A rotating mandrel in a tubing die produces multiaxial orientation in the extruded melt. If the polymer melt is quenched rapidly, some multiaxial orientation is retained in the resultant tubing. Multiaxially oriented tubing exhibits reduced crack propagation and some enhancement of yield and fracture strengths. During the processing of multiaxially oriented tubing, relaxation occurs after the melt leaves the die and gives rise to wall thickening and reduction in the lumen of the tubing; the magnitude of these effects is a function of the rate of mandrel rotation.
Polymerization rates a t 60 and 95 "C. and molecular weights have been measured for vinyl benzoate. Copolymerization and branch sites in the polymer involving the aromatic ring were h n d t o Le subtantially absent. The rate of polymerization was found tn-he proportional to the square root of the initiator concentration and to the reciprocal of the degree of polymerization. The slow polymerization rate is explained in terms of reversible complex formation between the vinyl radical and the aromatic ring.
ZUSAMMENFASSUNG:Die Polymerisationsgeschwindigkeiten bei 60 und 95 "C sowie Molekulargewichte fiir die Polymerisation des Vinylbenzoats wurden bestimmt. Es wurde gefunden, daR der aromatische Ring weder zu Copolymerisation noch zu Kettenverzweigungen AnlaR gab. Die Polymerisationsgeschwindigkeit ergab sich proportional zur Quadratwurzel aus der Starterkonzentration und proportional zum reziproken Polymerisationsgrad. Die niederen Werte der Polymerisationsgeschwindigkeit wurden durch die Annahme einer reversiblen Komplexbildung zwischen dem Vinylradikal und dem aromatischen Ring erklart.
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