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SynopsisPolycaprolactone is degraded by the mold P . pullulans in the presence of other nutrients. The weight loss from solid polymer films covered by a nutrient agar gel on which colonies are growing is used to establish comparative rates of degradation. There is substantial loss (16 mg/cm2 surface area) from a whole polymer of low (2,000) molecular weight in three weeks at 30°C. A high (30,000) molecular weight whole polymer degrades about 0.15 as much in the same time period. A fraction in the same range (38,000) but with a narrower molecular weight distribution shows no significant loss. This indicates that whole polymers of high molecular weight may lose only a portion of their distribution by microbial degradation in short-term tests. This hypothesis is tested by making mixtures of high (61,000) molecular weight with low (2,000) molecular weight polymer. Degradation is directly proportional to the low molecular weight content in these short-term tests with a single species of mold. Other workers have shown previously that in long-term, soil-burial tests, even a high (40,000) molecular weight polycaprolactone is essentially completely degraded after one year.

SynopsisAqueous solutions with 1.5 to 6.5 wt-% poly(viny1 pyrrolidone), PVP, are converted to stable gels by reaction with potassium persulfate. Large quantities of persulfate are needed for high-modulus gels, 50% to 150% of the weight of PVP being required typically. The shear modulus G' can be measured during reaction by making the gel the restoring element in a simple torsion pendulum. The increase in modulus to a maximum plateau value of GLm can be expressed as a first-order process:where t is elapsed time of reaction and K increases with the square root of polymer concentration. G-varies with the second power of the polymer concentration. It also increases rapidly with increasing temperature of reaction and with persulfateIPVP ratio.

A dilatometric technique was used to obtain conversion–time data for the polymerization of acrylamide initiated by potassium persulfate in water. The results are summarized by the empirical rate expression, −d[M1]/dt = Rp = k1.25[K2S2O8]0.5[M1]1.25, and k1.25 = 1.70 × 1011 exp {−16,900/RT} 1.0.75/mole−0.75‐min. Persulfate was varied over the range 9.5 × 10−4 to 5.2 × 10×2 mole/l., and initial monomer concentration [M1] was varied from 0.05 to 0.4 mole/l. The temperature range was 30−50°C. Results of analysis of the kinetics and energetics of the polymerization favor a cage‐effect theory rather than a complex‐formation theory to explain the order with respect to monomer.

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