Polymers thermal response

Key words thermal-responsive polymer, moisture-responsive polymer, thermal-responsive hydrogel, pH-responsive hydrogel, smart textiles. 

The problems related to the colloidal stability of amphiphilic polymers in water are reviewed by Aseyev, Tenhu, and Winnik in the first chapter of volume 196. The focus is on the derivatives of thermally responsive smart macromolecules - both on copolymers and homopolymers - which are present in a solution as stable micelles potentially having various applications. 

In the previous sections, we described the overall features of the heat-induced phase transition of neutral polymers in water and placed the phenomenon within the context of the general understanding of the temperature dependence of polymer solutions. We emphasised one of the characteristic features of thermally responsive polymers in water, namely their increased hydropho-bicity at elevated temperature, which can, in turn, cause coagulation and macroscopic phase separation. We noted also, that in order to circumvent this macroscopic event, polymer chemists have devised a number of routes to enhance the colloidal stability of neutral globules at elevated temperature by adjusting the properties of the particle-water interface. 

Laukkanen A (2005) Thermally responsive polymers based on N-vinylcaprolactam and an amphiphilic macromonomer. Academic Dissertation. Yliopistopaino, University of Helsinki, http //ethesis.helsinki.fi/julkaisut/mat/kemia/vk/laukkanen... 

The aromatic structure of these materials is of major importance in their thermal response and in their inherent fire resistance according to established criteria. Approaches to fire retardants that have been studied for this class of polymers are reviewed, and illustrative data on performance are presented. 

El Sherbiny IM, Lins RJ, Abdel-Bary EM, Harding DRK (2005) Preparation, characterization, swelling and in vitro drug release behaviour of poly [N-acryloylglycine-chitosan interpoly-meric pH and thermally-responsive hydrogels. European Polymer Journal 41 2584-2591. 

Increasing the temperature of the solution surrounding a thermally responsive gel based on a polymer with a LCST in the solution will cause it to shrink, while decreasing the temperature will cause it to swell. The rate limiting step for this could be either heat transfer or mass transfer. Since convection does not occur within conventional non-porous gels (microporous gels will be discussed in... 

Chilkoti, A., Dreher, M. R., Meyer, D. E., and Raucher, D. (2002). Targeted drug delivery by thermally responsive polymers. Adv. Drug Deliver. Rev. 54, 613-630. 

Yu, C., Mutlu, S., Selvaganapathy, P., Mastrangelo, C.H., Svec, E, Frechet, J.M.J., Flow control valves for analytical microfluidic chips without mechanical parts based on thermally responsive monolithic polymers. Anal. Client. 2003, 75, 1958-1961. 

Thermally responsive polymers, such as poly( V-isopropyl acrylamide) (NI-PAm), have also been studied extensively for applications related to those previously discussed [112], De las Heras et al. described the synthesis and patterning of NIPAm brushes on SAMs and their subsequent performance during temperature-dependent adhesion assays of BSA and Streptococcus mutans (Fig. 7). The authors employed p.CP to pattern features of hydrophobic hexadecanethiol and backfilled the surface with an initiator-functionalized alkanethiol. Polymer brushes were grown via surface-initiated atom transfer radical polymerization (ATRP). FITC-BSA was then... 

Instability of the polymer is responsible for the primary step in decomposition and is attributed either to fragments of initiator or to branched chains or to terminal double bonds. The appearance of branching is the result of reactions of chain transfer through the polymer, while that of unsaturated terminal groups results from reaction of disproportionation and chain transfer through the monomer. During thermal and thermo-oxidative dehydrochlorination of PVC, allyl activation of the chlorine atoms next to the double bonds occurs. In this volume, Klemchuk describes the kinetics of PVC degradation based on experiments with allylic chloride as a model substance. He observed that thermal stabilizers replace the allylic chlorine at a faster ratio than the decomposition rate of the allylic chloride. 

Further heating of the sample to I (250°C) produces no further interpretable thermal response. And since another test, thermogravimetric analysis (TGA), which I will not discuss in this chapter, shows that the polymer sample loses a little weight (suggestive of decomposition) at approximately 250 °C, we heat the sample no further but now immediately begin to cool it at 10°C/min. 

Other information can be obtained from thermal studies of TPU elastomers which is also helpful in understanding and improving these high performance, easily processed polymers. But it was the intention to limit this chapter to the basic DSC thermal responses which forecast strengths and weaknesses in TPU processing and performance characteristics and to indicate the parts of the TPU structure that are responsible for these thermal responses. Hopefully, this has been accomplished. 

Interesting thermal response of the polystyrene nanocomposites was reported when untreated and polystyrene grafted nanotubes were used for the reinforcement of polymer (49). The glass transition temperature of the pure polystyrene matrix was observed to be 99 °C. Similar transition temperature of 98 °C was observed for the composites containing 2.5 vol% of the untreated nanotubes. The nanocomposites containing polymer functionalized nanotubes... 

Peters EC, Svec F, and Frechet JMJ. Thermally responsive rigid polymer monoUths. Adv. Mater. 1997 9 630-633. 

The "survey" studies can indicate potentially interesting polymers such as products showing unusual and/or potentially useful thermal responses. 

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