John M. Warakomski

Crystallization kinetics and morphological features of star-branched nylon-6: effect of branch-point functionality

Abstract Bulk crystallization rates, nucleation density, general morphological features, equilibrium melting point and absolute crystalline percentage of linear and star-branched nylon-6 have been studied as a function of branch-point functionality and temperature. Overall bulk crystallization rates were described in terms of the Avrami equation and crystallization half-times. No significant differences in bulk crystallization rates as a function of crystallization temperature or absolute crystalline percentage were observed between linear, three-arm and six-arm samples with identical thermal history. Equilibrium melting points obtained by Hoffman Weeks analysis were reduced in star-branched nylon-6 compared to the linear polymer of comparable molecular weight. In order to deconvolute the effects of a decreased thermodynamic driving force for formation of crystals of branched polymers, crystallization half-times were measured as a function of supercooling. The crystallization half-times of star-branched nylon-6 as a function of supercooling were reduced compared to those of linear nylon-6 of comparable molecular weight. The general spherulitic superstructure appeared unaffected by increasing branch-point functionality up to six. However, irregularities in lamellar structure were implied by SAXS experiments on samples with branch-point functionality as low as three.

Benzocyclobutenes as styrene monomer scavengers and molecular weight “stabilizers” in atactic and syndiotactic polystyrenes

Syndiotactic polystyrene (SPS) is a semicrystalline polymer with a melting point of 270°C. At processing temperatures of 300°C or higher, SPS begins to decompose with loss of molecular weight and the formation of styrene monomer. Under these conditions, atactic polystyrene also decomposes. One approach to controlling this generation and buildup of styrene and the molecular weight loss during processing is to add a compound that will react with styrene and/or with the polymer decomposition products at the processing conditions. This report describes the use of three benzocyclobutene (BCB) compounds (ethylene bis-BCB, divinyl disiloxane bis-BCB, and a copolymer of styrene and 4-vinyl BCB) during SPS and atactic polystyrene processing. The conclusions are: 1. BCB moieties, when extruded with SPS at the 2 wt % level, caused a substantial decrease in residual styrene compared with a control SPS; 2. BCB compounds, when extruded with SPS, resulted in high molecular weight fractions. The result with the divinyl disiloxane bis-BCB was especially dramatic; and 3. BCB functionalized materials may find utility as additives in SPS during processing to minimize loss of molecular weight and buildup of styrene.