Polymerizations of methyl methacrylate (MMA) in ternary
oil-in-water microemulsions using
the cationic surfactants stearyltrimethylammonium chloride (STAC),
cetyltrimethylammonium bromide
(CTAB), or a mixture of nonionic nonylphenoxy poly(ethylene
glycol) surfactants produce latex particles
having weight average diameters of 17−41 nm. The small particle
sizes and high molecular weights
(M
w = (2.5−6.5) × 106)
indicate that most samples consist mainly of particles containing one
polymer
chain. The particle size varies little when the surfactant to
monomer weight ratio is ≥1. Polymerizations
using STAC at 35 °C produce smaller particles than at 60 °C.
Radical polymerization of MMA in
microemulsions produces predominantly syndiotactic PMMA containing
58−61% rr triads at 60 °C and
63−65% rr triads at 35 °C. The high molecular
weight PMMA samples have T
g = 125−126
°C.
An upper-division undergraduate polymer
chemistry course was developed
as a blended/hybrid course. The students met face-to-face once a week
for 75 min with all other components being available online. Face-to-face
meetings were used for class discussions/problem-based lectures, student
presentations, hands-on activities, and examinations. Online components
included study guides, the Macrogalleria, and online quizzes. This
course is appropriate for students who have had one year of organic
chemistry.
In today's world of instant coffee, instant meals, and instant messaging, undergraduate students prefer not to have to wait 30−60 min for an organic reaction to take place. Heating with microwaves is rapidly becoming more commonplace due to dramatically reduced reaction times and higher product yields. Students appreciate the short reaction times and like working with advanced technology by means of the commercial microwave reactors available today. Furthermore, undergraduate organic students like being able to relate an experiment to something that they see every day. For these reasons, the synthesis of pharmaceuticals, extracting caffeine from tea, and isolating trans-cinnamaldehyde from cinnamon sticks are popular experiments. One such experiment is the synthesis of the artificial sweetener dulcin (4ethoxyphenylurea), which can be prepared from the reaction of p-phenetidine and urea. Artificial sweetening agents are extremely important to the food industry because of the national concern with diet and weight control. The synthesis of this particular sweetener typically takes at least 30 min to reach completion. However, using microwave irradiation, the reaction reached completion in 5 min using a temperature of 125 °C. This procedure was implemented into the second semester undergraduate organic chemistry laboratory curriculum where students successfully prepared dulcin with reported yields ranging from 10% to 86% and an average yield of 39% after recrystallization.
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