Polystyrene narrow molecular weight

Standard Reference Material 705, Polystyrene (Narrow Molecular-Weight Distribution)... 

Fig. 2 Typical polystyrene narrow molecular-weight range standard chromatograms and calibration curve.

The isothermal curves of mechanical properties in Chap. 3 are actually master curves constructed on the basis of the principles described here. Note that the manipulations are formally similar to the superpositioning of isotherms for crystallization in Fig. 4.8b, except that the objective here is to connect rather than superimpose the segments. Figure 4.17 shows a set of stress relaxation moduli measured on polystyrene of molecular weight 1.83 X 10 . These moduli were measured over a relatively narrow range of readily accessible times and over the range of temperatures shown in Fig. 4.17. We shall leave as an assignment the construction of a master curve from these data (Problem 10). 

Three polystyrene samples of narrow molecular weight distribution were investigatedf for their retention in GPC columns in which the average particle size of the packing was varied. In all instances the peaks were well resolved. The following results were obtained ... 

Polystyrene produced by free-radical polymerisation techniques is part syndio-tactic and part atactic in structure and therefore amorphous. In 1955 Natta and his co-workers reported the preparation of substantially isotactic polystyrene using aluminium alkyl-titanium halide catalyst complexes. Similar systems were also patented by Ziegler at about the same time. The use of n-butyl-lithium as a catalyst has been described. Whereas at room temperature atactic polymers are produced, polymerisation at -30°C leads to isotactic polymer, with a narrow molecular weight distribution. 

Determinarion of MW and MWD by SEC using commercial narrow molecular weight distribution polystyrene as calibration standards is an ASTM-D5296 standard method for polystyrene (11). However, no data on precision are included in the 1997 edition of the ASTM method. In the ASTM-D3536 method for gel-permeation chromatography from seven replicates, the M of a polystyrene is 263,000 30,000 (11.4%) for a single determination within the 95% confidence level (12). A relative standard deviation of 3.9% was reported for a cooperative determination of of polystyrene by SEC (7). In another cooperative study, a 11.3% relative standard deviation in M, of polystyrene by GPC was reported (13). 

Traditionally, column efficiency or plate counts in column chromatography were used to quantify how well a column was performing. This does not tell the entire story for GPC, however, because the ability of a column set to separate peaks is dependent on the molecular weight of the molecules one is trying to separate. We, therefore, chose both column efficiency and a parameter that we simply refer to as D a, where Di is the slope of the relationship between the log of the molecular weight of the narrow molecular weight polystyrene standards and the elution volume, and tris simply the band-broadening parameter (4), i.e., the square root of the peak variance. 

Furusawa and Yamamoto [16] studied the adsorption process of polystyrene samples (M ranging from 16700 to 2xl06) with narrow molecular weight distribution (Mw/M = 1.01-1.07) at the -conditions (cyclohexane, 35 °C). Controlled pore glass with pore diameter of 1000 A was used as an adsorbent. 

Polystyrene standards used were narrow molecular weight distribution sample produced by anionic polymerization and available from Pressure Chemical Co. Also sample NBS7C from the National Bureau of Standards was used. The sample of poly n-butyl methacrylate was obtained from Aldrich Chemical. It was produced by free radici polymerization with an Mw of 320,(XK) and an Mn of 73,500 (Cat. No. 18,153-6). 

Polystyrene/polyethylene oxide dendrimers were prepared by ATRP using tri- and tetra (bromomethyl) benzene as the initiators [207]. Each bromine end-group of the resulting stars was transformed first to two - OH groups and subsequently to potassium alcholate, as shown in Scheme 114. These - OK sites served to initiate the anionic polymerization of EO. The synthesized dendritic copolymers were found to display monomodal and narrow molecular weight distribution. 

Materials. Four samples of sodium poly(styrenesulfonate) (NaPSS) prepared by sulfonation of polystyrenes with narrow molecular weight distribution were purchased from Pressure Chemical Co. The characteristics of the samples, according to the manufacturer, are listed in Table I. The intrinsic viscosities of NaPSS in aqueous NaCl solution were measured using an Ubbelhode viscometer at 25 °C. 

The above data prove that the polystyrene-h-polybutadiene prepolymer is quantitatively transformed into block copolymers with perfluorinated side chains. The narrow molecular-weight distribution (I) = MW/MN) of the prepolymers is maintained by the described reaction sequence. 

Novolac molecular weights were measured in THF at 35°C by high pressure size exclusion chromatography using a Waters Model 510 pump (flow rate=1.0 ml/min), 401 differential viscometer detector and a set of Dupont PSM 60 silanized columns. A universal calibration curve was obtained with a kit of 10 narrow molecular weight distribution, linear polystyrene standards from Toya Soda Company. Data acquisition and analysis were performed on an AT T 6312 computer using ASYST Unical 3.02 software supplied with the Viscotek instrument. 

The properties of the hybrid diblock structures can be altered drastically by simply taking advantage of the high terminal functionality of the dendritic block. For example unusual diblock structures useful for the modification of surfaces have been prepared by ATRP of polystyrene (PS) initiated from the benzylic halide focal point of Frechet-type dendrons with terminal isophthalate ester groups [9b], Well-defined copolymers with narrow molecular weight distributions were obtained and excellent agreement was observed between calculated... 

GPC calibration curves are established based on the radius of gyration of known-molecular-weight polymers, such as well characterized, narrow-molecular-weight distribution polystyrene. Branched polymers have a lower radius of gyration for their molar mass than the corresponding linear molecule. Thus, as branching increases the GPC numbers become less and less accurate and so should only be used for trends, and not exact calculations as some authors have done. 

Little is known about the chain dimensions of PPC in solution. Recently, a comparison of the hydrodynamic volume of polystyrene (PS) and PPC has been reported for tetrahydrofuran (THF) as solvent in connection with a size exclusion chromatography (SEC) analysis [78, 79]. The basis for the calculation was the assumption of an immortal PO/CO2 alternating copolymerization, and thus that absolute values of Mn relate to starter and PO/CO2 ratios. Narrow molecular weight distributed PPCs with various molecular weights were prepared from adipic acid as starter. The absolute molecular weight has a relationship of K = K(ps)... 

Effect of Injected Solvent. It was eventually determined that the mobile phase injected from the first SEC (i.e., pure THF) affected the separation in the second SEC. This is dreunatically demonstrated in Figure 13 which shows the result of injecting a narrow molecular weight distribution polystyrene sample directly into the second SBC. Mobile phase was of constant composition throughout (63.8% n-heptane in THF). However, the solvent used to dissolve the polystyrene was varied from 0% n-heptane in THF to 50% and plotted on the abscissa versus peak retention time on the ordinate. Peak retention time varied from 915 seconds at 0% n-heptane to 960 seconds at 50%. 

Figure 7.56 Extrudate swelling in polystyrene melts for ( ) broad molecular weight distribution and (O, a) narrow molecular weight distribution samples. From Z. Tadmor and C. G. Gogos, Principles of Polymer Processing, Copyright 1979 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

The polystyrene (PS) and polymethylmethacrylate (PMMA) narrow molecular weight standards were obtained from three kits (Polymer Laboratories, S-L-10, S-M-10 and M-M-10) covering the range from 3,000,000 to 500. Five nonylphenyl-terminated polyethylene oxides (Aldrich, Igepals)... 

Preparation of desired molecular weight polystyryl carbanion ( Living Polystyrene ) by anionic polymerization (Fig. 2). Anionic polymerization has been used extensively to provide control over molecular weight with narrow molecular weight distribution. 

---