Polystyrenes low-molecular-weight

Class and Chu demonstrated that if a tackifier is chosen that is largely incompatible with the elastomer, a modulus increase due to the filler effect is observed and little change in Ta results, and once again a PSA would not be obtained. This was observed for mixtures of low molecular weight polystyrene resin and natural rubber. The same polystyrene resin did tackify SBR, a more polar elastomer that is compatible with the resin. Hydrogenating the polystyrene to the cycloaliphatic polyvinylcyclohexane changed the resin to one now compatible with the less polar natural rubber and no longer compatible with SBR. These authors also provide... 

Small particle size resins provide higher resolution, as demonstrated in Fig. 4.41. Low molecular weight polystyrene standards are better separated on a GIOOOHxl column packed with 5 /u,m resin than a GlOOOHg column packed with 10 /Ltm resin when compared in the same analysis time. Therefore, smaller particle size resins generally attain a better required resolution in a shorter time. In this context, SuperH columns are best, and Hhr and Hxl columns are second best. Most analyses have been carried out on these three series of H type columns. However, the performance of columns packed with smaller particle size resins is susceptible to some experimental conditions such as the sample concentration of solution, injection volume, and detector cell volume. They must be kept as low as possible to obtain the maximum resolution. Chain scissions of polymer molecules are also easier to occur in columns packed with smaller particle size resins. The flow rate should be kept low in order to prevent this problem, particularly in the analyses of high molecular weight polymers. 

A study of methods for controlling the grafting sites of polystyrene polymers may serve as an example for the quantitative and structural analysis of the site of lithiation. Trimethylsilyl chloride serves as the quenching agent owing to the low incidence of side reactions besides metal replacement. Thus, on varying the conditions of metallation of low molecular weight polystyrene (409) and poly(4-methylstyrene) (410), aromatic and... 

Sakamoto N, Hashimoto T (1995) Order-disorder transition of low molecular weight polystyrene-block-polyisoprene. 1. SAXS analysis of two chracteristic temperatures. Macromolecules 28(20) 6825-6834... 

Fig. 13. (a) Overlay of absorption and emission spectra of 67 in chloroform at room temperature, (b) Overlay of absorption and emission spectra of 67 in low molecular weight polystyrene at 77 K. 

When we determine values of 7 for benzene rings attached to polymers, we find that they are much shorter than for benzene itself they are in fact at the lower limit of usefulness of the direct method. We have found (3) that for the phenyl resonance of a low molecular weight polystyrene in carbon disulfide 7 is only about 0.4 0.1 sec. at 25°. For the backbone protons, 7 is even shorter and cannot be measured by the direct method. For the phenyl groups of poly-y-benzylglutamate in trifluoroacetic acid, 7 is 0.7 0.1 sec. Recently, more reliable values have been obtained for polystyrene by the spin echo method (72). For a polymer of molecular weight 63000 in tetrachloroethylene, three 7 X values could be resolved. At 25°, these were 0.033 sec. for the aliphatic protons, 0.076 sec. for the ortho protons and 0.20 sec. for the meta-para protons. The temperature coefficients for all three Tt values correspond to a heat of activation of about 3 kcal/mole. The differences in the absolute Tx values at the aromatic positions can be explained in terms of of differences in the sums of r e in equation (56). The shorter aliphatic Tj value probably reflects also a longer correlation time for backbone... 

Fig. 16.9 shows the low frequency slopes of 2 and 1, respectively, as expected for viscoelastic liquids and the high frequency slopes Vi and 2/3 for Rouse s and Zimm s models, respectively. Experimentally it appears that in general Zimm s model is in agreement with very dilute polymer solutions, and Rouse s model at moderately concentrated polymer solutions to polymer melts. An example is presented in Fig. 16.10. The solution of the high molecular weight polystyrene (III) behaves Rouse-like (free-draining), whereas the low molecular weight polystyrene with approximately the same concentration behaves Zimm-like (non-draining). The higher concentrated solution of this polymer illustrates a transition from Zimm-like to Rouse-like behaviour (non-draining nor free-draining, hence with intermediate hydrodynamic interaction).

To illustrate the advantages of the technique, we apply it to narrow molecular weight fractions of low molecular weight polystyrene. 

Living radical dispersion polymerization is a promising way to expand the design and scope of functional polymer colloids to a wider range of other monomers. The 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO)-mediated living radical dispersion polymerization of styrene has been carried out in presence of PS-h-P(PP-aZt-E) in decane at 135 °C [95] or PVP in alcohol-water at 130 °C [96] in order to produce microspheres with a very broad size distribution, consisting of relatively low molecular weight polystyrene (M =10 ) with M /Mn=l.l. 

Illers and Jenckel [36] studied aPS plasticized with diethyl, dibutyl and dioctyl phthalate. The mechanical measurements of tan<5 at 1 Hz showed the a relaxation moving rapidly to lower temperatures with increasing plasticizer content. The (3 relaxation was submerged below the a relaxation in the plasticized systems. A relaxation process was reported with a peak temperature ranging from 180 up to 267 K on addition of diethyl, dibutyl and dioctyl phthalate, respectively. The authors called this relaxation process y but they were inclined to ascribe it to the motion of low molecular weight polystyrene dissolved in discrete droplets of plasticizer. According to Heijboer [4], this can also be a motion within the plasticizer molecule, e.g. of the n-butyl group in dibutyl phthalate. 

The meta photocycloaddition of cis-cyclooctene to benzene was one of the first examples of this reaction reported, and the addition of this cycloalkene to low molecular weight polystyrene and mono- and di-aromatic model-compounds has now been described. The results were analysed by mass spectroscopy, and it was reptorted that for polymers having up to six styrene units, more than one phenyl group in each chain had reacted. In the 2 1... 

The photoinduced polyaddition of l,l -(2,6-naphthalenedicarbonyl)diaziri-dine and 1,5-dihydroxynaphthalene occurs in high yield via the mechanism shown in Scheme 7. In the photocycloaddition of cis-cyclooctene to low molecular weight polystyrene, " the conversion is low. Poly-(4-methyl-4-trichloro-... 

It was shown that 2 mol of the living polymer reacts rapidly with the DPE derivatives to form the dilithium adduct in hydrocarbon solvents, whereas in THF monoaddition is reported.7>26>78 80 This reaction was monitored by UV—visible spectroscopy. The analysis revealed that the stoichiometric addition of PSLi was quantitative. However, PDDPE exhibited less tendency to form the diadduct both in polar and nonpolar solvents. This behavior can be attributed to the better delocalization of the negative charge in the para than in the meta isomer. Mainly, low molecular weight polystyrenes have been used for these studies. 

In 19A6, Baxendale, Evans, and Parks reported (25) on a stepwise formation of an (A-B)jj block polymer in which low molecular weight polystyrene and methyl acrylate prepolymers were linked with diisocyanate to form a high molecular weight, multiblock polymer. 

For the low molecular weight polystyrenes and poly(methyl acrylates), the end groups were clearly observed in H-NMR spectra. The concentrations of head groups... 

Example 7.8 Polymerization of styrene in liquid ammonia gave high yield of low-molecular-weight polystyrene, whereas methacrylonitrile gave high conversion of high-molecular-weight polymethacrylo-nitrile. Explain. 

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