Incomplete polymerization

Short PS macromonmers (DP = 4 or 9) polymerized completely under ROMP conditions. Macromonomers with DP = 14 to 46 invariably led to incomplete polymerization, suggesting that the dense polymacromonomer imposes steric limitations on the polymerization. Heroguez et al. studied the ROMP of polyethylene oxide) macromonomers [111, 112], The macromonomers are prepared from a norbornene derivative according to the following sequence ... 

BPA can occur due to an incomplete polymerization, followed by migration into the food or environment [200], Furthermore, BPA monomer is used as color developer in thermal paper and is consequently also present in recycled paper and paperboard which can be used as food packaging material [201]. Human exposure to BPA is believed to occur mainly through contaminated food, although recently dermal exposure and absorption have gained attention [202-204]. 

The considerable increase in water uptake, as much as two-fold (Fig. 8), caused by replacing MMA with TGDM is surprising. It does not seem to be due to incomplete polymerization because similar results were calculated from data previously reported (2 ) for specimens made at the much higher temperature of 120°C. 

Some bird repellents are composed of viscous, sticky materials that birds dislike having on their feet (17). These compounds, eg, Tanglefoot, Roost-No-More, and TackTrap, are often based on incompletely polymerized isobutylene and thinned with aromatic solvents. They should be formulated to have the proper blend of tackiness and viscosity for the weather, method of application, and pest species. They are applied to leave sticky residues on perching locations in buildings and roosts in trees. Because these materials do not have an obnoxious odor, the birds must land on and learn its location in order to avoid it, as there are no long-range cues in the treatment itself for conditioning. 

More than a dozen biocompatible and biodegradable polymers have been described and studied for their potential use as carriers for therapeutic proteins (Table 13.5). However, some of the monomer building blocks such as acrylamide and its derivatives are neurotoxic. Incomplete polymerization or breakdown of the polymer may result in toxic monomer. Among the biopolymers, poly-lactide cofabricated with glycolide (PLG) is one of the most well studied and has been demonstrated to be both biocompatible and biodegradable [12]. PLG polymers are hydrolyzed in vivo and revert to the monomeric forms of glycolic and lactic acids, which are intermediates in the citric acid metabolic pathway. 

The following suggestions should minimize problems of incomplete polymerization. Warm all refrigerated gel solutions to room temperature prior to use and always deaerate the gel solution 5 to 10 min with at least a water aspirator. It is helpful to warm the gel solution to 20° to 25°C after deaeration and allow it to polymerize at or slightly above room tempera-... 

The polymer manufacturing industry monitors extractables in their products for a variety of purposes. Polymers contain a variety of additives such as anti-oxidants, mineral oils, and waxes as well as incompletely polymerized dimen and trimen that have a pronounced effect in the finished product (17). This study illustrates the efficiency of SFE in the extraction of polystyrene samples containing mekon and polystyrene waxes as well as mineral oil, dimen, and trimen. 

This experiment works well if both the ethylene glycol and glycerol are very dry. Since both are hygroscopic, it is best to take them from sealed bottles. Water contamination causes incomplete polymerization, resulting in product with very low viscosity. 

Exact proportions of resin and hardener must be weighed out on an accurate balance or in a measuring container for best adhesive quality and reproducibility. Possible problems that can occur by not adhering to the proper mixing proportions can include incomplete polymerization (too little catalyst), brittleness (excessive catalyst), and corrosion of metallic adherends (excessive catalyst). 

Color of the uncured epoxy resins is an indication of contamination, incomplete polymerization, oxidation, and other factors. Aromatic resins with lower molecular weight generally have better (lower) color. Color is usually reported in terms of the Gardner liquid color standards or the Hellige color comparator or by means of the APHA number. 

In addition, styrene reacts irreversibly with SbCls to form 1,2-dichIoro-adducts and inactive SbCU. In fact, all of the Lewis acid is consumed by addition at low concentrations of initiator, resulting in incomplete polymerization [144]. 

Termination has no effect on the final number-average molecular weights, because it does not change the total number of chains. However, termination may lead to incomplete polymerization if the initiator concentration is too low. In the case of unimolecular termination, the final monomer conversion is set by Eq. (1). 

Monomers and higher molecular weight oligomers derived from incomplete polymerization reactions. 

Predictable set characteristics are also important to process control. Predictability of set is often a factor of application environment (humidity, temperature) and material purity. The prevalence of unstable and contaminated monomers in conservation laboratories (possibly a result of the infrequency of consolidation treatments) can be a significant problem, as incomplete polymerization and retarded transition can occur. 

The adhesive of this study has been designed for an automotive under-hood application. Accordingly, It was Important to understand the behavior of the adhesive over a wide frequency (engine RPM) and temperature range. Time-temperature superposition allows characterization beyond the frequency range of our Instrumentation (4). More significantly. It Is hoped to use time-temperature superposition data to explore the molecular weight Implications of Incomplete polymerization. 

As Indicated above a goal of the next phase of this work Is to study the molecular Implications of Incomplete polymerization. Wu (6) has proposed that this can be done by studying the terminal plateau modulus data for a series of test specimens. Accordingly, we attempted in this phase to show that the mechanical spectroscopy data generated from the adhesive specimens could be subjected to time-temperature superposition to yield complete modulus mapping over an extended frequency scale. Figure 9 Illustrated the Isothermal frequency scans obtained for time-temperature superposition. A master curve was constructed at reference temperature (To 75°C) approximately equal to the glass transition temperature (Tg.)... 

While this paper reports only preliminary findings. It does Illustrate the usefulness of photocalorimetry to define optimum cure conditions for UV curable adhesives. In addition, once the mechanical spectrum of fully cured adhesive has been mapped, mechanical spectroscopy can be used to monitor cure efficiency. In this paper we have not explored the molecular weight Implications of Incomplete polymerization. Preliminary evaluation of loss and storage modulus data would suggest that time-temperature superposition may be necessary to evaluate molecular welght/degree of cure relationships and terminal, plateau, and transition zones (4). 

Since absorbed water can cause catalyst decomposition and hence incomplete polymerization and since lactam monomer flakes are highly hygroscopic, the melting of monomer is carried out under appropriately controlled temperature and humidity conditions. All additives are also completely dried and then mixed with the monomer in stainless steel vessels while flushing with inert gas under thermostatically controlled temperature. Molds can be of the single type fabricated from silicone rubber, epoxy, or sheet steel or the more expensive tool steel used in tight tolerance cast-to-size parts casting. 

Ebecryl 284), which yields an elastomeric material allowing nearly complete polymerization, and with an aromatic polyether-acrylate (Ebecryl 600), which yields an incompletely polymerized glassy material. 

The conditions for step-growth polymerization are summarized in Fig. 3.13. The much more stringent conditions than customary in general organic syntheses that must be satisfied to produce macromolecules are listed as points a to d. Limits to the molar mass are not only set by incomplete polymerization reactions, as expressed by the... 

---