Star‐type polystyrenes, polymers with p branches attached to a common multifunctional center, and comb‐type polystyrenes, polymers with an average of p branches attached at random to a polymeric backbone, have been prepared by the reactions, respectively, of polystyryllithium of narrow chain length distribution with appropriate p‐functional molecules or with backbone polystyrene chains of narrow chain length distribution, containing the prerequisite number of benzylic‐type chloromethyl groups. The synthesis, isolation, and characterization of these types of polymers are illustrated by specific examples. Problems which are inherent to the system, e.g., metal–halogen interchange reactions, different reactivities of the chloromethyl groups, isomerization of the polystyryllithium, and other possible reactions and their consequences are discussed.
Data on the viscosity coefficient 7J in the limit of zero shear on binary polystyrene mixtures having identical number average chain length Z" (hence identical density) but different weight average Z .. establishes that 7J"'Z", when Zw<630 chain atoms, confirming the theory of Bueche for the viscosity of short polymer chains. Strong support for Bueche's theoretical equation, is provided by the successful quantitative prediction of the observed value of 7J from the independently measured values of the unperturbed reduced mean-square radius of gyration of the polymer coil (so')A,IM, of the specific volume v, the friction coefficient per chain atom I, and Avogadro's number, No. Application of this equation now permits ready evaluation of I from viscosity measurements on short chain polymers.
Samples of poly(vinyl chloride) polymerized at different temperatures (+30, 0, −30, and −78°C) and a commercial sample were chlorinated by a photoinitiated, free‐radical method in o‐dichlorobenzene at ambient temperature. The chlorine content was determined by difference by using a carbon‐hydrogen analyzer. High‐resolution infrared analysis revealed a selective attack on the methylene hydrogens along with a concomitant decrease in intensity of the isotactic methylene deformation band and the syndiotactic carbon‐chlorine stretching band. Graphical representation of the relative intensities of the v(CH), δ(CH2), and v(CCI) modes indicate that the chlorine radical preferentially attacks the middle carbon of the heterotactic triad. The increased “stiffness” of this unit causes the rotational energy of the system to be transferred to the syndiotactic portion of the chain. It is proposed that this additional energy causes the TTTT conformer of the syndiotactic unit to rotate into the less‐preferred TTGG conformation, which would be more reactive. Facile chlorination of this latter conformer is predicted. This mechanism is in accord with the reported equilibrium composition of the different conformers.
SynopsisAnionic polymerization techniques have been used to prepare low molecular weight (A4 _< l0,OOO) polystyrene of a,Jan 5 1.1. The preparation and characterization of polymers are described. Good agreement with results reported by others was obtained for the viscosity-molecular weight relation in benzene a t 25"C., via.[ q ] = 1.0 X a -0 . 6 , for 500 < g,, 5 10,000. For high molecular weight fractions (2.5 X lo4 < A4 -< 1.5 X lo6) of anionically prepared polystyrene, the expression, [TI benzene = 8.5 X lO-6M0.76, w a~ found to be applicable and in agreement with relations given in the literature. Under theta conditions-cyclohexane as solvent a t 34.5"C.-a single expression, [q] = 8.4 x 10-4Mc.6, was found to apply over the entire molecular weight range, 500 < M 5 1 .5X 106.
A benzene solution of polystyryllithium of narrow chain length distribution was found to react with carbon dioxide to form (upon acidification) not only the corresponding polystyrene carboxylic acid but also significant amounts of di‐polystyryl ketone and tri‐polystyryl carbinol. The amounts of the latter two products were somewhat dependent on the rate at which carbon dioxide could be added to the system. Thus, the yields of di‐polystyryl ketone and tri‐polystyryl carbinol were 28% and 12% respectively, if termination was accomplished by allowing gaseous carbon dioxide to diffuse into the system, but the total yield of these products was only 22% if the termination was carried out by pouring the polystyryllithium solution onto crushed, solid Dry Ice. Lithium polystyrene carboxylate was found to be partly associated in benzene and cyclohexane, but the free acid was not.
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