toxin B Subunit Homopentamer Binding to GM1 Pentasaccharide

Direct electrospray ionization mass spectrometry (ESI-MS) assay was used to investigate the stepwise binding of the GM1 pentasaccharide β-D-Galp-(1→3)-β-D-GalpNAc-(1→4)[α-D-Neu5Ac-(2→3)]-β-D-Galp-(1→4)-β-D-Glcp (GM1os) to the cholera toxin B subunit homopentamer (CTB₅) and to establish conclusively whether GM1os binding is cooperative. Apparent association constants were measured for the stepwise addition of one to five GM1os to CTB₅ at pH 6.9 and 22 °C. The intrinsic association constant, which was established from the apparent association constant for the addition of a single GM1os to CTB₅, was found to be (3.2 ± 0.2) × 10⁶ M^–1. This is in reasonable agreement with the reported value of (6.4 ± 0.3) × 10⁶ M^–1, which was measured at pH 7.4 and 25 °C using isothermal titration calorimetry (ITC). Analysis of the apparent association constants provides direct and unambiguous evidence that GM1os binding exhibits small positive cooperativity. Binding was found to be sensitive to the number of ligand-bound nearest neighbor subunits, with the affinities enhanced by a factor of 1.7 and 2.9 when binding occurs next to one or two ligand-bound subunits, respectively. These findings, which provide quantitative support for the binding model proposed by Homans and coworkers [14], highlight the unique strengths of the direct ESI-MS assay for measuring cooperative ligand binding.

STUDIES ON THE KINETICS OF PROPYLENE POLYMERIZATION WITH THE COMPLEXTYPE TiCl_3 CATALYST

The active center concentration C_p, the rate constant k_p, and the activation energy of chain propagation E_p in the polymerization of propylene with complex-type TiCl_3-(C_2H_5)_2AlCl catalyst system were studied. The Mn was corrected by (?) value determined by GPC. The values thus obtained for C_p, k_p, and E_p at 50℃were 3.01 mol/mol Ti, 6.27 1/mol·sec, and 5.10 Kcal/mol respectively.The kinetic parameters were compared with those obtained from conventional TiCl_3·AlCl_2 catalyst, showing that the higher activity of the complex-type catalyst over the conventional catalyst is not only due to the higher C_p of the former, but to a greater extent due to the increase of the k_p value.     

丙烯酰胺在离子液体中的原子转移自由基聚合

在1-丁基-3-甲基咪唑四氟硼酸盐离子液体中以氯化苄为引发剂,氯化亚铜/2,2’-联吡啶为催化剂成功实现了丙烯酰胺的原子转移自由基聚合(ATRP)。用IR对聚合物的结构进行了表征,证实聚合物链端具有-Cl端基。考察了引发剂用量、催化剂和配体用量、单体用量和反应时间等因素对丙烯酰胺在离子液体中的原子转移自由基聚合的影响,结果表明,反应时间为1.5 h时转化率达到31.43%,M_n^GPC=4451,M_w/M_n=1.38。且80 ℃下丙烯酰胺在离子液体中的最佳聚合工艺条件为：单体浓度3 mol/L,引发剂浓度0.010 mol/L,催化剂浓度0.015 mol/L,反应时间1 h。     

Synthesis and Polymerization of Surface-Active Sodium Acrylamidoundecanoate

The polymerizable surfactant sodium 11-acrylamidoundecanoate (Na 11-AAU) was synthesized from acryloyl chloride and 11-aminounde-canoic acid. It had a low critical micelle concentration (CMC) of 4.3 × 10^?4 mol/L. Polymerization of Na 11-AAU initiated by K₂S₂O₈ was very fast in aqueous solution, with an activation energy of only 63.2 kJ/mol. The polymerization followed first-order kinetics with respect to Na 11-AAU and one-half order with respect to K₂S₂O₈. The MW of poly(Na 11-AAU) was very high (1–2 million) but the MWD was rather narrow ( M _w / M _n = 1.45). Polymerization of Na 11-AAU in the micellar state may be responsible for the phenomena observed.     

Diffusion of water in solutions of alkali metal bromides,tetraalkylammonium bromides and ammonium bromide

The diffusion coefficient of water D _w in aqueous solutions of the alkali metal bromides, tetraalkylammonium bromides (methyl, ethyl, n-propyl, and n-butyl) and ammonium bromide at 25°C is reported for concentrations up to 2 mol-dm^–3. In addition, values for D _w in 2 mol-dm^–3 solutions of CsBr, KBr, NaBr, LiBr, and fully deuterated methanol, acetonitrile, and acetone have been measured for temperatures in the range 5 to 50°C. The concentration dependence of the relative water diffusion coefficient D _w /D _o , where D _o is the self-diffusion coefficient of water, has been analyzed in terms of an equation analogous to the Jones-Dole equation for relative viscosity. The B-coefficient for diffusion is well correlated with the viscosity B-coefficient. For the structure-breaking electrolytes CsBr and KBr, D _w /D _o decreases rapidly with increasing temperature, whereas for the structure-makers NaBr and LiBr, the temperature dependence of D _w /D _o has the same sign but is much smaller in magnitude. For the nonelectrolyte solutions, the structure-making effect decreases with increasing temperature and the temperature coefficient of D _w /D _o is positive. It is apparent that, when diffusion of the solvent is being considered, the temperature must be taken into account in the classification of an electrolyte as a structure-breaker or structure-maker.     

Laser light-scattering investigation of the density of pauci-chain polystyrene microlatices

The average density (〈ρ〉) of the pauci-chain polystyrene microlatices (PCPS), which contains a few linear polystyrene chains, was investigated by laser light scattering (LLS) including both angular dependence of absolute integrated scattered intensity (static LLS) and of the line-width distribution G(Γ) (dynamic LLS). In static LLS, the weight-average particle mass (M_w) and the z-average radius of gyration (R_g) were measured; and simultaneously in dynamic LLS, the hydrodynamic radius distribution was obtained from Laplace inversion of very precisely measured intensity-intensity time correlation function. A combination of both the static and dynamic LLS results leads us to a value of 〈ρ〉. For comparison, we also determined 〈ρ〉 of conventional multichain polystyrene latex (MCPS) by following the same LLS procedure. It was found that 〈ρ〉_MCPS = 〈_bulk〉 = 1.05 g/cm^3, but 〈ρ〉_PCPS = 0.92 g/cm^3. This difference in density suggests that the intersegmental distance in MCPS or bulk polystyrene is smaller than that in PCPS, even the chains in PCPS are confined to a smaller volume. This might attribute to the fact, namely the intersegmental approaching inside PCPS is mainly the intrachain crossing which is more difficult in comparison with the interchain crossing inside MCPS or bulk polystyrene.